Maine Coastal Mapping Initiative

What is the Maine Coastal Mapping Initiative?

The Maine Coastal Mapping Initiative (MCMI), created by the Maine Coastal Program in 2012, is acquiring critical data about the seafloor and our oceanic environment, including bathymetry (seafloor depth), sediment information, fauna type and abundance, and water column information. This seminal dataset has several derivatives that will aid coastal managers and planners, private industry, fishermen, and academics to carry out the following activities:

  • Improve maritime navigation and safety;
  • Maintain vibrant marine ecosystems;
  • Inform offshore economic development permitting;
  • Increase Maine’s resiliency to environmental changes;
  • Promote informed regional ocean planning;
  • Conduct habitat classification and modeling.

History of Seafloor Data Collection in Maine

Historically, little has been done to understand the bathymetry (i.e. shape) and composition of the seafloor off the coast of Maine. Most of our existing seafloor maps were generated by dropping lead lines to the ocean bottom to estimate the depth of the overlying water column. In the 1980s, the Maine Geological Survey (MGS) in collaboration with the University of Maine used side-scan sonar to map small portions of the seafloor and collected sediment samples to ground truth those readings. These data were used to improve bathymetric maps and to model the composition of the seafloor along the entire coast of Maine. Because side-scan sonar only collects narrow swaths of data and because of the limited overall scope of the project, much of the coast is still data-insufficient, and in large areas of the coast we rely heavily on models that have not been ground-truthed or updated for many years.

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Impetus and Aims for Our Work

In 2006, the Maine Coastal Program (MCP), in partnership with several other state natural resource agencies, began work on the Bay Management Study. Bay Management had a number of potential goals and outcomes including the investigation of developing an embayment management scheme as opposed to the "one size fits all" regime that was currently in place for a variety of management issues (e.g. fisheries, eelgrass, runoff contamination, etc.). Upon completion of the study, a series of recommendations were presented in report format, and the Bay Management team concluded that a wide variety of spatial data sets was necessary to make even the existing management regime more effective. Bathymetry and benthic habitat were identified as information vital to accurate and informed decision-making on the state's submerged lands. In 2009, the MCP conducted a comprehensive, interagency poll to collect additional feedback and prioritize data collection efforts to fill in critical data gaps identified by the Bay Management Study. Bathymetry was again identified as the State's number one data need.

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MCMI Timeline

MCMI timeline diagram

In 2013, the MCMI collected bathymetric and backscatter data for approximately 25 mi2 of seafloor in Midcoast Maine. These data were used to generate bathymetric and habitat maps as a proof of concept that high quality data could be acquired on a small platform with minimal crew and equipment. After a successful season of data collection, the MCMI purchased its own multibeam sonar and ground truthing equipment. In 2014, the MCMI entered into a multi-year cooperative agreement with the Bureau of Ocean Energy Management (BOEM), a division of the U.S. Department of the Interior, to identify and characterize surficial sediment deposits in federal waters (3-8 nautical miles (nm) offshore) off of Maine’s southern and mid-coasts. Since then, approximately 125 mi2 of bathymetry have been collected by the MCMI (Figure 1; five square miles of coverage in the vicinity of Boothbay Harbor not shown). Ninety-four sites were ground truthed using underwater video and sediment collection. In 2014 MCMI maped 40 mi2 off of Kennebunkport, and in the following year, MCMI collected ~80 mi2 of bathymetry in coastal waters off of Midcoast Maine. An additional five square miles of area were covered closer to shore around Boothbay Harbor and Ocean Point to assist the Department of Marine Resources with a scallop habitat mapping project in 2015.

After completion of 2014 data processing, the MCMI has received approval from the National Oceanic and Atmospheric Administration’s (NOAA) Integrated Ocean and Coastal Mapping unit that data collected were of "hydrographic quality," which means that NOAA will use MCMI data to update hydrographic charts for distribution to mariners. In 2016, the MCMI is continuing with the mission of the BOEM cooperative agreement and is continuing to collect bathymetry and backscatter data in a Midcoast focus area that is located near the Kennebec River Paleodelta (Figure 1).

