When people sense big trouble, they call for help. When the Pacific coral Acropora nasuta senses danger, it summons its own version of 911—an inch-long goby fish. The coral produces a compound that alerts the goby fish of the presence of poisonous seaweed that threatens the coral reefs. In response, the fish quickly gobble it up, thus protecting their own cozy reef home.
This complex symbiotic relationship was discovered by AAAS Fellow Mark Hay, a marine ecologist at the Georgia Institute of Technology, after analyzing hundreds of hours of underwater video.
"They [goby fish] are like little bionic hedge trimmers, they trim this alga enough so that it doesn't touch the coral," he said.
The Pacific has lost about 50 percent of its coral cover in the last 30 years, he noted. Climate change, bleaching, disease, and overfishing are all contributing to reefs being overwhelmed by seaweeds, turning them into what Hay describes as "algal-covered parking lots that look like nuclear winter." Since 2004, Hay has been studying corals in the Fiji Islands. Understanding the connections among Fiji's ocean creatures could be a key to assisting coral survival, and much more—from deciphering evolutionary changes to creating new medicines.
Hay's experiments focus on many interrelationships to try to pinpoint why reefs are struggling: Which fish are eating the destructive seaweeds? Which fish are the villagers catching and eating? And how does the chemical defense-system work?
In addition to his science-based research, Hay has developed a deep awareness and respect for local culture, which he says is as critical to coral protection as are his experiments. Even when some customs are a little out of the ordinary for a Western researcher.
"There, I wear a dress, I go and I sit on the floor with the chief [of the village]," he says. Custom demands that he partake in extract of kava, a native root with sedative properties.
After earning trust, he shares with villagers his research that shows certain fish are particularly important in eating these destructive algae. He tries to dissuade them from catching those fish so the reefs can recover. As a result of these efforts, several villages have created Marine Protected Areas, (MPAs) where fishing is prohibited.
Hay says even if residents don't understand all the science, they know a healthy reef is crucial to their survival: "Is there a way they can preserve their lifestyle, get protein, feed their kids, but still have pretty reefs? They are actually much more interested in that than Americans are. They are tied to this, and so they appreciate it," he said.
Many local villages are self-policing, he notes. "We've got three villages that have got Marine Protected Areas that are really well enforced. If you fish there, someone will ask you very nicely not to," he said. And because they are very serious about safeguarding these reefs, a second violation is likely to have more severe consequences.
Already the payoff for the marine ecosystem has been dramatic.
"In their MPAs, there is 40-60 percent live coral cover, with zero to two percent seaweeds. Immediately adjacent to that, where it is fished, there's 4-16 percent live coral, and 50-90 percent seaweeds. So in those places at least, not fishing makes a huge difference, " said Hay.
Hay's current experiments focus on the chemical cues that apparently guide marine juveniles toward a safe spot to settle "Most things on Earth don't have eyes or ears," he notes. "They decide whether to eat the thing next to them, or mate with it, or run away from it, based on smell.
"[Our research team] tends to work with things that are stuck, that can't run away—seaweeds, sponges, corals. We look at how they have evolved to use chemistry to poison their neighbors, keep things from eating them, and find good sexual partners."
Hay's research, detailed in Science 22 August 2014, reveals important data about the role smell can play in protecting marine ecosystems. "Baby fish and baby coral smell the fished area," notes Hay. "They can smell something.\" In tests with three different species of corals, he noted, babies swam to the protected area 90 percent of the time, indicating coral larvae can make pretty refined decisions using chemical cues about detecting a safe neighborhood to settle in.
He says understanding enough of this chemical crosstalk could provide valuable insight for protecting these ecosystems. It also has led researchers to study marine organisms for possible new drugs. In ongoing work, Hay and his colleagues are looking at molecular structures in red seaweed (PDF) with the potential to kill cancer cells, bacteria, and antibiotic resistant Staphylococcus.
Meanwhile, Hay says the right intervention tactics at the right time could help jump-start the recovery of now-overfished coral reefs.
"What this means is we probably need to manage these reefs in ways that help remove the most negative seaweeds, and then help promote the most positive corals," Hay said.