By Dr. Jen Karberg, Research Program Supervisor

This November, Nantucket Conservation Foundation, in collaboration with the Town of Nantucket Natural Resource Department, completed the final step in a 2 year long restoration project to create a new oyster reef in Polpis Harbor. The first reef of it’s kind in Massachusetts, this project will show one way to bring more stability and resilience to shorelines around New England.

With climate change bringing rising sea levels, higher storm surges and more intense storm waves; healthy and intact salt marshes are key protecting our shorelines. If you have been following this blog for awhile, you may remember hearing about salt marsh dieback and the purple marsh crab eating away at Nantucket salt marshes. We have begun to find solutions to control the crabs and restore the salt marsh grasses but it takes time and while it happens, we risk loosing salt marsh soil. Less salt marsh means less area to hold flooding and storm waters, less area to filter nutrients and less area to support the amazing food webs depending on salt marshes! In 2016 I began researching ways to protect the salt marsh and this project is the result of years of planning, research and collaboration.

Solution? Find a way to (naturally?) reduce wave and tide impacts to the salt marsh and maybe improve ecologic health at the same time. Since it’s a conservation area, we didn’t want a hard wall – we wanted something that would slow down water movement but not stop it.

Strategically designed Oyster Castle® reef taking shape just off shore of the primary salt marsh dieback area at Medouie Creek, Polpis Harbor. Drone footage by Nick Larrabee.

How? Build a protective reef using Oyster Castles®! We gave oysters a new and fancy home just off the shore of our Medouie Creek salt marsh by building a reef out of Oyster Castles®! Oyster Castle® reefs allow water to move over and around and through them while slowing down water AND building up a water quality improving oyster population.

An intertidal oyster reef slows water movement, breaks up waves and helps protect adjacent salt marsh shorelines

What!? If you haven’t heard of Oyster Castles® before – that’s because this is the first time they’ve been used in Massachusetts. Oyster Castles® are made by Allied Concrete with a proprietary concrete mix used to make lego-like building blocks. The castle blocks interlock and allow the building of many different reef configurations. And the concrete mix is proprietary because it is specialized to attract oyster spat. Oyster spat (baby oysters) need a solid structure to attached to and once attached they grow and mature and produce more babies, building up an oyster reef. But without that harder structure to attach too, oysters won’t move into an area.

Oyster Castle® reef being built in Polpis Harbor, Nantucket. Oyster spat (baby oysters) is attached to castles in the top two rows of the reef. Photo credit: Neil Foley

At Medouie Creek – an Oyster Castle® reef provides two amazing benefits – slowing down water velocity to buffer the shoreline and hosting a growing oyster population that filters water and grows with sea level rise. As this is the first of it’s kind in Massachusetts, we will be monitoring and studying many things: how the reef survives storms, reef effects on water movement and velocity, how to the oysters survive and how the salt marsh survives and grows. A really neat piece of equipment called a tilt current meter, courtesy of Lowell Instruments, will actually let us continuously see how the reef changes water direction and speed around the salt marsh!

This project was only possible through collaboration with the Town of Nantucket Natural Resource Department which used the Brant Point Shellfish Hatchery to encourage millions of baby oysters to attach to the castles and begin growing! In early 2021, with shipping delays and stormy weather, we rushed to get 1000 Oyster Castles delivered to Nantucket with the help of Cape Cod Express – a plea to save the baby oysters can make a lot of things happen!

Moving the castles to the Shellfish Hatchery took a lot of hands. NCF’s Chris Iller is seen unloading castles from a truck bed while TON NRD staff placed them in these tanks. (Photo credits: Neil Foley)

About 1/3 of the castles went to the Shellfish Hatchery at Brant Point and were placed in tanks designed to help oyster spat (baby oysters!) settle, attach to the blocks and begin growing.

Teeny tiny oyster spat seen under a microscope at the TON Hatchery (photo credit: Neil Foley) and oyster covered castles awaiting transport to the restoration site (photo credit: Tara Riley)

Getting all those castles with baby oysters out to the restoration site took MANY hands and thanks to Anderson’s Stillwater Moorings for help with castle transportation!

Loading castles covered in oysters into boats for the trip up harbor to the restoration site!

And building a suite of oyster castles took many many hands – each castle is about 35lbs! With the help of many groups and individuals and unseasonably warm November weather – we constructed the reef over three days at low tide. Fondly nicknamed McKarberg’s Navy, we loaded castles into skiffs and walked them over to the restoration site, avoiding impact to the salt marsh. Then teams worked together to fit the interlocking castles into a stable reef, three rows built on top of each other at angles to the shoreline.

Seth Engelbourg (LLNF), Cormac Collier (NCF), Will Kinsella (ACKlimate) and Jack Dubinsky (MMA) load castles into a small skiff as Richard Mack (NCF) pushes loaded boats to the restoration spot (Photo credits: Neil Foley).
Jen Karberg (NCF) places castles on one reef while Tara Riley (TON NRD), Kelly Omand (NCF), and Chad Kilvert (ACKlimate) unload a full skiff on another reef. Karen Beattie (NCF), Danielle O’Dell (NCF) and Thais Fournier (TON NRD) finish build the last section of another reef (Photo Credits: Neil Foley).

The completed reef spans ~200 feet of salt marsh shoreline in Polpis Harbor and will now spend the winter shifting and settling in place. Over the next few years, we will study how the oysters grow, how the reef holds up to Nantucket weather and how the reef protects the salt marsh shoreline. One benefit we hope to document is the growth of the salt marsh out towards the reef. As sea levels rise, salt marshes need to migrate away from the shoreline to stay above the rising water. If an oyster reef can slow down waves, allow sediment to settle out, maybe a salt marsh can respond to sea level rise by growing into the harbor. The oysters on the reef will be growing upwards as sea levels rise so together, these two important ecosystems can work to make this little shoreline much more resilient to coming climate change impacts.

Phot credit: Nick Larrabee

Thanks to so many groups and individuals for donating their muscles and time to get these castles in place in the cool waters of November. Linda Loring Nature Foundation, Massachusetts Nantucket Audubon, Nantucket Shellfish Association, Maria Mitchell Association, ACKlimate, Nantucket Land Council, and Champoux Landscape THANK YOU!

And this project would not be possible without funding support from the Nantucket Shellfish Association and the MA In Lieu Fee Program. Thank you for believing in this project and helping advance coastal research and resilience in Massachusetts.

The Nantucket Conservation Foundation is a private, non-profit land trust that depends on contributions from our members to support our science projects, conservation property acquisitions, and land management efforts. If you are not already a member, please join us!