MCMI map

Figure 1. The Maine Coastal Mapping Initiative collected ~120 mi2 of coastal bathymetry in Southern and Midcoast Maine in the 2014 and 2015 seasons (red lined polygons) to complement the bathymetric mapping that has already been completed in this region by the NOAA,UNH and GOMMI (bathymetric data without red outline). The mosaic of the hydrographic surveys in Southern Maine was provided by Daniel Martin (NOAA affiliate). The remainder of the 2015/2016 focus area (red polygon in right panel) is currently being surveyed by the MCMI.

Further sampling collects information from a wide range of benthic habitats and substrates in order to verify seafloor sediment interpretations of backscatter data and develop a predictive benthic habitat model based on correlations between the physical conditions of the seafloor with the organisms living there. Ground truthing includes collecting grab samples for sediment grain size analysis and infaunal processing, collecting water column measurements of temperature, salinity, pH, dissolved oxygen and chlorophyll concentrations with a water quality sonde, and recording underwater video to document observations of seafloor sediment and organisms living on the surface of the seafloor (Figure 2). These data are also used to classify habitat at ground truthing sites using the Coastal and Marine Ecological Classification Standard (CMECS; FGDC 2012).

MCMI map

Figure 2. Our benthic sampling platform (modeled after the USGS mini SEABOSS) allows the MCMI crew to simultaneously collect benthic samples and underwater video to ground-truth backscatter data and inform habitat classifications.

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Hydrographic Data Collection Process

Hydrographic data are those that describe the ocean’s environment. This includes information about depth, currents and tides, water temperature, salinity, pH, and other qualities, and the location of rocks, shoals, and other seafloor characteristics. The MCMI uses specialized equipment to collect and ground truth offshore hydrographic data. A multibeam sonar collects bathymetric (depth) and backscatter data; backscatter data are used, in part, to infer substrate type (i.e. whether the seafloor is composed of mud, sand, gravel, etc.). These data are georeferenced with a high precision GPS unit and compiled to form a three dimensional map of the seafloor. Because backscatter data are challenging to interpret, substrate type is ground truthed with a sampling platform equipped with a sediment grab sampler, water quality sonde and an underwater video camera (Figure 2). The grab sampler collects a sample of sediment for grain size and color analyses, the water quality sonde continuously records measurements of various physical and chemical parameters through the water column, and the camera takes video of the seafloor. In rocky environments the grab sampler returns only a sample of water with the occasional attached organisms, like the red northern anemone caught in the sampler’s jaws, as seen in the center picture below. Upon collection of a successful sample, the platform is brought back on board and samples of muddy, sandy and gravelly seafloor sediment are processed to collect the organisms living in the sediment, called infauna.

In addition to understanding the geology of the seafloor, the MCMI investigates the biological community to conduct benthic habitat classification and modeling, which is integral to the ocean planning process and to maintaining the health of our coastal and marine ecosystems. For this work, the sediment sample collected by the grab sampler is washed through a sieve with 1mm sized mesh holes to isolate the small organisms living within or on the seafloor (infauna). Infaunal samples are collected into jars, preserved in alcohol to prevent their decay, and are later analyzed to determine the assemblages of species supported by the coastal benthic habitats the MCMI sampled.

Bathymetry and Backscatter Data Collection and Processing

multibeam sonar

Figure 3. NOAA portrayal of seafloor mapping indicating vessel and sonar “swath”. Credit, National Oceanic and Atmospheric Administration, Office of the Coast Survey.

A multibeam sonar (Kongsberg EM 2040C multibeam echosounder) is used to collect the bathymetric and backscatter data. This piece of equipment sends out high-frequency acoustic pings as multiple beams arranged in a fan-shaped swath approximately four times as wide as the depth at that location (Figure 3). The amount of time it takes for each beam to bounce off the seafloor and return to the sonar head is used to calculate the depth of the water at that location. The speed of sound traveling through water is affected by temperature and salinity. Sensors mounted to the sonar head take continuous recordings of these and a hand-held sound velocity probe is deployed as needed to take readings throughout the water column. Ultimately, thousands of data points are compiled to generate a seamless mosaic of the seafloor bathymetry.

