Biodiversity & Conservation

CR.MCR.XFa.ErSEun

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Most of the characteristic species in the biotope are permanently attached to the substratum (e.g. the sponges, sea fans and bryozoans) and will not re-attach once displaced. Substratum loss will result in loss of these species and so intolerance of the biotope is high. Pentapora foliacea has good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998b). Eunicella verrucosa is long lived, slow growing, and little is known of its reproduction. It is known to colonize wrecks at least several hundred metres from other hard substrata with sea fans, but is thought to have larvae which generally settle near the parent. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges but branching sponges have not been observed to colonize wrecks and growth rate of Axinella dissimilis at Lundy is extremely slow (less than 1mm a year) (K. Hiscock, pers. comm.). In monitoring studies at Lundy, branching sponges showed no recruitment, only losses over a 13 year period (K. Hiscock pers. comm.). Recovery of some parts of this community may therefore take a long time or not occur. Other species in the biotope may have long-lived widely dispersing larvae. Mobile species such as the echinoderms and fish should be able to return rapidly.
Smothering
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Some of the species in the biotope are upright and branching (e.g. Axinella dissimilis and Eunicella verrucosa). These species project above the substratum to sufficient height not to be covered completely by 5 cm of sediment and consequently may not be killed by smothering. Other more low lying or encrusting species (encrusting sponges, hydroids, bryozoans etc.) are more likely to be completely covered and will probably die. Many of the species are sessile and attached to the substratum so recovery of the population through immigration of adults is not possible. Mobile species such as the echinoderms and fish may be able to return more rapidly. Pentapora fascialis has some regenerative ability as well as good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998b). Some species such as Nemertesia ramosa are annuals and recruit readily over short distances. The long-lived slow growing and infrequently recruiting species are likely to survive smothering and the ones that are likely to be lost are also likely to recolonize within a few years. Recovery of the biotope as a whole is, however, likely to take more than five years. Therefore, a recovery rank of moderate is suggested.
Increase in suspended sediment
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Many of the species are suspension feeders and increase in suspended sediment may cause interference and blockages, for example in sponge canals and pores. However, the anthozoans and sponges produce mucus which is shed with attached silt to clean the external surface. Mortality is not therefore expected with increased suspended sediment levels but some reduction in fitness may occur as a result of energy being expended in cleaning.
Decrease in suspended sediment
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Many of the species are suspension feeders and decrease in suspended sediment may reduce interference and blockages, for example of sponge canals and pores. However, the species in the biotope may rely of suspended organic material that is a part of the suspended material for feeding. Overall, there are both likely favourable and unfavourable effects of decrease in suspended sediment so that not sensitive is indicated.
Desiccation
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The biotope is entirely subtidal and will not be subject to desiccation.
Increase in emergence regime
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The biotope is entirely subtidal and will not be subject to emergence.
Decrease in emergence regime
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The biotope is entirely subtidal and is not subject to emergence.
Increase in water flow rate
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The biotope consists mainly of species firmly attached to the substratum and which would be unlikely to be displaced by an increase in the strength of tidal streams. Many of the species in this biotope are suspension feeders and rely to some extent on water flow to ensure their food supply. However, an increase in tidal flow rate to strong or greater (i.e. above 3 knots) may cause loss of posture and interfere with feeding mechanisms, particularly in the more delicate species like hydroids. Mobile species may be displaced or washed away but species such as the echinoderms and fish may be able to return rapidly after flow rates return to normal. There would be loss of feeding and a decline in species richness as mobile species might be swept away.
Decrease in water flow rate
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Many of the species in this biotope are suspension feeders and rely to some extent on water flow to ensure their food supply. Also, reduced water flow is likely to lead to siltation and therefore effects similar to those described in 'smothering'. Overall, the long-lived, slow growing and poor recruitment species are likely to survive albeit with reduced food supply and a small number of other species may succumb to smothering.
Increase in temperature
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The biotope is found mainly in the south west of England and the west coast of Ireland. Long term increases in temperature may cause an increase in the abundance of the southern species that characterize it and more southern species may colonize the biotope. Expansion of the geographic range of the characterizing species may also expand the geographical range of the biotope northwards. In the case off an acute rise in temperature at the warmest time of year, it is not expected that temperature will be harmful as the characterizing species generally occur much further south than the British Isles. Overall, an increase in temperature is likely to be favourable to the presence of this biotope.
Decrease in temperature
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The distribution of the sponge Axinella dissimilis and the soft coral Alcyonium digitatum extend to Iceland so these species may be tolerant of long-term decreases in temperature. Long-term decrease in temperature is likely to lead to a poor year for recruitment of Eunicella verrucosa but is unlikely to lead to mortality. A live specimen collected from shallow depths off North Devon in 1973 exhibited growth rings that demonstrated that the colony had survived the 1962/63 cold winter. Also, large colonies were being collected from Lundy in the late 1960's suggesting no significant loss in 1962/63 (Keith Hiscock, own observations.). Assuming that temperature decrease reduces recruitment, the population size might decline for a year but recovery will occur following a successful recruitment. Therefore, it appears that the biotope may be able to tolerate a long term decrease in temperature. However, the response of these species to larger short term acute decrease are not known and may lead to a reduction in species diversity. Any losses are likely to be amongst species that recolonize rapidly. A rank of intermediate, but with very low confidence is reported.
