Kelp Forest Hydrodynamics around an Island

Margaret Daly1, Stephen G Monismith2, Clifton Brock Woodson3, Arnoldo Valle-Levinson4, Fiorenza Micheli1, Diego Sancho1 and Morgan Jones5, (1)Stanford University, Stanford, CA, United States, (2)Stanford University, Stanford, California, United States, (3)University of Georgia, Athens, GA, United States, (4)University of Florida, Department of Civil and Coastal Engineering, Gainesville, United States, (5)Trinity University, Engineering, San Antonio, TX, United States
Abstract:
Kelp forests influence transport mechanisms such as surface waves, internal tides and waves, and local circulation. In turn, complex interactions between these hydrodynamic processes and the kelp forests themselves govern transport of food, nutrients, and larvae. To better understand the local oceanographic variability (<1km) in kelp forests, an array of fourteen moorings around Isla Natividad, Baja California, Mexico were deployed in the summer of 2018. Oceanographic measurements included pressure, velocity, temperature, and dissolved oxygen, pH, and salinity. The island is broadly characterized to have a protected bay side and an exposed side. On the protected side of the island, EOF analysis of the cross shore velocity shows evidence for barotropic stratified flow. Along shore, the velocity is sheared. Current ellipses show that the presence of kelp modifies the direction and magnitude of flow. During large ebb tides, a pressure gradient from a surface height differential up to 25 cm significantly increase along shore and across shore velocities. There is a power law relationship between the surface height differential and velocity. On the exposed side, velocity profiles are highly variable. However, the first mode at the majority of the sites show a uniform shift in velocity over the entire depth. One site behind a headland point in a dense kelp forests has shear in both the along shore and cross shore velocities. Temperature on the protected side is mainly barotropically driven, while on the exposed side, temperature is driven by synoptic events and upwelling. Wave statistics, internal wave presence, and rotary spectra will be analyzed. Future studies will include a similar design with the addition of accelerometers and pressure sensors on individual kelp plants to study movement of plants. Additionally, drone aerial imaging will quantify kelp coverage and improve our understanding of surface canopy movement. This work compliments research by Valle-Levinson, Woodson, and Micheli.
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