The reduction in growth of Mytilus edulis in fluctuating salinity regimes measured using laser diffraction patterns and the exaggeration of this effect by using tap water as the diluting medium

Abstract

In experiments to investigate the effect of low salinity on growth in Mytilus edulis, unexpected depression of growth occurred, even in sinusoidal regimes falling to only 90% of the full salinity, when tap water was the diluting medium used. The effect of various additives to the domestic water supply on the growth of Mytilus was investigated. Chlorine and fluoride had no effect although fluoride (as sodium fluoride) inhibited faeces production in a 7-day experiment. Determinations of the level of copper in the laboratory's tap water showed these to be high enough to cause depression of growth even at low dilution levels. When distilled water or lake water was used to dilute the sea water, shell growth was not affected until a sinusoidal fluctuation reaching a minimum of 50% sea water was used. Such effect did not become significant until the mussels were kept in pure fresh water for an extended period in each cycle of sinusoidal salinity variations.