Disturbances drive changes in coral community assemblages and coral calcification capacity

Abstract

Anthropogenic environmental change has increased coral reef disturbance regimes in recent decades, altering the structure and function of many coral reefs globally. In this study, we used coral community survey data collected from 1996 to 2015 to evaluate reef-scale coral calcification capacity (CCC) dynamics with respect to recorded pulse disturbances for 121 reef sites in the Main Hawaiian Islands and Mo'orea (French Polynesia) in the Pacific and the Florida Keys Reef Tract and St. John (U.S. Virgin Islands) in the western Atlantic. CCC remained relatively high in the Main Hawaiian Islands in the absence of recorded widespread disturbances; declined and subsequently recovered in Mo'orea following a crown-ofthorns sea star outbreak, coral bleaching, and major cyclone; decreased and remained low following coral bleaching in the Florida Keys Reef Tract; and decreased following coral bleaching and disease in St. John. Individual coral taxa have variable calcification rates and susceptibility to disturbances because of their differing life-history strategies. As a result, temporal changes in CCC in this study were driven by shifts in both overall coral cover and coral community composition. Analysis of our results considering coral lifehistory strategies showed that weedy corals generally increased their contributions to CCC over time while the contribution of competitive corals decreased. Shifts in contributions by stress-tolerant and generalist corals to CCC were more variable across regions. The increasing frequency and intensity of disturbances under 21st century global change therefore has the potential to drive lower and more variable CCC because of the increasing dominance of weedy and some stress-tolerant corals.

Recovery disparity between coral cover and the physical functionality of reefs with impaired coral assemblages

“…Furthermore, we found greater changes over time in coral assemblages compared to those of trait assemblages due to the widespread dominance of non‐framework species and the stasis of reef framework corals in the region, which suggests that reef functions were already limited at the onset of our study. Our findings correspond to those obtained by other studies that have found that opportunistic coral species are increasingly dominating Caribbean reefs with no evidence of the functional recuperation of main reef‐builders (e.g., Alvarez‐Filip et al., 2013; Courtney et al., 2020; Green et al., 2008; McWilliam et al., 2020; Perry et al., 2015; Toth et al., 2019), suggesting that the decoupling between coral recovery and functional recovery that we report here might also be likely to occur in other reef areas in the Caribbean.…”

“…Consequently, future ecosystem functionality depends on which species successfully recover (Alvarez‐Filip et al., 2013; Cabral‐Tena et al., 2018; Perry & Alvarez‐Filip, 2019). Therefore, assessments of the trajectories that determine the physical functionality of reefs after a disturbance are particularly relevant given that there is little evidence that reefs recover to their initial functional states (Courtney et al., 2020; McWilliam et al., 2020).…”

Hurricane impacts on a coral reef soundscape

“…Ecosystems throughout the world are increasingly threatened by multiple natural and anthropogenic stressors, often leading to ecosystem shifts from desirable to less desirable states [ 1 – 4 ]. Coral reefs are the some of the most diverse ecosystems on Earth, and the transition between disturbance states is often observed through changes in coral reef community composition and ecosystem function [ 5 – 7 ]. The desired state is an environment that supports critical ecological processes and resulting patterns across space and time, such as overall system production, key predator-prey (or grazer) interactions, and reproduction across multiple functional groups [ 8 , 9 ].…”

Global coral reef ecosystems exhibit declining calcification and increasing primary productivity

“…Shifting community structure can also alter metabolic estimates 10,31 . In times of stress, fast-growing, habitatforming coral groups are replaced with weedy coral and algal species 27 .…”

“…Changing rates of G net and P net can indicate growth 9 , degradation [16][17][18] or phase shifting 16,19,20 . Higher rates of G net tend to indicate reefs with higher coral cover 9,21,22 , and ecosystems which have not been impacted by significant stressors [23][24][25][26] , whereas declining and net-dissolving calcification rates indicate stressed corals 16,18,27 or ecosystems which have little to no live corals 25,28 . Therefore, G net and P net are increasingly used as proxies for coral reef ecosystem health 10,29,30 .…”