Phytoplankton settles the upper water layers and is the main producer of organic sea substance.  The most numerous species from the phytoplankton group in Possiet Bay are diatomic (up to 60 percent) and peridinium algae (up to 27 percent). Eleven diatomic algae species, the cause of annual УfloweringФ observed in the Bay in various times of the year, dominate in cell density per unit volume and, as a rule, in biomass.
   Two peaks have been noted for microalgae populations, one in winter (December-February) and one in summer (July-August). During summer blooming, the cell density reaches 1-2 million/liter at biomass of 2-5 g/cu. m.
   Phytobenthos. The Sanctuary floor vegetation is typical of open coasts of Peter the Great Bay. Alga communities are most often distributed in belts. In the littoral zone, the belts are narrow, 10-20 cm vertically, and in the sublittoral several meters wide. Two horizons are distinguished in the littoral zone of Peter the Great Bay. In the upper horizon, in low tide, a belt of forked gloiopeltis, which grows on rocky and stony open beaches, becomes exposed. The vermiform nemalion and the beaded chetomorph form deeper, sparse settlements. Passing still lower are belts of the Japanese analipus, the Japanese polysyphony and the ball-bearing corallin.
   The Iwate phyllospadix, a seagrass species, grows in the upper sublittoral in small inlets on sandy soil mixed with rocks and pebbles. It forms turf sites several square meters in area, in-between which the rhodomela, the chorda and other alga species grow on rocks and shells. In direction of inlet exits at 1.5-2 m deep, the phyllospadix is replaced by the eelgrass, which forms dense settlements not infrequently occupying almost the entire sandy floor of inlets up to 8-10 m deep.
   On open coast areas washed by moving and well-aerated water, at 3-5 m deep, calcareous algae, viz. the cork lithophyllum and lithotamnium Pacifica, dominate on rocky soil in a biocoenosis of Gray mussels, sea urchins and starfish. Concomitant with them are the soft cork peisonelia Pacifica, the elegant rholophysema, and the small bushy species (the random helidium, the branchyoglossum minoris and others).
   The chicory-like laminaria, the codiyum iesoensis and the cystosira cohabitate with the Primorye pecten at 6-12 m deep on sand-shell soil. Starting from 7 m deep, the laminaria is replaced with the dichloria and ulva, which occur at 12-15 m deep. The latticed agar is noted together with them, and calcareous algae grow deeper.

A. TIURIN, Cand. Sci (Biology).