Circalittoral caves and overhangs

30-10-2000
Researched byDr Keith Hiscock Refereed byThis information is not refereed.
EUNIS CodeA4.71 EUNIS NameCommunities of circalittoral caves and overhangs

Summary

UK and Ireland classification

EUNIS 2008A4.71Communities of circalittoral caves and overhangs
EUNIS 2006A4.71Communities of circalittoral caves and overhangs
JNCC 2004CR.FCR.CvCircalittoral caves and overhangs
1997 BiotopeCR.C.CvCaves and overhangs (deep)

Description

Caves and overhanging rock in the circalittoral zone, away from significant influence of strong wave action. This habitat may be colonized by a wide variety of species, with encrusting sponges including some that are seldom seen such as Dercitus bucklandi and Thymosia guernii, anemones Parazoanthus spp. and the cup corals Caryophyllia inornatus, Hoplangia durotrix. In the south-west, Leptopsammia pruvoti may be abundant in restricted areas. (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

Occurs at widely separated locations generally in open coast waters on wave sheltered coasts with moderate tidal flow. Whilst the structural and functional aspects of the biotope are similar across its range, species composition varies.

Depth range

10-20 m, 20-30 m, 30-50 m

Additional information

The biotopes classification lists the scarlet and gold star coral Balanophyllia regia as characteristic but that coral occurs in shallow (infralittoral) depths and is a feature of overhangs, often exposed to strong wave action, there.

Listed By

Further information sources

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JNCC

Habitat review

Ecology

Ecological and functional relationships

The main components of the biotope probably interact very little and live independently. However, the corals provide a host for the barnacle Boschia anglica (in the south-west) and a calcareous substratum for boring species such as Hiatella arctica, Potamilla reniformis and the horseshoe worm Phoronis hippocrepia to live. Boring species may weaken the skeleton of the corals to the extent that they are easily detached (see Hiscock & Howlett,1976). The soft coral Alcyonium glomeratum may be predated on by the prosobranch Simnia patula. Encrusting sponges may overgrow other species and Harmelin (1990) has shown how encrusting bryozoans may engulf cup corals and kill them. Grazers such as the sea urchin Echinus esculentus, may occasionally pass through the biotope grazing away barnacles and erect bryozoans especially , possible freeing space for new colonization (Keith Hiscock, own observations).

Seasonal and longer term change

Most of the species in the biotope are long-lived. However, seasonal change occurs in the light-bulb ascidian Clavellina lepadiformis which grows rapidly in the spring to die-back in winter. A longer term decline has been recorded in the abundance of long-lived species (especially Leptopsammia pruvoti, Hoplangia durotrix and Alcyonium coralloides) at Lundy (K. Hiscock, own observations).

Habitat structure and complexity

There is little complexity in the habitat, most species living directly attached to the rock and not offering architectural complexity as shelter for other species.

Productivity

No information found

Recruitment processes

Several of the species in the biotope appear to have short-lived benthic larvae. For instance, the soft coral Alcyonium hibernicum broods planulae larvae that are released at a late development phase and so probably has a short planktonic life (Hartnoll 1977 as Alcyonium coralloides). Leptopsammia pruvoti also seems to have short-lived planulae larvae which may settle immediately or very soon after release and recruitment at a site at Lundy has been extremely small (as low as 1% over the years 1983 to 1999 at least) (K. Hiscock, own observations). Sponges are likely to have a longer lived larva. Some species, such as the zoanthid anemones Parazoanthus axinellae and Parazoanthus dixoni, reproduce asexually to produce large colonies..

Time for community to reach maturity

As recruitment processes are so slow for many species and individual species will not colonize readily, the community will most likely take in excess of 25 years to reach maturity.

Additional information

Alcyonium hibernicum is named as Parerythropodium coralloides in the Species Directory (Howson & Picton 1997). Subsequently, McFadden (1999) has shown that it is taxonomically distinct species and should be known as Alcyonium hibernicum.

Preferences & Distribution

Recorded distribution in Britain and IrelandOccurs at widely separated locations generally in open coast waters on wave sheltered coasts with moderate tidal flow. Whilst the structural and functional aspects of the biotope are similar across its range, species composition varies.

