Last updated: January 22, 2024
Article
Algae from Above: Scientists Pilot Aerial Mapping of Park Rocky Intertidal Zones
By Science Communication Assistant Avani Fachon, San Francisco Bay Area Inventory & Monitoring Network Science Communication Team
Nathan Duggins, NPS Permit No. PORE-2022-SCI-0017
For decades, San Francisco Bay Area Network (SFAN) biologists have used on-the-ground monitoring techniques to gather data on how small rocky intertidal areas along the central California coast are responding to changing environmental conditions. They are learning a lot, but can’t be sure how broadly their findings apply across whole sites. In order to find out, the team is on the lookout for new, efficient ways to record how these ecosystems are shifting—at a wider scale.
How can we leverage advances in technology and artificial intelligence to create a more comprehensive record of these important ecosystems and track how they are changing? One possibility lies in the power of aerial mapping.
How can we leverage advances in technology and artificial intelligence to create a more comprehensive record of these important ecosystems and track how they are changing? One possibility lies in the power of aerial mapping.
From Up Close to Up High
Biodiversity surveys, sea star counts, surfgrass line transects, and photo plots— tried and true methods used by the NPS rocky intertidal monitoring team– all involve heading out every year onto slippery rocks during extreme low tides for up-close data collection. These long-term data allow biologists to have a detailed understanding of biodiversity in small areas within broader rocky intertidal habitats.
NPS / Environment for the Americas / Avani Fachon
“As long as people have been doing rocky intertidal monitoring, we’ve been down on our knees and looking at these small little areas that might be... 1m x 1m and we’re counting up and classifying all the organisms inside these small areas. That’s good because we get a lot of detail,” says Dr. Ben Becker, a marine ecologist with the National Park Service (NPS). “What isn’t as good is we don’t always get a... picture of what’s happening across that whole reef, or a really large area of hundreds of meters up and down the coast.”
The key to getting a bigger picture? Moving from up close to up high.
In May 2022, a team of scientists used an unmanned aerial vehicle (UAV, aka a drone) to take a series of photos of the rocky intertidal zone. The drone moved in a lawnmower-like pattern, collecting many high-resolution images of the landscape at study sites in Golden Gate National Recreation Area and Point Reyes National Seashore. Each image contained some overlap with the previous, allowing scientists to stitch them together and create a detailed “orthomosaic” map.
The key to getting a bigger picture? Moving from up close to up high.
In May 2022, a team of scientists used an unmanned aerial vehicle (UAV, aka a drone) to take a series of photos of the rocky intertidal zone. The drone moved in a lawnmower-like pattern, collecting many high-resolution images of the landscape at study sites in Golden Gate National Recreation Area and Point Reyes National Seashore. Each image contained some overlap with the previous, allowing scientists to stitch them together and create a detailed “orthomosaic” map.
Jennifer Muha / Jamie Hoover / Nathan Duggins
“If you’ve gone on Google Maps and looked at the satellite imagery...that is a completed, cleaned orthomosaic photo,” says Jennifer Muha, geospatial sciences program lead at Front Range Community college and a lead on the 2022 rocky intertidal mapping image collection team. “[Our orthomosaics of the rocky intertidal zones are] the same idea, we’re just doing everything on a much tinier scale [and with higher resolution].”
Becker compares the process to taking a “whole body scan versus. a blood test or … [versus] just looking for abnormal skin cells on your arm.” With regular on-the-ground monitoring, scientists can understand how many mussels are within a particular plot and how big they are, or whether a species of sea snail is at a specified point along a line transect. In contrast, high-resolution orthomosaics provide a more comprehensive overview of the entire landscape and the abundance of organisms which inhabit it. “With advances in technology, and especially using UAVs, we’re able to get this high-resolution imagery and get almost the sort of detail from those as we could when we were looking down on our knees in the quadrats. But we’re able to make much stronger statements about if certain algae are declining, or if certain mussel beds are increasing... and take a much better sample and description [of species assemblages],” he explains.
