Poop corals may need their predators

Coral-eating fish can pay off with poop.

It is an unexpected reversal of coral reef symbiosis, said Adrienne Correa, a marine biologist at Rice University, who discovered that coral predator feces are full of live symbiotic algae on which corals depend on survival . The finding confirms that poop from coral-eating fish is an important environmental source of symbiotic dinoflagellate algae on coral reefs.

Correa said coral-eating predators are thought to typically bite and weaken reef structures, thus generating hiding places for other organisms and, ultimately, beach sand. In contrast, grazing fish that lay down shrubby algae receive the light to help reefs maintain healthy coral cover.

“The message is, ‘Move across pastures, it’s not just you who are helping to maintain coral control. These coral-eating fish also seem to be helping to control coral.’ distribution of beneficial coral reefs, “she said.

Carsten Grupstra, a Rice doctoral student, lead author of the study in Animal microbiome, he said, “This tells us that we are not really aware of all the interactions that occur on coral reefs, and that some species may be important for the conservation of coral reefs in Scotland. ways we never thought possible. “

In exchange for a sheltered life, dinoflagellates feed the hosts by sharing the food they make pictures. Millions of symbionts live in each coral, but some corals are not born with dinoflagellates. They get them as babies.

“When a lot of baby corals settle to the bottom of the reef, they have to get their symbionts from the environment,” said Correa. “We saw symbionts in the water and sediments and on large shrubby algae on reefs, but we didn’t look. certainly how these microorganisms reach these places. “

Thinking of ways in which symbionts could be transmitted on reefs, Grupstra, Correa, graduate student Lauren Howe-Kerr and undergraduate Kristen Rabbitt were inspired by studies of pollinating insects and birds that infect passing beneficial bacteria between flowering plants. Like pollinating bees that visit many flowers in one fly, coral-eating fish constantly crawl reefs and interact with many corals every day.

“Most of them take small bites of adult corals and do not kill the colonies they eat,” Grupstra explained.

On a trip to the Mo’orea Coral Reef long-range ecological research station in Polynesia, France, Grupstra, Howe-Kerr, Rabbitt and Correa followed fish that ate different amounts of coral and algae. Using underwater boards, they made a note of what the fish ate and where and how often they fished. Grupstra also collected samples of predator and poop grazer for laboratory study.

“I left some specimens in the window sill for a week or two in Mo’orea” he said. “Later, when I started looking at them (under a microscope), I found tons of symbionts. A lot of them were swimming around and some were splitting.”

The actual number of live symbionts was both unexpected and potentially important in the larger picture of reef ecology, Correa said. Although symbionts have previously been reported in feces from a limited number of coral predators, it was not clear how many of them were alive and potentially useful to corals. Her group found a high density of live assemblages in the feces of a diverse group of coral predators. For example, Rice’s team estimated that the Mo’orea research station had two species, Chaetodon ornatissimus and Chaetodon reticulatus, each spreading approximately 100 million live symbionts per day over a range of reefs around six parking spaces.

“This expands the way we can think about the responsibilities of coral fishing on reefs,” said Correa. “They don’t just break reef frames. They also transmit samples that corals and other organisms need. “

The knowledge that predatory poop creates ‘hotspots’ of live symbiotic dinoflagellates on reefs raises questions about whether and how corals use them. The Correa team has designed a series of experiments on both adult and weight corals to determine how easily they can absorb beneficial symbols from the pole.

She said there are still many questions about how and how often corals pick up symbionts from the environment. For example, marine biologists widely agree that many coral babies get their symbionts from the environment, but it is not clear how often adults do this and under what conditions. A better understanding of symbiont acceptance could lead to new methods to help reefs recover from stress-induced “swelling”.

Glazing occurs when weighted corals put their symbionts en masse, often leaving colorless corals, as the name implies. Clean-up events are becoming increasingly common due to climate change. While some corals never recover from swelling, others do, which raises the question of how swollen corals recycle their symbiont communities. Grupstra and Correa are conducting research to determine if contact with coral predator feces can improve swelling recovery levels and long-term coral health.