OysterBlitz

Last October, the Phillips Wharf Environmental Center was awarded an Oyster Innovation Award grant to create a new program called OysterBlitz. Modeled after the BioBlitz program, the goal was to train students to measure oyster spat, identify other aquatic organisms, and measure biodiversity in oyster spat bags. On Friday, April 28th, the very first students participated in this program.

For context, the Phillips Wharf Environmental Center runs an oyster restoration program that is housed under the state-wide Marylanders Grow Oysters program. Our sub-program, called Tilghman Islanders Grow Oysters, provides baby oysters (spat on shell) in cages for volunteers to hang from their docks for approximately 9 months beginning in the fall. During this time, volunteers are asked to periodically shake the cages, which helps keep the oysters clear of mud and prevents them from growing through the bars of the cages. In the late spring/early summer, Phillips Wharf staff and volunteers collect all the cages and plant the oysters in the Harris Creek Oyster Sanctuary. 

During the growing period, we monitor a sub-sample of oysters for growth rate and mortality. In the fall, we set up measuring bags with 100 oyster spat in each bag and place them in volunteer cages around our growing area, from Black Walnut Cove to Irish Creek and even to our home in Easton Point Park on the Tred Avon. Each of these bags is pulled once a month and the oysters inside are measured and counted.

In years past, we’ve observed that the oysters stop growing when water temperatures drop below a certain point (~55 degrees Fahrenheit). We’ve also observed a variety of other animals using the oysters as habitat but this data was only ever casually noted – not recorded in a meaningful way.

The goal of the OysterBlitz program was to provide hands-on opportunities for students from Talbot County to engage with oysters and learn about the ecosystem services that they provide. In addition, we created a data collection system for recording the additional species found in with the oysters – basically, now we have a standardized method for recording what animals we see each month. The hope is that we’ll be able to use this data to understand the seasonality of these other species, highlight the use of even temporary oysters as habitat, and explore biodiversity across different waterways within the Choptank sub-estuary.

A single oyster growing on a cultch shell (the original oyster shell that new spat attaches to). This cultch shell happens to also be home to a thriving bryozoan colony.

So, with our first OysterBlitz completed, what did we see?

We saw the greatest number of different species in the oysters that hang in Harris Creek, with students finding 7 different species in both sets of oysters that came from this waterway. The most common species, other than the oysters, was barnacles, followed by amphipods. Students also found several different types of eggs, suggesting that the oyster shells provide nursery habitat for eggs and juvenile animals, as well as adults. We also saw a lot of bryozoans, which are a simple colonial animal that are often referred to as moss animals. They are typically considered a fouling organism as they grow on hard surfaces, such as crab pots, crab shells, and on oyster reefs. However, they can serve as a food source for aquatic snails and slugs (nudibranchs), crustaceans, starfish, and even some fish.

The average size for the oysters measured was 23 mm (0.9 inches), which is a big increase from the average size of 5.9 mm when the oysters were first received in October. The average growth rate between when the oysters were measured in March and then again in April was 5.6 mm.

Water temperatures were relatively warm, ranging from 67 F to 75 F – keep in mind all of our readings are taken at docks so the water is relatively shallow. Salinity was stable across at the sites, ranging from 15 ppt to 17 ppt.

Even though water temperatures have likely cooled off in the last week or so, we still expect to see higher growth rates when we take our next measurements at the end of May. Shortly after that, in the first few weeks of June, we’ll be picking up everyone’s oyster cages and planting the oysters in Harris Creek. If you’re interested in growing oysters with us (no measurement taking required – that part is optional), send us an email at oysters@pwec.org as we will be putting together our volunteer list beginning in June.

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