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The Abstract

Fish Pee Helps Keep Coastal Ecosystems Healthy, Thriving

Researchers examined the importance of fish pee to Caribbean ecosystems. Photo courtesy of Craig Layman.

Life in the Caribbean islands is an idyllic bliss.

You can picture it, right? The sparkling clear water. The pristine coral reefs. The perfect amount of fish pee …

It turns out that the proper amount of fish excretion – and the proper ratios of chemicals emitted in the waste – is key to keeping these Caribbean ecosystems healthy.

Jake Allgeier, a post-doctoral researcher currently working at the University of Washington, studies fish pee. After studying 172 different fish communities in the northern Caribbean, Allgeier shows – in two recent papers co-authored with NC State applied ecologist Craig Layman – how the ecosystem relies on a delicate balance of factors, including fish waste.

In a paper just published in the February edition of Ecological Monographs, Allgeier, Layman and colleagues examine the potential implications of different levels of fish biodiversity and scenarios of species loss for the amounts of nutrients supplied to the entire ecosystem through fish excretion. It shows, specifically, that species richness – the diversity of fish – and the size of fish are the most important factors for maintaining healthy biogeochemical conditions in coral reefs, seagrass beds and mangrove ecosystems in the Caribbean. Loss of fish diversity – and the nutrients supplied by their excretion – would create less healthy coral reef environments.

In a paper published in Global Change Biology in August, Allgeier, Layman and colleagues show that the ratio of nitrogen and phosphorus in the water of healthy fish communities matches the ratio at which coral tend to optimally thrive – suggesting that fish excretion essentially fertilizes the coral at the optimal level of nitrogen to phosphorus.

“These two studies represent the first comprehensive exploration of fish excretion for coral reef, seagrass and mangrove ecosystems and highlight the clear importance of this nutrient source for these ecosystems – as it is among, if not the, greatest source of nutrients to these ecosystems,” Allgeier says. “These studies also underscore the need to increase our resolution of understanding about these pathways if we are to help restore them from their current states of disrepair.”

Allgeier’s work with Layman in the Caribbean will expand to rebuilding coastal fisheries. In the meantime, he will take advantage of his Pacific Northwest surroundings and study the potential role of salmon excretion in different strategies of river restoration.