Preliminary studies of grazing by Bittium varium on eelgrass periphyton

Abstract

The grazing activities of Bittium varium Pfeiffer on periphyton colonizing live eelgrass ( Zostera marina L.) and artificial eelgrass (polypropylene ribbon) were investigated. Quantitative measurements of grazing impact on artificial substrates were determined by periphyton pigment extraction and dry weight differences between grazed and ungrazed blades. Significant differences occurred in phaeophytin and dry weight calculations, but chlorophyll a measurements were not significantly different. This suggests that senescent diatoms constituted the bulk of the periphyton weight and were selectively removed over more actively photosynthesizing diatoms. An examination of scanning electron micrographs further elucidated the impact of grazing by Bittium varium. Some micrographs revealed that B. varium removed primarily the upper layer of the periphyton crust on both artificial substrates and living Zostera marina. The diatom Cocconeis scutellum Ehrenb. which attaches firmly to living Z. marina blades was less commonly removed than Nitzchia or Amphora. Through its grazing activities, B. varium may maintain community dominance by tightly adhering diatoms such as C. scutellum. Evidence of the complete removal of periphyton exposing the Z. marina epithelium was revealed in other micrographs. The grazing activities of Bittium varium, which removes periphyton from seagrass blades, could have important implications for the distribution and abundance of Zostera marina in the Chesapeake Bay.