Abstract
Big Glory bay is a semi-enclosed bay located in the south-east of Paterson Inlet, Stewart Island. The bay has been used for commercial sea cage rearing of chinook salmon (Oncorhynchus tshawytscha Walbaum) since 1981 and long-line culture of green-lipped mussels (Perna canaliculus) since 1987. Extensive aquaculture expansion within the bay has placed considerable demand on the allocation of resources. The understanding of this ecosystem is required in order to facilitate effective environmental management. This study investigated the exchange of nutrients between Big Glory Bay, Paterson Inlet and the adjacent coastal water. A build-up of nutrients in the bay may induce the development of eutrophic conditions and increase the probability of the occurance of algal blooms. Conversely, a lack of nutrients in the water column could impede mussel growth.
Temperature, salinity, density, current velocity and nutrient levels were measured in the entrance of Big Glory Bay to determine the exchange of nutrients for the bay during well mixed (2 to 4 September 1996) and stratified (3 to 6 February 1997) conditions. Water currents in the entrance of the bay were affected by a strong baroclinic flow during September 1996. A mechanism for the intrusion of adjacent coastal water into the bay was documented. This mechanism was dependent upon the occurrence of strong wind events. During September 1996 the oceanic intrusion was high in dissolved reactive phosphate (DRP) and lower in nitrite, total phosphate (TP) and total nitrogen (TN) compared to levels in Big Glory Bay. During February 1997 the intruding water was characterised by high levels of nitrate. All nutrient species exhibited a net export from Big Glory Bay during well mixed and stratified conditions.