Biological performance of the penshell Atrina maura and mussel Mytella strigata under different water flow regimes

Abstract

Three water flow rates (3.1, 7.3, and 12.1 cm s^–1) were used during a 26-day period to determine their effects on shell dimensions, tissue mass, condition index, biochemical composition of tissues, and mortality of the penshell Atrina maura and mussel Mytella strigata kept in an open-flow flume. These parameters were measured at the beginning and end of the trial and significant differences were determined using non-parametric comparisons of multiple independent samples. Both species were able to withstand high seston loads and daily oscillations of temperature, which yielded negligible mortalities. Both species were affected differently by water flow. Atrina maura grew significantly larger above a flow of 7.3 cm s^–1, which appears typical of species inhabiting tidal channels. At this flow, there was a significant increase in lipids and acylglycerols within the digestive gland, adductor muscle, and mantle tissue, accompanied by a significant decline in proteins and carbohydrates within the same organs. In contrast, the flow did not have a significant effect on M. strigata, except for increased lipid and acylglycerol reserves within body tissues at 3.1 and 7.3 cm s^–1, and increased lipid and acylglycerol levels within the gonad at 7.3 and 12.1 cm s^–1. Digestive gland proteins, carbohydrates, and glycogen increased at the highest flow. Data suggest that the penshell is a flow-conforming mollusk that prefers flows exceeding 7.3 cm s^–1, and that the strigate mussel is a flow-regulating species in the range of flows that were studied.