seagrass that make it special , but the fact that the canopy acts as a refuge , so they tend to carry on with their lives in front of you rather than dash away .
Crabs are among the most prominent seagrass residents ; if there ’ s any carrion around , you quickly see a good variety of species . Velvet swimming , harbour , shore and hermit crabs will all gather to feast on a fish carcass and the frequent disputes that occur , despite there being more than enough food to go round , are always entertaining . I find it can be worth having a close look at the small hermit crabs because there are often hairy hermit crabs ( Pagurus cuanensis ) as well as the common ones ( Pagurus bernhardus ). Their shells , particularly those of the hairy hermits , are sometimes encased in surprisingly large growths of sponge and watching one of these tiny weightlifters hauling its burden through the seagrass is a wonderful sight .
Shore crabs tend to be the bosses of this crustacean collective but , because they often ‘ walk tall ’ among the seagrass rather than hide away , you might spot that some have a nasty affliction . A conspicuous smooth yellow bulge under their tail flap
Shore crab with the tell-tale bulge of a parasitic barnacle beneath its tail flap
Cuttlefish couple with , at the far right of the picture , the arm of an intruding male that I didn ’ t spot at the time !
( unlike an egg mass which is granular ) is the reproductive tissue of an extremely unpleasant parasitic barnacle that has invaded their body and stopped them moulting their armour .
Seagrass is renowned as an important nursery habitat and this is borne out by the number of small fish sheltering among its leaves . Corkwing wrasse youngsters are particularly numerous , along with gobies , flatfish and baby bream . The other tell-tale
sign is the variety of egg masses , with many of these belonging to molluscs such as cuttlefish (‘ sea grapes ’), various nudibranchs ( usually white coils or ‘ bead strings ’) and sea hares ( pink ‘ spaghetti ’). The impressive sea hare mating chains that produced those eggs may also be on show , with each individual acting as a male to the one in front of it and as a female to the one behind .
Despite sea hare hijinks I think the ultimate seagrass sighting must be cuttlefish , and it was in the seagrass of the Helford that I saw their courtship and egg laying for the first time , an experience that also showed me how a camera ’ s viewfinder can stop you appreciating what ’ s in front of you . I have used my favourite photograph from that dive many times , but it was only recently that I spotted the intruding arm of a second male cuttlefish at the very edge of the frame . What I had always assumed was a dramatic ‘ keep away ’ signal to me and my camera from the large male was almost certainly a signal directed at his competitor ! �
Miniature weightlifter – hairy hermit crab with an impressive growth of sponge on its back
Young corkwing wrasse are abundant in seagrass
Get involved
BSAC is urging members to help scientists learn more about the seagrass habitats of the UK . Over the late Bank Holiday weekend ( 27-29 May ), the Great Seagrass Survey will see divers , snorkellers and beachcombers take to the UK coastline to record locations of seagrass beds . To participate in the Great Seagrass Survey , go to bsac . com / great-seagrass-survey where you can download survey resources . For more details , turn to this issue ’ s HUB , page 10 .
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