MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Ocnus planci aggregations on sheltered sublittoral muddy sediment

07-11-2002
Researched byDr Harvey Tyler-Walters Refereed byThis information is not refereed.
EUNIS CodeA5.344 EUNIS NameOcnus planci aggregations on sheltered sublittoral muddy sediment

Summary

UK and Ireland classification

EUNIS 2008A5.344Ocnus planci aggregations on sheltered sublittoral muddy sediment
EUNIS 2006A5.344Ocnus planci aggregations on sheltered sublittoral muddy sediment
JNCC 2004SS.SMu.IFiMu.OcnOcnus planci aggregations on sheltered sublittoral muddy sediment
1997 BiotopeSS.IMU.MarMu.OcnOcnus planci aggregations on sheltered sublittoral muddy sediment

Description

Dense aggregations of Ocnus planci (or Ocnus brunneus?) on various substrata, typically muddy but sometimes with stones or shells, in sheltered conditions such as sea lochs. Associated species vary but are typical of very sheltered muddy habitats. Melanella alba, which parasitises holothurians, was found in large numbers at one site. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

Recorded from Wide Firth in Orkney; Carlingford Lough, Northern Ireland, and Loch Goil, Loch Craignish, and Loch Erisort in western Scotland.

Depth range

0-5 m, 10-20 m, 20-30 m, 5-10 m

Additional information

The description of this biotope is based on only four records (Erwin et al., 1990; Connor et al., 1997a). The taxonomic status of Ocnus planci and Ocnus brunneus is under review and the species may have been confused. However, the two species are ecologically similar and have been discussed together for the sake of this review.

Listed By

Further information sources

Search on:

JNCC

Habitat review

Ecology

Ecological and functional relationships

Little information on this biotope was found. Shallow records of the biotope are similar to IMU.PhiVir with the addition of epifaunal species including abundant Ocnus, while deeper records share some species with sea pen and burrowing macrofauna communities (see CMU.SpMeg). The following information has been inferred from survey records (Erwin et al., 1990; Connor et al., 1997a; Howson et al., 1994; Dipper & Beaver, 1999; Murray et al., 1999; JNCC, 1999), papers on general ecology of Ocnus planci (Ölscher & Fedra, 1977) and reviews of sublittoral mud communities (e.g. Hughes, 1998b) and MarLIN reviews of IMU.PhiVir and CMU.SpMeg. Many of the species living in deep mud biotopes are generally cryptic in nature and not usually subject to predation. Evidence of predation on Virgularia mirabilis by fish seems limited to a report by Marshall & Marshall (1882 in Hoare & Wilson, 1977) where the species was found in the stomach of haddock. Many specimens of Virgularia mirabilis lack the uppermost part of the colony which has been attributed to nibbling by fish. Observations by Hoare & Wilson (1977) suggest however, that predation pressure on Virgularia mirabilis is low.

Epifauna probably compete for the limited space for attachment provided by cobbles, pebbles and shell debris, with ascidians, sponges and soft corals probably representing later stages in colonization (succession) (see MCR.Flu for further detail). However, Ocnus species are probably capable of climbing on any available surface, including other epifauna, to raise their feeding tentacles into the prevailing current (see Ölsher & Fedra, 1977; McKenzie, 1991). Bioturbation by deposit feeding or infaunal species is likely to modify the substratum and resuspend sediment, potentially inhibiting suspension feeding organisms, especially small colonies or juveniles.

Seasonal and longer term change

Species such as the sea pen Virgularia mirabilis appear to be long-lived and are unlikely to show any significant seasonal changes in abundance or biomass. Sea pen faunal communities appear to persist over long periods at the same location. Movement of the sea pen Virgularia mirabilis in and out of the sediment may be influenced by tidal conditions (Hoare & Wilson, 1977; Hughes, 1988). The numbers of some of the other species in the biotope may show peak abundances at certain times of the year due to seasonality of breeding and larval recruitment.

Microphytobenthos and algal production may increase in spring, resulting in the formation of mats of ephemeral algae, and be reduced in winter. High summer temperatures may increase the microbial activity resulting in deoxygenation (hypoxia or anoxia), or alternatively result in thermoclines in shallow bays and resultant hypoxia of the near bottom water (Hayward, 1994; Elliot et al., 1998; Hughes, 1998). Flatfish and crabs often migrate to deeper water in the winter months, and therefore, predation pressure may be reduced in this biotope. Mud habitats of sheltered areas are relatively stable habitats, however especially cold winter or hot summers could adversely affect the macrofauna (see sensitivity). In addition, extreme freshwater runoff resulting from heavy rains and storms may result in low salinity conditions in the most shallow parts of the biotope or in haloclines, again potentially causing local hypoxia. No information on long term change was found. But storms events and extreme wave action may resuspend the bottom sediment and move the cobbles, pebbles and shell debris, resulting in loss or burial of epifauna at irregular intervals.

Habitat structure and complexity

This biotope is characterized by a soft to flocculant mud substratum with the presence of hard substrata such a shell debris, living epifauna, rock, cobbles and pebbles. The soft mud supports epifauna and infauna typical of sheltered soft mud habitats (e.g. IMU.PhiVir), while the hard substrata provides habitat for attached epifaunal species and niches and interstices for other epifaunal species (e.g. brittlestars and Ocnus). The habitat can be divided into the following niches:
  • a mobile epifauna of scavengers and opportunistic predators;
  • a sediment surface flora of microalgae such as diatoms and euglenoids, together with aerobic microbes;
  • an aerobic upper layer of sediment (depth depending on local conditions) supporting shallow burrowing species;
  • a reducing layer and a deeper anoxic layer supporting chemoautotrophic bacteria, burrowing polychaetes (e.g. terebellids), burrowing synaptid holothurians (e.g. Leptosynapta sp.) and bivalves (e.g. Abra alba and Mya truncata) that can irrigate their burrows.
  • an epifauna of sea pens, burrowing anemones, scallops or horse mussels sitting in or on the sediment surface;
  • an epifauna of tubeworms, barnacles, sponges, and ascidians attached to hard substrata;
  • a more mobile epifauna of brittlestars on or between hard substrata and Ocnus on any available raised surface.
Burrowing megafauna are generally rare or absent, therefore there will be few burrows available for colonization by other species. Several species, such as the sea pen Virgularia mirabilis, the anemone Cerianthus lloydii, the tubeworm Chaetopterus variopedatus and fan worms Sabella pavonina and Myxicola infundibulum extend above the sediment surface. Apart from a couple of species of nudibranch living on the sea pens and the tubiculous amphipod Photis longicaudata associated with Cerianthus lloydii (Moore & Cameron, 1999) the large species characteristic of the biotope do not provide significant habitat for other fauna. Brittlestars such as Ophiothrix fragilis probably utilize gaps between cobbles and pebbles and inside dead shells of bivalves. Excavation of sediment by infaunal organisms, such as errant polychaetes, bivalves and Philine aperta, ensures that sediment is oxygenated to a greater depth but little information on the infauna was found.

Productivity

Primary productivity is derived from phytoplankton, benthic microalgae and from macroalgae. However, most of the productivity with the biotope is probably secondary, derived from zooplankton, detritus, dissolved organic material and organic particulates. The biotope is dominated by suspension feeding organisms, especially passive suspension feeders such as brittlestars, sea pens and abundant Ocnus. Ölscher & Fedra (1977) examined passive suspension feeding in the brittlestar Ophiothrix quinquemaculata and the holothurian Ocnus planci (as Cucumaria planci). They noted that passive suspension feeders usually constitute about one third of the community biomass in suspension feeder communities but that they metabolic activity of passive suspension feeders is twice as great due to their small size. They noted the importance of suspension feeding communities to linking the pelagic and benthic ecosystems. Similarly, the importance of bivalve suspension feeding in 'pelago-benthic coupling' has been discussed by Dame (1996) (see also MCR.ModT).

