Although there are no authenticated records of human illness due to PSP in New Zealand, nationwide phytoplankton and shellfish toxicity monitoring programmes have revealed that the incidence of PSP contamination and the occurrence of the toxic Alexandrium species are more common than previously realised (Mackenzie et al., 2004). A full understanding of the mechanism of uptake, accumulation and toxin dynamics of bivalves feeding on toxic algae is fundamental for improving future regulations in the shellfish toxicity monitoring program across the country. This thesis examines the effects of toxic dinoflagellates and PSP toxins on the physiology and behaviour of bivalve molluscs. This focus arose because these aspects have not been widely studied before in New Zealand. The basic hypothesis tested was that bivalve molluscs differ in their ability to metabolise PSP toxins produced by Alexandrium tamarense and are able to transform toxins and may have special mechanisms to avoid toxin uptake. To test this hypothesis, different physiological/behavioural experiments and quantification of PSP toxins in bivalves tissues were carried out on mussels (Perna canaliculus), clams (Paphies donacina and Dosinia anus), scallops (Pecten novaezelandiae) and oysters (Ostrea chilensis) from the South Island of New Zealand. Measurements of clearance rate were used to test the sensitivity of the bivalves to PSP toxins. Other studies that involved intoxication and detoxification periods were carried out on three species of bivalves (P. canaliculus, P. donacina, P. novaezelandiae), using physiological responses (clearance and excretion rate) and analysis of PSP toxins in the tissues over these periods. Complementary experiments that investigated other responses in bivalves fed with the toxic cells were also carried out. These included byssus production, and the presence of toxic cells in the faeces of mussels, the siphon activity and burrowing depth in clams and the oxygen consumption in scallops. The most resistant species to PSP toxins were the mussel, Perna canaliculus and the clam, Dosinia anus. Both species fed actively on toxic dinoflagellates and accumulated toxins. The intoxication and detoxication rate of the mussel was faster than the other species of bivalve studied (P. donacina and P. novaezelandiae) which confirm mussels as a good sentinel species for early warning of toxic algal blooms. The clearance rate of the clam, Paphies donacina decreased when fed on Alexandrium species but the effect of the PSP toxins on this physiological response was not confirmed. Over the detoxification period of 8 days, this clam did not detoxify which suggests that its ability to retain high level of toxins for an extensive period may be critical for public health management. The scallop, Pecten novaezelandiae was clearly the most sensitive species to the PSP toxins and the clearance rate was significantly lower in the presence of the toxic dinoflagellate A. tamarense. Although the clearance rate was low, the scallops still fed on the toxic dinoflagellate and accumulated PSP toxins in the tissues. The scallops detoxified slowly which would affect the market for this bivalve in the presence of a toxic algal bloom. This bivalve would retain PSP toxins for longer period of time than other species such as mussels. The oyster, Ostrea chilensis, had erratic clearance rate and did not respond clearly to any of the variables tested over the time. Oysters accumulated more toxins than the sensitive species, but they had been exposed to two more days of feeding with A. tamarense; therefore this species may actually have a similar intoxication responses to P. novaezalandiae and P. donacina. The results from this thesis suggest further directions for the aquaculture sector and ongoing research in this field, which in future will lead to a better selection of suitable species for culture as well as species for monitoring of PSP toxins. In the future, research that integrates field and controlled laboratory studies will expand to other species of interest and a more complete record will in time be available in order to manage more efficiently the negative effects that harmful algal blooms may have in New Zealand.