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Researchers are studying the important role of marine carnivores in supplying coral reef ecology with nutrients



Credit: Darcy Bradley

It has long been known that sharks help to nourish coral reefs, but to the extent that has never been scientifically researched – until now.


A groundbreaking study ̵

1; led by scientists at Imperial College London in collaboration with marine biologists at UC Santa Barbara – found that the predators use their feces material to transport important nutrients from their open feeding grounds to shallower reef environments, thus improving the overall health of these fragile ecosystems. Specifically, the researchers investigated the role of Gray Reef Sharks ( Carcharhinus amblyrhynchos ), a predatory species commonly associated with coral environments, but whose extensive ecological role has long been debated. The results of the international team appear in the journal Proceedings of the Royal Society B .

"Our study shows that large mobile predators such as sharks can be a very important nutrient source for even the smallest reef inhabitants, such as corals," said co-author Jennifer Caselle, a researcher at the UCSB Marine Science Institute. "The role of sharks as top predators is well understood, but their role as nutrient vectors is much less studied."

Working in the waters around the Palmyra Atoll – a national wildlife sanctuary managed by the US Fish and Wildlife Service miles south of Hawaii – scientists used acoustic markers to map shark movements across the atoll. They combined these findings with existing knowledge about shark dietary habits in pelagic environments where they consume a large portion of their prey.

The researchers analyzed this tracking data as a spatial motion network and, for the first time, were able to estimate the amount of nitrogen deposited around the remote, unfinished reef of the Palmyra atoll over the shark's feces material. The results suggest that this specific population of gray reef sharks – which is believed to number about 8,300 individuals – contributes a total of 94.5 kg (208.3 pounds) of nitrogen per day to the reef ecosystem, which is likely to be a major contributor to primary productivity Contributes to riffs.

By searching for prey in deep pelagic waters, often miles offshore, these mobile predators can serve as vital "nutrient vectors" to shallow reefs. They bring with them valuable nutrient sources, such as nitrogen, which effectively act as fertilizers for the thousands of other species that call these reef environments their home.

This research has implications for the scientific understanding of fragile coral reef ecosystems and the ecological importance of gray reef sharks. The species is currently classified as "near threatened" by the International Union for the Conservation of Nature.

"Combined with their more prominent role as predators, our study underscores another less obvious role of reef sharks in improving the resilience of these fragile habitats, and underscores the vital importance of preserving this and other widely ramified predators," said Senior Researcher. Author David Jacoby from the Zoological Society of London Institute of Zoology.


Further research:
Reef sharks prefer bite-sized meals

Further information:
Jessica J. Williams et al. Mobile Marine Robber: A Nutrient Source for Coral Reefs in an Untreated Atoll, Proceedings of the Royal Society B: Biological Sciences (2018). DOI: 10.1098 / rspb.2017.2456

Sources in Journal:
Proceedings of the Royal Society B

Provided by:
University of California – Santa Barbara


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