Monday, 25 June 2007

Rock star

I haven't been out on my morning seaside rambles at Williamstown for the past few days, so here's something I prepared earlier.

Little black cormorants hang around in large numbers at low tide but they're cautious and easily spooked. I took these pictures with the zoom at maximum focal length.

I didn't notice that I'd photographed more than just the cormorants. The rocks are covered in mussels. Big ones, thanks to the ban on collecting molluscs in the intertidal zone. But that ban only applies to humans. The feathered marauders have immunity, as do the invertebrate ones.

Also on the rocks is a North Pacific sea star (Asterias amurensis. This species in native to the NW Pacific but was inadvertently brought in Australia in ships' ballast water. It was first recorded from Tasmania in 1992 (although it had probably been introduced in the previous decade). From there, it spread to Port Phillip Bay.

Like many other large (and small) sea stars, it is a voracious predator, taking on just about anything and everything. In SE Tasmania, it had been implicated in the decline of the endangered spotted handfish (Brachionichthys hirsutus). The sea star's impact is twofold: it feeds both on the egg masses and on the colonies of sea squirts used as nurseries by the fish.



How long can the sea star survive out of the water at low tide?

Snail said...

The little (big!) beggars are pretty tough. I haven't tried any experiments but I suspect they're good at surviving emersion.