Size of eggs and nauplii of calanoid copepods in the Barents Sea; influence of environmental and maternal factors
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During the years 1986 to 1988 eight cruises were conducted in the central and western parts of the Barents Sea. The cruises, together spanning the time period from January to July, covered most developmental stages of the phytoplankton spring bloom. Temperature, salinity, nutrients, chlorophyll a, and zooplankton were generally sampled at each station. Size frequency distributions of eggs and nauplius stages of the copepods Calanus finmarchicus, C. glacialis, C. hyperboreus, Pseudocalanus sp., and Metridia sp., are given. Cluster analysis and a subjective method of classification grouped the sampling stations into environmental regions on the basis of environmental variables. The environmental variables were related to size of eggs (diameter) and nauplii (carapax length) of C. finmarchicus by a linear method of canonical ordination (Redundancy Analysis). A significant overall difference in size of eggs and nauplii between environmental regions was demonstrated. The size of eggs and nauplius stages N1 to N3 were positively correlated with distance from the Norwegian Sea, and the size of the females were positively correlated both with distance from the Norwegian Sea and egg size. Egg size was negatively correlated with temperature. lt was concluded that advection of smaller sized adult females into the Barents Sea gave rise to a population of small sized eggs and young nauplii. The maternal effect may be a direct process where bigger females spawn bigger eggs, or more indirectly where the females spawn bigger eggs at low temperatures. The feeding stages N4 and N6 were positively correlated with chlorophyll content (assumed to represent food supply), and negatively correlated with temperature. Chlorophyll and temperature were inter-correlated, and the contribution of each particular variable to the relationship could not be estimated. Thus, after the nauplii start to feed, food supply and/or temperature have greatest influence on size, and soon mask size patterns due to maternal effects.