Publication Date:
2016-02-27
Description:
Anthropogenic carbon dioxide (CO 2 ) emissions simultaneously increase ocean temperatures and reduce ocean surface pH, a process termed ocean acidification (OA). OA is expected to negatively affect the growth and physiology of many calcified organisms, but the response of non-calcified (fleshy) organisms is less well understood. Rising temperatures and p CO 2 can enhance photosynthetic rates (within tolerance limits). Therefore, warming may interact with OA to alter biological responses of macroalgae in complicated ways. Beyond thresholds of physiological tolerance, however, rising temperatures could further exacerbate negative responses to OA. Many studies have investigated the effects of OA or warming independently of each other, but few studies have quantified the interactive effects of OA and warming on marine organisms. We conducted four short-term independent factorial CO 2 enrichment and warming experiments on six common species of calcified and fleshy macroalgae from southern California to investigate the independent and interactive effects of CO 2 and warming on growth, carbonic anhydrase (CA) enzyme activity, pigment concentrations, and photosynthetic efficiency. There was no effect of elevated p CO 2 on CA activity, pigment concentration, and photosynthetic efficiency in the macroalgal species studies. However, we found that calcareous algae suffered reduced growth rates under high p CO 2 conditions alone, although the magnitude of the effect varied by species. Fleshy algae had mixed responses of growth rates to high p CO 2 , indicating that the effects of p CO 2 enrichment are inconsistent across species. The combined effects of elevated p CO 2 and warming had a significantly negative impact on growth for both fleshy and calcareous algae; calcareous algae experienced five times more weight loss than specimens in ambient control conditions and fleshy growth was reduced by 76%. Our results demonstrate the need to study the interactive effects of multiple stressors associated with global change on marine communities.
Print ISSN:
1054-3139
Electronic ISSN:
1095-9289
Topics:
Biology
,
Geosciences
,
Physics
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