Northwest Dive Club

Very nice work. Two enthusiastic thumbs up.

Could the explosion in sea urchins be linked to the decline of sea stars perhaps?

Probably, although I see more and more healthy looking stars every dive.

From Dr Paine:

I'd expect nothing less from sea urchins. A thought and a question. There's no doubt that Pycnos eat urchins but there has to be a question of relative body size of predator and prey. If small urchins continue to recruit, and small Pycnos eat them [that's unknown], they should be able to grow. But those urchins look almost uniformly large.

He also noticed the same thing some folks have commented on, that these urchins are not "1 year old" urchins, and are of reasonably uniform mature size. The recruits on the passenger ferry pier are new and possibly there in mass due to a lack of predation due to sea star wasting. The question then is: "why and where did these urchins come from?" Prevailing wisdom would indicate its due to lack of predation from the large sunflower stars, meaning Cove 2 is now 'safer' with lots of vegetation and algae for them to nosh on - therefor they are moving in where the food is, perhaps from deep water or ??

We are also seeing a lot more cockles in the shallows. Not that there are "more" per se, just that they are less hidden.

Hi Laura,

Thanks for posting this video; it's the first thing I've seen that gives an idea of the size of the urchins that everyone is concerned about. As you mentioned, these animals are too large to have settled after SSWD was first noticed and must have migrated from elsewhere. It's interesting to think about how the reduction in predators might have affected the movement of urchins
For anyone interested, here's a paper on the growth rates for Green Urchins on various diets:
http://myweb.dal.ca/rescheib/marbio129_159.pdf

Predaciously yours,
Alex

They move in giant hoards out in the straits as well. Most recently it seems after the Elwha undamming. Both the understory and overstory kelp was wiped out so pretty much all the urchins moved west out of the plume and descended upon Bachelor rock and west. This caused an impressive urchin barren. Some footage of the urchins on Bachelor can be seen in the Otter story from Quest/PBS.

It will be fascinating to watch what happens come spring/summer when all the foliage starts growing... Will we see 'urchin barrens' in Cove 2? On the bright side, we could perhaps encourage them to hang out on the boundary line and keep it clean