Short communicationNear-edge wrack effects on bare sediments: Small scale variation matters in the monitoring of sandy beaches

- Wrack patches spike density of beach invertebrates and increase variation.
- Small-scale variation near the edge of wrack patches has not been explored.
- Surveys and an experiment were done to assess densities near wrack edge.
- Results suggest that wrack effects extend beyond their edge within 1 m.

The influence of wrack on sandy beach communities is well-documented but its effect on bare sediments located immediately beyond its edge has not yet been tested. This study aimed to explore these effects by surveying bare sediments located at increasing distances (0.5-2 m) from the wrack in five sandy beaches on Prince Edward Island, Atlantic Canada. In addition, we tested the influence of wrack with a field manipulation using wrack patches made up of rockweed bundles. The survey indicated that a modest but significant number of amphipods and beetles occupied bare sediments located 0.5 m from the edge of the wrack, but that those numbers dropped in sediments 1 m away and farther. The outcome of the field manipulation showed a similar pattern. Although small in spatial scale, our results have implications for the monitoring sandy beaches affected by scattered as well as heavy wrack input.