Mapping Seagrass in New Jersey's Coastal Bays
Introduction
Seagrass is an important resource off of New Jersey's coastal bays, acting as a habitat, food source, and source of carbon sequestration.
Understanding the extent and locations of seagrass meadows is important for developing effective coastal management strategies.
Traditional forms of seagrass surveys, typically in situ experiments or aerial surveys, are limited by time and money.
This project used remote sensing methods to attempt to quantify the summer extent of coastal seagrass in New Jersey over the last 4 years.
Seagrass and the Environment
- Seagrass meadows can be found worldwide, typically in temperate and tropical environments (Traganos et al. 2018).
- Seagrass acts as an important habitat to many species, including endangered species like seahorses and sea turtles (Traganos et al. 2018).
- Seagrass acts as a primary producer and takes up carbon dioxide from the atmosphere (Marcello et al. 2018).
- Seagrass protects shorelines from eroding by accumulating and stabilizing soil (Marcello et al. 2018). This is especially important in places like New Jersey where we love our beaches!
- Seagrass is highly sensitive to water quality. Anthropogenic influences and climate change affect seagrass habitat (Traganos et al. 2018).
- Past studies of coastal seagrass in New Jersey have observed decreases in the amount of seagrass present over time (Lathrop et al. 2001).
Photo from: P.Lindgren [CC BY-SA 3.0 ( https://creativecommons.org/licenses/by-sa/3.0 )]
Why remote sensing?
- In situ or aerial surveys can be expensive and time consuming.
- Satellites, like the Copernicus Sentinel-2, provide vast amounts of visual data that can be analyzed with programs like Google Earth Engine.
- Past studies have performed seagrass studies using satellite data in different areas of the world (Traganos et al. 2018).
Study area of project outlined in green.
- Using imagery from the Copernicus Sentinel-2 satellite, seagrass habitat was analyzed for the last four summers in New Jersey (2017-2020).
- The goal of this project was to explore the use of Google Earth Engine in identifying seagrass and to observe how seagrass habitat has changed over the last four years.
- Images were then compared to submerged aquatic vegetation (SAV) data collected from in situ and aerial surveys conducted in Barnegat Bay in 2009 (Lathrop & Haag, 2011).
Results
2020 Summer Seagrass Cover. Left map shows summer seagrass extent in 2020. Right map shows accuracy assessment from Lathrop & Haag, 2011. Zoom in, slide between maps, and toggle the legend.
2019 Summer Seagrass Cover. Left map shows summer seagrass extent in 2019. Right map shows accuracy assessment from Lathrop & Haag, 2011. Zoom in, slide between maps, and toggle the legend.
2018 Summer Seagrass Cover. Left map shows summer seagrass extent in 2018. Right map shows accuracy assessment from Lathrop & Haag, 2011. Zoom in, slide between maps, and toggle the legend.
2017 Summer Seagrass Cover. Left map shows summer seagrass extent in 2017. Right map shows accuracy assessment from Lathrop & Haag, 2011. Zoom in, slide between maps, and toggle the legend.
Conclusion & Discussion
- Google Earth Engine is a valuable, free resource that can be used to assess seagrass habitats off the New Jersey coast.
- This project's accuracy assessment concludes that the information made is not accurate. Ways to improve the accuracy include:
- Including atmospheric corrections for sunglint.
- Insuring cloud masks don't interfere with classification.
- Performing an assessment based off of satellite data from the same year as in situ surveys were performed.
- Seagrass is an extremely important resource and habitat in New Jersey's coastal waters. Understanding the location and extent of seagrass will be critical in planning for the future of New Jersey's coasts as they continue to change.
Who wouldn't love seagrass? Image source: IUCN (https://www.iucn.org/commissions/ssc-groups/plants-fungi/plants/plants-h-z/seagrass)
