Diversity of Coral Reef Fishes in the Western Indian Ocean: Implications for Conservation

Abstract

Communities of coral reef fishes are changing due to global warming and overfishing. To understand these changes and inform conservation, knowledge of species diversity and distributions is needed. The western Indian Ocean (WIO) contains the second highest coral reef biodiversity hotspot globally, yet a detailed analysis of the diversity of coral reef fishes is lacking. This study developed a timed visual census method and recorded 356 species from 19 families across four countries in the WIO to examine patterns in species diversity. Species richness and composition differed most between the island countries of Madagascar and Comoros and both these locations differed from locations in Tanzania and Mozambique which were similar. These three regional groupings helped define WIO ecoregions for conservation planning. The highest species richness was found in Tanzania and Mozambique, and the lowest and most different species composition was found in Comoros. Biogeography explains these differences with naturally lower species diversity expected from the small, oceanic, and isolated islands of Comoros. Present day ocean currents maintain these diversity patterns and help explain the species composition in northeast Madagascar. Species distributions were driven by 46 of the 356 species; these provide guidance on important species for ongoing monitoring. The results provide a benchmark for testing future changes in reef fish species richness.

Distribution Pattern of Coral Reef Fishes in China

“…With more than 1700 species distributed across 200 genera, it is a major part of the diversity of coral reef ecosystems [56]. However, in a study by foreign scholars [3,57,58], Labridae was the family with the largest number of species. In fact, the Labridae family is also rich in the number of species in China's coral reef, second only to the number of Gobiidae.…”

“…However, the coral reefs of Taiwan, Hainan Island, Dongsha, Nansha, Xisha, and Zhongsha Islands in the South China Sea are barrier reefs or atolls [35]. Offshore fishes mostly live in environments of high temperature and salt and are affected by the diffusion of ocean currents [3,35,64]; therefore, they have similar and high coral reef fish species diversity, and all belong to offshore coral reef fishes.…”

“…Coral reefs provide living areas for many marine organisms and, to a large extent, affect the physical and ecological conditions of the surrounding environment [2]. However, in recent years, coral reef ecosystems have faced land pollution, destructive fishing, overexploitation, climate change pressure, and other factors, and 19% of coral reefs have disappeared globally [3][4][5]. Owing to various forms of water pollution, such as sewage and industrial and aquaculture wastewater, the coral coverage rate continues to decline, affecting the long-term stability of the coral reef system [6][7][8].…”

“…Since the 1980s, 80% of coral reefs around mainland China and Hainan Island have been destroyed by human activity [7]. In particular, destructive fishing has affected the stability of the ecological environment of coral reefs, and habitats that many species depend on for survival have been destroyed [3,9,10]. These incidents also directly or indirectly have an important impact on coral reef ecosystems, biological diversity, indigenous coastal residents, and fishery economies [11].…”

Local heterogeneity of coral reef diversity and environmental stress provides opportunities for small‐scale conservation

“…Studies of fish communities find biogeographic variation within and between regions (McClanahan, 2015, 2019; Samoilys et al, 2019, 2022). These studies indicate the importance of biomass, habitat, isolation and other local environmental conditions in influencing community and diversity patterns.…”