The life cycle and growth of Heleobia australis (d'Orbigny, 1835) and H. conexa (Gaillard, 1974) (Gastropoda: Rissooidea) in Mar Chiquita coastal lagoon (Argentina)

CLAUDIO GERMAN DE FRANCESCO; ISLA, F.I.

Journal of Molluscan Studies

The Malacological Society of London

Lugar: London; Año: 2004 vol. 70 p. 173 - 178

The variations in the life cycles and growth of the brackish-water rissooidean snails Heleobia australis (d’Orbigny, 1835) and Heleobia conexa (Gaillard, 1974) were studied along a gradient of estuarine conditions from the outer to the inner reaches of the Mar Chiquita coastal lagoon (Argentina). The study focused on the results obtained in a sampling period of 1 year from August 1998 to June 1999. Species have a seasonal cycle of reproductive activity from spring (October) to early winter (June). The breeding period is longer for the population of H. conexa inhabiting the innermost shallow area, which may be related to the higher temperature there. Increased growth rates of both species were observed during late spring and summer. Growth rates of H. australis decreased in the inner areas in coincidence with decreasing salinity and tidal exposure. The opposite pattern was observed for H. conexa, probably due to the influence of higher temperature in the shallow low-migration environments in the middle part of the lagoon.