This past year, while living for a while on the Monterey Peninsula, I found myself drawn time and again from the cafes and shops of Pacific Grove down to the waters of Monterey Bay. Sometimes I would just sit on a bench and look for sea otters resting and feeding their pups in the undulating kelp beds. On other days, I would head out to Point Pinos and find a good spot to watch the relentless waves blasting the rocky headland. Or, if I wanted to see more of what was going on underneath those waves, I would head over to the exhibits at the nearby Monterey Bay Aquarium.
My time along the shore of Monterey Bay was a small but privileged window into the wonderful diversity that makes the central coast of California one of the richest marine ecosystems in the world. The area of the Pacific Ocean from the shore to the edge of the continental shelf along the Central California coast is recognized as a globally significant resource. So significant, in fact, that much of it is contained within three contiguous national marine sanctuaries—Gulf of the Farallones, Cordell Bank, and Monterey Bay—that together encompass over 7,100 square miles.
THE EXTRAVAGANT LIFE OF THE CALIFORNIA CURRENT
This particular stretch of ocean is shaped by a unique set of conditions that make the ecosystem phenomenally productive. A combination of wind, currents, and upwelling make potential prey so abundant that marine mammals, sea turtles, and seabirds travel great distances to feast on the vast numbers of jellyfish, krill, and fish. Sooty shearwaters fly in each year from New Zealand by the millions, leatherback sea turtles swim over from their Indonesian breeding grounds, and humpback whales swing up from Costa Rica to join one of the greatest gatherings of marine predators in the world. And these large and charismatic visitors are just the most visible tip of an immense iceberg: Beneath the ocean surface lurks an immense number and variety of other organisms at all levels of the food web.
To fully understand this complicated story one must first step back and look at a larger picture, because the coast of California does not exist in isolation; it’s intimately connected with the rest of the planet via winds and ocean currents that balance energy and heat across the earth’s surface.
In a nutshell, California’s rich marine environment originates in the Gulf of Alaska as the eastward-flowing North Pacific Current approaches Vancouver Island and turns southward along the coast to form the cold, south-flowing California Current. Transporting cold, low-salinity subarctic water rich in oxygen and nutrients, the California Current eventually reaches Baja California, where it mixes with warm, saltier subtropical waters that are relatively nutrient-poor.
Moving over the top of the California Current are spring and summer winds that push forcefully out of the northwest. As a consequence of the earth’s east-to-west rotation, these winds steer warm surface waters away from the coast and draw the deep nutrient-rich waters of the California Current up to the surface in a process called upwelling.
The California Current is one of only four major “eastern boundary current” regions in the world. In each of these systems, winds and currents along the eastern edge of an ocean basin create upwelling that brings deepwater nutrients to the surface.
However, this combination of current and wind is not a straightforward equation; the California Current eddies and swirls as it flows along at 20 centimeters per second past the promontories, river mouths, beaches, and bays of the rugged coastline. At the same time, winds gust and ebb on a continual basis, causing periods of strong upwelling followed by days of relaxation. The hourly, daily, and weekly shifts in these patterns create patches of water with distinctly different salinity, temperature, and nutrient profiles. What looks like a uniform ocean surface is in fact a complex and ever-shifting mosaic.
THE UNDERWATER FOREST
- The kelp forests of Monterey Bay provide habitat for over700 species of animals, including the ochre stars, bat stars,strawberry anemones, and hydrocorals competing for space on this rocknear Otter Point. Photo (c) .
The kelp beds of Monterey Bay are an excellent example of the interplay between currents, winds, and food webs. Found along the temperate coasts of North and South America, Africa, Australia, and New Zealand, kelp forests reach their greatest biological diversity on the Central California coast, where they host three to four times more species than the world’s other kelp habitats.
This outsized alga begins life as a microscopic spore that settles on the bottom at depths of one to 100 feet, generally on rocky substrate that provides a solid surface for the plant to grab on to in the strong currents. Eager to reach the sunlit world of the ocean surface, it grows 18 inches a day and produces a prodigious amount of biomass in the form of a stout stem and lanky leaf blades that float from air-filled chambers. In great numbers, kelps form dense forest-like stands with leafy canopies that harvest and filter sunlight and create a magnificent cathedral-like atmosphere underneath.
