Invasive Species in a Changing World:
By Carolyn Tepolt     

I study green crabs, a species that most people would rather not have around. They're highly invasive, voracious omnivores that often take a huge ecological toll on their new homes. Green crabs are native to Europe, but have spread to every other continent except Antarctica, and are one of the world's most successful invasive marine species. There are now green crab populations in California, Argentina, South Africa, Australia, and Newfoundland, just to give a few examples. Green crabs are survivors. 

My research interest is in figuring out the secret to their success: what makes this particular species so good at surviving and thriving in new environments? Specifically, I'm interested in how they respond to different temperatures across their range. This is interesting, in part, because understanding how green crabs cope with novel temperatures can be useful in understanding how many marine species will react to climate change. The idea is the same, but in reverse: climate change brings new temperatures to an animal, while in species invasion, the animal goes to the new temperatures.

Green crabs have been on the east coast of North America for around 200 years, and the west coast for 25. On an evolutionary time scale, this is not very long; we tend to think of animal adaptation as a slow process, involving small changes over millennia. But sometimes adaptation can be much faster, and it's this rapid adaptation that's likely to be important in how animals respond to changing climate. However, many of the examples of rapid adaptation are from land-dwelling animals, and life in the sea can be very different. Marine populations are often much larger and better-connected than those on land, and scientists don't have a very good understanding of how rapid adaptation works in the ocean. This question of rapid adaptation in the marine realm is the focus of my thesis. I use green crabs as my study species, because their ability to survive and thrive across such wide environmental gradients suggests that they might be rapidly adapting to their new homes.

To test this, I look at how green crabs from different environments cope with high and low temperatures. So far, I've driven over 15,000 miles across North America to examine invasive green crab populations from California to Newfoundland. This summer, I'm chasing them to Europe, to see how they deal with temperatures from Portugal to Norway in their native range.

Everywhere I go, I test how crabs' heart rates respond to extreme high and low temperatures using a sort of non-invasive crab EKG. If green crabs are adapting to their new homes, we expect crabs from cold areas (like Newfoundland) to have stronger heart rates in the cold than crabs from warmer areas (like New Jersey), and vice-versa with warmer-water populations and hot temperatures.

It's also possible to use a crab's DNA to figure out what genes it's using to deal with hot and cold temperatures, and how it's using them. I collect heart tissue at every site I visit, and use new DNA sequencing technologies to take an in-depth look at their genetic makeup. These genetic data allow me to determine the specific genes that help green crabs thrive in the heat and the cold. This way, I can see if different crab populations are using the same genes in the same ways, or if they are using different genes to deal with temperature.

Ultimately, all of these data together will help uncover the secret to the green crab's success. In turn, knowing how green crabs adapt to the wide range of temperatures they see across the globe may shed a little more light on how marine animals in general deal with changing temperatures.