Abstract
Deeper reefs are often considered to be less susceptible to local and global disturbances, such as overfishing, pollution and climate change, compared to shallow reefs and therefore could act as refugia for shallow water species. Hence, the interest on deeper reefs has happened at a time when shallow reefs are undergoing unprecedented changes. Here we investigated the hypothesis that fish community differed from shallow to deeper reefs due to factors apart from habitat structure and quality and therefore discuss for the first-time insights of a “deep refuge hypothesis” from Brazilian reefs. We collected data on fish community, benthic community and physiological conditions of two coral species on shallow (< 6 m) and deep reefs (> 25 m). No significant difference on substratum composition was observed comparing sites and depths. Additionally, physiological data on corals also showed similar oxidative status and growth conditions when comparing the two-coral species in shallow and deep reefs. Conversely, our study demonstrated strong differences on reef fish communities in terms of abundance, species richness, trophic groups, size classes and groups of interest when comparing shallow and deeper reefs. Fish abundance was 2-fold higher and species richness was up to 70% higher on deeper reefs. Also, a significant difference was observed comparing trophic groups of reef fish. Macrocarnivore, Mobile invertebrate feeders, Planktivores, Sessile Invertebrates Feeders and Roving Herbivores were more abundant on deeper reefs. On the other hand, Territorialist Herbivores almost exclusively dominated shallow reefs. Strong differences were also observed comparing the abundance of reef fish groups of interest and their respective size classes between shallow and deeper reefs. Ornamental, Great Herbivores and Groupers showed clear differences, with higher abundances being observed in deeper reefs. Considering size classes, larger individuals (> 15 cm) of Great Herbivores, Groupers and Snapper were uniquely recorded at deeper reefs. Additionally, individuals with > 30 cm were recorded almost exclusively on deeper reefs for all the analyzed groups of interest. Our findings suggest that fishing pressure on the target species may be attenuated on deeper reefs, and these regions may therefore be considered as areas of refuge from shallow water impacts. Therefore, the likely potential for deeper reefs protect species from natural or anthropogenic disturbances increases the attention of marine conservation planning and resource management on including deeper reefs in protected areas.
Highlights
Coral reefs are among the most diverse and productive ecosystems on earth [1, 2]
The present study aims to test the effects of depth on reef fish communities analyzing abundance, species richness, size classes, trophic guild and groups of interest
Our study demonstrated strong differences in reef fish communities in terms of abundance, species richness, trophic groups, size classes and groups of interest when comparing shallow and deep coral reefs communities from the South Atlantic Ocean
Summary
Coral reefs are among the most diverse and productive ecosystems on earth [1, 2]. They play important economic, ecological and social roles such as coastal protection, maintenance of ocean ecological processes and climate regulation [3, 4, 5]. Coral reefs are in intense decline due to several local and global disturbances such as climate change, overfishing, coral bleaching, predator outbreaks and biological invasion[2, 6, 7];) These disturbances can affect the structure and composition of corals and fish communities and key ecological processes, such as herbivory and recruitment, and the maintenance of ecosystem functioning It has been currently suggested that some coral species exhibit distinct and sometimes opposing physiological adaptations due to low light attenuation; [10, 15] It is still unclear if differences in depth could influence the ecophysiology of coral species (e.g. bleaching susceptibility) and few studies have attempted to understand this relationship so far Studies assessing the structure of coral reef communities have been strongly focused on shallow reefs and only in the last decades researches have endeavoured to explore deeper and mesophotic coral reefs on the South Atlantic Ocean [22, 23, 24, 25]
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