Tuesday, November 16, 2010

HUGE swarms of Pycnopodia helianthoides (Sunflower Stars) in British Columbia! Starfish Swarms?? Has the Invasion finally come?

(Image courtesy N. McDaniel)
A slightly different kind of post today. One that is a little more in the category "citizen science" than my usual stuff.

So, about a week ago, I received an email report from Neil McDaniel, a marine photographer and cinematographer. (His website with stunning pix is here) regarding an unusual occurrence.

Pycnopodia helianthoides, the large sized and immediately recognizable "sunflower star" present on the west coast of North America, from Alaska to Southern California was being observed in MASSIVE numbers in British Columbia. In Mr. McDaniels' own words:
....Hordes, and I mean hordes of Pycnopodia can be found in the shallow subtidal in Howe Sound, a coastal fjord near Vancouver. During one dive where I covered all of 100 metres horizontally I found densities like this in a band perhaps 3 metres across starting at about 2 m below datum and extending downward to about 5 m below datum. It’s not an exaggeration to say there were several thousand just in this area. Not all of Howe Sound is like this but many areas are. So what’s happening here?
Normally, when one encounters Pycnopodia, its found by itself or rarely in the company of one or two other individuals and they're usually competing for food.. This video gives you a general idea of what Pycnopodia is typically like...

But pictures from Howe Sound in BC shows this:
(Image courtesy N. McDaniel)
(Image courtesy N. McDaniel)
(Image courtesy N. McDaniel)
(Image courtesy N. McDaniel)
and then, I put it together with a Vancouver Aquarium video on YouTube from August 2009. Note the ABUNDANCE of sunflower stars! Based on what I know of, that's unusual....

The Vancouver Aquarium account reads
Research diver Donna Gibbs was able to record on videotape a remarkable event that occurred at the time of an extreme low tide along the shoreline of West Vancouver, just east of Whytecliff Park. As Donna prepared to start a dive with Jeff Marliave at Kettle Point, the crew exchanged comments about the strong shoreline current, as well as the apparent red tide condition. The sea surface was also at a record 23 degrees Celsius. Donna and Jeff went down on a planned drift dive toward the west, counting rockfish at an artificial reef and along natural shoreline reef areas that have been monitored for this entire decade.

The water clarity was excellent at depths below the red tide, and the dive plan proceeded normally until an area was reached where vast numbers of the giant sunflower sea star were covering the rock surfaces. At this point, a down-welling component of the shoreline current was evident and the sea stars were rapidly moving down the slope of the rock. The sea stars were traveling so quickly that they were running over each other, creating slow-motion landslides of sea stars tumbling down the slope.
So, what's going on???
I've asked around my network of scientist and diver colleagues in more southern regions..i.e., California and none of them has seen more than a couple of individuals of Pycnopodia together at one time.

I've even consulted with my colleagues who work in the deep-sea around California.. They see the deep-sea cousin of Pycnopodia, Rathbunaster...and although it can occur in high numbers, its generally different than what's being seen with Pycnopodia... Here's a couple of examples:

Are there possible explanations? Sure. For example....

1. Populations are high because juvenile survivorship is high. This is basically what happened with the crown of thorns (Acanthaster planci) in Australia.

Some environmental factor is different leading to a high survivorship of juveniles leading to a huge abundance of adults. In the case of Pycnopodia, this has not been documented. Could it be Food? Water temperature? Nutrients? Hard to say.

2. Could they be spawning? A lot of invertebrate species gather in large aggregations in order to facilitate spawning. The males produce their sperm and the females are handily nearby to facilitate fertilization between sexes.

That said, most observations of Pycnopodia have never documented more than a few specimens at a time at most... and none of the pictured/recorded individuals seem to be producing reproductive material...
(pic courtesy of Allison Gong, UCSC)
Speaking of which, one of my colleagues Dr. Allison Gong has helped produce an account of the subsequent development of Pycnopodia. You can see that here...

So where does that leave us??
This huge, dense clustering of Pycnopodia is something that I, and many of my colleagues have never seen before. And when the combined experience of close to a dozen scientists haven't seen something on the west coast of North America??? Something weird is going on..

What could be causing it? What could be causing these mysterious swarms of giant, sunflower starfish? Are they just well-fed starfish? Climate change? Food? Social gathering? How does this affect the ecology of the area? How often do these high populations persist?
Could they be preparing an invasion? :-) (disclaimer: the great starfish invasion may not be real...)
(please note that this photo was performed by a professional-please don't try this at home!)

Unlike my other posts-this is NOT a report on a paper...I thought I would throw this out there as a general announcement to divers, scientists and interested folk!

Has anyone out there seen these massive, dense aggregations of sunflower stars? Do you have additional video? Pictures?

Contact me through my profile and let me know!
(THANKS again to Neil McDonald for allowing use of his pictures!)


tshilson said...

My first thought was a mating swarm, but they seem to be moving too fast. Any idea of the lunar cycle at that time. Isn't mating in other critters usually done at high tide?

You mentioned Red Tide and down-welling. Are the stars sensitive to the Red Tide organisms. Could they be migrating (stampeding) away from the tide? (I am having trouble recalling the name of the Red Tide critter. Dinoflagellates?)

P.S. The hyphen in down-welling is to keep the spellchecker happy.

ChrisM said...

Both interesting ideas.

The mating swarm issue I addressed- there don't seem to be any reproductive materials being produced. And Pycnopodia occurs in California-so why have these huge numbers never been seen?

I don't know much about the effect that red tides would have on Pycnopodia, but there's no evidence that harmful algal blooms are so toxic to this species that it would create such an extreme reaction. Not saying its not-but none of these individuals look sick (and in fact they look pretty healthy)

Plus, if something was that toxic to Pycnopodia it would probably be toxic to other asteroids or even to other echinoderms, which are not apparently affected or even moving away.