Friend Feature: Sunflower Sea Star

Creature Feature: Sunflower Sea Star Pycnopodia helianthoides

Living dangerously, a young Salish Sea explorer inspects a sunflower star on the docks in Friday Harbor. Don’t let its limp and helpless guise fool you. Yes, she did escape with her hands intact, luckily. Image by Kathy Finholm, Salish Sea In Focus

Armed and dangerous

Sunflower sea stars may be sunshine-shaped and pretty, but don’t be deceived. This voracious predator can move at a quick clip (okay, for a sea star), laying waste to any living things in its path along rocky kelp forest floors and sandy bottoms (sea bottoms, don’t fret) up to 435 meters deep. More like death star than sunflower if you ask me. Armies of these many-armed wonders once plundered the seafloor all along the Pacific coast.

A bright orange Pycnopodia patrolling a gravelly seafloor. Image by Janna Nichols, REEF

Just what are they laying waste to? Nearly anything that will fit into their maws, which can be quite large. These are the largest sea stars in the WORLD! Some reach a diameter of 1 meter with any number of rays (arms), some of which may be regenerating after being lost to unfortunate encounters with prying predators or humans; they are a bit fragile. It uses the hundreds of tube feet on its rays to suction onto and hold prey. Note: this suction can be so strong that prying a sea star off of a rock can remove its tube feet, and even an arm! Be gentle.

Everything on the menu

The unmistakable shape of a sunflower star chowing down. Notice the humped up body or central disc.

Pycnopodia’s favorite food is bivalve molluscs, like clams, mussels, and scallops, but these stars will also eat snails, limpets, dead fish, sunken squid, sea cucumbers, crabs, barnacles, sand dollars, and sea urchins, helping to keep these populations in-check. Where there are no more sunflower stars, urchins can get a little rowdy. More on that below.

Escape tactics

Just sensing one touch from the tube feet of a sunflower star can spark astonishing invertebrate acrobatics. No one said it better than the infamous marine scientist and friend to many SeaDoctors, Eugene Kozloff in his good, old Seashore Life of the Pacific Northwest Coast:

“The large sea cucumber, Parastichopus californicus, which is about as lethargic as any of our animals, will work itself into a writhing gallop if the tube feet of a Pycnopodisa make contact with its skin. Some bivalves, stimulated by the prospect of being eaten, go into violent activity in order to escape. Scallops, for instance, clap their valves together to swim out of danger, and the common cockle extends its foot and pushes it against the substratum to get away. Sea urchins respond to Pycnopodia by extending their pedicillaria” (pincers).

And that’s not all invertebrates have evolved to fend them off. Abalone can do the twist to shake off a too-friendly star and the keyhole limpet has something up its sleeve for sea stars that touch too much. Watch the video above to discover its surprising secret weapon. Sunflower stars do seem make their neighbors a bit touchy.

Unlucky prey find themselves in the gut of these giants inside its body or out. They will swallow urchins and other hingeless prey whole, even if urchin spines or squid pens puncture their stomach and poke right through their topsides. An endoskeleton that disconnects in a few places also allows its mouth to open wide for large prey. This is also what makes them floppier than other stars. Like other sea stars, they can also extrude their stomach into clams or mussels and digest them outside of their bodies. Would that be allowed at your dinner table? Pizza anyone?

Shooting for the stars

Sunflower star predators are few, but do include king crabs, the morning sun star Solaster dawsoni ,and the occasional (and likely super-hungry) gull or sea otter. Any of these predators must have a hankering for a crunchy snack; sea stars have an endoskeleton made up of bone-like discs (ossicles) plus spines and miniature beaks (pedicillaria) on the surface of their skin. Another warning to predators, yes, these beaks can bite! They also remove bits of unwanted debris from the star by passing it from beak to beak.

Some softer tissues between the spines and beaks are dermal gills. They can absorb oxygen through their skin with every fresh breath of water, striking envy into SCUBA divers everywhere.

One more trick up their 25 sleeves is dropping an arm when threatened. So those hungry gulls and otters

Rowdy urchins

Where there are no sunflower stars and no sea otters, sea urchins populations can grow large fast. Their favorite meal is kelp. An army of sea urchins can mow down a kelp forest fast, and eat any seaweed in its understory next. These spots are called “urchin barrens,” as they’ve left mostly bare rock behind.

Where have all the flowers gone?

First image: Sunflower stars abound on Croker Rock outcrop near Vancouver, BC, October 2013. Second image: same rock later the same month. Images by Neil McDaniel in Montecino-Latorre et al. 2016

In 2013-2014 sea star wasting disease spread like wildfire from Mexico to Alaska all along the coast, wiping out millions of sea stars in its wake. Areas filled with sea stars were laid to waste in short order. Sea stars went from plump and bright to piles of pedicillaria, and goo within days to weeks. Arms crawled away from bodies, bodies split in half, ultimately to disintegrate to dust. Even this mighty predator lost the battle. Out of the 20 species affected the sunflower stars were hit the worst of all.

SeaDoc scientists and colleagues put science to work to hunt down the cause. The culprit? A densovirus already living on sea star skin, possibly gone wild when waters warmed along our coast.

Hope!

On a recent dive survey, SeaDoc and Paua research divers found more than one sunflower sea star not far from our island home. Does this mean they are starting to recover? We don’t yet know, but it is sure a good sign!

A healthy sunflower star on a rock near Orcas Island, Washington brings new hope to SeaDoc scientists. Pictured: Bob Friel, SeaDoc videographer and new sea star friend. Image by Amanda Bird, Paua Marine Research Group

How can you help sea stars recover?

Everything you do to help keep our water clean and greenhouse gases from entering the air is a big help to sea star recovery. And when you’re exploring your underwater friends at the beach, leave those stars and urchins in their place or lift them very gently. They’d rather keep the tube feet and arms they have than grow new ones, even though they can.

You can be a sea star, too!