How does rising atmospheric CO2 affect marine organisms?

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Larval Development of Barnacles in a Future CO2-Enriched Ocean
Pansch, C., Schlegel, P. and Havenhand, J. 2013. Larval development of the barnacle Amphibalanus improvisus responds variably but robustly to near-future ocean acidification. ICES Journal of Marine Science 70: 805-811.

The authors write that "the bay barnacle Amphibalanus improvisus is (1) "a prominent filter-feeder in many fouling communities," (2) "globally widespread, occurring in shallow, tidal areas in both salty and brackish waters," and (3) "common throughout the Baltic Sea system, extending from near-full-salinity waters of the Skagerrak to nearly fresh waters of the Bay of Tothnia."

What was done
In two separate experiments conducted over two successive years, Pansch et al. first assessed larval survival and development while rearing nauplius larvae in 6-well plates over ten days in response to three different pH treatments (8.02, 7.80 and 7.59), while in the second experiment larval stage and size were assessed by rearing nauplius larvae in 5-l glass bottles over 6 days in response to two different pH treatments (8.09 and 7.80).

What was learned
Quoting the three scientists, "larval development of the barnacle was not significantly affected by the level of reduced pH that has been projected for the next 150 years," for "after 3 and 6 days of incubation, we found no consistent effects of reduced pH on developmental speed or larval size at pH 7.8 compared with the control pH of 8.1." Likewise, they say that "after 10 days of incubation, there were no net changes in survival or overall development of larvae raised at pH 7.8 or 7.6 compared with the control pH of 8.0." In all of their many individual trials, however, they determined "there was significant variation in responses between replicate batches (parental genotypes) of some larvae," with some batches actually responding positively to reduced pH."

What it means
Pansch et al. say their results suggest that "the non-calcifying larval stages of A. improvisus are generally tolerant to near-future levels of ocean acidification," and that "this result is in line with findings for other barnacle species and suggests that barnacles do not show the greater sensitivity to ocean acidification in early life history reported for other invertebrate species," while adding that the barnacle's "substantial genetic variability in response to low pH may confer adaptive benefits under future ocean acidification."

Reviewed 30 October 2013