When sea lions started dying in Monterey Bay, scientists raced to discover the cause.


Written by: Liese Greensfelder
Illustrations by: Sarah L. Donelson

An hour before midnight on Saturday of Memorial Day weekend, 1998, Chris Scholin and his wife, Edie Rue, were docking their sailboat in Monterey harbor at the south end of Monterey Bay when they spotted something odd. A man was herding a young sea lion down the launch ramp with a large board, trying to force it into the water.

S cholin and Rue—both marine researchers familiar with sea lions—grew concerned when they saw the animal’s unsteady movements and weaving head. They questioned the man, who told them he was a volunteer with an animal protection organization. He said his group had been overwhelmed in recent days by dozens of sick sea lions that he and others had picked up and taken to their treatment center. Supervisors at the center had directed the volunteers to patrol the shores at night and move sick animals back into the bay to prevent potentially dangerous contact with humans.

E arlier in the day, Scholin and Rue had seen another sea lion that appeared ill. And during the past week they’d heard that dazed sea lions were washing up on beaches south of Monterey. Now at the sight of yet another affected animal, Scholin’s thoughts coalesced. He used a nearby pay phone to call all the marine and health agencies he could think of, leaving the same message at each place. “I’m with the Monterey Bay Aquarium Research Institute,” he said, “and I think I know what’s going on with the sea lions.”

S cholin came to work at the institute in 1992, the year after hundreds of brown pelicans and cormorants had staggered around and died on local piers and beaches. The animals had been poisoned after feasting on fish that had just fed on masses of a toxic microalga called Pseudo-nitzschia australis. Although this organism had long been known to exist in normally innocuous numbers in local waters, something had caused its population to explode—a phenomenon known as a marine bloom. The incident left scientists and public health officials worried. It was the first documented case of wildlife poisoning on the West Coast of North America attributed to Pseudo-nitzschia. In fact, only once before had any Pseudo-nitzschia species been implicated as the cause of widespread poisoning, but with devastating results. In 1987, three people died in Canada’s eastern province of Prince Edward Island after eating mussels loaded with domoic acid, the potent toxin produced by the microalga. Another 107 people fell seriously ill after eating the mussels. Ten survivors remained permanently disabled with total loss of short-term memory. Domoic acid, a neurotoxin, had created lesions in the hippocampal region of their brains.

S cholin set to work as soon as he arrived at the institute to develop a method to warn of potentially devastating marine blooms. In a few years of driven research, he devised an ingenious system that could rapidly detect and identify 12 separate species of toxic microalgae based on their genetic makeup. Now Scholin realized he might be one of the few people who understood the significance of the ailing sea lions. With the phone calls he had made, he joined a growing team of scientists who would work together through the coming weeks and months to probe the cause and consequences of a rare epidemic that had swept through Monterey Bay.

B y the time Scholin and Rue set off for their Saturday sail, he had been drawing seawater samples from various locations around the bay for nearly three years, analyzing them for telltale rises in populations of microalgae using the detection system he had devised. Just two weeks earlier, he had noticed a small increase in his normal background readings of Pseudo-nitzschia australis. Each ensuing sample had produced a higher reading. He’d called various agencies to report the worrisome finding. “We were calling just about anybody we could think of, telling them there was an algal bloom going on,” he said. But blooms had never been predicted before, and officials were virtually unfamiliar with Pseudo-nitzschia. “They would just say, ’Domoic what?’” Scholin recounted. With no previous experience in monitoring a bloom, Scholin himself did not know how to interpret the significance of his findings.

B uton Saturday, Scholin and Rue had noticed oily brown patches dotting the bay. “It smelled like fresh-cut grass,” Rue said, “or like a salad that got put through a blender.”

S omething else was not right that day. “It was like a smorgasbord for fish. They were feeding like crazy,” Rue said. When she thinks back on it, she believes the fish they saw were anchovies, probably in a frenzy of feeding on a dense bloom of Pseudo-nitzschia. But not until she and Scholin saw the dazed sea lion on the launch ramp did the jumbled pieces of the puzzle suddenly fit together.

