By: Jonathan Zhao ‘27
Edited by: Yilin Xie ‘26
Healthy Sunflower Sea Star
Source: Sam Wilson, 27 June 2007, posted on Wikimedia Commons
Healthy Sunflower Sea Star
Source: NOAA Photo Library, 24 September 2010, posted on Wikimedia Commons
Diseased Sunflower Sea Star
Source: brewbooks, 7 June 2016, posted on Wikimedia Commons
With up to twenty-four arms, 1,500 tube feet, and an intricate disjointed skeleton, this echinoderm crawls along the seafloor, hunting for sea urchins, fish, mollusks, or even other sea stars. Thick shells won’t deter it—it can eject its stomach out of its mouth to digest prey in its own shell! This echinoderm is no other than the sunflower sea star, the fastest and largest sea star species on Earth. It is difficult to miss, with its striking colors ranging from pink to orange.
Sunflower sea stars can be found in the intertidal and subtidal waters of the Northeast Pacific Ocean, from Mexico to Alaska. In this region, the California current brings cool, nutrient-rich waters, creating the perfect conditions for kelp forests. These are some of the most productive and biodiverse ecosystems in the world, serving as a home and food source for countless marine animals, from young whales and seals to invertebrates such as jellyfish and squids. Moreover, kelp forests absorb carbon dioxide from the seawater, effectively increasing local seawater pH and helping to counteract ocean acidification. They are also an important carbon sink- this makes kelp forests critical in counteracting some of the effects of anthropogenic climate change.
However, the threat of an ecological nightmare constantly looms over this delicate ecosystem: grazing sea urchins can easily devour kelp and other species of algae when not kept in check by predation. In the blink of an eye, large swaths of kelp forests and other vegetative ecosystems can be reduced to barren sea floors. Even though a small number of species can prey on sea urchins, sunflower sea stars are one of the only predators that can truly make a dent in the number of sea urchins, making them a keystone species for the health of the ecosystem (1).
Unfortunately, a disease called sea star wasting syndrome is threatening these sunflower sea stars. It has caused a massive die-off of sea stars in 2013 and 2014 — including sunflower sea stars — and continues to persist in many areas, killing sea stars at rates that point to a bleak future for these echinoderms. This silent killer is not well understood. It is thought to be caused by bacteria that are in overabundance due to an imbalance of microorganisms in the sea stars’ habitat. Such an imbalance can be linked to the effects of climate change, such as marine heatwaves and ocean acidification that disturb normal ecological processes. The bacteria would coat the surface of sea stars and block the diffusive layer, essentially causing them to suffocate. Even worse, the dead and decaying sea stars are thought to provide the food for the bacterial populations to proliferate and infect other sea stars, creating a feedback loop that leads to massive die-offs. (2) Over the span of a few days to weeks, an infected sea star can develop a range of gruesome symptoms, including the loss of arms, the appearance of white lesions, twisted arms, and the deflation and softening of the body, or as NOAA Fisheries put it, “disintegrate into gooey masses” (3).
The loss of this keystone predator is one of the reasons why kelp forests are in decline around the world, especially off the coast of Northern California. Now, the once vibrant kelp forest communities are on the verge of collapse. Sunflower sea stars have already been put on the critically endangered list by the International Union for Conservation of Nature’s Red List of Threatened Species, and there is currently a proposal to classify this species as threatened under the Endangered Species Act. (4) To save this amazing species and entire ecosystems that depend on it, we, as informed citizens, should support this proposal to give special protection to sunflower sea stars as well as support research into this disease and how it can be cured.
Thankfully, some scientific progress has been made since the outbreak of the disease. A recent research study found that a genetic diversity associated with an allele at the EF1A locus may be key to decreasing the mortality rate of the sea stars for heterozygotes of this allele. Thus, further research into the relationship between genetic diversity and survival in the context of the disease may be instrumental in predicting the uncertain future of sunflower sea stars and the kelp forests that they protect. (5) Other researchers have found some success in treating diseased sea stars. Veterinary staff at the Oregon Coast Aquarium was able to save sea stars plagued with the disease using Seachem Reef Dip to remove external bacteria and fungi, followed by probiotics to promote healthy internal bacteria and flora. (6) Such progress is promising, but there is still much to learn about this terrible disease plaguing sunflower sea stars. Such success stories in saving individual sea stars offer a glimmer of hope, and practical solutions for entire ecosystems may be on the horizon. Equally important, everyone can play a role in ensuring the survival of this keystone species. This can take the form of making sure all our wastes are disposed of properly to prevent water pollution, reducing our carbon footprint, or donating to marine conservation groups.
Works Cited
1. Galloway AW, Gravem SA, Kobelt JN, Heady WN, Okamoto DK, Sivitilli DM, et al. Sunflower sea star predation on urchins can facilitate kelp forest recovery. Proceedings of the Royal Society B: Biological Sciences. 2023;290(1993). doi:10.1098/rspb.2022.1897
2. McCracken AR, Christensen BM, Munteanu D, Case BKM, Lloyd M, Herbert KP, et al. Microbial dysbiosis precedes signs of sea star wasting disease in wild populations of Pycnopodia helianthoides. Frontiers in Marine Science [Internet]. 2023;10. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2023.1130912
3. NOAA fisheries proposes listing Sunflower Sea Star as threatened under Endangered Species Act [Internet]. NOAA Fisheries; 2023 [cited 2023 Oct 23]. Available from: https://www.fisheries.noaa.gov/feature-story/noaa-fisheries-proposes-listing-sunflower-sea-star-threatened-under-endangered-species
4. Osborne M. These sea stars are literally wasting away-but they may soon receive protection [Internet]. Smithsonian Institution; 2023 [cited 2023 Oct 23]. Available from: https://www.smithsonianmag.com/smart-news/these-sea-stars-are-literally-wasting-away-but-they-may-soon-receive-protection-180981848/
5. Wares JP, Schiebelhut LM. What doesn’t kill them makes them stronger: An association between elongation factor 1-α overdominance in the sea star Pisaster ochraceus and “sea star wasting disease” [Internet]. PeerJ Inc.; 2016 [cited 2023 Oct 4]. Available from: https://peerj.com/articles/1876/
6. Rudek T, Collura EM. Sea star illness treatment protocol [Internet]. protocols.io; 2023 [cited 2023 Oct 23]. Available from: https://www.protocols.io/view/sea-star-illness-treatment-protocol-q26g7yxjkgwz/v1