BIOFAQs Amsterdam Meeting Amsterdam Meeting January 2003January 2003

University of Haifa, IsraelUniversity of Haifa, Israel

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

zooplankton

Grazing

Grazing may be an important factorGrazing may be an important factor and it can be expressed in several levels: and it can be expressed in several levels:There are huge quantities of wild fish in the There are huge quantities of wild fish in the vicinity of the cages and bio-filters. vicinity of the cages and bio-filters.

1. Some may use the cages/bio-filters just for 1. Some may use the cages/bio-filters just for shade/shelter (like in FADshade/shelter (like in FAD – – FishFish AttractingAttracting DeviceDevice(.(.

GRAZING (continue)

22 . .Some fish may feed directly on the remains of the Some fish may feed directly on the remains of the commercial fish feed (and secretion of the commercial fish feed (and secretion of the cultured fish?)cultured fish?)..

33 . .Some fish may use the above artificial food and Some fish may use the above artificial food and when it is unavailable - graze on the bio-filters. when it is unavailable - graze on the bio-filters. Other may graze on the bio-filters directlyOther may graze on the bio-filters directly..

• Our estimation of the biomassOur estimation of the biomass can be strongly can be strongly affected by the grazing. If grazing is affected by the grazing. If grazing is considerable we may greatly underestimate the considerable we may greatly underestimate the biomass of our bio-filters (just measuring what biomass of our bio-filters (just measuring what left AFTER grazingleft 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 Harvesting the wild fish out of the cages may be one way to remove part of the excess be one way to remove part of the excess organic loading from the marine environment.organic loading from the marine environment.

• There are also invertebrates grazers – such as There are also invertebrates grazers – such as sea urchins. We found them frequently in the sea urchins. We found them frequently in the

bio-filtersbio-filters

GRAZING (continue)

Preliminary sea-urchins count in bio-filters

(mean number / bio-filter / month)

MONTHMONTHFish CagesFish CagesReferenceReference

October 0111

December 0121

February 0222

April 021-

June 021-

– 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 wasdominants on ropes near thefish cages (F) while the spongeMycale and other invertebrates were common on the ropes inthe reference site (R). However we would like to continue monitoring the ropes to see the development (succession, etc).

““MUSSELS' ROPES"MUSSELS' ROPES" IN EILAT IN EILAT

F

R

In Eilat we are planning a quantitative survey of In Eilat we are planning a quantitative survey of the 4 major taxonomic groups found on the bio-the 4 major taxonomic groups found on the bio-filters in several OTHER artificial and natural filters in several OTHER artificial and natural substrates and to refer the findings to possible substrates and to refer the findings to possible artificial source of nutrients (e.g., sewage).artificial source of nutrients (e.g., sewage).

Considering using the idea of bio-filters in other Considering using the idea of bio-filters in other areas where there is organic loading – e.g., sewage areas where there is organic loading – e.g., sewage outlets, openings of fish ponds, etc.outlets, openings of fish ponds, etc.

FUTURE SURVEYFUTURE SURVEY

Mono-species cultureMono-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 isotopesStable isotopes We are processing more material for Sonja stable isotopes will collect more in Eilat and Mediterranean (the above experiment).

Some thoughts, questions and ideasSome thoughts, questions and ideas for the Future for the Future

•Timing - Timing - do we deploy the bio-filters in do we deploy the bio-filters in the proper time?the proper time?

Recruitment, especially in Eilat, may be Recruitment, especially in Eilat, may be considerably different in different seasons. considerably different in different seasons. The first recruit may determine the fate and The first recruit may determine the fate and the character of the bio-fouling.the character of the bio-fouling.

Some thoughts, questions and ideasSome thoughts, questions and ideas for the Future – for the Future – TimingTiming (continue) (continue)

Also, as Anat Tsemel have shown, bio-fouling on excitingAlso, as Anat Tsemel have shown, bio-fouling on exciting

bio-filters may be the source of recruits for the new bio-filtersbio-filters may be the source of recruits for the new bio-filters.

100%

+33+ + 55+ + 77+ + 99+ + 1111+ + 33 , ,20022002 MonthsMonths

Some thoughts, questions and ideasSome thoughts, questions and ideas for the Future – for the Future – material and designmaterial and design

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

Some thoughts, questions and ideasSome thoughts, questions and ideas for the Future – for the Future – Utilization of theUtilization of the

bio-filtering organismsbio-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 e.g., in Eilat true scleractinian, hermatypic corals grow better under the fish cages (on the corals grow better under the fish cages (on the benthic reefs , on bio-filters and on the buoys of benthic reefs , on bio-filters and on the buoys of the bio-filters than in other places - it is quite the bio-filters than in other places - it is quite remarkableremarkable. .

These corals can be transplanted to natural These corals can be transplanted to natural deteriorating coral reefs and be used for deteriorating coral reefs and be used for mitigation of such natural habitats.mitigation of such natural habitats.

Organisms with high Organisms with high environmental valueenvironmental value

Corals developed on the benthic reefsCorals developed on the benthic reefs

Corals developed on the bio-filtersCorals developed on the bio-filters

Corals developed on the buoys ofCorals developed on the buoys of the bio-filters the bio-filters