Danielle Dixson has a theory about moonless nights on the coral reefs of Belize, the Central American country along the Caribbean Sea.

Fish and coral larvae normally feed during the day, but during the phase when they move from the open ocean to settle into their permanent reef habitat, they may stay up late and head to the reef when the night is darkest. The key is avoiding predators that feed on the tiny fish and coral larvae.

Dixson, an assistant professor at the University of Delaware who specializes in the sensory behavior of marine organisms, is part of a team that received a $1 million grant from the Gordon and Betty Moore Foundation to look at how larval marine organisms, including fishes, corals and other invertebrates, select coral reef habitat. The three-year research project aims to find ways to use chemistry – the natural cues between reefs and the animals that colonize them – to restore degraded reefs.

Dixson plans to look at the role chemical cues play when fish and other marine invertebrates select habitat.

As reefs degrade, there is a cascading downward spiral, she said. New larvae aren't attracted to the reef so the habitat gets worse and worse.

The attraction larvae have to reef habitats causes them to gather to specific sites.

“We’re trying to gain a more complete understanding of the recruitment process and how chemistry can be used to impact conservation,” Dixson said.

As part of a research team working at the Smithsonian Marine Station at Carrie Bow Cay field station in Belize, she will collaborate with Valerie Paul, a natural products chemist and lead scientist at the Smithsonian and director of the Carrie Bow Cay; Tony MacDonald, director of the Urban Coast Institute at Monmouth University, in New Jersey; and Jay Odell, Mid-Atlantic marine program director at the Nature Conservancy in Richmond, Virginia.

From previous research, Dixson knows that larvae can distinguish between a reef that is healthy and one that is not. Degraded reefs produce a chemical that keeps fish and corals from colonizing. The result: Once a reef is degraded, chances of recovery diminish because fish and new animals that would colonize there stay away.

Think of how diverse populations of land animals like birds or deer no longer visit a site once the trees are cut and a shopping center parking lot replaces it.

In the complex world of a reef – which is made of the animals that inhabit it – the habitat depends on new colonization to stay healthy.

“If we are to understand reef ecology – or to wisely manage threatened reefs, we need to recognize and understand the chemical cues promoting or hindering reef recovery,” Dixson said.

As reefs deteriorate, algae moves in. But if scientists can figure out the chemical cues from the complete reef system, they may be able to attract the fish that feed on algae.

The idea is to learn more about conditions when reef activity is greatest and least.

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Dixson will look at coral larvae to see if they are responding to chemical cues from the reef community. In addition, she'll test whether low activity reefs give off a negative cue.

Once a source of negative or positive cues is identified, Paul, a chemical ecologist, will try to figure out the chemical compounds.

One thing that might be a factor is the tendency of larvae to recruit to reefs in high numbers at night, especially dark, moonless nights.

Recruitment levels are highest when light levels are lowest, around the new moon, so scientists typically do surveys the next day. Dixson worries the flaw in the survey system could be that the data only includes fish that survived the night.

“The reef with low recruitment could have high recruitment but low survivorship and scientists just don’t know it because they surveyed at the wrong time,” she said.

To learn more, Dixson will study the reef at night. She'll also take small pieces of coral and plant them on sandy bottoms. She'll introduce variables such as a caged predator, to see how the sample reef responds. In these tiny, created reef habitats, she'll be able to manipulate the conditions to see what is happening and how big a role predators play.

The work could ultimately guide conservation and restoration of coral reefs.

“If we can identify the cues that are important, especially for fish species that eat problematic algae, then hopefully we can develop strategies to improve reefs using the evolution of fish rather than marine protected areas that may not mean anything to the fish itself,” Dixson said.


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