Algal Recolonization of Frog Island, Nova Scotia after Large-scale Removal of Algal Species through Anthropogenic Activity

Abstract

Macrophytic algae, which are at the base of inte1tidal food webs, provide food and shelter to organisms of higher trophic levels. Rocky substrata and macroalgae are essential to the physical and biological sustainability of intertidal ecosystems. In 2007 the owner of Frog Island, Nova Scotia removed boulders, cobble, and algae from an 800 ft. x 80 ft. (244 m x 24 m) section of the beach to build an erosion control rock wall around the perimeter of the island. Consequently,fish habitat provided by macrophytic algal species was destroyed. To our knowledge, there are limited published studies regarding the recovery process of macrophytic algae after a disturbance of this magnitude. To restore the intertidal habitat,a remediation plan was proposed and implemented, followed by a five-year monitoring program. The purpose of this research was to determine a rate of macrophytic algal recolonization on Frog Island and to understand what physical and biological factors may affect the recovery process.The study site had 17 sampling transects: 14 in an experimental site and three in a control site. The research involved an analysis of percentage of algal coverage and an analysis of dry biomass. Algal coverage increased over time, increased towards the sub tidal zone from the high intertidal zone, and was significantly different between the control site and the experimental site. Dry biomass increased with vertical zonation towards the sub tidal zone, varied between two sampling seasons, and varied between the control site and the experimental site. At the end of the five-year monitoring period, dry biomass and percentage of algal coverage were still less in the experimental site than in the control site. However, there was a. progressive and healthy reestablishment of Fucoid algae species to the impacted rocky intertidal section of Frog Island.