W hile Scholin stood at the pay phone doing his best to raise an alarm, another scene was unfolding just a few miles north. Overwhelmed staff and volunteers at the Marine Mammal Center in Moss Landing were working 24-hour shifts trying to save the lives of dozens of desperately ill California sea lions. Some of the sea lions were having seizures, others were semi-comatose. Many were foaming at the mouth and weaving their heads in random circles, like the young animal Scholin and Rue saw on the launch ramp. Because they didn’t know the cause of the sea lions’illness, the only thing workers could do was treat visible symptoms—giving Valium injections to control seizures, and injecting fluids under the skins of the animals to counter dehydration caused by fits of diarrhea and vomiting.

A nonprofit organization, the Marine Mammal Center has rescued more than 5,000 injured, ill, or stranded marine mammals in its 25-year history. Sick and injured animals found in the Monterey Bay area are taken first to the center’s Moss Landing facility, where they are stabilized before being trucked to the main treatment center in Sausalito, five miles north of San Francisco.

“W e were trying to make contact with any labs we could on Saturday, Sunday, and Monday. But it was a holiday weekend, and no one answered their phones,” said Frances Gulland, director of veterinary services for the center in Sausalito. Gulland, a veterinarian and epidemiologist, suspected at first that the sea lions could be suffering from a highly potent virus, like the one that killed more than 18,000 harbor seals in the North Sea between England and Denmark in the late 1980s. Though the logistics of keeping all the animals separated at the crowded facility in Sausalito were staggering, Gulland knew it was imperative to keep the sea lions quarantined. Without knowing whether they suffered from a contagious disease, she dared not risk them coming into contact with the 150 harbor seals, elephant seals, and sea lions already being treated at the Center. Most of these animals were underweight victims of the brutal storms that wracked California’s coast through the long El Niño winter of 1997-98.

T hrough the weekend, volunteers at Moss Landing were working all three of the center’s phones almost continuously, responding to people calling in reports of ill animals along a 100-mile stretch of coast. Other volunteers were sent out to find sea lions and load them into trucks. “Normally, you put a net on them and use boards to maneuver them into a carrier,” said Shelbi Stoudt, the center’s stranding coordinator at Moss Landing. “These animals were virtually comatose. Their eyes were open, but they weren’t really conscious. We disregarded the typical rescue equipment and basically physically lifted these animals into carriers. What we remember is our pure exhaustion.”

B y the end of the weekend, the center’s pickup proved inadequate for the growing load. “Literally, our trucks were moving nonstop, going from one beach to the next, loading animals, bringing them in and unloading them,” Stoudt said. Finally, she rented a U-Haul truck and sent 18 sea lions, each weighing about 225 pounds, to Sausalito.

C oastal dwellers have observed marine or “algal” blooms for centuries. These phenomena occur when populations of microalgae—a component of the ocean’s microscopic plankton community—explode in response to just the right amount of sunshine and nutrients in the sea. Algae with a normal population of 1,000 individuals per liter of seawater can quickly reach concentrations of 60 million per liter during a bloom. In such huge numbers, the tiny algae impart different colors to the water. Some species turn water red, giving rise to the popular term “red tides.” But this is a misnomer, for blooms can be brown, green, yellow, or even colorless, and they are not influenced by tides.

A lgal blooms occur more frequently in the shallow, warmer waters along the coast than in the deep sea. Some blooms complete their growth cycle then disappear quietly, leaving no trace of their presence. But some blooms can severely damage the marine environment, killing other creatures when the blooms’ vast masses deplete the water of oxygen or by simply shading out other life dependent on clear water and sunlight. Numerous algal species produce potent toxins that can work their way up the food chain from shellfish and smaller fish to large fish, birds, and mammals, including humans. Most of these toxins act upon the nervous system of mammals, and many are so powerful that humans can be affected just by inhaling them in a sea-borne mist.

