The study published the journal Nature, which is based on 20 years of data from the US island of Hawaii, says that combining local efforts to limit the impact of humans on both the land and sea give coral reefs a greater chance at bouncing back. [1]

"We found that both land-based (for example wastewater pollution) and sea-based human impacts (for example fishing) must be reduced together to ensure coral reef persistence," the study’s co-lead author Gareth Williams, a marine ecologist at the UK’s Bangor University, told AFP. The release came just days after it was revealed that the temperature of the world’s oceans rose to their hottest level ever recorded on July 30.

Using high-resolution data and thousands of hours of underwater surveys, the researchers looked at connections between human impacts and the recovery of the reef. They found that not all coral reefs suffer equally during heatwaves.

In 18 percent of the reefs surveyed during an unprecedented marine heatwave in Hawaii in 2015, coral cover remained unchanged — and in some cases, increased — despite the heat.

Their ability to recover was dependent on how strained they were by various human pollutants and how many algae-eating fish were around to pave the way for regrowth, the study said. The more negative impacts that were remedied, the better the reefs recovered, offering a potential path ahead for conservation efforts.

Action is required on all fronts

The researchers carried out modelling which indicated that simultaneously reducing these problems on land and sea gave reefs an up to six times higher chance of regrowing after a heatwave than if the efforts were carried out separately.

"Resource managers have aspired to manage land and sea together, but because governance tends to be centralised, most terrestrial- and ocean-management efforts remain siloed," said the study’s co-lead author Jamison Grove of the US National Oceanic and Atmospheric Administration.

But the researchers warned that the frequency and severity of coral bleaching as ocean temperatures rise due to human-caused climate change could "simply overwhelm the positive effects of local management actions".

According to the IPCC, since 1982, marine heat waves have been twice as frequent as befor. And by 2100, they could be 10 times more intense if greenhouse gas emissions are not drastically reduced.