More than a quarter of Australia's tropical seabirds nest on the Great Barrier Reef. As they feed entirely on marine resources, they transfer nutrients from the sea to the land (like islands) and being able to travel large distances, they also disperse seeds and nutrients from outer areas of the Reef to middle and inner areas.
Changes in the climate
Research has suggested that longer-term changes to weather patterns and atmospheric temperatures from season to season will have a significant impact on seabirds. It was recently revealed that day-to-day weather can also affect seabirds.
Evidence indicates that during frequent or intense ENSO (El Niño/La Niña-Southern Oscillation) events in tropical waters like the Great Barrier Reef, seabirds have fewer breeding cycles, slowed chick development and a decrease in nesting success. This is because the sea temperatures during ENSO events disrupt the nutrient cycling of the ecosystem, affecting the availability of food for seabirds.
The research suggests these wide-scale climate changes impacts already have a major effect on seabird populations in the Great Barrier Reef. A steady decline in most seabird species at Raine Island (the biggest seabird nesting colony in the Great Barrier Reef) has been recorded over the last 12 years. The cause is unknown, however in the absence of human interference and apparent good nesting conditions at the site, the most likely option is a decline in marine food resources due to the changing climate and over-fishing.
On a daily scale, a large body of evidence suggests that seabird foraging success (the amount of food they are able to access) is directly related to sea temperature. There is a correlation between sea temperatures and some seabird species' growth, where once the sea reaches these temperatures, those species do not grow. This is due to a lack of food, which has been caused by the sea temperature changing the distribution and range of prey for seabirds.
Storms and rainfall
Seabirds are one of the few Great Barrier Reef species in danger of immediate death during a cyclone or storm. Eggs and chicks are most likely to be harmed during a major storm, with the nest providing limited protection. Due to the loss of infants, species populations may take some time to re-establish following a cyclone, particularly when food availability is reduced and their habitats have been destroyed.
Sea Level Rise
Also threatening seabirds' habitats, where nesting takes place, is rainfall and sea level rise. These can cause erosion of the land, threatening plants and vegetation growth.