[Coral-List] Ship wrecks and reefs?? [SEC=UNCLASSIFIED]

CARILLI, Jessica jes at ansto.gov.au
Wed Nov 28 17:42:38 EST 2012

I tried to send this to the list yesterday but did something wrong--so here goes again:

Dear All,

I think it is important to remember the original "Iron Hypothesis" by Martin (1990):

The key is that extra iron should stimulate algal growth [and perhaps contribute to bleaching susceptibility in this way, as discussed] in places where:
-there are abundant nutrients (P and N)
-there is not enough iron

These high-nutrient low-chlorophyll (HNLC) regions can be visualized by maps of surface nitrate (which should be used up by algae if not limited by iron or other micronutrients), and are places that have very low dust deposition. They are: the Southern Ocean, the central and eastern equatorial Pacific, and the north Pacific (see references below)

Maps of HNLC areas and dust deposition indicate that the Caribbean is not iron limited, probably largely due to dust supply; therefore additional iron supplied by shipwrecks, pier pilings, etc. should not stimulate additional algal growth because they are theoretically limited by other nutrients, or all nutrients are in sufficient supply and growth is limited by top-down control or other mechanisms instead.

So, it is not totally surprising that luxuriant coral growth occurs on newly available hard substrates outside the HNLC areas (I saw a nice mini-reef on a plane wreck in the middle of a sand apron in Honduras), even if these substrates are a source of iron. Within HNLC areas, it's a different story (recall the Black Reef discussion last year).

Jessica Carilli
Postdoctoral Fellow
Institute for Environmental Research, Australian Nuclear Science and Technology Organization


HNLC and dust maps nicely presented here: http://www.atmosphere.mpg.de/enid/1vv.html

Martin (1990) Glacial-interglacial CO2 change: The Iron Hypothesis. Paleoceangraphy: http://www.agu.org/journals/pa/v005/i001/PA005i001p00001/

Limitation by iron due to low dust supply in:
-equatorial Pacific: Kolber et al. (1994) Iron limitation of phytoplankton photosynthesis in the equatorial Pacific Ocean. Nature: http://www.nature.com/nature/journal/v371/n6493/abs/371145a0.html;
-Southern Ocean: Cassar et al. (2007) The Southern Ocean Biological Response to Aeolian Iron Deposition. Science: http://www.sciencemag.org/content/317/5841/1067.short

Kelly et al. (2012) Black reefs: iron-induced phase shifts on coral reefs. ISME: http://www.ncbi.nlm.nih.gov/pubmed/21881615

From: coral-list-bounces at coral.aoml.noaa.gov [coral-list-bounces at coral.aoml..noaa.gov] on behalf of John Ware [jware at erols.com]
Sent: Thursday, 29 November 2012 8:54 AM
To: coral-list at coral.aoml.noaa.gov
Subject: [Coral-List] Ship wrecks and reefs??

A quote from: Black reefs: iron-induced  phase shifts on coral reefs.
Linda Wegley Kelly et al., ISME, Mar 2012

"Here we use a combination of benthic surveys, chemistry, metagenomics
and microcosms to investigate if and how shipwrecks initiate and
maintain black reefs. ...   Together these results demonstrate that
shipwrecks and their associated iron pose significant threats to coral
reefs in iron-limited regions."

Contrasted with this from Alina Szmant's e-mail of 26Nov:

"FYI, every place I dive where there is metal structure (old ship hulls, navigation pilings etc) they are covered with nice looking corals of all species."

Am I the only one that sees some sort of disconnect here??

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