Ecological Effects of Removing Ulva spp. fromAvon-Heathcote Estuary: Macroalgal Blooms

Macroalgal blooms are increasing world-wide and havenegative effects on benthic invertebrates andsediments. These include loss of species diversityand development of hostile sediment environments.This book considers ecological effects of Ulva spp.,and its mechanical removal on benthic invertebratesand sediments in Avon-Heathcote Estuary, New Zealand. Experimental removal of Ulva spp. was conducted bymechanical broom at two sites; an open, exposedcentral sand flat, and McCormacks Bay, a shallow,sheltered mud flat. Removing Ulva spp. had severalimmediate effects these included a significantdecrease in abundance of mobile epifauna and anincrease in abundance of infauna. There was no effectof Ulva spp. removal on Austrovenus stutchburyicondition and 46 days following removal, invertebrateabundances approached pre-removal levels at eachsite. Ulva spp. removal also caused short-termincreases in dissolved oxygen and temperature of porewater. The greatest visual impact of removing Ulvaspp. was to sediments in McCormacks Bay fromtrampling. Removal by mechanical broom was effectiveand had low impact on benthic invertebrates andphysico-chemical variables.