Sea Star Wasting Syndrome

There is a new threat to sea stars called ‘sea star wasting syndrome’, which is responsible for mass killings of these important keystone species.  In November 2013, the disease killed up to 95 percent of the sea star populations from Alaska to Orange County.  Little is known about the origins of the syndrome, or even what causes it.  Scientists are trying to determine the cause of this lethal disease before time runs out.

Picture by Jonathan Martin

Typically, a sea star infected with the syndrome will have lesions that appear in the ectoderm followed by decay of tissue surrounding the lesions, which leads to eventual fragmentation of the body and death (see picture above).   A deflated appearance can precede other morphological signs of the disease.  “True” wasting disease will be present in individuals that are found in suitable habitat, often in the midst of other individuals that are affected.  The progression of wasting disease can be rapid, leading to death within a few days, and its effects can be devastating on sea star populations. 

“They essentially melt in front of you,” said Pete Raimondi, chairman of the Department of Ecology and Evolutionary Biology at UC Santa Cruz's Long Marine Lab.  The University of California Santa Cruz is currently mapping all events along the West Coast, and people are encouraged to report these sea star wasting events to them.  They classify the syndrome into four categories, with 1 being mild, and 4 being severe.  Pictures and descriptions for the severity of the syndrome can be found here.   

At first, the disease only infected one species, Pycnopodia helianthoides, also known as the sunflower star.  Then the disease began to affect a more common sea star species, Pisaster ochraceus (Robert Paine’s keystone species).  Now, there are about 12-15 species that are dying along the West Coast from sea star wasting syndrome.  And wild sea stars are not the only ones in danger-- in September 2013, sea stars in an aquarium at the Gulf of the Farallones National Marine Sanctuary visitor center at the San Francisco Presidio contracted the syndrome in water pumped from the ocean.  Eels, sculpin and anemones that were in the same aquarium were unaffected.

The probable cause of the disease on the west coast of the US is caused by a pathological agent, such as bacterium (vibrio), although a recent wasting event on the east coast of the US has been attributed to a virus.  Sea star wasting events have also occurred from British Columbia down to the Gulf of California, the Mediterranean and the North Atlantic coast of North America, but not in the Southern Hemisphere.  Some researchers have suggested that Fukushima could be a cause, but the sea stars are being affected on the east coast, so this is not likely.  The ultimate cause is not clear although such events are often associated with warmer than typical water temperatures as was the case for the major die off in southern California in 1983-84 and again in 1997-98.  Sea stars are susceptible to bacterial infection, and warmer water boosts bacteria growth, Raimondi said.  

If the cause for sea star wasting syndrome is not uncovered, ecosystem balance can be disrupted with the disappearance of sea stars.  As we have learned in class, removing Pisaster ochraceus from tide pools causes unchecked population growth of mussels and other organisms.  Also, with global climate change, temperatures will rise in the ocean, which could have significant or even profound effects on populations.  Hopefully the cause of sea star wasting syndrome can be solved before it is too late.

Terrific Threads

Mussels use their byssal threads to attach and cling to rocks; on average, each individual mussel has 50 to 100 threads. As mussels inhabit rocky shores they are exposed to the constant pressure of pounding waves, without these byssal threads these organisms would be immediately swept out to sea. Although the function of byssal threads were known, scientists were unsure of the physical characteristics which allowed byssal threads to successfully secure the mussels. Previously researchers from the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany hypothesized the byssal threads must be both hard and stretchy however, they were unsure of the exact composition.
The physical and chemical makeup of the byssal threads was determined using a microscopic technique. It revealed the center of each thread was composed of stretchy collagen – like material coated in hard material made of proteins linked together with iron ions. The coating (Figure 1) is compared to having a sandpaper – like texture. This outer coating selectively manages where any damage will occur. As waves crash against the mussels, small cracks develop in the threads however; they will only occur between the iron ions. This spreads out the damage along the byssal thread and prevents breakage.
The researchers from this study hope to apply this new found knowledge to engineering materials to be both stretchy and hard.

Full text of this article may be found at: http://www.npr.org/templates/story/story.php?storyId=124319594