Sunflower Sea Star

Pycnopodia helianthoides
Photo: Jackie Hildering, Marine Detective

Sunflower sea star
Pycnopodia helianthoides

Wolves of the Sea

The sunflower sea star, Pycnopodia helianthoides, is deeply connected to the bull kelp forests of the North Pacific. Its biogeography matches bull kelp almost precisely, ranging from the middle of the Aleutian Islands down through the Pacific Northwest and California to become rare south of Monterey. But Pycnopodia is not one of the sea star we find among the rocks at the edge of the beach at low tide; it inhabits the deeper waters. The most common sea star to find in the intertidal zone, where bull kelp will wash ashore, is the ochre star, or Pisaster ochraceus, the purple or orange five-armed sea star with bony white patterns on its surface. There are also brightly colored bat stars and leather stars in the intertidal. 

Sunflower sea star larvae
Photo by Denis Wise, UW
Sunflower sea star larvae
Photo by Denis Wise, UW

Sunflower sea stars are the deep water “wolves” of the sea—as big as a pizza—with 15–24 arms radiating out from a large fleshy middle. They are known as “ragmops” by fishermen when they are brought up as bycatch, for obvious reasons. They are vibrantly colorful ranging from reddish-orange, purplish, yellow or violet-brown on the top side and sport over 15,000 suctioned tube feet on its bottom side. They move swiftly (for a sea star) on these tube feet to swarm over and eat other invertebrates, both alive and dead, living in their ocean bottom habitat. They can sense light and dark and chemical cues guide them towards a food source. Their favorite prey is sea urchin which can make up almost all of their diet. They are an impressive predator, and, in the absence of sea otters in the kelp forests, they can keep urchin populations in check, maintaining these thriving habitats of biodiversity.

Sunflower sea star life cycle: from planktonic larvae to tiny juvenile with five legs to 24"-wide, 20-armed, soft-tissued hunter.

Pycnopodia are in the class Asteroidea and like sea urchin, they are broadcast spawners, where, during the peak months of May and June the males and females each release their egg or sperm into the water column where fertilization happens by chance. The fertilized egg develops into a bilaterally symmetrical arabesque of a larvae, swimming in the water column, living as plankton for two to ten weeks. After settling on the bottom the larvae metamorphose into a tiny sea star as big as a pinhead with five perfect rays. As they grow, these juvenile sea star become efficient urchin predators, eating juvenile urchin at a rate of four or five a day. It is surmised that these juveniles can be as or more important than the adults at keeping urchin populations down, as adult sea stars will eat only one larger urchin a day. As the sea star grows it adds rays in between the existing legs. If a Pycnopodia loses a leg, to an accident or predator, it can grow it back. It can even regenerate an entire body from a single leg, if some of the central portion is attached. But the sunflower sea star has no serious predator, animal predator that is.

Redundancy at the Top 

The bull kelp forests of the North Pacific evolved with two urchin predators doing their work to maintain ecological balance: the sea otter and the sunflower sea star. Redundancy at the top of the trophic cascade is often the norm, adding resilience and stability to an ecosystem: think wolves and bears in Yellowstone. When sea otters were extirpated in the early 1800s along the Pacific coast, sunflower sea stars not only preyed on sea urchin but, like otters, elicited a behavioral response from urchin to stay hidden, and kelp forests maintained viability but lost resilience. Sea otters have returned to some areas of Alaska and British Columbia so the relationship between these two mesopredators of the kelp forest could be studied. Jenn Burt found that otter and sunflower sea stars go after different urchins, creating a greater buffer against urchin barrens with two predators at work rather than with just one. Otters are pretty picky about what they will eat, only choosing urchin full of gonads that offer the caloric benefits they need, i.e. the big and juicy ones. Sunflower sea stars, on the other hand, will forage for the smaller urchin that otters will leave behind. Both turn out to have an enormous impact on the kelp forest. 

The importance of redundancy was driven home in 2014 when the SSWD—Sea Star Wasting Disease wasting disease wiped out almost every single sea star along the West coast of North America. With the resiliency already compromised by the extirpation of the sea otter, many kelp forests along the coast were left with no urchin predator at all. Freed from the threat of the hunter sea star, urchin populations came out of the cracks and started eating down the kelp, and in turn increasing their numbers by 60 times in some regions. The regime shift from kelp forest to urchin barren was a quick switch.

