“We saw on several reefs that a significant amount of corals were broken, rolled around on the bottom and killed, or just smashed up to the point that the actual structure of the reef itself was reduced to rubble,” said Craig Dahlgren, lead researcher at the Perry Institute, which has been examining effects of the hurricane since October.

Reef structures the size of small cars were dislodged or buried in debris, mud and sediment several feet deep in some instances, Dr. Dahlgren said.

Reef diving and snorkeling are an important part of the of the country’s tourism industry, which accounts for some 50 percent of G.D.P.

Even before Hurricane Dorian, the reefs were in jeopardy. In 2016, the Perry Institute, based in Waitsfield, Vt., found reefs in the Bahamas to be under stress and classified them as impaired, the category just above poor.

Healthy reefs are vital to marine ecosystems in the area, and the storm damage appears to have hit the country’s fisheries, as well. Dr. Dahlgren’s team reported a significant decline in fish populations linked to habitat damage.

In addition to extremely turbulent waters, Dorian brought a surge of rainwater that changed sea salinity. The storm also caused water temperatures to fluctuate rapidly — both conditions that quite likely shocked the corals, according to researchers.

But the report’s news was not all bad. “We did see some areas that came out of it looking almost untouched, amazingly,” Dr. Dahlgren said. “The patterns of damage that we saw were not consistent. You could have reefs that were a few miles apart. One would be totally destroyed and the other, you couldn’t even tell a hurricane was there.”

Some of the fragmented corals could be regrown in nurseries and then reattached to dead pieces to replenish them. But that would take time, as some species take many years to grow.

Researchers from the Perry Institute have studied reefs in the Bahamas for years. When Dorian hit, they were in position to assess the damage quickly even though boats and scientific equipment were also damaged in the storm.

“This study speaks strongly to the importance of long-term monitoring,” said Kim Cobb, a professor at Georgia Institute of Technology’s School of Earth and Atmospheric Sciences who was not involved in the research. Coral ecosystems are highly sensitive to climate change and monitoring them is crucial, she said.

“Corals are early warning signs of the kind of system failures that we know are coming down the pipe,” Dr. Cobb said.

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