Investment in eggs in lagoonalHydrobia ventrosaand life-history strategies in north-west EuropeanHydrobiaspecies

Expected lifetime investment in eggs and related parameters are described for a lagoonal population ofHydrobia ventrosa(Mollusca: Gastropoda) in East Anglia, UK, and these are compared with those of East Anglian lagoonal populations ofH. neglectaand both lagoonal and intertidal-marine populations ofH. ulvae. In contrast to an earlier study on Danish populations, which suggested thatH. neglectaandH. ventrosaare at opposite ends of the hydrobiid spectrum of investment in reproduction, the order of increasing relative allocation of resources to egg production runsH. neglecta=H. ventrosa→ lagoonalH. ulvae→ intertidal-marineH. ulvae. That is, from the two small, short-lived, specialist lagoonal species producing few, large, directly-developing eggs, to the larger, potentially longer-livedH. ulvaethat produces many small eggs which develop into veliger larvae. The lagoonal populations of all threeHydrobiaspecies, however, are very similar to each other in terms of reproductive investment. When like cohorts are compared, in each, the annual egg weight is equal to the annual adult growth increment, and the weight of eggs produced per expected lifetime is half the adult growth increment at the time of death. These lagoonal populations are markedly dissimilar to intertidal-marine populations ofH. ulvae, which produce an annual weight of eggs some 15 times the annual adult growth increment, and an expected lifetime egg weight some two-and-a-half times the adult growth increment at the time of death.