Certain groups of invertebrate animals inhabiting the Sanctuary waters have been studied non-uniformly. Consequently, the assessment of the number of species for most of them is still tentative. Yet, it may be accepted that at least 2,000 species of various invertebrates live here. Let us examine some mass invertebrate representatives included in the composition of basic ecological groupings.
    Zooplankton. Prevalent in the zooplankton of Peter the Great Bay are various crustaceans (chiefly Copepoda, Cladocera and Euphausidae), setimaxillae, appendicularia, infusoria, and in seasons of mass development also medusas, Ctenophora, and larvae of bottom invertebrates. The zooplankton biomass substantially varies in different seasons. Prevalent in winter are cold-water Copepoda crayfish and Euphausiidae
species, some of which are major food objects of fish. In summer, following development of phytoplankton, the amount of zooplankton was noted to abruptly increase to subsequently gradually decrease.
    The one-cell predatory flagellate night-lighter evokes major interest. It can fluoresce at mechanical or chemical irritation to largely cause coastal waters to fluoresce. The night-lighter occasionally forms large accumulations with density ranging from 0.5 to 0.7 million cells per liter. In this case, the surface water acquires a brown or red color to allow calling the phenomenon red high tide or red florescence.
    Zoobenthos. Gastropods and bivalve mollusks, Polychaeta worms and varipod crayfish are the most numerous species on the Sanctuary littoral and upper sublittoral. At the same time, representatives of most other invertebrate groups also occur here. On the rocky littoral, especially in its upper part, gastropod mollusks, viz. the littorina and sea limpets sharply prevail. Also numerous here are settlements of cirriped crayfish attached to cliffs. Among mobile crustaceans, both on rocky and sandy soils, amphipods, which sometimes form accumulations of up to 100,000 specimens per square meter, and equipod crayfish occur on a mass scale. Starfish, sea urchins, Polychaeta, and Actinia, which are more characteristic, however, of the next zone, are also noted in the lower part of the littoral.
         Bivalve mollusks and echinoderms create the greatest biomass in the upper sublittoral on all soils. Near rocky coasts, solid soils (cliffs and rocks) normally occupy the first 10-15 m in depth, the communities there changing rather rapidly. These soils are followed by soft soils, viz. sand and silt. The largest numbers of animal and plant species are noted at 5-10 m deep. In the upper sublittoral, thickets of laminaria, sargassa and other algae occur often along with the sea grasses Phyllospadix and Zostera with their numerous invertebrate inhabitants. Dwelling on algae are amphipods, small gastropods, and the sedate worm cellular spirorbis, which forms spirally coiled tubes attached to leaves and thalluses. Small alga crabs, hermit crabs, starfish creep on the sea floor; spherical sea urchins also occur.
 Some areas of the topmost sublittoral are devoid of dense plant thickets. This is normally observed on cliffs and large boulders at open surf coasts. Sea acorns and Actinia attach themselves to rocks, and numerous echinoderms (sea urchins and starfish) also occur. Druses of the large Gray mussel attach themselves in-between boulders. The Far Eastern trepang also occurs here, and the Actinia in cracks filled with sand.
    The large reticulate evasteria, up to 0.5 m in diameter, a crimson color species with wide-loop blue network occurs in the upper sublittoral of islands at depths of 10-20 m and more.  Again, here researchers of the Institute of Marine Biology had for the first time found a colonial hydroid, Solanderia mysachinensis, frequently attaching itself to overhanging cliffs and reminiscent in appearance of a cypress branch. Sand octopuses settle on deeper rocky floor sites. Large accumulations of the highly valuable commercial Kamchatka crab young were noted near underwater cliffs.
    Large aggregations (banks) of Gray mussels, which form concomitant community species richest in biomass and composition, present particular interest. Gray mussels form such aggregations at depths ranging from 4-5 to 20 m and deeper in the presence of solid substrate. The biomass of the mussels per se is up to 40 kg per square meter. Among the aggregations, specimens occur aged 100 and more years. The external layer consists of adult specimens, while the young are in the bissus threads of adults. Living on mussels are Bryozoa and Spongia; and sedate worms build their houses. Algae, hydroids and many other animals attach themselves to mussel shells. However, the total biomass of these concomitant organisms is usually several times less than the biomass of the Gray mussels themselves. At present, the Gray mussel population in Peter the Great Bay has been undermined by commercial fishing and poaching; this species should be under universal control and protection, since specimens of this species normally attain commercial size (over 10 cm) after the age of fifteen, and without special reproduction measures their reserves would continue to diminish.
    Epifauna (organisms connected with sea floor surface) is rather poor on soft substrates in open parts of the Bay at depths ranging from 15 to 20 m. Primorye pectens occur on sandy and silty-sandy soils. Their convex valve submerges in a specially formed hole so that with closed upper valve it protrudes from the sea floor surface. Also dwelling here are starfish, viz. the pectinate Patiria, the Amur starfish and others, spheroid sea urchins, and the Far Eastern trepang. Polychaeta worms that form up to 40 percent of the total biomass, bivalve mollusks and the cordiform sea urchin are characteristic of in-fauna, organisms that dig themselves into the soil.
    Few hermit crabs, amphipods and gastropods occur in the topmost sublittoral of open sandy beaches. Significantly more numerous here are digging-in forms: large bivalve mollusks Spisula sachalinensis, the striped mactra, the fibrous Peronidia, the California cordiform species, Stimpsons mercenaria, etc. Usually the sea grass Zostera, with which numerous amphipods, isopod, polychaeta, gastropod and bivalve mollusk young are related, is noted to grow deeper (3-5 m). Tectonatica jantostoma, a predatory gastropod mollusk, occurs in the epifauna. It bores holes in the shells of bivalve mollusks to then eat them. Three flat sea urchin species, the largest of which is the dark-violet uncommon Scaphechinus, also live in sandy soil.
    The invertebrates of half-closed and closed inlets, some of which are moreover subject to freshening, substantially differ in community composition. Among the mass species that dwell here, we find giant oysters, occasionally creating banks and special communities. The Gray mussel is substituted by the long-bristle modiolus, which also forms aggregations. Characteristic of inlets is large bivalve mollusks, viz. Browtons anadar and Bowcards arc. The fauna of the freshened sector of Inlet Sivuchya, into which a channel from Lake Ptichye flows, is diverse and includes a number of salt-water and even fresh-water mollusk species not found in other Sanctuary areas.

A. TIURIN, Cand. Sci (Biology).