By Xiaoshen Yin
As a high-yielding species tolerant of environmental stresses, Pacific oysters have been widely studied.
One of their well known features: Pacific oysters bear a high mortality rate in their early life stages, especially during settlement and metamorphosis. But why? What is happening in that stage? What is the mechanism underlying it? My summer research on Catalina, supported by the WIES Summer Graduate Fellowship, is to explore those arcane stories.
In order to observe the life cycle of Pacific oysters, I usually create oyster babies through a spawn. After collecting eggs and sperm from parent oysters and fertilizing them, I have tons of oyster larvae. It is then both easy and challenging to take care of these babies. The husbandry of baby oysters is simple because I only need to change water every other day from two days post fertilization, record how many I have, take pictures (for sizing purpose), and feed them with tasty algae!
However, while the description is very straightforward, there are many challenges in practice. Sometimes, those baby oysters refuse to grow up, staying at the first stage of life — a “trochophore”– instead of moving on to become a “veliger” (D-hinge shape), and finally to metamorphose and settle into a non-swimming juvenile oyster. Sometimes they won’t grow as fast as they should. Sometimes only a few of them survive at all.
I always wonder why these things happen and how I can explain them. According to many earlier studies by other researchers, there are several possibilities. It might be because they prefer a lower or higher temperature, or that the food I provide for them is not as palatable as they desire, or that their tank houses are too crowded. I am still unable to determine the cause, but I am confident I can figure it out one day. Through the language of research, those oysters will tell me what’s going on.
At this moment, what I really want them to tell me is how their genetics play a role in determining their success in settlement and metamorphosis. This is the focus of my research this summer and fall.
Around 18 days after fertilization, I will offer them “new carpets” in their tank houses by covering the bottom of their 200-liter bucket tanks with empty oyster shells. This is the surface where they will hopefully settle down. Then I will observe how many of those baby oysters settle on the shells or continue to swim in the water column every day.
After that, I will provide bigger tanks for those that successfully settle, hoping they’ll grow into adults large enough for me to run genetic tests so that I can understand the characteristics of those that survived.
If you are curious about what they tell me, come back and ask me three months later. I am sure an exciting story is waiting for us.