Variation in development and growth rates of larval and juvenile spider crabs Hyas araneus reared in the laboratory

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Abstract
Statistically significant differences were found in development duration of H. araneus L. larvae hatching on different days from the same egg batch. Larvae from different females show a decreasing trend in development time the later they hatch during the season. This trend was found in all larval instars; it was particularly apparent in the megalopa. Development durations in the 2 zoeal stages are positively correlated with each other; i.e., individuals developing more slowly than the average in the 1st larval instar tend to delay molting also in the 2nd instar. There are negative correlations between larval development time in all stages and the size of juvenile crabs; i.e., weak individuals tend to develop more slowly and to become smaller juveniles than the average. These larvae show lower accumulation rates of biomass (measured as dry weight, C and N) already during the 1st zoeal stage. Larval development rates (at 12.degree. C) were not clearly affected by the temperature prevailing during previous embryonic development, but embryos incubated at higher temperatures tended to become smaller crabs. Further correlations suggest that crabs (instar I) developing slower than the average will show prolonged intermolt periods also in later instars, and will have smaller body size throughout their juvenile life. Relative growth rates (percentage gain of carapace length) remain fairly constant (circa 20-25% per molt). Absolute variation in body size increases from instar to instar. It is partly compensated by differential mortality being higher in the smallest and largest individuals of a population.