Unlike a vascular plant that takes up nutrients through its roots, an alga absorbs nutrients through all of its tissues, a process that is amplified in kelp as it sways back and forth in the current. Michael Graham, a kelp expert at Moss Landing Marine Laboratories, explains, “This high rate of nutrient absorption magnifies the amount of food available in a kelp forest.” Unlike other nonvascular plants, though, kelp moves nutrients through a series of vascular-like sieve tubes that run the length of its stem, an essential adaptation for a plant that links the bottom world of near-total darkness to the sunlit surface.
Two primary types of large, canopy-forming kelp occur along the California coast. From Monterey Bay southward, the leafy giant kelp (Macrocystis pyrifera) is the dominant species, while the bull kelp (Nereocystis luetkeana), with one softball-sized air chamber on each plant, predominates north of Monterey Bay.
Underwater, these majestic stands provide habitat for over 700 species of fish, sea stars, crabs, anemones, and other animals. At every level from sea floor to ocean surface, the kelp strands provide a home and resting place for algae (400 species in Monterey Bay alone), microorganisms, and invertebrates that would otherwise float aimlessly in the open water. Even the tangled basketball-sized holdfast that attaches a kelp strand to the rocky bottom can contain thousands of individual organisms, says Graham.
Although kelp forests mostly grow on rocky substrates that are relatively scarce along the California coast (comprising about 5 percent of the total ocean bottom within three miles of shore), they are far more ecologically significant than their limited distribution might suggest. According to Graham, kelp forests in California have a higher rate of biological productivity than coral reefs or rain forests, and are more productive per unit area than the krill-based food web of the open ocean.
One of giant kelp’s many benefits is that its leafy fronds provide refuge for fish of all ages while at the same time dampening the destructive force of incoming waves. At the Monterey Bay Aquarium’s excellent kelp forest exhibit, you can see how fish rest among the kelp fronds. Some species, like the cabezon, even take on patterns that camouflage them against the kelp backdrop. Juvenile fish, especially rockfish, find food and safety among kelp leaves, making kelp a vital nursery ground for many fish species.
Due to their highly efficient photosynthetic ability and their ability to “scrub” mineral nutrients out of the water, kelp forests create a superabundant supply of food. However, surprisingly few animals graze directly on living kelp. The true importance of kelp lies in the prolific phytodetritus (debris) it generates. These are pieces of kelp, ranging from microscopic bits to entire plants, that break off and drift in the water. Such fragments contain photosynthetic energy and nutrients that stoke food webs wherever they end up and are consumed: in the water column, on the bottom of the ocean, or on the beach.
California’s purple sea urchins are a classic example of an organism that feeds on particles of drifting kelp. Staying mostly hidden in sheltered cavities, these prickly invertebrates extend their tube feet into the current to snare fragments of floating kelp and other debris. In an El Niño year, however, when north winds are subdued and upwelling weakens, nutrients and drift particles become scarce and sea urchins leave their shelters in search of food. As a result, hordes of hungry urchins may literally mow down entire kelp forests and create “sea urchin barrens” stripped of algae. The potential impact of this was demonstated when kelp was removed from a reef near San Luis Obispo: Fish biomass decreased by 63 percent due to the loss of food, shelter, and nursery sites.
For a long time, it was assumed that the kelp forest’s food chain was relatively simple: The kelp is eaten by sea urchins, which in turn are eaten by sea otters, a threatened species whose numbers were reduced from a historic high of 15,000 down to 50 by the early 1900s. Ergo, once their population returned to historic levels, otters would keep urchin outbreaks under control. This is, in fact, true in the kelp forests of the Aleutian Islands, where despite the diversity of species present, the functional players are limited to a few species of kelp and one species of urchin.
