Submerged marine habitat mapping at Sandy Hook Unit, Gateway National Recreation Area: A post-Hurricane Sandy study

Grothues, Thomas; Levin, Douglas; Psuty, Norbert; Habeck, Andrea; Petrecca Rosemarie; Dobarro, Joseph; Taghon, Gary; De Luca, Michael

This product responds to a need by the National Park Service (NPS) to map, describe, and inventory submerged features in the National Parks (Parks) of the North Atlantic that border on and include marine habitats. This report specifically addresses the southern portion of the bi-state Gateway National Recreation Area (GATE), the aquatic areas within the jurisdiction of the Sandy Hook Unit of GATE, New Jersey. The project encompasses dynamic elements on tidal, daily, episodic, seasonal, annual, and inter-annual time scales. Of major importance, bottom surface features and overlying hydrography are interactive and are important to any aquatic mapping objectives, as recognized in the Coastal and Marine Ecological Classification Standard (CMECS). The overlying hydrography shapes potential habitats for benthic biota and the food resources available to nekton. Because maps are a static representation of conditions within a restricted period, they infrequently define dynamics. However, they are nevertheless valuable in providing a reference point that establishes a base from which change can be registered. Therefore, this work focused initially on the relatively stable features of bathymetry, sediment, bedform, the seasonally stable benthic community structure, and anthropogenic targets. Secondarily, the results included measures of benthic feature change at representative areas of the Sandy Hook Unit. Acoustic data to produce the base map were collected simultaneously by a shallow draft vessel with bow-mounted multibeam and side scan sonar units to determine bathymetry and seabed surface (geoform and anthropological) respectively. Acoustic survey covered 2136 acres (8.64 km2). Acoustic data were georectified, represented as depth relative to NAVD88, and corrected for pitch and roll. Grab sample locations (n = 45) to inform classification algorithms, identify and enumerate biota, and quantify sediment size and organic properties were identified by preliminary scrutiny of side scan sonar reflectivity for area-weighted stratified ground truth sampling. Grab sampling was completed in triplicate (135 grabs for biota total) at the sample location sites in October of the year following mapping efforts (2014 for the bayside and 2015 for the oceanside of the Sandy Hook spit). Repeated sampling of half of these (n = 11 on bayside and oceanside each), also in triplicate (66 grabs for biota total), occurred in October of the following years (2015 and 2016 respectively) to quantify habitat stability and variance. An additional grab sample at each station occupation (67 total including repeat samples) were dedicated to sediment characterization. An autonomous underwater vehicle (AUV) was deployed to repeat acoustic mapping over time scales ranging from hourly to annually. This provided a way to measure variance associated with the acoustic technique arising from path or depth deviation and noise in the ambient acoustic environment, and as well as seasonal and interannual change as a measure of confidence in the static map product, a resource useful for management and ecological understanding. The bathymetry of the submerged area of the GATE Sandy Hook Unit mapped in the current effort extended from intertidal to 7 m depths. The eastern exposed ocean coast has a slope that is.......

Submerged marine habitat mapping at Sandy Hook Unit, Gateway National Recreation Area: A post-Hurricane Sandy study

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