Submerged marine habitat mapping, Cape Cod National Seashore: a post-Hurricane Sandy study

Abstract

Coastal storms are the primary drivers of coastal change, but submerged areas historically have been difficult to map and consequently to document change. Hurricane Sandy had a dramatic impact along coastal areas in proximity to landfall in late October 2012 and those impacts have been well-documented in terrestrial coastal settings, however, due to the lack of data on submerged marine habitats similar studies have been limited. One of the motivations for this study was to provide park managers with a baseline inventory of submerged marine habitats to measure change during future storm events. A three-year study to map submerged habitats in Cape Cod National Seashore was recently completed. This was one of four contemporaneous studies that developed maps of submerged shallow water marine habitat in and around coastal national parks along the east coast of the United States. These four projects used similar methods of data collection, processing and analysis for the production of benthic habitat maps. Data from a phase-measuring sidescan sonar, bottom grab samples, seismic reflection profiling, and sediment coring we all used to develop submerged marine habitat maps using the Coastal and Marine Ecological Classification Standards (CMECS) in Cape Cod National Seashore. Over 76 vessel-based acoustic surveys were conducted in extreme shallow water, across four embayments from 2014-2016. Sidescan sonar imagery totaling 83.1 km2 were collected and within that area 61.3 square kilometres of collocated bathymetric data were collected with a mean depth of 4.6 m. Bottom grab samples (n = 476) and ancillary data were collected, macroinvertebrates were identified and used within the CMECS framework along with the geophysical and coring data to develop final habitat maps.

Vessel-Based, Shallow Water Mapping with a Phase-Measuring Sidescan Sonar

“…Greene et al (2018) stated that no acoustic methods existed for mapping SAV in waters less than 1 m with a traditional sidescan. The mapping of SAV in < 1 m with a PMSS was recently completed (LaFrance Bartley et al 2018a;Borrelli et al 2019b;Mittermayr et al 2020a). The co-location of bathymetric and sidescan data increases the efficacy of using PMSS systems for mapping and analysis of eelgrass and other SAV resulting in more efficient use of survey time, decreased processing time, and helps to eliminate sources of uncertainty associated with the co-location of multiple data sets during post-processing (Komatsu et al 2003).…”

“…Less than 2 km away from that area an existing eelgrass bed was being buried by the natural movement of sediment into the area, both the loss and gain of eelgrass habitat in the embayment might have falsely attributed to other factors without these data (Borrelli et al 2020). The co-location of the sidescan backscatter and bathymetry also make these instruments ideal for the creation of benthic habitat maps in shallow waters (LaFrance Bartley et al 2018b;Borrelli et al 2019a;Grothues et al 2019;Trembanis et al 2019;Mittermayr et al 2020b).…”

“…The area shown in Fig. 6 (top) was mapped in 2014 (Borrelli et al 2019b), and in 2017 for the Town of Chatham, Massachusetts (bottom). The 2019 study required 200% sidescan coverage.…”

“…Some discussion of nomenclature regarding Phase-Measuring Sidescan Sonars is warranted as terminology in the peer-reviewed literature is varied. Four terms, or variants, frequently appear: (1) interferometric sonar (McRea Jr et al 1999;Forte 2007;Eilertsen and Hansen 2008;Borrelli et al 2011;Schwab et al 2017) and (2) multi-phase echo-sounders (Brisson and Hiller 2015;de Souza et al 2015;Purser et al 2018), phase-measuring (or phase-differencing) bathymetric sonars (Cuadrado and Gómez 2011;Eisenberg et al 2011;Raineault et al 2011;Trembanis et al 2013;Porpilho et al 2014), and phase-measuring (or phase differencing) sidescan sonar (Jerram and Schmidt 2015;Raineault et al 2011;Brisson et al 2014;Porpilho et al 2014;Schmidt et al 2014;Borrelli et al 2019b). We suggest that "interferometric sonar" should not be term used as the current generation of instruments discussed here neither produce, nor quantify, interference fringes with regards to signal processing, thus, etymologically, appears incorrect.…”

The impacts of hydraulic clamming in shallow water and the importance of incorporating anthropogenic disturbances into habitat assessments

“…Following the significant impacts Hurricane Sandy had on coastal communities and ecosystems in 2012, the National Park Service sought to create a baseline inventory of existing marine habitats in coastal parks for the purpose of using these baseline data to measure future natural and anthropogenic change in these environments (Borrelli et al, 2019). One of these coastal systems included the area called Herring Cove off the coast of Provincetown, Massachusetts, and the baseline inventory was to be accomplished in the summer of 2015.…”