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20 Scientists, 1 Boat, Countless Biodiversity

Marine scientists survey border waters for wildlife.

Split between two countries, the Channel Islands and Coronado Islands are one continuous archipelago that share species, habitat, climate, currents, and a complex history. Although it is one geological formation, the islands differ in their management, anthropogenic pressures, and impacts.   

The same can be said about most borderland habitats found along the almost 2,000 miles of U.S.-Mexico border: they are continuous bioregions that are artificially split by political boundaries. 

The Border BioBlitz is a binational effort that seeks to record as many species as possible along the U.S.-Mexico border through the community science platform, iNaturalist. In addition to providing scientists with information about species in their field of study, the data from this project gives us insight into how or why differences in biodiversity may occur across border lines. 

A recent three-day expedition to both the Channel and Coronado Islands was intended to survey marine life in these borderland waters. The crew—made up of marine biology experts and community members from Mexico and the U.S.—used environmental DNA sampling, plankton tows, kelp pulls, hydrophone surveying, fishing, and good old-fashioned binoculars to make their observations.  

Read below to learn all about their observations!


Landscape image of San Clemente Island. Photo by Michael Ready.

Environmental DNA (eDNA) 

Environmental DNA (eDNA) is DNA expelled from different organisms (through mucus, fecal matter, shedding, feeding, or other biological activity) that accumulates in the surrounding environment. Oceanic eDNA can give scientists insight into the types of marine wildlife and algae present in an area and is collected by carefully filtering a sample of marine water. 

Using a Niskin bottle—a marine water sampling device—water samples were obtained from different depths on both sides of the border. After filtering them with a special membrane, the minute particles extracted from the sample were dried and placed in bags filled with silica gel to absorb moisture and preserve the DNA. 

Later, the extracted particles are taken to a lab for analysis, where a single water sample can yield up to 3,000 individual DNA fragments potentially representing different species. Of those fragments, 50% can be identified to the genus level, while 30% can be identified to the species level. A single, 2-liter sample of filtered ocean water can yield more information than an entire day of BioBlitzing! 

The samples are still undergoing analysis, but the results will allow scientists to have a glimpse into the kind of wildlife present and compare how it may differ on either side of the border. 


Crew members filtering water sample to extract eDNA. Photo by Michael Ready.

Plankton tows 

Although there was no full microscope on board, the team was still able to appreciate the small array of life that can be found drifting in the water column. While many types of plankton are microscopic, some are still visible to the naked eye.  

Copepods, arrow worms, ctenophores (comb jellies), and fish larvae were collected by the plankton nets and observed by the crew. The tiny but intricate organisms pulsated with life, awakening awe in all who took the time to examine them. 


Crew members looking at plankton using a digital microscope. Photo by Michael Ready.

Kelp pulls 

In the northern hemisphere, kelp forest habitat is present along most of the eastern Pacific, including Southern California and northern Baja California. Kelp forests provide invaluable habitat to a plethora of marine life—even kelp fronds that have been dislodged from forests and are floating at the ocean’s surface host a vast array of tiny wildlife—the expedition's crew took their time exploring the kelp’s nooks and crannies to find them all. 

By pulling floating kelp fronds on board and looking closely, a diverse community of miniature invertebrates became evident: polychaetes (worms), anemones, barnacles, crabs, shrimp, urchins, brittle stars, nudibranchs, and more were all thriving on floating strands of kelp. Other types of red and brown algae and even sea grasses were also tangled in the kelp and documented via iNaturalist.


Compilation of small marine invertebrates extracted from kelp fronds. Photo by Michael Ready.

Hydrophone surveys 

Many marine animals heavily rely on non-visual senses like electroreception, touch, and of course, sound. Hydrophones are underwater devices that detect, and record ocean sounds from all directions, giving us a glimpse into the underwater world without the need for scuba gear.  

When the boat’s motor was turned off and the hydrophone was dropped in the water, clicking, whistling, and chirping chimed from the speaker. The sound of dolphins. The BioBlitz crew quickly looked up and around the boat, but there were no dolphins nearby. Finally, far out into the horizon splashes were seen—the dolphins were heard from miles away before they were spotted! 

The sounds from the hydrophone can also give scientists insight into dolphin behavior. High-pitched clicking sounds are a form of echolocation and are made by forcing air through a nasal passage just beneath the dolphin’s blowhole. On the other hand, whistles and chirps from dolphins are chatter and a way for them to communicate with each other. 


Crew member listening to hydrophone. Photo by Michael Ready.


As predators, prey, and important components in marine food webs, fish were important additions to the BioBlitz. Through catch-and-release fishing, the crew was able to document different species of fish, including kelp bass, California sheephead, ocean whitefish, pacific barracudas, rock fish, and more.  


Crew member holding up a kelp bass. Photo by Michael Ready.

Pelagic observations 

Although they require more patience, pelagic (open ocean) observations made by looking carefully at the horizon with the naked eye or binoculars were extremely fruitful. Huge fish, birds, marine mammals of all kinds, megaplankton, and land and seabirds alike were all part of the BioBlitz observations. 

Some marine mammal favorites included fin whales, Minke whales, Risso’s dolphins, sea lions, and common dolphins. Bird enthusiasts indulged in different species of terns, pelicans, seagulls, cormorants, boobies, egrets, and even warblers that flew too far from land!

Although megafauna was abundant, tunicates were also seen floating at the ocean’s surface. Tunicates are colonies made up of hundreds to thousands of individuals known as zooids—they’re spectacularly alien.  

Another memorable pelagic organism were sea sailors, or vellelas: free-floating hydrozoans (which is a relative of jellyfish) that live on the surface of the ocean, navigating open waters with small sail-like membranes. They were present by the thousands, covering the sea surface like glittering stars—and being feasted on by giant sunfish! 


Brown pelican soaring over open water. Photo by Michael Ready.

What happens next? 

The vast amount of wildlife observations made during the three-day cruise are evidence of the abundant biodiversity present on the Pacific coast of northern Baja California and Southern California. The information gathered during this expedition will help fill information gaps that are crucial for the effective conservation of borderland habitats. 

While the Border BioBlitz is a fantastic scientific collaboration, it also forges community for people on both sides of the border. Regardless of scientific background or country of origin, this project encourages people come together to care and learn about nature. 

During the entire month of May, the Border BioBlitz seeks to record as many species as possible along the U.S.-Mexico border through iNaturalist. The Next Generation Sonoran Desert Researchers and collaborating organizations invite researchers and community members to document the stunning biological diversity of the borderlands.

To join the 2024 Border BioBlitz and find events near you, click here.

All photographs in this blog were generously shared by Michael Ready.

Crew member performing a plankton tow. Photo by Michael Ready.

Crew members pointing out plankton. Photo by Michael Ready.

Wilson's warbler perched on crew member's head. A few land birds flew too far from land and decided to rest on the boat. Photo by Michael Ready.

Crew member looking through the kelp's holdfast, and finding a small sea urchin. Photo by Michael Ready.

Crew member documenting fish before releasing it back into the water. Photo by Michael Ready.

Crew member collecting water sample or eDNA analysis using a Niskin bottle. Photo by Michael Ready.

Close up image of isopod on a sea grass frond. Photo by Michael Ready.

Common dolphin surfing waves created by the boat. Photo by Michael Ready.

Crew members looking at underwater topography to decide eDNA sampling site. Photo by Michael Ready.

Close up image of Steinberg's corambe sea slug. This specimen was smaller than your pinky fingernail! Photo by Michael Ready.

Posted by Paula Sternberg Rodríguez, Science Communications Manager on May 10, 2024

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