Michael Graham is one of several scientists who have now determined that California’s kelp forests sustain a far more complex food web, comprising five species of kelp and a plethora of kelp-grazing species, including three species of urchins, 11 mollusks, two fish, and about 20 species of crabs and shrimp. Furthermore, predators on sea urchins include not only sea otters but ten species of sea stars, crabs and shrimp, and many species of fish.
Graham notes that “the importance of this food web is that, like the environment they grow in, California’s kelp forests are incredibly diverse and multilayered, creating a buffer against population crashes in single species.” When the sea otter population was reduced, other predators helped keep sea urchin populations from exploding out of control and knocking the entire food web out of balance.
However, Graham adds, California’s kelp forest ecosystems now face two serious challenges: overfishing and climate change. Over the past two decades, some formerly abundant rockfish populations have been depleted by commercial and recreational fishing. Rockfish don’t feed directly on kelp, so the structure of the system remains intact, but a lot of the biodiversity it fostered is disappearing. “It’s like a redwood forest without the birds and the squirrels and the bears and the foxes,” says Graham. “The big trees are still standing, but the forest itself is no longer the same.”
As for the impact of climate change, he says, “Everything is up for grabs.” Rising water temperatures will likely favor some species and harm others, but with such a complex system, it is impossible to predict the consequences. So, Graham notes, our best bet would be to do all we can to keep the current system intact, from the algae to the sea stars to the urchins to the rockfish and the otters. Establishing no-take zones here—a step currently under consideration by the state of California—might be a good place to start.
THE OPEN OCEAN
- Two humpback whales “lunge feeding” in the waters of theCordell Bank National Marine Sanctuary. The whales lunge upward, mouthsopen, through schools of anchovies and juvenile rockfish that thrivehere on abundant zooplankton. Photo by Cornelia Oedekoven, SouthwestFisheries Science Ctr, NOAA Fisheries Service (permit 774-1714-00).
Nearly 100 miles north of Monterey Bay, Point Reyes juts westward from the Marin coast like a hawk talon grasping for a hold on the ocean. Standing at the guardrail above the Point Reyes lighthouse on a clear day, you can take in the dramatic sweep of the Pacific Ocean surging in massive undulations below while the sky reflects gray-blue on trillions of cross-ripples. Here the winds that generate upwelling strike the coast with blistering force, making outer Point Reyes one of the windiest places in North America.
Breaking the horizon to the southwest is the jagged shape of the Farallon Islands, home to the largest gathering of nesting seabirds in North America south of Alaska. If you could follow the wind-driven currents swirling off the cliffs below and trace the plumes of upwelling nutrients to their seaward destination, you would find yourself amid the tumult and stench of shrieking murres, cormorants, gulls, and storm-petrels that blanket these granitic outposts. Here, one comes face-to-face with the true wealth of wildlife fueled by the California Current.
After a disastrous spell in the mid- to late-1800s, when egg collectors harvested 300,000 common murre eggs a year to feed the booming Gold Rush metropolis of San Francisco, the Farallones are now a wildlife refuge and once again teeming with murres, tufted puffins, pigeon guillemots, western gulls, pelagic cormorants, California and Steller sea lions, and elephant seals. Endangered blue and humpback whales, great white sharks, several species of dolphin, and many other marine predators patrol the rich waters around the island.
The sea surface here overflows with life. Visitors approaching the islands by boat may encounter hordes of noisy western gulls converging as a white shark tears apart a sea lion; or several black-footed albatrosses that have traveled from their Hawaiian breeding grounds flocking around the boat; or humpback whales lunging upward from the water to gorge themselves on the abundant krill and schools of fish; or Pacific white-sided dolphins suddenly appearing and racing alongside the boat. For miles around, the sea is dotted with countless black-and-white common murres resting from their arduous nesting duties or diving in search of juvenile rockfish to feed their youngsters.
In a way, it is this very meeting of rock and water that makes such a surfeit of life possible. These predators are responding to the superabundant food supplies that form around rocky islands and underwater banks in the California Current. Off the coast of the Bay Area, the continental landmass extends seaward for many miles as a shallow shelf that sends up underwater pinnacles like the Cordell Bank, or breaks through the ocean surface as islands, like the Farallones. Here phytoplankton communities are nourished by localized upwelling centers, while the rocky substrates provide resting spots for a great variety of invertebrates, as well as abundant shelter for commercially and ecologically valuable predators like rockfish.
