Integrated Biological and Physicochemical Assessment of Ecological Condition in Two Oyster-producing Brackish Systems: Implications for Sustainable Fisheries Management
Sandra Akugpoka Atindana *
Department of Fisheries and Aquaculture, University of Technology & Applied Sciences, Navrongo, Ghana.
*Author to whom correspondence should be addressed.
Abstract
Background: Oyster-producing lagoons and estuaries are exposed to environmental pressures that may affect habitat condition and fishery sustainability.
Aims: To assess and compare the ecological condition of the Densu estuary and Anyanui lagoon by integrating benthic macroinvertebrate assemblages with physicochemical characteristics and water-quality indices and to examine the implications of the findings for sustainable oyster fisheries management in Ghana.
Study Design: Water and benthic macroinvertebrate samples were collected from four ecologically distinct zones selected to represent the major environmental gradients within the lagoon: (i) the upstream freshwater-influenced section, (ii) the central channel, (iii) the downstream section adjacent to the lagoon outlet, (iv) an area adjacent to agricultural lands/graveyards where diffuse runoff was expected to influence water quality (mapped using QGIS). These locations were selected to capture spatial variability in physicochemical conditions and benthic communities across the lagoon. The modified Delphi technique was adopted to identify priority water quality parameters affecting Crassostrea tulipa growth.
Place and Duration of Study: The Densu Estuary and Anyanui Lagoon were studied from November 2023 to December 2024.
Methodology: Physicochemical variables were analysed using the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), while benthic macroinvertebrate assemblages were used as biological indicators of ecological integrity. Expert consultation informed the selection and weighting of key physicochemical variables included in the index. Macroinvertebrate assemblages revealed greater taxonomic diversity and ecological integrity in the Anyanui Lagoon than in the Densu Estuary.
Results: Macroinvertebrate assemblages revealed greater taxonomic diversity and ecological integrity in the Anyanui Lagoon than in the Densu Estuary.
The occurrence of taxa such as Lithophaga lithophaga and Leptocerus sp. indicated relatively stable environmental conditions in Anyanui, whereas the higher Hilsenhoff Biotic Index in Densu (5.06), compared with Anyanui (3.82), suggested greater organic pollution pressure in the Densu Estuary. CCME-WQI scores classified the Anyanui lagoon as marginal (47.14) and the Densu estuary as poor (38.69), indicating environmental conditions that may limit oyster growth, recruitment and long-term fishery productivity. Although both approaches provided complementary information, benthic macroinvertebrates offered a more integrative assessment of ecological condition than physicochemical measurements alone.
Conclusion: These findings demonstrate the value of integrating biological and physicochemical indicators for ecosystem assessment and provide a scientific basis for prioritising habitat restoration, long-term ecological monitoring and adaptive management to sustain Ghana's brackish-water oyster fisheries.
Keywords: Ecological integrity, biomonitoring, environmental status, indices, water quality