Itty bitty echinoderms

Introducing my next science + comics interviewee:

Name: Karen Chan
Job: Postdoctoral scholar at WHOI
Field of Study: Larval ecology

Karen is a good friend of mine who has recently completed her PhD. Congrats, Karen!

Karen’s overall research interest is in looking at how tiny little marine invertebrate larvae respond to climate change conditions. For many of them, the planktonic stage is their only big chance in life to get to their ideal home, because movement while in their adult forms can be very difficult. But with the changes in the ocean brought on by increased atmospheric CO2 e.g., ocean acidification, these larval echinoderms could be adversely affected. Not only do they need to survive, but they also need to maintain a certain level of mobility to get to where they need to go.

To try to get a handle on how they might respond, Karen has taken the larval sea urchins and sand dollars and subjected them to ocean acidification conditions in the lab. She has spent the last few years watching what they do, and also modeling how their swimming behaviors might be affected.

Urchin babies and ocean acidification
Karen has made some interesting observations of how sea urchin and sand dollar babies react to the changing carbonate chemistry resulting from ocean acidification. It turns out, they tend to be smaller, eating less than they normally would, and at the same time, they’re swimming faster. This seemed like a weird combination to me, a non-biologist, so I asked her about it. She explained that the same appendages are actually used for both swimming and eating, so if they are doing one thing, they can’t really do the other well.

One explanation, said Karen, might be that the larvae are simply trying to escape from the unpleasant conditions. If they experience, say, a pH level that they don’t like when they’re in the ocean, they will typically try to swim away from it. And in a vertically stratified ocean, they would likely make a quick swim upwards to kinder waters. However, in the case where the ocean acidification conditions are everywhere, they might just swim and swim and keep on swimming, and not really find a better spot. In the meantime, all this swimming may mean that they’re not eating efficiently and not growing as fast. Karen describes it as a trade-off between survival in the short term and long term: they’re using up energy now to escape, but they’re paying the price in the long term. Being small means being in the plankton stage longer, and being more susceptible to predation.


Purple urchin clone wars

While conducting her research on purple sea urchin larvae, she found something surprising: her larvae were cloning. They would actually bud off a part of themselves when under ocean acidification conditions. It’s not the first time an echinoderm has ever cloned itself – in fact, you’ve probably heard that some starfish have this ability. Even larval purple urchins are known to do it, but it is not a normal occurrence, and it has not previously been associated with ocean acidification conditions. In very special scenarios, it would have been a big deal to see 10% of the population exhibiting this behavior. Karen saw it happening roughly 60% of the time! Since they just stumbled on this behavior unexpectedly, there is still a lot to figure out – like why they do it? And what is the survival rate of the parent and child clones?


Karen is continuing her research as a postdoctoral scholar at WHOI, looking at how multiple stressors related to climate change affect early larval stages of several marine invertebrates. What she’s learning about larvae is a very important piece of the puzzle in understanding how the ocean might be affected by a rapidly changing climate.

*disclaimer: larval echinoderms don’t have cute little faces as depicted in these comics – I took a lot of artistic liberty here. If you want to know what they really look like, you should definitely look it up in a reliable source. They are super adorable!


Chan, Kit Yu Karen, Daniel Grünbaum, and Michael J. O’Donnell. “Effects of ocean-acidification-induced morphological changes on larval swimming and feeding.” The Journal of Experimental Biology 214, no. 22 (2011): 3857-3867.

Chan, Kit Yu Karen, Daniel Grünbaum, Maj Arnberg, Michael Thorndyke, and Sam T. Dupont. “Ocean acidification induces budding in larval sea urchins.” Marine Biology: 1-7.

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