While attention concerning impacts of predicted acidification of the world's oceans has focused on calcifying organisms, non-calcifying plankton may also be vulnerable. In this project, the investigator will evaluate the potential for impacts of ocean acidification on the reproductive success of three species of planktonic copepods in the genus Calanus that are prominent in high latitude oceans. C. finmarchicus dominates the mesozooplankton biomass across much of the coastal and deep North Atlantic Ocean. C. glacialis and the larger C. hyperboreus are among the most abundant planktonic copepods in the Arctic Ocean. Previous research showed that hatching success of C. finmarchicus eggs was severely inhibited by increased CO2 and lower pH in seawater, but only tested at an extreme level. Preliminary results in the investigator's laboratory indicate that hatching success of C. finmarchicus is substantially reduced at increased seawater CO2 concentrations corresponding to pH levels between 7.9 and 7.5. Predictions of likely decline of surface pH levels to 7.7-7.8 over the next century raise questions about impacts on Calanus population dynamics if these preliminary results are confirmed. C. finmarchicus, for example, is presently at the southern edge of its range in the Gulf of Maine. The combination of higher surface layer temperature and lower pH may inhibit reproductive success during the late summer/fall bloom, which the PI hypothesize is critical to sustain the overwintering stock in this region. The investigators will collect C. finmarchicus females from the Gulf of Maine and, with the assistance of Canadian colleagues, C. glacialis and C. hyperboreus females from the deep lower St. Lawrence Estuary. They will conduct laboratory experiments in which hatching success, development and growth of Calanus nauplius stages are measured in controls of natural seawater and at a series of treatments in which CO2 concentrations, pH and temperature are rigorously controlled to represent possible future states of the northern ocean. The investigators will measure present surface and deep pCO2 and pH across the Gulf of Maine, including its deep basins, during a research cruise. The study will evaluate the hypothesis that predicted levels of CO2 increase in the northern ocean will impact population dynamics of the Calanus species. Using the results from the research cruise and a recently developed 1-D, Individual-Based life cycle model, the PI will explore in detail scenarios of impact of higher temperature and lower surface and deep pH on population dynamics of C. finmarchicus in the Gulf of Maine.
Broader impacts: The lipid-rich Calanus species are considered key intermediary links between primary production and higher trophic levels in North Atlantic and Arctic Ocean food webs. Impacts of higher surface temperature and lower pH on reproductive success may potentially lead to profound changes in energy transfer and structure of pelagic ecosystems in the northern oceans. In the Gulf of Maine, C. finmarchicus serves as primary prey for herring, sand lance, and mackerel, as well as the endangered northern right whale, warranting thorough evaluation of ocean acidification effects on its population dynamics. This research will provide cross discipline training to a graduate student and undergraduate student interns. Data will be deposited in a recognized data archiving center and results disseminated through presentations at scientific meetings and peer reviewed research articles. Public outreach will be planned as part of the Gulf of Maine Research Institute community activities, including learning opportunities associated with the Cohen Center for Interactive Learning directed at fifth and sixth graders in the state of Maine.
It is well established that carbon dioxide (CO2) concentrations in the ocean are increasing as a consequence of rising CO2 levels in the atmosphere. Due to a series of chemical reactions in seawater, higher CO2 concentrations result in a lower pH, more acidic surface ocean. This National Science Foundation award addresses concerns about the long term effects of this change on marine life. Research supported by this award investigated whether lower seawater acidity would affect planktonic animals that support the marine food web in the coastal and deep North Atlantic Ocean. One species of zooplankton, the planktonic marine copepod, Calanus finmarchicus, is particularly important in coastal ocean food webs on both sides of the North Atlantic Ocean. This energy rich species, about the size of a grain of rice, is the primary prey for herring and other forage fish as well as for the endangered northern right whale in the productive ecosystems of the Gulf of Maine including Georges Bank. It is also the foundation species supporting herring, cod and other groundfish species in the Norwegian Sea. A series of experiments conducted at the Darling Marine Center, University of Maine, and with Norwegian colleagues at the Austevoll Research Station near Bergen, Norway, did not find any significant effects of increased CO2/lower pH levels predicted to occur over the next century. C. finmarchicus grew just as well in tanks at pH 7.6 (the most severe prediction for year 2100) as in tanks using ocean water at today’s present CO2 concentrations. The species' feeding rates, growth rates, metabolism and the hatching success of its eggs were not signficantly different between the present day and representative future CO2/pH conditions. In the Gulf of Maine, C. finmarchicus resides at the southern edge of its subarctic range. Over the past decade, temperatures have been warming in the Gulf of Maine at a rate that is 10-20 times faster than the average over the past century. Research supported by this award indicates that rising temperature, changes to transport from Canadian waters where Calanus is abundant and the timing of winter-spring blooms of planktonic algae will be more important than ocean acidification in determining whether this key species will persist in the Gulf of Maine in the coming decades.
