Aquatic biologists have long known the importance of algae-eating fish to the overall health of coral reefs. But new research documents just how important species like surgeonfish and parrotfish are to Hawaii’s coral reefs.

A study by Mary Donovan of Arizona State University and other island colleagues indicates that the fishing of herbivore species to less than 80% of their unfished local density undermines the health of coral reefs due to the overgrowth of algae these fish consume.

“Herbivores play critical roles in the ecosystem, so their function needs to be supported to ensure a future for our reefs,” said Donovan, a former student and researcher with the Hawaii Institute of Marine Biology, in a news release.

The research, published Tuesday in the U.K.-based journal Proceedings of the Royal Society B, comes in the same week the state Board of Land and Natural Resources will consider more restrictive regulations on the fishing of herbivores.

The board today is also expected to consider requiring marine commercial operators to collect a $1 user fee from each passenger to pay for enhanced ocean stewardship and to weigh regulations aimed at reducing crowding at Molokini Shoal Marine Life Conservation District.

Additional herbivore fish protections, two years in the making, are expected to help the resilience of Hawaii’s coral reefs as they face an uncertain future under the spell of climate change.

According to the Nature Conservancy, reef-related tourism adds an estimated $1.2 billion-plus to the state’s economy, while reef fisheries generate some $13.4 million annually, much of it providing food and income for local families.

Despite the importance of reefs to the islands, overfishing and other factors have contributed to an estimated 60% decline in live coral cover on some of Hawaii’s reefs in the past 40 years, and climate change is adding more threats in the form of coral bleaching and ocean acidification.

Donovan’s study suggests that herbivorous fish populations are critical for ensuring the future of reefs and the benefits they provide to people.

The research was conducted through the Hawai‘i Monitoring and Reporting Collaborative, drawing on more than 20,000 surveys across the islands. The work produced results for every reef around the state — approximately 130,000 sites in total.

Corals and algae compete for space on Hawaii’s reefs, and the herbivores play a key role in maintaining balance, the researcher said. But if herbivore numbers are too low, algae can grow uncontrollably and lead to declines in reef health.

Donovan said fishing is important to the people of Hawaii and that access must be maintained. But “our results show that herbivores are in high abundance in some places and those reefs are healthy. But that is not true everywhere, so fishing sustainably will help ensure that healthy places stay healthy and that degraded places can recover.”

In the future, Donovan and other HIMARC researchers will continue to study the condition of Hawaii’s reefs and their fish diversity. They are also looking into the role of herbivores following marine heat waves that cause coral bleaching and mortality. They want to determine whether reefs with more herbivores have better outcomes.

The Land Board today will be asked to grant final approval to what the department is calling “science-based and stakeholder-informed regulations” governing the taking and selling of key herbivorous reef fish, plus the Kona crab.

Each of the species — manini, kole, kala and uhu — are important food fish targeted by fishers for recreational, subsistence, cultural and commercial purposes. Papai kualoa, or Kona crab, is targeted by some noncommercial fishers and a small-scale commercial fishery.

The proposed rule changes include:

>> Increasing the minimum length for manini (convict tang) to 6 inches from 5 inches.

>> Establishing a new minimum length of 5 inches for kole (goldring surgeonfish).

>> Establishing a new noncommercial bag limit of four kala (bluespine unicornfish) per person per day.

>> Establishing new restrictions on the commercial harvest and sale of kala.

>> Increasing the minimum length for large-bodied uhu (parrotfish) species to 14 inches from 12 inches.

>> Establish a minimum length of 10 inches for all other uhu species.

>> Establishing a new noncommercial bag limit of two uhu per person per day.

>> Establishing restrictions on the commercial harvest and sale of uhu, including:

1. Requiring commercial uhu fishers to first obtain a $100 annual commercial uhu fishing permit.

2. Prohibiting the commercial harvest of any uhu species other than Scarus rubroviolaceus (uhu palukaluka and uhu eleele).

3. Setting a commercial annual catch limit for uhu of 30,000 pounds.

4. Requiring commercial marine dealers who sell uhu to register with the department as commercial uhu dealers.

>> Extending the current closed season (May-August) for Kona crab to May-­September but allowing the take of females.