Dear Christian,

> There is another interesting thing, called MARBENA, which is a European
organizer of internet conferences (some are ongoing, worth looking at).  A
couple years ago they had a meeting here in Mallorca, and I had the
opportunity toi speak with its coordinator.  He was striving to find good
bio-indicators for coastal ecosystems throughout the continent.  I suggested
looking at the abundance and sizes of cockles -the abundant, moderately
diverse Cardiidae.

That sounds good. Some thoughts: A good bioindicator should be easy to
identify correctly, not a web of closely related species. Its abundance
should be measurable in a repeatable manner using only inexpensive means
(shovel, bucket, thermometer, etc., not molecular genetics). It should be
photographically documentable so identifications can be confirmed.

Edible species such as cockles have advantages and disadvantages as
bioindicators. Their historical and present distribution and behavior tends
to be better understood than that of other species, but because they are
edible, their size and abundance may depend locally on human predation
rather than on water quality and other environmental factors.

Practice and theory can be very different! On Alabama's Gulf of Mexico
coast, David Kopaska-Merkel and I counted the holes of ghost crabs (Ocypode
quadrata) in standard transects, and the number of coquina clams (Donax
variabilis) in a square 0.3 m on a side. These are common beach animals and
we anticipated that their abundance might be related to a general
"environmental health" of individual beaches. It turned out that the ghost
crabs, which are scavengers, thrive on trash and their numbers actually
increase in built-up areas, if enough of the dunes are left undisturbed for
them to dig their holes in. And the coquina clams' distribution, as
discussed previously on Conch-L, is very patchy on any one beach, making it
necessary to repeat the measurement many times -- so much for quick
observation!

The presence or absence of plant species can be excellent indicators of the
health of sand dunes. On the Alabama coast, the single most important dune
plant is sea oats (Uniola paniculata). It's common in healthy natural dunes,
uncommon in overdeveloped areas, persistent through the year, and easy to
recognize and to photograph -- a very good bioindicator.

Dead shells can be very helpful to round out a species list, but recent
carbon-dating by Kowalewski and others shows that shells thousands of years
old may look like recent ones, so dead shells (especially of robust species)
may not accurately reflect the current fauna. However, it's not a good idea
to throw away easily collected data either! On the Alabama coast, we often
find the Eastern oyster (Crassostrea virginica) cast up on the beach, but
all of these robust shells look reworked (discolored, disarticulated,
abraded, always dead). That makes sense, because this species thrives in
brackish water and we know that brackish-water deposits are currently being
eroded offshore. As far as I can tell, FRAGILE shells on the Alabama coast
are much more likely to reflect current conditions, because they cannot be
moved far without being broken up. Look for signs of recent life such as
articulation, living color, preservation of organic tissues (muscle,
ligament, periostracum), sharp margins, and so on.

It can be very difficult to interpret data if they are collected in many
different ways. (For example, if one person always measured Donax
populations at low tide but another always measured them at 10 o'clock in
the morning regardless of tide, the results would be difficult to compare.)
So I'd advise local shell clubs to standardize their data collection within
each group, and also pay attention to what other shell societies are doing.
These procedures can be posted on the Web for anyone to see and comment on.
Each group should be willing to change their procedures based on new
understanding. As it turns out, David and I found that Ocypode quadrata is
an excellent bioindicator even though it does not indicate what we thought
at first. Donax variabilis is more problematic and we are still testing it
as a bioindicator.

Cheers,
Andrew

Andrew K. Rindsberg
Geological Survey of Alabama

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