Algal-faunal interactions in a mat ofUlva fenestratain false bay, Washington

Abstract

Abstract The events associated with the annual formation of algal mats in a shallow bay were studied for 36 months. Maximum net primary production, estimated from change in weight of thalli (compound production) in mesh bags plus weight of algae which amphipods may have eaten, was 10.2% · day−1 for Ulva fenestrata and 20.8% · day−1 for Monostroma fuscum. The compound production of Ulva was 8.0% · day−1 in June and 1.4% day−1 other months. In the laboratory Eogammarus confervicolus consumed 0.21 mg Ulva · mg amphipod−1 · day−1. At this rate the amphipod population could have consumed over half of the annual net production of Ulva (46.3 metric tons). Wind and tidal patterns in the bay May through September were favorable for the formation of Ulva mats, 400–1200 g · m−2. After the mats were dispersed when environmental patterns changed in October, 8–20% of the algal biomass could be accounted for in the sediment. Numbers of the dominant polychaete, Rhynckospio glutaea, declined as the biomass of the mat increased. Oligochaete numbers declined 4–10 fold in the fall and winter as did the quantity of organic matter in the sediment.