STABLE ISOTOPIC SHIFTS IN ARCHAEOLOGICAL FISH BONES REVEAL A WIDESPREAD DECLINE IN EELGRASS BIOMASS DURING THE ANTHROPOCENE, PENOBSCOT BAY, GULF OF MAINE

The carbon, nitrogen, and sulfur stable isotope compositions of organic matter extracted from well-preserved archeological fish bones provide information on fish diets, primary production, and food web dynamics through time. Shell middens in Penobscot Bay, Maine, provide a record of human occupation dating back approximately 5000 years and contain large numbers of fish and mammal bones and invertebrate shells. We analyzed stable C, N and S isotopes of bulk collagen and the C isotopes in individual amino acids of winter flounder (Pseupleuronectes americanus), Atlantic cod (Gadus morhua), and longhorn sculpin (Myoxocephalus octodecimspinous) bones from several coastal middens in Penobscot Bay spanning the last 5000 years to reconstruct fish diets. The combined isotope datasets reveal that there was approximately ~50% more eelgrass biomass available to fuel the base of the food web in Penobscot Bay prior to 1300 years ago relative to today. The most accelerated rates of eelgrass loss occurred over the last 400 years. The decline in eelgrass biomass may have resulted from a combination of factors, including increases in water turbidity (brought about by land-use changes and/or increases in nutrient delivery), disease and climate change. This study provides information on shifts in baseline conditions in coastal ecosystems that occurred after western European settlement of the North American continent and argues for the importance of analyzing materials from the geological and archaeological records to better understand ecosystem function, potential, and resilience.