A combination of selected indices for assessing the environmental impact of marine fish farms using long term metadata analysis

Abstract

Several biological indexes can be used to assess environmental impacts of aquaculture in the aquatic ecosystem. Some biological indices are used within environmental legislative and policy frameworks which aim to monitor the impact of marine aquaculture and regulate the operation of fish farms. In Scotland, the impact of fish farms is assessed according to benthic ecosystem status compared with modeled organic loading. The purpose of this paper is to evaluate the benefits of using an optimal combination of a minimal number of selected benthic and aquatic parameters which can provide accurate and reliable information about the benthic status around the fish farm sites in Scotland. The data analyzed in this paper were obtained from the Institute of Aquaculture (IoA), of University of Stirling, and were collected from various fish farm sites across Scotland over several years. Macrofaunal and physico-chemical parameters included in the analysis were: Median Particle Size Analysis (MPSA); total sediment Carbon (C% by dw); total sediment Nitrogen (N% by dw) and Redox Potential (Eh). In this analysis a number of diversity and trophic level based indices were also used - including the Shannon Index (H'), the Infaunal Trophic Index (ITI) and the Azti's Marine Biotic Index (AMBI) - to asses the biotic status of the sites. Univariate and multivariate analysis of the data indicated that a combination of Abundance (N), H' and AMBI as biological indexes for describing the status of the ecological level along with the carbon percentage and redox potential appeared to be the give the best representation of change. This combination is even more accurate over a series of sampling stations and time points, rather than for a single site only, offering a convenient method for assessing the risk of aquaculture pollution of biotopes bellow or adjacent to floating marine fish farm cages.