Resting eggs, seasonal dynamics, and production of Bosmina longispina maritima (P. E. Müller) (Cladocera) in the northern Baltic proper

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Abstract
The seasonal dynamics and production of B. longispina maritima were studied in the pelagic zone and bottom sediments of the northern Baltic proper in 1979. Resting eggs started to hatch in April-May, but the pelagic zone population did not show signs of increase until Aug., this is typical for the species in this area. Relatively few of those hatched in the spring and early summer survived the low temperatures, and lack of food below the thermocline. The population increase started with individuals hatched after the thermal stratification weakened. From August-Oct. the number of resting eggs in the sediment rose in direct response to their production in the pelagic zone. A new hatching period began in Oct.-Nov., but conditions in the pelagic zone were not suitable for their further development. Such mistiming of hatching may, along with other factors, help to explain the large annual variations in the productivity of B. longispina maritima in the Baltic. Sexual reproduction was of relatively greater importance in the study area than in the areas where Bosmina reaches higher productivity. This was assumed to be due to more intense selection pressures in the prevailing conditions.

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