The Surrounding Sea - Gower - page 110

On the vertical sides of rock platforms there are communities of sponges, sea squirts, red algae and
bryozoans (moss animals). In some locations the platforms can be almost completely covered by sponges
such as breadcrumb sponge Halichondria panicea (Fig. 59), boring sponge Cliona celata and Hyme-
niacidon perleve . In the shaded areas of overhangs there tend to be more red algae such as Ceramium
virgatum , a small red seaweed growing up to 30 centimetres tall, often on the stipes and fronds of larger
seaweeds.
Particularly characteristic of the lower shore are the limestone boring species including the small
anemone Fagesia carnea and the sponge Cliona celata , which appears above the rock surface as small
yellowspots.Theareaalsoattractslargenumbersofthecommonstarfish Asterias rubens (Fig.60),which
often has the amphipod Pariambus typicus clinging to its upper surface; this was first recorded in Bri-
tain on the Gower coast. Under the rock overhangs at extreme low water a variety of sponges occur, in-
cluding the purse sponge Grantia compressa and the syconoid sponge Sycon ciliatum . The latter prefers
more sheltered conditions than the purse sponge, but both are seen in the greatest numbers during the
autumn. Stunted white growths of deadman's fingers Alcyonium digitatum are quite frequent under these
overhangs, together with various sea squirts upon which the spotted cowrie Trivia monacha feeds. Other
species that occur on the lower shore include the isopods Dynamene bidentata and Gnathia maxillaris . In
drier crevices around the mid-tide level these are replaced by a sea slater Sphaeroma serratum , which is
particularly abundant on the Worms Head causeway.
FIG 59. Breadcrumb sponge, a common species in the intertidal zone. (Margaret Hodge)
Often associated with the sea firs and bryozoans on rock surfaces and seaweeds are the sea spiders.
TwelveoftheeighteenorsoBritishspecieshavebeenrecordedontheGowershores.Themostfrequently
found species are Nymphon gracile , Nymphon rubrum , Endeis spinosus , Achelia echinata and Achelia
longipes , with the first two being the most abundant. Nymphon gracile occurs highest on the shore in the
spring and summer, being found particularly on the hydroid Dynamena pumila that grows abundantly on
serratedwrack,while Achelia echinata occursinverysheltered,detritus-coveredsituationsontheseamat
Crisia eburnea .