Floating Islands 2.0

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Saltmarsh Sparrow chicks are most susceptible to flooding during the spring tides when the marshes are completely flooded. Photo by: Jeanna Mielcarek/UConn SHARP

By: Bri Benvenuti @UNH

With sea-level on the rise, Saltmarsh Sparrows are facing new challenges when it comes to nesting success.  As ground nesting birds, they are highly vulnerable to nest failure due to flooding by spring tides, which are increasing in duration and frequency as sea levels rise. Last year SHARP grad student, Bri Benvenuti of the University of New Hampshire, installed a pilot floating island in Maine (you can read more about that effort here and here). The goal of this pilot study was to determine if island structures would be able to support the growth of tidal marsh vegetation in a hydroponic environment in an effort to provide Saltmarsh Sparrow nesting habitat that is free of tidal flooding.

This past week, we bid adieu to our pilot island and replaced it with four new islands. While our pilot island was free of tidal flooding from July to November, it suffered under all the ice and snow this winter. However, despite losing buoyancy, the vegetation on the island remained healthy, and was even sending out new shoots. This demonstrated that it is possible for the salt marsh vegetation Spartina alterniflora and S. patens to survive in these artificial conditions.

Although the vegetation on the pilot island survived a brutal winter, coming back to life this spring, it was lacking the buoyancy necessary for successful nesting habitat. Photos: B. Benvenuti

Although the vegetation on the pilot island survived a brutal winter, coming back to life this spring, it was lacking the buoyancy necessary for successful nesting habitat. Photos: B. Benvenuti

This year, we’re using a proven design created by Chris Streb and BioHabitats Incorporated with the intention of providing quality nesting habitat that is free of tidal flooding. BioHabitats Inc.’s design uses a cedar frame, synthetic planting substrate, and plastic flotation  to create a plantable floating island. We modified the BioHabitat design by using 2 in. foam core, capped PVC pipe as flotation The islands also possess an anchoring system that allow them to rise and fall with the tide, but maintain a stationary position within the marsh pool. Each island was planted with ~130 2 in. plugs of Spartina alterniflora and Spartina patens.

Diagram of how the BioHabitat Inc. floating islands are constructed (Streb and Biohabitat Inc. 2012).

Diagram of how the BioHabitat Inc. floating islands are constructed (Streb and Biohabitat Inc. 2012).

Four islands were constructed with different vegetation scenarios based on previously collected nest vegetation data. Two islands of 100% S. patens, and two islands of 75% S. patens and 25% S. alterniflora were created. By creating islands with different plant compositions, we will be able to provide habitats similar to those of known nest sites, as well as provide insight into plant species competition and survival in a restricted, hydroponic environment.

Floating island with a mixture of vegetation. Photo: B. Benvenuti

Floating island with a mixture of vegetation. Photo: B. Benvenuti

With the islands in place, we will now be monitoring them to ensure they are free of flooding, that the vegetation is growing successfully, and whether they are used by the target species. Additionally monitoring will be conducted during the flood tides to determine if the islands remain free of inundation are critical nest-height levels.

 

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