Coral reefs benefit from reduced land–sea impacts under ocean warming

Abstract

Coral reef ecosystems are being fundamentally restructured by local human impacts and climate-driven marine heatwaves that trigger mass coral bleaching and mortality1. Reducing local impacts can increase reef resistance to and recovery from bleaching2. However, resource managers lack clear advice on targeted actions that best support coral reefs under climate change3 and sector-based governance means most land- and sea-based management efforts remain siloed4. Here we combine surveys of reef change with a unique 20-year time series of land–sea human impacts that encompassed an unprecedented marine heatwave in Hawai‘i. Reefs with increased herbivorous fish populations and reduced land-based impacts, such as wastewater pollution and urban runoff, had positive coral cover trajectories predisturbance. These reefs also experienced a modest reduction in coral mortality following severe heat stress compared to reefs with reduced fish populations and enhanced land-based impacts. Scenario modelling indicated that simultaneously reducing land–sea human impacts results in a three- to sixfold greater probability of a reef having high reef-builder cover four years postdisturbance than if either occurred in isolation. International efforts to protect 30% of Earth’s land and ocean ecosystems by 2030 are underway5. Our results reveal that integrated land–sea management could help achieve coastal ocean conservation goals and provide coral reefs with the best opportunity to persist in our changing climate.

Evidence for managing herbivores for reef resilience

“…Efforts focused on land-based pollution are thus all worthwhile endeavors; however, the mixed results for the direction of the effects of land-based pollution on benthic condition and the relatively stronger effects of herbivores on benthic condition also underscores the complexity of land-sea linkages [48]. It is likely necessary to consider where land and sea impacts are overlapping, and understand the tradeoffs and potential benefits associated with coordinated actions on land and at sea [49], especially in a changing climate [50].…”

Evidence for managing herbivores for reef resilience

“…Efforts focused on land-based pollution are thus all worthwhile endeavours; however, the mixed results for the direction of the effects of land-based pollution on benthic condition and the relatively stronger effects of herbivores on benthic condition also underscores the complexity of land-sea linkages [ 48 ]. It is probably necessary to consider where land and sea impacts are overlapping, and understand the trade-offs and potential benefits associated with coordinated actions on land and at sea [ 49 ], especially in a changing climate [ 50 ].…”

Mapping Water Quality in Nearshore Reef Environments Using Airborne Imaging Spectroscopy

“…Accelerating pressure on coastal ecosystems from the combined influence of climate change and land-based pollution means there is a growing need for large-scale monitoring of coastal water quality to inform management strategies aimed at protecting and restoring coral reefs [4]. Corals are highly sensitive to water quality because differences in light availability, nutrient levels, organic matter, sedimentation regimes, and contaminant loads impair coral function and decrease coral resilience to heat stress [5][6][7]. Large-scale monitoring to detect water quality impairments on reefs and to characterize their magnitude, severity, and frequency will help guide reef restoration and pollution mitigation [8][9][10].…”