The Attack of Vibrio and the Plummeting Deaths of Sea Stars

— Written by Vivian Lee

A keystone species, one that is largely depended upon by other species, acts as a fundamental instrument for balancing an ecosystem at a constant equilibrium. Thus, when a keystone species population declines or has an absence in an ecosystem, the consequences are detrimental. Recently, the Rocky Intertidal Community of the West Coast has been facing consequences such as overpopulation since the sea star wasting epidemic. In 2013, a mysterious disease spread from Washington State to as far North as Alaska and as far South as  Mexico, sweeping across the coast and taking away many sea stars species in its path.

As white lesions form on the body, the disease takes away each arm at a time, and clinging onto what becomes the last of themselves, the sea stars waste away until only a sheer outline of ossicles remain ghostly on the rocks of the intertidal. The wasting disease leaves sea stars hopeless as the progression to death can take less than a few days, leaving them unable to salvage themselves; causing populations to plummet to the verge of local extinction. Amongst the many species, Pisaster ochraceus was among those attacked the hardest by the disease,producing questions and possible hypothesis not only for the Pisaster ochraceus but the rest of the sea stars. Being one of the biggest marine epizootic outbreaks that occurred, questions are still on the rise, parameters have been continuously observed as the cause of the disease are countless.


Figure 1: Photos above display three different species of sea stars. 1a displays  two Pisaster ochraceus sea stars (orange and brown) and Pisaster brevispinus (pink). 1b is a closer view of the brown Pisaster ochraceus. 1c. Sea star species known as Pisaster giganteus

Is it the rise of seawater temperature along the west coast? Could the El Nino event have played a part in intensifying the pathology in infected stars from certain sites compared to others? Perhaps the salinity of the water? Has something changed in these Echinoderms’ diets? Finding a concluding answer has been as difficult as finding a needle in a hay stack; however, an explanation of the disease has been monitored. Vibrio, a bacteria found in sea water and some marine organisms such as crab and eel can affect both humans and other marine organisms. Vibrio was found on many sea stars that were collected for observation. This bacterium may have opened the doors that weaken the sea star, causing the white lesions to form and eventually leading to death. Site by site along the Southern California Coast, multiple bacterial swab samples of sea stars were collected during the time span during and after the outbreak. Whether the stars showed phenotypic/ physical attributes of sickness or not, samples were taken to observe the presence of the bacteria.

Previously, a collaborative team from Dr.Hofmann’s lab at UC Santa Barbara collected swab samples of Pisaster ochraceus from sites in Southern California ranging from Lompoc to San Diego, including the Channel Islands. This summer, a continuation of detecting the presence of the bacteria will be studied. Through this, we anticipate grasping a better understanding of the biodiversity of the bacterial community associated with sea stars from  samples collected during and after the outbreak. We hope to find current sea stars in sites locally around Santa Barbara as well to understand and monitor the differences compared to when the outbreak occurred.

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