The Isles of Scilly Biodiversity Audit 2008 - Cornwall Wildlife Trust

2.2.1.11 Crustacea – Crabs, lobsters,shrimps and relativesOverviewThe crustaceans are a group of animals with jointedlegs and chitinous exoskeletons which are shedperiodically. The largest order is the Decapoda whichincludes shrimps, crabs and lobsters. There are over2000 species of crustacean in the waters surroundingthe British Isles, many are planktonic. Mostcrustaceans are mobile but some, like the barnacles,adopt a sessile lifestyle in their adult form.Crabs and shrimps are very common in intertidalareas. Shrimps are targeted by an artisanal fishery atspring low tides during the summer months in Scilly.Some crab species, lobsters and crayfish are caught bypotting in the fishing season. There is a high diversityof isopods in Scilly; they are common under algae andin fresh water seeps on the shore (Parslow, 2007).Important AreasCrustaceans are found in a wide range of habitatssuch as intertidal pools, under boulders and in softsediment. One species, the chameleon prawn Praunusflexuosus, is found in vast numbers in Bryher Pool, abrackish environment, but most are marine (Parslow,2007).Conservation ImportanceCthalamus barnacles dominate the rocky shores inScilly, unlike on mainland Southwest coasts whereSemibalanus balanoides is often dominant. This isthought to be due to larval supply problems for S.balanoides, which is rare in Scilly (English NatureNatural Area Profile).A rare hermit crab Cestopagarus timidus has beenrecorded in intertidal areas in Scilly (Harvey, 1964),this is a species which typically has a more southerlydistribution. There are also two recent records of rareslipper lobsters Scyllarus arctus another species at thenorthern limit of its range around Scilly (Herdson,2001). One individual was caught in a lobster pot andis now in the National Marine Aquarium in Plymouth.Typton spongicola, the sponge shrimp is a nationallyrare southern species which occurs in the Isles of Scillyon sponges. Cranch’s spider crab Achaeus cranchii isfound on subtidal hydroids, bryozoans and seasquirts(Barne et al, 1996).Several nationally rare or scarce amphipods have beenrecorded in Scilly. Microdeutopus stationis, Ampherusaclevei and Pereionotus testudo are nationally rare (NBN)and Apherusa ovalipes is nationally scarce (Barne et al,1996). Synisoma lancifer a nationally scarce sea slater isalso found in the Isles of Scilly.Trends and IssuesResearchInventories of some crustacean groups have beenpublished in the Journal of Natural History. These arethe Eucarida (Thurston, 1969), Harpacticoid copepods(Wells, 1970), Ostracods (Neale, 1970) and Mysidshrimps (Makings, 1987).Release of captive bred lobstersThe National Lobster Hatchery at Padstow has workedwith members of the Isles of Scilly Sea FisheriesCommittee and local divers to release 500 juvenilelobsters in 2002 and 120 in 2007 in the Isles of Scilly.These were released by hand in suitable habitats andwill take many years to grow large enough to enter thefishery.FishingPotting for lobsters, crayfish and crabs has occurred inScilly for many years. The impact on local populationsis largely unquantified. See section 3.3 on Fisheries.Spiny spider crab Maja squinado on dead man’s fingers Alcyonium digitatum. Photo: Frank GloysteinIsles of Scilly biodiversity audit Page 24