SUNFLOWER SEA STARS
Sunflower sea stars (Scientific name: Pycnopodia helianthoides) are one of the most interesting and unique sea stars. They are the biggest and fastest and have the most arms. The radiant colors they come in — shades of red, yellow, brown, orange and purple — and their shape are also unique. Sunflower stars can reach one meter (three feet) across and have more than 20 arms. They can reach speeds of one and half meters (five feet) a minute or 66 meters (200 feet) an hour. using 15,000 tube feet — amazingly quick for a sea star. Their tube feet also help them hold their prey.
Sunflower sea star occurs throughout intertidal and subtidal coastal waters of the Northeast Pacific Ocean from the Aleutian Islands, Alaska, to at least the Southern California Bight around San Diego. They commonly reside in shallow marine environments less than 120 meters (400 feet) deep but can be found in depths up to 435 meters (1427 feet). They live in mud, sand, and gravel, and among boulders and rock. They usually have a life span between three and five years. [Source: Shayna Yagoda, Animal Diversity Web (ADW), NOAA]
Sunflower sea stars play important roles in the ecosystems they occupy. They regulates the structure of the benthic community, especially when it comes to sea urchins. Between Oregon and the northern Gulf of Alaska, they are regarded as the most positive sea urchin predator. Sunflower sea stars coexists with sea urchins while sea otters can decimate urchin populations. If there are sunflower stars, sea urchins may become so numerous they seriously damage kelp forests. Sunflower sea stars sometimes create small-scale, prey-free patches by consuming few prey individuals, while the remaining prey exhibit a strong escape response. Since the urchins are herbivorous, the short-term existence of prey-free patches can influence plant diversity and community primary productivity.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Global Coral Reef Monitoring Network gcrmn.net
Sunflower Sea Star Characteristics and Behavior
Sunflower sea stars are the heaviest sea stars, weighing up to around five kilograms. Radially symmetrical — symmetrical around a central axis — they have between 15 and 24 arms (most sea stars have between 5 and 14). Their arms are up to 40 centimeters (1.3 feet) long and big ones are around 80 centimeters (2.6 feet) in diameter.
The sunflower sea star stomach is found on the underside of the center body, or the oral surface. The area around it is usually a lighter color with yellow or orange tube feet. Their 15,000 tube feet have suction cups that allow them to cling to rocks. The suctions cups have such a strong grop that that if you try to pull a sunflower sea star off a rock, the suctions cups often break off the sea star and continue to stick on the rock.
Sunflower sea stars are solitary and migratory. They get around by walking on their tube feet. They can move more quickly that other sea stars because they have a flexible body and aboral skeletal plates are loosely connected to one another. Sunflower sea stars migrates up and down the shore with the tide and exhibits annual migration as well. There is no sexual dimorphism: males and females are about the same size and shape.
Sunflower stars have the ability to regenerate their arms. A whole new sea star may form if a detached arm has a portion of the central disk attached to it. If a predator attacks, the sea star can detach an arm and send a chemical that causes an alarm response to other sunflower stars in the area. If its arm is irritated or disturbed by a predator, can detach or autotomize an arm. The autotomy is triggered by a chemical that is released by injured tissues. This allows sunflower stars to escape from the predator holding onto its arm.
Sunflower Sea Star Feeding and Predators
Sunflower sea stars are primarily carnivorous, feeding on mussels, sea urchins, fish, crustaceans (crabs and barnacles), sea cucumbers, clams, gastropods, sand dollars, and occasionally algae and sponges. According to Animal Diversity Web: However, the diet varies with geographic location and the availability of prey. For example, on the west coast, studies show that sea urchins are its main prey. For most sunflower stars, sea urchins make up 21-98 percent of their diet. [Source: Shayna Yagoda, Animal Diversity Web (ADW)
Sunflower sea stars use their strong sense of smell and very sensitive indicators of light and dark to find their prey, and can move at a quick rate of 10 centimeters per second or 18 feet per minute. While moving, it puts its leading 8 arms in front and when it contacts the prey, it throws the leading arms down on top of the prey. Sunflower sea stars then protrudes its stomach, envelops the entire prey, and digests it. The arms and greatly expandable tube feet are the basic tools of prey capture. Many species have developed escape responses to sunflower stars. For example, the abalone Haliotis accelerates and at the same time whips it shell back and forth to break the grasp of the tube feet of the sea star.
According to the New York Times: Scientists found that sea stars were passionate consumers of both juvenile and large adult sea urchins. When sea stars attack, urchins fight back, often pinching off pieces of the sea star’s arms and making the attacker back off. If the sea star can persist, it surrounds the urchin and ingests it through the mouth on its underside. After about 18 to 24 hours, it spits out the empty shell, having digested the soft parts, including the roe, which is also a delicacy among sea otters and human sushi eaters.
Sunflower sea stars have very few predators, especially P. helianthoides. Sometimes Alaska king crab and sea otters may attack sea stars. Birds such as gulls have been known to prey upon sunflower stars. The magnitude of loss of intertidal P. helianthoides is enough to explain the near absence of these soft-bodied sea stars in the intertidal zone of Tatoosh. Sunflower sea stars can have large subtidal populations that do not experience bird predation resulting in a little effect on their total population sizes. Predators mainly eat the sea stars during their larval and juvenile stages. The availability of food, rather than predation, limits the number of adult sunflower stars.
Sunflower Sea Star Reproduction and Development
Sunflower sea stars are oviparous (young are hatched from eggs) and engage in external reproduction in which sperm from the male fertilizes the female’s egg outside her body. They employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. Sunflower sea stars employ seasonal breeding, usually between March and July, with the main peak is May and June. Each separate sex sheds its eggs or sperm into the water where the fertilization takes place by chance. There is no parental care after the eggs and sperm are released. [Source: Shayna Yagoda, Animal Diversity Web (ADW)]
The eggs develop into swimming, bilateral larvae that usually remain in the plankton for no more than 10 weeks. The larval form feeds on single-celled plants. When the larva settles on the bottom it metamorphoses into a young sea star with five arms. The young P. helianthoides initially feeds on the thin layer skin-celled plants that coat the bottom of their marine habitat. The juvenille soon adds an arm clockwise from the bivium. Additional arms are added bilaterally in pairs to either side of the sixth ray. Each new pair is inserted between the last pair formed and the adjacent original arms. (Alender, et al., 1966; Lambert, 2000)
Endangered Sunflower Sea Star
Sunflower sea stars are a candidate for the U.S. Fish and Wildlife Endangered Species Act (ESA,) throughout their range. Scientists estimate that there once were as many as five billion sunflower sea stars along the coast from Alaska to Baja California. But sea star wasting disease, possibly caused by a virus, has killed most of them. [Source: New York Times]
Disease, specifically sea star wasting syndrome, appears to be the primary threat to the species.Sunflower sea stars are broadcast spawners that require close proximity to mates for successful fertilization. [Source: NOAA]
There is no single, systematically collected data set that provides population size or long-term trend data for sunflower sea stars throughout their range. However, from 2013-17, an outbreak of sea star wasting syndrome contributed to precipitous population declines in several areas, with impacts progressing sequentially from south to north.
Reintroducing Sunflower Sea Stars to Fight Sea Urchins
Sunflower sea stars have a huge appetite for sea urchins and could help control the spread of sea urchins that are devouring kelp. The New York Times reported: Scientists say that reintroducing the fast-moving predators to the West Coast could help control the spread of sea urchins. A team of scientists suggests that the population explosion in sea urchins could not have happened if sunflower sea stars had been there to prey on them, and that restoring the population of the colorful creatures may help in the recovery of the kelp forest and the ecosystem it supports. The study appeared last month in Proceedings of the Royal Society B. [Source: New York Times, March 6, 2023]
To test whether introducing captive-bred sunflower sea stars could help, the researchers collected 24 sunflower sea stars and 300 purple sea urchins near the San Juan Islands in Washington and observed them under experimental conditions, recording hunting activity and food preferences. These were healthy sea stars, survivors unaffected by the wasting disease, possibly because they were resistant to the illness. The researchers hope that their offspring will share their characteristics.
Is re-establishing the sunflower sea star population with captive-bred animals practical? Aaron W.E. Galloway, who is an associate professor of marine biology at the University of Oregon and an author of the paper, believes it could be. “Just a few sunflower sea star individuals can produce millions of larvae,” he said. If they are successful, he says, even a small restoration effort “could easily lead to millions of sea stars returning to the wild.” Dr. Galloway acknowledged that there are many other factors besides the diminishing sea star population that affect the health of the kelp forest, like climate change and increased periodic heat waves. And he makes no claim that a healthy sea star population is the ultimate solution.
Image Source: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated May 2023