Effects of elevated levels of suspended particulate matter and burial on juvenile king scallops Pecten maximus

Abstract

The effects of exposure to elevated levels of suspended particulate matter (SPM) and burial on juvenile king scallops Pecten maximus L. were assessed in 2 separate experiments. Shell gape activity was monitored during exposure to no SPM and 'low' (50 to 100 mg l �1 ) and 'high' (200 to 700 mg l �1 ) levels of SPM for 18 d. The frequency of shell 'claps' (a complete shell closure) and shell movements (of ≥10°) differed significantly among treatments. Shell 'claps' and move- ments were significantly greater under high SPM than under low or control conditions. Scallops under low and high levels of SPM showed significantly lower growth rates compared to scallops under control conditions. The response to burial was assessed under varying burial duration (1 to 8 d), depth (0 to 5 cm) and size-fraction of sediment (fine: 0.1 to 0.3 mm, medium fine: 0.4 to 0.8 mm and coarse: 1.2 to 2.0 mm diameter). All 3 conditions had a significant influence on the ability of scallops to emerge from burial, as well as on mortality while buried. Emergence was higher at shallower depths and in coarse to medium grain sizes. Mortality rates while buried under coarse and medium grain sizes were low and appeared unrelated to depth, while within fine sediment, mortality increased with depth of burial. Survival decreased across all 3 sediment types with increasing burial duration. Comparison with earlier studies indicates that P. maximus appears more tolerant of burial and elevated levels of SPM than the queen scallop Aequipecten opercu- laris. Elevated SPM did not have any short-term effects on survival; however, the reduction in growth rate observed has implications for the management of scallop fishing grounds.