from Wind to Whales:
Understanding an Ecosystem

By Tim Stephens



At sea, surveying Monterey Bay's vast web of life are (from top) Donald Croll, observing whales, dolphins, birds, and other animals; Baldo Marinovic, collecting samples of the tiny pelagic crustacean, krill; and Nancy Gong, filtering seawater samples to measure concentrations of chlorophyll, an indicator of phytoplankton abundance.
Photos: Tim Stephens

In 1996, Donald Croll set out to answer a simple question: What makes Monterey Bay such a great place for blue whales? Probably the largest creatures ever to live on Earth, blue whales congregate in the bay every summer, feeding on swarms of shrimplike crustaceans called krill.

So the simple answer to Croll's question is that blue whales come here to eat. But Croll, an assistant professor of ecology and evolutionary biology at UCSC, wanted a deeper understanding of the relationships between blue whales, krill, and conditions in the bay.

It turns out that the whales come for the same reason that Monterey Bay attracts all kinds of marine life: It is quite simply one of the most fertile marine ecosystems in the world. And Croll, in collaboration with a diverse group of researchers at UCSC and other institutions, is starting to develop a comprehensive picture of how this highly productive ecosystem works.

"Our research centers around how physical processes, from water chemistry to wind dynamics, ultimately determine how much food is available for animals at the top of the food chain, like whales and seabirds," Croll says.

Croll's investigation is one of many such projects in which UCSC researchers are sorting out the complex and elegant networks of interactions that govern marine ecosystems. Their work is helping to establish a solid scientific basis for the conservation and management of marine resources and the protection of endangered species.

A blue whale's feeding lunge captures a swarm of krill. Photo by Doc White/

While Croll's group focuses on the open-water or "pelagic" habitat, other researchers are studying the nearshore habitats--the rocky reefs and intertidal zone. Biologists in both groups work with oceanographers to get a better understanding of the physical processes that influence these ecosystems.

By studying the dynamics of marine ecosystems over a long period of time, researchers hope to understand them well enough to tell the difference between natural variability and disturbances caused by human activities.

"That's what this is all about," Croll says. "If you're trying to manage resources, you have to understand what creates variability in those resources. Humans are affecting the world in so many ways, but at the same time we know that we live in a variable world. The problem is that we haven't had the long-term data to know what the natural variability is."

Ultimately, Croll's concern is the health of the marine ecosystems on which blue whales, and so much else, depend. Important fisheries, such as squid, rockfish, and salmon, rely on these ecosystems. So do seabirds, dolphins, many kinds of whales, and other wildlife.

It's all part of a natural environment that draws millions of people to the California coast. The challenge is to manage these marine resources and protect the natural habitats so that people can enjoy them without destroying them.

The driving force behind the high productivity of California's coastal waters is wind. Every spring and summer, winds blowing from the north act in combination with the rotation of the Earth to move warm surface waters offshore, drawing cold, nutrient-rich deeper water to the surface. This seasonal upwelling of nutrient-rich water sparks massive blooms of phytoplankton, microscopic algae that support a rich web of marine life.

Krill graze on phytoplankton, and blue whales feed almost exclusively on krill. It's a pretty simple food chain, but its simplicity offers a window onto more complex aspects of the Monterey Bay ecosystem and the upwelling process that drives its productivity.

There are only a few major coastal upwelling regions worldwide. While they make up about one-tenth of a percent of the ocean's surface area, 95 percent of the global marine biomass is produced in these regions. Not surprisingly, upwelling regions support many of the world's most important fisheries.

Along the coast of California and Oregon, intense upwelling tends to occur in certain places due to complex interactions of wind, currents, and topographic features of the coastline. Plumes of upwelled water enter Monterey Bay mainly from the north, from an upwelling center off Point Año Nuevo, about 20 miles north of Santa Cruz.

Spring is a crucial time in the annual cycle, when wind-driven upwelling typically stimulates the first big phytoplankton blooms of the year. Krill populations respond with a burst of reproductive activity, leading to a peak in the abundance of larval krill in April and May. These larvae reach adult size by July, when the blue whales start to show up, migrating north from their winter breeding grounds in the Gulf of California and other more southerly waters.

Regular pulses of upwelling are needed to keep the system going through the summer, but that doesn't always happen, says Baldo Marinovic, a research biologist at UCSC's Institute of Marine Sciences (IMS) and one of Croll's longtime collaborators.

