Amsterdam Meeting BIOFAQs Amsterdam Meeting January 2003 January 2003 University of Haifa, Israel

Eilat workshop: Missing an important stage in the food web – zooplankton

Grazing

Grazing may be an important factor and it can be expressed in several levels: There are huge quantities of wild fish in the vicinity of the cages and bio-filters. Grazing may be an important factor and it can be expressed in several levels: There are huge quantities of wild fish in the vicinity of the cages and bio-filters. 1. Some may use the cages/bio-filters just for shade/shelter (like in FAD – Fish Attracting Device (.

GRAZING (continue) 2. Some fish may feed directly on the remains of the commercial fish feed (and secretion of the cultured fish?). 3. Some fish may use the above artificial food and when it is unavailable - graze on the bio-filters. Other may graze on the bio-filters directly. Our estimation of the biomass can be strongly affected by the grazing. If grazing is considerable we may greatly underestimate the biomass of our bio-filters (just measuring what left AFTER grazingOur estimation of the biomass can be strongly affected by the grazing. If grazing is considerable we may greatly underestimate the biomass of our bio-filters (just measuring what left AFTER grazing).

GRAZING (continue) Since many of the fish hovering around the bio-filters and the fish cage in Eilat are herbivores, rabbit fish of the genus Siganus – macro algae eaters, we proposed to hang plates with known amount of the green algae of the genus Ulva on both sites and measure the disappearance of the algae after several hours in each sites as a measure of the intensity of grazing. We tried this method at the end of December with Gracillaria, and it did not work. We plan to repeat the experiment with Ulva, soon

Harvesting the wild fish out of the cages may be one way to remove part of the excess organic loading from the marine environment.Harvesting the wild fish out of the cages may be one way to remove part of the excess organic loading from the marine environment. There are also invertebrates grazers – such as sea urchins. We found them frequently in the bio-filtersThere are also invertebrates grazers – such as sea urchins. We found them frequently in the bio-filters GRAZING (continue)

Preliminary sea-urchins count in bio-filters (mean number / bio-filter / month)Reference Fish Cages MONTH 11October 01 12December 01 22February 02 -1April 02 -1June 02

– recruited a small number of bivalves but attracted many other organisms - algae, sponges, hydroids, many similar to the bio-fouling of the bio-filters. There were clear differences between the sites - the algae of the genus Jania was dominants on ropes near the fish cages (F) while the sponge Mycale and other invertebrates were common on the ropes in the reference site (R). However we would like to continue monitoring the ropes to see the development (succession, etc). “MUSSELS' ROPES" IN EILAT F R

In Eilat we are planning a quantitative survey of the 4 major taxonomic groups found on the bio- filters in several OTHER artificial and natural substrates and to refer the findings to possible artificial source of nutrients (e.g., sewage). Considering using the idea of bio-filters in other areas where there is organic loading – e.g., sewage outlets, openings of fish ponds, etc. FUTURE SURVEY

Mono-species culture Stable isotopes Mono-species culture We are working on using the bivalves of the genera Pinctada and Spondilus under fish cage in the Mediterranean. We had some problems of mortality (and boxes and nets with bivalves that were stolen…). We continue this experiment. Stable isotopes We are processing more material for Sonja stable isotopes will collect more in Eilat and Mediterranean (the above experiment).

Some thoughts, questions and ideas for the Future Timing - do we deploy the bio-filters in the proper time?Timing - do we deploy the bio-filters in the proper time? Recruitment, especially in Eilat, may be considerably different in different seasons. The first recruit may determine the fate and the character of the bio-fouling.

Some thoughts, questions and ideas for the Future – Timing (continue) Also, as Anat Tsemel have shown, bio-fouling on exciting bio-filters may be the source of recruits for the new bio-filters bio-filters may be the source of recruits for the new bio-filters. 100% , 2002 Months , 2002 Months

Some thoughts, questions and ideas for the Future – material and design Do we use the right material? design? – a different structure may results in different type of settlement (e.g., comparison of different parts of our present bio-filters, comparing the bio- filters with the "Hawaiian skirt" structure or the benthic reefs).

Some thoughts, questions and ideas for the Future – Utilization of the bio-filtering organisms The usefulness of the bio-filtering organisms: we could think on commercial value such as food for people and/or animals (may be problematic in many sites), chemicals for the pharmacological industry, but also….

e.g., in Eilat true scleractinian, hermatypic corals grow better under the fish cages (on the benthic reefs, on bio-filters and on the buoys of the bio-filters than in other places - it is quite remarkable. These corals can be transplanted to natural deteriorating coral reefs and be used for mitigation of such natural habitats. Organisms with high environmental value Organisms with high environmental value

Corals developed on the benthic reefs

Corals developed on the bio-filters

Corals developed on the buoys of the bio-filters