How does rising atmospheric CO2 affect marine organisms?

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The Climate Envelope Concept Is Not Applicable to the Real World
Wieters, E.A., Medrano, A. and Quiroga, G. 2013. Spatial variation in photosynthetic recovery of intertidal turf algae from acute UVB and temperature stress associated with low tides along the central coast of Chile. Journal of Experimental Marine Biology and Ecology 449: 340-348.

The authors write that "ecological consequences of punctuated, extreme climate events depend largely upon species' physiological capacity to tolerate and recover from such stressful events," but they say that "physiological responses of intertidal organisms to repetitive exposure to severe conditions using natural patterns are rarely explored, and we know little about how physiological sensitivity within a species varies over local scales or among natural populations, making it difficult to extrapolate results to the naturally variable environmental conditions encountered in the field."

What was done
In exploring this dilemma, Wieters et al. say they simulated "realistic scenarios of the exposure of the turf-forming alga (Gelidium chilense) to atmospheric stressors (UVB and temperature) associated with natural mild or harsh weather conditions that occur when summertime midday low tides coincide with unusually calm seas and particularly warm, sunny days along the central Chilean coast."

What was learned
The three Chilean researchers found that (1) "sudden, short-term exposure to artificial UVB radiation during daytime low tides represents a strong stress factor for Gelidium turf algae as measured by the changes in maximal photosynthetic quantum yield," that (2) "repetitive exposure over a period of five days, as it occurs naturally during spring-summer days, can critically compromise the ability of the fronds to recover once the stressor is removed," but in contrast that (3) "while increased aerial temperature had important effects on the photosynthetic system, this source of stress had no lasting effects on the fronds' capacity to recover, nor did it modify the UVB effects on photosynthesis," and that (4) "the ability of turf to recover from UVB-induced damage to the photosynthetic apparatus differed between tidal heights and among populations from different sites along the central coast."

What it means
Wieters et al. conclude their paper by stating that their study "adds to growing empirical evidence that physiological traits that determine a species' sensitivity to environmental stress vary in a complex manner across its distributional range (e.g. Gilman et al., 2006; O'Neill et al., 2008; Sorte et al., 2011)." And they say that the data they collected suggest that "traits that buffer turf ability to recover rapidly from acute stress events vary over meso-scales of 10s-100s of kilometers along the coast, challenging the relevance of predictive methods that view physiological traits as fixed within a species (e.g. species distribution models, 'climate envelope')."

Gilman, S.E., Wethey, D.S. and Helmuth, B. 2006. Variation in the sensitivity of organismal body temperature to climate change over local and geographic scales. Proceedings of the National Academies of Science USA 103: 9560-9565.

O'Neill, G.A., Hamann, A. and Wang, T. 2008. Accounting for population variation improves estimates of the impact of climate change on species' growth and distribution. Journal of Applied Ecology 45: 1040-1049.

Sorte, C.J.B., Johns, S.J. and Miller, L.P. 2011. Geographic variation in temperature tolerance as an indicator of potential population responses to climate change. Journal of Experimental Marine Biology and Ecology 400: 209-217.

Reviewed 6 August 2014