Scallops Under Stress
When problems pile up, will scallops adapt?
Cailan Sugano came to Woods Hole Oceanographic Institution (WHOI) with hopes of studying the effects ocean acidification may have on marine life. Sugano, who majors in aquatic biology at the University of California, Santa Barbara, had worked there on projects related to ocean acidification and was eager to do more. So he was thrilled to work with WHOI scientists Dan McCorkle and Anne Cohen, and Lisa Milke of the National Marine Fisheries Service laboratory in Milford, Conn., on a project examining the effects of ocean acidification on bay scallops.
The increase of anthropogenic carbon dioxide (CO2) in the atmosphere has prompted a process of lowering the pH of ocean waters and the availability of dissolved calcium carbonate for marine organisms to use. Like other shellfish, scallops are potentially vulnerable to ocean acidification because their shells are made of calcium carbonate. In water with a pH lower than today's oceans, it becomes harder for them to make their shells, and already-made shells can begin to break down.
Sugano set up a lab apparatus that would allow him to grow scallop larvae in conditions that the Intergovernmental Panel on Climate Change predicts will exist in many parts of the ocean within the next century. His study focused on two stressors that scallops are currently up against: lower pH (due to increased atmospheric CO2) and food availability. Scallops are filter feeders, sifting nutritious bits of organic matter out of the water. Those bits include live and dead algae or other organisms. In many parts of scallops’ range, the warming climate may reduce the abundance of algae, which in turn may reduce the amount of food available to the scallops.
The laboratory setup allowed Sugano to regulate water temperature and circulation and to bubble in varying amounts of carbon dioxide to change the pH. Scallops were grown under one of three levels of CO2, varying from the ocean’s current conditions to two higher levels. Sugano provided scallops at each CO2 level with high or low numbers of algal cells.
After one week, the experiment ended and he preserved the scallops and used a scanning electron microscope to examine their shells. He also weighed and measured the shells and assessed their development by counting and categorizing shell deformities. Recording deformities was not part of the original experimental plan, but because they were abundant among scallops that had been exposed to high levels of carbon dioxide, they soon became of interest.
Sugano said the main purpose of the study was to evaluate how scallops will react to the combination of acidification and nutritional stress, but it could also show whether boosting their food supply might mitigate the effects of ocean acidification. “Maybe the scallops that are fed more, even though they’re exposed to elevated carbon dioxide levels, will still be able to build their shells just as well,” he said.
The lab at WHOI offered Sugano a new scientific playground, as he was able to continue studying a topic he was already deeply involved with, while learning new tools and techniques. “I’m able to get my hands on different instruments and measurement parameters that I never would have known about or been able to do at UCSB,” he said.
Outside of the lab, Sugano enjoys surfboarding wherever a good wave can be found, as well as hiking and skateboarding. In the coming year, he hopes to complete his senior thesis on ocean acidification.
Sugano and his research were supported by the National Science Foundation and National Oceanic and Atmospheric Administration.