Habitat preferences

Depth Range 10-20 m, 20-30 m, 30-50 m
Water clarity preferences
Limiting Nutrients Not relevant
Salinity Full (30-40 psu)
Physiographic
Biological Zone Circalittoral
Substratum Bedrock
Tidal Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave Exposed, Moderately exposed, Sheltered, Very exposed
Other preferences Deep shade

Additional Information

The habitat is distinctively one of vertical cliffs with a degree of overhang and small (shallow) caves.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

Additional information

Whilst the structural and functional aspects of the biotope are similar across its range, species composition varies. The species composition of the biotope includes a small number of nationally rare or scarce species.

Sensitivity reviewHow is sensitivity assessed?

Explanation

The biotope is particularly characterized by sponges and anthozoans including several cup coral species. In the absence of full MarLIN research for all but Leptopsammia pruvoti, research has been undertaken on relevant aspects of the biology of particular species and a knowledge of the results of monitoring the biotope in south-west England (Fowler & Pilley, 1992 and researchers own observations). Two of the species of coral have different life cycles with Caryophyllia smithii producing a planktotrophic larva and likely to colonise readily whilst Leptopsammia pruvotihas a lecithotrophic probably short-lived larva and most likely also represents Hoplangia durotrix in its larval biology. The reproductive biology of Alcyonium hibernicum has been researched (Hartnoll, 1977 as Alcyonium coralloides) whilst Alcyonium glomeratum is known to colonize wrecks readily (researchers own observations) suggesting good recolonization potential.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingAlcyonium glomeratumRed sea fingers
Important characterizingCaryophyllia smithiiDevonshire cup coral
Important characterizingLeptopsammia pruvotiSunset cup coral

