As well as the benthic samples, articifial substrata were also deployed to investigate development of fouling communities and their uptake of organic matter from the farm.
Deposit collected in sediment traps beneath the cages.
Black symbols: under cages; Grey: 25 m; white: 200m. The study showed that Ascidiella aspersa, a filter feeder, presented enriched δ15N at sites under the farms. This result indicates that tunicates efficiently filter and assimilate particulate fish waste.
Extent of influence of salmon farms on benthic community and trophic structure - Myriam Callier
Extent of influence of salmon farms on benthic community and trophic structure Myriam Callier School of Biology and Environmental Science, University College Dublin now at IFREMER, Palavas Station, FranceS. Lefebvre, K. Dunagan, M-P Bataille, J. Coughlan and T. Crowe
Aquaculture waste into the food web Food dissolved Excretion Secondary N 60%, P 10% consumer C 1% Primary Primary Organic producers Faeces Lost consumers matter N 15%, P 60%, C 25% Various pathwaysAssimilation of aquaculture waste by the biota (Sara et al. 2004, Lojen et al. 2005, Dolenec et al. 2007)
Objectives• Determine the influence of aquaculture waste on benthic communities2. Assess the contribution of aquaculture waste to benthic organisms’ diet
• Influence of aquaculture waste on benthic communitiesHypotheses:3. Abundance and diversity of benthic macrofauna will vary along transects leading away from salmon cages2. Benthic community structure will differ between sites located at different distances from the farm3. Extent of fish farm influence depends on residual water current direction
Study sitesMulroy Bay, Co. Donegal, Republic of Ireland Mulroy Bay Millstone T2 T1 Main current direction Cranford T12 km N T2
0m 25m 20 200m b b b 1- ResultsNumber of species 16 b 12 b b a a 8 a a a a 4 0Abundance per core sample M-T1 M-T2 C-T1 C-T2 300 b 225 a 150 a a a a a a 75 a a a a 0 M-T1 M-T2 C-T1 C-T2 2.5 b b 2 b b bShannon H b Diversity: lower under the cages and 25m, 1.5 in the current direction a a 1 a a a a 0.5 0 Callier et al., in M-T1 M-T2 C-T1 C-T2 revision
0m 25m 20 200m b b b 1- ResultsNumber of species 16 b 12 b b a a 8 a a a a 4 0Abundance per core sample M-T1 M-T2 C-T1 C-T2 300 b 225 a 150 a a a a a a 75 a a a a 0 M-T1 M-T2 C-T1 C-T2 2.5 b b 2 b b bShannon H b 1.5 a a 1 a Abundance: no significant difference, a except Cranford, under cages a 0.5 a 0 Callier et al., in Increase based on opportunisticC-T1 M-T1 M-T2 species C-T2 revision
1- Community structure Maldanidae Stress: 0.13 0m 200 mMalacoceros sp. Capitella sp. Obusa M-T1-25m C-T2-25m M-T2-25m Lucinidae C-T1-25m Organic enrichment gradient Callier et al., in revision
1- Summary Localised organic enrichment due to salmon farming Effects extend < 25 m, perpendicular to current Effects extend 25-200m downstream Under cages: low diversity, high abundance of opportunistic species Are these species benefiting from the organic input ?
2. Assess the contribution of aquaculture waste in the benthic organism’s dietStable isotope (SI) increasingly used to determine:• Trophic level, pathways of OM in food webs• Contribution of food sources to organisms’ dietCarbon (δ13C) and Nitrogen (δ15N) efficient tracer of salmonfood: Compared to other sources: • Enriched in 15N as contain fish/crustacen meal (Mazzola and Sara 2001) • Depleted in 13C as contain terrestrial vegetables (wheat, soya) (Yokoyama and Ishihi, 2007)
3- MethodologyArtificial substrates 200 m 25 m 0m 2 months
2- MethodologySOURCES OF ORGANIC MATTER CONSUMERS Salmon Faeces Salmon Food pellet macroalgae POM- Water samples Stable isotope composition Carbon and Nitrogen
2- Summary• 13C and 15N are effective tracers• Benthic organisms feed on fish farm waste• Fouling organisms assimilate particulate material released from fish cages
Conclusions Increased biomass of suspension feeders (eg. Tunicates) could decrease levels of particulate and dissolved material in the surrounding environment Potential mitigation strategy? Substrates could be used in highly sensitive environments, where small reductions in nutrient loading could be critical
PerspectiveCould the biomass of fouling organisms be increased to increase uptake of organic material?Could benthic species (polychaetes) be used in integrated aquaculture systems to valorise fish farm waste
AcknowledgementHELP AND ADVICE• Francis O’Beirn, Marine Institute• Grainne O’Brein, BIM BIM• Catherine McManus, Marine Harvest IrelandFIELD and LAB WORK• MarBEE team!• Special thanks to Julien, Paul and Silvia• Divers and staff from Marine Harvest, Mulroy Bay!FUNDING AGENCY• Environmental Protection Agency, NDP, SSTI