Collaborators: Andone Lavery (WHOI), Peter Wiebe (WHOI), Zhaohui 'Aleck' Wang (WHOI)A key problem facing both marine scientists and managers of ocean resources concerns the impacts on marine ecosystems of changing seawater chemistry associated with continued increases in atmospheric CO2. Absorption of anthropogenic CO2 by the oceans reduces seawater pH and the concentration of carbonate ion, in a process commonly referred to as ocean acidification.
Thecosome pteropods, commonly known as ‘sea butterflies,’ are a group of planktonic molluscs widely distributed in pelagic ecosystems of the world’s oceans that in many regions are a key prey item for higher trophic levels, including commercial fishes such as salmon. Thecosome pteropods form an aragonite (i.e., calcium carbonate) shell and are thus highly sensitive to the water column’s changing carbonate chemistry under ocean acidification, and particularly to the shoaling of the ‘aragonite compensation depth’ at which seawater becomes corrosive to aragonite. Relatively little is known, however, about the distribution, movements, and ecological role of pteropods, nor about the way in which they might be expected to respond to ocean acidification.
Through survey work employing a suite of sophisticated devices to sample pteropods and carbonate chemistry simultaneously, our project will capitalize on present-day variability in the aragonite compensation depth within and between the Atlantic and Pacific Oceans as a ‘natural experiment’ to address the hypothesis that pteropod vertical distribution, species composition, and abundance vary as the compensation depth becomes shallower; in this way, we seek to use current spatial differences in ocean chemistry to understand the likely impacts of future changes predicted to occur under continued ocean acidification. These hypotheses and objectives will be addressed through two cruises along survey transects between 35 and 50°N in the northwest Atlantic (in 2011) and northeast Pacific (2012) involving a combination of station-work and underway measurements, and a comprehensive array of instruments, including acoustic, optical, net, hydrographic, and carbonate chemistry sensors.