1. 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
Website:

2. 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

3. 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 ± 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

4. 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 Each line was suspended at a depth of 10 m and at a distance apart of 0.25 m.

5. 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)

6. Video Survey
Fish Farm
Control

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

8. 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

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

10. 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

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