Meeting Abstract

35.3  Sunday, Jan. 5 08:30  Effects of floats on how seaweeds move in unidirectional and wave-driven flow BURNETT, N.P.; Univ. of California, Berkeley burnettnp@berkeley.edu

Seaweeds are an important group of organisms in marine ecosystems, serving as major primary producers, providing habitat for smaller organisms, and competing for space with other sessile organisms. Each of these important ecological roles is influenced by the movement of the seaweed in ambient water flow: moving higher in the water column increases light exposure for photosynthesis, fluttering induces mixing and gas exchange, and large sweeping motions can dislodge or damage neighboring organisms. I used physical models of strap-like algal blades to identify how the movement of the blade is impacted by buoyant floats (pneumatocysts), a common feature of intertidal kelp, such as Egregia menziesii. The buoyancies and arrangements of the model pneumatocysts were manipulated and the height, flapping amplitude, and speed of the models were measured in both unidirectional and wave-driven flow conditions in laboratory flumes. In both unidirectional and wave-driven flow, positively buoyant pneumatocysts along the length of a blade increased the height and the amplitude of blade motion. However, manipulating the drag and buoyancy of pneumatocysts at the base or middle of blades had different effects in waves than in unidirectional currents. For example, in wave-driven flow, blades maintained a higher position in the water column after basal and middle pneumatocysts were removed or made neutrally buoyant, whereas this generally had the opposite effect in unidirectional flows. This model-based study suggests that the position, buoyancy, and drag of pneumatocysts can influence seaweed motion differently in waves versus unidirectional currents, thereby impacting how those seaweeds interact with the surrounding community.