Shocking marine invertebrate news...

The Diasan Shinsho-maru, a Japanese fishing trawler, will certainly regret this bycatch. The ten ton vessel capsized, sending its three crew members into the drink, while trying to haul out a net full of Nomura's jellies off the coast of Chiba, Japan. The crew members were thankfully rescued by another vessel, but this incident marks another bout of trouble with the giant Nomura's (Nemopilema nomurai). The largest jellies in the world, Nomura's can grow as large as two meters in diameter. Although some years bring virtually no sightings, this year has seen massive blooms of the monsters in the Yellow and South China Seas. Their unwelcome presence, promoted by climatic conditions and a decline in predators, has come at an enmorous cost to the commercial fishing industry. To learn more about the jellies that sank a ship, read the article in The Telegraph.

Photo: The giant Nomura's jelly, Environmental News Network

End of a Dynasty: The Loss of the King Salmon

The river canyons, where the old bars were located, were romantic places previous to being disturbed and torn up by the gold-digger. The water was as clear as crystal, and above each ripple or rapid place was a long, deep pool, with water as blue as turquoise, swarming with fish. Salmon at that time ran up all the streams as far as they could get, until some perpendicular barrier which they could not leap prevented further progress.
Angel M. History of Placer County, California. 1882.

The Central Valley Chinook Salmon (Oncorhynchus tshawytscha), also known as the King Salmon, is one of the most iconic species of the Bay Area. In four seasonal runs, the Chinook salmon used to slam the rivers of the Central Valley Basin to spawn in the cold, well-oxygenated water draining from the Cascades and the Sierra Nevada. Every winter, spring, fall, and late-fall these anadramous fish would return from the Pacific Ocean, charging through the San Francisco Bay in numbers reaching the hundreds of thousands. As the largest of all salmon species, with adults often exceeding 40 pounds, the Chinook are important for commercial and recreational anglers alike, supporting the billion dollar California fishing industry. Since the era of California dam building, however, the Chinook populations have plummeted. All four runs have been listed under the Federal and State Endangered Species Acts. Even with hatchery stocks augmenting the wild population, the commercial salmon fishing season had to be closed this year for the second year in a row in order to protect the once robust fall run. The staggering decline of the Chinook spells both ecological and economic ruin for Northern California. Last year's closure of the salmon fishing season amounted to a loss of $255 million and 2,263 jobs.

While some of the salmon runs were nearly extirpated by dam installation in Central Valley Rivers, the unique life history of the fall run allowed it to persist as the backbone of the West Coast fishery for many years. The fall run spends less time in rivers than the other runs, so it is less impacted by land based activities. Also, it tends to spawn downstream of the other runs, so its passage is not blocked by the upstream dams. In recent history, the fall run population had been fairly stable, even experiencing a huge increase in 2000. Despite the large numbers of fish returning to spawn, the fall Chinook run was not as strong as it appeared. In fact, it was on the verge of an unexpected collapse. The fall run experienced record low returns in 2007, prompting the closure of the fishing season in 2008. Even when the fishery was closed, only 66,000 salmon returned to spawn.

Fisheries biologists believed that most, if not all, of the fall salmon returning to spawn came from the hatchery stock. Salmon hatcheries were originally established as part of a compromise between the fishing industry and California energy interests to sustain salmon populations that would be hindered by dam construction. However, the hatcheries have done more harm than good. The addition of a hatchery stock creates the illusion of a robust wild population, even though the wild population is no longer self-sustaining. In fact, the hatchery stocks have reduced the vitality and resilience of the wild population.

But how did the fall run, augmented by hatchery-borne fish, collapse? At the 2009 State of the Estuary Conference, Steve Lindley of NOAA explained how fisheries biologists were able to solve this mystery. Knowing the salmon’s age of sexual maturity, fish that should have been returning to spawn in 2007 and 2008 are from the broods that hatched in 2004 and 2005. Spawning of the wild population and the hatchery population was normal in those years, but survival rates between the broods’ departure from the estuary and their return to spawn were terrible. Therefore the secret to the broods’ failure lies in the environmental conditions they encountered in their three years at sea.

In 2005 and 2006 the water off the California coast was unusually warm. The spring upwelling, which is usually activated by shifting winds to deliver cold, nutrient-rich waters to the surface, had a late start in 2006. As a result, the Chinook salmons’ typical prey species struggled, while anchovies, a fish too large for the young salmon to eat, thrived. The Farallon Islands population of the Cassin’s Auklet, a seabird with the same diet as the Chinook salmon, completely failed to reproduce in 2005. The struggle of the Cassin’s Auklet population should have been a warning sign for salmon returns. Without a reliable food source, the 2004 and 2005 salmon broods suffered in the ocean, unbeknownst to biologists and fishermen until their poor returns in subsequent years.

