Measuring the contribution of ecological composition and functional services of estuaries ecosystems to the dynamics of Kwazulu-Natal coast fisheries

Abstract

The Millennium Ecosystem Assessment (MEA) defines ecosystem services (ES) to be the direct and the indirect contributions of ecosystems to human well-being and emphasized that regulating ES are amongst the least understood but potentially most valuable services offered by ecosystems. On the one hand, this lack of understanding of regulating ES has been a major reason for the overexploitation and degradation of ecosystems but at the same time causing unnecessarily risk-averse environmental policy leading to delays in economic development interventions. The value of regulating ES is best determined through an economic-ecological production function approach, which derives the value of regulating services as intermediate inputs into the production of final economic goods and services. This study applies the ES framework of the MEA and uses the ecosystems’ concepts of composition, structure, and function to formulate and estimate economic-ecological production functions. Regulating services analysed here included various habitat services, salinity regulation and nutrient cycling. The objective of the research was to find empirical evidence of the significant effects of these services on fish species diversity and fish biomass or stock. The research is based on a case study, and uses existing ecological and economic knowledge and data sourced from existing scientific databases and studies, to develop and demonstrate empirical production functions that measure relationships between ecological infrastructure and the economy in the KwaZulu-Natal (KZN) fisheries along the east coast of South Africa. The study was implemented in two phases. The first phase used cross section data and a static model to measure relationships between fish production and compositional and functional elements of both estuarine and marine ecosystems and allowed for estimation of accounting prices of the KZN estuarine and marine ecosystems’ attributes. A system of ecological production functions was estimated to measure the effects of estuarine ecosystem compositional and structural elements on fish production using the SURE regression analysis method with highly significant statistical performance and estimated parameter effects consistent with scientific knowledge. The results provided compelling evidence of the importance of estuarine composition and structure on fish species diversity and fish biomass production. The second phase extended a bio-economic fishery model to establish an explicit link between coastal ecosystems’ ecological composition (biodiversity) and functional (nutrient supply) attributes and the dynamics and productivity of KZN coastal fisheries. Results confirmed the importance and strong contribution of the tested ecological attributes. In-sample simulation indicates that current fishing efforts and harvest rates are sustainable, but are sensitive to changes in nutrient influx and rainfall. This confirms the need to modify conventional fisheries models to include environmental variables as additional predictors of fish stocks in addition to historical catch records and catch effort for short-term management and control of fishing efforts and permits. This study provided strong empirical evidence for the linkage between nutrient levels and productivity of coastal fisheries and enabled investigating runoff and rainfall related climate change effects on the KZN fisheries. The research results provided strong empirical evidence that ecosystems play a significant role in economic production. In the case study, the regulating services relating to species diversity, extent and type of habitat, salinity and nutrient cycling all displayed significant effects on fish production, particularly for their impacts on commercial line-fishing and recreational angling along the KZN coast. Various coastal developmental and global change hazards may put the functioning of these ecosystems at risk and this research demonstrated how these risks may be evaluated and prudently managed.