Browsing by Subject "Food webs"
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Item Hydrological and ecological observations along the eastern Beaufort Sea coast of Alaska(2015-12) Harris, Carolynn Maxene; Dunton, Kenneth H.; McClelland, James W; Hardison, Amber KThe US Beaufort Sea coast is fringed by barrier islands, which enclose numerous bays and lagoons that provide habitat for migratory fish and waterfowl that are essential to the subsistence and culture of Iñupiat communities of northern Alaska. In the eastern Beaufort, in particular, residents of Kaktovik rely heavily on the high benthic productivity of these lagoon systems to support the fish and bird populations that they depend on for subsistence. We monitored aspects of hydrology and ecology in several lagoons in the eastern Alaskan Beaufort Sea coast from 2011 to 2014. Our hydrographic data from continuous in situ measurements of temperature and salinity revealed that lagoons possess unique regimes that vary seasonally and reflect unique hydrologic and geomorphic characteristics. H2O-δ18O and salinity measurements revealed that meteoric water is the dominant source of low-salinity water in all lagoons in June and August, though sea ice melt water was also present. Most differences among lagoons were caused by variation in circulation and connection to adjacent marine waters. We also used stable C and N isotopic analysis to determine trophic structure and assess dependence of fauna on terrestrial (CT) vs. marine sources of carbon, with particular focus on animals widely used by local subsistence hunters. Our mixing model results suggest that terrestrial carbon (CT) may be assimilated by upper trophic level consumers, though marine-derived C sources dominate. For example, 15 - 70% of polar bear and 0 - 60% of beluga whale carbon was of terrestrial origin. Our results suggest that 1) CT assimilated by benthic omnivorous invertebrates is transferred to the highest trophic levels in the Beaufort Sea, and 2) arctic cod are the most likely intermediary for transferring CT from lower to upper trophic levels.Item Trophodynamics of the benthic food webs in the Chukchi and Beaufort Seas, Alaska(2013-12) McTigue, Nathan David; Dunton, Kenneth H.The Chukchi and Beaufort Sea shelves host diverse and productive seafloor ecosystems important for carbon and nitrogen cycling for the Arctic Ocean. The benthic food web transfers energy from primary producers to high trophic level organisms (e.g., birds, fish, and mammals), which are important for cultural practices and subsistence hunting by Native Alaskans. This work focuses on the trophic ecology of arctic food webs through use of several different approaches. First, variation in the natural abundance of stable carbon and nitrogen isotopes facilitated the identification of trophic pathways and, subsequently, allowed the comparison of trophic guilds and food webs from the Chukchi and Beaufort Seas. Compared to water column and sedimentary organic matter end-members, second trophic level grazers and suspension feeders were conspicuously ¹³C-enriched throughout the Chukchi Sea, which supports the hypothesis that microbial degradation of organic matter occurred prior to metazoan assimilation. Second, food web recovery from disturbances caused by exploratory oil drilling at the seafloor that had occurred approximately 20 years prior were assessed in both the Chukchi and Beaufort Seas. Based on isotopic trophic niche overlap between organisms common to drilled and reference sites in the Chukchi and Beaufort Seas, the oil drilling sites had similar food web structure, indicating recovery from the activity associated with the drilling process. Third, photosynthetic pigment biomarkers were used to better understand the diagenetic process, specifically focusing on how both microbial and metazoan grazing pathways degrade organic matter in relation to seasonal sea ice retreat in the Chukchi Sea. The benthic macrofaunal and microbial food web caused rapid degradation of organic matter upon the initial pulse of microalgal food sources to the seafloor. These diagenetic pathways are linked to the ¹³C-enrichment of residual organic matter, which corresponds to the stable isotope values measured in the benthic macrofauna. Lastly, high-precision liquid chromatography and spectrophotometry were compared for estimating sedimentary pigments in the marine environment. Substantial differences in pheopigment (chlorophyll degradation products) concentrations were observed between the two techniques, suggesting the need for revisions to the monochromatic spectrophotometric equation that relates absorbance to pigment concentrations. One pheopigment, pheophorbide, was found to interfere with the accuracy of the spectrophotometric equation and caused the overestimation of pheopigments.