Invasive species are an increasing threat to seagrass ecosystems worldwide. It has been suggested that in Europe alone there are over 87 marine invasive species. Some of these alien species can alter the fish community composition within an area and in some cases cause reductions in the population densities of commercially important fish species. The invasive seaweed, Sargassum muticum was first identified in the UK in the 1973 and has recently been identified off the coast of the Isle of Arran, Scotland. The coasts of this island are host to several eelgrass beds (Zostera marina) which provide food, protection and nursery habitat for many commercially important fish species, some of which are vulnerable such as the Atlantic Cod (Gadus morhua) and Haddock (Melanogrammus aeglefinus). Because these seagrass habitats are home to several commercially important fish species the aim of this study was to determine if S. muticum can alter the species richness and population densities of these fish.
The findings from this study show that areas containing only Z. marina had the highest species richness and population density of commercial species. Of the five commercial species identified in the videos, only two species were shown to have significant differences in population density between sites, G. morhua and M. aeglefinus. Both species had a higher population density in seagrass only habitats compared to S. muticum or mixed habitats.