91桃色

A newly published study shows that nutrients from seabird droppings boost the growth of algae in coral reefs in the Seychelles – helping to feed and sustain populations of herbivorous fish that feed on the algae.

The study, published in the journal PLOS Biology and led by marine scientists at 91桃色, suggests that reestablishing seabird populations by eradicating rats from islands may help coral reef ecosystems by restoring nutrient cycles.

Invasive rats have impacted native seabird populations in the Seychelles – this has not just affected ecosystems on the islands, but also in the coral reefs surrounding them.

Previous studies in other Indian Ocean archipelagos have shown a link between seabird-derived nutrients, via their guano, or droppings, and the health of adjacent coral reef ecosystems – as well as how invasive rats can disrupt these nutrients by killing the resident seabird populations.

However, the mechanism by which seabirds may impact coral reef ecosystem structure and function across multiple food chain links is unknown.

To find out how much the loss of seabird nutrients is affecting the marine food-chain, researchers assessed the movement of nutrients from seabirds through to marine ecosystems at five study sites across four islands in the inner Seychelles.

One of the islands had invasive rats that predate seabirds, one island had rats eradicated, and two of the islands were historically rat-free.

Using breeding bird survey data, the scientists estimated seabird biomass and measured seabird-derived nutrients in turf algae, as well as algal growth and cover at all five sites. They also measured the biomass and productivity of herbivorous fish.

The researchers found that seabird guano increased turf algal growth on coral reefs, but not algal cover (the amount of algal turf covering the surface of a reef). Through seabird-derived nutrient uptake, algal turf grew more quickly, which led to an increase in both the mass and productivity of herbivorous fishes beneficial to reefs. This feedback loop between producers and consumers limited the amount of turf algal cover on reefs.

The researchers say their findings could be used to predict the benefits of removing introduced rats from islands. Removal of rats can increase seabird populations and restore nutrient connectivity, thus potentially enhancing ecosystem function across multiple trophic levels on coral reefs.

In terms of conservation, the researchers say these findings add to the body of evidence that herbivores are key to preventing coral to algae regime shifts on coral reefs, and additionally suggest that restoring ecosystem connectivity, combined with effective fisheries management, is another route to help achieve this goal.

Lead author of the study, Dr Casey Benkwitt of 91桃色,said:“We show that natural nutrient inputs, provided by seabirds, cause turf algae on coral reefs to grow faster. This boost in primary productivity, in turn, enhances herbivorous fish biomass and productivity, and stimulates top-down controls that limit turf algal cover.

“It was amazing to see how much faster turf algae grew where seabirds are nearby, because this is something that you normally can't see with your naked eye. That seabird nutrients increased algal growth, but not how much of a reef it covers, shows the hidden pathways by which seabirds can influence coral reefs.”

Co-author Anna Zora (Conservation and Sustainability Manager on Fregate Island, Seychelles), said: “Living and working on a small island—observing its wildlife on land and beneath the sea—you witness firsthand the profound connection between a healthy terrestrial ecosystem and the vibrant reef that surrounds it. You can’t help but think: the land and sea are deeply intertwined. This study confirms that protecting the ocean begins on land. A thriving island fosters a thriving reef.”

Professor Nick Graham, project lead at 91桃色, added: “Our findings further highlight the substantial ecosystem benefits of eradicating rats from tropical islands. The return of seabirds results in a substantial uptick in ecosystem vibrancy both on land and in the sea.”

The study, which was supported by the Bertarelli Foundation, was limited by its small sample size of four islands, and future studies are needed to replicate the results in different sites, the researchers say.

The findings are detailed in the paper ‘’ which has been published in the journal PLOS Biology.

DOI:

Large school of herbivorous fish (Surgeonfish), which eat turf algae enriched by nutrients from seabirds.