Hawaii’s coral reefs have both suffered from and safely withstood the presence of people in the isles, according to a study that examines 700 years of human-reef interaction.

The findings indicate that while the reefs in the main Hawaiian Islands are up against the ropes, there still exists a chance of recovery if key, comprehensive steps are taken.

"If we look at historical ecosystem recoveries, reversing this decline will require protection of a broad range of habitat types over large areas, such as marine no-take reserves," said Stanford University researcher John Kittinger, lead author of the study and a former graduate fellow in the Department of Geography at the University of Hawaii at Manoa. "Additionally, appropriate institutions and policies will need to be in place to effectively engage the diverse community of ocean-users in Hawaii in collaborative marine ecosystem stewardship."

With researchers at the University of Hawaii, Stony Brook University in New York and elsewhere, Kittinger found that marine exploitation was highest soon after Polynesians arrived in the main Hawaiian Islands more than 700 years ago.

Within a century, however, Native Hawaiians had come to rely more on domesticated animals than reef fish for food, which allowed the coral to recover, thanks also in part to "conservation strategies" adopted by Hawaiian communities, the researchers say. The reefs also benefited from a reduction in subsistence fishing as the Hawaiian population sharply declined from diseases introduced after contact in 1778.

So there was a reef recovery period in the main Hawaiian Islands from 1400 to about 1820, the scientists say.

Due to overexploitation, land-based pollution and other factors, the degradation resumed in the mid-1800s and has continued since, except during World War II, when near-shore marine areas were off-limits as a defensive perimeter.

"Reefs in the Main Hawaiian Islands have been declining for more than 150 years, and similar degradation that has occurred in other reef ecosystems indicates that we may be approaching a tipping point or threshold, beyond which recovery is doubtful," Kittinger said in a release announcing the findings, which were published online Monday in the journal PLoS ONE.

In contrast, the reefs of the Northwestern Hawaiian Islands have fared much better since World War II, when there was a large military presence. Coral was dredged to build runways at Midway and French Frigate Shoals.

After the war, reefs in this region began to recover due to human depopulation in the area, conservation efforts and decreases in commercial activities involving the reefs. The area is now among the most diverse and abundant coral reef ecosystems in the world, and provides an example of how reefs that have recovered from human impacts can look, the researchers said.

"The substantial resilience and adaptive capacity of coral reefs demonstrated in this study provide reason for hope and suggest that we should not dismiss the possibility of bringing even the most degraded reefs back to health," said Ellen Pikitch, executive director of the Institute for Ocean Conservation Science at Stony Brook.

Co-authors of the study include Jonathan Blodgett, now with the Hawaii Division of Aquatic Resources; UH researchers Terry Hunt, Hong Jiang, Jennifer Schultz and Bruce Wilcox; and Kepa Maly of Kumu Pono Associates on Lanai.