Research Document - 2010/140

Potential effect of eelgrass (Zostera marina) loss on nearshore Newfoundland fish communities, due to invasive green crab (Carcinus maenas)

By C.J. Morris, R.S. Gregory, B.J. Laurel, D.A. Methven, and M.A. Warren

Abstract

Green crab (Carcinus maenas) is an invasive species in Newfoundland that may impact eelgrass habitats. High densities of green crab were first observed in Placentia Bay during 2007, in shallow water habitats used by juvenile fish of many species. This report synthesizes the results of several research projects conducted on eelgrass habitat in Newfoundland that have investigated the effects of loss of eelgrass on fish communities in coastal waters. Eelgrass habitat in Newfoundland has been shown to be preferred habitat for demersal juvenile Atlantic and Greenland cod, and various life-stages of several other fish species. In several studies during 1995-2009 we monitored fish densities, and conducted in-situ habitat manipulation experiments to identify possible changes in nearshore fish communities when eelgrass habitat is lost. Experimental removal of eelgrass resulted in an 80% decline in fish abundance and biomass. Eelgrass loss also altered the relative abundance of species resulting in declines in abundance of most species, including Atlantic and Greenland cod, white hake, and sticklebacks. In contrast, abundance increased for three species: rainbow smelt, shorthorn sculpin, and winter flounder. This research demonstrated the magnitude of effect of eelgrass habitat loss on fish communities, which is an important consideration when evaluating the potential impact of invasion and potential spread of green grab along the Newfoundland coast.

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