Even though Delta water management and land-based activities impact Chinook salmon populations indirectly, the proximate cause of the fall run’s most recent collapse was simply a lack of adequate prey. Poor feeing conditions, often driven by natural climate variability, are in no way unprecedented, but the Chinook salmon was not resilient enough to overcome this challenge. Wild fish populations maintain their resilience by having a high degree of biocomplexity, described by Steve Lindley as a portfolio of environmental conditions, such as habitat and prey, which can satisfy the animals’ requirements. If the different runs, including those differentiated by spawning site as well as time, exhibit a diversity of life history patterns, the population as a whole is not intensely impacted by a shift in environmental conditions. In the case of the Central Valley Chinook, however, hatchery stocks have diluted the biocomplexity of the population, so that all the animals exhibit similar life history patterns. Whereas historically there was variability across the runs, today the reliance on hatchery production has pruned back the life history diversity of the Chinook salmon, making the population more prone to booms and busts.

Unfortunately the management strategy of the Central Valley Chinook salmon must rely on hatchery stocks to produce numbers of salmon great enough to sustain the fishing industry. When the salmon returns are poor, managers increase hatchery production, causing overall fitness of the population to decline. But even when the returns are great enough to reopen the fishing season, the apparent strength of the population is merely an illusion. When environmental conditions are favorable, the Chinook population appears to thrive, but the success of the hatchery stock makes it nearly impossible to detect inevitable declines in the wild population. When environmental conditions shift again, the homogeneous population will be vulnerable to another devastating crash.

Decades of hatchery-dependent management of the Chinook has produced a population that is unreliable for the fishing industry and deleterious to the recovery of wild stocks. Even if the fishing season is re-opened for 2010, the idea that a large number of salmon reflects the strength of the population is a dangerous misconception. To ensure long-term viability of the Central Valley Chinook as a species, something must change in order to improve wild salmon production. While there are management options, including brood stock selection and more variability in the timing of hatchery stock release, the best way to improve the fitness of the wild stock is to eliminate the hatcheries entirely. Without hatcheries, however, the wild population may never return in numbers great enough to harvest. Even though the small wild population could regain some of its biocomplexity and vitality, salmon fishing would have to end altogether, an admission of the failure of hatchery-dependent management. It is likely that Californians will have to mourn the end of their famed Chinook fishery in order to celebrate the survival of the species.

Photo: Late-fall Chinook salmon spawning, courtesy of USFWS

Lindley, Steve. 2009. The Once and Future Kings. Presented at the State of the Estuary Conference. Oakland, CA.

Yoshiyama, Ronald M., Eric R. Gerstung, Frank W. Fisher, and Peter B. Moyle. Historical and Present Distribution of Chinook Salmon in the Central Valley Drainage of California. Contributions to the Biology of Central Valley Salmonids. Fish Bulletin 179: Volume One.

The Woods and Your Health

The opportunity to hike beneath the orange and red foliage of a deciduous forest in autumn is one of the greatest perks of living in New England. I spent a fair amount of time in the wooded margins of the Colby College campus, drawn out of bed at sunrise and enduring chilly mornings on the cusp of winter to collect field data. While studying the relative distribution and abundance of small mammals, I had several opportunities to walk beneath the fall foliage, wrapped in silence except for the sounds of our footsteps and our research subjects scurrying through discarded leaves. Despite the obvious ecological transition into dormancy, the New England woodland in autumn conjures feelings of freshness and vitality rather than decay. However, beneath the duff on the forest floor and within the variegated canopy lurks an invisible threat. Secretly, this serene setting could be a hotbed of disease.

Richard Preston’s The Hot Zone, painted a thrilling picture of an exotic disease festering in a remote jungle until it aggressively emerged into a vulnerable human population through an unconfirmed, but likely encounter with a reclusive animal. A more temperate, developed setting, however, is certainly not disease-free. Extremely virulent pathogens can lurk in your own backyard in natural reservoir species as common as the white-footed mouse. Zoonotic diseases, or those that can be transferred to humans from other vertebrate animals, are so common that the majority of the diseases that infect humans today originated in other animals. According to the CDC, approximately 75% of recently emerged infectious diseases, including West Nile virus, Eastern Equine Encephalitis, and Lyme disease, are zoonotic. The natural reservoir of these diseases is an animal that acts as a long-term host for the pathogen and for which an infection is non-lethal. The natural reservoir therefore acts as a continual source of a pathogen, which would otherwise eliminate itself by killing hosts too quickly to perpetuate the infection.

