Detecting the presence of fish farm-derived organic matter at the seafloor using stable isotope analysis of phospholipid fatty acids

Daniel J Mayor,Barry Thornton,Nia B Gray,Giannina S I Hattich

doi:10.1038/s41598-017-05252-w

Abstract

The expansion of global aquaculture activities is important for the wellbeing of future generations in terms of employment and food security. Rearing animals in open-exchange cages permits the release of organic wastes, some of which ultimately reaches the underlying sediments. The development of rapid, quantitative and objective monitoring techniques is therefore central to the environmentally sustainable growth of the aquaculture industry. Here, we demonstrate that fish farm-derived organic wastes can be readily detected at the seafloor by quantifying sediment phospholipid fatty acids (PLFAs) and their carbon stable isotope signatures. Observations across five farms reveal that farm size and/or distance away from it influence the spatial distribution of the generated organic wastes and their effect on benthic bacterial biomass. Comparison to the isotopic signatures of fish feed-derived PLFAs indicates that 16:0 and 18:1(n-9) are potential biomarkers for fish farm-derived organic wastes. Our results suggest that stable isotope analysis of sediment PLFAs has potential for monitoring the environmental performance of aquaculture activities, particularly given the increasing prevalence of terrigenous organic matter in aquaculture feed stocks because it is isotopically district to marine organic matter.

Highlights

Global aquaculture production must double by 2050 if current per-capita consumption levels of aquatic, animal-derived protein are to be sustained as the human population reaches 9 billion[1, 2]
This study quantified the concentrations of phospholipid fatty acids (PLFAs) and their isotopic signatures in the sediments underlying five fish farms in Scotland
If the presence of cod had exerted a major influence on the relative abundance of sediment PLFAs we would have expected to see this emerge when the data were re-plotted to show the effect of distance but no such effect was apparent (Figs 2c and 3c respectively)

Summary

Introduction

Global aquaculture production must double by 2050 if current per-capita consumption levels of aquatic, animal-derived protein are to be sustained as the human population reaches 9 billion[1, 2]. The effects of fish farming activities on the underlying sediments can be quantified by examining changes in the structure of benthic macrofaunal communities, which exhibit predictable and readily discernible changes in response to organic enrichment[10] This sensitive and reproducible approach has been widely-adopted[6, 11], but is time consuming and expensive[12]. The advent of CSSIA techniques has enabled the carbon isotopic (δ13C) signatures of individual PLFAs to be accurately determined, providing insight into the source of organic matter used by microorganisms[27] This is useful in the context of marine finfish aquaculture, where the feedstock may be isotopically distinct from benthic microbial communities, e.g. because it is derived from terrestrial sources[28] and/or from fishmeal/oil harvested in other regions of the globe[29]. Our study explores the overarching hypothesis that aquaculture-derived organic matter at the seafloor, and the influences of fish farm size (maximum consented biomass, MCB), average current speed and distance from the cage edge, can be detected using CSSIA of sediment PLFAs

Methods

Results

Conclusion