Meeting Abstract
Invasive wireweed (Sargassum muticum) may be causing changes in the distribution and abundance of native bull kelp (Nereocystis luetkeana) beds in the Salish Sea. S. muticum is a perennial seaweed species that may outcompete juvenile N. luetkeana, an annual species, for light and/or space at the beginning of the growing season. This interspecific competition prevents the formation of bull kelp forests that are a critical habitat for many ecologically and economically important species. The Northern Kelp Crab, Pugettia producta, lives on both N. luetkeana and S. muticum but previous whole tissue feeding assays in the lab indicate that P. producta prefer to eat N. luetkeana over S. muticum. Here we created artificial food (agar discs “flavored” with N. luetkeana or S. muticum) to remove the individual algal morphology as a confounding factor in feeding choices. Choice and no choice feeding experiments in this study show that P. producta do not show a clear preference for N. luetkeana or S. muticum when provided with a single food option (“no choice”). However, when given a choice between the two, P. producta unexpectedly consumed greater quantities of food containing the invasive S. muticum. This has possible implications for the integration of S. muticum into nearshore food webs, but surveys are still needed to determine if kelp crabs are actually eating S. muticum in the field. If S. muticum is consumed in the field and/or has favorable nutritional value, this could help explain our unexpected result. Additionally, kelp crab feeding on S. muticum might also indicate some level of top-down control of this introduced species by native herbivores, ultimately leading to additional changes in community structure within nearshore ecosystems.
