Untangling the Kelp Forest

“I hope we get 200 red sea urchins,” Donham says, just before she rolls backward off the inflated pontoon of the Zodiac and sinks beneath the surface of Monterey Bay. She and Lummis carry yellow mesh bags for collecting red sea urchins as part of a study run by ecologist Kristy Kroeker of UC Santa Cruz. Kroeker’s team studies how a phenomenon called ocean acidification affects ecosystems along the U.S. West Coast, from the cool waters of Alaska down to the warm waters of Baja California, Mexico.

Scientists have been studying ocean acidification—the rise in ocean acidity driven by human activity—for 15 years. Traditionally, researchers have studied this process by focusing on individual species in a lab, but Kroeker is taking a broader approach. She is directly studying how acidification affects organisms in their natural habitat: the kelp forest.

Emily Donham heads out to the kelp forest site in her little skiff. Photo: Teresa L. Carey

The acidifying sea

Ocean acidification is the progressive increase in acidity caused by a chemical reaction as the ocean absorbs excess carbon dioxide from the atmosphere. It is driven by carbon emissions from burning fossil fuels. Scientists once thought the ocean would scrub the atmosphere of this carbon dioxide. But over the past 15 years they have watched acidity of seawater rise at an unprecedented rate. The relentless process is weakening the shells of lobsters, crabs, and other commercially important animals, raising concern about the health of ocean life.

For years, scientists studied how ocean acidification would affect sea life by looking closely at an individual animal’s response to acidic water. The quintessential experiment involved placing a snail in an aquarium, cranking up the acidity, and watching what happened. A clear pattern emerged: In most cases, increased acidity caused the animal’s shell to dissolve, killing the animal.

Below the surface the kelp forest seems like a towering jungle, but only the tops of the kelp are visible on the surface. Photo: Teresa L. Carey

But while diving in the Mediterranean Sea in 2007, Kroeker noticed that this pattern didn’t seem to hold up in real life. Kroeker swam among carbon dioxide vents, areas where water acidity is naturally elevated because of carbon dioxide seeping from beneath the seafloor. Nearby, where she expected to see thin shells and run-down animals, she instead saw thriving shelled creatures. “What I was seeing in the field didn’t match with the laboratory studies,” she recalls.

Tha experience made Kroeker think that research in the lab might not reflect what happens in nature. While lab studies assessed one organism’s vulnerability to acidification, Kroeker wanted to design studies to understand the effects across an entire ecosystem. That launched her mission to move beyond the classic snail-in-a-tank experiment and take a new perspective on researching ocean acidification.

From individual to community

Emily Donham and Sarah Lummis count the sea urchins they collected on their dive. Photo: Teresa L. Carey

In four research sites—Baja, Mexico; Alaska; Monterey Bay; and Santa Barbara—Kroeker and her team dive ten meters down into kelp forests. The forests are underwater ecosystems, extending from the seafloor to the water’s surface. An important habitat-forming species, kelp hosts a large diversity of sea life, from sardines and rockfish in the upper layers to sea urchins and snails at the bottom.

At the seafloor, Kroeker’s team works in pairs, stretching out a meter-long tape measure and positioning two dive buddies on either end of the tape. To reliably count the abundance and diversity of bottom animals, the team places plastic one-meter-square frames on the seafloor and counts all animals inside, noting each observation on their slates. Holdfasts anchor the kelp to the rocky floor, which looks barren from a distance. But up close, Kroeker and her team sees crabs, snails, sea urchins, chiton, and brittle stars—up to 40 different species.

The seafloor is like another space that I live in.

“The more you look, the more you see,” Kroeker says of the seafloor. She never feels claustrophobic there, despite the dim light, silence, and a dive mask that restricts her peripheral vision like horse blinders. “It’s like another space that I live in.”

Kroeker is documenting the kelp forest community makeup and how it changes in a variety of acidic conditions. Comparing this catalog of life in each of the four research sites, which have differing levels of acidity, will allow Kroeker to draw conclusions on how ocean acidification affects survivorship and resilience.

Kroeker’s team is also observing the behaviors of species and their interactions. She studies animal grazing rates by seeding the seafloor with treats for the animals: homemade algae roll-ups, which look like fruit roll-ups. Comparing before-and-after photos of the treats will give Kroeker a measure of how hungry the animals are, and how high their feeding activity is. The team measures the kelp growth rate by tagging fronds and measuring their height with each visit. They also observe how much algae grows on a clean white tile as a measure of biomass productivity.

Multiple stresses

Ocean acidification doesn’t act alone. With climate change come rising temperatures, shifting seasonal characteristics, species loss, and lower oxygen levels. While building her kelp study, Kroeker didn’t stop with investigating acidification as the sole stressor. To see how other factors, such as temperature, have combined with acidification to impact the community, she chose four research sites to capture a gradient of conditions along which the kelp forest can live.

From Alaska to Baja, the water becomes warmer. However, sites such as Monterey Bay and Alaska represent areas of higher acidity due to oceanographic processes or seasonal upwelling. Over the next five years, Kroeker’s team will continue to track the quality of key characteristics in the four kelp forests. In addition to counting the abundance and diversity of seafloor species, they are using sensors to measure the acidity level, oxygen content, light, and temperature.