D uring the past two decades, the frequency of algal blooms has increased in almost all coastal areas of the world. Scientists suspect a variety of causes, including the worldwide destruction of wetlands that normally serve as a natural filter for storm runoff. Sediment that used to lodge in the wetlands now flows straight to sea where it provides plankton with an overabundance of mineral nutrition. Numerous species of harmful algae have expanded their range in recent years, many hitchhiking into new territory in the ballast water of ships. Shifts in ocean currents and nutrient cycling as a result of global warming may also contribute to increased frequency of blooms. Many pollutants, such as industrial waste, inadequately treated wastewater, and agricultural run-off contaminated by pesticides and fertilizers, find their way directly into the sea, where they alter the natural balance of marine life, causing erratic population explosions of certain microalgae.

D etecting an algal bloom or tracking a poisoning incident back to a particular species is always difficult and sometimes impossible. Even using microscopes, scientists cannot identify many species in the field. Diatoms, the algal subgroup that includes Pseudo-nitzschia, present scientists with a notoriously challenging identification problem. Normal microscopes don’t have the magnification power required to reveal the intricate geometric patterns of the diatoms’ shell-like bodies, the only visible distinguishing characteristics of many species. Only by viewing diatoms with a scanning electron microscope, a time-consuming and expensive process, can scientists make a positive identification.

B ut identification is only the first step in tracking a bloom. Water taken from Monterey Bay at any time will reveal large numbers of several Pseudo-nitzschia species. To determine whether populations are high enough to cause a problem, the algae must be counted, one by one, a process described by one scientist as “a hideous and evil thing made even more difficult by trying to pick out one specific kind in the midst of a hodgepodge.”

S ometimes the only physical evidence of a toxic bloom may be a group of convulsing pelicans or seals, or desperately ill people. Public health officials must consider every possible factor when confronted with an epidemic: injury, pollution, and disease are other possible causes. Even the toxin itself may have disappeared from the animal’s system, leaving only its grim symptoms. It took researchers years to discover the cause of the two documented Pseudo-nitzschia epidemics.

“I t’s like searching for disease organisms where there are zillions of things that might be responsible for an infection,” Scholin said. “And you want to know as quickly as possible which thing it is so you can treat it appropriately.” Scholin wanted to arm public health officials with an early warning system for toxic blooms. His vision was to develop a field kit for monitoring seawater samples that relied on easy-to-read chemical reactions, something like the color changes of litmus paper or the pattern of a home pregnancy test kit.

T he biologist knew that a good model for his task already existed in biotechnology and medicine. Scientists in those fields have developed molecular “probes,” designer-engineered molecules that hunt ("probe") for a specific molecular construction unique to the organism the scientists wish to identify. Usually this is a sequence of DNA or its single-stranded cousin, RNA. The probe not only finds and chemically latches itself to the sequence, but also produces a detectable signal once it has attached itself to its target.

B efore coming to the Monterey Bay Aquarium Research Institute, Scholin studied the molecular biology of toxic microalgae at Woods Hole Oceanographic Institute in Massachusetts. That work gave him a running start at the institute, where his first task was to determine which microalgae species in Monterey Bay presented the greatest threat. Eventually, he chose 12 species. His first years of work were devoted to mapping or “sequencing” the molecular structure of the RNA of these organisms. Upon completing this job, he compared all the maps, selecting from each a short segment of RNA that was unique to the species. Then he set to work developing a series of molecular probes, one for each selected segment.

S cholin designed two probes for the RNA sequence he chose from Pseudo-nitzschia australis. The first he bound to a fluorescent compound. When the probe latched onto the RNA inside an intact Pseudo-nitzschia, the tiny organism glowed a fluorescent green. But these glowing cells could only be seen and counted through a microscope, a cumbersome procedure in the field. The second probe acted on a solution of chemically macerated Pseudo-nitzschia. Scholin designed this probe to turn blue when it captured the targeted RNA. The higher the concentration of Pseudo-nitzschia in the water sample, the bluer the solution. A person in the field could rapidly estimate the concentration of the microalgae in the water by mixing seawater with this probe and comparing the resulting color to a chart prepared by Scholin.

