The influence of several substratum variables, particularly structural complexity and Live coral cover, on coral reef fish species richness and abundance was investigated. By surveying fish species with varying strengths of association with the substratum and at different sampling scales, this study aims to assess the scale-dependence of correlations between substratum characteristics and fish comn~unity parameters. Fish from 5 families (Acanthuridae, Chaetodonhdae, Labridae, Pomacentridae and Scaridae) were counted along transects by visual census. Substratum charactenstics were measured from stereophotographic transects. Three measures of structural complexity were used: (1) an index of surface area, (2) the vanety of different substrata (biological diversity), and (3) numbers of holes (of hfferent sizes). Although the depth of peak specles richness varied between families, overall there was a trend of increasing species richness with increasing depth. Surface index was a poor predictor of overall species richness but was significantly correlated with pomacentrid species richness and abundance on 200 m transects. In contrast, biological diversity of the substratum (H') was highly correlated with overall fish species nchness. Numbers of holes of 3 sizes taken together accounted for 77 O/ O of the variance in overall fish abundance on the 200 m transects. None of the measures of structural complexity were significantly correlated with species nchness or abundance of small, strongly siteattached fish. Live coral cover was not significantly correlated w t h species richness or abundance of fish from any family (except for a weak correlation w~t h abundance of obligate corallivorous chaetodontids).

The global decline of coral reefs heightens the need to understand how corals respond to changing environmental conditions. Corals are metaorganisms, so-called holobionts, and restructuring of the associated bacterial community has been suggested as a means of holobiont adaptation. However, the potential for restructuring of bacterial communities across coral species in different environments has not been systematically investigated. Here we show that bacterial community structure responds in a coral host-specific manner upon cross-transplantation between reef sites with differing levels of anthropogenic impact. The coral Acropora hemprichii harbors a highly flexible microbiome that differs between each level of anthropogenic impact to which the corals had been transplanted. In contrast, the microbiome of the coral Pocillopora verrucosa remains remarkably stable. Interestingly, upon cross-transplantation to unaffected sites, we find that microbiomes become indistinguishable from back-transplanted controls, suggesting the ability of microbiomes to recover. It remains unclear whether differences to associate with bacteria flexibly reflects different holobiont adaptation mechanisms to respond to environmental change.

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Coral-associated bacteria play an increasingly recognized part in coral health. We investigated the effect of local anthropogenic impacts on coral microbial communities on reefs near Jeddah, the largest city on the Saudi Arabian coast of the central Red Sea. We analyzed the bacterial community structure of water and corals (Pocillopora verrucosa and Acropora hemprichii) at sites that were relatively unimpacted, exposed to sedimentation & local sewage, or in the discharge area of municipal wastewaters. Coral microbial communities were significantly different at impacted sites: in both corals the main symbiotic taxon decreased in abundance. In contrast, opportunistic bacterial families, such as e.g. Vibrionaceae and Rhodobacteraceae, were more abundant in corals at impacted sites. In conclusion, microbial community response revealed a measurable footprint of anthropogenic impacts to coral ecosystems close to Jeddah, even though the corals appeared visually healthy.