>The purpose of this posting is to inject a somewhat different
>perspective into the concept of biodiversity in a single point in
>time and space.  While this is not a "controlled" or truly
>quantitative, unbiased study, it gives me a sense of what's there,
>how many one can get with minimal (field) effort, yet these samples
>have not been ostensibly winnowed by mechanical (dredge) or
>geological (fossil concentrations) machinations. The diversity in a
>few handfuls of beach sand can be astounding and informative.
>Furthermore, these results underscore the fact that one is
>well-advised, within the obvious constraints of time, etc., to look
>nearly everywhere and look often to get the best picture of
>biodiversity.

I find that dredgings in coarse sediments (sands, gravels) are indeed
winnowed by the water flowing through the dredge. On several canyon
hauls I have had the rockdredge (steel cage w/steel mesh) come up
clean except for say a lone Calliostoma alertae or Columbarium
mariae. BUT if you hit gluggy mud the case is entirely different...
it sits there in a rticky coherent lump and resists all attempts by
the water to steal the contents... this is the jackpot. I don't know
how many species my last mud haul brought up (have to admit the
dredge travelled about 300m vertically as it went up the canyon
wall), but my split of the mud has yielded a very large fauna.
Collected 6 years ago, I STILL haven't finished sorting the
material... so can't give a meaningful count.

The funny thing is, such a sample may contain literally billions of
one species, but only one of another (and who knows how many species
present were not collected at all, as the dredge churned its way past
the nearest specimen?). I suppose I sorted a lot of liters of mud &
muddy sand, and handpicked the entire seived results (seived to about
6 particle-sizes), so I know I missed nothing over 4mm... and I'm
resorting just to make sure. So there were a number of species
represented by ONE specimen, eg a tiny articulated Acesta maui and
?Electroma. Some were very rare (~20 specimens of a species of
Vacerrena first known from this haul) and others were abundant
(Thieleella flemingi, Thieleella probably being a synonym of Anatoma;
present in many dozens) to plague-proportions (Turritella
symmetrica). I just wish I knew what was found in the larger
fraction, held by a museum.
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
<[log in to unmask]>
Seashell, Macintosh, VW/Toyota van nut

----------------------------------------------------------------------
[log in to unmask] - a forum for informal discussions on molluscs
To leave this list, click on the following web link:
http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1
Type your email address and name in the appropriate box and
click leave the list.
----------------------------------------------------------------------