The population dynamics and production of Corophium salmonis (S.) and Macoma balthica (L.) on an estuarine mudflat in response to effluent diversion from a sewage plant, Sturgeon Bank, British Columbia
Creators: name: Arvai, Joseph Louis
Publisher: name: University of British Columbia
Year: 2009

description: In an attempt to determine the biological changes that have taken take place in the Fraser Estuary following the cessation of direct disposal of primary treated sewage effluent, the population dynamics and productivity of two robust indicator invertebrates, the amphipod Corophium salmonis and bivalve Macoma balthica, were monitored for a period of 2 1/4 years. Monitoring of these species, which took place between 10 May 1994 and 22 November 1996, involved assessing their in situ density, biomass, and production at four sampling stations on Sturgeon and Roberts Bank in the Fraser River Estuary, British Columbia. These stations were located on the nearby mudflats at various distances south of the direct effluent dumping zone at the Iona Island Sewage Treatment Plant. For both species, extensive recolonization of the previously azooic zone was observed. At control stations, Corophium salmonis density was similar to that observed prior to the cessation of direct effluent dumping which occurred in 1988. However, the observed biomass in this study exceeded that observed in previous research, indicating that individuals of this species were likely living longer and/or growing larger. In terms of productivity, values observed for C. salmonis (a maximum level of 0.78 g m-2 y-1 afdw) in this study were lower than those observed for this and other species of the same genus in other research. Within this study, high winter density, biomass, and productivity were observed at the two stations that were still under the influence of effluent disposal. It is likely that food availability, longer potential feeding times, and sediment grain preference contribute to this finding at these stations. For Macoma balthica, population and productivity parameters were found to be more stable over the study period than those determined for Corophium salmonis. In general, density observed at contaminated stations exceeded values found in previous studies at the same locations. Densities at control stations, however, were found to be similar to those found at the same stations in previous research. M. balthica productivity (a maximum level of 1.86 g m-2 y-1 afdw) on Sturgeon and Roberts Bank was found to be similar to values observed in other areas around the world. Therefore, it was concluded that the M. balthica population and productivity has recovered (from an azooic condition) since effluent diversion with respect to its population dynamics and productivity. The processes supporting these improvements are likely associated with sediment grain preferences of the organism, food availability, and nutrient assimilation times. Also, a lessening of toxicity associated with effluent disposal (metals, organics, etc.) on Sturgeon Bank may also explain this observation. No relationship was observed between mortality and body size, sampling time, or density for either species. Many agents of individual loss probably act upon all age and size classes of these organisms at any given time obscuring mortality relationships. More study in this area is necessary within field enclosures or in a laboratory to determine the relative importance of the various mortality agents present in these organisms' environment.