Shift in benthic assemblages and organisms’ diet at salmon farms: community structure and stable isotope analyses

Mp Bataille,Mk Dunagan,J Coughlan,S Lefebvre,Md Callier,Tp Crowe

doi:10.3354/meps10251

Abstract

The extent of the influence of salmon farming on the environment and on the uptake of particulate and dissolved effluents by benthic organisms was assessed using community structure and stable isotope analyses. Sediment cores were collected in 2 directions: perpendicular and parallel to the main residual current, 0, 25 and 200 m from 2 salmon farms (Millstone and Cranford) located in Mulroy Bay, Ireland. In addition, artificial substrates were placed for 2 mo at 1 m depth 0, 25 and 200 m from one farm to trace the uptake of farm-related nutrients by fouling organisms. The extent of measurable change in benthic communities (abundance, diversity, structure, trophic composition) depended on residual current direction. Intraspecific variation in isotopic values in benthic invertebrates was mostly explained by distance from cages. Organisms collected at impacted sites exhibited a shift in isotopic composition towards that of farm wastes. A shift in δ13C was observed in several invertebrates, including the polychaetes Malacoceros fuliginosus and Nephtys hombergii, Nematoda and the anemone Anthopleura balii. Fouling communities collected on artificial structures, mainly composed of the tunicate Ascidiella aspersa, showed higher δ15N values at fish cage sites compared to sites 200 m away. The study demonstrated that fish effluents were assimilated and became food sources for several organisms.

Highlights

Aquaculture contributes almost 50% of the global aquatic food supply
Benthic marine food webs are an important component of coastal ecosystems as they contribute to organic matter recycling, linking the pelagic and benthic compartments through various processes (Herman et al 1999)
Potential source of particulate nutrients in the vicinity of salmon farms feed pellet composition was similar throughout the year, significant variation in nitrogen and carbon isotopic composition was measured in fish feed pellets between the 3 sampling dates (Table 1; δ15N: March 2009 ≠ June 2009 ≠ May 2010, p < 0.001; δ13C: March 2009 ≠ June 2009 = May 2010, p = 0.002)

Summary

Introduction

Aquaculture contributes almost 50% of the global aquatic food supply. As the demand for aquatic food is increasing, the sustainable development of aquaculture is crucial to contribute to food safety, community development and to reduce overexploitation of natural aquatic resources (FAO 2010). Most aquaculture activities are located in coastal areas, where anthropogenic pressures are already high. A better understanding of aquaculture−environment interactions is needed to determine the environmental carrying capacity of coastal areas for on-going and future aquaculture operations (McKindsey et al 2006). Benthic marine food webs are an important component of coastal ecosystems as they contribute to organic matter recycling, linking the pelagic and benthic compartments through various processes (e.g. feeding and bioturbation) (Herman et al 1999). Little is known about how changes in biodiversity affect these processes and the extent to which

Objectives

Methods

Results

Discussion

Conclusion