Since 2013, a devastating disease known as sea star wasting disease has been wreaking havoc on populations of sea stars, particularly the sunflower sea star (Pycnopodia helianthoides). Researchers have recently identified a leading suspect: a bacterium called Vibrio pectenicida, as reported in a study published in Nature Ecology & Evolution. This discovery is a pivotal step towards understanding and combating the disease, which has caused significant declines in sea star populations, particularly during epidemics in 2015, 2018, and 2023. The sunflower sea star, in particular, has experienced a staggering population reduction of nearly 91%, equating to over a billion individuals lost.
The disease manifests as twisted arms, lesions, and rapid mortality, severely disrupting marine ecosystems. Sea stars are vital predators in their habitats, particularly in controlling sea urchin populations. Without them, unchecked sea urchin populations have devastated kelp forests, which play a crucial role in sequestering carbon dioxide and providing habitat for numerous marine species, including fish, otters, and sea lions. The ecological ramifications of these declines extend beyond the immediate loss of sea stars, affecting biodiversity and the overall health of marine environments.
In a significant advance, marine ecologist Ian Hewson from Cornell University expressed optimism about the implications of this identification for protecting sunflower sea stars, especially in captivity. By targeting specific bacteria with antibiotics, it may be possible to treat affected sea stars in clinical settings. Previously, Hewson and his colleagues had believed they had pinpointed the responsible pathogen but couldn’t replicate their findings. The ambiguity surrounding the disease’s cause has hindered effective protection efforts in zoological settings aimed at conserving sea star populations.
To isolate and identify the pathogen behind the wasting disease, researchers, including Alyssa-Lois Gehman from the Hakai Institute, conducted meticulous studies. They quarantined healthy wild and captive-bred sunflower sea stars before exposing them to various methods that induced the disease. The results were alarming, with 92% of the once-healthy sea stars succumbing within an average of 12 days. This high mortality rate underscored the lethality of the disease, prompting the researchers to further investigate the microbial communities present in both healthy and afflicted specimens.
Through genetic analysis of the coelomic fluid, which acts like blood for sea stars, the researchers were able to compare the microbial makeup of sick versus healthy individuals. They identified over 55,000 bacterial species and pinpointed V. pectenicida as prominent in afflicted specimens. Although a small number of healthy sea stars also carried this bacterium, its prevalence was significantly lower, indicating a correlation between V. pectenicida and disease manifestation. Additional experiments, where the bacteria were injected into healthy sea stars, confirmed their pathogenic role when all subjects died within a week of exposure.
Despite these promising findings, some researchers remain cautious. While the data pointing to V. pectenicida is compelling, doubts linger. Ian Hewson highlighted inconsistencies in previous studies where the bacterium did not consistently appear in affected sea stars, suggesting that multiple factors could lead to the disease’s presentation. He emphasized the complexity of sea star health, which can deteriorate due to various stressors, potentially misguiding researchers seeking to identify a singular cause of wasting. Nonetheless, the methodology improvement—focusing on isolated coelomic fluid—may clarify previously ambiguous results.
Looking forward, Gehman aims to develop rapid diagnostic kits for V. pectenicida, akin to those used for COVID-19, which could enhance field detection and foster timely intervention strategies. As the stakes rise for sunflower sea stars and the ecosystems they sustain, these efforts reflect a crucial endeavor by the scientific community to safeguard marine biodiversity amid rising threats.
