From coral reefs in the tropics to Oregon’s rocky banks, Mark Hixon investigates coastal marine fishes.
OSU zoology professor Mark Hixon’s research on fish population dynamics has taken him to most of the planet’s oceans, both temperate and tropical. He’s dived in the Pacific, the Atlantic, the Caribbean and the Coral Sea. He’s graduated from the bone-chilling dives in cold-water kelp forests that he made as a doctoral student in the 1970s to using small research submarines in frigid northern waters.
Hixon’s research is driven by a mystery relevant to both fisheries management and marine conservation — whether and how isolated populations of adult fish are linked. “One of the most important challenges in marine science today is to understand how the decline of a species in one part of the ocean affects the same species elsewhere — how spawning in one region replenishes populations in other areas,” says Hixon.
In two ongoing studies — one in Hawaii, the other in the Bahamas — Hixon and his graduate students are investigating connections among isolated populations of coral-reef fishes. They are studying the demographics of the yellow tang on Hawaii’s Big Island and the bicolor damselfish in Exuma Sound off the Bahamas. They are sampling DNA from adult and juvenile fish at multiple reefs. Their goal is to understand the drift patterns of fertilized eggs and larvae that travel with tides and currents in a process known as “larval dispersal.” And they are testing whether a high level of larval connectivity between two populations is reflected in the population dynamics of adult fish in those populations.
Ultimately, the answers will guide conservation and management, not only of fish, but of the reefs themselves. These complex ecosystems brim with more species than anyplace on the planet, even tropical rainforests. And many are dying. Pollution, global warming and overfishing have degraded about 20 percent of Earth’s coral reefs so far. Another 50 percent are at risk. In Hawaii, the yellow tang, coveted by the aquarium trade for its brilliant color, was depleted until the state created marine reserves along the Kohala-Kona coast of the Big Island to protect them.
Preliminary data from Hixon and his colleagues suggest the reserves are working. “Comparisons inside and outside protected areas demonstrate that the reserves produce larger populations of spawning adults, and the aquarium fisheries are thriving as a result,” he says. The yellow tang genetics, still being analyzed in Hixon’s lab, will reveal which of Hawaii’s reefs need replenishment from spawn drifting in from highly productive “source” reefs and where those respective reefs are located.
Hixon’s tropical reef research, part of OSU’s top-ranked efforts in conservation biology, has relevance here in Oregon. “Off Oregon, it’s impossible to gather the enormous amount of data we can extract from warm, clear tropical waters,” Hixon says. “However, once our methods are developed and tested in the tropics, we can bring them home to Oregon.”
One of the world’s leading authorities on coral reefs, Hixon has been cited in scientific journals more often than any other coral-reef ecologist in the Western Hemisphere over the past decade, according to the Thomson Institute for Science Research. He was ranked third worldwide behind two scientists who live adjacent to coral reefs year-round.
In the end, Hixon wants our progeny to inherit a world still relatively intact. He wants tomorrow’s children to have a chance to dive into the pulsating rainbow of biodiversity that is the tropical reef. “You feel as if you’ve fallen into a universe of stars,” he says. “It really, truly is amazing.”
More on Mark Hixon’s research can be found in the Spring 2008 issue of Terra