THE BLACK SEA 439 



rarer crustaceans of the pseudolittoral. In Mokievsky's opinion the population 

 of the supralittoral is characterized by the amphipod Talorchestia deshayesei 

 with a maximum biomass of 121 g/m 2 and a maximum number of specimens 

 of up to 48,400 per m 2 , and by the isopod Tylos latrelei var. pontica with a high 

 population-density (up to 129 g/m 2 and 11,800 specimens per m 2 ) and also, 

 among specimens washed ashore, some insects, arachnids and oligochaetes, 

 and the amphipods Orchestia gamarellus and Orchestia montagui. 



The biocoenosis of the inhabitants of the coastal cliffs and immobile rocks 

 sinks at times in the open parts of the Sea to a depth of 28 m ; more usually, 

 however, to 15 m, and inside inlets to a few metres only. Above sea-level a 

 true littoral fauna finds shelter on the cliffs, although there are no tides in 

 the Black Sea. 'Together with the algae (Scythosiphon, Ceramium, Entero- 

 morpha, Corallina) some molluscs, Littorina neritoides and Patella pontica ; 

 the barnacles Chthamalus stellatus; the crabs Pachygrapsus marmoratus and 

 Eriphia spinifrons ; the isopod Lygia brandtii (which lives only above sea-level), 

 and the land snail Aplexia myosothis (under the rocks) come out of the water, 

 sometimes to a height of two or three metres above it. 



On the more sloping shores, at the very edge of the water and slightly 

 above it, dead eel-grass, Cystoseira, Phyllophora and other algae are com- 

 monly washed ashore. A specific refuse fauna washed up by the Sea settles 

 down on these heaps of dead plants, and especially under them, a mass of 

 oligochaetes, amphipods and isopods. 



Just below sea-level thick growths of Cystoseira invest all the cliffs with a 

 dense covering ; there are also some Mytilus galloprovineialis. In more polluted 

 places Cystoseira is replaced by green algae, sea lettuce and sea grass. Apart 

 from Cystoseira the cliffs are overgrown, to a much lesser extent, by other sea- 

 weeds. These sea-weed beds are inhabited, besides the forms mentioned, by a 

 large number of gastropods: Rissoa, Nassa reticulata, Trochus; the cliff 

 oyster ; the crab Xantho rivulosus ; the shrimps Hippolyte varians and Leander 

 squilla ; many Porifera, hydroids, bryozoans (especially Membranipora) and 

 polychaetes, often with lime tubes, amphipods and isopods. Rock-burrow- 

 ing molluscs, commonly Petricola lithophaga, bore passages through the cliffs. 



Sand and mud shore biocoenoses. These produce a whole number of modifi- 

 cations depending on the depth of their occurrence and on the structure of 

 the floor; they sometimes spread down to 18 to 27 m. The coarser sand 

 stretching directly from the water's edge, called by Zernov ' Saccocirrus sand ', 

 gives shelter to an original fauna of worms. It is inhabited by a number of 

 Turbelaria, Procerodes lobata and Cercyra papillosa ; by the archiannelides 

 Saccocirrus papillocercus and Protodrilus flavocapitatus ; the polychaetes 

 Nerine and Spio ornatus ; by nemerteans, Lineus lacteus, Eunemertes gracilis, 

 Borlasia vivipara ; various amphipods and nematodes ; the gastropods Nassa 

 reticulata and Rissoa; hermit crabs {Diogenes varians); decapod crayfish, 

 Gebia littoralis and Calianassa subterranea; and, under the rocks, a great 

 number of isopods, Sphaeroma and Idothea. Farther up the bays, on the 

 slightly silted saccocirrus sand, live a number of polychaetes : Arenicola, 

 Glycera and Nereis. 



