Local Persistence of Large Benthic Foraminifera (LBF) under Increasing Urban Development: A Case Study from Zanzibar (Unguja), East Africa

• Published in: Journal of earth science (Wuhan, China) Vol. 33; no. 6; pp. 1434 - 1450
• Main Authors: Narayan, Gita R., Herrán, Natalia, Reymond, Claire E., Shaghude, Yohanna W., Westphal, Hildegard
• Format: Journal Article
• Language: English
• Published: Wuhan China University of Geosciences 01.12.2022; Springer Nature B.V; School of Geosciences,The University of Sydney,Sydney NSW 2006,Australia%Institute of Marine Sciences(IMS),The University of Dar es Salaam,Zanzibar,Tanzania%Leibniz Centre for Tropical Marine Research(ZMT),Bremen,Germany; Department of Geosciences,Bremen University,Bremen,Germany; King Abdullah University of Science and Technology(KAUST),Thuwal,Kingdom of Saudi Arabia; Leibniz Institute for Baltic Sea Research(IOW),18119 Rostock,Germany%School of Earth Sciences,China University of Geosciences,Wuhan 430074,China; Leibniz Centre for Tropical Marine Research(ZMT),Bremen,Germany%Leibniz Centre for Tropical Marine Research(ZMT),Bremen,Germany
• Subjects: Benthos; Biogeosciences; Bioindicators; Carbonates; Coastal ecosystems; Coastal management; Coral reefs; Earth and Environmental Science; Earth Sciences; Ecosystems; Environmental degradation; Foraminifera; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; Indicator species; Marine ecosystems; Marine invertebrates; Phosphates; Quality assessment; Regular Article; Sewage; Sewage effluents; Species diversity; Strategic management; Sustainability; Urban development; Urbanization; Water quality; Water quality assessments; Zanzibar; East Africa; bioindicator; Western Indian Ocean; coral reef; carbonate; FoRAM Index; sewage effluent; nutrients; coastal development; coastal marine management
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-022-1702-5

Coastal marine management is vital for socio-ecological sustainability of developing, tropical ecosystems, which calls for diverse tools to monitor and assess water quality. The carbonate-dominated habitats off Zanzibar were chosen for study due to potential water quality degradation in a rapidly developing tourist destination heavily reliant on its coral reefs. These reefs are largely unmonitored and subject to local and global stressors. A widely used method for assessing reef health, as an early detection method of ecological changes, is the application of large benthic foraminiferal bioindicators, i.e., the FoRAM Index. We expected to find poor water quality conditions in the unmanaged reefs supported by stress-toelerant (opportunistic) foraminiferal assemblages. The dissolved inorganic nitrogen and phosphate values derived from untreated sewage effluent from Stone Town were highly variable (ranging 0.05–3.77 and 0.05–1.45 µM, respectively), moderate, and occasionally approached or exceeded critical threshold values for oligotrophic ecosystems. The analysis of total assemblages indicated an abundance of symbiont-bearing large benthic foraminifera, dominated by prolific Amphistegina species, comparatively low-moderate diversity, high FI values (7.6 on average), and high coral cover. A water quality gradient was reflected by subtle assemblage differences, suggesting that LBF can provide early warning signals of benthic changes, indicating the importance of long-term monitoring programs in vulnerable, rapidly developing coastal ecosystems exposed to increasing pressures.