Dear Alex,

Although the concepts of meta-population and chaotic fluctuation of natural populations were
proposed and being developed fairly recently, fisheries biologists have been working on these
for many decades. Larval dispersal, retention and recruitment of fishes and invertebrates,
including molluscs, has been a focal point in the population dynamics in the marine environments.
There are several good technical or professional books on this topic, such as (Ecology of Marine
Invertebrate Larvae by Larry McEdward (Editor) 464 pages (May 1995) CRC Press; ISBN: 0849380464).

I have accumulated numerous examples for teaching and for my own research. We should
distinguish between "species extinction" and "commercial extinction" , the latter being the
case when a target species population (or stock) has been depleted to very low level that
does not provide any chance for anyone to harvest. We also need to recognize the problem
of local extinction as you pointed out.

There is a report that the endocrine disruption by TBT was responsible to a case of local
extinction (I guess it was still the commercial level) of the gastropod Babylonia japonica
at a certain bay in Japan. The stock was confined within a bay (being a soft bottom scavenger)
and its reproduction was blocked by sexual disorder by the pollutant. For those open and
inter-connected population of gastropods under TBT threats, locally affected unit population
may be able to persist by replenishment through larval supply from healthy environments.
However, the fishery statistics revealed a very rapid decline of the catch of the babylon shell
(and the end), so there might be a poor connection of this local stock with others located in
distant bays.

One of the sub-population of Donax cuneatus in my study was destroyed by a reclamation
of one sandy beach in southern Okinawa, forcing me to visit other beaches located far away
in less disturbed areas. I am interested in this species because its habitat is very specific
sandy beaches, so that adult populations exist at well-defined locations. Extensive color-
polymorphism of this wedge clam provides a tool to understand the connectedness between
locally-isolated populations. I hope to establish a good example of marine meta-population.

Masashi Yamaguchi