Dr. Jacqueline Grebmeier's presentation on marine ecosystem impacts in warming Arctic waters
built upon both the information about the physical aspects of Arctic ice given to us by Dr. Perovich, and information about Arctic biota provided by Dr. Kelly. Dr. Grebmeier's lecture examined how the changing duration and extent of sea ice is affecting the Arctic's bottom-dwelling organisms and the subsequent impact on biota that depend them.
Changing timing and location of sea ice has important implications for primary production, and this
variable production has crucial consequences as it sinks to supply the benthos. Dr. Grebmeier emphasized that pelagic and benthic processes are intimately intertwined, and that benthic fauna can be an excellent indicator of climate change and reflect larger biological processes.
Drawing upon the North Bering Sea time series study that was conducted, Dr. Grebmeier
discussed one case study of St. Lawrence Island, in which a species of bird, the Spectacled Eider, has been declining. This bird dives to the bottom to retrieve bivalves as its food supply. Benthic data from 1973-2004 was examined to try to figure out if changes in bivalve supply might be affecting the eider population. It was discovered that there is a potential restructuring of the marine ecosystem taking place, as there has been progressively earlier retreat of sea ice, a decrease in carbon supply to the benthos, and a decrease in benthic biomass. It was also observed that there has been a decline in bivalves belonging to the Nuculanidae family, which are large and well-Iiked by the eiders, and an increase in the level of bivalves in the Nuculidae family, which are less nutritious and harder for the eiders to gather. This change in population structure in the benthos may be what is driving the decline in the Spectacled Eider.
Dr. Grebmeier also drew upon other faunal change examples and their implications. For instance,
data has shown that as Arctic temperatures have been warming, populations of Pollack and salmon have been shifting north, and this resulted in the presence of 10 million new salmon in the North Bering Sea in 2004. This change will have important fisheries considerations.
In another example, in the Chirikov Basin, there has been a drop in benthic productivity since the 1990s, including a decline in biomass and reduction of amphipods. This, in turn, has led to a shift in range of Gray Whales, which have now moved to north of the Bering Strait and are facing increasing confrontation with people as they encroach on human hunting grounds. The whales can be aggressive and have been known to flip hunters out of boats.
In addition to these examples, Dr. Grebmeier also discussed one of her chief projects, the Western
Arctic Shelf-Basin Interactions (SBI) Project, which is an ongoing multi-year project that focuses on the Chukchi and Beaufort Sea shelf and basin region, and seeks to elucidate the impacts that global change (such as melting ice) have on the biology, chemistry, and physics of Arctic ecosystems. This includes investigations of increasing levels of CO2 and the corresponding impact on calcium carbonate animals, and also in the type of carbon being delivered to the benthos due to nutrient shifts. This is an extremely rich biological area, and will yield useful results that range on information from benthos to walruses.
Dr. Grebmeier closed her lecture by reiterating that changes in the Arctic and its sea ice
(including earlier spring transition and increasing seawater temperatures) are generating changes in the timing of productivity and grazing in the marine ecosystem. This in turn, is altering carbon export to benthic and trophic structures and generating important change in these structures. Data gathered from time series stations has shown significant decreases in carbon deposition and decreased biomass since the early 1990s, with those lower levels being maintained in the 2000s, and changes in bivalve community composition in the 2000s.
Grebmeier concluded by emphasizing that time series observation sites will play an increasingly critical role for identifying the nature of the changes taking place in marine ecosystems in the Arctic in years to come. |
