title: Black reefs: iron-induced phase shifts on coral reefs.
abstract: The Line Islands are calcium carbonate coral reef platforms located in iron-poor regions of the central Pacific. Natural terrestrial run-off of iron is non-existent and aerial deposition is extremely low. However, a number of ship groundings have occurred on these atolls. The reefs surrounding the shipwreck debris are characterized by high benthic cover of turf algae, macroalgae, cyanobacterial mats and corallimorphs, as well as particulate-laden, cloudy water. These sites also have very low coral and crustose coralline algal cover and are call black reefs because of the dark-colored benthic community and reduced clarity of the overlying water column. Here we use a combination of benthic surveys, chemistry, metagenomics and microcosms to investigate if and how shipwrecks initiate and maintain black reefs. Comparative surveys show that the live coral cover was reduced from 40 to 60% to <10% on black reefs on Millennium, Tabuaeran and Kingman. These three sites are relatively large (>0.75 km(2)). The phase shift occurs rapidly; the Kingman black reef formed within 3 years of the ship grounding. Iron concentrations in algae tissue from the Millennium black reef site were six times higher than in algae collected from reference sites. Metagenomic sequencing of the Millennium Atoll black reef-associated microbial community was enriched in iron-associated virulence genes and known pathogens. Microcosm experiments showed that corals were killed by black reef rubble through microbial activity. Together these results demonstrate that shipwrecks and their associated iron pose significant threats to coral reefs in iron-limited regions.
authors: Department of Biology, San Diego State University, San Diego, CA 92182, USA. lwegley@gmail.com
authors: Linda Wegley
authors: LW
authors: Kelly
authors: Katie L
authors: KL
authors: Barott
authors: Elizabeth
authors: E
authors: Dinsdale
authors: Alan M
authors: AM
authors: Friedlander
authors: Bahador
authors: B
authors: Nosrat
authors: David
authors: D
authors: Obura
authors: Enric
authors: E
authors: Sala
authors: Stuart A
authors: SA
authors: Sandin
authors: Jennifer E
authors: JE
authors: Smith
authors: Mark J A
authors: MJ
authors: Vermeij
authors: Gareth J
authors: GJ
authors: Williams
authors: Dana
authors: D
authors: Willner
authors: Forest
authors: F
authors: Rohwer
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000254:growth & development*; D001105:Archaea / Q000235:genetics; D001419:Bacteria / Q000235:genetics; D057894:Coral Reefs; D015698:Genomic Library; D005843:Geography; D007501:Iron / Q000009:adverse effects / Q000737:chemistry*; D056186:Metagenomics; D010140:Pacific Ocean; D000461:Rhodophyta / Q000737:chemistry; D012623:Seawater / Q000737:chemistry; D012624:Seaweed / Q000737:chemistry*; D012767:Ships; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors; D007501:Iron