The emergence of new zoonotic pathogens in human populations has risen in recent years due to increased contact between humans and wildlife. As humans push back the margins of animal habitat for settlement and exploit animal resources through hunting and husbandry, we increase our contact with animals that may harbor pathogens, thereby increasing our exposure to zoonotic disease. Zoonotic pathogens do not require humans to complete their life cycle; under natural conditions the pathogen would stay within the animal population. If exposed to a disease reservoir or vector, however, humans can become an incidental host. Habitat destruction and resource exploitation increases our risk of infection by potentially deadly pathogens simply by accident.

My research partner and I were warned about disease exposure as we emptied Sherman traps, studying the relative abundance of the white-footed mouse (Peromyscus leucopus) and the deer mouse (P. maniculatus) in the margins of the woodland surrounding Colby College. Worldwide, rodents are natural reservoirs for over 35 diseases. The pathogens that cause these diseases can be spread to humans either directly through contact with saliva, urine, and feces; or indirectly via insect vectors. Lyme disease is a well-known and well-publicized disease that is caused by bacteria harbored in a mouse reservoir but spread by ticks as vectors. When summer ends and ticks overwinter on the forest floor, humans can still fall victim to the potentially deadly hantavirus pulmonary syndrome. Hantavirus is spread to humans by direct contact with the feces and urine of an infected mouse, causing renal failure and fatal hemorrhagic fever. While the symptoms sound like something straight out of The Hot Zone, there are no monkeys, fruit bats, or protective suits involved. Hantavirus can be contracted by inhaling aerosolized waste of common and abundant rodents, and hundreds of cases have been reported in the United States, especially in the western states.

While disease was not the primary focus of our research, it had very clear epidemiological implications. As humans encroach upon animal habitat, we upset the population balance of the ecological community by eliminating cover, introducing invasive species, and reducing food availability. Some species, such as the white-footed mouse, are generalists that can thrive in highly-disturbed, marginal habitat. Their populations tend to explode when specialist species populations decline. Therefore, as we push into deciduous and mixed forests, the white-footed mouse may benefit under the altered ecological conditions and increase in numbers, but overall biodiversity collapses. Incidentally, the white-footed mouse is a reservoir for both Lyme disease and hantavirus.

Zoonotic diseases are caused by pathogens that will readily infect a variety of different host species, but for which there are very few natural reservoir species. This means that only a few species can survive and spread the infection, thereby assisting the long-term survival of the pathogen. A high density of a natural reservoir species in a community would increase the presence of the pathogen and also increase the likelihood that the disease will be passed to another host or vector species. In contrast, high biodiversity would reduce the density of the natural reservoir species and increase the number of incompetent reservoirs that cannot spread the disease. It has therefore been hypothesized that biodiversity can prevent the spread of zoonotic disease and in this way protect human health.

In a ground-breaking 2000 paper in the journal Conservation Biology, Richard Ostfeld and Felicia Keesing applied this hypothesis to the spread of Lyme disease, calling it the “dilution effect.” They predicted that high species diversity within the host community would increase the likelihood that ticks would feed on animals that do not harbor the Lyme disease bacteria. As a result the infection power of the natural reservoir, the white-footed mouse, would be diluted. With a lower prevalence of infection in ticks, the vectors of the disease, Ostfeld and Keesing hypothesized that high species diversity would also reduce transmission of Lyme disease to humans. Sure enough, through analysis of state level ecological and epidemiological data, they found that states with a greater number of small mammal species in the host communities had fewer reported cases of Lyme disease per capita.

The work of Ostfeld and Keesling demonstrates that the dilution effect can apply to indirect infection through an insect vector. A recently published study in the journal PLoS One, however, took their theory one step further. While studying the relationship between small mammal biodiversity and the prevalence of hantavirus in Panama, scientists from the Museum of Southwestern Biology and the University of New Mexico found that the dilution effect holds up for direct infections as well. They theorized that when species diversity in a host community is reduced and the density of the natural reservoir species increases, infected reservoirs will have more encounters with uninfected reservoirs and therefore more opportunities to transmit the virus. In contrast, high species diversity would reduce the encounter rate and similarly reduce the transmission rate. After setting up experimental field plots, the researchers reduced species diversity within some of the plots by removing the non-reservoir species. When the number of species was reduced, both the density of the natural reservoir population and the prevalence of hantavirus among those individuals increased. From this finding one could hypothesize that high biodiversity would consequently reduce the rate of direct infection to humans who are exposed to the reservoir species.

