Salinity effect on the embryonic development, larval growth and survival at metamorphosis of Placuna placenta Linnaeus (1758)

Abstract

The effects of salinity on the embryonic development, growth, and survival of D-larvae to plantigrade as well as settling in <i>Placuna placenta</i> were studied. Embryos were developed to D-larvae of shell length (SL) 86±12 μm (SL±S.D.) after 20 h at salinities of 22–34 ppt, but not at lower salinity levels. Percentage production of straight-hinged larvae from fertilized eggs at these salinities ranged from 51% to 63% (<i>P</i>≥0.05). <i>P. placenta</i> larvae survived and settled in salinities of 16–34 ppt. Settlement occurred first (14 days) in salinities of 22–34 ppt and later (19 days) in 16 ppt when SL≥200 μm. Larval size at metamorphosis was not significantly different among these salinities (<i>P</i>≥0.05). Percentage survival of plantigrades at 34 ppt (13%) was significantly higher (<i>P</i>≤0.05) than at 16 ppt (4.5±3%), but not greater than at 22 (6.3±3%) or 28 ppt (7±4%) salinity. The best salinity levels for embryonic development and larval survival at metamorphosis ranged from 22 to 34 ppt and larval growth from 16 to 34 ppt. The tolerance of <i>P. placenta</i> to lower and higher salinities progressively increased as larvae develop from embryo to the plantigrade stage.