Once brought to the surface by the strong spring and summer winds, the suspended sediments bathe sunlight-dependent phytoplankton in a continual supply of food, fueling photosynthesis. The resulting explosion of diatoms, dinoflagellates, cyanobacteria, and other microorganisms that comprise phytoplankton becomes the basis of the entire marine food web as these primary producers use sunlight energy to build cellular tissue from carbon dioxide, minerals, and other inorganic chemicals. Phytoplankton reproduce rapidly and respond quickly to the favorable conditions, creating blooms of life that cascade upward through the food web and fuel everything from success-ful seabird colonies to healthy sea lions.
Due to their microscopic size, however, phytoplankton would be unavailable to larger predators if they weren’t first eaten by those intermediary consumers called krill. Two species of the inch-long shrimplike creatures inhabit California’s coastal waters, while a smaller southern species shows up during El Niño events. Also known as euphausiids, krill feed on plankton and are in turn eaten by everything from seabirds to squid to blue whales.
Virtually every larger predator found in the California Current feeds on krill or on some other species that feeds on krill. Many of these are familiar to anyone who has been to a fish market: anchovies, sardines, rockfish, market squid, mackerel, hake, salmon, and others. The juveniles of many of these krill-eating species are then eaten by other predators. For instance, the number one food item for fledgling common murres is juvenile rockfish, small in size and rich in the vitamins and minerals required by growing chicks. Even the juveniles of powerful top-level predators such as tuna feed on krill, before they grow up to feed on larger fish that eat krill. Sea lions eat krill-fed mackerel, salmon, and squid. And in turn, white sharks hang out around places like the Farallones where they can feed on seals and sea lions.
When everyone wants you for dinner, your life becomes an exercise in escape. By day, krill (and many other small prey species) descend into the ocean’s dark depths to avoid visually oriented predators. Then every night, all across the continental shelf, trillions upon trillions of krill rise out of the protective depths to feed on the bands of phytoplankton that stay near the ocean’s surface.
As krill descend to depths of 400 to 600 feet during the day, they become concentrated into super-dense schools that are perfect targets for whales and basking sharks that need to eat as much as a ton of krill a day. Diving down and swimming through these schools of krill, a blue whale can gulp up to a thousand krill in a single mouthful and take up to 13 mouthfuls on each dive.
UPWELLING, THE FICKLE MASTER
An ecosystem that can produce enough food to satisfy the hunger of a blue whale, the largest animal on the planet, is only possible due to the conditions created in a typical year by the California Current, says James Harvey, a vertebrate ecologist at Moss Landing Marine Laboratories. But the wind-driven upwelling that is the engine of this productive marine environment is a fickle master. Excessive wind and upwelling can be counterproductive if it pushes nutrients and prey far offshore and out of reach of nearshore species. On the other hand, too little wind and upwelling diminishes food supplies by starving phytoplankton of nutrients and causing prey to disperse widely throughout the calmer waters.
Perfect conditions along the California coast exist when there is a mix of upwelling and relaxation events spaced weeks or days apart throughout the spring and summer. A pulse of cold-water upwelling followed by a reverse flush of warm offshore waters supercharges the ecosystem with nutrients, then allows for phenomenal growth of phytoplankton and krill populations. At the same time, this mix of events stirs up the water column in a way that concentrates prey in dense pockets.
At times, however, this elegant system gets thrown off balance. Until the 1950s, oceanographers assumed the ocean was a fairly uniform place that remained relatively constant from year to year. According to Frank Schwing, an oceanographer at the National Marine Fisheries Service in Pacific Grove, a severe El Niño event along the coast of Peru in 1957-58 alerted scientists to the fact that oceans can change in ways that ripple to faraway places.
During an El Niño event, the warming of ocean water near the equator leads to a northward push of warmer subtropical waters, often associated with the arrival of warm-water species in California waters. Diminished upwelling along the California coast during a strong El Niño year results in plankton and krill crashes and near-collapse of the entire food web. The milder El Niño events are typically short-lived and occur every three to five years, while major El Niño events occur about once every ten years.