The idea that biodiversity can offer a service to human health is not a new concept. In fact, when people mobilize to save large swaths of highly diverse habitat from destruction, human health is one of the most argued cases for its preservation. However, people usually argue that within these areas of high biodiversity may be un-studied organisms with compounds for potential pharmaceuticals or that can act as laboratory models. While certainly compelling, this case incentivizes the preservation of certain species of potential value, not necessarily biodiversity. The ability of a diverse community to dilute the presence of a zoonotic pathogen and reduce human exposure to some of the deadliest diseases is an even stronger correlation between high biodiversity and improved human health.



Ostfeld, Richard S. and Felicia Keesing. 2000. Biodiversity and Disease Risk: the Case of Lyme Disease. Conservation Biology. 14(3):722-278

Suzan, Gerardo, Erika Marce, J. Tomasz Giermakowski, James N. Mills, Gerardo Ceballos, Richard S. Ostfeld, Blas Armien, Juan M. Pascale, Terry L. Yates. 2009. Experimental Evidence for Reduced Rodent Diversity Causing Increased Hantavirus Prevalence. PLoS One. 4(5)

Photo: Peromyscus leucopus; Encyclopedia of Life

Solar Power

The act of eating is, without a doubt, the most enjoyable way of obtaining energy. As I sink my teeth into a juicy cheeseburger or try the first bite of an unusual new dish, I am blissfully unconcerned with the fact that I am meeting my metabolic obligation as a heterotrophic organism. My focus is exclusively on pleasing my senses of smell and taste while achieving that completely satisfied, comfortably-full feeling, not meeting my body’s caloric demand to ensure continued growth, maintenance and response. It is so easy to forget that we eat to live, that savoring a grilled cheese sandwich is merely a delicious way of staying alive.

While humans have made seeking, preparing, and consuming food a delightful means of survival, it is arguably an inefficient way to obtain energy. Heterotrophs like us must devise some scheme of capturing the appropriate food, the energy expenditure of which can be enormous. Autotrophic organisms such as plants and algae utilize solar (and sometimes chemical) energy to fix atmospheric carbon through photosynthesis and build the complex organic compounds needed for metabolism. In doing so they create their own food, skipping the expensive steps that we so enjoy. Autotrophs are the primary producers in the food web, creating the organic compounds upon which all other organisms rely for energy. Heterotrophs are the consumers, filling distant trophic levels which correspond to the number of links separating them from the sun’s energy. Humans typically eat as primary and secondary consumers, although consumption of some foods, such as large prize fish, can make us quaternary or even more distant consumers.

Over the course of evolution, organisms have spread out among different trophic levels. While humans enjoy the role of apex predator, occupying the end of the food web, some animals have moved in the opposite direction. Outdoing other primary consumers, some marine invertebrates have managed to acquire most of the energy they need without hunting or even eating. The ultimate convenience in predation, this unique trophic status is made possible by a special partnership between select invertebrate species and zooxanthellae algae. This partnership is considered an endosymbiotic relationship because the zooxanthellae live inside the body of the host, allowing both organisms to enjoy mutual benefits. (Our intestinal micro-flora and fauna are endosymbionts as well). Zooxanthellae are single-celled organisms that line the superficial tissues of the host like tiny solar panels, performing photosynthesis which provides the host with the organic compounds it requires for metabolism. In exchange the zooxanthellae receive shelter, nutrients and a constant supply of carbon dioxide – metabolic waste from the host. To maximize the benefits of this relationship, the invertebrate host seeks environments with conditions that are favorable for photosynthesis, as if it were an autotroph itself. The nudibranchs, sea anemones, jellies and reef-building corals that host zooxanthellae all live in shallow water for maximum sunlight.

Behind the scenes at the New England Aquarium, Upside-Down Jellies, Cassiopea andromeda, are raised under high-powered sun lamps in shallow tanks that re-create their natural sandy-bottom habitat. The Cassiopea rests on its flat bell, its reduced tentacles extended up towards to the light. At some point in the jelly’s lifecycle, zooxanthellae are incorporated into its tentacles, causing them to appear many different shades of blue-green. While they rest comfortably on the bottom, Cassiopea are by no means sessile. If you gently agitate the sand below their bell, they will casually swim off, still upside down, to another sunny spot. Small Cassiopea, about the size of a quarter, are held in a separate tank under the sun lamps. With a few exceptions, these young organisms do not appear to have zooxanthellae in their tentacles, and they must be provided with a normal diet. When the jellies are large enough, they are moved to the main tank where their tentacles eventually develop that typical blue-green color. It is likely that the adult jellies regularly expel excess zooxanthellae into the water in order to maintain a balanced number. The free zooxanthellae can then be absorbed by other jellies and will proliferate to colonize their new hosts. Even though they actively produce their own food, we would still feed adult Cassiopea small amounts of zooplankton to supplement their photosynthetic diet.