Recruitment processes

Ocnus planci and Ocnus brunneus are dioecious, with separate sexes but are also capable of reproducing asexually by fission. Fertilization is external and spawning occurs in March and April. The eggs are retained after spawning on the tentacles of the female. Development is direct, the larvae adopting the adult body plan without metamorphosis. The larvae are released as a ciliated vitellaria larvae, which is lecithotrophic, completing its development in the plankton (Hyman, 1955; Smiley et al., 1991). No estimate of fecundity was found but other Cucumariidae exhibit clutch sizes between 19 and 340 (Smiley et al., 1991). Planktonic development provides the larvae with potentially long range dispersal capabilities. However, recruitment in echinoderms is known to be sporadic, unpredictable and poorly understood. Ocnus planci and Ocnus brunneus are fissiparous, each individual being able to divide into two or more fragments, over a period of about 14hrs, which then regenerate into complete individuals (Emson & Wilkie, 1980; Smiley et al., 1991). McKenzie (1991) suggested that the large aggregations of Ocnus brunneus may be clones. Fissiparity may provide Ocnus with a mechanism to exploit favourable conditions quickly, although no evidence to this effect was found.

The reproductive biology of British sea pens has not been studied but, in other species, for instance Ptilosarcus guerneyi from Washington State in the USA, the eggs and sperm are released from the polyps and fertilization takes place externally. The free-swimming larvae do not feed and settle within seven days if a suitable substratum is available (Chia & Crawford, 1973). The limited data available from other species would suggest a similar pattern of patchy recruitment, slow growth and long life-span for Virgularia mirabilis.

The associated macroalgae, epifauna and interstitial fauna probably depend on locality and recruit from the surrounding area. Many hydroids, ascidians and probably sponges have short lived planktonic or demersal larvae with relatively poor dispersal capabilities. Exceptions include Alcyonium digitatum and hydroids that produce medusoid life stages and probably exhibit relatively good dispersal potential. Hydroids are opportunistic, rapid growing species, with relatively widespread distributions, which colonize rapidly and are often the first groups on species to occur on settlement panels. Sponges may take longer to recruit to the habitat but are good competitors for space. Recruitment in epifauna communities is discussed in detail in the faunal turf biotopes MCR.Flu, CR.Bug and in Modiolus modiolus beds (MCR.ModT).

Mobile epifaunal species, such as echinoderms (starfish and brittlestars), crustacea, and fish are fairly vagile and capable of colonizing the community by migration from the surrounding areas. In addition, most echinoderms and crustaceans have long-lived planktonic larvae with potentially high dispersal potential, although, recruitment may be sporadic, especially in echinoderms.

Time for community to reach maturity

No information concerning community development was found. Recruitment to available hard substrata by epifauna such as hydroids, and ascidians is probably fairly rapid (see MCR.Flu or CR.Bug), with sponges and soft corals taking longer to develop. Very little is known about the population dynamics and longevity of Virgularia mirabilis in Britain, however information from other species suggest that this species is likely to be long-lived and slow growing with patchy and intermittent recruitment. Other burrowing species representative of this biotope vary in longevity and reproductive strategies. The time taken for the population of Ocnus to grow to the abundances reported in this biotope, by either sexual and/or asexual reproduction, is unknown.

Additional information

None entered

Preferences & Distribution

Recorded distribution in Britain and Ireland

Recorded from Wide Firth in Orkney; Carlingford Lough, Northern Ireland, and Loch Goil, Loch Craignish, and Loch Erisort in western Scotland.

Habitat preferences

Depth Range 0-5 m, 10-20 m, 20-30 m, 5-10 m
Water clarity preferencesNo information found
Limiting Nutrients Not relevant
Salinity Full (30-40 psu), Variable (18-40 psu)
Physiographic Enclosed coast / Embayment, Sea loch / Sea lough
Biological Zone Circalittoral, Infralittoral
Substratum Cobbles, Mud and muddy sand, Pebbles, Small boulders
Tidal Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave Extremely sheltered, Moderately exposed, Sheltered, Very sheltered
Other preferences Hard substrata

Additional Information

The biotope is characterized by the presence of hard substrata (cobbles, pebbles, gravel, and shell debris) in muddy or sandy habitats.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

-

Additional information

The MNCR recorded 131 species within this biotope, although not all species occurred in all records of the biotope.

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

This community is characterized by the abundance of Ocnus planci (or Ocnus brunneus). Loss of the Ocnus population would result in loss of the biotope as described and, therefore Ocnus is considered to be important characterizing.  Therefore, the sensitivity of the biotope is dependent on the sensitivity of Ocnus planci (or Ocnus brunneus).

The other species in the community are common and characteristic of the wave sheltered muddy habitats in which the biotope is found. Therefore, the dominant associated species vary with location and have little significant association with the Ocnus population itself. Reference is made to Nemertesia ramosa to represent hydroids Pomatoceros triqueter to represent tubeworms, Ciona intestinalis to represent ascidians, and Alcyonium digitatum to represent anthozoans, and Echinus esculentus, Ophiothrix fragilis, Amphiura filiformis to represent echinoderms, where required.

Resilience and recovery rates of habitat

Ocnus planci and Ocnus brunneus are dioecious, with separate sexes but are also capable of reproducing asexually by fission. Fertilization is external and spawning occurs in March and April. The eggs are retained after spawning on the tentacles of the female. Development is direct, the larvae adopting the adult body plan without metamorphosis. The larvae are released as a ciliated vitellaria larvae, which is lecithotrophic, completing its development in the plankton (Hyman, 1955; Smiley et al., 1991). No estimate of fecundity was found but other Cucumariidae exhibit clutch sizes between 19 and 340 (Smiley et al., 1991). Planktonic development provides the larvae with potentially long range dispersal capabilities. Therefore, local recruitment may be good but long distance recruitment will depend on the local currents. However, recruitment in echinoderms is known to be sporadic, unpredictable and poorly understood. Ocnus planci and Ocnus brunneus are fissiparous, each individual being able to divide into two or more fragments, over a period of about 14hrs, which then regenerate into complete individuals (Emson & Wilkie, 1980; Smiley et al., 1991). McKenzie (1991) suggested that the large aggregations of Ocnus brunneus may be clones. Fissiparity may provide Ocnus with a mechanism to exploit favourable conditions quickly, although no evidence to this effect was found. Ocnus is probably fairly long-lived. A specimen of Ocnus planci (as Cucumaria planci) was maintained in an aquarium for three years and four months (Hyman, 1955).

The associated macroalgae, epifauna and interstitial fauna probably depend on locality and recruit from the surrounding area. Many hydroids, ascidians and probably sponges have short lived planktonic or demersal larvae with relatively poor dispersal capabilities. Exceptions include Alcyonium digitatum and hydroids that produce medusoid life stages and probably exhibit relatively good dispersal potential. Hydroids are opportunistic, rapid growing species, with relatively widespread distributions, which colonize rapidly and are often the first groups on species to occur on settlement panels. Sponges may take longer to recruit to the habitat but are good competitors for space. Recruitment in epifauna communities is discussed in detail in the faunal turf biotopes CR.HCR.XFa.FluCoAs and  Modiolus modiolus beds (SS.SBR.SMus.ModT).

Mobile epifaunal species, such as echinoderms (starfish), crustacea, and fish are fairly vagile and capable of colonizing the community by migration from the surrounding areas. In addition, most echinoderms and crustaceans have long-lived planktonic larvae with potentially high dispersal potential, although, recruitment may be sporadic, especially in echinoderms.  Brittlestars vary in their recruitment ability. Ophiothrix fragilis produces numerous, long-lived planktonic larvae capable of long distance dispersal, and reach reproductive maturity with six to ten months, and are probable capable of recovery within less than five years. Amphiura filiformis also produces numerous planktonic larvae with high dispersal potential but exhibit high juvenile mortality, so that net recruitment is probably low. Adults also take five to six years to reach maturity, so that recovery may be prolonged. However, Amphiura filiformis was reported to recover to a population of 100/m² within two years. Brittlestars are mobile, potentially able to migrate from the surrounding area but the above species are not thought to be actively mobile. Therefore, the recovery of brittlestars will depend on the sporadic good larval recruitment, local hydrography, and will vary between species, some recovering with a few years while other may take longer.

