Antarctic Sea Ice Changes Affect Krill, the Marine Food Base

by Cameron Lukos

Flores et al. 2013, hoped to create a synoptic investigation that showed seasonal changes in depth distribution of macrozooplankton and micronekton and their relationship to environment. They used data from three different expeditions that were part of a larger multi-year experiment that sailed the Lazzarev Sea collecting data on Antarctic krill in the Lazzarev Sea, creating an inventory of the pelagic macrozooplankton and micronekton from the surface down to 3000 meters, and exploring the seasonal changes in depth distribution and the relationship between communities and environmental drivers. The samples were collected via trawl nets at varying depths up to 3000 m and were done at different times of the year in order to run statistical analysis. Flores et al. found that the majority of the species sampled were found in the deep layer at depths that have not previously been studied, but there also was a higher number of species in the epipelagic layer than has been previously recorded. The higher richness in the epipelagic layer may confirm that the differences in species composition were caused by higher sampling effort or by species avoiding the surface layer. When the authors compared seasons with depth layer there were significant differences. In one instance there was a large dissimilarity between the surface layer and the overlapping epipelagic layer in each season.

Flores H., Hunt B., Kruse S., Pakhomov E., Siegel V., van Franeker J., Strass., Van de Putte A., Meesters E., Bathmann U., 2014. Seasonal Changes in the Vertical Distribution and Community Structure of Antarctic Macrozooplankton and Micronekton. Deep- Sea Research 1 84, 127–141.

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Rising Temperatures will Affect Primary and Secondary Production and Change the Nature of Pelagic-Benthic Species Relationships in the Pacific Arctic and Sub-Arctic

As temperatures rise due to global warming, changes in the formation of sea ice and water temperature in the Pacific Arctic will influence the entire marine ecosystem. A reduced amount of sea ice cover and an earlier retreat is predicted to either increase or decrease primary production. Warmer water temperatures and the possible increase in phytoplankton available as nutrients are causing a shift in the species composition of zooplankton, the secondary producers. Because conditions are increasingly favorable further north, zooplankton species that would normally be found in more temperate waters have been recorded in the Pacific Arctic and Sub-Arctic (Grebmeier 2012). While Arctic zooplankton do not consume the majority of the primary production nutrients, the newcomers do, leaving less carbon available for the benthos region (Grebmeier 2012). This may be causing a decrease in major groups of benthic fauna such as bivalves, amphipods, polychaetes, and sipunculids, which in turn affects species’ population density and growth rates up trophic levels, including the Pacific walrus, California gray whale, and spectacled eider. Correspondingly, pelagic organisms may begin to increase in number (Grebmeier 2012). Continual monitoring and additional studies are being conducted by several organizations to keep track of the changing nature of Arctic marine ecosystems.-Katherine Recinos

Grebmeier, Jacqueline M., 2012. Shifting Patterns of Life in the Pacific Arctic and Sub-Arctic Seas. Annual Review of Marine Science 4, 63–78.

Jacqueline Grebmeier used data from a series of other studies to illustrate the changes taking place in Pacific Arctic and Sub-Arctic. The formation and melting of sea ice is intricately connected with seasonal phytoplankton blooms and chlorophyll a levels. Phytoplankton blooms begin as the sea ice starts to melt. There are two opposing theories on the effects of earlier ice degradation caused by global warmer. The first is that lack of corresponding sunlight will inhibit phytoplankton blooming. The second hypothesizes that the additional time gained will allow for increased phytoplankton blooming. Data may prove the second to be true. Increased primary production and warmer water temperatures are fueling the migration of larger Pacific zooplankton to northern Arctic regions. This is changing the ecosystem there as the new zooplankton consume more nutrients so fewer nutrients make their way to the benthos from the pelagic . Also, the species composition of pelagic zooplankton will differ because the new zooplankton cannot survive Arctic winter temperatures.

Grebmeier goes on to demonstrate the lack of nutrients in the benthic by citing studies on sediment community oxygen consumption which show carbon usage in the benthos. Because the area in question is “benthic-dominated,” reduced benthic nutrient supplies will negatively impact populations of key benthic species such as those mentioned above. These species are the main food source for larger marine predators. Grebmeier presents the example of bivalves in the northern Bering Sea. Spectacled eiders, a type of sea diving duck, feed on them. A decrease in bivalves has led to an observed decrease in spectacled eiders. “Clustered community” interactions are common in the Pacific Arctic and Sub-Arctic so direct effects such as this would significantly affect species populations, growth rates, and ecosystems.

Grebmeier stresses the effects that changes in species populations and distribution could have on higher trophic levels. Walruses, gray whales, and other species are beginning to exhibit different behaviors to cope with environmental changes. Fish and invertebrates native to further south in the Pacific are also being observed in the Arctic and Sub-Arctic regions. This could stimulate the same type of competition between native and non native species seen in zooplankton population.

Grebmeier concludes by mentioning several initiatives including the Circumpolar Biodiversity Monitoring Program (CBMP) and the Pacific Arctic Group’s Distributed Biological Observatory (DBO), that are monitoring Arctic ecosystems. Specific location studies at stations and transects are especially useful methods. International cooperation is necessary for effective study and preservation.