Backscatter data are also collected by the multibeam sonar. Backscatter readings are proportional to the amount of energy that is reflected back to the sonar after an interaction with the seafloor and are used to estimate the nature of the substrate. For example, when the bottom is rocky more energy is returned to the sonar, and the backscatter readings are higher than if the seafloor is muddy. We ground-truth backscatter data using a drop camera that takes pictures of the seafloor and a Ponar grab sampler collects surficial sediment. Additionally, infauna and epifauna (organisms living inside and at the surface of the sediment) are identified and analyzed to characterize benthic habitat type (see below for more details).

Another challenge of analyzing multibeam data is determining precisely where the data were collected. In other words, we need to know our ship’s x-, y-, and z-coordinates to put the bathymetry accurately on a map. Thus, a very precise GPS system (SeaPath 330) is used to obtain the ship’s latitude and longitude (i.e. x- and y-coordinates), and nearby tide gauges are used to determine the ship’s relative height at the time the data were collected (i.e. z-coordinate). Additionally, a motion reference unit is used to measure the ship’s pitch, roll, and yaw (i.e. movement around the x-, y-, and z-axes) to remove error from movement of the boat as data are being collected. All of these variables are required for the processing of the raw multibeam data before a final bathymetric or backscatter map can be generated.

Infaunal Analysis and Habitat Classification and Modeling

Infaunal sample analysis involves two major steps: 1) sorting the sample based on organism identification, and 2) taking a variety of measurements of the populations observed within the samples. In the sorting process all infauna are separated into one of five phyla (major taxonomic groups) listed in the table below, or into a miscellaneous Phyla category that includes less common infaunal organisms. Individual infauna in each Phylum are then identified to the lowest practical taxonomic level (to species where possible) and the biomass of each species is measured to the nearest 0.01 g with a scale. Species abundance, the count of individual organisms in each species’ population, and species richness, the number of different species found at each sampling site, are documented for each grab sample site. In general, higher numbers of biomass, species abundance and species richness indicate the presence of a high quality habitat.

PhylumOrganism Examples
CnidariaAnemones, corals
MolluscaClams, mussels, scallops, snails
AnnelidaMany Families of polychaete worms
ArthropodaLobster, crab, barnacles, amphipods, isopods
EchinodermataSea stars, brittle stars, urchins, sea cucumbers, sand dollars

Data collected on infauna and measurements of the physical variables of the environment including proximity to the coast, seafloor substrate or sediment type, water depth, temperature, salinity and clarity are combined to characterize coastal benthic habitat with the Coastal and Marine Ecological Classification Standard (CMECS,FGDC 2012). Infaunal species assemblage data and data collected from the physical environment at grab sampling sites are explored using both statistical and spatial analyses to determine correlative linkages between biotic and abiotic factors. Where strong correlations between biological community and physical data variables exist, predictions on habitat may be made with confidence. The correlative relationships determined from these investigations can be used to model habitat in areas where only information on the physical environment is available.

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MCMI Alumni Crew

  • Emily Norton — MCMI Project Manager, 2013 – 2016
  • Rob Hallinan — Marine Mammal and Avian Observer, 2015
  • Dana Bloch — Marine Mammal and Avian Observer, 2015
  • Emily Shumchenia — Seafloor and Habitat Mapping Consultant, 2013, 2015
  • Eliza Cronkite — Sediment processor, 2014-2015
  • David Armstrong — Multibeam Sonar Technician, 2013-2014
  • Jennifer McHenry — Benthic ecology specialist, 2013-2014

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MCMI Partners

MCMI is a coalition of state, federal, private, and non-profit partners.

mcmi partners

Biodiversity Research Institute
Bowdoin College
Bureau of Ocean Energy Management
Maine Coastal Program
Maine Department of Transportation
Maine Geological Survey
Maine Department of Marine Resources
National Oceanic and Atmospheric Association
The Nature Conservancy
University of Maine

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Bathymetry — the shape of the seafloor; analogous to topography for a terrestrial system.
Backscatter — the degree to which the sonar is reflected or scattered when it hits the seafloor. High backscatter indicates that the seafloor is hard (i.e. bedrock or boulder); low backscatter indicates that the seafloor is relatively soft (i.e. sand or mud).
BOEM — Bureau of Ocean Energy Management, located within the Federal Department of the Interior.
Epifauna — biological organisms that live on the surface of the seafloor.
Infauna — biological organisms that live in the sediment of the seafloor.
MCMI — Maine Coastal Mapping Initiative
MCP — Maine Coastal Program

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