Spatiotemporal Variability in Water Properties at a Newly Constructed Clam Garden: The Influence of Physical Forcing Mechanisms

Water properties in the intertidal vary on hourly and seasonal time scales, bringing change to this unique marine habitat. The impact of water properties and their associated variability on intertidal organisms is dependent on their tidal depth, the magnitude of the tide, and the ability to flee abnormal conditions. In the Salish Sea, clams are an important traditional food sourced from the intertidal that have served as a reliable protein source for millennia. Many coastal Indigenous communities utilized unique management strategies to increase traditional food security spanning from prairies to beaches. Clam gardens, also known as sea gardens to some communities, are one of these management tools. Clam gardening is a traditional mariculture technique that alters beach slope in the intertidal, increasing available optimal clam habitat. These structures have been noted to increase the biomass and growth rate of butter and littleneck clams. The Swinomish Indian Tribal Community is building a clam garden on Kiket Island as a biocultural restoration project to revive this traditional practice and improve climate resiliency. The SITC fisheries department is conducting a long-term water property monitoring study to complement traditional knowledge of clam gardens and understand the changes in water properties as they relate to the presence of a clam garden. Here, I quantify the spatial and temporal variance in water properties at this newly constructed clam garden compared to an unwalled neighboring beach. The water properties included in this observational study are: temperature, salinity, dissolved oxygen, pH and chlorophyll concentration. Each of the water properties recorded in this monitoring study play an important role in clam's individual biology, life history patterns and population dynamics. The variance in these properties can be attributed to both physical and biologic processes, though here I focus on physical processes. Tidal exchange is a dominating influence leading to the variance at the Swinomish clam garden. River discharge and localized weather events also influence the variance of water properties at synoptic frequencies. This study provides context for conditions that shape the intertidal zone, including the clam garden, while encouraging informed management decisions to support a healthy and sustainable ecosystem in the Salish Sea.