Many epifaunal species, e.g. hydroids, colonial ascidians, some sponges and Metridium senile are capable of asexual reproduction and colonize space rapidly. For example, in studies of subtidal epifaunal communities in New England, Sebens (1985, 1986) reported that cleared areas were colonized by erect hydroids, bryozoans, crustose red algae and tube worms within one to four months in spring, summer and autumn. Tunicates such as Dendrodoa carnea and Aplidium spp. appeared within a year, Aplidium sp., and Halichondria panacea achieved pre-clearance cover within >two years, while only a few individuals of Metridium senile and Alcyonium sp. colonized within four years.  Other burrowing species representative of this biotope vary in longevity and reproductive strategies.

The time taken for the population of Ocnus to grow to the abundances reported in this biotope is unknown. Ocnus is a mobile species, using raised surfaces to aid feeding, and would probably recruit to, and aggregate, in areas of raised hard substrata from the surrounding area. Subsequent development of large populations is probably aided by fissiparous asexual reproduction, although the rate of reproduction is unknown. Recruitment is likely to be slow and recovery of a large population may be prolonged by sexual reproduction alone.  However, its ability to reproduce asexually may allow the population to grow relatively quickly. Therefore, where a significant proportion of the population remains resilience may be High (< 2 years).  But recovery may take longer where a significant proportion of the population is removed (e.g. resistance is 'Low' or 'None') and recovery is dependent on recruitment alone, in which case, resilience is probably Medium (2-10 years).

Hydrological Pressures

 ResistanceResilienceSensitivity
High High Not sensitive
Q: Medium
A: Low
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Low
C: Medium

Hughes (1998a) suggested that in shallow sea lochs, sedimentary biotopes would probably experience a seasonal temperature range between about 5-15 °C. Greater temperature extremes may be experienced in unusually warm summers or cold winters, although the effects on sedimentary communities is unknown (Hughes, 1998a). Burrowing species would probably be able to avoid extreme temperatures within the sediment so that epifauna were likely to be more vulnerable.

Ocnus planci and Ocnus brunneus reach their northern limit in northern Europe and the British Isles. Ocnus brunneus is reported from France and Denmark while Ocnus planci is reported from the Mediterranean and Senegal. Therefore, they are unlikely to be adversely affected by a long-term temperature rise. Similarly, most other dominant species within the biotope are found to the south of the British Isles and unlikely to be affected adversely by long-term temperature rise. The growth and fecundity of Amphiura filiformis may increase with increased average temperatures while Ophiothrix fragilis was reported to recruit in high numbers after mild winters (see MarLIN reviews).

Overall, most species in the biotope are unlikely to be adversely affected by long-term temperature rise and are buffered from extremes of temperature by their depth. Therefore, a resistance of High has been recorded to represent effects on growth rates and metabolism. Therefore, resilience is High and the biotope is assessed as Not sensitive at the benchmark level. In shallow, isolated waters (e.g. sea lochs) increased summer temperatures may result in stratification of the water column (a thermocline) and increased oxygen demand resulting in deoxygenation of the bottom waters (Hughes, 1998a)(see  deoxygenation below).

High High Not sensitive
Q: Medium
A: Low
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Low
C: Medium

Ocnus planci and Ocnus brunneus reach their northern limit in British waters, however, no information on their temperature tolerance was found. Most of the other common species within the biotope are recorded north of British and Irish waters and are unlikely to be affected by long-term decreases in temperature. However, shallow waters population may be more vulnerable to low temperatures in extreme winters (Hughes, 1998a). For example, a population of Amphiura filiformis at 27 m depth off the Danish coast was killed by the winter of 1962-63 (Muus, 1981) and a population at 35-50 m depth in the inner German Bight was killed in the winter of 1969-1970 and a new population did not re-establish until 1974 (Gerdes, 1976). Ursin (cited in Gerdes, 1978) suggested that Amphiura filiformis did not occur in areas with winter temperatures below 4°C although in Helgoland waters it can tolerate temperatures as low as 3.5°C. Low temperatures are a limiting factor for breeding in this species, which takes place during the warmest months in the British waters. Similarly, Ophiothrix fragilis occurs in shallow, enclosed waters that regularly drop to 3 °C but is absent from areas where temperatures drop to 0°C. In addition, temperature influences growth and reproduction in many species of hydroids and ascidians (see species reviews).

Overall, most species will probably not be adversely affected by a long-term decrease in temperatures, although short-term acute decreases in temperatures associated with extreme winters may result in loss of a few species. Therefore, resilience is High and the biotope is assessed as Not sensitive at the benchmark level.

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Echinoderms are generally regarded as stenohaline and most species are exclusively marine (Binyon, 1966; Pawson, 1966; Stickle & Diehl, 1987; Lawrence, 1996, Russell, 2013). An increase in salinity at the benchmark level would result in a salinity of >40 psu, and as hypersaline water is likely to sink to the seabed, the biotope may be affected by hypersaline effluents. Roberts et al. (2010b) suggested that hypersaline effluent dispersed quickly but was more of a concern at the seabed and in areas of low energy where widespread alternations in the community of soft sediments were observed. In several studies, echinoderms and ascidians were amongst the most sensitive groups examined (Roberts et al., 2010b).

Sensitivity assessment. An increase in salinity from full to >40 psu is probably detrimental to the important characteristic species of the biotope. Although, there is no direct evidence of the effects of hypersaline water, the stenohaline nature of the echinoderm dominated community suggests that hypersaline conditions may cause mortality. Therefore, a resistance of Low is recorded but at Low confidence. Resilience would probably be Medium so that sensitivity may be Medium.

None Medium Medium
Q: Medium
A: Medium
C: Medium
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Echinoderms are generally regarded as stenohaline and most species are exclusively marine (Binyon, 1966; Pawson, 1966; Stickle & Diehl, 1987; Lawrence, 1996, Russell, 2013). Lawrence (1996) cited several examples of mass mortalities in echinoderms due to sudden increases in river discharge or localized heavy rains. However, some euryhaline species have been reported and local adaptation may occur in some species (see Binyon, 1966 and Stickle & Diehl, 1987 for reviews). A decrease in salinity from e.g. full to reduced for a year (see benchmark) is likely to result in marked changes in community composition, including loss of the Ocnus aggregations. Therefore, a resistance of None has been suggested.  Resilience is probably Medium so that sensitivity is assessed as Medium.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

The biotope is only found in areas of weak or very weak tidal streams and so a decrease in flow is unlikely but it is likely to be intolerant of increases in water flow.  Some tidal flow is necessary for the supply of food in the form of organic particles by resuspension and advective transport, gaseous exchange and the removal of wastes, influencing the growth rate of suspension-feeding benthos (Dauwe, 1998).  Ocnus planci has been recorded from moderately strong to very weak tidal streams (Connor et al., 1997b). The feeding efficiency of suspension feeding species may be impaired in strong flow, while allowing other species to colonize.

An increase in water flow will probably result in a marked change in the community due to modification of the substratum, removing finer particulates such as muds and favouring the deposition of coarser deposits. The resultant sediment scour may adversely affect epifaunal species. Increased water flow may also cause small stones, pebbles, and cobbles to roll along the substratum resulting in further abrasion for epifauna.  

Sensitivity assessment.  A significant increase in water flow may winnow away the mud surface or even remove the mud habitat and hence the biotope if prolonged. An increase of 0.2 m/s may begin to erode the mud surface where the site is already subject to flow (e.g. weak flow at the seabed), based on sediment erosion deposition curves (Wright, 2001). However, the dominant suspension feeding echinoderms position themselves on the stones, shells and rocks on the surface of the muddy substratum, and may not be affected adversely by an increase of 0.1-0.2 m/s. Therefore, a resistance of High is recorded but with Low confidence. Therefore, resilience is probably High so that the biotope is assessed as Not sensitive at the benchmark level.  

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Ocnus planci was recorded from moderately wave exposed to extremely wave sheltered habitats (Connor et al., 1997b). But this biotope (IFiMu.Ocn) is only recorded from moderately wave exposed to extremely wave sheltered conditions. An increase in wave exposure and the resultant increase in oscillatory water movement at the sediment surface is likely to resuspend fine particulates, and deposit coarser sediment types, e.g. sands and gravels resulting in loss of many of the mud dwelling species. Water movement is also likely to roll, or move stones, cobbles , pebbles and shell fragments, resulting in increased sediment scour and abrasion, and probably loss of many of the epifaunal species. Ocnus species may survive on coarser substrata but are rare in wave exposed environments (Connor et al., 1997b). Overall, the community is likely to change significantly and the aggregations of Ocnus lost.  However, a change of 0.3-0.5% of significant wave height (the benchmark) is unlikely to be significant, especially at depth. Therefore, a resistance of High is suggested so that resilience also High and the biotope is assessed as Not sensitive at the benchmark level.

