How does rising atmospheric CO2 affect marine organisms?

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Coral-Algal Competition: The Impact of the Presence of Humans
Barott, K.L., Williams, G.J., Vermeij, M.J.A., Harris, J., Smith, J.E., Rohwer, F.L. and Sandin, S.A. 2012. Natural history of coral-algae competition across a gradient of human activity in the Line Islands. Marine Ecology Progress Series 460: 1-12.

The authors write that "competition between corals and benthic algae is prevalent on coral reefs worldwide and has the potential to influence the structure of the reef benthos." They also state that human activities may influence the outcome of these interactions, and that "this type of change in competitive dynamics is a potential mechanism driving coral-algal phase shifts."

What was done
To learn more about this phenomenon, Barott et al. surveyed the types and outcomes of coral interactions with benthic algae in the Line Islands of the Central Pacific, which ranged from "nearly pristine to heavily fished," where they observed "major differences in the dominant groups of algae interacting with corals between sites, and the outcomes of coral-algal interactions."

What was learned
In the words of the seven scientists, "corals were generally better competitors against crustose coralline algae regardless of location, and were superior competitors against turf algae on reefs surrounding uninhabited islands." But on reefs surrounding inhabited islands, they found that "turf algae were generally the superior competitors."

What it means
The final and ultimate conclusion of Barott et al. is that "human disruption of the reef ecosystem may lead to a building pattern of competitive disadvantage for corals against encroaching algae, particularly turf algae, potentially initiating a transition towards algal dominance." And thus it would appear that the mere presence of humans along a seacoast - and the host of normal daily activities in which they engage - ultimately leads to the demise of any corals that may have been indigenous to that coastline, which further suggests that the global phenomenon of gradually degrading coral reefs need not be so universally associated with ocean acidification and global warming. Mankind's much more mundane activities may well be the primary cause of the planet-wide degrading of earth's coral reefs.

Reviewed 23 January 2013