Similarly, reef-building corals (which, like the jellies, are members of the Phylum Cnidaria) acquire about 90% of the energy they need from zooxanthellae. Corals can capture and consume other plankton, cnidarians and sometimes even small fish, but they are completely dependent on their endosymbiotic relationship with zooxanthellae for survival. Research has shown that host-zooxanthellae associations in corals are extremely specific. This means that only one species of zooxanthellae will populate a colony of coral. As the zooxanthellae multiply, the host coral must regulate the number of individuals it holds within its cells in order to maintain its finite capacity. One way that the coral achieves this balance is by digesting excess zooxanthellae or expelling individuals into the water column. Zooxanthellae expulsion is responsive to environmental changes and often occurs when the corals are under stress caused by rising temperatures, changes in water chemistry, reduced light and disease. The expulsion of zooxanthellae is called coral bleaching, because the loss of the pigmented algae leaves the corals bone-white. If the corals survive the period of stress, zooxanthellae may be able to repopulate the colony within a few months. At first the species of zooxanthellae that repopulates the colony may be different from the species that was expelled, but over time the species will be replaced much like forest succession, eventually leading to that original inhabitant.

An endosymbiotic relationship with zooxanthellae may seem like the most efficient way for an animal to acquire energetic organic compounds, but one unique group of sea slug has managed to get even closer to autotrophic status. Sacoglossans, or solar-powered sea slugs, are small marine gastropods - the herbivorous cousin of the predatory nudibranch. These organisms are absolutely animals, yet amazingly they can perform photosynthesis on their own without the help of functional zooxanthellae. As a sacoglossan feeds on algae, it can isolate intact chloroplasts (the cellular machinery that performs photosynthesis) from its food and retain the chloroplasts within specialized cells in its body. While the other components of the algae are digested as food, the chloroplasts are incorporated into the body of the sacoglossan and perform photosynthesis the same way they did in the algae. This symbiotic phenomenon, aptly known as kleptoplasty, enables the sacoglossan to reap the energetic benefits of photosynthesis without playing host to an independent organism. While the functionality of the chloroplasts within the sacoglossan’s body is finite, the species Elysia chlorotica can maintain its chloroplast associations for up to ten months.

Sacoglossans thrive with the convenience of independently producing food within their own tissues, and even though they cannot glean as much pleasure from meeting their caloric requirements as we do, they don’t have a sense of taste either. Kleptoplasty and zooxanthellae endosymbiosis have allowed some animals to enjoy the ultimate reliable food source by acting more like plants. So the next time you are hungry enough to eat a horse, imagine yourself as a solar-powered sea slug, bathed in sunlight – warm, energized, and comfortably full.

To learn more about sarcoglossans and nudibranchs that host zooxanthellae, visit The Sea Slug Forum.



Dimond J. and E. Carrington. 2008. Sybiosis regulation in a facultatively symbiotic temperate coral: zooxanthellae division and expulsion. Coral Reefs. 27: 601-604

Toller, W. W., R. Rowan, and N. Knowlton. 2001. Repopulation of Zooxanthellae in the Caribbean Corals Montastraea annularis and M. faveolata following Experimental and Disease-Associated Bleaching. Bio.Bull. 201: 360-373

Photo: The sarcoglossan Placida dendritica. Photo by Bill Rudman

Jellies. Of course.

An aquarium crowd pleaser and anathema of the beach, jellies are by no means rare animals, yet they never cease to fascinate and terrify their human audience. Their simple design and alien appearance combine in awe-inspiring beauty – a diaphanous bag of cells operating at the most basic level of functionality. It is this simplicity of jellies that amazes. It is hard for us to believe that these are actually animals, yet they manage to thrive with the most primitive tissue structure, lacking viscera, and possessing only a rudimentary nervous system. The thick, brown sea nettles that contrast so attractively with a blue aquarium background and the heavy, dinner-plate shaped moon jellies that wash up on the beach are actually far more complex than many jellies in the ocean. Although they resemble their stinging cousins, the animals of Phylum Ctenophora, are usually classified separately from the more well-known jellies of Phylum Cnidaria.

