08 June, 2021

Oyster Reefs and Salt Marsh Resilience

 On an island like Nantucket it’s hard lately to not read something about climate change, sea level rise, coastal resilience, erosion, etc. These buzz words can be heard all around the island from the flash flooding on Easy St to storm erosion near Hummock Pond. From south shore to harbor – Nantucket is starting to feel the impacts of climate change but we are also starting to figure out how to respond to this change.

At the Nantucket Conservation Foundation, we recognize the wealth of resources we have in our acres of permanently protected open space and in the past few years we have focused our coastal research on resilience, particularly in our salt marshes. Of approximately 1600 acres of salt marsh on Nantucket, NCF owns approximately 1200 acres, so we have a lot of area to work with!

Medouie Creek salt marsh in eastern Polpis Harbor, future home of a coastal resilience improving oyster reef?!

The Medouie Creek salt marsh in eastern Polpis Harbor has been the focus of over 15 years of restoration and research on salt marsh ecology from salt marsh restoration to spotted turtle habitat to salt marsh dieback and purple crab invasions. In 2020 we started preliminary research to see if the intertidal shore of Medouie would make good habitat for an oyster reef.

Why an oyster reef? There are so many amazing ecological reasons to have an oyster reef! One of the biggest being the potential to increase water quality. This summer we collected water samples to document how much nitrogen and phosphorus was in the intertidal flats near Medouie Creek, both to make sure oysters would be happy here but also track if and how a reef improves water quality over time.

An oyster reef can provide coastal resilience, decrease erosion, stabilize the shore, reduce wave impacts all while the oysters work to improve water quality!

Oyster reefs can slow down normal and moderate waves and storm surges, reducing shoreline erosion. Oyster reefs placed near a salt marsh can also help sediment drop out of the water and settle, building up soil and potentially allowing a salt marsh to migrate outwards over time!

Oyster reefs can potentially capture sediments, allowing salt marsh vegetation to migrate seaward and increasing resilience

In 2020, we began the work to find out if Medouie Creek would be a good spot to place an oyster reef and this involved the collection of ALOT of data, in partnership with the Town of Nantucket Natural Resources Department. Data like water depth over the whole summer is important, we don’t want oysters out of water for too long! How much light gets down through the water, how warm is it in the summer? Does anything else important live there?

Snorkel surveys with TON NRD showed very few other things living where we want to place a reef: bad for Polpis Harbor right now but very good for our plans to establish a reef! No eelgrass, shellfish or other aquatic plants were found in the reef area.

Seine netting sweeps found a few different fish, crabs and shrimp (so many shrimp!) but nothing unusual or unexpected.

One of the more exciting monitoring pieces was the placement of a tilt current meter courtesy of Lowell Instruments! Few oyster reef restoration project have actually documented how a reef can change tidal patterns in a near shore area. To demonstrate how a reef can improve coastal resilience near a salt marsh, we placed a tilt current meter out on the site and will leave it out after the reef is in place!

Now, it doesn’t look like much but this meter is constantly measuring water velocity – both direction and speed of water moving around it! The logger is buoyant and we anchor it to the harbor floor on a short, flexible tether. As water moves around the logger, it tilts in the flow direction and the logger can record tilt direction and angle, allowing us to calculation velocity. Larger storms and increased wind lead to increased velocity. If the oyster reef slows the velocity and associated erosion potential, this lovely meter will help us track that!

Now that NCF understands the current habitat near Medouie, we will begin the planning and permitting process and hope to install an oyster reef in the summer of 2021. Stay tuned!

Thank you to the Nantucket Shellfish Association for supporting purchase of pre-restoration monitoring equipment.

Questions? email Dr. Jen Karberg jkarberg@nantucketconservation.org

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