Tropical dead zones and mass mortalities on coral reefs.
Degradation of coastal water quality in the form of low dissolved oxygen levels (hypoxia) can harm biodiversity, ecosystem function, and human wellbeing. Extreme hypoxic conditions along the coast, leading to what are often referred to as "dead zones," are known primarily from temperate regions. However, little is known about the potential threat of hypoxia in the tropics, even though the known risk factors, including eutrophication and elevated temperatures, are common. Here we document an unprecedented hypoxic event on the Caribbean coast of Panama and assess the risk of dead zones to coral reefs worldwide. The event caused coral bleaching and massive mortality of corals and other reef-associated organisms, but observed shifts in community structure combined with laboratory experiments revealed that not all coral species are equally sensitive to hypoxia. Analyses of global databases showed that coral reefs are associated with more than half of the known tropical dead zones worldwide, with >10% of all coral reefs at elevated risk for hypoxia based on local and global risk factors. Hypoxic events in the tropics and associated mortality events have likely been underreported, perhaps by an order of magnitude, because of the lack of local scientific capacity for their detection. Monitoring and management plans for coral reef resilience should incorporate the growing threat of coastal hypoxia and include support for increased detection and research capacity.
Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama; AltieriA@si.edu knowlton@si.edu.
Andrew H
AH
Altieri
Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
Seamus B
SB
Harrison
Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.|Freie Universität Berlin, 12249 Berlin, Germany.
Janina
J
Seemann
Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
Rachel
R
Collin
Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062.
Robert J
RJ
Diaz
Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013 AltieriA@si.edu knowlton@si.edu.
Nancy
N
Knowlton
D000818:Animals; D037421:Anthozoa / Q000502:physiology*; D044822:Biodiversity; D003247:Conservation of Natural Resources; D057894:Coral Reefs; D010100:Oxygen / Q000032:analysis*; D010176:Panama; D011157:Population Dynamics; D014329:Tropical Climate; D060753:Water Quality
D010100:Oxygen
biodiversity; coral bleaching; dissolved oxygen; hypoxia; water quality