Seasonal and Spatial Patterns of “Green Tides” (Ulvoid Algal Blooms) and Related Water Quality Parameters in the Coastal Waters of Washington State, USA1

This study examines the species composition and seasonality of “green tides” (i.e., blooms of ulvoid macroalgae including Enteromorpha Link, Monostroma Thuret, Ulva (L.) Thuret, and Ulvaria Ruprecht spp.) in the northeastern Pacific region. Macroalgal blooms have been blamed for eradicating seagrass meadows, altering faunal community structure, and creating unsightly, malodorous piles on beaches (e.g., Valiela et al. 1997, Hauxwell et al. 2001). They are extremely productive, albeit ephemeral, communities. Blooms are often associated with eutrophication (e.g., in the Venice lagoon), although a variety of abiotic and biotic factors may limit ulvoid algal abundance and productivity (Kida 1990, Henley et al. 1991, Geertz-Hansen et al. 1993, Rivers and Peckol 1995, Anderson et al. 1996). Problematic macroalgal blooms are typically reported to be monospecific (Valiela et al. 1997), although species composition may be dependent on environmental conditions (Lotze and Schramm 2000). The genera involved in “green tides” are superficially similar, despite significant differences in life cycles and developmental patterns, and can be impossible to distinguish reliably in the field. The three Ulvacean genera (Enteromorpha, Ulva, and Ulvaria) have isomorphic gametophytic and sporophytic stages. In contrast, the bladed form of Monostroma is the larger gametophytic stage in a heteromorphic life cycle (Bold and Wynne 1985). At least part of the Enteromorpha thallus is tubular. Ulva is an entirely flat, distromatic blade. Ulvaria and Monostroma are both monostromatic blades (Gabrielson et al. 2000). The variety of Ulvaria found in the northeastern Pacific region [U. obscura v. blyttii (Areschoug) Bliding] darkens to olive drab or black on drying allowing it to be distinguished from Monostroma (Scagel et al. 1989). Little is known about the causes, extent, or history of ulvoid blooms in this region (Bulthuis 1991). Anecdotal evidence suggests that significant interannual variation in the intensity of the blooms occurs in some locations, while ulvoid algae are always abundant during the summer at other sites (T. Mumford, personal communication). Areas with excessive green algal growth elicit odor-related complaints from waterfront residents (G. Frankenstein, personal communication) and blooms can be sufficient to inhibit the growth of eelgrass (Zostera marina L., Nelson and Lee 2001). Problematic blooms of green algae are not, however, associated with locations Seasonal and Spatial Patterns of “Green Tides” (Ulvoid Algal Blooms) and Related Water Quality Parameters in the Coastal Waters of Washington State, USA1