ИСТИНА

Harpacticoida (Copepoda) group is one of the main components of marine meiobenthos. Harpacticoid copepods are associated with different bottom substrates and macrophytes, while its contribution to planktonic biodiversity was traditionally considered to be rather little. This study aimed to test the relevancy of this statement. We analyzed species composition and interannual dynamics of Harpacticoida in coastal zone of the Iturup Island (the Sea of Okhotsk). Studies of were carried out in May andJuly, 2013 – 2015. Samples were taken along two transects,located above isobaths 10, 20, 50 and 100 m. Within this research we found 73 copepod species and species groups. The highest species richness however was observed for Harpacticoida group – 48 species, whereas Calanoida and Cyclopoida were represented by 20 and 5 species respectively. Recognized Harpacticoida from zooplankton samples mainly belong to phytal or epibenthic fauna. The only exception is the planktonic species Microsetella norvegica (Boeck, 1865). Harpacticoids occurred within the coastal zone of depth up to 10 m. Above isobaths of 50-100 m only typically planktonic representatives harpacticoids were found. The greatest number of adult harpacticoids in plankton was recorded in May and June. The interannual variability of their abundance depended on hydrological characteristics. The number of harpacticoids in warm-weather year (2015) was much higher than in the cold one (2013) (194 and 6 specimens/m3 respectively). Thus, considerable harpacticoid diversity and abundance in the plankton refute the prevailing statement that this group is exclusively near-bottom. Harpacticoids probably go into the water column to feed on planktonic microalgae. Besides, the wave turbulence may contribute their emergence in plankton.