Multiple stressor effects on coral reef ecosystems

Abstract

The first two authors listed are primarily responsible for the conceptual and statistical framework for the paper. The contributing authors are listed in alphabetical order. The last two, also in alphabetical order, are the senior authors responsible for the ecological survey and physical modeling component of the effort, respectively. AbstractGlobal climate change has profound implications on species distributions and ecosystem functioning. In the coastal zone, ecological responses may be driven by various biogeochemical and physical environmental factors. Synergistic interactions can occur when the combined effects of stressors exceed their individual effects. The Red Sea, characterized by strong gradients in temperature, salinity, and nutrients along the latitudinal axis provides a unique opportunity to study ecological responses over a range of these environmental variables. Using multiple linear regression models integrating in situ, satellite and oceanographic data, we investigated the response of coral reef taxa to local stressors and recent climate variability. Taxa and functional groups responded to a combination of climate (temperature, salinity, air-sea heat fluxes, irradiance, wind speed), fishing pressure and biogeochemical (chlorophyll a and nutrients -phosphate, nitrate, nitrite) factors. The regression model for each species showed interactive effects of climate, fishing pressure and nutrient variables. The nature of the effects (antagonistic or synergistic) was dependent on the species and stressor pair. Variables consistently associated with the highest number of synergistic interactions included heat flux terms, temperature, and wind speed followed by fishing pressure. Hard corals and coralline algae abundance were sensitive to changing environmental conditions where synergistic interactions decreased their percentage cover. These synergistic interactions suggest that the negative effects of fishing pressure and eutrophication may exacerbate the impact of climate change on corals. A high number of interactions were also recorded for algae, however for this group, synergistic interactions increased algal abundance. This study is unique in applying regression analysis to multiple environmental variables simultaneously to understand stressor interactions in the field. The observed responses have important implications for understanding climate change impacts on marine ecosystems and whether managing local stressors, such as nutrient enrichment and fishing activities, may help mitigate global drivers of change. K E Y W O R D S coral reefs, fishing pressure, macroalgae, nutrients, synergistic interactions, temperature stress

Local Human Impacts Disrupt Relationships Between Benthic Reef Assemblages and Environmental Predictors

“…Island relief was also identified as being a strong predictor of benthic community structure (despite being found to be a weak predictor on central-western Pacific reefs − Robinson et al, 2018), and interestingly this role was maintained regardless of local human impact level. Importantly, when considering latitude-collinear with DHW/cumulative thermal stress-as an individual predictor, our results neither contradict nor confirm previous observations that local impacts exacerbate the sensitivity of coral communities to thermal stress (Wiedenmann et al, 2013;Ellis et al, 2019), instead highlighting a large variance among sites.…”

Towards an End-to-End Analysis and Prediction System for Weather, Climate, and Marine Applications in the Red Sea

“…Satellite-derived estimates of phytoplankton size structure are in good agreement with the in situ measurements, and also capture the spatial variability related to regional mesoscale dynamics (Gittings et al 2019b). iReds outputs were also used along with in situ and satellite observations to investigate the basin ecological responses to the combined effects of biogeochemical and physical environmental stressors (Ellis et al, 2019).…”

Coral bleaching patterns are the outcome of complex biological and environmental networking

“…Importantly, all environmental factors noted above have been documented to influence the severity with which heat stress‐induced bleaching occurs, when and where—such that we now have an exceptionally complex environmental network where in effect, “all roads can lead to [some form of] coral bleaching” (Figure ). Interactions among environmental factors regulating coral metabolism operate in several key ways to determine how the “winners and losers” are observed at the ecosystem scale (e.g., Ban et al, ; Carilli, Norris, Black, Walsh, & McField, ; Ellis et al, in press), yet we are still far from a complete understanding of this network.…”

“…This is likely also true for the regulatory factors, notably oxygen availability, where eutrophication events that drive hypoxia are occurring against the backdrop of ocean warming‐driven deoxygenation (e.g., Altieri et al, ). Consequently, while environmental models describing reef trajectories are becoming increasingly sophisticated (e.g., Baird et al, ; Ellis et al, in press; Kumagai, Yamano, & Committee Sango‐Map‐Project, ; Wolff et al, ), we now need to urgently develop these to account for how net bleaching outcomes reflect dose dependencies within the entire environmental network (Figure ), and in turn the affect the inherent underlying metabolic network(s) (Figure ). This is no small task but central to guiding more informed management decisions and interventions based on what will bleach, where and when.…”

“…However, in doing so, management (re‐) prioritization must be careful that efforts to minimize exposure to one stressor does not increase exposure to another (see Bruno et al, ), returning us a central issue: how can MPA (re‐) planning be effectively achieved without understanding the complex environmental network that governs bleaching susceptibility? Realizing such a goal clearly rests on rapidly improving capacity to monitor reef environment condition, but also applying these data to more advanced network models that can track how changing reef environments (Figure ; see also, Ellis et al, in press) trigger alternate metabolic cascades and hence bleaching outcomes (Figure ; Baird et al, ; Kumagai, Yamano, & Committee Sango‐Map‐Project, ).…”