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

Abstract

BSTRACT: Statistically significant differences were found in developmentduration of Hyasraneus L. larvae hatching on different days from the same egg batch.Larvae from different femaleshow a decreasing trend in development time the later they hatch duringthe season. This trend wasound in all larval instars; it was particularly apparent in the megalopa.Development durations in thezoeal stages are positively correlated with each other, i.e. individualsdeveloping slower than theverage in the first larval instar tend to delay moulting also in thesecond instar. There are negativeorrelations between larval development time in all stages and thesize of juvenile crabs, i.e. weakndividuals tend to develop more slowly and to become smaller juvenilesthan the average. Thesearvae show lower accumulation rates of biomass (measured as dry weight,carbon, and nitrogen)lready during the first zoeal stage. Larval development rates (at12 'C) were not clearly affected by theemperature prevailing during previous embryonic development, but embryosincubated at higheremperatures tended to become smaller crabs. Further correlations suggestthat crabs (instar I) develop-ng slower than the average will show prolonged intermoult periodsalso in later instars, and they willave smaller body size throughout their juvenile life. Relative growthrates (percentage gain ofarapace length) remain fairly constant (ca. 20 to 25 % per moult).Absolute variation in body sizencreases from instar to instar. It is partly compensated by differentialmortality being higher in themallest and largest individuals of a population.