Tropical Seabirds Affect Coral Reefs
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Biologists have often wondered why being 250 times higher than islands with following coral die-backs, such as the large- coral reefs are among the most diverse and rats, with knock-on effects for the islands’ scale coral bleaching that occurred in the productive habitats on earth, even though plants and animals. area in 2016. they occur in largely nutrient-poor tropical The study showed that these differences Parrotfish feeding also creates sand, oceans. Graham et al. suggest that seabirds extend to adjacent coral reef communities, which is important for maintaining the provide part of the answer. Their study with algae, sponges and reef fish all bene low-lying atolls. Thus seabirds indirectly took advantage of an unfortunate natural fiting from nutrient inputs from seabirds. assist in sustaining their own breeding sites experiment created by the introduction Reef fish are more abundant and grow – an increasingly important function as of rats to some islands in the Chagos Ar- faster at islands with seabird colonies. Im- climate change drives sea levels higher. The chipelago in the Indian Ocean, about 500 portantly, the researchers found that two study concludes that rodent eradications kilometres south of the Maldives. Rats key ecological processes critical for coral should be prioritised as a conservation are efficient predators of seabird eggs and reef health are enhanced at islands with tool not only to bolster threatened seabird chicks, and even kill adults of smaller seabirds: grazing pressure is three times populations and restore the delicate terres- species. As a result, islands with rats have greater and the removal of dead coral by trial island ecosystems, but also to promote virtually no breeding seabirds compared parrotfish is almost four times greater. the conservation of coral reefs, which are to rat-free islands. This results in the nu- Both processes promote coral settlement home to so much marine biodiversity. trient content of soils on rat-free islands and are crucial to allow reefs to recover PETER RYAN
chris jones seabird saviours Tropical seabirds affect coral reefs
lthough the oceans make up 70 per are especially large in areas where there are Nutrient imports by seabirds also affect cent of the world’s surface, only few islands. inshore marine communities on islands. In three per cent of bird species make The high densities of seabirds breeding the 1980s, research by Phil Hockey, Alison theirA living at sea. One reason why seabirds on islands play a key role in shaping the Bosman and George Branch revealed the are much less diverse than terrestrial spe- islands’ terrestrial ecology. In addition to complex web of interactions that results cies is the requirement to return to land their physical impacts through trampling from nutrient runoff from guano islands to breed. Although seabirds are the most and/or nest construction, seabirds import off the west coast of South Africa. Simi- stand out Chris Oosthuizen/British Ecological Society mobile organisms on earth, their ability marine nutrients through their faeces (and, larly, Anne Treasure recently modelled r Chris Oosthuizen of the University the department’s Mammal Research conservation messages,’ says Oosthui- to fully exploit marine ecosystems is lim- to a lesser extent, feathers and carcasses), the impact on coastal communities of the of Pretoria’s Department of Zoology Institute, was chosen as the overall zen. ‘Although the global population ited to some extent by the distribution of with knock-on effects for the plants and hundreds of tonnes of nitrogen and phos- Dand Entomology recently won the British winner with his image of a lone adult of King Penguins is large, populations oceanic islands. Seabirds breed in colonies animals found on islands. Some of the best- phorus excreted each year by seabirds at Ecological Society’s annual photography King Penguin standing among a crowd inhabiting islands around the Antarctic for a variety of reasons, but their colonies studied examples are in the Gulf of Mexico, South Africa’s Prince Edward Islands. competition, Capturing Ecology. of chicks on the remote subantarctic face an uncertain future. Many seabirds where Gary Polis and his colleagues showed Now Nicholas Graham and his col- The independent judging panel Marion Island, which is part of the are more endangered than elephants above Large seabird colonies, such as this that islands with seabird colonies had plants leagues have shown the importance of comprised six eminent ecologists and Prince Edward Islands. and rhinos, and deserve the same at- Sooty Tern colony, import nutrients that im- with a higher nutrient content, as well as tropical seabird colonies on coral reef award-winning wildlife photographers. ‘Photography is a key science engage- tention that these conservation icons pact the surrounding reef habitats as well as greater abundances of invertebrates, than ecosystems in the Indian Ocean (Nature Oosthuizen, a postdoctoral fellow at ment tool that can convey important receive,’ he says. terrestrial ecosystems. similar islands lacking seabirds. 559: 250‒253).
10 african birdlife january/february 2019 news & views 11