Sea Star Wasting Disease (SSWD) is a marine affliction that has caused mass mortality among various sea star species. This disease leads to rapid tissue decay and disintegration in affected animals. Scientists have been working to understand its causes and widespread impact on marine environments.
Recognizing the Disease
The initial signs of sea star wasting disease include white lesions or patches on the body surface. These lesions can spread rapidly, leading to the decay of surrounding tissue. The sea star’s body may also soften, and its arms might twist or detach from the central disc.
As the disease progresses, the sea star becomes limp due to the failure of its water vascular system, losing its ability to grip surfaces. The body structure begins to break down, resulting in a disintegrated mass. This progression can be remarkably swift, with individuals often succumbing to the disease within a few days of symptom onset.
Where and When It Occurs
Sea star wasting disease has been observed sporadically since the 1970s. The most severe event began in 2013 along the Pacific coast of North America. This major outbreak stretched from Alaska to Mexico, affecting over 20 sea star species.
The disease spread quickly through populations, with initial reports in British Columbia in early 2013, followed by observations in Washington, California, and Oregon throughout 2013 and 2014. This die-off resulted in the loss of billions of sea stars, making it one of the largest marine epidemics recorded. While the 2013 event was prominent, SSWD has continued to persist at lower levels in many areas.
Scientific Investigations into Causes
Early research into sea star wasting disease explored various hypotheses, including a viral pathogen. The Sea Star Associated Densovirus (SSaDV) was initially identified as a significant factor due to its abundance in diseased sea stars. However, subsequent studies in 2018 and 2020 refuted SSaDV as the primary cause, suggesting it is a normal resident or a consequence of the disease, not the cause.
Recent findings in 2025 identify Vibrio pectenicida strain FHCF-3 as the causative agent of SSWD. This bacterium, known to affect shellfish, causes characteristic lesions and rapid tissue decay in sea stars, leading to their demise within two weeks. Researchers discovered this bacterium by analyzing coelomic fluid, which provided a clearer picture than tissue samples alone.
Environmental stressors are also co-factors that can exacerbate the disease. Warmer ocean temperatures, in particular, correlate with SSWD outbreaks and increased mortality rates. Elevated temperatures can stress sea stars, weakening their immune systems and increasing susceptibility to infection or accelerating progression. SSWD is a complex, multi-factorial condition, likely involving Vibrio pectenicida interacting with environmental factors that compromise sea star health.
Impact on Marine Ecosystems
Mortality from sea star wasting disease has had ecological consequences, particularly for keystone predators. Sea stars, such as the sunflower sea star and the ochre star, play an important role in maintaining marine ecosystem balance by preying on other species. Their decline can initiate a chain of effects known as a trophic cascade.
For example, the reduction in sunflower sea star populations, which prey on sea urchins, has led to an increase in urchin numbers in many areas. These urchins can overgraze kelp forests, converting thriving habitats into “urchin barrens.” The loss of kelp forests impacts other marine species that rely on them for food, shelter, and breeding grounds, altering the biodiversity and structure of coastal ecosystems.