The interaction between incoming salt water from the ocean, which is driven by tides, and exiting freshwater from rivers drives circulation through estuarine environments. As a result of the interaction between the incoming water and the exiting water, nutrients and sediment are moved around the estuary. This study focuses on the interaction between tides and the Snohomish River as it enters the Possession Sound estuary, located in Everett, Washington. To acquire data, I deployed a boat-mounted acoustic Doppler current profiler (ADCP), which uses sound to measure water current direction and velocity. I collected these data at varying tide stages at three different sites between the Snohomish River’s southern output to nearby Mount Baker Terminal, located 3.6 miles southwest of the river output. I have collected 8 samples over the course of 7 months at both ebb and flood tide stages. Each transect survey lasted 3-6 minutes and collected data from the first 20 meters of the water column. To get accurate analysis of current velocity and direction I split the data into categories based on depth. Preliminary analysis shows a southward current at many sites during all tide stages and depths. This raises questions about the scope of the river influence and the potential for southward currents regardless of tidal stage. However, further analysis of current velocity and river discharge are needed. Due to the complexity of the currents in the area, understanding how the river and the tides are interacting can provide a greater understanding of how these currents are impacting the dispersal of sediment and nutrients throughout the estuary.

The marine intertidal is subject to challenging hydrodynamic forces. Organisms that reside within these zones; such as purple (Strongylocentrotus purpuratus) and green (Strongylocentrotus droebachiensis) sea urchins, must have strong attachment to prevent dislodgement, ambulate, and feed in intense environmental conditions. Sea urchins attach to the substrate via their podia (tube feet). The disc found in the distal part of tube feet has a duo-gland that releases specialized adhesive compounds and de-adhesive enzymes to achieve adhesion. Adhesive performance was evaluated to determine if purple sea urchins, that are predominantly found in high wave exposure areas, have better adhesive performance than green sea urchins, which are abundantly found in areas protected from wave action. We evaluated the following adhesive performance variables: stem mechanical properties, tube foot disc tenacity, attachment area, speed of detachment and whole animal adhesive force. We found that for most adhesive performance metrics, purple urchins performed better than greens, except for detachment speed. These results suggest that, in the field, behavioral changes may play an important role in determining risk of detachment for sea urchins. Understanding how morphology, behavior and mechanical properties of tube feet work in conjunction to provide strong attachment, is critical to predict sea urchin fitness in challenging environmental conditions.