With a cooler full of newly collected sea urchins, Emily Donham and Sarah Lummis haul their gear ashore. Photo: Teresa L. Carey

According to Donham, looking across a gradient of an ecosystem allows the researchers to see how organisms adapt simultaneously to a change in both temperature and acidity. “We are expecting to see a decrease in animal grazing rates with colder temperatures in Alaska,” she says. But due to oceanographic processes, Alaska is naturally higher in acidity. The team is eager to find out how that will also influence grazing rates.

“This fieldwork gives us a timescale that is different from laboratory research. The timescale of evolutionary change and adaptation can’t really be done in the lab,” says Donham.

Kroeker says that studying the many aspects of a community is complicated. “It’s sort of like Pickup Sticks,” she says: By shifting one stick in the pile, you could inadvertently shift them all. “Except I’m studying the effect of ocean acidification and temperature tugging all the sticks at the same time.”

Scientists say her work is critical because it allows researchers to understand how the minutiae of simple lab studies apply to the greater picture. “There is no species on the planet that operates in isolation,” says ecologist Brian Gaylord of Bodega Marine Laboratory at UC Davis, who is not working with Kroeker. “Studies like these are the next generation of ocean acidification research.”

Marine ecologist Philip Munday of James Cook University in Cairns, Australia, agrees. “Her study will give clues to the adaptive potential of the animals and their ability to cope with a range of conditions,” he says.

Planning for the future

Even if we could flip a switch and cease the world’s output of excess carbon dioxide, scientists believe the ocean could still continue to become more acidic before it reaches a stable level.

“We really are in a situation where the focus is on what can we do in the face of increased acidity in the ocean,” Gaylord says.

Adina Paytan, a biogeochemist at UC Santa Cruz, says that despite the daunting scope of ocean acidification, broad studies like Kroeker’s can lead to small-scale, doable solutions. In what she calls “an experiment that nature designed,” Paytan travels to the Yucatan Peninsula, where 14 submarine carbon dioxide springs create a localized area of elevated acidity. By transplanting corals between the areas of high acidity and moderate acidity, Paytan hopes to identify corals that can adapt to future acidic conditions. This could help marine ecologists identify areas that would yield the most conservation success, if protected.

Ruth Gates, a biologist at the University of Hawaii at Manoa, anticipates that without intervention, more than 90% of the world’s coral reefs will be massively degraded by 2050. Gates hopes to harness the adaptive power of animals to build a coral reef community provisioned to face the harsh future conditions of ocean acidification. To do that, she is identifying resilient microorganisms that live on and support healthy corals, and transferring them to weakened coral colonies. By doing so, she hopes to create hardy partnerships. She is selecting those with strong survival tendencies for what she calls the “double whammy of climate change,” the simultaneous warming and acidifying of the ocean.

“Can we really pull them apart when really they are two facets of a problem that tend to happen together?” Gates asks, echoing Kroeker’s penchant for studying acidification in conjunction with other stressors.

According to Meg Chadsey, the real problem of acidification is the daunting scale. Chadsey is an ocean acidification specialist at Washington Sea Grant and the Pacific Marine Environmental Laboratory in Seattle. Her team proposes farming plants to restore balance to local ecosystems. During photosynthesis, aquatic plants take up carbon dioxide from the water and release oxygen. Farming marine plants could draw down nearby carbon dioxide levels, reducing the local effects of acidification. Cultivating marine plants alongside animals that are sensitive to acidification, such as juvenile shellfish, could create oases where those organisms could live, Chadsey says. The key is harvesting and removing the plants regularly, she adds, noting that the plant waste could be used as biofuel.

This method, called phytoremediation, is a more tractable effort than combating atmospheric carbon dioxide, Chadsey believes: “You don’t have to wait for the whole world to limit carbon dioxide emissions; you can work within your watershed or state.”

Graphic: Teresa L. Carey

Untangling it all

An hour after sinking beneath the surface, Donham and Lummis emerge with about 90 sea urchins each, just slightly less than their goal of a collective 200. They count them one by one as they fill the cooler with the spiny red organisms, each about the size of a golf ball.

“This wily urchin was eating the algae off a tegula shell,” says Donham, pointing out one particular specimen. Tegula, also known as “wavy tops,” are Donham’s favorite marine snails.

Once their tally is complete, Donham starts up the Zodiac’s motor and heads back to shore, passing sea otters floating lazily on their backs. The smooth water is dotted with the tops of kelp stalks, which look like clumps of hot chocolate mix floating on the surface. Below them, a towering kingdom of 30-foot-tall kelp sways with the waves.

Sarah Lummis finds an idotea on a kelp frond. Photo: Teresa L. Carey

“If our study can provide information about changes in ecosystems, then we can prepare for the future,” Donham says.

Lummis grabs a stalk of kelp from the water and uses her teeth to break the end off. As she drapes it over the urchins to protect them from the dry air, she spies a tiny idotea, a crustacean that hitchhiked aboard on the piece of kelp. “Look at this little guy,” she says. After observing the animal with wonder for a moment, Donham takes it in her hands and gently returns it to the ocean.

© 2017 Teresa L. Carey / UC Santa Cruz Science Communication Program