GC Marine Program
Blog
08.03.2017

Mangroves from Above and Below

Blog, Coastal & Marine, Conservation, General

Today’s rapid pace technological evolution has created exponential growth in the research capabilities of scientists. For example, we’ve seen a tremendous increase over the last few years in the use of unmanned aerial vehicles (UAVs), also known as drones. This past summer, I and others from Gulf of California Marine Program (GCMP) were lucky enough to team up with UCSD’s Engineers for Exploration (E4E) to use drones to identify and quantify mangrove species in Bahia Magdalena, Baja California Sur, Mexico.

In Baja California, there are three species of mangroves: red (Rhizophora mangle), black (Avicenna germinans), and white (Laguncularia racemosa). Though each species differs slightly in their capacity, collectively these mangroves provide critical ecosystem services such as fisheries production, coastal protection, and carbon sequestration. Unfortunately, mangrove habitats are not well monitored and are under-studied, partially because they are difficult to access. As you can see in the photo below, mangroves can be quite dense. The same unique mangrove root system that make a great nursery habitat for animals also made it tough for us researchers to maneuver and collect data!

 

Working our way towards our low intertidal quadrat. Taking data along the intertidal range helps us understand how species composition can change along this gradient. Photo by: Astrid Hsu.

 

Together with E4E, we are exploring how UAVs might be part of the solution to our accessibility problem. We wanted to know: what data can we gather from the air, how can we get it, and how accurate is this information?

Headed by Scripps Institution of Oceanography’s (SIO) PhD student, Matt Costa, SIO Master student Joy Kumagai, and Colorado College Undergraduate Alexander Makic were on-the-ground to collect data on mangrove biomass, and species identification and distribution. They did this by measuring the diameter at breast height (DBH) and identifying the species of each individual mangrove tree within a 2 by 2 meters quadrat, as well as recording the maximum canopy height and circumference of dead wood along a 5 meter transect. Depending on what was captured in the quadrat, we could spend up anywhere from 30 minutes to 2 hours counting everything. In one site, we measured and identified over 120 individual mangroves! At each site, we also took a quadrat at low and high intertidal to better understand the transition of diversity and biomass along the intertidal range.

 

Buried in the mangroves to measure biomass and species identification. In this quadrat, we found mainly black mangroves, which have grey-colored leaves. Photo by: Astrid Hsu

At the same time that we traversed these dense forests, Eric Lo of E4E navigated Bahia Magdalena’s mangroves from the skies with UCSD Undergraduates Nikko Bouck and Brynn Hall, as well as Benigno Martinez Guerro of Centro para la Biodiversidad Marina y la Conservación A.C. Together, they flew transects at a 10 meter altitude (a relatively low height) over the area where on-the-ground methods would be employed, capturing high-resolution imagery to estimate percent coverage of each species. They then flew again at 100 meters to cover a much larger area. During flight, the pilot would take photos every couple of meters, with over 70% of overlap between the images in each instance. These photos will be stitched together to not only give us a great visual and multi-spectral map of the flight path, but will also produce a 3D model of the area! However, as is often the case in this digital age, our flights were limited by battery capacity. In between flights, we’d have to run back to the hotel to charge up the batteries and download data. Who knew that field work could consist of hanging out in a hotel room?

 

E4E setting up the drone—there are a lot of components to consider, from putting on the drone’s propellers to setting up the multi-spectral camera. Photo by: Astrid Hsu

 

Eric and Beni navigate the skies—and the ground. Baja’s unique landscape places cacti right next to mangroves. These two take careful consideration of their—and the drone’s—surroundings during flight. Photo by: Eric Lo

 

With data from the on-the-ground surveys, we will be able to verify the results of the drones. While I personally don’t mind diving into the mangroves, this trip was the first step to building a robust and highly efficient method of collecting high-resolution data, especially in remote and difficult-to-access mangrove regions. Stick around and follow us on Facebook for this project’s updates!

Author:

Astrid Hsu
Research Associate at SIO. As a recent MAS graduate in Marine Biodiversity and Conservation at Scripps Institution of Oceanography, Astrid focuses on generating interest and interdisciplinary support of marine conservation through science communications and collaborative research.