Trophic Dynamics In Marine Nearshore Systems Of The Alaskan High Arctic (Kelp, Laminaria, Carbon Isotope, Productivity)

Abstract

This dissertation describes two ecological studies in the arctic Alaskan nearshore zone: the productivity and growth strategies of arctic kelp and the use of natural carbon isotope abundances to examine food web structure and energy flow in the marine ecosystem. Linear growth of the kelp, Laminaria solidungula is greatest in winter and early spring when nutrients are available for new tissue growth. Since over 90% of this growth occurs in complete darkness beneath a turbid ice canopy, the plant draws on stored food reserves and is in a carbon deficit during the ice covered period. Annual productivity of L. solidungula under these conditions is about 6 g C m('-2) compared to about 10 g C m('-2) if light penetrates the ice canopy. Carbon isotope abundances were used to assess food web structure and energy flow in the Boulder Patch, an isolated kelp bed community, and in the Alaskan Beaufort Sea fauna. Isotopic analyses of the resident fauna of the Boulder Patch revealed that kelp carbon contributes significantly to the diet of many benthic animals, including suspension feeders. Some crustaceans, such as mysids and euphausiids (which are key prey species for fishes, birds and marine mammals), also incorporate large amounts of kelp carbon into their tissues when resident in the Boulder Patch. Across the shelf of the Alaskan Beaufort Sea, a distinct gradient in the isotopic composition of marine zooplankton and benthic fauna was related to the intrusion of the Bering Sea water and upwelling in the eastern Beaufort Sea near Barter Island. The ('13)C depletion in fauna of the eastern Beaufort Sea is presumed due to the cycling of ('13)C depleted inorganic carbon into the euphotic zone.