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Marine invertebrates have the greatest abundance and biomass of animals in the Earth system. As a result, they exert a major influence on the structure and function of marine ecosystems through food-web interactions and as ecosystem engineers. Marine invertebrates are also important in terms of the ecosystem services they provide to humankind. In this chapter we review Red List assessments for marine invertebrates, summarise the levels of extinction threat within this group of animals and examine the drivers of decline in affected species. Our findings suggest that only a small fraction of marine invertebrate species have been assessed for extinction threat and even within ‘well’-assessed groups a large proportion of species are categorised as Data Deficient. We find that the proportion of species threatened with extinction can be extremely high (33% in reef-forming corals), with lower levels found for other, less comprehensively assessed groups. The main drivers of extinction risk include habitat loss or degradation through coastal development, pollution or other human activities, overexploitation of species for fisheries, or other purposes, and climate change. Approaches to improve the conservation of marine invertebrates are discussed.
Benthic habitat composition is a key factor that structures assemblages of coral reef fishes. However, natural and anthropogenic induced disturbances impact this relationship. This study investigates the link between benthic habitat composition and fish functional groups in four countries in the Western Indian Ocean (WIO). Benthic composition of 32 sites was quantified visually from percentage cover of hard and soft corals, rubble, turf, fleshy and crustose coralline algae. At each site, abundance of 12 coral-associated fish functional groups in 50 × 5 m transects was determined. Cluster analysis characterized reefs based on benthic cover and revealed five habitat types (A, B, C, D and E) typified by decreasing cover of hard corals, increasing cover of turf and/or fleshy algae and differences in benthic diversity. Habitat type A was present in all four countries. Other habitats types showed geographic affiliations: notably Comoros sites clustered in either habitats B or E, northern Madagascar had B, C and D type habitats, whereas sites in central Tanzania and northern Mozambique had habitats D and E. Fish functional groups showed significant linkages with some habitat types. The abundances of corallivores, invertivores, detritivores and grazers were higher in habitat B, whereas planktivores and small excavators showed lower abundances in the same habitat. These linkages between benthic habitat types and fish functional groups are important in informing priority reefs that require conservation and management planning.