Award: PLR-0944201

The Southern Ocean, the ocean that surrounds the continent of Antarctica, is thought to be the first in time to experience the deleterious effects of ocean acidification, the reduction of ocean pH due to the absorption of man-made carbon dioxide (CO2) by oceans. Understanding how changes in ocean pH alters the growth and survival of marine species is a core goal of research in polar oceans. Many of these organisms are key players in the food webs. And, although they are small and we are not very familiar with them, these organisms are key members of a healthy marine ecosystem in the Antarctic. The goal of this particular project was to study one such organism, in this case, an Antarctic sea urchin called Sterechinus nemayeri. A commonly found marine invertebrate in coastal regions, S. neumayeri is a grazing urchin and an important member of the marine community. The early life stages of S. neumayeri develop in seawater, forming small skeletons in the larval stage that are made of calcium carbonate. Interestingly, it is the formation of these "hard parts" that is challenged by ocean acidification. On one hand the low pH can cause actual dissolution of these calcium carbonate structures; it can also make them energetically difficult to form. Thus, when the larval urchins are in the water, they can act as small bioassays, telling us about how they are responding to a changing ocean. For this project, we wanted to determine how early stage urchins would respond to future ocean acidification. But first, we needed to know what the pH of the Southern Ocean is now. Here, we collected the first high-resolution pH data in near-shore Antarctica from spring to winter. These data were used to design our lab experiments. Observations from our pH sensors (called SeaFETs) revealed a seasonal increase of 0.3 pH units and short-term pH variability from December to April. Given the presence of (sub)seasonal pH variability, Antarctic marine species have an existing physiological tolerance of seasonal pH change that may influence adaptation to future acidification. Our lab experiments have shown that some aspects of development are resilient to low pH (e.g., gastrulation), but other processes such as fertilization and calcification are more sensitive. Overall, the project has revealed new data about the nature of the pH of todayÆs Southern Ocean, and has also shown us that some organisms living there will likely tolerate future acidification to some degree. One thing we do not know is whether future acidification, the rate at which the ocean pH changes, will out-strip the ability of marine organisms to adjust to or adapt to environmental change. Last Modified: 10/29/2014 Submitted by: Gretchen E Hofmann