биота российских вод японского моря - Materials of Alexey Shipunov

water from year to year. For example, in cold years (1975) only E. nordmanni and Podonleuckarti were found in this area (Bokhan, 1984).In the southernmost part of the Russian Far East waters (Peter the Great Bay) E.nordmanni appears in spring and reaches maximum density in early summer and inautumn. Thus, in Amursky Bay (Alekseev Bight of Popov Island) the species occurredin the plankton May through January and had two peaks of density, from mid-June tomid-July and from mid-October to mid-November. First specimens were recorded inMay at a water temperature of 5°C, in June at an average temperature of 13.2°C thedensity was 230 sp./m 3 , and in autumn, when temperature ranged from 9 to 3°C, apopulation maximum of 162 sp./m 3 was recorded (Mikulich & Biryulina, 1977).Chuchukalo et al. (1980) show that E. nordmanni appeared in Amursky Bay(near Reineke Island) in early June at a water temperature of 11–13°C, and in July (at21°C) the density already attained 7 thousand sp./m 3 . Temperature rising to 21–22.3°CJuly through late August, E. nordmanni decreased in numbers to 0.5 thousand sp./m 3 .In late autumn (November) at a temperature of 7.1°C the abundance of the speciesslightly enhanced (Chuchukalo et al., 1980).In the south-western part of Peter the Great Bay E. nordmanni is vertically distributedfrom 0 to 50 m. Its peak density was recorded for July (in Kalevala Bight, 3.5thousand sp./m 3 ); in August, when temperature was the warmest (21°C), the densitysharply decreased; and in September rose again (Shkoldina & Shevchenko, 2001).Kos’ records (1976) display that in mid-summer (late June–early July) the density ofE. nordmanni was low (5–25 sp./m 3 ) in Possjet Bay at a temperature of 17–20°C. Inthis bay the species was found at a temperature of 6.6–21°C and a salinity of 26.31–33.17‰. A maximum density of E. nordmanni (260 sp./m 3 ) was registered at offshorestations (Kos, 1977).In the south-western part of Peter the Great Bay gamogenetic females with latenteggs were recorded for July and September, and were not found in August. It may indicatethat E. nordmanni has two reproduction cycles in the southern part of its distributionalrange. In 2002 in Vostok Bay E. nordmanni occurred in the plankton untillate October, at a temperature of 12–13°C, and females with well-developed restingeggs constituted the bulk of the population.The biology and ecology of E. nordmanni are most extensively studied for the InlandSea of Japan (34°N). In this area the species appears in March-April and disappearsin June; it attains a maximum density of 2.7–3.4 thousand sp./m 3 at 15–16°C. E.nordmanni appears in the plankton at a temperature from 8 to 11°C and disappears at atemperature from 21.4 to 23.8°C (Onbe, 1974). In March and April females have thelargest size (length up to 0.55–0.6 mm) and highest fecundity (up to 10–12 embryos).Males and gamogenetic females appear in the population in mid-June, and by the endof the month parthenogenetic females almost disappear (Onbe, 1974). Resting eggsare light brown and have a size of about 200 µm (Onbe, 1985).The analysis of the intestine’s content showed that E. nordmanni feeds on largecentric diatoms, particularly Skeletonema costatum. On other evidence, the podonidsmay also consume dinoflagellates (Kim et al., 1989).24