"It's like getting someone going on a swing. It takes a big kick-start in the spring to get the productivity going, and then just a push now and then to keep the system productive," Marinovic says.

The strength of the upwelling determines how many of the juvenile krill survive to become adults, and also whether the krill stay bunched up in the dense swarms blue whales like to feed on, Marinovic says.

The system varies from year to year and also from place to place along the coast. If the upwelling is weak in one area, it may be strong somewhere else, and the whales move around accordingly, says Croll.

"I realize now that, in terms of the spatial scale, Monterey Bay to a whale is probably like a grocery store is to us, and they're in this grocery store looking for the krill aisle," Croll says. "But that store may be all out of krill, so they have to go across town to another store. For a whale, that might mean going from Monterey Bay to the Channel Islands off southern California or the Cordell Bank north of San Francisco--that's their idea of local stores."

Because of their great size, blue whales have the highest average daily energy requirements of any species. As a result, they only feed in areas of exceptionally high productivity, Croll says.

People often marvel that blue whales, which are far bigger than the largest dinosaurs were, eat something as small as krill. An average blue whale is about 80 feet long and weighs about 110 tons, while the krill species found along the West Coast are less than an inch long.

The driving force behind the high productivity of California's coastal waters is wind. Every spring and summer, winds blowing from the north act in combination with the rotation of the Earth to move warm surface waters offshore, drawing cold, nutrient-rich deeper water to the surface. This seasonal upwelling of nutrient-rich water sparks massive blooms of phytoplankton, microscopic algae that support a rich web of marine life.

But Croll points out that blue whales don't eat individual krill, they eat entire schools of them.

"They're really eating a superorganism, and the way they do it is pretty amazing. The blue whale has a tremendously bizarre feeding apparatus," Croll says.

A feeding blue whale, as Croll describes it, swims toward a school of krill at about 15 miles per hour and engulfs the krill along with the entire volume of water they occupy. The whale does this by dropping its mouth open until the lower jaw is at an angle of 90 degrees to the body. The whale's tongue inverts into its gullet as the mouth inflates with about 17,000 gallons of water. Then the whale shuts its mouth and forces the water out through the baleen, fibrous plates that hang down from the upper jaw and filter out the krill.

"It's one of the largest biomechanical events that has ever occurred on this Earth," Croll says.

A single whale can consume more than two tons of krill a day during the peak summer feeding season. But the krill come and go, and a blue whale may have to travel great distances and go for long periods without food before it finds another good spot to gorge itself on krill. Their large size is a key feature that enables blue whales to survive on patchy, ephemeral concentrations of krill.

"They have large energy stores, so they can go a long time without feeding while they travel from one patch of krill to another. Their size also helps them take in a lot of food once they find it," Croll says.

Croll's research on the upwelling-driven ecosystem in Monterey Bay grew out of a general interest in the ecology of all the great whales--including blue, fin, and humpback whales--that forage for food along the West Coast. As a research biologist at UCSC in 1996, he and a group of collaborators began conducting systematic surveys of several areas regularly visited by these whales. They mapped the distribution of whales over large areas, attached monitoring devices to whales to follow their diving behavior, and used echo sounders to locate and track aggregations of krill.

The researchers found that blue whales tend to feed in certain spots along the coast where the continental shelf drops off steeply into deeper water. One of the most dramatic examples is Monterey Bay, where the immense Monterey Submarine Canyon cuts a big wedge out of the continental shelf. By tracking both krill concentrations and the diving patterns of whales, the scientists could see that the blue whales dove directly down to the densest swarms of krill along the edge of the canyon.

"Whether here in Monterey Bay, or north of the Channel Islands, or off the coast of Mexico, it was always the same pattern--they were feeding on dense aggregations of krill off the edges of these steep underwater cliff faces," Croll says.

The researchers recognized that all of these places are associated with major upwelling centers. With a classic upwelling region practically in his backyard, Croll decided Monterey Bay was the best place to try to understand the behavior of the whales in relation to the dynamics of upwelling systems.

Croll's main collaborators include Marinovic, an expert on krill; UCSC research biologist Bernie Tershy; and Scott Benson, a graduate student at Moss Landing Marine Laboratories working with MLML professor James Harvey. Every summer, the group conducts regular surveys of Monterey Bay from Moss Landing's research vessel John Martin.

The boat plows back and forth across the bay in straight, parallel lines, while researchers and volunteers perched on the flying bridge record every sign of life on the bay--including whales, dolphins, and seabirds, sometimes in astonishing numbers. The scientists also take water samples, collect krill, and gather oceanographic data, such as water temperature and salinity.

