January 9, 2017

Dr. Robyn Hannigan: Using Lobster Shells to Understand the Past

Dr. Robyn Hannigan is fascinated by lobsters. But don’t assume that she actually likes the creatures. “Lobsters are just a factory to me,” says Hannigan. Hannigan received funding from MIT Sea Grant to look at how ocean acidification is impacting lobsters’ ability to form their shells.

“I’m sure someone must love [lobsters], I don’t,” says Hannigan “But, they make fascinating composites of proteins and minerals. And the way in which they do it is unique, it’s distinct. In light of climate change and ocean acidification, studying lobster shell formation really allows us to get a deep understanding of how pH and temperature changes will impact how an animal makes those things.”

As a self-proclaimed ‘lab rat’, she is the founding Dean of UMass Boston’s School for the Environment where she runs a bustling geochemistry lab with six PhD students and several undergrads. Hannigan grew up in Rhode Island, where her cousin Nikki and uncle Paul were lobster fishers. As a child, her job was to jump up and down on the hold below decks so they could cram as many lobsters in as possible before heading back to shore. But her path to studying lobsters wasn’t a straight one. She actually started her college career by studying music, changing to biology midway through. Her initial graduate work was in paleontology at SUNY Buffalo, but after a summer geochemisty internship she finally found her place and went on to get her PhD in geochemistry, recreating historical ocean environments at the University of Rochester. Still it wasn’t until her second postdoc, when a surprising opportunity came along for a geochemical postdoc in a fisheries lab at Old Dominion University, that she found her calling. It was there that she was introduced to otoliths, the little minerals made of calcium inside fish heads that help them sense gravity and movement.

“I fell deep in love, and I realized that was what I was meant to do, to study the minerals that are produced by animals, and use their chemistry to reconstruct their environments. And that’s what I’ve been doing ever since” – Robyn Hannigan, PhD

Suddenly Hannigan’s entire meandering path appeared to have a purpose. She realized that the minerals animals form contain chemical clues that reflect the current environment; likewise, the chemical make up of a fossil could enable her to decipher what the environment looked like when that animal roamed the earth.

“The mass extinction we primarily work on is the Permian-Triassic, which is the largest extinction in the earth’s history, where 98% of all ocean organisms went extinct. There was an ocean acidification event associated with that. So if I understand how the bio-minerals today are recording climate change (pH, temperature) and then I look at the fossil record and the chemistry of the rocks, then I can put the two together” – Robyn Hannigan, PhD

“I look at the fossil record and the chemistry of the rocks then I can put the two together”

Lobsters are an extremely valuable fishery in the Gulf of Maine. Anyone who has visited New England knows that these iconic shellfish are sold at almost every restaurant. Hannigan and her collaborators are looking at how the combined effects of increasing ocean acidity and increasing ocean temperature affect lobster shells. Higher ocean temperatures can promote bacterial growth – which can actually infect lobster shells in what is known as epizootic shell disease. What’s odd is that this bacteria is everywhere, so what makes it infect one lobster and not the next? One thing we do know is that higher acidity lowers the lobster’s natural ability to fight off the bacteria. Hannigan and her colleagues are looking into the relationship and what it means for future lobster stocks. This means that Hannigan’s lab is raising a whole ton of baby lobsters, something that has been quite a learning experience for this mineralogist.

“We’d like to have an experiment that runs three months. So far, we have been able to do it for 8 days, which gets them through 3 molts. One issue we have is that while the lobsters are very fragile at this young age, they are also very active. They flip out of their cups a lot. We lost a lot in the last round when they jumped out of their cups and attacked each other. I’m surprised that anyone has any lobster to eat based on how fragile they are, really.” – Robyn Hannigan, PhD

They’ve created a full on lobster rearing aquarium set up, with 72 tanks, each with the ability to precisely adjust both the acidity and the temperature of the ocean water. The lobsters float in small Dixie cups inside the tanks – they have to be kept separate otherwise they’ll eat one another. It is a messy process, but it is worth it. Hannigan and her student Christine San Antonio use scanning electron microscopes to examine each molt in exquisite detail. They painstakingly count pores in each image, looking for signs of bacterial infection. Hannigan and her colleagues will use what they find to learn more about what’s in store for future lobsters.