Genetic and physiological traits conferring tolerance to ocean acidification in mesophotic corals

Abstract

The integrity of coral reefs worldwide is jeopardized by ocean acidification (OA). Most studies conducted so far have focused on the vulnerability to OA of corals inhabiting shallow reefs while nothing is currently known about the response of mesophotic scleractinian corals. In this study, we assessed the susceptibility to OA of corals, together with their algal partners, inhabiting a wide depth range. We exposed fragments of the depth generalist coral Stylophora pistillata collected from either 5 or 45 m to simulated future OA conditions, and assessed key molecular, physiological and photosynthetic processes influenced by the lowered pH. Our comparative analysis reveals that mesophotic and shallow S. pistillata corals are genetically distinct and possess different symbiont types. Under the exposure to acidification conditions, we observed a 50% drop of metabolic rate in shallow corals, whereas mesophotic corals were able to maintain unaltered metabolic rates. Overall, our gene expression and physiological analyses show that mesophotic corals possess a greater capacity to cope with the effects of OA compared to their shallow counterparts. Such capability stems from physiological characteristics (i.e., biomass and lipids energetics), a greater capacity to regulate cellular acid-base parameters, and a higher baseline expression of cell adhesion and extracellular matrix genes. Moreover, our gene expression analysis suggests that the enhanced symbiont photochemical efficiency under high pCO 2 levels could prevent acidosis of the host cells and it could support a greater translocation of photosynthates, increasing the energy pool available to the host. With this work, we provide new insights on the response to OA of corals living at mesophotic depths. Our investigation discloses key genetic and physiological traits underlying the potential for corals to cope with future OA conditions.

Soft coral reproductive phenology along a depth gradient: Can “going deeper” provide a viable refuge?

“…It would seem that coral planulae may be less successful in migrating from deeper habitats to shallow ones and establishing there, than the other way around (Prada & Hellberg, 2021; Rippe et al, 2021; Serrano et al, 2014; Shlesinger & Loya, 2021). Indeed, the current findings are consistent with several studies suggesting that population connectivity along depth may be relevant only for some depth‐generalist species but not for all, or not in all biogeographic regions (Bongaerts et al, 2017; Drury et al, 2020; Liberman et al, 2018; Rippe et al, 2021; Scucchia et al, 2021; Serrano et al, 2014; Shlesinger et al, 2018; Shlesinger & Loya, 2021). Taken together with our findings of reduced reproductive activity at mesophotic depth, it seems less likely that migrating into the deeper MCEs can provide corals with a long‐term viable refuge that will enable them to successfully replenish and sustain shallow‐water populations.…”

Energetics, but not development, is impacted in coral embryos exposed to ocean acidification

“…Such stimulation can enhance host fitness under acidification (Guillermic et al, 2021). In this study, the enrichment of terms related to coral oxidative stress under pH 7.6 (low; Table S5) suggests increased photosynthetic activity in the endosymbiotic algae due to the higher availability of CO2 in seawater, as observed in the endosymbionts of Stylophora pistillata primary polyps and adults (Scucchia et al, 2021a;Scucchia et al, 2021b). It has been hypothesized that at higher concentrations of CO2 the stimulation of symbiont photosynthesis could prevent acidosis of the host cells, thus helping with preserving cellular acid-base homeostasis (Gibbin et al, 2014), and ultimately alleviating the effects of OA on the host fitness, as observed here in planula developing at pH 7.3.…”

“…Genes involved in calcium ion binding like calreticulin provide structural and cell adhesion functions that aid in the biomineralization process (Mass et al, 2016) and may be upregulated to compensate for the chemical shift in carbon equilibrium in the seawater (Comeau et al, 2018;DeCarlo et al, 2018;Zhao et al, 2020). However, upregulation of these genes in response to OA may increase energetic demand, as observed in some adult (Davies et al, 2016;Vidal-Dupiol et al, 2013;Scucchia et al, 2021b). This increased demand could potentiate the rapid depletion of larval lipid stores if the energy derived from their endosymbionts is insufficient to keep up with demand (Alamaru et al, 2009;Ben-David-Zaslow and Benayahu, 2000;Harii et al, 2010), ultimately decreasing larval size.…”

Exposure to global change and microplastics elicits an immune response in an endangered coral

“…This pattern was accompanied by enrichment of terms associated with amino acid catabolism, suggesting A. cervicornis may have mediated physiological stress through protein catabolism (Davies et al, 2016; Aguilar et al, 2019; Rädecker et al, 2021). While we did not assess host or symbiont physiological traits along with these gene expression profiles, it is likely that the growth and/or energy reserves may have been impacted as a result of treatment conditions (Aichelman et al, 2021; Scucchia et al, 2021; Bove et al, 2022a).…”