The effects on invertebrates of Spartina control by the herbicide dalapon

Abstract

Areas of Spartina anglica at Lindisfarne N.N.R have been controlled with the aquatic herbicide Dalapon in combination with a wetting agent (Agral), in order to reclaim areas of mud-flat, lost as potential feeding areas for bird and fish populations. A study was carried out on the longterm implications of this control programme, and showed that an increase in diversity and density of macroinvertebrates occurred in the sprayed areas of Spartina. The implications of this increase in potential food resource is discussed. Investigation of the sediment in the sprayed areas showed significant variation in physico-chemical factors in comparison to the sediment in the Spartina sward and open mud-flat. This difference was accounted for by the tidal removal of fine sediment from the sprayed areas after the destruction of the Spartina sward. Many of the observed changes in macroinvertebrate density were considered to be caused by these changes in sediment character. Field studies on the immediate effect of the Dalapon and Agral spray, found a significant absence of Carcinus maenas in areas after treatment. This was considered most likely to have been caused by the direct toxic effects of the spray. No other species of macroinvertebrate studied showed any detectable decline after spraying. Laboratory studies were carried out on the mud-flat macroinvertebrates Corophium volutator, Hydrobia ulvae and Nereis diversioolor. The two former species showed toxic effects at concentrations of spray equal to 1/10 to 1/100 the working spray concentration. However, Nereis divergioolor only showed a mortality response between 1/10 and the equivalent of the working spray concentration. These results are discussed in relation to the likely concentrations encountered by the mud-flat invertebrates.