Mapping Aquatic Vegetation in Maine

Tiffany Wu has officially joined the GEOTalks co-host club! Tiffany is an R&D Analyst focused on containerizing machine learning pipelines and spatial data processing for Global Mapper®. In episode 11 of the GEOTalks Podcast, we discussed the role of GIS software in her master’s thesis about Zostera marina (a.k.a. Common eelgrass) in Casco Bay, ME. We were joined by Tiffany’s collaborators on this project—Cheyenne Adams from the Maine Department of Environmental Protection (DEP) and Janelle Goeke from the Casco Bay Estuary Partnership (CBEP).

What is Aquatic Vegetation?

In a broad sense, aquatic vegetation can be defined as plants that grow underwater. Common eelgrass is a type of seagrass that grows in shallow, coastal environments, including Casco Bay, ME. Believe it or not, submerged aquatic vegetation like Zostera marina plays an important role in coastal ecosystems.

Zostera Marina – A “Common” Type of Seagrass

The vegetation that grows in aquatic ecosystems like ponds, rivers, and salt marshes (just to name a few) can indicate the overall health of the habitat. In the episode, Tiffany shared the importance of eelgrass, stating that “[it] is considered a major global carbon sink… We’re focusing on Z. marina because of the study context of Maine, but all species of seagrasses play an important role in ecosystem health and function.”

In addition to their role as a carbon sink, healthy eelgrass meadows play a vital role in Maine’s economy. Eelgrass provides essential nutrients and shelter, making it an ideal habitat for lobsters, juvenile fish, and bivalves (such as scallops, clams, and oysters). Therefore, the decline of eelgrass directly threatens crustaceans and other organisms vital to the state’s economy.

In the abstract of her thesis, Tiffany states that this research “Can inform conservation strategies and management practices aimed at preserving and restoring eelgrass habitats in coastal Maine, ensuring their resilience in the face of climate change and anthropogenic pressures.” Understanding the health of eelgrass populations provides a foundation for further environmental studies and conservation efforts.

Mapping Eelgrass Presence & Absence in Casco Bay

With data provided by Cheyenne and Janelle—plus some elbow grease—Tiffany’s project came together. Tiffany mapped known eelgrass meadows using known presence points, environmental variables (covariates), and the Casco Bay study area to determine where eelgrass might be located presently with a MaxEnt predictive modeling approach. Tiffany’s project and others like it enable the community to make informed decisions about eelgrass distribution and monitoring in Casco Bay.

Using GIS to Analyze Eelgrass Covariates

As I stated above, covariates, or environmental variables, inform how researchers approach mapping vegetation underwater. They are environmental factors that can impact the presence (or absence) of a species. Wu selected a range of covariates, including temperature, salinity, bathymetry, total nitrogen, dissolved oxygen, and turbidity (as a proxy for light attenuation), to create this model for eelgrass in Maine. Global Mapper Pro® is ideally suited to process bathymetric data and analyze the terrain beneath the water’s surface.

One way to visualize bathymetric data is to create contour lines depicting the depth of the terrain. In Global Mapper, users can generate contours from their loaded elevation data. Since eelgrass is commonly found in shallow waters, we recommend adjusting the contour intervals to a smaller scale to visualize the depth of the terrain more accurately. Dive into this further and learn How To Create a Contour Map in this short article.

Using Global Mapper for Change Detection

GIS software users require versatile solutions to solve real-world problems. Global Mapper is designed to streamline workflows with robust options for visualizing, modifying, and exporting GIS files. Global Mapper supports 380+ file formats, enabling users to leverage it as a vital resource in a range of industries and projects. Change detection has become one of the most accessible workflows in Global Mapper for environmental research as a result.

With this file format flexibility, users can detect changes across their spatial data collected over time. Wu used an open-source spatial statistics software to bring a .SHP file into Global Mapper. Then, she leveraged the library of Online Data Sources for both of the basemaps (above). Specifically, she used the NASA DEM Elevation Data (1-arc-second resolution SRTM) and the World Topo Map to create insightful maps of the study area.

Learn about Ecology on the GEOTalks Podcast

Throughout the episode, we discussed how aspiring ecologists can get involved with this kind of work in their own communities. Tiffany and I shared how we contributed to local field studies like this when we were younger. Listen to the episode for more insights.

Take these tools for a test drive by downloading a 14-day trial of Global Mapper. Want to learn more about mapping eelgrass in Maine? We’ve got you covered. Watch the show or get involved with the GEOTalks podcast:

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