Hi Dan,

Glad to hear that you're still doing outreach with children. Here's my take
on the first two questions, but these are big broad topics and others should
feel free to continue the discussion.

> 1. Seeing various sizes in the species, (some from deeper waters and
> others intertidal), is there a reason for this difference?  Is there
> an advantage to a bigger size... for the animal?  No, not the
> collector/dealer.

For animals that have many young, large size means more offspring, a
competitive adavantage. For animals that have only a few young, like people
or elephants, large size often allows better care for offspring.

Large size can also mean fewer predators; not many animals dare to attack a
whale. But for mollusks today, large size can result in a higher risk of
predation from people. There aren't many large abalone (Hasiotis) left in
easy reach on the California coastline, are there?

Cause and effect are very often indirect and may be subtle. A large,
intertidal bivalve may be able to burrow more deeply, thus avoiding not only
predation, but also rapid changes in environment, since the burrow will
remain wet when the tide goes out. We don't know many of the why's and how's
of this kind. Victorian naturalists made great progress in understanding
natural history at this scale -- enough to make it clear that they just
scratched the surface. Amateurs today have much greater resources at their
disposal to play this game (time, cameras, online publication of results),
but it does take patience and self-discipline.

2. Having many color variations and color banding, as are found in Northern
Vancouver Island, Canada, is there a cause of this, besides genetics?  (For
those interested in Port Hardy specimens photo, please e-mail privately)

This is a HUGE topic. In some cases, color variation is rife because it
doesn't matter to the animal; for instance, color patterns underneath a
periostracum, in a deep dark burrow, or on the interior of a shell don't
have any obvious evolutionary significance, at least not visually. In some
cases, notably where the main predators use their eyes to spot prey, a broad
range of colors and patterns can confuse these predators or make the prey
look like something else. And so on and on ... As visual animals, people
tend to assume that anything they see has a visual significance, but some
predators (crab, octopus) use eyes and others (starfish) feel or 'taste'
prey instead.

A lot more could be said on each of these topics, let alone the others that
Dan Yoshimoto brought up.

Cheers,
Andy

Andrew K. Rindsberg
Geological Survey of Alabama