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Very low / none Very High Major decline Moderate
Removal of the substratum will remove the sessile fauna that characterizes this biotope. Whilst some species such as Caryophyllia smithii and branching and encrusting bryozoans are likely to colonize bare rock rapidly, others such as Leptopsammia pruvoti and Hoplangia durotrix (K. Hiscock, own observations) and probably Alcyonium hibernicum (Hartnoll, 1977) have short lived larvae and appear to reproduce very infrequently so that recolonization is likely to take at least 25 years and may not occur at all.
Intermediate Low High Decline Moderate
The corals and zoanthid anemones in this biotope would mostly extend above a layer of silt or survive smothering by 5 cm of silt (the benchmark) by 'inflating' their polyps. Others, such as encrusting sponges may not survive. Encrusting bryozoans may survive: they survive overgrowth by encrusting tunicates (Turner 1988). Smothering may not be highly relevant to this biotope as it occurs on vertical and overhanging surfaces. Overall, some species in the biotope are intolerant but some important species may survive.
Tolerant Not relevant Not relevant No change Moderate
The species in the biotope are most likely tolerant of increases in suspended sediment. For instance, the corals have cilia on their tentacles capable of clearing silt (K. Hiscock, own observations) whilst sponges produce mucus which is discarded with silt to clear surfaces. Since the biotope occurs on vertical or overhanging rock, increased fall-out of silt being deposited on surfaces is unlikely.
Tolerant Very low / none Not sensitive* Major decline Moderate
Whilst some of the species (particularly sponges) in the biotope might obtain some food from organic matter associated with suspended sediment, it is not considered a major food source.
Not relevant Not relevant Not relevant Not relevant Not relevant
The biotope is circalittoral in Britain and Ireland and desiccation is not relevant.
Not relevant Not relevant Not relevant Not relevant Not relevant
The biotope is circalittoral in Britain and Ireland and emergence is not relevant.
Not sensitive* Not relevant
The biotope is circalittoral in Britain and Ireland and emergence is not relevant.
Low Immediate Not sensitive Minor decline Low
The species present in the biotope are capable of living in strong to weak currents and, although feeding in particular might be affected, it is not thought that individuals will be killed by increases or decreases in flow rate. Recovery of condition is likely to be rapid following return to previous conditions.
Tolerant Not sensitive* No change Moderate
The species present in the biotope are capable of living in strong to weak currents and, although feeding in particular might be affected, it is not thought that individuals will be killed by increases or decreases in flow rate. Recovery of condition is likely to be rapid following return to previous conditions.
Tolerant* Not relevant Not sensitive* No change Moderate
Many of the species that characterize this biotope are southern in distribution and increase in temperature by up to 5°C above average or normal maximum is likely to have a positive influence on reproduction. For instance, Leptopsammia pruvoti transferred from their natural habitat to aquaria have, on three occasions, produced planulae - possibly due at least in part to increased temperatures (Keith Hiscock, own observations). Even a short-term increase in temperature may therefore encourage recruitment into the community that will increase abundance of long-lived, slow-growing and infrequently recruiting species considerably.
Low Immediate Not relevant No change Moderate
Decrease in temperature is unlikely to affect survival of established individuals although there is little direct evidence for characteristic species. Lower temperatures may adversely affect prospects for successful production of propagules and therefore long-term survivability. However, as reduction in temperature at the benchmark level is for only one year, long-term prospects for the biotope are likely to be unaffected.
Tolerant Not relevant Not relevant No change Moderate
Species in the biotope do not depend on light and so increase in turbidity is not likely to have an adverse effect.
Tolerant Not sensitive* No change Moderate
Decrease in turbidity may result in increased light levels but, in the vertical and overhanging habitats in which the biotope occurs, it is unlikely that there would be any algal growth and not smothering growth.
Intermediate Low High Minor decline Moderate
The species present in the biotope are capable of living in strong to weak wave action and, although feeding in particular might be adversely affected by increased or wave strength, it is not thought that individuals will be killed except where the biotope is already in a top-of-the-range situation where increased wave action may cause mortality of species. This mortality may especially be the case where the skeleton of cup corals is weakened by boring organisms. Recovery of condition is likely to be rapid following return to previous wave action although, if a proportion of corals have been lost, the population is unlikely to build to previous numbers for many years.
Tolerant Not sensitive* No change Moderate
The biotope occurs in wave sheltered conditions where wave action (for feeding or to remove silt) does not seem to be a requirement. Providing that tidal flow is sufficient to bring food in the absence of significant wave action, no adverse effects are to be expected.
Tolerant Not relevant Not relevant No change High
Species present in the biotope are not known to have receptors for noise and are not likely to be affected.
Tolerant Not relevant Not relevant No change High
Species present in the biotope are not known to have visual receptors and are not likely to be affected.
Intermediate Low High Minor decline High
Physical disturbance and abrasion will remove much of the sessile fauna that characterize this biotope. Whilst some species such as Caryophyllia smithii and branching and encrusting bryozoans are likely to colonize bare rock rapidly, others such as Leptopsammia pruvoti and Hoplangia durotrix and probably Alcyonium hibernicum most likely have short lived larvae and appear to reproduce very infrequently so that recolonisation is likely to take many years. However, some species such as encrusting sponges are likely to survive in concavities and fissures and regrow from there.
High Very low / none Very High Major decline High
The species that characterize this biotope are sessile and displacement will involve removing them from their substratum. Whilst individual species may survive for a short time in a detached state, the biotope will no longer exist. Whilst some species such as Caryophyllia smithii and branching and encrusting bryozoans are likely to colonize bare rock rapidly, others such as Leptopsammia pruvoti and Hoplangia durotrix (Keith Hiscock, own observations), and probably Alcyonium coralloides (Hartnoll, 1977), have short lived larvae and appear to reproduce very infrequently so that recolonization is likely to take at least 25 years and may not occur at all.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information No information No information Insufficient
information
Not relevant
No information was found on effects of synthetic chemicals on component species.
Heavy metal contamination
No information No information No information Insufficient
information
Not relevant
No information was found on effects of heavy metals on component species.
Hydrocarbon contamination
No information No information No information Insufficient
information
Not relevant
No information was found on effects of hydrocarbons on component species.
Radionuclide contamination
No information No information No information Insufficient
information
Not relevant
No information was found on effects of radionuclides on component species.
Changes in nutrient levels
No information No information No information Insufficient
information
Not relevant
No information was found on effects of nutrients on component species.
Not relevant None Not relevant Not relevant Moderate
The biotope occurs on the open coast in normal salinity. An increase in salinity would not be expected.
High Very low / none High Major decline Moderate
This biotope only occurs in open coastal and offshore areas and it is expected that lowered salinity will have an adverse effect on species in the biotope and will result in the death of the sessile fauna that characterizes this biotope. Whilst some species such as Caryophyllia smithii and branching and encrusting bryozoans are likely to recolonize rapidly, others such as Leptopsammia pruvoti and Hoplangia durotrix (K. Hiscock, own observations) and probably Alcyonium hibernicum (Hartnoll, 1977) have short lived larvae and appear to reproduce very infrequently so that recolonization is likely to take at least 25 years and may not occur at all.
Intermediate Very low / none High Major decline Low
Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l. The biotope lives on the open coast in normally good water exchange conditions. Whilst some species or individuals of some species may survive deoxygenation, the biotope will most likely no longer exist. Whilst some species such as Caryophyllia smithii and branching and encrusting bryozoans are likely to recolonize the habitat rapidly, others such as Leptopsammia pruvoti and Hoplangia durotrix (K. Hiscock, own observations) and probably Alcyonium hibernicum (Hartnoll, 1977) have short lived larvae and appear to reproduce very infrequently. As the species has not been observed to colonize apparently suitable new habitats such as wrecks or the Plymouth breakwater, it seems that recolonization from distant populations is unlikely. Hoplangia durotrix (K. Hiscock, own observations) and Alcyonium hibernicum (Hartnoll, 1977) at least are believed to have similar reproductive infrequencies and short larval life span so that recolonization is likely to take at least 25 years and may not occur at all.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information No information No information Insufficient
information
Not relevant
No information has been found on effects of microbial pathogens.
Tolerant Not relevant Not relevant No change Low
There are no non-native species currently (November 2001) known to colonize this biotope.
Intermediate Low High Minor decline Moderate
Although extraction does not occur at present, the assessment here is for possible extraction, for instance for the aquarium trade. In this case, intermediate intolerance has been suggested to reflect the possibility that some species may be targeted. Recovery is based on the likelihood that a proportion of the population would be left behind, grow and reproduce. However, species such as Leptopsammia pruvoti and Hoplangia durotrix (K. Hiscock, own observations) and probably Alcyonium hibernicum (Hartnoll, 1977) have short lived larvae and appear to reproduce very infrequently so that recolonization is likely to take up to 25 years. The biotope would remain but possibly as an impoverished example.
Low Low Moderate Minor decline Moderate

