VIZAG: In a world where coral reefs face increasing threats from climate change, there appears to be some hope emerges from an unexpected source: seabirds. A recent study led by researchers at Lancaster University reveals the vital role seabirds play in enhancing the resilience of tropical coral reefs. Published in Science Advances, the study, ‘Seabirds boost coral reef resilience,’ reveals how the presence of seabirds on islands adjacent to coral reefs significantly accelerates reef recovery following bleaching events, offering new insights into conservation strategies for these vulnerable ecosystems.
The research, conducted on a remote atoll system in the Indian Ocean, focused on Acropora corals, which are vital for supporting reef structure and marine biodiversity. The study period spanned from one year before a major marine heatwave and subsequent mass coral bleaching event in 2015-16 to six years after, allowing for a comprehensive assessment of reef recovery dynamics.
The findings demonstrate that Acropora corals near islands with thriving seabird populations recovered from bleaching events approximately 10 months faster than reefs located away from seabird colonies. This faster recovery is attributed to the nutrient-rich droppings of seabirds, which enrich the surrounding marine environment.
Seabirds feed on fish in the open ocean and return to land to roost, depositing nitrogen- and phosphorus-rich guano on nearby islands. Rainfall washes these nutrients into the surrounding seas, where they fertilise corals and other marine species.
The study compared reefs adjacent to islands with healthy seabird populations against reefs near islands with few seabirds, often due to the presence of invasive rats, which devastate bird populations. The researchers found that coral colonies near seabird-rich islands exhibited approximately 1.1 times higher nitrogen stable isotope values in their symbionts, indicating higher seabird-derived nutrient levels compared to colonies near rat-infested islands or islands with no nearby bird populations.
Experimental evidence confirms the direct link between seabird nutrients and coral growth rates. Acropora corals transplanted to seabird-rich islands grew twice as fast as those transplanted to rat-infested islands. Moreover, natural coral colonies near rat-free islands experienced an estimated 2.4 times faster growth rate compared to those around rat-infested islands.
The study underscores the importance of restoring seabird populations and their associated nutrient flows to coral reefs, particularly in the context of increasing climate disturbances. Restoring healthy seabird populations can occur relatively rapidly following invasive rat eradication from islands, providing a viable short-term conservation strategy.
The environmental benefits of seabird nutrients extend beyond coral recovery. Reefs adjacent to islands with large seabird colonies also support faster fish growth rates and higher fish biomass compared to reefs near islands with rats. Consequently, rates of grazing and bioerosion by fish are three times faster on islands with seabirds, contributing to overall reef health and resilience.
Overall, the study highlights the interconnectedness of terrestrial and marine ecosystems and emphasises the importance of conserving seabird populations for the health and resilience of coral reefs in the face of ongoing environmental challenges.