Sentinel Species Research

Guano Versus El Niño

Warming sea surface temperatures have destructive effects on coral reefs, as shown during the 2015-2016 El Niño global bleaching event.

Corals rely on a highly important symbiotic relationship with an algae, called zooxanthellae. When sea temperature rises these algae can become toxic to the coral and are thus expelled, causing the coral to loose its color and appear “bleached”. Nonetheless, corals can eventually recover from bleaching events in the right circumstances and if given enough time.

Nitrogen and phosphorus occur naturally at very low levels on coral reefs, making them a notoriously nutrient-poor environment. These elements are key to the photosynthesis of the plants and algae on which coral reef ecosystems rely and act as limiting factors. To the surprise of researchers in BIOT, it seems that seabird’s guano (rich in nutrients) can provide an essential “boost” triggering coral recovery.

Indeed, seabirds are known to defecate frequently and most of this guano ends up in coral reefs ecosystems (directly or indirectly). A recent study states that this nutrient enhancement is critical for corals after a bleaching event.

The same study investigated on the coral saving guano by looking at ten islands. They found that reefs surrounding islands with a substantial seabird population had a greater growth of calcareous algae This particular seaweed serves as glue for reefs to form a barrier and is an indicator of a healthy ecosystem. Therefore, scientists suggest that guano provides optimal nitrogen to phosphorus ratios essential to reefs recovery and that we can’t replicate. Moreover, reefs surrounding healthy populations of seabirds experienced a healthier and more resilient fish population than reef with no birds.

“There is no example that is as clear cut and effective in enhancing the functioning of coral reefs in the face of climate change.”