Increase in turbidity
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The biotope occurs in the circalittoral and none of the characterizing species are algae likely to be adversely affected by decreased light levels. However, increased turbidity is usually caused by increased silt levels in the water so that the intolerance and recoverability characteristics are likely to be similar.
Decrease in turbidity
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Decreased turbidity is likely to lead to increased algal growth with the potential to smother some of the species especially where they live close to the seabed. Also, drift from ephemeral algae growing as a result of increased water clarity may clog branches of sea fans and branching sponges reducing feeding ability. Effects of increased algal growth on this biotope have been observed at Lundy (Keith Hiscock, own observations) where the biotope and its component long lived, slow-growing and poorly recruiting components persisted. There effects are likely to be short-term and result in reduced feeding ability.
Increase in wave exposure
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The biotope exists in moderately exposed areas (Connor et al., 1997(a)). Increases in wave exposure may interfere with the posture of upright species in the biotope. Sea fans will be detached from the substratum by storms. For example, detached colonies are frequently seen on the seabed and after severe storms may be washed-up on the strandline. The surface of Axinella dissimilis cracks if bent more than 90 ° (Moss & Ackers, 1982). After prolonged easterly gales in the winter of 1987 at Lundy, branching sponges were damaged and some lost from monitoring sites (K. Hiscock pers. comm.). The erect bryozoan Pentapora foliacea has brittle lamellae and is known to be severely damaged by extreme wave action (Cocito et al., 1998(a)). The biotope MCR.PhaAxi occurs in more wave exposed areas although the effects of wave action would be reduced in the deeper waters in which the biotope occurs. Many of the species are sessile and attached to the substratum so supplementation of the population through immigration of adults is not possible. Mobile species such as the echinoderms and fish may be able to return more rapidly. Pentapora foliacea has some regenerative ability as well as good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998(b)). Eunicella verrucosa is long lived, slow growing, and little is known of its dispersal and reproduction. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges. Some annual species such as Nemertesia ramosa are annuals and recruit readily over short distances. Providing that not all individuals of the characterizing species are lost during a storm, the biotope will remain but recovery to previous abundances in likely to take a long time so recovery is rated low.
Decrease in wave exposure
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Whilst water movement is required to bring food to suspension feeding species in the biotope, tidal streams are generally more important than wave oscillation in doing so. However, decreased wave exposure may lead to increased siltation and smothering effects. Therefore, some loss of species living close to the substratum might occur. Those species are generally fast to settle and grow.
Noise
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It is unlikely that any of the benthic key or important characterizing species are sensitive to noise disturbance. Some of the biotopes characterizing species, namely the wrasse (Labrus bergylta, Labrus mixtus), may have low intolerance to noise but this will not have a major impact on the biotope as a whole.
Visual Presence
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It is unlikely that any of the benthic key or important characterizing species are sensitive to visual presence. Some of the characterizing species in the biotope, namely the wrasse (Labrus bergylta, Labrus mixtus), may have low intolerance to visual disturbance but this will not have a major impact on the biotope as a whole.
Abrasion & physical disturbance
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The three selected key or important characterizing species in this biotope are highly or intermediately intolerant of abrasion. Other species in the biotope that are upright and protrude above the substratum will also be damaged or killed by abrasion (e.g. hydroids, branching and cup sponges etc). Also, mobile surface species that are not fast movers, for example Echinus esculentus. Pentapora fascialis has good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998b). Eunicella verrucosa is long lived, slow growing, and little is known of its reproduction. Nevertheless, Eunicella verrucosa does appear to recruit well providing there are extant populations nearby. On the other hand, Axinella polypoides (one of the species often present in the biotope) is unlikely to recover if lost (Keith Hiscock, pers comm.). Sponges are often slow growing and long lived. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges. Recovery of some parts of this community and biotope may take a long time. Other species are annuals and may have long-lived widely dispersing larvae. Many of the species in the biotope (including the 3 selected characterizing species) have permanent attachments to the substratum so immigration of adults into the biotope is not possible. Mobile species such as the echinoderms and fish will be able to return more rapidly.
Displacement
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Many of the species in the biotope, including the three that have been selected to represent the intolerance of the biotope, are permanently attached to the substratum and will die if displaced from their attachment. Pentapora foliacea has good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998b). Eunicella verrucosa is long lived, slow growing, and little is known of its reproduction. Sponges are often slow growing and long lived. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges. Recovery of some parts of this community and biotope may take a long time. Other species are annuals and may have long-lived widely dispersing larvae. Many of the species in the biotope (including the 3 selected characterizing species) have permanent attachments to the substratum so immigration of adults into the biotope is not possible. Mobile species such as the echinoderms and fish may be able to return more rapidly.

