National Park Service

Keeping Up With the Kelp

Meet the scientists tracking the health of underwater forests, one dive at a time

Jim McMahon/Mapman

Joshua Sprague and his team finish loading up the boat for a week at sea. Then they set sail for the Channel Islands, about 30 miles off the coast of Ventura, California. But the team of marine biologists won’t explore the islands. Instead they set anchor off the coast, shimmy into their scuba gear, and dive underwater to check on the kelp below.

Kelp is a large, greenish brown seaweed. In the waters off the Channel Islands, thousands of kelp plants grow in enormous underwater forests. These kelp forests are one of the most productive ecosystems in the world. They’re home to more than 1,000 species of marine algae, plants, and animals.

Scientists like Sprague began monitoring the forests’ health in 1983 for the Channel Islands National Park Kelp Monitoring Program. Divers have returned to the same areas for over 30 years to collect data.

Joshua Sprague and his team load up a boat. They’re preparing for a week at sea. They set sail for the Channel Islands, about 30 miles off the coast of Ventura, California. Sprague and his team are marine biologists. They’re not planning to explore the islands on land. Instead they set anchor off the coast. They shimmy into their scuba gear. Then they dive underwater to check on the kelp below.

Kelp is a large, greenish-brown seaweed. Thousands of kelp plants grow in the waters off the Channel Islands. They form enormous underwater forests. These kelp forests are home to more than 1,000 species of marine algae, plants, and animals. That makes them one of the busiest ecosystems in the world.

Scientists like Sprague began checking on the forests’ health in 1983. They’re part of the Channel Islands National Park Kelp Monitoring Program. Divers have returned to the same areas for over 30 years. They collect data on every trip. 

Under the sea, Sprague dives through massive, 80-foot-tall towers of kelp. When he looks up, he sees light shining through a canopy of kelp bunched on the water’s surface. Looking down, he sees fish, sponges, sea urchins, and other critters. Then he gets to work. First, Sprague lays out plastic tubes on the ocean floor to create 1-meter squares. Next he counts how many organisms are inside the square. He then moves the tubes and repeats this process in the new square. Finally, he estimates the density of the kelp and animals living in each column of water within the square meter. 

Gathering this data is important because the researchers will notice right away if the kelp or animals start dying. Sprague is like an underwater doctor, monitoring his patient. “It’s like a checkup,” he says.

In the early 1990s, the scientists found that the kelp forest ecosystem was struggling: The kelp was dying and fish were scarce. Overfishing of spiny lobsters and fish like the California sheephead led to a takeover by kelp-eating sea urchins. So in 2003, California created 13 protected marine areas around the Channel Islands to protect the kelp forest ecosystem, with no fishing allowed.

Since then, the Channel Islands’ kelp forests and many other species have started to recover. Sprague sees the comeback firsthand every dive. “That’s one of the most rewarding parts of the job,” he says.

Under the sea, Sprague dives through massive towers of kelp. Some are 80 feet tall. When he looks up, he sees light shining through bunches of kelp on the water’s surface. Looking down, he sees fish, sponges, sea urchins, and other critters. Then he gets to work. First, Sprague lays out plastic tubes on the ocean floor. He arranges them into a 1-meter square. Next he counts how many organisms are inside the square. He then moves the tubes to make a new square. He repeats the process. Finally, he tallies the organisms he found in each square meter. He uses this to estimate how many kelp and animals live in the column of water above the square.

Gathering this data is important. It means the researchers will notice right away if the kelp or animals in the area start dying. Sprague thinks of himself like an underwater doctor, monitoring his patient. “It’s like a checkup,” he says.

In the early 1990s, the scientists found that the kelp forest ecosystem was struggling. The kelp was dying and fish were becoming scarce. People had caught too many spiny lobsters and fish like the California sheephead. That allowed kelp-eating sea urchins to thrive. In 2003, California created 13 protected marine areas around the Channel Islands. Fishing isn’t allowed in these areas in order to protect the kelp forest ecosystem.

Since then, the Channel Islands’ kelp forests have started to recover. So have many species that live among the kelp. Sprague sees the comeback for himself on every dive. “That’s one of the most rewarding parts of the job,” he says.

Use Sprague’s kelp and animal density calculations to learn more about the kelp forests of Channel Islands National Park in California. Round your answers to the nearest whole number. Record your work and answers on our answer sheet.

Use Sprague’s kelp and animal density calculations to learn more about the kelp forests of Channel Islands National Park in California. Round your answers to the nearest whole number. Record your work and answers on our answer sheet.

A. In 1996, divers surveyed 200 square meters of a kelp forest surrounding San Miguel Island. They found that the density of giant kelp was 0.220 kelp plants per square meter. How many kelp plants did they count?

A. In 1996, divers surveyed 200 square meters of a kelp forest surrounding San Miguel Island. They found that the density of giant kelp was 0.220 kelp plants per square meter. How many kelp plants did they count?

B. In 2017, the density of the same forest was 0.475 kelp plants per square meter. How many giant kelp plants was that?

B. In 2017, the density of the same forest was 0.475 kelp plants per square meter. How many giant kelp plants was that?

A. Divers also count a sea creature called a white-spotted rose anemone. In 1995, the density was 0.179 anemones per square meter over an area of 720 square meters. How many anemones were there?

A. Divers also count a sea creature called a white-spotted rose anemone. In 1995, the density was 0.179 anemones per square meter over an area of 720 square meters. How many anemones were there?

B. In 2015, there were 0.423 white-spotted rose anemones per square meter. How many anemones was that?

B. In 2015, there were 0.423 white-spotted rose anemones per square meter. How many anemones was that?

A. The orange puffball sponge is another species that lives in the Channel Islands. In 1995, 0.072 sponges per square meter were in an area of 720 square meters. How many sponges did divers count?

A. The orange puffball sponge is another species that lives in the Channel Islands. In 1995, 0.072 sponges per square meter were in an area of 720 square meters. How many sponges did divers count?

B. By 2015, the density rose to 0.122 sponges per square meter in the same area. How many more sponges were counted in 2015 than in 1995?

B. By 2015, the density rose to 0.122 sponges per square meter in the same area. How many more sponges were counted in 2015 than in 1995?

Which species do you think recovered the best when comparing the 1990s data with the 2000s data (parts A and B)? Why do you think using the density unit rate is important?

Which species do you think recovered the best when comparing the 1990s data with the 2000s data (parts A and B)? Why do you think using the density unit rate is important?

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