A manipulative experiment demonstrates that blooms of the macroalga Ulvaria obscura can reduce eelgrass shoot density

Abstract

This study reports on a manipulative experiment demonstrating that natural blooms of Ulvaria obscura (Kützing) Gayral, a relatively understudied and easily misidentified green alga, can cause the loss of eelgrass shoots in a subtidal meadow. A total of 20 1 m 2 quadrats were set at the inshore edge of an eelgrass ( Zostera marina L.) meadow near Blakely Island, Washington State, USA. Ulvoid algae were removed from experimental quadrats and left in control quadrats. Experimental quadrats lost 12% of their eelgrass shoots over 5 weeks, while control quadrats lost 54% of their eelgrass shoots. Thus, we conclude that natural blooms of U. obscura at the study site reduce eelgrass shoot density.