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Eric Crandall

$1.6 M from NSF to improve models that inform marine protected areas

21 March 2024

To better understand how populations of tropical reef fish are connected, the U.S. National Science Foundation has awarded a three-year, $1.6 million biological oceanography grant to a team co-led by Eric Crandall, assistant research professor of biology in the Penn State Eberly College of Science. This work aims to help improve models used in fisheries management and may guide the creation of new protected areas for marine species.

The team is also co-led by Michelle Gaither, associate professor of biology at University of Central Florida. An additional £300,000 will be awarded to Maria Beger, associate professor of conservation science at Leeds University, through a collaboration with the U.K. Natural Environmental Research Council.  

“As with any species, the fate of marine species and populations is largely dependent on the fate of their offspring,” Crandall said. “The problem is, the offspring of most marine species are tiny larvae, about the size of a period at the end of a sentence. These larvae are released into ocean currents where they can spend days or months feeding and growing before finding a place to settle as a juvenile.”

Understanding how far these larvae travel from home and in what direction can help predict if a population will persist, a core concern for marine conservation. However, the microscopic nature of larvae makes them difficult to track, so larval dispersal has been directly measured for only a very few species.

“Imagine trying to manage a population of deer, but you have no idea where the fawns go after they’re born — that’s what it’s like to manage a modern marine fishery,” Crandall said. “To date, fisheries managers have relied on computer models of ocean currents that simulate virtual larvae dispersing. However, the lack of measurements of larval dispersal in the wild means that these models have almost never been validated as being accurate.”

Recent advances in theory have suggested that patterns of genetic distance can be used to predict how far larvae travel, Crandall said. The researchers will leverage this theory to estimate the average distance that larval fish offspring travel from their parents. This information can then be integrated into the computer models, to construct a sort of map, sometimes called a dispersal kernel, that illustrates where millions of larvae might settle. This integrated modeling approach, with models validated for the first time with actual estimates of dispersal distances, will allow the team to overcome the limitations of cost and time associated with directly measuring larval dispersal in the wild.

Crandall and his research team will describe dispersal kernels in six common species of reef fish present in the Fijian, Vanuatu and New Caledonian archipelagos in the South Pacific Ocean. These three semi-isolated island systems each present a distinct seascape of islands and currents that might shape the dispersal kernels of each species differently. In addition, each of the six species vary in larval traits such as the length of time that larvae spend as microscopic, drifting plankton, before settling at a location such as a reef. Taken together, the archipelagos present a unique opportunity for researchers to investigate how far and wide the offspring of a grouper, for instance, travels in Fiji, compared to the other archipelagos, according to Crandall.

According to the researchers, these results may help to tease apart how much of the dispersal kernel is shaped by the traits of individual species, as opposed to the seascape through which the larvae are dispersing

Finally, the researchers will apply their findings to the conservation and management of marine fisheries in the South Pacific archipelagos.

“Just like on land, marine fishery species are often managed through the use of protected areas, where fishing and other activities are banned or heavily regulated,” Crandall said. “For example, in Fiji, these areas are called ‘qoliqoli’ and have been customarily managed by local villages for thousands of years.”

The researchers said they hope to engage with local and national governments as well as non-governmental organizations to use their validated computer models to create new protected areas that will enhance fisheries while also protecting the rich coral reefs and marine biodiversity heritage of these South Pacific archipelagos.

International researchers on the grant include Cecile Fauvelot, French National Institute for Sustainable Development; Brian Stockwell, University of the South Pacific; Cynthia Riginos and Eric Treml, Australian Institute for Marine Science; and Grace Chang from Integral Consulting Incorporated.