Thursday, July 28, 2016

The Crown of Thorns Starfish in Macro! Acanthaster planci? or alien landscape?

Acanthaster plancii détail

Today as I was scrolling through the many years of posts I realized that I have NEVER written about the Crown of Thorns starfish, Acanthaster planci!  If you don't live in the Indo-Pacific you might not realize that this is actually one of the most heavily studied starfish in the world!  There are whole BOOKS written just about the biology and ecology of this single starfish species! 

Why? What makes this species so important?
This starfish is a voracious coral predator!  It just extends its stomach onto the fleshy tissue of a "hard coral" (i.e. scleractinian) and a little while later, only the "cleaned" skeleton of the coral remains! 
If it was a reasonable number of these animals feeding on coral, it would actually be healthy for the ecosystem. Predators control community structure and are important to ecosystem function..

The thing is though that this species, for reasons which have been studied since the 1960s, have undergone sporadic and localized HUGE population explosions! Their incredible abundance results in the wholesale LOSS of complete coral reefs! 
 Crown-of-thorns starfish

They have become especially infamous in the Great Barrier Reef and to many Australians who have become accustomed to physically destroying them on contact. They actually have developed ROBOTS to seek them out and destroy them.. 

So, unlike most starfish, they aren't very popular....

The Beauty of the Beast...

Image from Wikipedia, taken by Jon Hanson, in Thailand:
Here's the thing though. In spite of all the hate that gets laid on these animals.. I STILL think they are kind of freakin' AMAZING! 

So, today, I thought I would exploit the wonderous world of Flickr and show off some of these spectacular macro shots displaying the surreal surface of these animals...

The crown of thorns occurs across a WIDE range. From Baja California to Hawaii and Japan and then down to the east coast of Africa in the Indian Ocean. The range of colors is similarly vast! Its not entirely clear if these might represent separate species or perhaps represent some other kind of variation based on the environment. Perhaps food? growth? Difficult to say...

But genetics DOES indicate that there are multiple "cryptic species" across this animal's wide range in the Indo-Pacific..

The big thorny bits are of course, the spines.. the dark dots on the surface are the papulae  (or gills) and if you see little white or dark beak like structures, those are called pedicellariae whose function in these animals is not entirely clear... But likely some kind of "in close" defense against parasites or what have you.... 
Crown of Thorns Sea Star

Crown-of-Thorns Sea Star
Crown of thorns closeup - Okinawa
Crown-of-Thorns Sea Star (Acanthaster planci) from Aliha Giri.
Close-Up Thorns
crown-of-thorns star: Acanthaster planci
Close up picture of a Crown of Thorns Starfish (Acanthaster planci)

and the ANUS of course! That's the dark spot, probably surrounded by spines...  this shot is nice because it not only shows off the papulae (the gills) but also the pedicellariae (the red tweezer like structures)
Crown of Thorns Sea Star Center Close
Crown-of-Thorns Starfish - Kailua-Kona, Hawaii

As one finds often time in nature.. you have some big animal with lots of complex surface textures.. so are there animals to take advantage of it! Shrimps often live closely and among the spines on the animals' surface...

here are tiny shrimps.. some in the genus Periclimenes...
Sea Star Shrimp
Periclimenes soror on Acanthaster ellisii

And the ORAL surface!
Strangely enough, the top surface of Acanthaster is remarkably well known but how many people have actually seen the ORAL surface where the mouth is???

In addition to the tube feet all converging at the mouth, you also see the oral spines projecting into the mouth itself! 
Side B
and in this one, you can actually see some of the cardiac stomach below the purple spines...
upside-down crown-of-thorns
Crown of Thorns sea star (Acanthaster planci)
Crown Of Thorns Sea Star

And a video to top it all off!

At some point, there will be much, much MORE about the Crown of Thorns!