The Israeli Journal of Aquaculture - Bamidgeh 54(2), 2002
The Annual Dan Popper Symposium


USE OF SOLID SUBSTRATES AND BIOFILTRATION
TO REDUCE MARICULTURE EFFLUENTS TO SURROUNDING WATERS -
PRELIMINARY RESULTS FROM THE GULF OF EILAT


Timor Katz¹*, Noa Eden¹, Ehud Spanier², Anat Tsemel², Stephan Breitstein², Amir Yurman², Dror Angel¹

1 Israel Oceanographic and Limnological Research, The National Center for Mariculture, P.O.Box 1212, Eilat 88112, Israel
2 Leon Recanati Institute for Maritime Studies, University of Haifa


Abstract

Eight biofiltration arrays (each consisting of 11 plastic mesh cylinders mounted on a PVC frame) were deployed in midwater (8 m below surface), four arrays adjacent to the Ardag fish farm and four arrays 300 m west of the farm (reference site). Identical biofiltration arrays were deployed and studied at net cage fish farms in Crete, Slovenia and Scotland as part of the EU-funded BIOFAQs (BIOFiltration and AQuaculture) project in June 2001. Every second month, one cylinder from each array was sampled and the community structure and distribution of organisms on the cylinders were documented. Dry weight, ash, P,N,C and energy of the total biomass on the cylinders and of selected invertebrate species representing the major groups were determined.

Invertebrates were also sampled for stable isotope composition analysis. In addition, we carried out measurements to determine the ability of the biotic communities associated with the biofilters to remove phytoplankton from the ambient water.

We found that there was a constant increase in biomass of attached organisms and a higher phosphorus content in the biomass of these invertebrates on the biofilters near the farm than on the biofilters at the reference site. The biomass on the biofilters near the farm was sevenfold higher than at the reference site and the phosphorus enrichment ratio (calculated as a comparison between the two sites) was 9.7. The composition of the organisms differed both qualitatively and quantitatively between the sites. Some organisms were found only near the farm and some were found only at the reference site. On average, we found 3.3 stony coral colonies per biofilter unit (mainly on the PVC frame) and there was a similar settlement rate at the two sites. The phytoplankton filtration capacity of the biofilters was measured, but the results have not been analyzed yet. Preliminary measurements indicated that the community associated with the biofilter (100 g, dry weight) consumed 5.1x10 7 cyanobacteria per minute, suggesting rapid removal of phytoplankton biomass and a potentially important role in particle capture.

*Corresponding author. E-mail: timor@ocean.org.il

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