Can we quantify primary productivity shifts with mollusk shell trace elements? Evidence from Burrard Inlet, British Columbia, Canada

Session: Timestamped Biomineralized Structures in Coastal Environmental Monitoring and Cultural Research

Presenting Author:

Natasha Leclerc

Authors:

Leclerc, Natasha¹, Kuehn, Sarah², Kommescher, Sebastian³, Prentice, Andrea⁴, Taft, Spencer⁵, Thébault, Julien⁶, Burchell, Meghan⁷

(1) Department of Archaeology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada, (2) Department of Archaeology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada, (3) Core Research Equipment & Instrument Training Network, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada, (4) Core Research Equipment & Instrument Training Network, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada, (5) Tsleil-Waututh Nation, Vancouver, British Columbia, Canada, (6) Laboratoire LEMAR, Université de Bretagne Occidentale, Plouzané, France, (7) Archaeology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada,

Abstract:

For millennia, Burrard Inlet has been the home of Tsleil-Waututh Nation (TWN), a distinct Coast Salish nation whose name translates to the People of the Inlet. Today, the inlet also houses Canada’s largest port and is surrounded by the city of Vancouver, Canada. Since colonization and the subsequent rapid expansion of industrial activities in the 19th and 20th centuries, the diets of Tsleil-Waututh people have shifted drastically from traditional diets primarily based on locally harvested marine foods to modern diets with little to no locally harvested marine foods. For instance, herring represented an important food source to TWN for millennia, but were extirpated in the 1880s, and shellfish, such as butter and littleneck clams, are now dangerous to eat due to contamination and toxic algal blooms. While overfishing and climate change are important contributors to these changes, urban and industrial nutrient pollution affecting primary productivity are also likely to play a role. To better understand these shifts, we investigated the trace element variations (e.g., Ba, Li, Mn and Mo) of butter and littleneck clam shells (Saxidomus gigantea and Leukomea staminea) via LA-ICP-MS. Our results show variations between the species in their shell trace elemental responses to phytoplankton blooms, specifically barium-calcium ratios. Barium-calcium ratios are higher in shell material deposited near timing of spring blooms, with peak heights varying between years with differential oxygen saturation and chlorophyll-a levels (i.e., bloom intensity). These results suggest that trace element and ratio variations, especially barium, may be useful proxies to investigate in archaeological and historical mollusk shells to track how primary productivity has shifted in Burrard Inlet over the last three centuries and provide a pre-industrial baseline of local primary productivity intensity. These measurements may then become useful benchmarks in shellfish and coastline environmental restoration efforts. This research is in collaboration with TWN but is not representative of TWN.