Global change differentially modulates coral physiology and suggests future shifts in Caribbean reef assemblages

Abstract

Global change driven by anthropogenic carbon emissions is altering ecosystems at unprecedented rates, especially coral reefs, whose symbiosis with algal endosymbionts ise particularly vulnerable to increasing ocean temperatures and altered carbonate chemistry. Here, we assess the physiological responses of the coral holobiont (animal host + algal symbiont) of three Caribbean coral species from two reef environments after exposure to simulated ocean warming (28, 31 °C), acidification (300 - 3290 μatm), and the combination of stressors for 93 days. We used multidimensional analyses to assess how multiple coral holobiont physiological parameters respond to ocean acidification and warming. Our results demonstrate significantly diminishing holobiont physiology in S. siderea and P. astreoides in response to projected ocean acidification, while future warming elicited severe declines in P. strigosa. Offshore S. siderea fragments exhibited higher physiological plasticity than inshore counterparts, suggesting that this offshore population has the capacity to modulate their physiology in response to changing conditions, but at a cost to the holobiont. Plasticity of P. strigosa and P. astreoides was not clearly different between natal reef environments, however, temperature evoked a greater plastic response in both species. Interestingly, while these species exhibit unique physiological responses to ocean acidification and warming, when data from all three species are modeled together, convergent stress responses to these conditions are observed, highlighting the overall sensitivities of tropical corals to these stressors. Our results demonstrate that while ocean warming is a severe acute stressor that will have dire consequences for coral reefs globally, chronic exposure to acidification may also impact coral physiology to a greater extent than previously assumed. The variety of responses to global change we observe across species will likely manifest in altered Caribbean reef assemblages in the future.

Physicochemical Control of Caribbean Coral Calcification Linked to Host and Symbiont Responses to Varying pCO2 and Temperature

“…Siderastrea siderea was found to maintain relatively unaltered symbiosis under experimental conditions, and relatively constant host energy reserves, consistent with its resilient calcification response [39]. Pseudodiploria strigosa did not maintain indicators of coral symbiont physiology under warming, such as chlorophyll content and symbiont cell density, and was the most bleached coral in the experiment [39]. Conversely, P. astreoides exhibited improved symbiont physiological indicators and chlorophyll content at 31 • C, which were reduced under the acidification conditions [39], although the 31 • C condition was characterized by lower survival rates [38].…”

“…Siderastrea siderea was the most resilient coral maintaining positive rates of net calcification under all conditions, even when seawater was undersaturated with respect to aragonite [38]. Siderastrea siderea was found to maintain relatively unaltered symbiosis under experimental conditions, and relatively constant host energy reserves, consistent with its resilient calcification response [39]. Pseudodiploria strigosa did not maintain indicators of coral symbiont physiology under warming, such as chlorophyll content and symbiont cell density, and was the most bleached coral in the experiment [39].…”

“…Here, we further explore the independent and combined effect of temperature and pCO 2 on coral and algal symbiont physiology in a study on four species of common Caribbean scleractinian corals Porites astreoides, Pseudodiploria strigosa, Undaria tenuifolia, and Siderastrea siderea (Figure 1). These corals were recovered from the Belize Mesoamerican Barrier Reef System, cultured at 28 • C and 31 • C, and at ~280 to 3300 µatm pCO 2 , and characterized for their structural and physiological responses to these conditions [38,39]. The coral species exhibited interspecific variations in host and symbiont responses to changing environmental conditions in the experiment, which allows us to investigate the link between host and symbiont physiology and the control of calcification and calcification fluid chemistry [38,39].…”

“…These corals were recovered from the Belize Mesoamerican Barrier Reef System, cultured at 28 • C and 31 • C, and at ~280 to 3300 µatm pCO 2 , and characterized for their structural and physiological responses to these conditions [38,39]. The coral species exhibited interspecific variations in host and symbiont responses to changing environmental conditions in the experiment, which allows us to investigate the link between host and symbiont physiology and the control of calcification and calcification fluid chemistry [38,39]. It was found that all four coral species exhibited nonlinear decreases in net calcification rate with increasing pCO 2 [38].…”

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

“…In addition to warming, ocean acidification represents a significant challenge to reef-building corals that can lead to reduced growth rates, dissolution of existing reef framework, and reduced holobiont physiology and metabolic rates (Anthony et al, 2008; Aichelman et al, 2021; Cornwall et al, 2021). While responses of corals under ocean acidification and warming can vary both within and across species (Bove et al, 2021), it is clear these global stressors represent immediate threats to the future of coral reefs.…”