New scientific evidence highlights the correlation between islands with large seabird colonies and increased coral reef growth rates.
While scientists have long known that seabird presence is necessary for supporting marine ecosystem health, no previous study had looked at the effects of seabird nutrients on coral growth rates. A collaborative research effort brings to light evidence of seabird produced nutrients directly increasing coral reef growth rates.
Coral reefs are some of the most precious and productive ecosystems in the world. However, corals reefs are only able to thrive under a delicate balance of environmental factors such as temperature, nutrient input, and species presence.
A new study published in the Journal Nature was conducted near an isolated island in the Pacific, Namenalailai (Namena), which demonstrates just that ecological balance. Home to a large nesting seabird population and an expansive marine protected area, Namena’s surrounding coral reefs are abundant. Samples of coral were taken from Namena to compare with coral samples from Cousteau, a neighboring island with a similar environment, also a marine protected area but with much fewer nesting seabirds. These samples, both Acropora formosa coral, were first tested for nutrient content, specifically nitrogen. Samples of coral from Namena were planted within Cousteau coral reefs and vice versa in order to analyze growth rates within both coral samples. The changes in these transplanted reefs were then monitored for one year.
The results spoke for themselves.
The coral near Namena, the island with a higher seabird population, showed increased growth rates in coral—four times greater than that grown without seabird nutrients. Seabirds are vital to coral ecosystem balance because when they nest on islands they leave behind guano filled with nutrients such as nitrogen. These nutrients eventually trickle down into the ocean where they provide corals a necessary food source, and in return coral obligate species such as damselfish can feed on the algae. Higher amounts of algae enhance photosynthesis and increase nutrients through fish waste, both contributing to coral growth rates. Not only does seabird nutrient positively affect corals directly but it also contributes to symbiotic relationships within the coral ecosystem.
Unfortunately, seabird populations are becoming increasingly threatened worldwide, one of the biggest factors being the presence of invasive species. Large seabird colonies often reside on islands where they are unable to escape the negative impact and threats of invasive predators including rats, mice, and feral cats to name a few. Not only does removing invasive species from islands allow seabird populations to flourish, but it also creates healthier coral environments. Abundant coral reefs bring far-reaching benefits such as higher rates in biodiversity, mitigation to climate change, and better stability in fish populations. Protecting our seabird populations from invasive species should be a top conservation priority.
This research was conducted by the Department of Marine Science at the University of Otago, Dunedin, New Zealand and the Department of Biological Sciences and Marine Research Institute of the University of Cape Town, Cape Town, South Africa.