Direct and indirect effects of simulated calcareous dredge material on eggs and larvae of pink snapper Pagrus auratus

The direct and indirect effects of a simulated, calcarenite-based dredge material on eggs and larvae of pink snapper Pagrus auratus were assessed. Direct effects were assessed by measuring hatch rate or survival of eggs and pre-feeding larvae, respectively, over a range of concentrations and exposure durations. Exposure of eggs to suspended solid concentrations up to 10 000 mg l-1 for 24 h did not affect egg buoyancy or hatch rate, despite sediment adherence occurring at the two highest concentrations tested. Newly hatched larvae, whose mouths were still closed, were relatively tolerant of suspended solids, with a 12 h lethal concentration resulting in 50% mortality, LC50, of 2020 mg l-1 and a first observable effect concentration of 150 mg l-1. Once the larvae's mouths opened, tolerance was significantly reduced, with a 12 h LC50 of 157 mg l-1 and a first observable effect concentration of 4 mg l-1. Tolerance of larvae to suspended solids was negatively correlated with suspended solids concentration and exposure time, with exposure durations of < 6 h being significantly less detrimental than those of 9 h or more. Indirect effects to larvae were assessed by measuring ingestion of copepod nauplii by 10 and 15 days post-hatch (dph) larvae at sediment concentrations from 0 to 200 mg l-1 in 50 mg l-1 increments over 4 h. Ingestion was not significantly affected by sediment for 10 dph larvae, but by 15 dph, sediment had a far greater impact on ingestion, with larvae in all sediment treatments eating significantly fewer copepods than those in the control.