Meeting Abstract
Competition is an important factor structuring where new bull kelp (Nereocystis luetkeana) recruits begin to grow in nearshore environments of the Salish Sea. This annual species must complete its entire life cycle, from swimming zoospore to mature, reproductive sporophyte, in a single growing season, often emerging into a subtidal “field” of perennial macroalgal species. However, it is not clear what the new bull kelp recruits are competing for: light or space. We established a subtidal field experiment near Point Caution, San Juan Island, Washington State to assess which of these factors is most important in determining where new bull kelp begin to grow. Our factorial design experiment included four treatments (n=5 each): cleared and shaded, cleared and unshaded, cleared and partially shaded (to control for the changes in flow attributable to the shade itself), and uncleared and unshaded. The “shades” were constructed of PVC pipe, plastic mesh, and window screen (fully shaded treatment only). Our data demonstrate that clearing and shading influence where new bull kelp begin to grow, indicating that there is likely some level of competition for both space and light. Fully “shaded” plots (either artificially with screens or naturally via interspecific macroalgal competitors) did not grow new bull kelp recruits while plots with some amount of light (cleared, partially shaded) and space did show growth of new individuals. This work helps to elucidate the possible effects of ecological succession in the nearshore subtidal and will help to inform future management and restoration efforts in a changing ocean.