Chemical Pressures

 ResistanceResilienceSensitivity
Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Bryan (1984) reported that early work had shown that echinoderm larvae were sensitive to heavy metals, e.g. the intolerance of larvae of Paracentrotus lividus to copper (Cu) had been used to develop a water quality assessment. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu) and heavy metals caused reproductive anomalies in the starfish Asterias rubens (Besten, et al., 1989, 1991). Sea-urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Crompton (1997) reported that mortalities occurred in echinoderms after 4-14 day exposure to above 10-100 µg/l Cu, 1-10 mg/l Zn and 10-100 mg/l Cr but that mortalities occurred in echinoderm larvae above10-100 µg/ l Ni.

Various heavy metals have been show to have sublethal effects on growth in the few hydroids studied experimentally (Stebbing, 1981; Bryan, 1984; Ringelband, 2001). Gastropod molluscs have been reported to relatively tolerant of heavy metals while a wide range of sublethal and lethal effects have been observed in larval and adult crustaceans (Bryan, 1984). Bryan (1984) suggested that polychaetes are fairly resistant to heavy metals, based on the species studied. Short term toxicity in polychaetes was highest to Hg, Cu and Ag, declined with Al, Cr, Zn and Pb whereas Cd, Ni, Co and Se the least toxic.

Tri-butyl tin (TBT) has a marked effect on numerous marine organisms (Bryan & Gibbs, 1991). Bryan & Gibbs (1991) reported that virtually no hydroids were present on hard bottom communities in TBT contaminated sites and suggested that some hydroids were intolerant of TBT levels between 100 and 500 ng/l. Copepod and mysid crustaceans were particularly intolerant of TBT while crabs were more resistant (Bryan & Gibbs, 1991), although recent evidence suggests some sublethal endocrine disruption in crabs. The effect of TBT on Nucella lapillus and other neogastropods is well known (see review), and similar effects on reproduction may occur in other gastropod molluscs, including nudibranchs. Rees et al. (2001) reported that the abundance of epifauna had increased in the Crouch estuary in the five years since TBT was banned from use on small vessels. Rees et al. (2001) suggested that TBT inhibited settlement in ascidian larvae. This report suggests that epifaunal species (including, bryozoan, hydroids and ascidians) may be at least inhibited by the presence of TBT.

Overall, while some invertebrate groups are tolerant, many of the other groups, including echinoderms are probably intolerant, especially their larvae. Nevertheless, the biotope is assessed as Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Sheltered embayments and lagoons, where this biotope is found, are particularly vulnerable to oil pollution, which may settle onto the sediment and persist for years (Cole et al., 1999). Subsequent digestion or degradation of the oil by microbes may result in nutrient enrichment and eutrophication (see nutrients below). Although protected from direct smothering by oil by its depth, the biotope is relatively shallow and would be exposed to the water soluble fraction of oil, water soluble PAHs, and oil adsorbed onto particulates.

Suchanek (1993) reviewed the effects of oil spills on marine invertebrates and concluded that, in general, on soft sediment habitats, infaunal polychaetes, bivalves and amphipods were particularly affected. Crude oil and refined oils were shown to have little effect on fertilization in sea urchin eggs but in the presence of dispersants fertilization was poor and embryonic development was impaired (Johnston, 1984). Sea urchin eggs showed developmental abnormalities when exposed to 10-30 mg/l of hydrocarbons and crude oil : Corexit dispersant mixtures have been shown to cause functional loss of tube feet and spines in sea urchins (Suchanek, 1993). Olsgard & Gray (1995) found the brittlestar Amphiura filiformis to be very sensitive to oil pollution. During monitoring of sediments in the Ekofisk oilfield, Addy et al. (1978) suggest that reduced abundance of Amphiura filiformis within 2-3 km of the site was related to discharges of oil from the platforms and to physical disturbance of the sediment. Although acute toxicity test showed that drill cuttings containing oil based muds had a very low toxicity (LC50 52,800 ppm total hydrocarbons in test sediment), Newton & McKenzie (1998) suggest these are a poor predictor of chronic response. Chronic sub-lethal effects were detected around the Beryl oil platform in the North Sea where the levels of oil in the sediment were very low (3 ppm) and Amphiura filiformis was excluded from areas nearer the platform with higher sediment oil content. Similarly, in Ophiothrix fragilis, exposure to 30,000 ppm oil reduces its load of symbiotic bacteria by 50% and brittle stars begin to die (Newton & McKenzie, 1995). Crude oil from the Torrey Canyon and the detergent used to disperse it caused mass mortalities of echinoderms; Asterias rubens, Echinocardium cordatum, Psammechinus miliaris, Echinus esculentus, Marthasterias glacialis and Acrocnida brachiata (Smith, 1968).

Suchanek (1993) reported that the anemones Anthopleura spp. and Actinia spp. survived in waters exposed to spills and chronic inputs of oils. Similarly, one month after the Torrey Canyon oil spill the dahlia anemone, Urticina felina, was found to be one of the most resistant animals on the shore, being commonly found alive in pools between the tide-marks which appeared to be devoid of all other animals (Smith, 1968). If the physiology within different animals groups can be assumed to be similar, then amphipods, echinoderms, and soft corals may be intolerant of hydrocarbon contamination while hydroids may demonstrate sublethal effects and anemones and some species of sponge are relatively tolerant.

Nevertheless, the biotope is assessed as Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Little information on the toxicity of synthetic chemicals to holothurians was found. Newton & McKenzie (1995) suggested that echinoderms tend to be very intolerant of various types of marine pollution but gave no detailed information. Cole et al. (1999) reported that echinoderm larvae displayed adverse effects when exposed to 0.15mg/l of the pesticide Dichlorobenzene (DCB). Smith (1968) demonstrated that 0.5 -1 ppm of the detergent BP1002 resulted in developmental abnormalities in echinopluteus larvae of Echinus esculentus. Smith (1968) also noted that large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m in the vicinity of Sennen, presumably due to a combination of wave exposure and heavy spraying of dispersants in that area. TBT was shown to inhibit arm regeneration in the brittlestar Ophioderma brevispina, at 10ng/l and produce significant inhibition at 100 ng/l. It was suggested that TBT acts via the nervous system, although direct action on the tissues at the point of breakage could not be excluded (Bryan & Gibbs, 1991) Therefore, holothurians and their larvae may also be intolerant of synthetic chemicals.

The species richness of hydroid communities decreases with increasing pollution (Boero, 1984; Gili & Hughes, 1995). Alcyonium digitatum at a depth of 16m in the locality of Sennen Cove (Pedu-men-du, Cornwall) died resulting from the offshore spread and toxic effect of detergents e.g. BP 1002 sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill (Smith, 1986). Possible sub-lethal effects of exposure to synthetic chemicals may result in a change in morphology, growth rate or disruption of the reproductive cycle.

