Shark Poo & Coral Reefs

April 2, 2018

Like farmers fertilising wheat fields, it turns out sharks are fertilising coral reefs! 🐠🐠

📸 Tomas Kotouc

 

Are they trying to grown their own coral?! Maybe…maybe not. But these five-finned fish do act like farmers for tropical coral reefs, moving precious nutrients around the ecosystem as they feed in the open ocean and poop in shallower coral reefs! 🦈💩

A brand-new study, led by @jjwilliams924, used acoustic tags to see how grey reef sharks (Carcharhinus amblyrhynchos) move across Palmyra Atoll (a circular shaped coral reef) in the centre of the Pacific Ocean. Acting as underwater spies, these tags recorded data on shark movements for 4 years!

Grey Reef Sharks       📸 Klaus M. Stiefel

 

Williams et al. used this data to map shark movements around Palmyra Atoll. Then, using data on shark body weight/length they examined how much Nitrogen (a vital nutrient for the ecosystem that's found in faeces 🦈💩) they absorb and release. Once you know where sharks move and how much Nitrogen they lose, you can estimate where they're distributing nutrients to when they use that big blue toilet! 🚽🌊🌎

With an estimated population of 8,300 grey reef sharks, Williams et al. think the sharks are contributing 94.5kg of nitrogen onto the reef ecosystem per day! This volume of Nitrogen is likely to substantially improve the health of the reef and the thousands of aquatic organisms that call it home! 🐠🐟🐡🦐🐙🐢🦀🐬

So, what does this new research tell us for the bigger picture? It again demonstrates the connectivity of our natural world. The butterfly effect for nature 🦋 The fact that all species on earth have evolved alongside one another, forming interconnected complex relationships in a giant global species web. And if we pull on those silky strands too hard, we compromise the whole system 🕸️🕸️🕸️

We see it with research on species all over the world: lions affect bush fires 🦁, wolves affect rivers 🐺, seabirds affect plant communities 🐦, and now we've found that shark poop affects coral reefs. If we lose sharks, we not only lose their role as top predators, keeping in check all those species below them in the fishy food-chain, but also, we lose their poop. And who could live in a world without shark poop? #TeamSharkPoop 🦈💩

Whitetip reef shark      📸 Tomas Kotouc

 

Paper: Jessica J. Williams, Yannis P. Papastamatiou, Jennifer E. Caselle, Darcy Bradley, David M. P. Jacoby (2018) Mobile marine predators: an understudied source of nutrients to coral reefs in an unfished atoll.

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