Algal Response to Removal of the Invasive CordgrassSpartina densiflorain a Salt Marsh at Humboldt Bay, California, USA

Abstract

There are few published studies examining the effects of invasive vascular plants on cooccurring nonvascular species, despite the fact that photoautotrophic algae and cyanobacteria exist at the base of the marine food web. This study tested whether the removal of the invasive dense-flowered cordgrass (Spartina densiflora Brogn.) resulted in an increase in biomass of micro- and macroalgae in a salt marsh located in northern California. The site was sampled over a two-year time period, and percent cover of benthic algae was measured using a point-intercept technique in treated and control areas. Treatment consisted of selective mechanical removal of S. densiflora. The functional groups green filamentous and green sheet algae as well as diatoms and cyanobacteria were found. Growth peaks in algal biomass were significantly lower in the control compared to the treated areas. In addition, successional trends were observed in treated plots; green filamentous algae and diatoms were first to colonize, followed by cyanobacteria during the second year's growth. Our results suggest that the presence of S. densiflora lowers both algal biomass and functional group diversity in an invaded salt marsh, with implications for resulting trophic cascades.