The effects of temperature, salinity, and heavy metals on the phototaxic and geotaxic responses of the larvae of S.constricta and C.gigas were examined under the laboratory conditions.The results may be summarized as follows: (1 )A decrease in temperature might increase the positive geotaxic response of S. constricta larvae while the oyster larvae (C.gigas) might change their positive geotaxis into negative response. Simulancously both larval photoresponses were inhibited. An increase in temperature had les...