At the New England Aquarium we distinguished the groups as true and comb jellies. The true jellies, members of Phylum Cnidaria, tend to have more robust bodies and possess venomous cells called nematocysts which can paralyze prey and sting a human interloper. The animals of Phylum Ctenophora are totally painless yet proliferate so aggressively that reaching into a tank feels like dipping your hand into a jar of, believe it or not, jelly. Comb jellies can bloom in extremely dense masses, flowing in to shore with the high tide where we would meet them with buckets, scooping them up with sore arms by the thousands. After an accidental introduction in the Black Sea, one type of comb jelly, Mnemiopsis, even caused the collapse of local fisheries by eating both fish larvae and fish prey and expanding to a devastating population size.

Comb jellies come in all shapes and sizes – from the marble sized gooseberry (Pleurobrachia) to the nearly flat, meter-long Venus’ Girdle (Cestum). The relatively few species of the phylum all have transparent bodies that appear as fine as a snowflake. The Venus’ Girdle, for instance, is so thin that divers can look through its body to see undistorted images on the other side. The only observable action of these animals is the rapid flutter of tiny cilia, organized in eight long stripes, which propel the animal through the water. Their swimming movement appears nearly effortless compared to the strenuous flex of a true jelly’s bell. The flutter of the cilia can also scatter light, creating a prismatic effect in many species. Most Ctenophore species are capable of bioluminescence, lighting up the dark ocean with flashes of blue and green. These nearly invisible oceanic lanterns add to the extraordinary experience of diving at night, which is at once strange and beautiful.

Read more about Phylum Ctenophora and one diver's encounter with the nighttime glow of Venus' Girdle here.

Photo: Mnemiopsis photographed by Herb Segars

Species Profile: Leopard Shark

Interested in San Francisco Bay wildlife? This is a species profile that I wrote on Triakis semifasciata, the Leopard Shark, for our Fall 2009 newsletter. This is the original, soon to be hacked away by the cruel hand of the redactor.

Where are Leopard Sharks found?
Leopard Sharks are found along the Pacific Coast - from Central Mexico to Oregon. One of the most common sharks in California, there is a large population of Leopard Sharks living in the San Francisco Bay. Most of them live in the Bay year round, with a few individuals migrating out in the fall. Leopard Sharks are often spotted near the bottom in the shallow waters of the sloughs and mudflats along the Bay margins. The Bay offers a safe haven for the Leopard Shark, because the water is too shallow and warm for predators, such as the Great White Shark. Plus the Leopard Shark finds abundant prey in the muddy bottom of the Bay. They often follow the high tide up to the shoreline to feed on animals in the shallow mudflats; then they move back out as the water recedes.

What do they look like?
The Leopard Shark is a slender fish with silvery-bronze skin and dark ovals arranged in neat rows across its back. Leopard Sharks are quite small. Their average length is around three to four feet, although they can grow up to seven feet. The Leopard Sharks in San Francisco Bay are more likely to be between two and three feet long.

What do they eat?
Leopard Sharks feast on small invertebrates, such as clams, worms and crabs that they find along the muddy bottom of the Bay. They also like small fish, eggs and the occasional Bat Ray. Sometimes the Leopard Shark can pluck prey right off the mud with its bottom-facing mouth. In other instances, the shark will shovel its nose into the bottom and toss the sediment away, exposing hidden clams or worms. Leopard Sharks may go to extreme lengths to eat small animals, but they will not attack humans.

How do they reproduce?
Leopard Sharks have ovoviviparous reproduction, which means that the baby sharks, or pups, develop in eggs that are retained within the mother’s body. The eggs hatch in the mother’s body, and then the pups are born live. A female Leopard Shark can have up to 29 pups in one litter.

What are the threats to Leopard Sharks in San Francisco Bay?
Leopard Sharks are fished both commercially and recreationally, with recreational fishing accounting for the majority of the catch. Even though it is an abundant species, Leopard Sharks grow so slowly that overfishing could deplete the population. Concerns about overfishing lead to the implementation of size limits by the Department of Fish and Game - Leopard Sharks smaller than 36 inches must be released. Leopard Sharks also contain high levels of mercury in their tissues. These animals have a greater exposure to mercury than other fish species because they spend so much time feeding in contaminated Bay sediments. It is unknown if the mercury is harmful to the Leopard Sharks, but it certainly exceeds the accepted safe limit for humans.

