Shifting the quality of a trophic subsidy: Does increased use of high omega-6 feeds in aquaculture impact on ecology of marine food webs?

The expanding aquaculture industry provides an increasing trophic subsidy to coastal and estuarine ecosystems worldwide through waste feed, faecal material and nitrogenous wastes. Over the past decade there has been a switch... [ view full abstract ]

The expanding aquaculture industry provides an increasing trophic subsidy to coastal and estuarine ecosystems worldwide through waste feed, faecal material and nitrogenous wastes. Over the past decade there has been a switch away from feeds high in omega-3 fatty acids based on fish oil, to feeds high in omega-6 fatty acids comprised mainly of terrestrial plant oils and animal fats. This has led to a shift in the composition and quality of the trophic subsidy provided to marine consumers. By using fatty acids common in terrestrial plant oils combined with stable isotopes as tracers, we were able to demonstrate that the trophic subsidy provided by aquaculture is widely consumed by organisms in both benthic and planktonic systems. We subsequently investigated health and reproductive consequences of consumption of this waste on several key groups of organisms. Single and multi-generational experiments were conducted on common, rapid production, fouling organisms, such as caprellid and corophiid amphipods. We also investigated health and reproductive outcomes on several sea urchin species, which have the potential to be ecosystem drivers in many coastal and estuarine systems worldwide. We found that urchins consuming aquafeed had enhanced gonad indices compared to those consuming a natural diet. However, this didn't necessarily translate into larval success, with larvae of adults consuming the natural diet surviving at significantly higher rates.