Coral reefs are colorful underwater forests which teem with life and act as a natural protective barrier for coastal regions. The fishes and plants which call them home belong to some of the most diverse ― and fragile ― ecosystems on the planet. Higher sea temperatures from global warming have already caused major coral bleaching events. Bleaching occurs when corals respond to the stress of warmer temperatures by expelling the colorful algae that live within them. Increased levels of atmospheric carbon dioxide result in higher levels of CO² in the water, leading to ocean acidification, which is also a threat to coral. As the oceans become more acidic, the corals' ability to form skeletons through calcification is inhibited, causing their growth to slow. Increasing sea levels caused by melting sea ice could also cause problems for some reefs by making them too deep to receive adequate sunlight, another factor important for survival.
(Adaptado de Coral Reefs, The National Wildlife Federation. Disponível em https://www.nwf.org/Wildlife/Threats-to-Wildlife/GlobalWarming/Effects-on-Wildlife-and-Habitat/Coral-Reefs.aspx. Acessado em 26/07/2017.)
Considerando o texto e seus conhecimentos, assinale a alternativa correta.
Os recifes de corais estão seriamente ameaçados pela combinação dos seguintes fatores: