Abstract
Estuaries represent a transitional environment influenced by both terrestrial and marine processes. There are several types of estuary defined by their connectivity with the marine environment that are found along coastlines worldwide. Estuarine sites hold significant ecological, cultural, recreational and aesthetic values. The East Otago area encompasses estuaries with permanent marine connection, intermittent connection, and a system that is highly modified and contains sites with virtually no marine connection. Comparisons in the ecology between estuaries of several types in this geographic area was conducted over a twelve-month period.
Physicochemical properties of these estuarine sites were measured at regular intervals. All sites had a different physicochemical make-up, which was influenced by the connectivity to the marine environment. The pH, salinity, phosphate and nitrate concentrations were the main physicochemical parameters from which differences between sites were measured. Primary producer biomass was measured on a seasonal basis at all sites and demonstrated the influence that drift macroalgae has on open estuarine systems, while phytoplankton cell density was measured higher in closed estuarine systems. The benthic macrofaunal community showed differences in the assemblage composition and abundance of organisms between the different sites. Open estuarine systems had a greater diversity of species and higher biomass compared to closed systems, which contained high abundance of the limited number of species present. A model was constructed using the sediment properties and macrofaunal data, which found that benthic macrofaunal assemblage composition in East Otago estuarine sites was influenced by sediment particle size.
Estuaries are environments undergoing rapid change as a result of anthropogenic influence. The analysis of the ecology in East Otago estuarine sites has highlighted the uniqueness of these systems on an individual level and will provide a data set for any future comparisons to be assessed against, and will also assist in the implementation of any future management initiatives.