After defending my Ph.D. in April on the mysterious and alluring giant sea scallop (Placopecten magellanicus), I jumped at the opportunity to join the Yund Lab for a six-month post-doc position.

In 2013, the Yund Lab based at the Downeast Institute, in collaboration with the Xue Lab at the University of Maine, the Etter Lab and the Hannigan Lab (both out of the University of Massachusetts Boston) began a four year NSF funded project (NSF-OCE 1333797, NSF-OCE 1458154) to study the population dynamics of blue mussels (Mytilus edulis) in Downeast Maine.

Donwneast Maine counties in dark green. Image From “Downeast Maine, Where Is It Exactly?”

The Xue Lab is creating a model that predicts, based on ocean currents, where mussel larvae released from known beds will end up settling to become new adults.

One prediction, based on known oceanography of the Gulf of Maine and the Eastern Maine Coastal Current, is that the northeastern populations are seeded mostly from up-shelf sources, while southwestern populations have a lot of local retention.

Image is from the Gulf of Maine Area Census of Marine Life. You can see the EMCC is all along the Downeast Maine coastline.

The Hannigan and Etter Labs are testing the population connectivity* predicted by the model based on elemental fingerprinting. The concept of using elemental fingerprinting for blue mussels was based on previously published research (Open Access journal article).

If you measure (with lasers!) the ratio of trace elements with a more common element like Calcium in a mussel larval shell, you can trace that larva back to the place where it made its shell. The larva presumably incorporated the same ratio of elements from its environment into its shell. This is called elemental fingerprinting.

The Yund Lab has been collecting site data with CTD casts and temperature loggers, conducting larval behavior experiments (see Morello & Yund 2016 and the Working Waterfront article), measuring mussel larval settlement, and locating and monitoring mussel beds in Downeast Maine.

Monitoring the mussel beds is particularly important for estimating reproductive output. This means measuring the density of reproductive adults, their size distribution, and estimating gonad mass and egg production.

The Yund Lab has been collecting data on these populations since 2014, thanks to Phil, Scott Morello (the previous post-doc) and many interns.

This is the final year of data collection and Phil, Taylor Donovan (our 2017 intern from Monmouth University) and I are completing the surveys this season. While we are based primarily at the Darling Marine Center, we make monthly trips Downeast to our field sites.

My role as a post-doc this year is to help with field work this season and develop a matrix population model for our known mussel beds that incorporates data the Yund lab has collected about mussel settlement, growth, mortality, and predicted population connectivity from the circulation model.

The mussel beds we are surveying are intertidal meaning they are exposed at low tides. We have to go out on the spring tide, which is usually the last week of every month this summer, so that we can have the lowest low tides to conduct our surveys.

One of the projects we are conducting this summer is measuring growth in smaller, younger mussels. We have collected mussels grown in the hatchery at the Downeast Institute, and are setting them out in chambers at several mussel beds to see how much they grow through the summer.

Downeast Institute hatchery reared mussels. No scale provided in this photo (mussels may appear larger than in real life). Photo by Skylar Bayer.

We do this by drying the shell, painting the edge of the shell red and letting the paint dry. The shell growth after we have painted the shell is all at the edge of the shell.

When we come back in a few months, we will measure the difference between the line of red paint and the new shell edge to estimate growth rates.

Check in again later this summer for more updates and photos of our Downeast mussel research journey!

Blue mussels (black, dark shells) with shells open, filtering, underwater. Photo by Skylar Bayer.

*A website with some handy definitions related to population connectivity can be found on the Pineda Lab website, but the Wikipedia page on metapopulations is helpful, too.




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