[Coral-List] Black reefs

Forest Rohwer frohwer at gmail.com
Thu Sep 1 20:10:10 EDT 2011

Black reefs are associated with shipwrecks or other debris in this
region of the world. These sites are interesting both from a
conservation and scientific point of view. As a conservation issue,
they are amazingly destructive. Kingman, one of the jewels of the USA
coral reefs, has lost >1 km of the lagoon in less than 3 years. An old
wreck on Fanning atoll has killed about 10% of their reef.

Visually, the black reefs are some of the eeriest places I've ever
seen. The bottom is completely covered in different algae (including
cyanobacterial mats), the water is filled with marine snow, and dark
precipitate on the benthos (probably sulfur). We just published a
paper in ISME where we have recreate the precipitate, cloudiness, and
coral death in microcosms by combining rubble from the black reefs,
with corals and an iron addition. Addition of antibiotics blocks the
coral death, precipitate, and marine snow, suggesting a microbial

The black reefs are probably caused by iron-enrichment from the wrecks
and debris. We think black reefs are specific to non-emergent coral
reefs, where iron is a limiting nutrient. Our current model is that
iron stimulation of algae leads to increased microbial activity and
coral death. In support of this, metagenomic analysis of the microbial
community showed an enrichment of iron-related pathogenicity factors.

If you are interested in the science, the please see the ISME journal

If you are interested in conservation, then please help us petition
the congress to support removal of the wrecks and debris. Please
contact Emily Douce <Emily.Douce at marine-conservation.org> at the
Marine Conservation Biology Institute.

To see how messed up these sites are, please look at the National
Geographic write up

Sorry for the long post,
Forest Rohwer
frohwer at gmail.com

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