Lange, I.D., Benkwitt, C.E. Seabird nutrients increase coral calcification rates and boost reef carbonate production. Sci Rep 14, 24937 (2024). https://doi.org/10.1038/s41598-024-76759-2
One of the hottest topics in ecology today is how human-made substances impact the environment. Trash, plastics, and chemicals from farming often find their way into natural ecosystems, altering biological processes and disrupting native species.
Guano?
Human-driven nutrient influxes frequently clash with natural nutrient cycles, especially in aquatic and marine settings. In freshwater, fertilizers and other runoffs can spur algae blooms and increase populations of filter feeders, shifting the balance of local ecosystems. In contrast, isolated island ecosystems rely on unique, natural nutrient sources, like seabird colonies, which provide a steady nutrient flow via guano (yes, seabird poop!).
Seabirds are able to take up and concentrate large amounts of nutrients, moving them from the open ocean to small islands. Their guano fertilizes the land, benefiting terrestrial plants, and even leaches into nearby coastal waters, where corals absorb these nutrients. Coral reefs, vital for marine life habitats, coastal protection, and climate resilience, benefit from nutrient-rich waters. Corals, with their symbiotic algae partners, use these nutrients to grow, with some species like the branching Acropora corals showing up to four times faster growth near seabird-populated islands. However, while branching species like Acropora are easy to study with respect to their growth rates, other species receive less attention.
A case study …for the birds
In a recent study, researchers explored this nutrient link on the Chagos Archipelago in the Indian Ocean, focusing on the Salomon Atoll. They studied two islands: Ile de la Passe, with a high seabird population, and Ile Anglaise, where a large rat population has reduced seabird numbers by preying on eggs.
The merry band of scientists from over the pond selected two coral species common to both islands: the submassive Isopora palifera and the branching Acropora vermiculata. Over nearly two years, they photographed coral colonies to track growth and collected small coral samples to measure “skeletal bulk density.” Using the “ReefBudget” method, they calculated overall carbonate production, which corals use to build their structures.
Seabirds, the reef MVPs
The findings were clear. Near the high-seabird-density island, both coral species showed 1-3 times higher growth rates across all metrics, with A. vermiculata corals showing up to a 4x increase in surface area. Carbonate production was also more than double near Ile de la Passe when using site-specific growth rates, underscoring the significant impact of seabird-derived nutrients.
This study highlights the importance of natural nutrient pathways. While prior research has focused on nutrient impacts on branching corals, this is the first to demonstrate seabird-driven nutrient benefits across multiple coral types. Further, the central lagoon in Salomon Atoll may lead to a higher retention of nutrients, amplifying the effects seen on the local reefs.
As land-dwellers, we often overlook the role of birds in ecosystems, from spreading seeds to delivering nutrients. This study shows that seabirds are vital for reef health and reminds us to prioritize the preservation of natural nutrient pathways. Ultimately, these connections are what sustain life on Earth and keep us all moving.
Cover photo by Dionysos1970, via Wikimedia Commons
I’m a former oceanographer with an MSc in Biological Oceanography from UConn where I studied mixotrophy in marine ciliates. After a year in Poland (studying freshwater critters) I moved to California. I currently work as a lab technician at Stanford. Outside of science, I enjoy a good book, a long run, and frozen fruit.
.jpg){kind=link}
