Effects of depth on reef fish communities: Insights of a “deep refuge hypothesis” from Southwestern Atlantic reefs

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.

Small-Scale Coastal Fishing Shapes the Structure of Shallow Rocky Reef Fish in the Aegean Sea

“…As our underwater visual survey can only provide a snapshot in time, it is possible that the present depthrelated observations reflect a natural seasonal variation in the distribution of fish communities. Nevertheless, similar to Pereira et al (2018), our results also suggest that fishing pressure, along with other natural or anthropogenic disturbances, may be attenuated in deeper waters, hence providing some protection that allows the persistence of higher biomass levels.…”

“…diversity and abundance of fish species in coral reef ecosystems (e.g., Tyler et al, 2009;Pereira et al, 2018) and Mediterranean MPAs (Claudet et al, 2010). The main reasoning in support of the "deep reef refugia" hypothesis is that as depth increases, deeper parts of the reefs are less exposed to existing pressures (e.g., overfishing, pollution, temperature rise) than shallow reefs (Bongaerts et al, 2010).…”

“…Clusters represent 50% similarity; continuous line indicates the most discrete clustering. management schemes (Claudet et al, 2010;Lindfield et al, 2014;Pereira et al, 2018).…”

The Future of Reef Ecosystems in the Gulf of Mexico: Insights From Coupled Climate Model Simulations and Ancient Hot-House Reefs

“…The combination of thermal and chemical stress will make these environmental changes even more damaging (e.g., Donner et al, 2007Donner et al, , 2018Rodolfo-Metalpa et al, 2011;Prada et al, 2017;Bahr et al, 2018). Deeper water, mesophotic reefs have distinct communities and ecosystems when compared to shallow water reefs (e.g., Bongaerts et al, 2010;Pereira et al, 2018;Rocha et al, 2018) but are, nevertheless, likely to experience severe thermal stress (Schramek et al, 2018). Given the issues of accuracy and resolution in predicting aragonite values at 100 m depth shown in this work, it is hard to make confident conclusions about the fate of mesophotic reefs.…”

“…More importantly, the combination of heat and acidity stresses can often act synergistically (e.g., Rodolfo-Metalpa et al, 2011;Prada et al, 2017), meaning that even moderate heating and aragonite decreases can amplify each other leading to intolerable conditions for coral reefs. Furthermore, with surface oceans getting warmer and more acidic (low ) waters at depth, it is possible that surface-adapted reef communities in the GoM will have no suitable refuge by the end of the century (e.g., Pereira et al, 2018;Rocha et al, 2018).…”