Biologists have long regarded fish, urchins and sea turtles as "secret weapons" in the fight to protect coral reefs from human pollution and activity.
The herbivores, as science has shown, keep corals and their ecosystems healthy by gobbling up harmful algae that grows in the presence of nutrient pollution.
But a new University of Florida study casts doubt on the idea, suggesting that the cleanup system may not be as effective as once thought.
While herbivores can control the effects of added nutrients in small-scale experiments, they can be overwhelmed by pollution at larger, more realistic scales, according to Mike Gil, a marine biologist who conducted the study as a doctoral student at UF.
"We can't just focus on protecting fish to keep coral reefs healthy," Gil said in a release Monday. "We have to take a more holistic approach."
Today's world is a stressful place for corals. Reefs around the world face an onslaught of threats, from rising ocean temperatures and acidification to overfishing, marine debris and land-based pollution.
Gil has seen the destruction firsthand in Akumal, Mexico, where he leads a field course in marine ecology. In an attempt to answer whether herbivores were up to the task of defending reefs on their own, Gil and his team turned to mathematical modeling and found that as the area affected by nutrient pollution increases, herbivores' ability to control the resulting algae decreases, even as their populations remain the same.
The findings suggest reefs may be more vulnerable than many scientists thought.
Gil and his team hope their research will "guide policy-makers in creating sustainable plans for industries such as tourism and fishing, which rely on healthy reefs," according to the release.
In October, the National Oceanic and Atmospheric Administration confirmed that a global coral bleaching event had occurred -- a phenomenon in which stressed corals expel algae and turn white. If not given time to recover, bleached corals can perish. The incident announced in October was only the third time in history scientists have observed the phenomenon on a global scale, with the first occurring in 1998 and the second in 2010.
An estimated 30 percent of the planet's coral has already perished as a result of above-average ocean temperatures, El Nino's effects and acidification.
Also on HuffPost: