Pycnopodia

Lore & Background

Sunflower sea stars can reach an arm span of 1 m (3.3 ft). They are the heaviest known sea star, weighing about 5 kg. They are the second-biggest sea star in the world, second only to the little known deep water Midgardia xandaros, whose arm span is 134 cm (53 in) and whose body is 2.6 cm (roughly 1 inch) wide. Growth begins rapidly, but slows as the animal ages. Their color ranges from bright orange, yellow-red to brown, and sometimes purple, with soft, velvet-textured bodies and 5–24 arms with powerful suckers. Most sea star species have a mesh-like skeleton that protects their internal organs.

Sunflower sea stars were once common in the northeast Pacific from Alaska to southern California, and were dominant in Puget Sound, British Columbia, northern California, and southern Alaska. Between 2013 and 2015, the population declined rapidly due to sea star wasting disease and warmer water temperatures caused by global climate change. The species disappeared from its habitats in the waters off the coast of California and Oregon, and saw its population reduced by 99.2% in the waters near Washington. Ecologists using shallow-water observations and deep offshore trawl surveys found that, in their study period (2004–2017), mean biomass of sunflower sea stars declined 80–100%. In 2020, the species was declared critically endangered by the International Union for Conservation of Nature. Sea star wasting disease is now known to be caused by the bacterial pathogen Vibrio pectenicida, which also infects scallops.

Sunflower sea stars generally inhabit low subtidal and intertidal areas up to 435m deep that are rich in seaweed, kelp, sand, mud, shells, gravel, or rocky bottoms. They do not venture into high- and mid-tide areas because their body structure is heavy, and requires water to support it.

Reader's Guide

The sunflower sea star is significant as a keystone predator in northeast Pacific kelp forest ecosystems. According to the article, they are one of sea urchins' main predators, controlling sea urchin populations and helping maintain the health of kelp forests. Due to the decrease in sea star population, sea urchin populations are increasing and posing a threat to biodiversity, particularly in kelp forests. The species' rapid decline from 2013, driven by sea star wasting disease (caused by the bacterium Vibrio pectenicida) and warmer water temperatures, led to its 2020 IUCN classification as Critically Endangered. Conservation efforts include captive breeding initiatives by The Nature Conservancy, partner institutions, and the University of Washington, focusing on seasonal production, larval development, and growth and feeding experiments. In March 2023, the National Marine Fisheries Service proposed listing the sunflower sea star as threatened under the Endangered Species Act. The species' near-total disappearance from California and Oregon waters and a 99.2% population reduction in Washington waters underscore its ecological legacy as a once-dominant predator whose loss has cascading effects on marine biodiversity.

Did You Know?

• They can move at a speed of 1 m/min using 15,000 tube feet.
• Juvenile sunflower sea stars begin life with five arms and grow the rest as they mature.
• Sea star wasting disease is caused by the bacterial pathogen Vibrio pectenicida.