This DNA parentage analysis allowed Thorrold and his colleagues to map and calculate the dispersal of 122 clownfish with detail never before achieved in the marine fish populations. Because they knew the exact locations of both the natal anemone and the anemone in which the juvenile settled, dispersal was simply the distance between those two hosts. According to Thorrold, "Our accuracy of dispersal is as accurate as the GPS measurements of the anemones."
Thorrold and his colleagues found juveniles as far away as 35 km from their natal lagoons. These wayward offspring play an important role in the ecosystem, contributing to the resilience of populations in distant reserves. The propensity for long-distance travel affects more than just a few meandering larvae: long-distance dispersers accounted for up to 10 percent of the populations they joined.
The study also showed surprising consistency in the proportion of juveniles returning to the lagoon where they were spawned. Regardless of time of year, species of anemone, or natal lagoon, 40 percent of the juveniles seemed somehow hardwired to settle close to their parents, the literal apple not falling far from the tree. These offspring also play a key role in population dynamics, sustaining the populations in the lagoons where they were spawned.
The research has significant implications for management of marine protected areas (MPAs), which are regions where fishing is prohibited. Implementation of MPA networks are widely recommended by policy makers as a way to conserve biodiversity in marine environments and as a hedge against over-fishing. However, as Thorrold points out, "Honestly, the policy has gotten a bit ahead of the science. What's important about this study is that it brings a scientific and quantitative understanding to the design of marine protected areas.
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Woods Hole Oceanographic Institution