Photo credit: Peter J. Bryant

Hospitality Returning to the Bottom of the Bay

We must consider many factors before settling our lives into a new place. Whether it is the school system, safety or convenience of transportation, people have a list of requirements for their suitable habitat. It is the services and infrastructure after all that distinguish our comfortable communities from hard life on the frontier. Whether dispersing from their population or remaining exactly where they were born, organisms seek to fill similar needs when settling into their habitat. Some plants and animals, known as foundation species, are specially equipped to satisfy these requirements for many different species. By virtue of their physical characteristics, foundation species provide three-dimensional habitat for entire ecological communities, and in doing so dramatically enhance biodiversity in a relatively small area. Reef-building organisms like corals and oysters, trees that form a dense canopy layer, and the impenetrable underwater forests of kelp are all examples of foundation species that host robust ecosystems.

As we have learned from the worldwide destruction of coral reefs, declines in foundation species pose an enormous threat to their associated, denizen species. For the same reason, the protection and restoration of foundation species could be the most important step to maximize the conservation of global biodiversity. This conservation strategy is currently underway in San Francisco Bay, as collaborative effort between Audubon California, Save the Bay, NOAA, and San Francisco State University strives to restore and enhance one of the most important foundation species in San Francisco Bay – Zostera marina, or eelgrass.

Eelgrass is a type of seagrass – a marine flowering plant (not a seaweed!) that grows submerged in shallow water areas worldwide. Seagrasses form vast meadows in coastal environments that resemble terrestrial grasslands, their dense root system and tall leaf canopy creating complex habitat in areas that are otherwise unvegetated. Seagrass beds provide food, cover, and spawning ground for a wide array of invertebrates, fishes, birds, and mammals. Found in tropical as well as temperate regions, seagrasses play host to hundreds of associated species including green sea turtles, manatees, seahorses, and countless species of fish. As a biodiversity hotspot, seagrass beds also attract hordes of predators that come to feed on their residents. Unfortunately, seagrasses are declining worldwide at an astounding rate. Like all foundation species, the destruction of seagrasses can have severe impacts on the many associated species that rely on seagrass bed habitat. A recent study by A. Randall Hughes of UC Davis found that nearly 15% of all seagrass species worldwide are currently listed as threatened in some portion of their range. For every species of seagrass, there is at least one associated species of concern, and in total there are 74 species of concern that are associated with seagrasses worldwide. These results come from a preliminary study, however, and the true conservation costs of seagrass declines have likely been underestimated. Moreover, there is a general lack of awareness of the importance of seagrass bed ecosystems on biodiversity.

Over the past few decades within the San Francisco Bay, the size and number of eelgrass beds has been steadily declining, mostly due to reduced light availability. Like all plants, eelgrass requires sunlight for photosynthesis; however, conditions within the Bay have severely limited the depth to which light can penetrate the Bay water. Dredging operations in the Bay destroy eelgrass beds either by physical disturbance or by stirring up sediments to increase turbidity. Construction activities in the Bay watershed release sediments to streams that eventually reach the Bay, smothering eelgrass beds. Even if there is enough light for the plants to growth, excess nutrients can accelerate algae growth beyond the feeding rates of grazers, allowing the algae to over take eelgrass leaves and block out light.

Biologists of the eelgrass restoration team are putting in a great effort to enhance existing eelgrass beds and restore this habitat to the fullest extent of its San Francisco Bay range. Richardson Bay in North San Francisco Bay is the ideal location for eelgrass restoration. It harbors the second largest eelgrass bed in the estuary, with plants that have the greatest genetic diversity of all beds sampled. Given its sheltered location and distance from dredging operations, Richardson Bay has the model environmental conditions for large eelgrass beds, but the genetic diversity of its plants also gives hope for successful transplanting to other sites in the Bay. Using a variety of techniques, biologists are hoping to discover the restoration method with the highest success rate. Both mature plants and seedlings are transplanted to sites at four different depths where they are either hand-planted by divers or tied to special grid-like frames which sink to the muddy bottom. At the same time the team is modeling Bay circulation patterns to better understand the potential for seed dispersal from existing beds. Divers are collecting mature eelgrass flowers from donor beds and using them for targeted seed dispersal at other sites in the Bay. Seeds can be deployed either by hand or from mesh bags attached to buoys which hold the flowers and distribute the seeds in a circular pattern, moving with the current.

