An increase in non-native Pacific oyster density in Newport Bay correlates with warmer summer seawater temperatures, marine ecology students taught by professor Danielle Zacherl at Cal State Fullerton have discovered. Their research, just published in the science journal PLOS ONE, describes a phenomenon that is also taking place elsewhere around the world.
The paper was published in May and was co-authored by 13 senior and graduate students with the guidance of Zacherl and biology professor William Hoese.
Zacherl has studied population demographics of the non-native Magallana gigas oyster, commonly known as the Pacific oyster, as well as the native Olympia oyster, in local estuaries for years.
“Pretty early in my career, I understood that we had this Pacific oyster present in our estuaries,” she said. “I wanted to start up a research model at the Cal State that could support a lot of undergraduate involvement in research. I started doing some basic monitoring of populations on both oyster species. And so I have these really nice, long-term datasets that extend pretty far back in time.”
Students in her marine ecology class used these datasets that Zacherl had created as the starting point for their research. “Every time that I teach that class, we take some of my long-term datasets and we expand them by going out and doing some more monitoring.” Following this work, students typically make a presentation of their findings.
“I had this particularly motivated cohort of students, who are many of the student co-authors on this particular paper,” she said. “They just went above and beyond.”
The students observed a massive increase in the density of the Pacific oyster in one specific location in Newport Bay. (This oyster is the kind that is widely grown with aquatic farming and eaten by seafood lovers, but Zacherl and her students only studied oysters growing in the wild which are typically not harvested for food.)
“The students went and got publicly available data and correlated it with this increase in summer seawater temperatures,” Zacherl explained. “They were reading in the scientific literature that elsewhere in the world, the Pacific oyster increased at a variety of locations and especially in Europe during periods when there were lots of warm summers.”
This connection got their attention. “They effectively saw a parallel pattern happening here in Southern California,” Zacherl said. “It was based on those presentations that I decided, yeah, it’s time to write up a paper about this.”
As scientists, students did not make a judgment about whether this increase in the Pacific oyster population points to good or bad consequences for the local waters, she said.
“I would predict that they’re going to continue to increase,” said Zacherl of the Pacific oysters. “They’re such a large oyster, and they are definitely a reef-forming oyster. And so, it will be impossible for them not to have an impact on Southern California estuaries. But whether we would characterize the impact as positive or negative remains to be seen,” she said.
Oysters provide many advantages for the environment, such as their water filtration capacity, she explained. Another is that they create reefs with their bodies that other species can live in.
“They’re considered foundation species,” Zacherl explained. “They basically build a whole community around the habitat that they build with their own bodies by cementing to one another and building this reef-like structure — an important source of habitat for lots of juvenile fishes and crabs.”
Oyster reefs can also provide erosion control. “Because the reefs have three-dimensional structure, they can slow the water velocity,” Zacherl said. “That means that not only is less sediment swept away from the shoreline or eroded away. But also, they actually encourage sedimentation by slowing the water velocity so that small particles can fall out of the water column and settle.”
Today, because habitats are disturbed by human activity, oysters in Southern California waters exist mostly on hard, man-made structures, according to Zacherl. “They settle on seawalls and on pier pilings. Even though they’re very common, they aren’t allowed the space anymore to form those complex reefs,” she said. “There’s very little attention put to growing that habitat again.”
Early in her life, Zacherl knew she wanted to study the natural world. “I used to go on forest walks with my mother, and that abiding love for biology stuck around all the way through when I started college,” she said.
She received her undergraduate degree at Brown University and taught high school for five years before going to graduate school at UC Santa Barbara, where she got her Ph.D. in ecology, evolution and marine biology. She has taught at Cal State Fullerton for 20 years.
