Egg Size and Reproductive Output in the Deep-Water Prawn Pandalus borealis Kroyer, 1838

The deep-water prawn Pandalus borealis Kroyer, 1838 was sampled at six locations from Krossfjord, Spitsbergen (79⚬N, close to the known northerly limit of distribution) to Kosterfjord, Sweden (58⚬N, close to the southerly limit in the eastern north Atlantic). Both egg volume and organic content increased towards high latitudes, ranging from 0.39 μ l and 0.21 mg at Bergen, to 0.67 μ l and 0.30 mg at Isfjord, Spitsbergen. Egg volume was positively correlated with both fresh mass and organic content. Reproductive investment (estimated as mass-specific egg biomass: reproductive output, RO) also varied from site to site, but was not correlated with either latitude or egg size. In five of the six populations sampled, reproductive investment calculated on a dry mass basis increased with size (and hence age), but this relationship was statistically significant only at two sites. These data indicate that both egg size and reproductive investment vary from location to location within species, and are uncorrelated. Egg size is related to feeding and other conditions awaiting the newly hatched larva, whereas reproductive investment is dictated by feeding conditions for the adult. The different time-scales over which these two parameters vary (from season to season in RO, and over evolutionary time for egg size) mean that any general relationship between reproductive investment and egg size (and by extension, larval development mode) will be very difficult to demonstrate.

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