Therefore, hydroids, crustaceans, gastropods, and ascidians are probably intolerant of TBT contamination. Echinoderms, including Ocnus, may be intolerant of synthetic chemicals. Nevertheless, the biotope is assessed as Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The biotope is assessed as Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Low Medium Medium
Q: High
A: High
C: Medium
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Lawrence (1996) reported mass mortality of echinoderms in the Gulf of Trieste due to hypoxia caused by a strong thermocline combined with high pelagic productivity and eutrophication. The brittlestar Ophiura quinquemaculata was killed with a few days, and holothurians including Ocnus planci (as Cucumaria planci), starfish Asteropecten sp. and the remaining brittlestars were killed within a week. In experiments, Amphiura filiformis only left its protected position in the sediment when oxygen levels fell below 0.85mg/l (Rosenberg et al., 1991). Mass mortality of Amphiura filiformis was observed during severely low oxygen events (<0.7 mg/l) (Nilsson, 1999). However, at oxygen concentrations between 0.85 mg/l and 1.0 mg/l Rosenberg et al. (1991) observed the species was able to survive for several weeks. Echinoderms were shown to be intolerant of the effects of algal blooms, resulting in mortalities of the sea urchins Echinus esculentus and Paracentrotus lividus, and the holothurian Labidoplax digitata amongst other echinoderms, probably due to hypoxia caused by death of the algal bloom algae (Boalch, 1979; Forster, 1979; Griffiths et al., 1979; Lawrence, 1996). Diaz & Rosenberg (1995, Figure 5)) suggested that shrimp and crustaceans were lost as oxygen levels dropped below ca 0.75 ml/l and that the macroinfauna was reduced below ca 0.4ml/l. Vaquer-Sunyer & Duarte (2008) suggested a median sublethal oxygen concentration of 1.22 mg O2/l (± 0.25) for a number of echinoderms reviewed in their study. Echinoderms were neither the most or the least sensitive of the taxonomic groups examined.  Riedel et al. (2012) examined the effects of hypoxia and anoxia on macrofauna in the North Adriatic, using in situ experimental apparatus.  The concluded that, decapods, echinoderms and polychaetes were amongst the most sensitive to hypoxia while ascidians and anthozoans were amongst the most resistant of the species encountered in their study. However, Ocnus planci survived moderate (<0.8 ml O2/l, <1.12 mg O2/l) to severe (<0.5 ml O2/l, <0.7 mg O2/l) hypoxia but died with several hours (median duration of 23.3 hrs) of anoxic conditions; anoxia was reached after 48 hrs of the onset of the experiment (Riedel et al., 2012).

Overall, based on the evidence cited above, echinoderms appear to be intolerant of hypoxic conditions. However, Ocnus planci may be amongst the most resistant of those studied by Riedel et al. (2012) in their 3 to 4 day experiment. Therefore, a decrease in oxygen levels to below 2 mg O2 /l for a week is likely to result in loss of most of the suspension feeding echinoderms and a proportion of the Ocnus spp. population, based on the observation in the Gulf of Trieste, and a resistance of Low is suggested. Resilience is probably Medium so that sensitivity is assessed as Medium.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Hughes (1998a) suggested that sea loch sediments, where this biotope occurs, were naturally rich in organic matter. Moderate enrichment is likely to increase food availability and hence, the abundance of deposit feeding organisms. Increases in nutrients and low oxygen conditions result in anaerobic conditions within the sediment. Nutrient enrichment may also result in algal blooms. For example Cerianthus lloydii was found near the centre of sewage sludge dumping groups at ca 10% organic carbon but more abundant at intermediate nutrient enrichment (Hughes, 1998a) and echinoderms were shown to be intolerant of the effects of algal blooms, resulting in mortalities of the sea urchins Echinus esculentus and Paracentrotus lividus, and the holothurian Labidoplax digitata amongst other echinoderms, probably due to hypoxia caused by death of the algal bloom algae (Boalch, 1979; Forster, 1979; Griffiths et al., 1979; Lawrence, 1996). Therefore, while moderate enrichment may be beneficial, echinoderms are indirectly intolerant due to sudden hypoxia resulting from the death of algal blooms.  

Nevertheless, the biotope is assessed as Not sensitive at the pressure benchmark that assumes compliance with good status as defined by the WFD.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Hughes (1998a) suggested that sea loch sediments, where this biotope occurs, were naturally rich in organic matter. Moderate enrichment is likely to increase food availability and hence, the abundance of deposit feeding organisms.

Cerianthus lloydii was found near the centre of sewage sludge dumping groups at ca 10% organic carbon but was more abundant at intermediate nutrient enrichment (Hughes, 1998b). But Borja et al. (2000) and Gittenberger and van Loon (2011) both assigned Cerianthus lloydii to their Ecological Group I, ‘species very sensitive to organic enrichment and present under unpolluted conditions (initial state)’ in of the AZTI Marine Biotic Index (AMBI) index to assess disturbance (including organic enrichment). The basis for their assessment and relation to the pressure benchmark is not clear.

However, no information on the effects of organic enrichment on Ocnus planci was found.

Sensitivity assessment. In the absence of direct evidence, it is assumed that muddy habitats in sea lochs are probably naturally rich in organic matter (Hughes, 1998a).  Therefore, a resistance of High is suggested with Low confidence. Hence, resilience is High and the biotope assessed as Not sensitive at the benchmark level.

Physical Pressures

 ResistanceResilienceSensitivity
None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’).  Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’.  Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

This biotope (IFiMu.Ocn) is an epifaunal overlay on an otherwise sedimentary biotope. The important charactersitic epifauna (Ocnus planci) position themsleves on stones, pebbles shells and other hard substrata to avail themsleves of the passing current. Other suspension feeding brittlestar may do the same.  Yet the biotope is only recorded on muddy habitats with stones and shell on the surface (Connor et al., 2004).  If sedimentary substrata were replaced with rock substrata the biotope would be lost, as it would not longer be a sedimentary habitat and no longer recognised under the habitat clasification.

Sensitivity assessment. Resistance to the pressure is considered ’None‘, and resilience ’Very low‘ or ‘None’ (as the pressure represents a permanent change) and the sensitivity of this biotope is assessed as ’High’.

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

This biotope (IFiMu.Ocn) is an epifaunal overlay on an otherwise sedimentary biotope. The important characteristic epifauna (Ocnus planci) position themselves on stones, pebbles shells, and other hard substrata to avail themselves of the passing current. Other suspension feeding brittlestars may do the same.Yet the biotope is only recorded on muddy habitats with stones and shell on the surface (Connor et al., 2004).  It is unknown why the aggregations of suspension feeding echinoderms occur in this habitat. But a change in sediment type by one Folk class t, for example, muddy sand or sand, would result in the loss of the biotope as described under the habitat classification.  

Sensitivity assessment. Resistance to the pressure is considered ’None‘, and resilience ’Very low‘ or ‘None’ (as the pressure represents a permanent change) and the sensitivity of this biotope is assessed as ’High’.

None Medium Medium
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR

This biotope (IFiMu.Ocn) is an epifaunal overlay on an otherwise sedimentary biotope. The important characteristic epifauna (Ocnus planci) position themselves on stones, pebbles shells, and other hard substrata to avail themselves of the passing current. Other suspension feeding brittlestars may do the same. The extraction of the sediment to a depth of 30 cm would remove the mud infauna and the surface epifauna with the affected area.  Therefore, a resistance of None is suggested based on expert judgement. Resilience is probably Medium so that the sensitivity is assessed as Medium.  

Low Medium Medium
Q: High
A: Medium
C: Medium
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Stable sedimentary habitats, such as mud were amongst the most vulnerable to fishing activities, e.g. otter board trawling (Ball et al., 2000b; Collie et al., 2000). Tracks left by otter boards were visible 18 months after experimental trawls in Gareloch (Ball et al., 2000b). Ball et al., (2000b) concluded that trawling modified the benthic community due to an increase in opportunistic polychaetes. However, Kaiser et al. (2006) concluded that otter boards had a significant initial effect on muddy sands and muds, but that the effects were short-lived in mud habitats.

Erect epifaunal species are particularly vulnerable to physical disturbance (Jenkins & Kaiser, 1998). Hydroids are likely to be detached or damaged by bottom trawling or dredging (Holt et al., 1995). Veale et al. (2000) reported that the abundance, biomass, and production of epifaunal assemblages decreased with increasing fishing effort. Hydroid and bryozoan matrices were reported to be greatly reduced in fished areas (Jennings & Kaiser, 1998). Mobile gears also result in modification of the substratum, including removal of shell debris, cobbles and rocks, and the movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998) on which many of the species in this community depend. The removal of rocks or boulders to which species are attached results in substratum loss (see above). For example, Magorrian & Service (1998) reported that queen scallop trawling flattened horse mussel beds and removed emergent epifauna in Strangford Lough. They suggested that the emergent epifauna such as Alcyonium digitatum, a frequent component of this biotope, were more sensitive than the horse mussels themselves and reflected early signs of damage. Species with fragile tests such as Echinus esculentus and the brittlestar Ophiocomina nigra and edible crabs Cancer pagurus were reported to suffer badly from the impact of a passing scallop dredge (Bradshaw et al., 2000). But brittlestars such as Ophiothrix fragilis probably have good powers of regeneration and infaunal species such as Amphiura filiformis may avoid the effects of a passing beam trawl. Scavengers such as Asterias rubens and Buccinum undatum were reported to be fairly robust to encounters with trawls (Kaiser & Spencer, 1995) may benefit in the short term, feeding on species damaged or killed by passing dredges. However, Veale et al. (2000) did not detect any net benefit at the population level. Greathead et al. (2011) were not able to conclude if the variation in Cerianthus abundance in the Fladden Grounds was due to miscounting, its patchy distribution, or fishing activity.

