As climate change continues to threaten coral reefs globally, a recent study published in Science sheds light on a natural ally in the fight for reef resilience: seabirds. The connection between seabird-derived nutrient subsidies, invasive species, and coral recovery holds valuable lessons for targeted conservation efforts. 

First things first – what are ‘seabird-derived nutrient subsidies’? This refers to the transfer of nutrients from marine environments, where seabirds eat, to terrestrial ecosystems. Seabirds feed in nutrient-rich marine areas and then return to their nesting or roosting sites on land.  

Human activities have disrupted the delicate balance of nutrient flows crucial for coral health. Agriculture and waste disposal are two prime examples of things that cause devastating, human-induced consequences for coral reef ecosystems. Increased anthropogenic inputs not only diminish coral resistance to bleaching but also interfere with the natural nutrient subsidies provided by mobile animals (like seabirds), exacerbating the challenges faced by coral reefs.  

In contrast to the detrimental impact of human-derived nutrients, seabirds emerge as nutrient providers with a unique offering. You guessed it (well, maybe) – their poop. Alongside urine and their feathers, seabird poop (guano) is a rich nutrient source that seabirds provide to their island homes. Seabirds are carnivorous and consume marine organisms rich in nitrogen and phosphorous. These nutrients are excreted by seabirds in a ratio that is beneficial for corals, potentially making them more resistant to bleaching.  

Removing introduced, damaging invasive species from islands takes center stage as a multifaceted conservation approach. Beyond successfully restoring seabird populations, this strategy re-establishes the flow of seabird-derived nutrients to islands and nearby marine environments. This dual benefit positions invasive mammal removal as a potent nature-based solution for bolstering climate change resilience. 

The study unfolds in a remote atoll system in the Indian Ocean, where islands with thriving seabird populations are juxtaposed with those lacking these avian inhabitants due to the presence of invasive rats. This setting provides valuable insights into the nuanced relationship between island ecosystems, seabirds, and coral recovery. 

The Findings:  

1. Seabird-derived nutrients were successfully assimilated by corals, leading to increased coral growth rates. 

2. Corals near seabird islands exhibited higher growth rates compared to those near rat-infested islands, indicating the positive impact of seabird-derived nutrients. 

3. Despite limited recruitment, rapid recovery of hard coral cover was observed around seabird islands, outpacing recovery around rat islands. 

The study concludes that the restoration of seabird populations and the associated nutrient pathways could contribute to increased resilience in coral reefs through improved growth and recovery rates. Understanding the intricate connection between natural nutrient subsidies, island ecosystems, and coral resilience provides a roadmap for conservation efforts like invasive species removal.  

Check out the full study in Science here >>