Such seasonal events are now recognized to be one of several types of regularly occurring—but poorly understood—flips in the ocean environment. And anomalies abound. For example, in 2005 and 2006, the strong winds that produce upwelling showed up two to three months later than usual. Although there was eventually a productive bloom of phytoplankton, its tardy arrival had devastating consequences for larger organisms that organize their yearly cycle around the bloom. Seabirds, like the common murres at the Farallones and Point Reyes, were particularly hard hit because their nesting success depends on finding juvenile rockfish during the time their chicks are growing, and juvenile rockfish depend on zooplankton that in turn feed on phytoplankton.
At the same time, Beach Watch volunteers for the Gulf of the Farallones National Marine Sanctuary noted a significant increase in the numbers of dead Cassin’s auklets washing up on area beaches during those two summers, corresponding with complete nesting failure of this krill-eating species recorded by PRBO Conservation Science biologists on the Farallon Islands.
Endangered leatherback sea turtles, which arrive in late summer to eat the large jellyfish that also feed on krill, and blue whales, which gather to eat krill directly, were both less seriously impacted because they can move on and look for food elsewhere. Data from radio transmitters attached to sea turtles show that they turned around and headed back to Hawaii instead of staying along the California coast, presumably due to the absence of their normal food species. Blue whales simply didn’t show up during the summers of 2005 and 2006.
If these perturbations to the California Current were to continue over several years, even such wide-ranging organisms could be harmed. Fortunately, the summer of 2007 has seen the return of strong winds and upwelling, and an apparent return in force of sea turtles, whales, and nesting seabirds.
Among the most mysterious and haunting recent changes has been the arrival of the Humboldt squid. Almost overnight, untold numbers of these giant subtropical squid have moved north into Central California waters, where their eerie presence piques curiosity while making fishermen nervous. One of the fastest-growing animals known, these squid—which can reach seven feet in length and 100 pounds or more—have a voracious appetite for everything and anything they can subdue, including long-lived but slow-growing rockfish whose populations are already stressed by past overfishing. For these reasons, the Humboldt squid’s unexplained arrival is setting off alarm bells among scientists and fishery managers.
On a recent summer day at the Monterey Bay Aquarium, the ominous invasion of the giant squid seemed far away as I stood amid dozens of excited schoolkids and enthusiastic parents. I watched the antics of a wild sea otter with aquarium biologist Michelle Staedler, who pointed out its colored tag and explained how every aspect of this otter’s life is being recorded by teams of volunteers and folded into a larger picture of how this threatened species is faring.
As a keystone species, sea otters both influence and reflect the health of the kelp forest ecosystem in which they live, but the female we were watching seemed perfectly content to doze in the softly rolling kelp bed and occasionally scratch her neck as we talked about the future of her species.
It’s encouraging to know that this delightful creature has managed to recover from a low of 50 individuals in the 1930s to as many as 3,026 in the spring of 2007. At the same time, signs of trouble lurk on the horizon. Staedler’s cell phone interrupts our conversation; it’s a volunteer calling to notify her that a female otter they have been tracking had lost its pup overnight, for as-yet-unknown reasons. Moments later, another aquarium volunteer runs up to point out a horned puffin on the rocks. This Alaskan seabird should be at a breeding colony far to the north, but like dozens of other horned puffins, it showed up on the California coast this year instead and no one knows why.
How is it that the California Current is being invaded simultaneously by a northern arctic seabird and a southern subtropical squid, while at the same time supporting a recovering sea otter population? Are these signs of an ecosystem in trouble or of the incredible diversity and adaptive capacity of the marine environment along the Central California coast?
With an impressive string of universities, research institutions, and nonprofit organizations from Monterey to Bodega bays, there is no shortage of professional and citizen scientists along the coast looking into such questions. While they do, there is still time for the rest of us to get out on (or even into) the ocean, to be awed and enchanted by this watery wilderness that protects such abundant and diverse life right at our doorstep.
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