Ocnus species are the most important characterizing species within the biotope, and may be damaged by physical disturbance due to an anchor or passing fishing gear. But they probably have good powers of regeneration (given their fissiparous habit) and would survive if the damage were not too severe. However, they may be displaced due to physical abrasion as the stones and shell they occupy are moved, rolled, or removed from the habitat.

Sensitivity assessment. Overall, physical disturbance by an anchor or mobile fishing gear is likely to remove a significant proportion of the epifauna within the community and attract scavengers to the community in the short term. Therefore, a resistance of Low is suggested. Resilience is probably Medium so that sensitivity is assessed as Medium.

Low Medium Medium
Q: High
A: Medium
C: Medium
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Sensitivity assessment. Based on the evidence present under abrasion above physical disturbance by mobile fishing gear is likely to remove a significant proportion of the epifauna within the community and attract scavengers to the community in the short term. Therefore, a resistance of Low is suggested. Resilience is probably Medium so that sensitivity is assessed as Medium.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

The biotope occurs in sheltered areas, in fine sediments, subject to high suspended sediment loads. The effect of increased deposition of fine silt is uncertain but it is possible that feeding structures may become clogged.  However, Ocnus planci (as Cucumaria planci) maintained a high filtration efficiency even at food concentrations (suspension densities) three times average natural levels (Ölsher & Fedra, 1977). Burrowing species are unlikely to be affected and suspension feeding species are likely to experience, and hence tolerate, periodic re-suspension of suspended sediment due to wave or current surges, storms or digging by predators. Therefore, they are likely to tolerate an increase in suspended sediment for a month, although feeding efficiency of some species, especially epifaunal suspension feeders, may be impaired.  Therefore, a resistance of High is suggested.  Hence, resilience is High and the biotope is assessed as Not sensitive at the benchmark level.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Deposition of a 5 cm layer of sediment is unlikely to disturb burrowing infaunal species. Kukert & Smith (1992) noted that deposition of 5-6 cm of sediment resulted in a 32% reduction in macrofaunal abundance in less than 1 month but that deposit feeders had returned to background levels within 3 months, while scavengers and carnivores took longer. Suspension feeding epifauna are likely to be the least resistant. Species that project above the sediment surface, such as sea pens and Sabella pavonina are probably tall enough to avoid the effects, while burrowing species such as Myxicola infundibulum, Chaetopterus variopedatus, Cerianthus lloydii and Amphiura filiformis could probably burrow up through the sediment. For example, in normal accretion, Cerianthus lloydii keeps pace with the accretion and, as a result, develops burrows much larger than the animal itself (Schäfer, 1972; Bromley, 2012). Schäfer (1972) reported that an increase in depositional rate led to an avoidance behaviour in Cerianthus lloydii. The organism ceases tube building activity and instead the animal bunches its tentacles and intrudes its way up to the new surface, where it establishes a new burrow. However, no information on the depth of material through which is can burrow was given

Other epifauna e.g. hydroids, tubeworms, ascidians are fixed to the substratum, the brittlestar Ophiothrix fragilis and smaller sea urchins are unable to burrow effectively and would probably be smothered, potentially succumbing due to clogged respiratory apparatus and temporary anoxia.

At up to 15 cm in length, Ocnus planci may be large enough to avoid the effects of smothering but Ocnus brunneus is a small species. However, holothurians are generally burrowing species and it is probably able to regain the sediment surface rapidly. Raised areas of sediment may even provide this species with a new feeding perch.

Sensitvity assessment. Ocnus and most of the species typical of mud communities would probably survive smothering by 5 cm of sediment. However, some epifaunal species, and juveniles of several species may be affected adversely, resulting in a short-term decrease in species richness. Therefore, a resistance of High is suggested.  Hence, resilience is High and the biotope is assessed as Not sensitive at the benchmark level.

Medium High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Deposition of 30 cm of fine sediment is likely to smother the entire community. In the sheltered low energy environment this biotope occurs, the sediment is likely to remain. Therefore, the effect on the community will depend on the ability of the species to burrow through the deposited sediment.  Small brittlestars and hydroids or ascidians affixed to stones and shell will be unable to burrow, while large burrowing species such as Chaetopterus variopedatus and Cerianthus lloydii may be able to regain the surface. For example, in normal accretion, Cerianthus lloydii keeps pace with the accretion and, as a result, develops burrows much larger than the animal itself (Schäfer, 1972; Bromley, 2012). Schäfer (1972) reported that an increase in depositional rate led to an avoidance behaviour in Cerianthus lloydii. The organism ceases tube building activity and instead the animal bunches its tentacles and intrudes its way up to the new surface, where it establishes a new burrow. However, no information on the depth of material through which is can burrow was given.

At up to 15 cm in length, Ocnus planci may be large enough to avoid the effects of smothering but Ocnus brunneus is a small species. However, holothurians are generally burrowing species and it is probably able to regain the sediment surface rapidly. Raised areas of sediment may even provide this species with a new feeding perch. But the stones and shell typical of the biotope would also be smothered and lost and with them the epifaunal perches they provide. As a result, the aggregations of Ocnus spp. that typify this biotope may also be lost, although the reason for their aggregation is unknown.

Sensitivity assessment. Smothering by 30 cm of sediment is likely to result in the loss of smaller species and epifauna while larger burrowing species may survive.  Therefore, a resistance of Medium is suggested to represent the loss of some of the Ocnus population and other epifauna. The resilience is probably High so that sensitivity is assessed as Low.

Not Assessed (NA) Not Assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Some of the characterizing species associated with this biotope, in particular, the epifauna, may respond to sound vibrations. Feeding will resume once the disturbing factor has passed. Therefore, this pressure is probably Not relevant in this biotope.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Epifaunal suspension feeders that feed on passing seston such as phytoplankton and a variety of marine organic particulates dominate the biotope.  Most of the productivity is probably secondary and not directly dependent on the availability of light , especially in the deeper examples of the biotope.  Therefore, this biotope is probably Not sensitive to changes in light (resistance and resilience are High).

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of seed or propagules.  But seed or propagule dispersal is not considered under the pressure definition and benchmark.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant to seabed habitats. 

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Most species within the biotope are burrowing and have no or poor visual perception and are unlikely to be affected by visual disturbance such as shading. Epifauna such as crabs have well developed visual acuity and are likely to respond to movement in order to avoid predators. However, it is unlikely that the species will be affected by visual disturbance at the benchmark level.

Biological Pressures

 ResistanceResilienceSensitivity
No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence of genetic modification, breeding, or translocation was found.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Sternapsis scutata is a non-native polychaete that has extended its range in inshore muddy sediments in the south west of the UK (Shelley et al., 2008). However, in mesocosm experiments, little effect on biological functioning was detected after the introduction of the polychaete and a doubling of its biomass (Shelley et al., 2008). No direct evidence on the effect of non-native species on mud communities was found. However, this assessment should be revisited in the light of new evidence.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

The gastropod snail Melanella alba parasites holothurians, probably by sucking their fluids (Graham, 1988) and has been recorded in this biotope (Connor et al., 2004). Any parasite is likely to reduce the viability of the host species, so a resistance of High has been recorded. Therefore, resilience is also High and the biotope is assessed as Not sensitive.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

None of the characterizing species within this biotope are currently directly targeted in the UK and, hence, this pressure is considered to be Not relevant.

Medium High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

The physical effects of fisheries or dredging activities are addressed under abrasion, penetration and extraction pressures above. No clear biological relationships between the important characteristic species were found. Therefore, removal of any one species may not affect other members of the community adversely.  However, is the important characterizing species were removed as by-catch, the character of the biotope would change. A significant decline in the abundance of either Ocnus planci would result in loss of the biotope as recognised by the habitat classification.  Therefore, a resistance of Medium is recorded, albeit at Low confidence. As resilience is probably High, sensitivity is assessed as Low.