Chemical Factors

Synthetic compound contamination
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Insufficient information
Heavy metal contamination
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Insufficient information
Hydrocarbon contamination
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Insufficient information
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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Insufficient information
Increase in salinity
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The biotope occurs only in fully saline waters (Connor et al., 1997a) . The three selected key or important characterizing species are highly intolerant of decreases in salinity. Other characterizing species may also be highly intolerant of decreases in salinity. Pentapora foliacea has good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998(b)). Eunicella verrucosa is long lived, slow growing, and little is known of its reproduction. Sponges are often slow growing and long lived. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges. Recovery of some parts of this community and biotope may take a long time. Other species are annuals and may have long-lived widely dispersing larvae. Many of the species in the biotope (including the 3 selected characterizing species) have permanent attachments to the substratum so immigration of adults into the biotope is not possible. Mobile species such as the echinoderms and fish may be able to return more rapidly.
Decrease in salinity
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Changes in oxygenation
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No information is directly available regarding the biotopes or the selected characterizing species tolerance to decreases in oxygenation. Pentapora fascialis and Axinella dissimilis have been assessed as of intermediate intolerance. Many of the species are sessile and attached to the substratum so supplementation of the population through immigration of adults is not possible. Mobile species such as the echinoderms and fish may be able to return more rapidly. Pentapora foliacea has some regenerative ability as well as good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998b). Eunicella verrucosa is long lived, slow growing, and little is known of its dispersal and reproduction. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges. Some annual species such as Nemertesia ramosa are annuals and recruit readily over short distances. Recovery of the biotope as a whole is likely to take a long time.

Biological Factors

Introduction of microbial pathogens/parasites
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Insufficient information
Introduction of non-native species
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Insufficient information
Extraction
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It is extremely unlikely that Pentapora fascialis would be targeted for extraction. However, Eunicella verrucosa is sometimes taken illegally (it is protected under schedule 5 of the Wildlife and Countryside Act 1981 against killing, injuring, taking possession and sale and is the subject of a UK Biodiversity Action Plan). Echinus esculentus, a characterizing species in the biotope, is also collected and an intolerance of intermediate has been suggested with a low recovery.

If, however, the biotope was targeted indirectly for other species, the damage resulting from bottom fishing would be considerably more severe and this has been addressed under Physical Disturbance.

Additional information icon Additional information

Predation
Eunicella verrucosa may be damaged or destroyed by the ovalid snail Simnia patula. The snails feed on (Lebour, 1932) and are expected to lay their eggs on Eunicella verrucosa. Theodor (1967) describes how the snail Simnia spelta causes denudation of branches of Eunicella stricta, rarely destroying the colony but causing bare skeleton to attract fouling organisms. The mechanism of destruction might be that described by Main (1982) for Simnia barbarensis which strips the soft tissues of the host and lays its egg capsules on the internal skeleton. In late July 2001, a high proportion of Eunicella verrucosa on the north coast of Lundy, England were observed to be dead or part dead with only the external skin of the coenenchyme remaining (K. Hiscock, own observations). Simnia patula were later found on colonies (R. Irving, pers. comm.).

Recoverability
Pentapora foliacea has good reproductive and recolonizing abilities. It has been recorded as recovering in 3.5 years after almost total loss of a local population (Cocito et al., 1998b). Eunicella verrucosa is long lived, slow growing, and little is known of its reproduction. It is known to colonize wrecks at least several hundred metres from other hard substrata with sea fans, but is thought to have larvae which generally settle near the parent. Little is known of the reproduction and recruitment mechanisms in Axinella dissimilis or other sponges but branching sponges have not been observed to colonize wrecks and growth rate of Axinella dissimilis at Lundy is extremely slow (less than 1mm a year) (Keith Hiscock, pers. comm.). In monitoring studies at Lundy, branching sponges showed no recruitment, only losses over a 13 year period (Keith Hiscock pers. comm.). Recovery of some parts of this community may therefore take a long time or not occur. Other species in the biotope may have long-lived widely dispersing larvae. Mobile species such as the echinoderms and fish should be able to return rapidly. The recoverability of the other 3 biotopes represented by this review is likely to be similar to MCR.ErSEun.


This review can be cited as follows:

Jackson, A. & Hiscock, K. 2000. Erect sponges, Eunicella verrucosa and Pentapora fascialis on slightly tide-swept moderately exposed circalittoral rock.. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 27/11/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=77&code=1997>