Abstract
Corals from the Gulf of Aqaba (northern Red Sea) are resilient to high temperatures and therefore this region is regarded as globally important for reef conservation. However, long-term dynamics of coral reef assemblages from the Gulf of Aqaba remain largely understudied. In this study, we analysed the change in benthic, fish and invertebrate assemblages of reefs around Dahab (South Sinai, Egypt) between 2009 and 2019. We also studied the individual trajectories of coral reef benthic categories, key invertebrate and fish species and their relationship. As site emerged as the main factor explaining the variability in coral reef communities, we identified three clusters of sites with similar assemblages. Both benthic, fish and invertebrate assemblages changed considerably at the three site clusters between 2009 and 2019. We found significant increases in fleshy macroalgae (~ 6 to 15%) and cyanobacterial mats (~ 6 to 12%) in all site clusters. Although not observing a significant reduction of hard coral cover, both macroalgae mat cover and cyanobacterial mat cover were significantly negatively related to hard coral cover and hard coral disease. Soft coral cover (mainly corals from the Xeniidae family) decreased significantly in two of the site clusters, their cover being negatively related to macroalgal and cyanobacterial cover. Significant declines in grazer urchins were observed at all site clusters, and a strong negative relationship was found with macroalgae and cyanobacterial mats cover, suggesting urchin decline as one of the main drivers behind algal increases. Different site clusters had different fish trajectories (butterflyfish, parrotfish, surgeonfish and predators), with only damselfish densities significantly decreasing at all sites. A significant decrease in damselfish densities was related to increases in cyanobacterial mats. These findings suggest that if macroalgae and cyanobacteria continue to increase, Dahab coral reefs could undergo degradation, and therefore, more studies are needed to elucidate the drivers behind these algal increases.
Highlights
Coral reefs, which harbour 25% of the marine biodiversity and provide ecosystem services to over 500 million people, are suffering severe degradation due to the combined effects of anthropogenic perturbations and global climate change (Hughes et al 2017; Lamb et al 2018)
We explored the relationships between different organisms to explore the following hypotheses: (1) whether macroalgae and cyanobacterial mats affect hard and soft coral cover and the abundance of hard coral diseases and (2) if top-down control is related to changes in fleshy macroalgae and cyanobacterial mats cover
We found that benthic assemblages in coral reefs around Dahab in the Gulf of Aqaba changed considerably a b
Summary
Coral reefs, which harbour 25% of the marine biodiversity and provide ecosystem services to over 500 million people, are suffering severe degradation due to the combined effects of anthropogenic perturbations and global climate change (Hughes et al 2017; Lamb et al 2018) Anthropogenic disturbances such as overfishing, coastal development and pollution, together with increasing climate. Despite the northern Red Sea displaying the highest rates of warming throughout the Red Sea (Chaidez et al 2017), including more severe thermal anomalies (Osman et al 2018), this region has not experienced massive coral bleaching events Due to this high coral heat tolerance, the northern Red Sea has been proposed as a coral refuge of global importance, as this region may host a gene pool of heat-resistant scleractinian corals that could be extremely useful for reef restoration efforts around the world (Fine et al 2013). Given the key importance of the Gulf of Aqaba region at a global scale, long-term studies are needed to investigate the dynamics and state of its coral reef assemblages and evaluate the full implications of the previously reported algal increases, in order to establish adequate conservation measures
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