Life cycle and production of Hydrobia acuta Drap. (Gastropoda: Prosobranchia) in a hypersaline coastal lagoon

The life cycle and annual production of Hydrobia acuta was studied in a hypersaline lagoon (s = 39 in summer), forming a part of solar salt works. Quantitative random samples were taken at regular intervals over a period of 15 months using a corer, and snails collected were counted and measured. Weight and biomass was calculated from a length-weight relationship and from measurements of ash content. H. acuta was a strictly annual species in the study lagoon. Recruitment takes place over a brief period in May and June, after which the breeding population dies. Growth of the new generation was slow during summer, probably due to the unfavourably high salinity. A period of rapid growth took place in autumn coinciding with a drop in salinity caused by rainfall. In winter Hydrobia hibernated by burrowing deeply into the sediment. Growth recommenced in spring when the lagoon was reflooded, but by this time the number of survivors was low.The maximum density of snails was 6 000 m^–2 and maximum biomass 500 mg organic dry wt · m^–2. Annual cohort production was estimated as 786 mg organic dry wt · m^–2 · a^–1. These figures are low compared to other studies on hydrobiid snails, and for production in inland waters, but the value for annual P/B = 4.5 is typical for a univoltine species. The relevance of the results to foraging by wading birds (the main consumers), is discussed.