Rock pools
VulcanSpirit
Richard & Alison Brunstrom
Fri 17 Feb 2012 13:05
|
I had not realised how rare the British seashore
rockpools are at global level. To get good tidepools there must be a large tidal
range, the right geology and coastal morphology, and a temperate climate.
We have seen nothing like them since leaving the UK, and there are certainly
none here!
Instead there are reefs. Here I am at low tide
(less than 1m range) walking out onto the reef. No pools just shallow water
which is difficult to see into because of the constant wind at this time of
year.
 And here is the best thing I found.
 This is the Caribbean Reef Octopus Octopus
briareus; he is about 30cm across, perhaps a little larger if he stretched
his legs out fully. He was crawling along hunting in the shallow
water - as you can see his eyes are above the surface so he was hunting by feel.
It was a quite extraordinary sight to see him crawling quickly along actively
searching in all directions with eight limbs at once, constantly changing colour
quite dramatically, from totally white to dark brown and an infinite number of
spotty and striped versions inbetween. Amazing.
You can just about see his eyes. Octopus eyes are
strikingly similar in morpholgy to human eyes. They are 'camera type' with a
lens, retina and pupil but have evolved completely separately from our eyes. In
zoology they are used as a classic demonstration of 'convergent evolution' -
starting from two very different positions the eyes of humans and octopuses have
independently evolved to be very similar because they are performing the same
function and evolutionary pressure has therefore driven their development in the
same direction.
It is one of the great ironies of our time that the
strangely resurgent creationists should use the structure of the eye to 'prove'
(with no evidence other than their conviction) that because of its complexity it
must have been created, complete, by God - while scientists use
exactly the same complexity to prove (but this time with rock solid evidence)
the fact of evolution. We now know, without doubt, that sight has evolved
independently at least six times (presumably because of the enormous advantages
it bestows), and use the similarity of the human and octopus eyes to demonstrate
the power of evolutionary pressure to drive development. But sadly no amount of
evidence is going to convince someone whoe mind is closed - and hence the
current frightening nonsense of the religious right in the USA which is
surfacing in the Presidential campaign. .
|