Ocean acidification induces multi-generational decline in copepod naupliar production with possible conflict for reproductive resource allocation

Climate change, including ocean acidification (OA), presents fundamental challenges to marine biodiversity and sustained ecosystem health. We determined reproductive response (measured as naupliar production), cuticle composition and stage specific growth of the copepod Tisbe battagliai over three generations at four pH conditions (pH 7.67, 7.82, 7.95, and 8.06). Naupliar production increased significantly at pH 7.95 compared with pH 8.06 followed by a decline at pH 7.82. Naupliar production at pH 7.67 was higher than pH 7.82. We attribute the increase at pH 7.95 to an initial stress response which was succeeded by a hormesis-like response at pH 7.67. A multi-generational modelling approach predicted a gradual decline in naupliar production over the next 100 years (equivalent to approximately 2430 generations). There was a significant growth reduction (mean length integrated across developmental stage) relative to controls. There was a significant increase in the proportion of carbon relative to oxygen within the cuticle as seawater pH decreased. Changes in growth, cuticle composition and naupliar production strongly suggest that copepods subjected to OA-induced stress preferentially reallocate resources towards maintaining reproductive output at the expense of somatic growth and cuticle composition. These responses may drive shifts in life history strategies that favour smaller brood sizes, females and perhaps later maturing females, with the potential to profoundly destabilise marine trophodynamics.

EP podcast: Ocean acidification (audio)

Human beings start domesticating crops only 12,000 or so years ago. Written history begins about 5,000 years ago. The modern era dates from — when? — maybe 100-200 years ago. Perhaps it’s no surprise, then, that we have some difficulty internalizing the idea that our burning carbon has, already, set into motion dramatic changes to the entire planet’s environment, changes that will persist for 100,000 years, or more. One of these is ocean acidification. Dr. Bärbel Hönisch and her co-authors of the paper “The Geological Record of Ocean Acidification,” Science (2 March, 2012), show that the rate of change of ocean acidification is greater today, by at least an order of magnitude, than it has ever been during any period over the past 300,000,000 years. Rate of change, not absolute pH level, being what matters. The deep past includes, notably, a couple of rapid ocean acidification/mass extinction events. This therefore, not unreasonably, should be of concern. Thanks, Bärbel! Total runtime fifty minutes. Potius sērō quam nunquam.