B y 1995, Scholin had taken his work out of the laboratory and into the field. Once or twice a week he and his students used the probes to analyze water samples they collected from Monterey Bay. On May 11, 1998, he noticed a rise in the count of Pseudo-nitzschia australis. The population of the microalgae peaked ten days later, the day before Memorial Day weekend.

W hen they returned to work on Tuesday following the three-day weekend, scientists from around the country started to return the calls placed to them by Frances Gulland. A biologist with the California Department of Fish and Game told the veterinarian about the message Scholin had left on his telephone answering machine on Saturday night. Intrigued that someone from the Monterey Bay Aquarium Research Institute was suggesting a cause of the epidemic, Gulland immediately called Scholin. They spoke only briefly, but Scholin’s information about his discovery of rising Pseudo-nitzschia counts was the key piece of evidence Gulland needed.

“T he great thing was when I finally made contact with him, here was a man who knew that it was a plankton,” Gulland said. “Once I’d talked with Chris (Scholin), I could convince the labs to run assays for domoic acid.” With so many other possibilities to consider until now, no lab was willing to run the expensive assay for domoic acid, a toxin that had never before been detected in a marine mammal.

W ithin days of Scholin’s call, both the National Marine Fisheries Services laboratory in Seattle and the National Ocean Services laboratory in Charleston, South Carolina, confirmed the presence of domoic acid in the samples sent to them earlier by Gulland.

A t last the fatigued rescue workers had a grasp on the nature of their invisible foe.

“W hen we found out that it was most likely domoic acid, there was a change of confidence,” Shelbi Stoudt said about her volunteers at the center’s Moss Landing facility. “Then we knew that what we were doing actually was good.” By treating the animals’visible symptoms with Valium and forced rehydration, workers had done the best thing possible. Domoic acid is soluble in water, so every time the sea lions urinated, they rid themselves of some toxin. In Sausalito, a relieved Gulland could stop worrying that the animals were suffering from an infectious disease. Her staff no longer needed to work under laborious quarantine measures in the overcrowded treatment center.

T he tiny organism responsible for the mass poisoning, Pseudo-nitzschia australis, is no newcomer to the West Coast. Identified in the 1930s, it is a dominant species of plankton up and down the coast of California. But until last year, its effects on people and wildlife had been documented only twice: the 1987 poisoning in eastern Canada and the 1991 pelican incident in Monterey Bay. “There actually have probably been tons of Pseudo-nitzschia blooms,” says Mary Silver, a marine biologist at the University of California, Santa Cruz. “But our awareness of them depends on a whole lot of events coming together.”

The first step is for the bloom to occur when anchovies, a migratory fish, are abundant in local waters, Silver says. Pseudo-nitzschia are so small that most fish ignore them. But anchovies have special gills that filter algae from water. During a bloom, anchovies gorge themselves on the tiny plankton.

The next step, says Silver, happens only when anchovy-eating predators are present. “Especially [predators] that humans are interested in,” she says. “If we had beach crabs dying in huge numbers, no one would know or care. But anchovies feed a lot of animals and birds that we care a lot about.” The five-inch-long silvery fish is a favorite food for seals, sea lions, pelicans, and many other animals.

Next, Silver says, a beach is necessary, so that sick and dying predators come ashore someplace where people notice them. Where the coastline is rocky, ailing and dead animals remain in the water, unnoticed by humans.

Silver tells the story of a 1961 incident in Santa Cruz when hundreds of deranged shearwaters, ocean-going birds that feed on anchovies, flew into the city, crashing into buildings and cars. According to local lore, Alfred Hitchcock, who lived in nearby Scotts Valley, called the newspaper and grilled the reporter who covered the story to find out all he could about the event. A year and a half later, The Birds, Hitchcock’s classic thriller about a coastal town terrorized by deranged seabirds, hit theaters across the country. Silver says the shearwater incident had all the earmarks of classic domoic acid poisoning.

