SHELL ASSEMBLAGES AS RECORDERS OF SALMON INDUSTRY: ANTHROPOGENIC DECLINE OF MARINE BENTHIC COMMUNITIES AROUND CHILOE ISLAND, CHILE

A survey of marine benthos, in a region largely sustained by salmon industry and shellfish fishery, has been conducted to assess the impact of aquaculture on local benthic communities. Nine benthic ecosystems were sampled around Chiloe Island (Southern Chile) in January 2011 to compare sites proximal to salmon farms with those unaffected directly by current aquaculture activities. At each site, a 10×1 m transect of the seafloor was sampled using surface air supply diving. Live and dead specimens of macrobenthos were collected exhaustively, sorted, and identified.

The sites yielded a total of 3233 live mollusk specimens and 14300 shells/valves of dead mollusk. A total of 32 species of mollusks were documented, with most being present both in life and death assemblages. In impacted areas, salmon farms exerted a steep anthropogenic gradient: over a distance of 6 km density of live shellfish declined by two orders of magnitude. Also, sites affected by salmon farming displayed depressed ratios of live-to-dead individuals, suggestive of localized declines in bioproductivity.

This study provides a direct quantitative documentation of a catastrophic decline in local benthic productivity triggered by fish farming. Because benthic organisms purify aquatic habitats, support higher trophic levels, and sustain fisherman communities, shellfish extirpation has profound ecological and societal consequences. While profitable, unregulated aquaculture can severely damage local ecosystems and undermine sustainable development of coastal economies. By combining paleontological and ecological approaches, anthropogenic decline of marine benthos can be assessed and monitored.