Breakwaters as habitat for sessile intertidal biota in the Southern Gulf of St. Lawrence

Abstract

Increasing human populations are causing rocky breakwaters to become common features along coastlines. However, knowledge is scarce about the role of breakwaters as intertidal habitat. This study is the first to investigate the assemblage ecology of habitat found on rocky breakwaters compared to natural rocky intertidal areas in the North Atlantic coast of North America so that the potential effects of artificial rocky structures can be understood. Percent coverage of macro-algae and macro-invertebrates were quantified on breakwaters near Arisaig, in the Southern Gulf of St. Lawrence (sGSL) to investigate possible temporal confounds in the main study, from June-August 2010. No significant differences were seen over the months for richness and abundance data, and June differed from the July and August for community composition. Then, percent coverage of sessile biota was quantified at exposed and sheltered areas on breakwaters and natural rocky shores along 430 km of the sGSL. Richness and abundance in sheltered areas of breakwaters were both less than in sheltered areas of natural rocky areas. Breakwaters had significantly different community composition compared to natural rocky shores and between wave exposed and sheltered areas. Semibalanus balanoides were more abundant on natural rocky shores than breakwaters and were found in higher abundance at exposed areas than sheltered areas. Ulva intestinalis had higher abundances on breakwaters than natural rocky shorelines and U. intestinalis, Fucus spp. and Ascophyllum spp. had higher abundances in sheltered areas than exposed areas of breakwaters. This study showed that biotic communities on breakwaters are substantially different than the surrounding natural rocky shores throughout the sGSL.