Relationships among salinity, egg size, embryonic development, and larval biomass in the estuarine crab Chasmagnathus granulata Dana, 1851

We studied interrelationships between initial egg size and biomass, duratio n of embryogenesis at different salinities, and initial larval biomass in a n estuarine crab, Chasmagnathus granulata. Ovigerous females were maintaine d at three different salinities (15 parts per thousand, 20 parts per thousa nd and 32 parts per thousand); initial egg size (mean diameter), biomass (d ry weight, carbon and nitrogen) as well as changes in egg size, embryonic d evelopment duration, and initial larval biomass were measured. Initial egg size varied significantly among broods from different females m aintained under identical environmental conditions. Eggs from females maint ained at 15 parts per thousand had on average higher biomass and larger dia meter. We hypothesise that this is a plastic response to salinity, which ma y have an adaptive value, i.e. it may increase the survivorship during post embryonic development. The degree of change in egg diameter during the embr yonic development depended on salinity: eggs in a late developmental stage were at 15 parts per thousand significantly larger and had smaller incremen t than those incubated at higher salinities. Development duration was longe r at 15 parts per thousand, but this was significant only for the intermedi ate embryonic stages. Initial larval biomass depended on initial egg size a nd on biomass loss during embryogenesis. Larvae with high initial biomass o riginated either from those eggs that had, already from egg laying, a high initial biomass (reflecting individual variability under identical conditio ns), or from those developing at a high salinity (32 parts per thousand), w here embryonic biomass losses were generally minimum. Our results show that both individual variability in the provisioning of eggs with yolk and the salinity prevailing during the embryonic development are important factors causing variability in the initial larval biomass of C. granulata, and thus , in early larval survival and growth. (C) 2001 Elsevier Science B.V. All r ights reserved.