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Phytoplankton pigment concentrations in the sur-face sediments of a fish and oyster farm in Dapeng Cove, South China Sea, were measured monthly to investigate the effects of mariculture on the envi-ronment from December 2011 to December 2012. The highest contents of the identified phytopig-ments, sulphides and total organic carbon in the surface sediments were all found at the fish farm, followed by the oyster farm; the lowest contents were detected at the control site. Fucoxanthin in the surface sediments was the most abundant car-otenoid and was significantly correlated with chlorophyll a (Chl a; r = 0.922, P < 0.01). This finding suggested that the deposited diatoms could be the main source of the Chl a concentration. Besides a differential sedimentation of phytoplank-ton (i. e. higher downflux at fish and oyster site than that at control site), we assume that the extent of pigment diminution from the fish site to control site was also controlled by the chemical conditions of the surface sediments. The fish farm provided the most optimum preservation condi-tions for the phytopigments and was a good sink for phytodetritus among the three sites because of its anoxic and reductive characteristics. Phyto-plankton pigments could be useful biomarkers to evaluate the influence of mariculture on sediment environment.

The sea cucumber Holothuria leucospilota is a good candidate for aquaculture, for large-scale production of this sea cucumber, it is imperative to know the effects of salinity on its physiological performance. In this study, ingestion, oxygen consumption and ammonium excretion rates of the adult sea cucumber H.leucospilota (16.98 +/- 1.14g, wet weight) at various salinity levels (18, 23, 28, 33 and 38PSU) were studied in the laboratory. The species were acclimated for 1week at the desired salinity before testing, and were fed with sediment from their natural habitat during this period. Results showed that the minimum ingestion rate (0.02 +/- 0.01gg(-1)d(-1)) at a salinity of 18PSU was significantly lower than those observed at salinities of 28, 33 and 38PSU, and there was no significant difference among the values at 23, 28, 33 and 38PSU. The maximum value of oxygen consumption rate recorded at a salinity of 28PSU was significantly higher than the minimum at 18PSU, no significant differences were observed among other treatments. The ammonium excretion rates of H. leucospilota also changed significantly in response to salinity variations, the maximum value observed at a salinity of 28PSU (0.09 +/- 0.03Mg(-1)h(-1)) being nearly five times higher than the minimum value at a salinity of 38PSU (0.02 +/- 0.01Mg(-1)h(-1)). The O:N ratio varied as a function of salinity. Lower O:N ratios (