EJ Cook, KD Black & MDJ Sayer (SAMS) In situ biofilters at commercial fish farms in Scotland – the effectiveness of mussel lines as biofilters EJ Cook, KD Black & MDJ Sayer (SAMS) BIOFAQs Workshop, Eilat (October 2002) EU 5th Framework: BIOFAQs – BIOFiltration & Aquaculture Q5RS-2000-30305 Website: www.sams.ac.uk/biofaqs

Introduction Question: Mono vs multi-species communities? Use of active suspension feeders (e.g. bivalve molluscs & ascidians) Use of species of commercial value Fish Farm Site, Lynne of Lorne Scallop farm, Loch Fyne

Active Suspension Feeders Expend energy to drive sea water and suspended seston across the filtration surface using ciliary or muscular pumps. Retains particles 1 – 100 m (incl. bacteria, diatoms, other phytoplankton & non-living detritus) Ascidiella aspersa dominant ascidian on biofilters in Oban Attained biomass of 86.12 ± 28.08g (AFDW m-2) after 5 months Clearance rates (ml g dry mass-1 h-1) = 3180 (Holmes, 1973) & 3240 (Randløv and Riisgård, 1979). Commercial value: Unknown – potential high pharmaceutical value Retains particles <1 – ? m (incl. bacteria, phyto-, zoo-plankton and particulate detritus) Mytilus edulis dominant bivalve on biofilters Attained biomass of 3.45 ± 0.38g (AFDW m-2) after 5 months Clearance rates (ml g dry mass-1 h-1) = 700 – 5300 (Prins et al. 1996). Commercially valuable seafood product

Construction/Deployment Mussel lines (ML) were constructed from 1m lengths of DANLINE mussel spat polypropylene rope. Each rope was weighted at one end to ensure that the rope remained vertical in the water column. Location of Biofilters The MLs were deployed in Oban at a fish farm (10 m from cages) and a control site (500 m from the salmon farm) in 25 May 2002. Each line was suspended at a depth of 10 m and at a distance apart of 0.25 m.

Methodology Sampling protocol = Bi-monthly intervals for 18 months. 1. Underwater video surveys 2. Removal of x4 MLs from fish farm and control site 3. ML sampling (including total biomass & species diversity/ abundance Video Survey Mussel Line (Control Site - Sept 2002)

Video Survey Fish Farm Control

Total Biomass A B *Data for mussel lines represents n=1, whereas n=4 for mesh data A - July 2002 B - Sept 2002

Species Diversity 4 months post deployment: Mussel Lines Species No. = 16 (FF) & 19 (CTL) Dominant Species:- FF – Mytilus, Caprellidae, Obelia & Ascidiella CTL – Obelia*, Ascidiella*, Terebellidae*, Pinnotheres* & Mytilus Mesh Filters Species No.= 23 (FF) & 21 (CTL) FF – Mytilus, Caprellidae, Obelia, Ascidiella, Pectinidae CTL – Ascidiella, Obelia, Pectinidae, Terebellidae Ascidiella aspersa Mytilus edulis Caprella linearis

Comparative Studies* * Comparisons made after 4 months of deployment (Mussel Lines – 2002)

Conclusions Still early days… Significant colonisation of mussel lines (MLs) within 4 months Total biomass is comparable to the mesh filters, although higher biomass is observed on the MLs at the control site compared to the fish farm Reduced species number on the MLs compared to mesh filters Increased abundance of Mytilus edulis and Caprellidae at fish farm compared with control site on the MLs Need for mesocosm trials using mussel lines colonised by M. edulis from Loch Creran (2003?) & for comparison with environmental data collected in Sept. 2002

Acknowledgements Simon Thurston (Diving & Video Footage) Alex Keay (Aquarium and construction) Seabird CTD Zooplankton sampling …sampling by day and night!!