USE OF RODEO(R) AND X-77(R) SPREADER TO CONTROL SMOOTH CORDGRASS (SPARTINA-ALTERNIFLORA) IN A SOUTHWESTERN WASHINGTON ESTUARY .2. EFFECTS ON BENTHIC MICROFLORA AND INVERTEBRATES

In August 1992, we conducted an intensive short-term (within 119 d) ex periment in southern Willapa Bay, Washington, to evaluate the potentia l effects on mudflat benthic communities of herbicide control of smoot h cordgrass, Spartina alterniflora Loisel. A mixture of glyphosate (Ro deo(R); 4.7 L ha(-1)) and an associated surfactant, alkylarylpolyoxyet hylene (AAPOE, X-77(R) Spreader; 1 L ha(-1)) was applied aerially to t hree mudflat sites with invasive S. alterniflora. Sediment structure ( grain size), edaphic microalgal biomass (chlorophyll a), and densities of benthic and epibenthic meiofauna and benthic macrofauna were sampl ed systematically in treated and adjacent control (untreated) plots 1 d before, immediately after, and 1, 14, 28 and 119 d after spraying. T hese mudflat biota showed no definitive differences in population tren ds that would indicate acute responses to the herbicide and surfactant applications over the 119-d duration of the experiment. Two-way ANOVA tests of differences in slope of linear regressions of mean plot micr oalgal biomass and invertebrate density of 19 taxa groups or species t esting short-term (2 weeks) and long-term (17 weeks) trends in respons e to the experimental treatment tests indicated no significant (p < 0. 1) treatment and only three site effects. Natural variability in the s tanding stocks (in the case of benthic microalgae) or densities (inver tebrates) of most of the 19 indicator taxa prior to spray application was sufficiently high within and between treatment and control plots a nd among sites to preclude strong inferential tests of acute effects. Although differences in mudflat habitats (e.g., tidal elevation, sedim ent structure) inherent in the sites prior to treatment affect the pow er of our ability to test direct effects, there were no indications of either short- or long-term effects on the mudflat community of aerial ly applying this concentration of herbicide and surfactant. This study did not explicitly address either sublethal or indirect ecological ef fects, such as associated with an observed decrease in the exotic eelg rass Zostera japonica, which might appear as a longer-term, more subtl e response by the mudflat community.