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A pyramid of spider crabs. Photo courtesy of Pink Tank Scuba |
PT Hirschfield and some friends were diving
near the Blairgowrie Pier in Port Phillip Bay, Victoria, in Australia when they
encountered a most unusual sight: close to 1,000 spider crabs crawling over
each other to make a huge pyramid on the ocean floor.
It’s the time of year when all the spider crabs gather for a mass
migration and simultaneous molt, so the divers were on the lookout for the
congregating spider crabs and found this (one minute of video captures the
essence):
The odd behavior comes as a pre-migration act, but not much is
known about it.
“Unfortunately, not much official research is done
on the spider crabs so it's more guesswork based on observation than anything,”
Hirschfield told GrindTV. “I hope to spend a solid week underwater
with them when the migration proper happens to continue studying them more
closely, but the pre-migration stages remain somewhat of a mystery.”
Hirschfield added that the sight of a spider
crap pyramid is “pretty unusual, at least in the shallows. I’m not aware of
anyone having seen a pyramid this high, though who knows what happens at depth?
“The behavior I observed was really just a lot of climbing and a
few scuffles as crabs got in each other’s faces…A few of the crabs in the
pyramid were also adorning themselves with sponges becoming decorator crabs,
which is a camouflage mechanism.”
All pre-migration behavior is short-lived. Hirschfield recently saw
a couple thousand spider crabs in the shallows at the start of a two-hour dive
and they had all but vanished by the end of the dive.
So it is unlikely that the pyramid lasted very long, making the
encounter that much more special.