The poor conditions of Hawaii’s nearshore reefs, covered in algae and bereft of fish, are well known.

Now we are learning more about the scope of the problem. A new mapping survey of nearly all the nearshore coral reefs of the main Hawaiian islands revealed with greater clarity than ever before the extent of the damage. The results are scary, but also hopeful.

Researchers spent some 30 days flying over Hawaii’s coasts, using laser-guided imaging spectroscopy to find live coral at up to 50 feet.

This airborne mapping, combined with other data, aims to fill a research gap: “geographically consistent and actionable high-resolution information on the specific location and extent of live coral” that can help guide decisions by policymakers, according to a paper published this week in the Proceedings of the National Academy of Sciences of the United States of America.

And decisions will need to be made.

“I had no sense of the vast amount of coral we have already lost and how degraded a lot of areas are,” said Greg Asner, lead author of the study. “It was eyeopening — like getting cold water splashed in your face.”

On Oahu, only 12% of its ocean substrate is covered by live coral, the lowest in the state. Asner said that while Oahu has plenty of space for coral to grow, “it is almost all covered with algae.”

Human activity bears much of the blame. Pollution and runoff from development, algae hitchhiking on oceangoing ships, and overfishing, which depletes the number of herbivorous fish that control algae growth, all contribute to the problem.

Now the hopeful news: First, there still are healthy reefs of the Hawaiian islands, mainly in places with little human interaction. Second, while much of the reefs are degraded, they are not past hope of recovery; and third, we now know, in unprecedented detail, what the situation looks like.

All this behooves state officials to place renewed emphasis on protecting our reefs, including periodic moratoriums on fishing and strictly controlling — and pushing back — shoreline development.

Gov. David Ige wants at least 30% of Hawaii’s nearshore marine region to be managed by 2030, a vast improvement from the current 6%. Still, if global warming continues, along with our natural tendency to exploit coastal resources — whether for fishing or developing properties along beaches — 30% may prove conservative.

The coral reefs aren’t just pretty; they protect our homes from storm surges and support a multitude of marine life, not to mention tourism (note the newly rejuvenated Hanauma Bay). They’re a vital component of Hawaii’s natural, economic and social health.