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Stargazing on rocky shores

Video transcript:

Eric Sanford, UC Davis:  I'm interested in how changing air and ocean temperatures will affect marine life along the California coast and so we've been working on the ochre sea star.  It's been called a keystone species because it's effect is so important in these marine ecosystems. So, the ochre sea star feeds on mussels and mussels are important for a variety of reasons. Mussels are the dominant competitors for space on rocky shores and mussels form beds that provide habitat for a variety of different species.

What we found is that sea stars are actually really sensitive to small changes in temperature, so if the sea stars experience these moderately warm low tides, they get really stressed out and they consume fewer mussels and end up growing a lot less.

Here you can see a sea star that's feeding on a clump of mussels.  In particular, this one that it's holding is the one that it is eating right now and you can see how it's using its tube feet to pull on each side of the shell.

So, most climate change studies have tended to focus on direct interactions on a single species. But we have to remember also that species are embedded in communities and they interact with dozens of other species.

Here at the Bodega Marine Lab we were interested in how warming air temperatures might affect these sea stars and so in these laboratory experiments, we hold the sea stars in tanks under simulated tidal schedules. 

Now that it's low tide we're going to turn on these ceramic heaters that are above the tanks and by raising or lowering these ceramic heaters, we change the distance between the heaters and the sea stars and therefore we change their body temperatures.

Our results suggest that if during the summertime there are more warm events, which is what's predicted by climate models to occur along the California coast, then this can have a really big effect on these marine ecosystems.

So, through its effects on these mussels, this sea star can play a keystone role because it can change the way the whole rocky coast system looks and how it functions through its predation on these mussels and because the mussels are such an important part of this community, it could actually change the composition of these rocky shore communities.