Soon after Scholin and Gulland realized that Monterey Bay was in the throes of a toxic bloom, Silver was in Monterey looking for anchovies. The fish are not a sports fish and not commonly caught or sold from the pier. An amateur fisherman happened to hear that she’d been asking for the fish. He’d caught some the day before and had them in his truck.

The fish were on ice, maybe 12 hours old, and Silver took them straightaway to Chris Scholin’s laboratory. There she found Peter Miller and Roman Marin, two graduate students who worked with her and Scholin. Silver and the students immediately cut the fish open. When Silver turned the brown contents from one fish gut under the microscope she instantly recognized hundreds of slender, spindle-shaped forms of Pseudo-nitzschia. But the light microscope could not tell her which of the many similar species she was looking at. Marin, meanwhile, was testing the contents of another gut with the molecular probe. Within minutes, the blue results told the researchers that they were looking at the deadly Pseudo-nitzschia australis. The next day, Miller confirmed the assay by checking the sample under the scanning electron microscope, the gold standard test for identifying the diatoms.

A s the evidence accumulated that the sea lions were indeed suffering from domoic acid poisoning, scientists from state and federal agencies flocked to Monterey Bay to glean all the information they could from the outbreak. They tracked the bloom for several months and found that it had probably originated at least 100 miles to the south, then continued to move slowly northward. By late July, researchers were finding razor clams contaminated with domoic acid along the coast of Washington. In September, levels had risen so high that authorities banned harvest of the clams.

S cientists are now analyzing the data they collected, hoping to explain the many unanswered questions surrounding the bloom. What caused the phenomenon? Why did it move north along the coast? Why were so few sea lions affected at a time when thousands were in Monterey Bay?

C hris Scholin is continuing to develop probes for even more microalgal species. He is also working with colleagues to design and construct automated monitoring stations that incorporate the probes. Attached to buoys, the stations would send microalgal counts and other data to computers on land, relieving scientists and officials who track marine blooms of the tedious chore of collecting water samples along hundreds of miles of coastline.

B y the time the Pseudo-nitzschia bloom in Monterey Bay ended in June, more than 50 of the sea lions treated at the Marine Mammal Center in Sausalito had died, another 29 survived, but needed extended care, and 19 appeared fully recovered. No reports surfaced of any human illness due to the bloom. Humpback whales feeding in the bay at the time also seemed unaffected. But domoic acid was found in samples taken from three ill sea otters. Two of the otters died and one remained permanently impaired, apparently with severe memory loss. The creature was so easily distracted it would seem to forget the food it held between its paws.

B y late fall the Marine Mammal Center in Sausalito had released all but three of the surviving sea lions back to sea. On November 6, the center’s biologist, Michelle Lander, loaded the three survivors into dog kennels in the back of a truck and drove to Point Lobos State Reserve, three hours away at the southern tip of Monterey Bay. There, Lander backed the truck as close as possible to the rocky shore of Weston Beach. With the help of colleagues, she carried the kennels to the water’s edge, where she opened the doors and guided the sea lions back to the ocean.

F or two months Lander received signals from radio transmitters she’d glued between each animal’s shoulder blades. The last transmissions she received before the instruments fell away told her that one of the animals still swam the waters of Point Lobos. The other two had made their way 50 miles north where they frolicked with hundreds of companions at Año Nuevo Point, a favorite haunt of California sea lions.

 

BIOs

 

WRITER Liese Greensfelder

certificate, agricultural sciences, Langvin School of Agriculture, Norway; B.S., plant science, agronomy, University of California, Davis; M.S., horticulture, pomology, U.C. Davis.
Internship: California Wild, quarterly magazine of the California Academy of Sciences.

ILLUSTRATOR Sarah Donelson

B.S., art photography, Ball State University, 1984 B.A., art photography, Cameron University, 1992 B.S., biology/chemistry, Ball State University, 1998.
Internship: Scientific American magazine, New York.