Scientists have found that protected marine reserves can help oyster populations recover by use of larval “spillover” if the conditions are right. In one of the first studies of its kind, researchers demonstrated the marine population benefits of combining different habitat restoration strategies.
Oysters are not only key components of marine ecosystems, but are also important for coastal economies. For thousands of years, oysters have been a source of food that supports commercial fisheries around the world.
Compared to past levels of oysters, there is now an 85 percent decline in oyster beds due to overfishing and habitat destruction. One way to restore oyster populations is by designating areas where fishing is not allowed.Fish that live in such marine protected areas (MPAs) often recover significantly in both size and abundance compared to areas where fishing is not restricted. MPAs may also boost fish populations through larval spillover, even though evidence of this is limited.
Marine ecologist Dr. David Eggleston has been coordinating with other scientists in an effort to restore oyster populations in Pamlico Sound, North Carolina, which is the second largest estuary in the country. The project has successfully restored oyster reefs in both reserves and harvested areas.
Dr. Eggleston and his team began this study over 20 years ago to determine whether habitat restoration and harvest protection are providing the intended benefits. In particular, they wanted to examine whether reserves are providing larval spillover to harvested areas.
The researchers compared oysters in the following three habitat types: natural reefs that are harvested, restored reefs that are harvested, and restored reefs that are protected from harvest. The findings confirmed the advantages of restored MAPs. The oysters were up to 72 times more abundant in these protected regions.
The evaluation also showed that potential larval output was around 6 times higher in the restored reefs, indicating that more larvae overflows from reserves to harvested reefs than the other way around. Therefore, reserves can contribute substantially to the larval supply of the overall oyster population.
“Marine reserves and habitat restoration offer clear demographic benefits to target oyster populations, particularly when used in concert,” said Dr. Eggleston. “Our research shows that no-take reserves with restored habitat can have significant positive impacts on oyster population densities, size-structure and potential larval output. Restored reefs that are harvested can also show increased potential larval output.”
The study is published in the journal Frontiers in Marine Science.