Hofmann, G.E., J.P. Barry, P.J. Edmunds, R.D. Gates, D.A. Hutchins, T. Klinger, and M.A. Sewell. 2010. The effect of ocean acidification on calcifying organisms in marine ecosystems: an organism-to-ecosystem perspective. Annu. Rev. Evol. Syst. 41: 127-147.
The photographic time series from the coral reefs of Moorea provides some of the quantitative data MCR is collecting on how the reefs are changing through time. These pictures (both 0.5 x 0.5 m) from a site at 10 m depth on the north shore of the island show a representative area of reef in 2005 (left) and 2011 (right). Over this 6 year period, the reef changed dramatically after the coral was eaten by seastars (2007-2009) and broken by a cyclone (2010). Diversity matters -- nestled within the diverse assemblage on the left is a combination of winners and losers. The massive coral in the center of the left picture (a species of massive Porites) appears to be one of the winners -- it endures cyclones and is less affected by ocean acidification -- as is the yellow fire coral (Millepora spp.) in the lower center of the picture on the right. Understanding the mechanisms that allow these species to survive will be critical to understanding the kinds of reefs that will occur in the future.
Experiments by MCR scientists are elucidating the fundamental mechanisms determining which reef organisms are winners and which are losers under the current onslaught of environmental assaults. In an experiment conducted in 2010, the calcification of a species of massive Porites (a potential "winner") was compared to the calcification of Porites rus under a variety of conditions designed to simulate the conditions on coral reefs in the future. Critically, the species differ strikingly in the way that they respond to high CO2 concentrations (HCO2, = 780 µatm) versus low CO2 concentrations (HCO2 = 413 µatm) under combinations of high temperature (HT = 29.4°C) and low temperature (LT = 25.4°C) (left graph shows mean ± SE, n = 10). These results illustrate the complexity of responses to elevated CO2 concentrations in seawater that can be expected: the massive Porites is hardly affected, while the growth of P. rus is greatly reduced during high summer temperatures. The graph on the right shows the calcification responses of the crustose coralline alga Hydrolithon onkodes collected from different environments to ambient, elevated, and variable seawater CO2 treatments. Calcification is depressed in both the elevated and variable treatments, however algae collected from downstream environments where CO2 levels in seawater vary considerably each day (due to reef metabolism) show an intermediate response, suggesting that some acclimatization to higher CO2 levels might be possible.
Left: P.J. Edmunds in prep. Right: R.C. Carpenter in prep.