[Coral-List] Black reefs

David Obura dobura at cordioea.org
Wed Sep 7 09:44:43 EDT 2011

HI all,

I think the key phrase in Forest's post was "emergent reefs". 

I have similarly used steel mesh, re-bar and other relatively raw-iron parts in the water in Kenya and not had any toxicity problems for corals, apart from the physical problems of the rust sloughing and thick bands of powdery oxide building up in some places. And I hadn't noticed any problems with shipwrecks ... until I dived in the iron-depleted central Pacific. In the Phoenix and Line islands, where there is low iron in the oceanic waters and no iron-bearing rock (as in e.g. the main Hawaiian islands, i.e. no 'emergent' rock other than carbonates), any iron artefacts or shipwrecks on the reefs clearly result in the 'black reef' phenomenon. 

The interesting thing about this case study to me is the illustration of what happens when you 'geo-engineer' and ecosystem - adding iron to oceanic waters to enrich planktonic production and sequester carbon may do that to some extent, but as in black reefs, it would likely completely change the nature of the ecosystem, very likely with many unintended consequences (such as, perhaps, a shut-down in the pathway that would leave to carbon sequestration).


David Obura

CORDIO East Africa
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