by Lindsey Wright
Scientists have been baffled by falling stars for many years, however marine biologists are now struggling to understand a new type of falling star. Many species of sea star have been found withering off of the rocky tide pools. A large-scale wasting epidemic, similar to a mass marine die-off, has been observed along the Pacific coast and a few other places in the world. It can be found locally on Humboldt County’s breathtaking beaches. The stars can be found melting off the rocks on the Trinidad beaches. The beautiful orange or purple colored Pisaster ochraceus, an intertidal sea star found locally, is one the star species that have been affected by this wasting epidemic.
Halle Shauer, a freshman marine biology student, uses her spare time to go explore the Trinidad tide pools in her wetsuit. “It is crazy how different the sea star tidal pool populations are from beach to beach,” said Shauer. “You go to some pools and the populations are largely healthy, but at some beaches the stars are twisted up and look like they are drooping off the rocks.” Shauer is describing some of the effects of the sea star wasting syndrome. This wasting event is worrying scientist and community members alike.
To understand the disease, a person must first know that sea stars are one of the marine organisms that are able to preform regeneration. That is, when they are healthy, as a response to predation, they will sometimes detach their arm or a portion of their arm. After some time the lost appendage will grow back. The casting off of the limb is called autotomizing.
A diseased sea star will usually develop white, fleshy lesions along their arms, sometimes extending onto the central disk. These lesions have been carefully monitored and it has been noted that they will sometimes heal before they become too extensive. The best indicator of the wasting syndrome is called posturing. The arms begin to intertwine with each other and the body twists. It looks as if a person tried to braid the arms together. They then start a rapid deterioration. The stars become visibly weak. The tube feet that suction the animal to the substrate no longer have strength to hold the sea star in place. The arms soon begin to autotomize. The rate at which they are autotomizing is too rapid for the star to regenerate. The sea star eventually loses all of its arms and deteriorates until it dies.
HSU’s own Professor, Dr. Kathryn McDonald, has been working throughout this school year with her research team at the Telonicher Marine Lab in Trinidad to analyze and study this syndrome. Her team includes Jana Hennessy, MC Hannon, Kristen Orth, Jacqueline Haggerty, Taylor Daniels and Jordan Smith. They have all put in countless hours at the lab monitoring the stars and collecting important data.
“We are working diligently to discover not the ‘what it is’ but the ‘how it works’,” said graduate student Jana Hennessy. “Being able to distinguish what may or may not exacerbate the lesions or provide an environment that allows some form of lesion healing may be our biggest advantage in narrowing down the potential causative agents.”
Hennessy hopes that if they are able to figure out how the syndrome works among sea star populations and within individual stars, then they will be clued into what exactly is causing the wasting.
The first experiment that they ran in the fall used 64 common Orche stars of the species Pisaster ochraceus. They looked specifically at the effects of emersion, exposure to air, verses immersion, submersion in water. They used precise temperature control in the small immersion tanks. When in the emersion stage the stars were kept in buckets with sponges soaked in seawater to create a moist air environment. The results were pretty surprising. Out of the 64 stars, there were only five star deaths. The deaths all occurred within the first two weeks of the six-week experiment. Many of the unhealthy looking stars seemed to heal. “They looked better in January than they did in November,” said McDonald. “One of the most hopeful and interesting things that we found is that sea stars are able to heal their lesions. They can look unhealthy and then again ‘fix’ themselves.” She and her team were impressed with these results.
The second experiment was run in the spring and focused on a smaller population of stars. They did only immersion. Twenty stars were placed in tanks at 10 degrees Celsius and 20 stars at 12 degrees Celsius. The water oxygen levels were also monitored very closely. The mortality rate was way higher than in the fall experiment. They also noticed that the lesions did not heal as often as they had in the fall experiment.
McDonald and her team are very intrigued by the data that they were able to collect from these preliminary experiments. McDonald said that if she was able to further continue this work she would want to formulate a question revolving around the effects that the wasting has on the different marine trophic levels or if other trophic levels are effecting the wasting. Many questions are still yet to be answered. What will the beaches be like if sea stars are absent? How are these deaths going to be stopped? Can the marine ecosystems survive this mass wasting event?