Slimey Seastars

Hi again! The last time I left you I mentioned a new experiment I would be starting on the seastar, Pteraster tesselatus.  Pteraster are commonly called the slime star because when agitated they produce massive amounts of a clear slime. Unlike the Pisaster and Evasterias, Pteraster do not have a feeding larval stage. Instead, Pteraster embryos hatch into larvae that do not feed before they settle and undergo metamorphosis to become a juvenile. There is not a large history of Pteraster research, especially in egg size manipulations, and I have never worked on this species before. Since it can be very difficult to work with this species, before we could do any true experiment to manipulate egg size, we had to make sure we would be able to spawn and fertilize the eggs.

To spawn Pteraster, the animals are injected with 1- methyladenine, much like the Pisaster and Evasterias to induce gamete maturation and release. The eggs are over a millimeter in diameter, bright orange, and float on the surface of the water so they are extremely easy to collect as the female spawns. I have never worked on a species that produces such large eggs, and Dr. Allen had only worked with them once before, years ago, so before we could do any experiments we needed to make sure we would be able to fertilize the eggs and take care of them well enough for them to hatch. Luckily, we were able to find both a male and a female seastar, fertilized the eggs, and then let them develop. In order for the seastars to have water flow before they hatched, we created mesh bottom containers that sit in a test tube rack, with a single egg in each container. The rack we used held 60 eggs, and after 3 days, when the eggs were supposed to hatch, 18 did so. While 18/60 may not seem like the best percentage, we were actually extremely excited we were able to have so many eggs hatch, thinking we wouldn’t be able to keep any alive long enough to hatch.

Since we were only able to rear 18 to hatching, and some of those 18 have died, we weren’t able to complete any experiments manipulating maternal investment. We still have a few more Pteraster that we have yet to spawn, so we are planning on spawning them later this week to run a bigger experiment where we have more than 60 individually sorted eggs. When we do this next experiment, we will measure all of the eggs we sort to collect egg size data, then compare larval time and size at metamorphosis across different egg sizes. We are also hoping to perform egg size manipulations to remove lipid stores from the eggs to see what the effects of reducing maternal investment are.

Life in Friday Harbor hasn’t been all work though. We’ve been going to many field sites to see the diversity in the invertebrate species as well as some vertebrates (including many marine mammals!). Below are some pictures of different animals and places we’ve visited since being here.

bucket of pteraster

A bucket of Pteraster that were collected for us by divers in the sub tidal.

pteraster slime

When agitated, the Pteraster produce slime as a defensive mechanism, as seen here

pteraster eggs

A couple Pteraster eggs. They are over a millimeter in diameter and contain a lot of yolk and lipids


We saw orcas near Lime Kiln while heading back from one of our field sites. The whale on the right is spy hopping, a natural behavior.

lime kiln

The view from Lime Kiln while we were looking for whales. If the picture was facing the water (off to the right), you would be able to see Canada.


While night lighting one evening, a seal (locally named Popeye) swam past our light and stayed for over 30 minutes!


A nudibranch native to the area another researcher is working on.

brittle star

A brittle star we found at Snug Harbor with a really cool pattern on its central disk.


  1. mvpolizzi says:

    This sounds so interesting! Why are you looking towards doing more research on this particular species? Why are you trying to manipulate the egg size?

  2. mkmcculla says:

    Stacy, I’ve loved following your research on spawning sea stars! Reading about your process to fertilize and hatch and study these marine invertebrates has been fascinating and also very enlightening as to all of the effort and trials scientists put into their research without a guarantee of success. I am so excited to hear more about your work with sea stars in the coming year, and I’m sure it will continue to be rewarding and informative.

  3. sntrackenberg says:

    We are looking into doing more research with this species because they have extremely large eggs compared to other species, and since we are trying to see differences between species with different egg sizes, we are using Pteraster as an extreme example for large eggs. We are doing the manipulations to see what the effects are of changing maternal investment and if the added energy in the eggs is used by different species in a different manner.