Figure 7. Zoeal stage 2 larval blue king crab were exposed to numerous pH level treatments.
Figure 8. Juvenile stage 1 blue king crab were exposed to numerous pH level treatments.
Scientists from the Shellfish Assessment Program at the Kodiak Laboratory have been conducting research in collaboration with scientists at the Auke Bay Laboratories to assess the effects of ocean acidification on blue king crab. In the past decade the potential affects of ocean acidification on calcifying organisms have been the focus of a number of studies. The 2007 reauthorization of the Magnuson-Stevens Fishery Conservation and Management Act recognized the importance of ocean acidification and recommended that the effects on the United States be studied.
Ocean acidification is the decrease in ocean pH due to the carbonate system response to increasing CO2 concentrations in the atmosphere and world’s oceans. Atmospheric CO2, rising since the beginning of the industrial revolution largely due to the burning of fossil fuels, has resulted in increased dissolution of CO2 into the ocean. This has triggered a decrease of carbonate ion concentration, thus limiting the ability of calcifying (carbonate dependent) organisms, such as corals and pteropods, to form support structures.
The fishery resources managed by NMFS in the North Pacific are among the most vulnerable to the effects of ocean acidification. The North Pacific has conditions less favorable for calcification due to the increased solubility of calcium carbonate at lower temperatures and the inflow of CO2-rich waters from deep ocean basins. As such, AFSC laboratories are ideally located to undertake research on ocean acidification and its impact on high latitude marine organisms.
Cold water corals with calcite skeletons provide important habitat for commercially valuable fish and crustaceans. Fish that may not be directly affected by changing pH may suffer indirectly if their food source is impacted, as would be the case with pink salmon that consume calcifying zooplankters such as pteropods. Crustaceans, such as the commercially valuable king and snow crabs, use calcite to harden chitinous exoskeletons.
In 2006 the Kodiak and Auke Bay Laboratories collaborated to investigate the effect of reduced pH on the calcium uptake, growth, and survival of the early life stages of blue king crab (Paralithodes platypus). Blue king crab larvae (Figs. 7 and 8 above) were exposed to seawater of three different pH levels: the ambient level at Kodiak and two lower pH levels adjusted using hydrochloric acid. Results indicated that lower pH negatively affected survival to and growth and calcium content of the first juvenile stage of blue king crab.
In 2007 we expanded the experimental design to include a broader pH treatment to reflect preindustrial oceanic pH levels and another low pH level. Additionally, we are assessing the progression of calcite and morphological development effects of acidification by sacrificing larvae at multiple developmental stages and taking calcite and morphological measurements.
Experiments are conducted in a controlled temperature setting at the Kodiak Fisheries Research Center. The Kodiak Laboratory will soon be home to a CO2 delivery system that will allow researchers to adjust the pH of treatment water with CO2. This system will better reflect the effects of changes in the carbonate system due to increases in CO2 on organisms than adjusting pH with hydrochloric acid. Kodiak Laboratory scientists are working with others in the AFSC to develop an AFSC ocean acidification research plan and will expand research to include additional crab species and life stages in future years.