Importance review

Policy/Legislation

Habitats Directive Annex 1Large shallow inlets and bays

Exploitation

No species are known to be exploited in this biotope.

Additional information

-

Bibliography

  1. Addy, J.M., Levell, D. & Hartley, J.P., 1978. Biological monitoring of sediments in the Ekofisk oilfield. In Proceedings of the conference on assessment of ecological impacts of oil spills. American Institute of Biological Sciences, Keystone, Colorado 14-17 June 1978, pp.514-539.
  2. Ball, B., Munday, B. & Tuck, I., 2000b. Effects of otter trawling on the benthos and environment in muddy sediments. In: Effects of fishing on non-target species and habitats, (eds. Kaiser, M.J. & de Groot, S.J.), pp 69-82. Oxford: Blackwell Science.
  3. Besten, P.J. den, Donselaar, E.G. van, Herwig, H.J., Zandee, D.I. & Voogt, P.A., 1991. Effects of cadmium on gametogenesis in the seastar Asterias rubens L. Aquatic Toxicology, 20, 83-94.
  4. Besten, P.J. den, Herwig, H.J., Zandee, D.I. & Voogt, P.A., 1989. Effects of Cd and PCBs on reproduction in the starfish Asterias rubens: aberrations in early development. Ecotoxicology and Environmental Safety, 18, 173-180.
  5. Binyon, J., 1966. Salinity tolerance and ionic regulation. In Physiology of Echinodermata (ed. R.A. Boolootian), pp. 359-377. New York: John Wiley & Sons.
  6. Boalch, G.T., 1979. The dinoflagellate bloom on the coast of south-west England, August to September 1978. Journal of the Marine Biological Association of the United Kingdom, 59, 515-517.

  7. Boero, F., 1984. The ecology of marine hydroids and effects of environmental factors: a review. Marine Ecology, 5, 93-118.
  8. Borja, A., Franco, J. & Perez, V., 2000. A marine biotic index to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments. Marine Pollution Bulletin, 40 (12), 1100-1114.
  9. Bradshaw, C., Veale, L.O., Hill, A.S. & Brand, A.R., 2000. The effects of scallop dredging on gravelly seabed communities. In: Effects of fishing on non-target species and habitats (ed. M.J. Kaiser & de S.J. Groot), pp. 83-104. Oxford: Blackwell Science.
  10. Bromley, R.G., 2012. Trace Fossils: Biology, Taxonomy and Applications: Routledge.

  11. Bryan, G.W. & Gibbs, P.E., 1991. Impact of low concentrations of tributyltin (TBT) on marine organisms: a review. In: Metal ecotoxicology: concepts and applications (ed. M.C. Newman & A.W. McIntosh), pp. 323-361. Boston: Lewis Publishers Inc.
  12. Bryan, G.W., 1984. Pollution due to heavy metals and their compounds. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters, vol. 5. Ocean Management, part 3, (ed. O. Kinne), pp.1289-1431. New York: John Wiley & Sons.
  13. Bullimore, B., 1985. An investigation into the effects of scallop dredging within the Skomer Marine Reserve. Report to the Nature Conservancy Council by the Skomer Marine Reserve Subtidal Monitoring Project, S.M.R.S.M.P. Report, no 3., Nature Conservancy Council.
  14. Chia, F.S. & Crawford, B.J., 1973. Some observations on gametogenesis, larval development and substratum selection of the sea pen Ptilosarcus guerneyi. Marine Biology, 23, 73-82.
  15. Cole, S., Codling, I.D., Parr, W. & Zabel, T., 1999. Guidelines for managing water quality impacts within UK European Marine sites. Natura 2000 report prepared for the UK Marine SACs Project. 441 pp., Swindon: Water Research Council on behalf of EN, SNH, CCW, JNCC, SAMS and EHS. [UK Marine SACs Project.], http://www.ukmarinesac.org.uk/
  16. Collie, J.S., Hall, S.J., Kaiser, M.J. & Poiner, I.R., 2000. A quantitative analysis of fishing impacts on shelf-sea benthos. Journal of Animal Ecology, 69 (5), 785–798.
  17. Connor, D.W., Dalkin, M.J., Hill, T.O., Holt, R.H.F. & Sanderson, W.G., 1997a. Marine biotope classification for Britain and Ireland. Vol. 2. Sublittoral biotopes. Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06., Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06.
  18. Crompton, T.R., 1997. Toxicants in the aqueous ecosystem. New York: John Wiley & Sons.
  19. Dauwe, B., Herman, P.M.J. & Heip, C.H.R., 1998. Community structure and bioturbation potential of macrofauna at four North Sea stations with contrasting food supply. Marine Ecology Progress Series, 173, 67-83.
  20. Dinnel, P.A., Pagano, G.G., & Oshido, P.S., 1988. A sea urchin test system for marine environmental monitoring. In Echinoderm Biology. Proceedings of the Sixth International Echinoderm Conference, Victoria, 23-28 August 1987, (R.D. Burke, P.V. Mladenov, P. Lambert, Parsley, R.L. ed.), pp 611-619. Rotterdam: A.A. Balkema.
  21. Dipper, F.A. & Beaver, R., 1999. Marine Nature Conservation Review Sector 12. Sea lochs in the Clyde Sea: area summaries. Peterborough: Joint Nature Conservation Committee. [Coasts and Seas of the United Kingdom. MNCR Series]
  22. Emson, R.H., & Wilkie, I.C., 1980. Fission and autotomy in echinoderms. Oceanography and Marine Biology: an Annual Review, 18, 155-250.
  23. Eno, N.C., MacDonald, D. & Amos, S.C., 1996. A study on the effects of fish (Crustacea/Molluscs) traps on benthic habitats and species. Final report to the European Commission. Study Contract, no. 94/076.
  24. Erwin, D.G., Picton, B.E., Connor, D.W., Howson, C.M., Gilleece, P. & Bogues, M.J., 1990. Inshore Marine Life of Northern Ireland. Report of a survey carried out by the diving team of the Botany and Zoology Department of the Ulster Museum in fulfilment of a contract with Conservation Branch of the Department of the Environment (N.I.)., Ulster Museum, Belfast: HMSO.
  25. Forster, G.R., 1979. Mortality of the bottom fauna and fish in St Austell Bay and neighbouring areas. Journal of the Marine Biological Association of the United Kingdom, 59, 517-520.
  26. Gili, J-M. & Hughes, R.G., 1995. The ecology of marine benthic hydroids. Oceanography and Marine Biology: an Annual Review, 33, 351-426.
  27. Gittenberger, A. & Van Loon, W.M.G.M., 2011. Common Marine Macrozoobenthos Species in the Netherlands, their Characterisitics and Sensitivities to Environmental Pressures. GiMaRIS report no 2011.08.
  28. Graham, A., 1988. Molluscs: prosobranchs and pyramellid gastropods (2nd ed.). Leiden: E.J. Brill/Dr W. Backhuys. [Synopses of the British Fauna No. 2]
  29. Greathead, C., Demain, D., Dobby, H., Allan, L. & Weetman, A., 2011. Quantitative assessment of the distribution and abundance of the burrowing megafauna and large epifauna community in the Fladen fishing ground, northern North Sea. Scottish Government: Edinburgh (UK).

  30. Griffiths, A.B., Dennis, R. & Potts, G.W., 1979. Mortality associated with a phytoplankton bloom off Penzance in Mount's Bay. Journal of the Marine Biological Association of the United Kingdom, 59, 515-528.

