Algal Wrack Community Composition and Succession on a Sandy Beach in San Diego, CA

Sandy beaches are a high energy impact zone that produce little to no organic material. Much of the organic matter on beaches is washed up on shore in the form of algal wrack, providing a vital source of nutrients, food, and habitat for a variety of organisms on the sandy beach. Over time wrack will decay and decompose, releasing nutrients such as nitrogen and phosphorus, which are consumed by benthic microalgae and bacteria. The type of wrack and structure of the beach environments affect decomposition, which in turn supports a variety of different wrack associated macrofauna communities. Different species of wrack will support different species of animals, and can affect taxonomic composition and number of species present. My research used a combination of manipulative and mensurative experiments to identify wrack associated macrofauna on a San Diego beach. I used the giant kelp species Macrocystis pyrifera to compare wrack associated macrofaunal community composition and abundance over a period of 21 days. I found that there is more macrofauna within the algal wrack relative to bare sand, and that macrofauna abundance increases over time in the algal wrack. Preliminary results show that community composition varies over time and abundance changes by orders of magnitude. These results confirm previous findings that algal wrack is an important primary food source and strongly influences macrofaunal communities and higher trophic levels.