Sunflower sea star, before and after
Photo by Neil McDaniel

Sunflower sea star, before and after sea star wasting disease

Photo by Neil McDaniel

5.75 Billion Sunflower Sea Stars—Gone 

There is a remarkable picture of an underwater rock in Washington State carpeted with hundreds of velvety sunflower sea stars. The date is October 9th 2013. A follow-up photograph taken of the same rock on October 29th shows completely barren rock. The sea star are gone. They have melted away. 

From the Aleutian Islands to Baja California, sea star of all kinds developed white lesions and, literally, melted away within hours as the sea star wasting disease spread through the ocean water through the new year of 2014. It was later determined to be a densovirus, a subset of parvoviruses, a group among the over ten million viruses found in a drop of surface ocean water. All sea star along the coast, billions of armed organisms, vanished. But the sunflower sea stars, whose populations were previously robust—as one diver said, like seeing robins in the neighborhood—were hit particularly hard. The ochre and bat stars have recovered in many places, but in Oregon and California the sunflower sea star is still missing. In February 2023, a diver off Fort Bragg, CA spotted a single, mature, sunflower sea star off the coast, clinging to its rock, in 30 feet of water. The video he took went viral on the internet: a Pycnopodia on the north coast! Farther north, however, recovery seems in progress. In spring 2023 seventy wild Pycnopodia were found off Whidbey Island in Puget Sound, and sunflower sea stars are not uncommon to find in northern BC waters or in Alaska. Hopefully the recovery will continue south into Oregon and California waters. 

How Old is this Sea Star? 

Like seaweeds and kelp, sea stars do not have a calcified shell to fossilize, so like seaweeds, they are not included in the archaeological record. Also, it is virtually impossible to tell a sea star’s age. It is thought that sunflower sea stars can live to be 20–65 years old.

A Perfect Storm

The years 2014–16 mark a confluence of events that affected the bull kelp forests so drastically that we can use this point along a timeline to demarcate a before and after in terms of bull kelp health. The sea star wasting disease was accompanied by an ocean heat wave—an intensely warm “blob” of ocean water that raised the temperature in the open Pacific off of North America by almost 2.5 degrees C. This warm blob was exacerbated by the periodic ocean warming of an El Niño cycle in 2015–2016. Bull kelp needs cold nutrient-rich oceans to thrive. The nutrient-poor, warmer water of the blob, combined with the intense grazing of the exploding urchin population created a “perfect storm” of stressors on the kelp. Very quickly the bull kelp was mown down by the urchin hordes, so that the historic bio-diverse kelp beds of Sonoma and Mendocino Counties quickly were reduced to impoverished urchin barrens. A year or so later the same shift was seen by divers to the north along the Oregon Coast at Port Orford. To the south in Monterey, even with sea otter in the mix, patches of kelp forest were devastated by urchin grazing as well. 

The Pycnopodia are missed in California and Oregon! Their essential role in holding a fragile ecology in place was underscored when multiple stressors came to bear on the kelp forest in such a compressed time period.

Juvenile sunflower seastars at Friday Harbor Labs
Photo by Josie Iselin
Juvenile sunflower sea stars at Friday Harbor Labs
Photo by Josie Iselin

Can sunflower sea stars be raised in a tank?

Jason Hodin at Friday Harbor Labs on San Juan Island, WA is trying. As of February, 2023 he has 109 one year olds, 23 two year olds, 12 three year olds and 5,000 larvae in the tanks. A one month old baby sea star is the size of a poppy seed! A one year old sea star is barely an inch across, and just budding extra rays out between its initial five rays or “podia,” but its sensory tube feet are madly active, sensing the world around it. These have been bred from the sixteen adult sunflower sea stars found from painstaking SCUBA searches and taken from the wild. No one knows how to age a sea star, so these mature Pycnopodia could be 2 years old or 50 years old! The goal is to release tank-bred sea stars back into the wild, but that won’t be anytime soon, and the initial numbers will be few. As broadcast spawners like abalone and urchin, sunflower sea stars need numbers in proximity to each other to make the odds of fertilization high enough to yield the number of larvae needed to result in more settled sea star…a game of long odds that can be supremely successful, until it isn’t.