  31. Hoare, R. & Wilson, E.H., 1977. Observations on the behaviour and distribution of Virgularia mirabilis O.F. Müller (Coelenterata: Pennatulacea) in Holyhead harbour. In Proceedings of the Eleventh European Symposium on Marine Biology, University College, Galway, 5-11 October 1976. Biology of Benthic Organisms, (ed. B.F. Keegan, P.O. Ceidigh & P.J.S. Boaden, pp. 329-337. Oxford: Pergamon Press. Oxford: Pergamon Press.
  32. Holt, T.J., Jones, D.R., Hawkins, S.J. & Hartnoll, R.G., 1995. The sensitivity of marine communities to man induced change - a scoping report. Countryside Council for Wales, Bangor, Contract Science Report, no. 65.
  33. Howson, C.M., Connor, D.W. & Holt, R.H.F., 1994. The Scottish sealochs - an account of surveys undertaken for the Marine Nature Conservation Review. Joint Nature Conservation Committee Report, No. 164 (Marine Nature Conservation Review Report MNCR/SR/27)., Joint Nature Conservation Committee Report, No. 164 (Marine Nature Conservation Review Report MNCR/SR/27).
  34. Hughes, D.J., 1998a. Sea pens & burrowing megafauna (volume III). An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. Natura 2000 report prepared for Scottish Association of Marine Science (SAMS) for the UK Marine SACs Project., Scottish Association for Marine Science. (UK Marine SACs Project). Available from:  http://www.ukmarinesac.org.uk/publications.htm

  35. Hughes, D.J., 1998b. Subtidal brittlestar beds. An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. Natura 2000 report prepared for Scottish Association of Marine Science (SAMS) for the UK Marine SACs Project., Scottish Association for Marine Science. (UK Marine SACs Project, Vol. 3). Available from: http://www.ukmarinesac.org.uk/pdfs/britstar.pdf
  36. Hyman, L.V., 1955. The Invertebrates: Vol. IV. Echinodermata. The coelomate Bilateria. New York: McGraw Hill.
  37. Jennings, S. & Kaiser, M.J., 1998. The effects of fishing on marine ecosystems. Advances in Marine Biology, 34, 201-352.
  38. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid,
  39. Johnston, R., 1984. Oil Pollution and its management. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters vol. 5. Ocean Management, part 3 (ed. O. Kinne), pp.1433-1582. New York: John Wiley & Sons Ltd.
  40. Kaiser, M., Clarke, K., Hinz, H., Austen, M., Somerfield, P. & Karakassis, I., 2006. Global analysis of response and recovery of benthic biota to fishing. Marine Ecology Progress Series, 311, 1-14.

  41. Kaiser, M.J. & Spencer, B.E., 1995. Survival of by-catch from a beam trawl. Marine Ecology Progress Series, 126, 31-38.
  42. Lawrence, J.M., 1996. Mass mortality of echinoderms from abiotic factors. In Echinoderm Studies Vol. 5 (ed. M. Jangoux & J.M. Lawrence), pp. 103-137. Rotterdam: A.A. Balkema.
  43. Magorrian, B.H. & Service, M., 1998. Analysis of underwater visual data to identify the impact of physical disturbance on horse mussel (Modiolus modiolus) beds. Marine Pollution Bulletin, 36, 354-359.
  44. Moore, P.G. & Cameron, K.S., 1999. A note on a hitherto unreported association between Photis longicaudata (Crustacea: Amphipoda) and Cerianthus lloydii (Anthozoa: Hexacorallia). Journal of the Marine Biological Association of the United Kingdom, 79, 369-370.
  45. Murray, E., Dalkin, M.J., Fortune, F. & Begg, K., 1999. Marine Nature Conservation Review Sector 2. Orkney: area summaries. Peterborough: Joint Nature Conservation Committee. [Coasts and sea of the United Kingdom. MNCR Series.]
  46. Newton, L.C. & McKenzie, J.D., 1995. Echinoderms and oil pollution: a potential stress assay using bacterial symbionts. Marine Pollution Bulletin, 31, 453-456.
  47. Newton, L.C. & McKenzie, J.D., 1998. Brittlestars, biomarkers and Beryl: Assessing the toxicity of oil-based drill cuttings using laboratory, mesocosm and field studies. Chemistry and Ecology, 15, 143-155.
  48. Ölscher E.M. & Fedra, K., 1977. On the ecology of a suspension feeding benthic community: filter efficiency and behaviour. In Biology of benthic organisms (ed. B.F. Keegan, P.O. Ceidigh & P.J.S. Boaden), pp. 483-492. Oxford: Pergamon Press.
  49. Olsgard, F. & Gray, J.S., 1995. A comprehensive analysis of the effects of offshore oil and gas exploration and production on the benthic communities of the Norwegian continental shelf. Marine Ecology Progress Series, 122, 277-306.
  50. Pawson, D.L., 1966. Ecology of holothurians. In Physiology of Echinodermata (ed. R.A. Boolootian), pp. 63-71. New York: John Wiley & Sons.
  51. Picton, B.E., 1993. A field guide to the shallow-water echinoderms of the British Isles. London: Immel Publishing Ltd.
  52. Rees, H.L., Waldock, R., Matthiessen, P. & Pendle, M.A., 2001. Improvements in the epifauna of the Crouch estuary (United Kingdom) following a decline in TBT concentrations. Marine Pollution Bulletin, 42, 137-144.
  53. Riedel, B., Zuschin, M. & Stachowitsch, M., 2012. Tolerance of benthic macrofauna to hypoxia and anoxia in shallow coastal seas: a realistic scenario. Marine Ecology Progress Series, 458, 39-52.

  54. Ringelband, U., 2001. Salinity dependence of vanadium toxicity against the brackish water hydroid Cordylophora caspia. Ecotoxicology and Environmental Safety, 48, 18-26.
  55. Roberts, D.A., Johnston, E.L. & Knott, N.A., 2010b. Impacts of desalination plant discharges on the marine environment: A critical review of published studies. Water Research, 44 (18), 5117-5128.

  56. Russell, M., 2013. Echinoderm Responses to Variation in Salinity. Advances in Marine Biology, 66, 171-212.
  57. Schäfer, H., 1972. Ecology and palaeoecology of marine environments, 568 pp. Chicago: University of Chicago Press.
  58. Shelley, R., Widdicombe, S., Woodward, M., Stevens, T., McNeill, C.L. & Kendall, M.A. 2008. An investigation of the impacts on biodiversity and ecosystem functioning of soft sediments by the non-native polychaete Sternaspis scutata (Polychaeta: Sternaspidae). Journal of Experimental Marine Biology and Ecology, 366, 146-150.
  59. Smiley, S., McEven, F.S., Chaffee, C. & Kushan, S., 1991. Echinodermata: Holothuoidea. In Reproduction of marine invertebrates, vol. 6. Echinoderms and Lophorates (ed. A.C. Giese, J.S. Pearse & V.B. Pearse), pp. 663-750. California: The Boxwood Press.
  60. Smith, J.E. (ed.), 1968. 'Torrey Canyon'. Pollution and marine life. Cambridge: Cambridge University Press.
  61. Stickle, W.B. & Diehl, W.J., 1987. Effects of salinity on echinoderms. In Echinoderm Studies, Vol. 2 (ed. M. Jangoux & J.M. Lawrence), pp. 235-285. A.A. Balkema: Rotterdam.
  62. Suchanek, T.H., 1993. Oil impacts on marine invertebrate populations and communities. American Zoologist, 33, 510-523.
  63. Tuck, I.D., Hall, S.J., Robertson, M.R., Armstrong, E. & Basford, D.J., 1998. Effects of physical trawling disturbance in a previously unfished sheltered Scottish sea loch. Marine Ecology Progress Series, 162, 227-242.
  64. Vaquer-Sunyer, R. & Duarte, C.M., 2008. Thresholds of hypoxia for marine biodiversity. Proceedings of the National Academy of Sciences, 105 (40), 15452-15457.

  65. Veale, L.O., Hill, A.S., Hawkins, S.J. & Brand, A.R., 2000. Effects of long term physical disturbance by scallop fishing on subtidal epifaunal assemblages and habitats. Marine Biology, 137, 325-337.
  66. Vella, G., Rushforth, I., Mason, E., Hough, A., England, R., Styles, P, Holt, T & Thorne, P., 2001. Assessment of the effects of noise and vibration from offshore windfarms on marine wildlife. Department of Trade and Industry (DTI) contract report, ETSU W/13/00566/REP. Liverpool: University of Liverpool., Department of Trade and Industry (DTI) contract report, ETSU W/13/00566/REP. Liverpool: University of Liverpool.

Citation

This review can be cited as:

Tyler-Walters, H., 2016. Ocnus planci aggregations on sheltered sublittoral muddy sediment. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/325

Last Updated: 31/05/2016