Date: 28 May 1998
From: Brian C. Paust <ffbcp@aurora.alaska.edu>
To: AQUA-L <AQUA-L@killick.ifmt.nf.ca>
QUESTION:
I am in the process of drafting a Pacific oyster site selection manual. There is, of course, an extensive literature base covering this specific question. Most references tend to agree that Crassostrea gigas will occupy the temperature range of 8-32 degrees C with the optimal range in the area of 15-18 degrees C.
However, much is being learned about the ability of these animals
to tolerate temperatures at the low end of this temperature scale. Some authorities have stated that the Pacific oyster will pass into a
hibernative state at temperatures lower than 5 degrees C. It is now
apparent that acclimated oysters can retain some level of metabolic
activity at temperatures as low as 1 degree C.
Oysters in Alaska grow very well within the temperature range of
8-12 degrees F. Alaskan experience is also changing our thoughts about the reproductive potential of these animals. According to various references, maturation commences at 12 degrees C and spawning at 18 degrees C and higher. Again, our experience in Alaska indicates that the Pacific oyster is a rather robust and resourceful critter - spawniness has been detected at even lower temperatures.
Brian Paust
University of Alaska
ffbcp@aurora.alaska.edu
***************
COMMENTS 1:
I have found with C. gigas intertidally they stop growing in the fall
around the end of October and start again around March/April.
Intertidal oysters must sort out food from silt, etc. and I suspect that
once the water cools down to around 9 degrees C. they are unable to
efficiently extract more energy from eating than they expend, and pass into stasis.
Subtidally, however, oysters will grow all year, depending on size. I have found in British Columbia, Canada, that oyster seed under 1/2 inch will not do well over winter. If they survive they are usually stunted. Once seed is greater than 5/8 or so they will do well over winter. As a result, subtidally I do not recommend seeding any oysters after September unless they are at least 5/8. This is obviously site dependent and will also depend on how often the seed has been screened. ie if the seed is at the top end of the size range or if you are receiving stunted seed to begin with.
My experience is that oysters, at least in the wild, will noticably be
differentiated around 17 degrees or so. They can spawn once they are mature and the temperature is at least a steady 20 degrees. A bump to 23 or 24 degrees in areas such as Pendrell Sound will make them spawn.
I suspect that hatchery experience is different.
The question from Sam also related to mussels being a transfer agent for seed. I have not see any oyster seed on LIVE mussel. I suspect that any larvae that gets close enough to a mussel to set is eaten by that same mussel. I have not even seen C. gigas oyster seed in mussel byssus. I have of course seen seed on dead mussel shell.
It is interesting to compare notes and it would be interesting to see some feed back from other areas as to their experiences.
W. E. Lorne Clayton, RPBiol.
President/Research Director
IEC COLLABORATIVE MARINE
RESEARCH AND DEVELOPMENT LTD.
4829 Maplegrove Street
Victoria, British Columbia
Canada V8Y 3B9
phone 250-658-0179
fax 250-658-4709
email claytonisg@pacificcoast.net
***************
COMMENTS 2:
The Gulf of St. Lawrence probably has the most extreme annual
variation in temperature and severe winter conditions in which oysters
occur naturally. Seawater temperatures are above 20C for several weeks in summer, approaching 30C in warm summers in some areas. In winter temperatures are at or below 0C for five months, a period of complete inactivity and shell closure for our native Crassostrea virginica. These winter conditions are limiting for some bivalve species, for example the Bay Scallop and at least some strains of the European Flat Oyster.
In 1969 when there was some interest in introducing C. gigas to
the region, I made observations designed to determine its reaction to our conditions and the prospect for successful, though undesirable,
colonisation.
The work was carried out at our Ellerslie Laboratory on Prince
Edward Island. The brood stock, which came from naturalised populations in British Columbia was held in quarantine and destroyed after spawning. Released eggs were reared in the hatchery and set on shell. Spat were held in controlled laboratory and field conditions with similar spat of C. virginica and O. edulis for 15 months when they were all sacrificed.
The C. gigas did extremely well, growing about twice as fast as
our native oyster and showing virtually no winter mortality, though they were also exposed to very low run-off salinities at that time. From my experience I would suggest that they are as tolerant of low temperature as any oyster!
One of my colleagues visited a marine lake situated in the extreme east of the Japanese islands where there is a natural population of
oysters in conditions which appear to be very similar to those at
Ellerslie. Perhaps someone can provide more information or I could try to find my records.
Roy
e-mail: rdrinnan@netcom.ca