Re: Microscopes anyone?
- From: "Tidepool Geek" <big_smegma@xxxxxxxxxxx>
- Date: 26 Oct 2005 11:42:02 -0700
> Anyone use a microscope to examine the life in their seawater that a
> magnafying glass alone won't reveal?
Hi Robert,
I volunteer at a small public aquarium and the microscopes are among
our most popular exhibits. We've got a couple of dissecting scopes for
the public to use and a compound scope which is hooked up to a small TV
camera and 'operated' by a member of the staff.
Our dissecting scopes deliver 10X or 20X magnification (switchable) and
this is fairly common for this class of scope. There are some on the
market that go as high as 30X or even 40X but, as may become clear
later in the message, that's not necessarily a good deal.
20X is usually plenty of magnification to see and identify most of the
larger phyto and zooplankton - diatoms, diatom chains, copepods, and
various kinds of larvae. Smaller stuff, like dinoflagellates, protists,
rotifers, etc. are basically going to be indistinct dots. OTOH: We
frequently switch down to 10X in order to gain a wider field of view
because some of these little beasties swim fast enough that it's hard
to keep them in frame at 20X. Higher magnifications obviously make that
situation progressively more difficult.
FWIW: We've found that the only satisfactory viewing with a dissecting
scope comes from having the subject(s) illuminated simultaneously from
both above and below.
If you want more power then you have to step up to a "compound"
microscope of the sort that Wayne recommended. Generally these have a
turret of objective lenses that give 40X, 100X, 400X, & 1000X (1000X
isn't really practical for the sort of stuff we're interested in).
These scopes can show you some amazing things but there are specific
considerations to be taken into account. First, you'll need at least
10X magnification in order to wrangle a single specimen onto a
microscope slide. Second, most zooplankters are too big to be displayed
on a flat slide; make sure to get a few slides with depressions for
examining things like copepods or larvae. OTOH: When you're looking at
the small stuff, you're better off with flat slides since you'll be
using a higher power with a much shorter depth of field. Slides are
fairly robust and should last quite a while with reasonable care but,
unless you've got a laboratory supply house in your neighborhood, lay
in a lot of slide covers. These things are so fragile that you can
break one with a hard stare - I don't think we've ever fired up the
compound microscope without breaking one or two of these things.
If you decide to get a compound scope then definitely do as Wayne says
and get the movable stage option. Most of the things you'll probably
want to look at will be constantly swimming out of frame and a movable
stage is really the only practical way to keep up with the little
buggers.
Regardless of which type of scope you choose the most important
consideration has to do with what you want to look at and to what
lengths are you willing to go to do it. If you're interested in
mid-water plankton you'll need to concentrate your sample or you
probably won't find much of anything. Here's an example: The northeast
Pacific ocean has some of the highest plankton densities on earth and
that's where our facility is located (Port Angeles. WA). In late spring
through mid summer the plankton is so thick that SCUBA divers often
report visibility of three feet or less. In spite of that, if we just
went out on the dock and dipped out a liter of water I doubt that we'd
have more than a handful of organisms in each 20cc sample that we put
under the scopes for the public to view. What we do is to take a
plankton net to the dock and drag it through the water for 5 to 15
minutes such that we've concentrated the plankton from several hundred
gallons of water into one liter. Google up some pictures of plankton
nets and I'm sure you could come up with a design for a miniature
version - perhaps using a non-disposable coffee filter.
OTOH: If you're interested in the denizens of your DSB you've got a
different problem. The density of life in and on the sand is probably
fairly high but if you can't separate the animals from the sand you
won't see them (or at least not very well). The sand will block
virtually all the light coming from below the sample and substituting
extra light from above doesn't seem to work. The only solution that
comes to mind at the moment is to use a technique analogous to panning
for gold - the difference being that you're interested in collecting
the lighter material that hopefully contains the animals.
Finally, if you're not interested in plankton sized animals, a
dissecting scope can show a ton of otherwise hidden detail in things
like barnacles, sponges, bryozoans, and even some cnidarians. If you're
willing to do some pretty finicky preparation, a compound scope could
show you some pretty amazing stuff about various filter feeding worms
and maybe even individual nematocysts from anemones or corals.
Magnifically yours,
Alex
.
- References:
- Microscopes anyone?
- From: Bob
- Microscopes anyone?
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