Additional information

-

Importance review

Policy/Legislation

Habitats Directive Annex 1Reefs, Submerged or partially submerged sea caves

Exploitation

No exploitation is known to occur.

Additional information

The biotope is very attractive but some species are easily damaged by mechanical disturbance. Care should especially be taken by photographers.

This biotope holds several nationally rare or scarce species and its protection is therefore important. The biotope occurs in 'Reef' habitats as defined in the Habitats Directive.

Bibliography

  1. Fowler, S.L. & Pilley, G.M., 1992. Report on the Lundy and Isles of Scilly marine monitoring programmes 1984-1991. English Nature, Research Report no. 9.
  2. Hartnoll, R.G., 1977. Reproductive strategy in two British species of Alcyonium. In Biology of benthic organisms, (ed. B.F. Keegan, P.O Ceidigh & P.J.S. Boaden), pp. 321-328. New York: Pergamon Press.
  3. Hiscock, K. & Howlett, R. 1976. The ecology of Caryophyllia smithii Stokes & Broderip on south-western coasts of the British Isles. In Underwater Research (ed. E.A. Drew, J.N. Lythgoe & J.D. Woods), pp. 319-344. London: Academic Press.
  4. Howson, C.M. & Picton, B.E. (ed.), 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]
  5. McFadden, C.S., 1999. Genetic and taxonomic relationships among northeastern Atlantic and Mediterranean populations of the soft coral Alcyonium corallioides. Marine Biology, 133, 171-184.
  6. Turner, S.J., 1988. Ecology of intertidal and sublittoral cryptic epifaunal assemblages. II. Non-lethal overgrowth of encrusting bryozoans by colonial tunicates. Journal of Experimental Marine Biology and Ecology, 115, 113-126.

Citation

This review can be cited as:

Hiscock, K. 2000. Circalittoral caves and overhangs. 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/10

Last Updated: 30/10/2000