The relative importance of pelagic and benthic primary production for Austrovenus stutchburyi in Blueskin Bay in the South Island, New Zealand
Bivalves are commercially and ecologically important in estuarine ecosystem. Austrovenus stutchburyi is a dominant bivalve species in the Blueskin Bay inlet, New Zealand, and has been considered as culturally, commercially and ecologically important (Irwin 2004). For long pelagic microalgae have been regarded as the main food source for A. stutchburyi in this inlet, while the importance of benthic primary production may have been overlooked. The present study aims to examine the contribution of pelagic and benthic primary production in support of the A. stutchburyi stock in Blueskin Bay inlet. Chlorophyll fluxes through the mouth of the Blueskin Bay inlet during tidal exchange were monitored using fluorometers as a proxy of the biomass of pelagic primary production. Spatial surveys of pelagic and benthic chlorophyll concentrations were conducted to assess spatial distribution. Suspended particulate organic matter (SPOM) and sediment organic matter (SOM) were sampled seasonally for stable isotopes to complement the chlorophyll data. A two-source mass balance model using stable isotopes 13C and 15N was applied to calculate the relative contribution of pelagic and benthic organic sources to the diet of A. stutchburyi in Blueskin Bay. Tidal and seasonal patterns can be seen from the concentration of chlorophyll detected at the entrance of the estuary. Chlorophyll concentrations in flood tides (2.73±0.29 ug/L to 1.41±0.04 ug/L) and the proportion of chlorophyll depleted on a tide (39.00±0.05 % to 18.66%±0.03 %) peaked in spring and reached their lowest point in winter. The SPOM data shows similar seasonal variation. A positive relationship was found between the concentration of benthic chlorophyll concentration and SOM and the distance from the estuary mouth. Areas with higher density of A. stutchburyi (average 6.2kg/m2) tend to have higher abundance of diatoms than areas with lower density of A. stutchburyi (<1kg/m2). Results from the stable isotope model indicates that while SPOM accounts for the majority of the carbon of A. stutchburyi, benthic organic matter source can be an important contributor to the diet of A. stutchburyi (11.82±3.93% to 34.10±1.78%). The proportion of food derived from the benthic environment becomes larger as the distance from the estuary mouth increases. The study shows that the relative contribution of pelagic versus benthic primary production to A. stutchburyi varies spatially and temporally within Blueskin Bay, which should be given consideration in ecosystem-based management of the species.
Advisor: Savage, Candida; Russell, Pete
Degree Name: Master of Science
Degree Discipline: Marine Science
Publisher: University of Otago
Keywords: Austrovenus stutchburyi; Blueskin Bay; chlorophyll; primary production; pelagic; benthic; stable isotope
Research Type: Thesis