The Crown-of-Thorns Starfish

Clouds of reef fish and corals at Papahānaumokuākea Marine National Monument.

I know I just did a post on National Donut Day, but that piece was both tongue-and-cheek and nakedly self-interested.  Clearly donuts are ephemera with transient importance—scraps of fried dough which stay tasty for less time than flowers bloom (indeed I enjoy juxtaposing their cheap impermanence with the vast seemingly eternal universe in my paintings).  Today I looked at my calendar to find that June 8^th is World Oceans Day!  Unlike National Donut Day (which is self-evidently a meretricious marketing “holiday”), World Oceans Day strikes me as an important and worthwhile day of observance.  The ancients celebrated the oceans with festivals and sacrifices to venerate the sea gods.  We tend to regard the oceans as an inexhaustible source of cheap fish and a place to dump our rubbish.  I worry that the careless industrialized spoiliation of the oceans is the gravest mistake humankind is currently making (and we have our grubby grasping fingers in lots and lots of pies—and are making plenty of errors).  Yet, I don’t want this blog to become an angry jeremiad or an environmentalist harangue.  I want to celebrate the beauty and grace of the oceans and their inhabitants while also underlining the stress and danger which these vast swaths of the world are facing.  What to do?

An infestation of Crown-of-Thorns Starfish

For World Ocean Day therefore I am writing about the lifeform which, to me, most exemplifies the oceans of the late Holocene/early Anthropocene, the crown-of-thorns starfish, Acanthaster planci. This echinoderm is a ravenous poisonous destroyer which is exploiting the sickness of the oceans to proliferate and succeed wildly (at the expense of everything else).  It is an amoral ravenous monster covered with toxic spines which is eating the coral seas bare.  It is also a beautiful creature magnificently evolved to thrive—we can hardly hold its horrifying success against it.  Maybe it should be on the cover of Forbes smoking a cigar and bloviating about its philosophy of success.  By chance the starfish also lies at an intersection of many blog topics—crowns, invaders, colors, poison, mollusks (for its fate is connected with that of predatory mollusks), opinion, and science…perhaps even “deities of the underworld”.  This is a lot of introduction…let’s meet our antihero!

Crown of Thorns (Acanthaster planci) photo by jon hanson

The crown-of-thorns starfish (or “sea star”), Acanthaster planci takes the form of a spiked disk with up to 21 prehensile arms (also covered in spines). On its underside, the starfish has numerous sticky tube-like suction feet running along the bottom of each arm. These legs run in parallel rows beside a series of closely fitting plates which form a central groove on the bottom of each arm.  The arm grooves each run ominously into the starfish’s horrifying stomach/mouth.  The starfish can grow to a diameter of up to 80 centimeters (31 inches) although they are more commonly found in the 35 centimeter range.  Acanthaster planci has a wide Indo Pacific range and lives in tropical and semitropical coastal waters from the Red Sea and the East Coast of Africa across both the Indian and Pacific Oceans all the way to the West Coast of Central America.  The starfish are usually dull grays and reds but they can range to brilliant purple, blue, orange, aqua (or display all sorts of mixed ranges). Their colors are highly mutable and variable! These starfish eat coral polyps!  It crawls into corals by means of its many sucker feet—compressing or elongating its body as needed.  When in position the starfish extrudes its stomach over the polyps it wishes to eat: the stomach can cover an area approximately equal to the starfish.  The creature then releases digestive compounds which dissolve the soft parts of the coral into a soup which the starfish slurps up.  It then retracts its stomach and moves on, leaving a bleached (i.e. dead) patch of coral skeleton.  A medium sized starfish can consume up to 6 square meters (65 sq ft) of living coral reef per year.  If times are lean the starfish can go for months (or longer) without eating. http://www.arkive.org/crown-of-thorns-starfish/acanthaster-planci/video-00.html Crown-of-thorns starfish are male or female and they do not reproduce by budding, but female starfish lay from 6.5 million to 14 million eggs each per breeding season [hereupon the author wiped his furrowed brow].  When the eggs hatch there are several interesting larval stages which the echinoderm goes through before reaching their adult form.  Suffice to say, the starfish reaches sexual maturity after 2 years and it lives as long as 8 years. Fourteen million offspring per season is a lot!  If predators do not keep the crow-of-thorns starfish in check, they can swiftly overrun entire reef systems and eat all the coral into bleached uninhabitable wasteland.  This leaves all of the multitudinous reef inhabitants homeless.  The reef skeletons dissolve in our newly acidified oceans and one of earth’s most diverse ecosystems becomes a weed-strewn graveyard. The starfish are hard to stop since they are provided with tremendous defenses: each animal is covered with 1-5 centimeter long razor sharp spines which in turn are covered with toxic saponins—soaplike chemicals which interact with cholesterols to tear holes in cell membranes.  The starfish can regenerate arms.  If removed from the water, the starfish develops holes in its body and loses its water, but it can swiftly reconstitute itself if placed back in the ocean.

Crown-of-thorns starfish wash up in Japan (BBC)

Fortunately there are some tough predators of the crown-of-thorns starfish.  Certain triggerfish, parrotfish, and blowfish can insouciantly crunch through the spines with hardened mouths.  Painted shrimp and polychaete worms can tear off and eat pieces of the starfish until the latter dies (whereupon the impatient scavengers devour the corpse).  Best of all, the magnificent Triton’s trumpet, a huge gastropod mollusk, can rasp the odious starfish to pieces with its sharpened radula and suck up the offending echinoderm!  Unfortunately, the fish are vanishing into the aquarium trade or the soup pot and the tritons have been killed en masse so their shells can be sold to tourists.  This results in a feedback loop wherein the crown-of-thorns devastate a reef to the extent that the predators can not survive at all.  The plague of starfish then descend of virgin reefs and kill them off too.

A plague of crown-of-thorns starfish (Photo: AFP/Getty Images)

Healthy reefs have a certain ability to fight off the crown-of-thorns star, but today’s reefs are coping with overfishing, invasive creatures, acidification, pollution, and fluctuating temperatures.  The crow-of-thorns is exploting these weaknesses (and the diminished stock of its predators) to run rampant.  Humans have stepped in late to try to kill of the rampaging multi-armed villains, but, for all of our skill at doing in other organisms, we seem to not be very good at killing these fiendish starfish.  They are difficult to rip apart.  They are hard to net or trap.  They are surprisingly resistant to punctures.  Recently divers have had success suppressing infestations by injecting the starfish all individually with sodium bisulphate (which echinoderms and my great uncle cannot abide, but which is relatively harmless to most other lifeforms).   Obviously this is an expensive and labor intensive solution (although if somebody wanted to hire me as a starfish bounty killer, I would not decline).

New frontiers of pest control (via DIVE QUEENSLAND)

The common name of the crown-of-thorns starfish is a reference to Christian mythology.  One of the tortures endured by Jesus was a crown woven of thorns (which pierced his temple and hurt him while simultaneously mocking his alleged crime—pretending to the throne of Judaea).  Throughout Christian art, the crown of thorns is the supreme crown of the king of kings which he wears during the passion or as he harrows the underworld.  The voracious starfish earned its sobriquet not by godliness, but by looking like a horrible alien crown made of thorns (and arguably also by bringing death and devastation to coral reefs).  I find it to be one of the most poetic and horrifying common names in all of taxonomy—and as the starfish destroys ecosystem after ecosystem, it seems fully earned.

A giant triton snail feeding on crown-of-thorns starfish. Image supplied by Australian Institute of Marine Science

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