MEPS 587:73-80 (2018)  -  DOI: https://doi.org/10.3354/meps12421

ABSTRACT: The rate of change in ocean carbonate chemistry is a vital determinant in the magnitude of effects observed. Benthic marine ecosystems are facing an increasing risk of acute CO₂ exposure that may be natural or anthropogenically derived (e.g. engineering and industrial activities). However, our understanding of how acute CO₂ events impact marine life is restricted to individual organisms, with little understanding for how this manifests at the community level. Here, we investigated in situ the effect of acute CO₂ enrichment on the coralline algal ecosystem—a globally ubiquitous, ecologically and economically important habitat, but one which is likely to be sensitive to CO₂ enrichment due to its highly calcified reef-like structures engineered by coralline algae. Most notably, we observed a rapid community-level shift to favour net dissolution rather than net calcification. Smaller changes from net respiration to net photosynthesis were also observed. There was no effect on the net flux of DMS/DMSP (algal secondary metabolites), nor on the nutrients nitrate and phosphate. Following return to ambient CO₂ levels, only a partial recovery was seen within the monitoring timeframe. This study highlights the sensitivity of biogenic carbonate marine communities to acute CO₂ enrichment and raises concerns over the capacity for the system to ‘bounce back’ if subjected to repeated acute high-CO₂ events.

KEY WORDS: Calcification · Photosynthesis · Community · Ecosystem · Maerl bed · Carbon dioxide · Acidification