Ecological insights from environmental disturbances in mesophotic coral ecosystems

Abstract

Mesophotic coral ecosystems (MCEs) have historically been considered more stable than shallow reefs and thus suggested to provide refuge to coral reef communities against natural and anthropogenic impacts. Despite this assumption, a growing body of literature has shown that deep reefs are not immune to natural disturbance. Here, based on our in situ observations, we propose that disturbance may actually represent an important mechanism for maintaining biodiversity in MCEs, as is the case for shallow reefs. Our observations suggest that disturbances can provide microhabitat and space necessary for the recruitment and occurrence of different species, increasing overall diversity. Since bioerosion rates are lower at depth, and most well‐developed coral reefs on MCEs are formed by dense aggregations of a single or a few species, intermediate levels of disturbance could represent a critical driver of community structure balancing. Therefore, instead of long‐term stability, intermediate disturbances should be expected on MCEs. However, high frequency and intensity of natural disturbances, or their association with anthropogenic stressors, might have stronger negative impacts on MCEs than on shallower reefs due to slower coral growth and calcification rates.

Coral Morphology Portrays the Spatial Distribution and Population Size-Structure Along a 5–100 m Depth Gradient

“…Such phenomena suggest that the mesophotic reefs of Eilat may have a potential role as a stable and sheltered environment for scleractinian corals, since corals can reach greater sizes there. However, these conclusions should be approached with caution, since there is evidence that the mesophotic reefs too may not always escape climate-induced disturbances (Eyal et al, 2019;Pinheiro et al, 2019). Indeed, since the mesophotic reefs comprise mostly slow-growing coral growth forms (e.g., encrusting), they are expected to require longer recovery periods after major disturbances, although they are generally considered more robust to physical and thermal stress (Torda et al, 2018).…”

“…Mesophotic corals impacted by tropical storms can be smothered beneath sediment and suffer physical damage, as well as impacted by extreme heatwaves that lead to coral bleaching. Since depth is a well-known factor affecting coral growth, it is expected that the recovery rate from disturbances may differ along a depth gradient (Rocha et al, 2018;Pinheiro et al, 2019). With increasing depth, coral individuals exhibit a decline in their linear extension and calcification rate, due to decreasing levels of photosynthetically-active radiation (Pratchett et al, 2015).…”

“…With increasing depth, coral individuals exhibit a decline in their linear extension and calcification rate, due to decreasing levels of photosynthetically-active radiation (Pratchett et al, 2015). Subsequently, stronger negative impacts on MCEs could affect the restoration of their population structures due to slower growth rates (Pinheiro et al, 2019).…”

Light-harvesting in mesophotic corals is powered by a spatially efficient photosymbiotic system between coral host and microalgae

“…CC-BY-NC-ND 4.0 International license perpetuity. It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted December 6, 2020. ; https://doi.org/10.1101/2020.12.04.411496 doi: bioRxiv preprint water reefs can experience impacts from extreme storms and heatwaves, although not at the same frequency or intensity as in the shallow environments [21][22][23].…”

A New Species of Chromis (Teleostei: Pomacentridae) from Mesophotic Coral Ecosystems of Rapa Nui (Easter Island) and Salas y Gómez, Chile

“…Recent studies of MCEs have revealed a dynamic ecology that is prone to shifts in species composition and varied levels of natural disturbances (Rocha et al, 2018;Shepherd et al, 2018b;Pinheiro et al, 2019b). The new species described here, along with two additional recently described species, adds to the high diversity and uniqueness of the fish fauna of Rapa Nui (Shepherd et al, 2018a(Shepherd et al, , 2019.…”