Mike Doherty | Program Naturalist
If you visited the Center recently, you may have noticed an odd-looking sea star or two. That is because many of them had begun to autotomise their own arms, meaning purposefully disconnecting them from their bodies.
Sea stars are known drop limbs for a number of reasons; one being to protect itself from a predator. If a predator has a hold on its arm, the sea star will release the arm in order to escape. While it is not ideal, the sea star is able to regenerate the arm, making autotomy worthwhile. Sea stars are also known to do this as a means of asexual reproduction. If an arm breaks off with some of the central disc attached, it will grow a new body, effectively creating a clone.
Unfortunately, the sea stars in two of our saltwater tank systems were loosing their arms due to Sea Star Wasting Disease (SSWD), which had found its way into the systems. SSWD has caused sea star die-offs, or mass mortality events, on the Pacific and Atlantic coasts over the last few years.
The first symptom of SSWD is white lesions that appear on the surface of the sea star, followed by decay of tissue. Next, the animal becomes limp as its water vascular system fails and it is no longer able to maintain its internal hydrostatic balance. The body structure continues to break down, the arms begin to fall off, and the animal dies. The progression of SSWD is rapid and the animal dies within a few days.
Scientists are researching why sea star die-off events take place. There is evidence that water temperature does affect mortality—the warmer the water, the faster sea stars succumb to the disease. What we do know is that the ecological impact of the sea star die-off will be vast. Because sea star species play such a vital role in coastal ecology, we can expect continued change of the biological makeup in the intertidal zone.
Scientists are currently testing hypotheses on what kind of effects smaller sea star populations will yield. Working to gain insight on expected changes in biodiversity in coastal water, they are asking questions such as how will mussel populations (which are common prey of sea stars) be impacted, and will a change in the predation habits of animals that usually eat sea stars occur?
Learning more about the complexity of our coastal ecology helps us better understand the interconnectedness of our ocean and planet and makes us better prepared for disruptive natural and anthropogenic events in the future.
Check back for updates on how SSWD is affecting the systems at the Seacoast Science Center and on the Gulf of Maine coast, and for ways you can help monitor populations.