In this research, I explore the changes in the functional diversity of herbivorous fishes in zones of coral reefs with different benthic composition: a zone dominated by corals, a zone dominated by algae and a transition zone in between the previous two. I choose to use functional traits which explain the feeding mechanics of this group of fish, as well their feeding rates and their previously established functional groups to understand how different assemblages of this fishes could affect their environment in different ways. I found clear differences in the functional diversity by calculating five indexes, functional dispersion (FDis), functional richness (FRic), functional divergence (FDiv), functional evenness (FEve) and functional specialization (FSpe). Each zone showed different species composition with different abundances; both parameters contribute to obtaining different values of the indexes. The coral-dominated zone showed the biggest multidimensional functional trait space (MFTS) with a value of FRic equals to 1 which means that its assemblage occupies 100% of the MFTS, while the transition zone assemblage occupied 83% and the algae-dominated zone occupied 16% of it. Thanks to this index I identified three functionally redundant species in the coral-dominated and the transition zones. The algae-dominated zone showed the lower FDis explained by the high abundance of grazers individuals. FDiv did not vary significantly between the three zones. FEve was higher in the algae-dominated zone; the index value decreased in the transition and coral-dominated zones, a similar tendency was shown by FSpe. Finally, to explore the importance of including functional diversity I made a comparison between the taxonomic and functional β-diversity. This research showed close relations of herbivorous fishes with their environment, but I could not establish if the benthic composition shapes the herbivorous fish assemblage or the other way around. This research can be a baseline to start working in functional diversity in the Red Sea coral reefs, can help to understand what to expect in the evaluation of reefs in different health state and to identify which herbivorous fish species or groups are more vulnerable and more important according to their function for coral reefs.

Worldwide, coral reefs are recognized as highly valuable ecosystems offering numerous environmental and economic services. In Saudi Arabia, the primary ecosystem service derived from coral reefs is the support of reef-based fisheries, accounting for ~75% of total fisheries landing in the kingdom. Saudi Arabian reefs experienced high fishing pressure for decades due to the growing population and associated fishing pressure. Despite the importance of the provisioning service there are limited ecosystem services valuations for this region. In the wake of a 2015 mass bleaching event, we quantified the effect of habitat degradation on the potential fisheries revenue in the central southern Red Sea. We conducted in situ reef fish surveys in 2014 and 2015 before the bleaching event and in 2019, nearly four years after the bleaching event. Using species-specific prices collected from local fish markets, we calculated values per hectare from multiple reefs in this region, to assess how the reef-based fishery was impacted by the bleaching event. A loss in live hard and soft coral cover was recorded after the bleaching event with associated shifts in the dominance of commercially important fish species. Notably, prior to bleaching, a larger proportion of the high value carnivorous species (70% carnivores, 25% herbivores) dominated the fish assemblage whereas post-bleaching reefs had a higher dominance of lower-valued herbivorous species (25% carnivores, 50% herbivores). While the total revenue was not significantly different before (7,913 USD/hectare) to after the bleaching event (6,814 USD/hectare), the loss of high value species observed suggests that if reefs continue to degrade there are potential negative flow-on effects impacting fisheries provisioning with time. Overall, an increasing percentage of live hard coral cover was positively correlated with fisheries revenue per reef, further providing evidence for the potential loss of revenue in degraded reef ecosystems in the region.