European green crabs are an invasive species in North America. Voracious predators, they seemed relatively unharmed by the more acidic seawater used in these experiments. Image: Josh Lord © 2017 MBARI
As humans release more and more carbon dioxide into the atmosphere, the gas is dissolving into the ocean, making seawater more acidic. This threatens the growth and survival of animals such as some corals and snails, whose skeletons and shells may become thinner under more acidic conditions.
But ocean acidification can have more subtle consequences, such as affecting animal behavior and the relationships between predators and prey. Researchers in Senior Scientist Jim Barry’s lab at MBARI have been studying these effects in the institute’s state-of-the-art seawater lab. They recently published a paper showing how ocean acidification makes some snails more susceptible to being eaten by invasive (and predatory) green crabs.
The study, published in early May 2019 in the journal Marine Ecology Progress Series, involved placing green crabs in containers with three different species of marine snails, and exposing the animals to seawater at different temperatures and levels of acidity. The idea was to simulate ocean conditions expected over the next 50 to 100 years. The experiments were conducted by Joshua Lord when he was an MBARI postdoctoral fellow, with assistance from Barry, as well as from Elizabeth Harper of Cambridge University.
The snails used in these experiments have shells made of two different minerals–calcite and aragonite. Two of the snail species used in the experiment had thick shells made of calcite, while the third species had thinner shells made of aragonite. Aragonite is stronger in proportion to its weight but is more sensitive to ocean acidity, and will dissolve more quickly than calcite under expected future ocean conditions.
Small changes in water temperature had little effect on the animals or their behavior. However, the snails with aragonite shells did not survive as well as the other two species in more acidic seawater. In fact, by the end of the five-month experiment, their shells had begun to visibly erode away. The snails with thicker shells, however, seemed better adapted to survival under more acidic conditions.
Kim Fulton-Bennett, 31 May 3019, MBARI. Press release.
