A prolonged and perplexing disease known as sea star wasting disease (SSWD) has plagued sea stars, particularly affecting the sunflower sea star (Pycnopodia helianthoides) significantly. In recent findings detailed in the Proceedings of the Royal Society B, scientists discovered a population of sunflower sea stars thriving in the colder fjords of British Columbia, suggesting that lower water temperatures might shield these organisms from SSWD. This breakthrough offers essential clues regarding the possible origins and mechanisms of the disease, initially believed to be viral. Ian Hewson, a marine ecologist with previous research into microbial causes, highlights that the earlier considerations about viral infection were hampered by flawed data.
SSWD has been characterized by gruesome symptoms, such as body contorting and rapid mortality, affecting an estimated 20 sea star species. The rare sunflower sea star, once abundant along the Pacific coast from California to Alaska, has seen a staggering 91% decrease, leading it to be classified as critically endangered. The importance of these sea stars extends beyond their survival; they play a crucial role in maintaining marine ecosystems, chiefly functioning as predators of sea urchins. Their declining numbers could allow urchin populations to flourish unchecked, leading to destruction of kelp forests essential to numerous marine species.
The Fjord system in British Columbia has emerged as an unexpected refuge for sunflower sea stars. Marine ecologist Alyssa Gehman, along with field biologist Tristan Blaine from the Central Coast Indigenous Resource Alliance, highlighted discoveries made during a crab survey in 2016 when coastal guardians observed giant sea stars in Dungeness crab traps. Subsequent dives into the fjords revealed a vibrant ecosystem teeming with life, including the seemingly resilient sea stars, contrasting sharply against the grim statistics observed elsewhere.
Between 2018 and 2023, Gehman and her team sampled sea star populations across various sites, unveiling a troubling picture of SSWD. While some lesions and body disintegration indicated the presence of the disease, the fjord populations were healthier, exhibiting more adults than their counterparts in warmer water around nearby islands. This trend suggests that SSWD becomes increasingly detrimental as sea stars mature, preventing island populations from achieving similar growth rates compared to those thriving in the fjords.
Research indicates that cooler, deeper, and saltier waters in the fjords likely contribute to the sea stars’ heightened survivability. It has been observed that these sea stars may seek out colder patches as warmer freshwater layers emerge from snowmelt. Conversely, populations in outer islands tend to inhabit warmer waters, which are associated with increased susceptibility to SSWD outbreaks, as highlighted by previous studies linking warmer temperatures to disease prevalence in sea stars.
Current investigations by Gehman and her team are expanding to explore the interactions between temperature and microbial influences on SSWD. They are on the cusp of elucidating the underlying causes of the disease, invigorated by their findings in the fjords. This research signifies a renewed focus on understanding SSWD from foundational principles, aiming to address the pressing question surrounding its pathology while fostering hope for the recovery of devastated sea star populations.