While it has never been easy for scientists to get funding for long-term monitoring of ecosystems, various agencies have provided funding for Croll's work, including the Office of Naval Research, the Environmental Protection Agency, California Sea Grant, and the Monterey Bay National Marine Sanctuary, which is especially interested in gathering data on the sanctuary.

Having years worth of data allows scientists to ask questions they couldn't otherwise address, Croll says. "These data start to take on a life of their own and suggest new questions to explore. Now that we have five years of good data, we have enough information to start to understand how the system works and how variability between years occurs."

One of the most important sources of variability from year to year is El Niño, which originates in the tropical Pacific and drastically alters the normal oceanographic and weather patterns along the West Coast. In an El Niño year, unusually warm, nutrient-poor water from the south moves up the coast and disrupts the usual layering of warm surface waters over deep cold water. Coastal upwelling becomes much weaker than usual, resulting in a drop in phytoplankton production that affects the whole coastal food web.

El Niño is important not only as a source of natural variability, but also as a possible harbinger of things to come as a result of global warming, Croll says. Sea-surface temperatures are expected to increase with global warming, as they do along the coast during El Niño. Furthermore, the frequency and intensity of El Niños may increase with global warming.

Croll's group already had one year of survey data when the 1997-98 El Niño came along. It was a perfect opportunity to study the effects of El Niño on coastal ecosystems.

Croll expected low krill populations to result in a bad year for whales in Monterey Bay. Instead, whales and other marine life showed up in record numbers and were seen much closer to shore than usual.

"Although there wasn't a lot of krill, this was probably one of the few places where there was any food at all," Croll says. "Ordinarily, they would be feeding in a number of places up and down the coast, but during El Niño this area became like an oasis in the desert. That means Monterey Bay may be even more important for the whales than we had thought."

In collaboration with UCSC environmental studies professor Marc Mangel, Croll's group is now beginning to develop and test computer simulations that could be used to forecast the abundance of krill, indicating whether it will be a good year for whales and other animals that feed on krill. Salmon and rockfish eat krill, as do sardines and anchovies, which in turn are preyed on by larger fish and marine mammals.

Squid also depend on krill for food, and the squid fishery is California's largest fishery in both volume landed and commercial value. Mangel is looking at how the abundance of krill influences the squid fishery, and developing computer models that could be used to guide the management of the fishery.

"If we can forecast krill dynamics, we may be able to forecast the fate of the squid fishery, and that could tell us how much squid the fishing boats should be allowed to take in a given year," Croll says.

This kind of forecasting, however, will require extensive monitoring of oceanographic conditions, as well as an understanding of ecosystem dynamics detailed enough to translate into mathematical formulas. Croll says scientists still have much to learn about how upwelling fuels the productivity of coastal ecosystems.

One of his collaborators, Francisco Chavez of the Monterey Bay Aquarium Research Institute, has established an intensive, long-term monitoring program to examine the physical dynamics and productivity of Monterey Bay, using instruments on moorings and ships. And Croll has been adding new collaborators, at UCSC and other institutions, as his research progresses. Their investigations are already revealing new layers of complexity in coastal ecosystems.

It turns out, for example, that some of the nutrients that stimulate phytoplankton blooms originate in runoff from the land. Kenneth Bruland, professor of ocean sciences, has shown that phytoplankton growth may be limited by the availability of iron, which enters coastal ecosystems in sediment from rivers and streams.

Croll is also working with Raphael Kudela, assistant professor of ocean sciences, who uses satellite images to measure phytoplankton productivity in coastal waters. His data provide detailed pictures of what's going on at the bottom of the food chain.

Pulling together data from diverse sources to obtain a comprehensive picture of the Monterey Bay ecosystem will not be easy. But Croll and others at UCSC have already gone a long way toward assembling the kind of broad-based interdisciplinary collaboration that can accomplish that goal.

"As we develop our understanding of the whales, we see where we need input from other disciplines. We've found that other scientists get excited when they see what we're doing, that we're not just hugging whales but trying to address important ecological questions," Croll says.


The Center for Ocean Health: Integrating science and policy

The new Center for Ocean Health at UCSC's Long Marine Laboratory is more than a state-of-the-art research facility. It is a building with a mission, serving as a focal point for scientific research, education, and policy programs that address ocean conservation and management issues. By bringing together university researchers, government agencies, and conservation organizations, the center encourages the integration of research and policy efforts to protect and manage marine ecosystems and biodiversity.


