Shipwrecked? Have no fear ‘Black Reef’ microbial community shunts will engulf you!

Black reefs: iron-induced phase shifts on coral reefs.

L W Kelly, K L Barott, E Dinsdale, A M Friedlander, B Nosrat, D Obura, E Sala, S A Sandin, J E Smith, Mark J A Vermeij, G J Williams, D Willner, F Rohwer (2011)

The ISME journal p. 1-12

The Line Islands are calcium carbonate coral reefs >0.75km² in size. These reefs are situated in iron poor regions of the central pacific. These islands are uninhabited and are not exposed to point sources of pollution, apart from shipwrecks, which have been documented on several of the line islands and surrounding reefs. There are also shipwrecks on carbonate atolls throughout the pacific.

In the Line islands, areas surrounding the shipwrecks become Black Reefs. They were noted by Kelly et al. 20011, to be characterized by high levels of turf and macroalgae, cyanobacterial mats, corallimorphs and an extensive loss of corals and crustose coralline algae. It was noted by the authors that similar community phase shifts in response to shipwrecks have been documented on other coral reefs. Literature flags up Rhodactis howesii has spread over coral reef terrace on Palmyra atoll, which also had a shipwreck (work et al., 2008). Authors referenced several cases of community phase shifts hypothesised to occur as a result of shipwrecks. It was also documented in the introduction that iron fertilization from the aftermath of wildfires in Indonesia (iron rich ash) enriched the coastal waters, which led to an explosion of dinoflagellates that suffocated and killed 100% of corals. Perhaps due to these literature insights and the fact that iron concentration is extremely limited in the Line Islands the authors hypothesised that: 1) Iron limits primary production of algae and cyanobacteria on central pacific coral atolls where there are no emergent basaltic rocks; 2) on these atolls shipwrecks associated iron release, releases these primary producers from bottom up control and 3) the resulting communities of fleshy algae cyanobacteria either directly compete with the coral or they promote bacteria that kill corals.

Kelly et al. used a combination of benthic surveys, chemistry, metagenomics and ex-situ microcosm experiments to investigate their hypotheses of shipwrecks potentially initiating and perpetuating Black Reefs.

Their research found that live coral cover was reduced from 60% to <10% on several of the Black Reef sites. There were increased abundances of turf algae, macroalgae, pathogen-like microbes and virulence factor genes (when compared to a virulence factor database) and corallimorphs in the Black Reefs when compared to the control sites. The water surrounding the polluted sites was found to be cloudy with elevated concentrations of organic matter. They provided evidence that the phase shifts occur rapidly as a result of studying and documenting the natural history of the Black Reefs. Iron concentrations from algae tissues were discovered to be six times higher than in algae collected from reference sites. Ex-situ experiments demonstrated that corals were killed by black reef rubble from microbial activity.

The authors suggest that benthic algal overgrowth combined with iron enrichment is a mechanistic stimulation of heterotrophic microbes, as result of organic carbon being released by benthic algae. Which in turn leads to asphyxiation of the coral. They also infer from their mesocosm experiments that Black Reefs rubble algae were lethal to corals without iron enrichment, which they suggest is a prediction (indicator) of the long term consequences of these phase shifts after the removal of iron.

Kelly et al. conclude with the following main points:

1. Due to the remote location data sets for analysis were incomplete for all the study sites. 2. Further metagenomics analysis of microbial communities would reveal more about the pathogenic bacteria. 3.comparasons of iron concentrations between reference sites and Black Reefs sites were not carried out on the same species. 4. The spreading pattern of the Black Reefs adopts a ‘ratchet like mechanism’; allowing the Black Reef to crawl along, as a result of a re-mineralization process were upon the death of the polluted microbial algal mats, the iron is made available to further the Black Coral. 6.That the new pathogenic microbial community phase shift is maintained following a shipwreck by self-reinforcing feedback mechanisms.

Their evidence provides significant results that shipwrecks detrimentally impact corals and associated algae in iron-limited regions. The evidence is amassed from a variety of techniques , microbial abundance counts to virulent gene comparisons . This use of multiple investigating strategies lead to a variety of findings that supported their hypotheses. The paper contains various grammatical errors, which confused me as to exactly what their findings were e.g. in the abstract. As they suggested themselves further metagenomics analysis of the microbial community would have been interesting. The further application of molecular techniques (FISH and DGGE) would have potentially revealed more about the pathogenic bacteria thought to be involved in the coral death. To conclude their research held substantial weight that shipwrecks cause iron induced phase shifts! The final recommendation was to remove the shipwrecks before detrimental ecological impact sets in. This concluding recommendation seems rather difficult to reinforce and would incur considerable cost, which in my opinion the merchant navy responsible for the vessel should take the damage not the corals. Perhaps call me idealistic but to me it seems a feasible responsibility of a ‘commendable’ company. After all if you break down on motorway or any road in fact you don’t just get out and leave you car for good, unless you’re a proper w*****. I’m a strong believer in a low footprint mentality, evidence like this reaffirms my conviction.