Sea stars are a charismatic member of local intertidal habitats, easily spotted by their bright colours and iconic star shape. If you’re an avid admirer of sea stars, you may have noticed it’s been more difficult to find them in the last few years due to a decline in their abundance around BC. Sea stars are in trouble because they are going through their own pandemic: sea star wasting disease (SSWD). A bit more physically noticeable than COVID-19, SSWD shows symptoms of white lesions on a sea star’s arms, severe tissue damage and sometimes causes arms to fall off all together.
Our research this week has focused on the lovable sea stars studying the performance of 2 species, Pisaster ochraceus and Evasterias troschelii, after placing them on different substrates. Sea star wasting disease is on my mind because our research was affected by this disease when it claimed some of our sea stars.
Although we’ve been dealing with COVID-19 for about a year now, sea stars have become pros at social distancing since SSWD was first observed in 2013 in Howe Sound, BC. Unfortunately for sea stars, they won’t be receiving any vaccine shipments any time soon, but scientists are trying to determine the cause of SSWD. Right now, we know that warmer temperatures may provide a better environment for the disease to persist, so we can expect that marine heatwaves = bad for sea stars (and a lot of other organisms).
A study by Dr. Drew Harvell at Cornell University in 2019 studied the sunflower sea star (creatively named since it has many arms comparable to sunflower petals) who have been hit hard by SSWD. They suggest that the disease could be linked to the sea star associated densovirus which when combined with warmer waters, becomes an issue for sea stars.
SSWD is problematic for a few reasons: it’s influencing the health of the beautiful sea stars but also indirectly impacts their role in maintaining ecosystem relationships. Like a good friend, sea stars keep the individuals around them in check. Especially in the intertidal regions, sea stars are predators who keep prey population numbers at stable levels; essential for a working natural system. Remember those funky sunflower stars? They have gotten to such low numbers in some areas that we see a huge change in the rest of the ecosystem.
Instead of balance, we now see that the sea urchins take over since they aren’t being eaten by sea stars, which also means the kelp preyed on by urchins gets decimated. It’s like when you try to pull out a piece in Jenga (removing sea stars from the ecosystem) and you end up causing the whole structure to collapse.
the ecosystem:
sea stars:
So, hopefully you agree that sea stars are interesting and ecologically relevant animals! Here are some resources if you would like to continue to nerd out about sea stars:
Research by Dr. Drew Harvell et al. https://advances.sciencemag.org/content/5/1/eaau7042
https://kids.nationalgeographic.com/animals/invertebrates/facts/sea-star
BIOL 326: Experimental biology of invertebrates 