The Center for Ocean Health

"We are targeting scientific questions that have strong policy implications, where there is a need for solid research to address issues of great importance to the region and the state," says Peter Raimondi, an associate professor of ecology and evolutionary biology.

Raimondi is one of about a dozen faculty and researchers in UCSC's Institute of Marine Sciences (IMS) who moved their offices and laboratories from the main campus to the Center for Ocean Health last year, bringing with them postdoctoral researchers, graduate students, and technical support staff. The center was dedicated in February (see story in Campus Update).

The researchers in the center are primarily involved in studies of marine vertebrates and coastal biology. The center gives them easy access to the other research facilities at Long Marine Lab, including tanks and pools for marine mammals and seawater laboratories for fish, plankton, and marine invertebrates.

Two nonprofit conservation groups have offices at the Center for Ocean Health: the Nature Conservancy's Coastal Waters Program and the Island Conservation and Ecology Group. Also located nearby are the Seymour Marine Discovery Center, with a university teaching lab and public education programs; the National Marine Fisheries Service Santa Cruz Laboratory, where federal scientists are studying major West Coast fisheries; and a marine wildlife center run by the California Department of Fish and Game.

"Having all these other groups around us has led to a lot of dynamic and healthy interactions. It's a really vital and vibrant place to work," Raimondi says.

"It's been exciting to see the synergy that's developed at the new center," adds IMS director Gary Griggs. "Bringing the scientists down here where they can be close to their research and interact with each other has paid off in a lot of ways."

Raimondi and Mark Carr, associate professor of ecology and evolutionary biology, lead UCSC's participation in the multi-institutional Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO), a large-scale research program that focuses on understanding the nearshore ecosystems of the U.S. West Coast. In many ways, PISCO exemplifies the aim of the Center for Ocean Health to integrate science, policy, and education. The project's findings are applied to issues of ocean conservation and management, and are communicated and shared through public outreach and student-training programs.

"Some of the most urgent issues in California and throughout the world involve these linkages of science and policy in the coastal zone, because that's where most of the people are and where so many conflicts occur between people and the coastal environment," Raimondi says.

UCSC researchers and students work closely with scientists at the state and federal laboratories adjacent to Long Marine Lab. Churchill Grimes, director of the Fisheries Service lab, notes that cooperative research projects involving the lab and UCSC scientists are currently supported by $1.2 million in federal funds.

The Fisheries Service lab, overseen by the National Oceanic and Atmospheric Administration (NOAA), is also home to NOAA's Institute for Marine Protected Area Science, established as part of a national effort to create a scientifically based, comprehensive national system of protected areas representing diverse U.S. marine ecosystems.

"We are in the middle of the nation's largest marine sanctuary here in Monterey Bay, with a national center at the fisheries lab that's looking at how to use protected areas to conserve marine resources, and the IMS is doing research that's helping them understand how to do this. All these things are complementary," Griggs says.

Michael Beck, director of the Coastal Waters Program for the Nature Conservancy, says his organization's partnership with UCSC is mutually beneficial.

"I'm able to transfer important new knowledge about marine science from UCSC researchers to the people working at our field sites. We have marine conservation practitioners on the ground in more than 25 countries, and it's important to connect them with sources of knowledge and expertise," Beck says.

In return, Beck gives feedback to UCSC scientists about what kinds of information are most needed to improve marine conservation and management efforts. UCSC graduate students and interns work on Nature Conservancy projects, gaining firsthand experience with marine conservation issues.

"There are few places in the world where there is such good synergy between scientists, managers, conservationists, and public educators working to understand and preserve marine diversity," Beck says.

The Island Conservation and Ecology Group (ICEG) was founded in 1994 by IMS researchers Donald Croll and Bernie Tershy. It is primarily concerned with problems caused by introduced species on islands. For example, the group is helping to save breeding colonies of marine birds that are threatened by introduced rats and other exotic species on coastal islands of Mexico and California. ICEG works with UCSC scientists, postdoctoral researchers, and graduate students involved in research projects related to the group's goals.

The Center for Ocean Health draws on the full range of expertise in the Institute of Marine Sciences. With 43 affiliated faculty and over 50 professional and postdoctoral researchers, the IMS is known for cutting-edge interdisciplinary research in environmental toxicology, marine mammal biology, nearshore ecological processes, marine biogeochemistry, paleoceanography, and continental margin geology.

-Tim Stephens

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