The Southwestern Mordecai Environmental Restoration II project incorporated the installation of 560 feet of geotubes filled with sand to act as a breakwater in the effort to protect the adjacent Mordecai island shoreline from further wave erosion. A secondary goal has been to allow accretion of material behind the tubes in order to rebuild that section of the island to its 1977 dimensions. To date, the geotubes are performing up to expectations with little or no maintenance required. Their intertidal surfaces are covered with a healthy growth of bladderwrack seaweed and barnacles with accompanying
periwinkles and small forage fish. In a way, a living breakwater already exists here, protecting the island, but not itself.
The geotubes are made of a heavy weave of polypropylene designed for many years of service. In marine environments they are often covered with sand or other materials to protect them from damage or wear from foreign objects, including boats and flotsam that might compromise their integrity. Understandably, they do not last forever. The near term purpose of the Oyster Living Breakwater (OLB) project is to develop a process using living oysters to act as a protective cover or barrier for the geotubes. Just as a living coral reef heals itself, the long term goal is that the OLB supplants the geotubes when the geotube material is no longer functional.
The Mordecai Island Trust is partnering with ReClam the Bay (RCTB) in this project. In 2014 we began the first of many research phases. We are in the process of evaluating substrate materials suitable for spat attachment directly to the geotubes. We have also installed small (5’x5’) test patches of shell in various configurations to evaluate their stability over the upcoming winter season. In the spring of 2015 we began work on a new method of remote spat set on these patches as well as onto small geotube patches. By the end of next year we hope to have a plan formulated for a pilot installation in 2016 on or near one of the tubes.
The next phase is to determine if oyster larvae will attach to the geotube surface or other substrate materials. Our plan has been to evaluate the different substrate samples under laboratory conditions. RCTB has been able to reserve two aquariums at the Long Beach Island Foundation facilities for this. Rutgers Hasken Lab scientists have been giving us guidance on setting up/balancing the aquariums and preparation of the substrate samples. We’ll stay in touch with them on their schedule for producing larvae for the growers and they’ll give us small samples of larvae from the big batches to test at LBIF aquariums. Depending on who you talk to, the ideal temperature is about 26 degrees C. so we assume the larvae will be available from Hasken later in the summer when they’re most likely to take.
Assuming the existing bags of shells from last November are still in place at the geotubes and the water temperature is around 26 degrees C, we plan to cover one or two piles with a Spat Dome (see concept sketch). We’ll feed
a suspension of larvae into the dome to see if they’ll attach to the shells. The dome serves to protect the larvae from predation while allowing oxygen and nutrients to circulate into the dome. This again will take place later in the summer when the bay is warm. As stated in the above OLB plan, by then we should be able to formulate agendas for next year.
During our meetings we learned that New Jersey oysters survive in sub tidal zones, so coating the entire geotube may be impractical. However, our anchor tubes are sub tidal. These anchor tubes may be appropriate for placement of bagged spat on shell. The new upweller at Beach Haven could supply test bags this summer. Last year we had limited success at Cattus, but the upweller near Mordecai should be successful due to the good water there. Another idea that came out of our meetings is that ribbed mussels may be a good substitute if the oyster larvae don’t attach successfully on the substrate samples. Hopefully we’ll be able to get our hands on some mussels to see how they survive at Mordecai.
In our meetings with different groups at Rutgers, interviews with Stockton, Stevens and Perdue engineers, and the USFWS, they all encouraged us to continue with our efforts and offered to help any way they could. The R&D approach may be slow, but we’ll know what we’re doing right (or wrong) as we go. So far, we’re on schedule.
For updates, or further information, contact Jim Dugan, Trustee, MLT at firstname.lastname@example.org .