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I know things have been slow lately and I want to commend MJB for two *consecutive* posts that contained no personal attacks or stupidity. I would like to know, however, what the life cycle of a zebra mussel has to do with tech diving? Is this more of the rec.scuba invasion we've been seeing lately? C. ----- Original Message ----- From: "Michael J. Black" <mjblackmd@ya*.co*> To: <techdiver@aquanaut.com> Sent: Sunday, August 26, 2001 7:17 PM Subject: Re: Zebra Mussel Temp is a factor! > Thanks for the scientific insight Richard. I haven't dived Whitefish > Point for a couple of years, but was impressed with the lack of zebra > mussels there in 1999. Given that upbound and downbound freighter > traffic is heavily concentrated there (hence the many wrecks) I was > pleased to see not a single living zeeb. A park ranger at Isle Royale > told me a couple weeks ago that there were a few zeebs spotted at Windigo > (west end of island) but nothing too worrisome. Lake Superior holds the > secret to knock off these pests, and hopefully guys like you will figure > that out. > > MJB > > --- Richard Hayward <hddiver@sy*.ca*> wrote: > > > > Hi my name is Richard Hayward, I have been on the list for about 6 years > > have posted a few times, I am originally from Sault Ste. Marie but now live > > in St. Louis (The techdiving scene is non existent in the midwest. Bonne > > Terre mines could have potential but they only give guided tours there at a > > cost of 130$ for two air or nitrox dives yikes! everything else is quarries > > unless someone can guide me to something better please!), and have dove > > Whitefish point and the Straights of Mackinaw tons and also am a well > > traveled commercial diver. > > > > Presently I work with an ecological firm called Ecological Specialists Inc. > > as the scientific diving co-ordinator. I am not a malacologist (specializing > > in mussels) but work directly with two very well respected malacologists > > Heidi Dunn and Charles Howard. Ecological Specialist Inc. is located in the > > midwest specializing primarily in freshwater mussels among other things. My > > job is the identification of North American freshwater mussels for the > > purpose of estimating population densities, identifying endangered species, > > relocation, also for conducting dives per OSHA and USACE regulations plus > > many other objectives depending upon the client. It is not scuba, all > > surface supplied to answer the curious. > > > > The ability for a zebra mussel to survive depends on several factors > > including: > > > > 1) Temperature > > 2) Dissolved Oxygen > > 3) PH level > > 4) Calcium levels > > 5) Salinity levels > > 6) Water Velocity > > 7) Turbidity > > 8) Substrate condition > > > > The most important of these factors is temperature, calcium levels and PH. > > > > Temperature - > > > > "Temperature plays an important role in the seasonal life cycle and > > physiology of the zebra mussel. Particular temperature regimes cue major > > life cycle events such as reproduction and larval development. Zebra mussel > > spawning (release of gametes into the water column) will not occur at > > temperatures below 10 - 16 degrees C for either North American (Herber et > > al. 1989, Griffiths et al. 1991, Claudi and Mackie 1994) or European > > (Kornobis 1977, Stanczykowska 1977, Walz 1978, Borcherding 1991, Sprung > > 1991) populations. Garton and Hagg (1993) report a threshold of 18 degrees C > > for spawning in southwester Lake Erie. Thew water temperature ranges > > coincide with June - September in most of the the North American temperate > > freshwater systems. As temperatures decline in the fall, zebra mussels begin > > gamtonesis while good supplies are still adequate... > > > > Temperature also has a significant effect on zebra mussel growth. The term > > growth is used to describe the accumalation of somatic body tissue. Shell > > growth will not occur at temperatures below 3 degrees C (Smit et al. 1992). > > Temperatures as low as 6 degrees C (Bij da Vaate 1991)... Claudi and Mackie > > (1994) report a growth range of 8 - 10 degrees C for Lake St. Clair mussel > > populations. > > > > Temperature plays a significant role in the survival success of zebra > > mussels. It is on of the factors that may play a role in limiting the > > distribution of the animal. However it is important to realize that once the > > animals become acclimatized to warmer habitats, the upper thermal tolerances > > could shift over several years. Although they can survive temperatures > > slightly in excess of 30 degrees C for short periods, optimum temperatures > > are 0 - 25 degrees C. > > > > Values used for determining risk for temperature by the risk assessment > > calculator are as follows; > > If the number of months above 12 degrees C is > > less than 1 - slim to none > > 1 to 3.999999 - moderate > > 4 or greater - high " Zebra Mussel information System version 3.0 > > > > Here is a link to current lake superior temperature as of today August 25 > > 2001 it appears to be on average about 12 degrees C > > http://www.coastwatch.msu.edu/superior/s32.html or > > http://coastwatch.glerl.noaa.gov/cwdata/lct/glsea.gif which is close to the > > right temperature for reproduction but is only that warm for very short > > periods of the year and it does not appear that it is in the ideal > > temperature range long enough to support reproduction. The hot spots MJB > > talks about in Lake Superior also get the warmest during the summer if you > > look at temperature histories at these links. > > > > > > Calcium Levels - > > "Calcium (Ca) is a necessary element in the composition of the bivalve > > shell. Sprung (1987) reported that 40 - 55 mg of Ca per liter was sufficient > > for larval development and that a minimum of 24 mg Ca per liter was > > necessary for 10% larval survival. Stanczykowska (1977) found calcium from > > 28 - 109 mg Ca per liter in lakes with successful zebra mussel populations. > > > > Zebra mussels do not survive to any great extent when there is insufficient > > calcium levels. Calcium is a necessary component for shell secretion and > > formation. > > > > The following table (taken from Claudi and Mackie (1994)) illustrate the > > growth and survival of zebra mussel from waters with varying calcium levles. > > > > Growth and survival Calcium range mg/l > > no survival 5 to 6 > > poor growth 10 to 11 > > Moderate growth 25 to 26 > > Good growth 35 to >35 > > > > Values used for determining risk for calcium values by risk assessment > > calculator are as follows > > less than 20.999999 - slim to none > > 21 - 54.999999 - moderate > > greater than 55 - high " Zebra Mussel information System version 3.0 > > > > PH - > > "The pH of a body of water will play a role in determining zebra mussel > > success. pH lower than 7.4 will inhibit zebra mussel larval development > > (sprung 1987). Kornobis (1977) reports pH from 7.2-8.7 as having little > > effect on veliger densities in the phytoplankton. Other authors (Dries and > > Theede 1974 as referenced by Sprung 1992) reported that survival of bivalves > > was higher at pH values between 7.0 and 7.5 Stanczykowska (1977) reported > > zebra mussels in lakes with hypoimnetic pH values from 6.6 - 8.0 and > > epilimnetic values from 8.5 - 7.7. > > > > The amount of hydrogen ions in the water or the pH can significantly impact > > aquatic life. Bivalve molluscs, such as zebra mussels, are at risk at either > > extreme of the pH scale (i.e., below 6 and above 9). > > > > The following table (taken from Claudi and Mackie (1994)) illustrates the > > survival and growth potential of zebra mussels from waters with different pH > > values. > > > > Growth and survival pH range > > no survival 0 - 6.8 > > poor growth 6.9 to 7.4 > > moderate growth 7.5 to 7.8 > > good growth 7.9 to 8.0 > > best growth >8.0 > > > > Note how there is no upper survival limit for the best growth which is > > contrary to other published information where the incipient lethal larval > > level is around 7.4. Apparently, there are different thresholds for both > > immatures and adult growth. > > > > Values used for determining risk for pH values by the risk assessment > > calculator are as follows > > 0 to 6.7999999 - slim to none > > 6.8 to 7.39999999 - moderate > > 7.4 to 8.999999 - high > > 9 to 10 - slim to none" Zebra Mussel information System version 3.0 > > > > > > > > Water quality also suggests a very low calcium level of 5.9 mg/l reported at > > one station which is directly related to shell production other stations > > also reported some low calcium levels. Data available at this link > > http://oaspub.epa.gov/storpubl/legacy/proc_generate_next and that pH is also > > marginally condusive as well relating to poor growth. > > > > If you were to put all of these factors together, not just one on its own, > > they are probably what is keeping zebras from invading Lake Superior. > > > > The international joint commission also has lots of resources available at > > this link http://www.ijc.org/ijcweb-e.html > > > > I can do much more research to this fact as I have a lot of professional > > resources at my fingertips. > > > > Keep diving everyone, because now that I am in the midwest I miss the good > > times. > > > > Also the wreck diving in the great lakes is amazing especially whitefish and > > the straights of mackinaw, to say they are the best in the world though is a > > bold statement. I would definately say that they are one of the best spots > > in the world, for number and quality of wrecks, whitefish is deep but > > amazing, the straights however offer very nice wrecks and most of them under > > 100 feet means you can take you whole family there which is nice. The thing > > to remember when diving in the Great Lakes is the distance to a half decent > > chamber and someone competent in hyperbaric medicine. Just make sure you > > have your DAN insurance. > > > > > > Dive safe configure right. > > Richard Hayward > > > > > > -----Original Message----- > > From: Michael J. Black [mailto:mjblackmd@ya*.co*] > > Sent: Saturday, August 25, 2001 9:01 PM > > To: Aquanaut Mail > > Subject: Zebra Mussels > > > > > > Lake Superior not only has some of the best wreck diving in the world, > > it has very few zebra mussels compared to the other Great Lakes. Anyone > > wanna give a good explanation as to why this is? And before you say that > > the water is "too clean" or "too cold," consider that even the scientists > > don't know, but the low Calcium levels in the water may be part of the > > reason for the inability of zeebs to thrive in Superior. I have seen > > shallow wrecks (less than 60 ffw) in Lake Michigan become smothered with > > zeebs, beginning around 1995, obscurring engine details to the point of > > making the wrecks undesirable to dive. Deeper wrecks are relatively spared, > > but even depth doesn't stop zeebs or their relatives (Quagga mussels) from > > latching on. Improved visibility from these filter feeders is often > > exaggerated by divers, but there is no question that water clarity has > > improved wherever zeebs have taken hold, some consolation. > > > === message truncated === > > > > __________________________________________________ > Do You Yahoo!? > Make international calls for as low as $.04/minute with Yahoo! 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