From: Robert Rheault <skid@gsosun1.gso.uri.edu>
To: AQUA-L@LISTSERV.ifmt.nf.ca
COPPER AND OYSTERS
COMMENTS 1:
Post-set oysters in open water probably can tolerate copper pretty well. I think dilution is the key - that and the fact that most metals rapidly adsorb onto particles and sediment out of the water column so that ambient concentrations in the water are low even if there is a good source of new metals to the water.
I believe it is a different matter with larvae - especially with Crassostrea virginica - I seem to remember that toxicity studies showed that the larvae were sensitive to copper at levels two orders of magnitude below those that impact adults. I will try and see if I can dig this up.Were the oysters on your salmon nets gigas?
In closed or semi-recirculating systems -like most larval rearing tanks
I think the problems can develop rapidly. I offer as evidence this story that was related to me by a hatchery operator who will remain nameless.
In a new facility copper pipes holding FW were suspended over setting tanks and on the cold water line condensate would occasionally drip into the tanks below. Until this was corrected this grower (with many years of experience) was unable to get survival and growth in this system.
I think you have to ask why you want to use copper in the system. There are suitable and economic alternatives available - plastic - fiberglass - even economical epoxy coatings that can be applied over metalic impellers to retard electrolysis and wear. Why risk toxicity and stress?
Robert Rheault <skid@gsosun1.gso.uri.edu>
Moonstone Oysters
COMMENTS 2:
I wasn't referring to C. gigas in describing the common settlement of oysters on copper-rich surfaces. Our native species is C. virginica, the only species in the areas I refer to and the only one which sets significantly in the field in Eastern Canada. Our production of this species has been well-known worldwide for more than a century. They can be found, along with your company's product, amongst the highest-priced half-shell oysters in better oyster bars in the U.S.
Surely you must admit that settlement of larvae on copper-treated nets or other surfaces clearly demonstrates tolerance of levels of copper
which must be quite significant, certainly high enough to deter all other species, including bivalves such as Mytilus and Mya which settle heavily on similar, untreated, materials at the same site. The act of attachment involves a very close contact with the surface and subsequent growth and survival takes place within millimetres or even microns of this same surface. I can't believe that the same phenomenon doesn't occur along the US Eastern Seaboard. Not, perhaps, on the netting of fish cages. Only in Eastern Canada will you find salmonid culture and virginica culture in the same area!
I agree completely that one should use materials with the least potential for toxicity. I was promoting a realistic appraisal of copper alloys and alternatives. In 45 years of experience with bivalve hatchery technology I have come to view the term 'inert' with great suspicion. I have seen toxicity associated with moulded plastics and fibreglass, stainless steel, air and even raw seawater!
As for drips from a copper pipe into a larval rearing tank, of course this is not acceptable. A facility so badly designed as to allow anything to drip into a rearing tank would be likely to have plenty of other problems!
Roy Drinnan e-mail: rdrinnan@netcom.ca
RR#1 Musquodoboit Harbour. Phone: (902) 889-3432
Nova Scotia, Canada, B0J 2L0. Fax: (902) 889-2905
COMMENTS 3:
I think the essential difference in apparent toxicity is the difference
between open systems and closed or semi-recirculating systems.
As the old adage goes.- Dilution is the solution to pollution.
As for the need for good science, you might want to check the latest
Journal of the Nat. Shellfish. Assn. vol. 15:3 p589-596 Chang et al. , Effect of biofilms on toxicity of Cu and Zn to virginica and gigas larvae. They seem to imply effects on setlement behavior and metamorphosis at rather low concentrations - but keep in mind this is in a beaker - a closed system!!
I think the open water is a whole different story too; however I believe the post that started this thread was one pertaining to bronze impellers that one might presume were pumping water into a hatchery with closed or semi-recirculating tanks. Here I would be very careful.
Robert Rheault <skid@gsosuni.gso.uri.edu>
Moonstone Oysters
oysters@ids.com
COMMENTS 4:
A few thoughts - first, despite its toxicity at higher doses, copper in very low doses is a trace element required by most organisms including bivalves.
Second - a "slime coat" or other thin, perhaps biotic layer may form up over the copper, rendering it less toxic to larvae looking for a place to set.
Third - oyster larvae can be attracted to substances one might reasonably think of as toxic or noxious. For example, don't have the ref. here, but Steve Coon and others have found ammonia to attract eyed oyster larvae.
Will Borgeson <wdborgeson@ucdavis.edu>
COMMENTS 5:
Well, oyster are filter-feeders and therefore obtain their food from the
particles in suspension in the water column. If these particles contain a toxic compound, it will enter the organism in a different way, potentially more dangerous. Few studies have been carried out in this particular field, but more are needed.
S.C.Charrier, <r_001f5_sc@southampton-institute.ac.uk>
Southampton Institute, UK
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