Low human activity helps corals despite warm ocean

Published - August 12, 2023 09:15 pm IST

Simultaneously mitigating human impacts on land and sea reduced coral loss during an unprecedented marine heatwave in Hawaiʻi and supported coral reef persistence after the heatwave, according to a paper in Nature. The findings demonstrate the potential of combined management strategies to protect coral reefs.

Coral reef ecosystems are frequently impacted by human activity on land and in the sea; land-based disturbances include wastewater pollution, and sea-based disturbances include overfishing. Corals are especially impacted by prolonged periods of warm ocean temperatures, known as marine heatwaves, which can cause coral bleaching and death.

Jamison Gove from National Oceanic and Atmospheric Administration (NOAA), Honolulu, Hawai‘i and others combined surveys of reef change with a unique 20-year time series (2003-2019) of land-sea human impacts that encompassed an unprecedented marine heatwave in Hawai‘i in 2015, when ocean temperatures were 2.2 degree C higher than normal. The human impacts analysed included urban runoff, wastewater pollution and fishing restrictions. Throughout the study period coral reef cover increased in some areas, decreased or remained stable. Reefs with mitigated land- and sea-based human impacts showed increased coral cover before the heatwave and reduced coral loss during the heatwave. Additionally, reefs with more herbivorous fishes and exposure to fewer land-based human impacts had increased reef-builder cover — more of the types of coral essential to reef growth — four years after the disturbance compared with reefs with reduced fish populations and exposure to more land-based human impacts.

The authors modelled scenarios that suggested reducing land- and sea-based human impacts results in a three- to sixfold greater probability of a reef having high reef-builder cover four years after a disturbance. “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,” they write.

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