Becker compares the process to taking a “whole body scan versus. a blood test or … [versus] just looking for abnormal skin cells on your arm.” With regular on-the-ground monitoring, scientists can understand how many mussels are within a particular plot and how big they are, or whether a species of sea snail is at a specified point along a line transect. In contrast, high-resolution orthomosaics provide a more comprehensive overview of the entire landscape and the abundance of organisms which inhabit it. “With advances in technology, and especially using UAVs, we’re able to get this high-resolution imagery and get almost the sort of detail from those as we could when we were looking down on our knees in the quadrats. But we’re able to make much stronger statements about if certain algae are declining, or if certain mussel beds are increasing... and take a much better sample and description [of species assemblages],” he explains.
Learning from Light
In addition to collecting imagery in the visible color spectrum, the drone also captured light on the near-infrared spectrum—which is invisible to the human eye. “The tools we have to see beyond our normal senses are just crazy,” exclaims Nathan Duggins, a geospatial sciences student at Front Range Community College, and a research associate on the 2022 rocky intertidal image collection team. The use of near-infrared technology has evolved over decades, and today has important implications for understanding and conserving rocky intertidal zones.Use of near-infrared light in aerial mapping technology began in World War II, when the U.S. military utilized infrared film in war-torn areas for camouflage detection. Each feature in a landscape has a special “spectral signature;” this can also be understood as the amount of different types of light (ex. blue, green, red, near-infrared) absorbed and reflected by an object. Plants absorb visible light, and reflect most infrared light. Due to the abundance of infrared light which hit the film used in WWII surveillance photography, vegetation lit up in a hot pink color, distinguishing it from camouflaged areas. As Muha puts it, “They figured out that painting something to look like plants is not the same spectral signature as plants.”
After the war ended, photo interpreters needed to find new ways to apply this valuable skill set. “That’s where the science of aerial photography and being able to take these snapshots in time …really started — with this big group of people we taught how to find the enemy during world wars. And then they were like oh, we can apply this to science,” Muha explains.
United States Geological Survey
As technology has advanced, scientists are continually finding more ways to learn from light. Spectral signatures can also be used to delineate and identify vegetation of specific groups. In the rocky intertidal zone, for example, near-infrared light can be used to differentiate between different types of algae. Duggins, who analyzed the imagery as part of his Associates of Applied Science capstone, shares his experience showing comparisons of regular and near-infrared images of algae to peers: “I would show them in regular color, and they couldn’t tell the difference between the two algaes. And then I would say, okay, let me show you some infrared bands, and it would look totally different,” he laughs.
Left image
Credit: Jamie Hoover
Right image
Credit: Jamie Hoover
The applications of aerial mapping are tremendously valuable to tracking the health of rocky intertidal ecosystems at a large scale, especially in the face of human disturbance. Rocky intertidal zones are highly vulnerable to climate change effects, such as sea level rise, changing air and ocean temperatures, and ocean acidification. Additionally, pollution from events such as oil spills can harm these ecosystems. Being able to track how a mussel bed, sea star community, algae, and other intertidal organisms are shifting over time at a site-wide scale would be extremely helpful for better-informing future restoration and conservation efforts.
A Roadmap for the Future
The 2022 rocky intertidal mapping project was a “proof of concept” for future use of this technology. The team was able to create a methodology for gathering the images, which “[set] the groundwork for future teams to come in and fine tune,” says Duggins. Now, the orthomosaic maps have been passed off to researchers at UC Santa Cruz, where they are developing the best approach to using artificial intelligence to classify the organisms into different species assemblages. Findings about the capabilities of this data will be another addition to the roadmap for future use of aerial mapping of intertidal zones.
This pilot looks promising for integration of these methods into the annual monitoring program, as an addition to the regular plot-level research. As Becker says, “It’s the next generation of helping us monitor the environment with technology.”
Acknowledgment: Many thanks to Dr. Jamie Hoover, Nathan Duggins, Jennifer Muha, Dr. Ben Becker, Darren Fong, and Jessica Weinberg McClosky for their contributions to this article.
For more information:
- Learn more about rocky intertidal ecosystems and monitoring:
- Contact Golden Gate National Recreation Area Aquatic Ecologist Darren Fong or Marine Ecologist Ben Becker