The restoration team and Bay Area naturalists alike hope that these efforts will reverse the Bay’s long-term decline in native biodiversity, giving us an example of the multi-layered ecosystem that this foundation species once supported. At the base of its complex food web, dense mats of eelgrass roots hold sediments in place and keep them well-oxygenated to support the growth of important bacteria. Eelgrass leaves provide substrate for algae and epiphytic plants which are grazed upon by a number of invertebrates. Even dead eelgrass plants that settle within the bed, develop a film of bacteria, fungus and detritus, which also feeds small invertebrates. During low tides, eelgrass beds hold moisture, so that these small organisms are protected. As a result, waterfowl arrive in droves to feast on a surfeit of invertebrate prey. The Pacific Herring, the largest commercial fishery in the Bay which has seen recent population declines, depends on eelgrass beds for spawning and cover. The herring lay their sticky eggs on eelgrass leaves so that the young will be protected until they reach maturity. The success of these restoration efforts could enhance the Pacific herring population, allowing for increased takes by local fishermen. Birders would also be happy to see the return of the diversity of native and migratory waterfowl that hunt the in eelgrass beds. To learn more about the progress of the San Francisco Bay eelgrass restoration, visit www.tiburonaudubon.org

Cited: Hughes, A. Randall, Susan L. Williams, Carlos M. Duarte, Kenneth L. Heck Jr., and Michelle Waycott. 2009. Associations of concern: declining seagrasses and threatened dependent species. Frontiers in Ecology and the Environment. 7:242-246

Photo credit: www.ceoe.udel.edu

Get Glowing.

Scientists at the Tohoku Institute of Technology in Japan recently made an amazing discovery - we glow. That’s right. Humans actually GLOW as we emit photons of light energy. And while our photon auras are far too dim to be seen by the human eye (but certainly sensed in other ways), super-sensitive cameras at the Tohoku Institute have captured the human glow which actually changes over the course of the day. We glow the most from our faces, with peak glow occurring in the late afternoon. You can read more about the discovery of your inner light on Ed Yong’s blog, Not Exactly Rocket Science.

I must have been glowing a little bit brighter as I read this exciting news. Bioluminescence, the emission of light by a living organism, is a phenomenon that is actually quite common among creatures in the ocean, but it continues to mystify us dull humans. Shared by some of the Earth’s strangest creatures – jellies, nudibranchs, squid, and the grotesque anglerfish to name a few – bioluminescence is a trait that adds to their mysterious appeal. Bioluminescence is fascinating to many of us, but its varied mechanisms and evolutionary purpose are not well understood. Some organisms manage their shine through a series of chemical reactions, while others rely on the glimmer of symbiotic bacteria. This ability to glow can be used for communication, attraction, and camouflage. It was only recently that the flashes of fireflies, one of the few terrestrial biolumineers, were translated, earning major coverage in the New York Times (see “Blink Twice if You Like Me” by Carl Zimmer, 6/29/09). Now scientists from NOAA are taking their search for biological shine to the bottom of the ocean.

From July 20 – 30 Doctors Tamara Frank (HBOI@FAU), Sönke Johnsen (Duke), Edith Widder (Ocean Recon), Charles Messing (Nova Southeastern) and Steve Haddock (MBARI) will be studying bioluminescence on the deep-sea floor off the Bahamas. While bioluminescence in pelagic (open water) organisms is well-studied, information on benthic (living near the ocean floor) organisms in deep-sea areas is still limited due to the difficulty of collecting live specimens. To get a better look, these researchers will be deploying the Johnson Sea-Link Submersible to sit among the glimmering animals of the ocean floor. They are also baiting the deep-sea ORCA Eye-in-the-Sea camera to get up close and personal images of some voracious predators. You can follow the expedition of Bioluminescence Team 2009 on NOAA’s Ocean Explorer through daily video logs, podcasts, and amazing photographs of never before seen ocean activity. The attack by Cuban Dogfish and the shimmering Sea Pens are not to be missed!

Learn more about the organisms that really shine on NOAA's Ocean Explorer!

(Photo: Luminescing Bamboo Coral, Bioluminescence Team 2009 NOAA-OER)

The Green Sturgeon's Dangerous Diet

The enigmatic Green Sturgeon (Acipenser medirostris) patrols the benthos of the San Francisco Bay and near shore oceanic waters as a living relic of ancient seas. This large, long-lived fish species, which has persisted for millennia in evolving oceans, may have finally met its match in the environmental impacts of Bay Area development. The Southern Distinct Population Segment (DPS) of the Green Sturgeon, which is listed as threatened under the federal Endangered Species Act, swims through the San Francisco Bay to reach its only remaining spawning ground in the Sacramento River. As these animals swim through the Bay and Delta, they face deteriorating water quality, reduction of freshwater flows, potential poaching for caviar or bycatch in other fisheries, entrainment in water intake structures, and impassable upstream barriers. The principle threat to the Southern DPS is the disappearance of its spawning ground. Now restricted to a very narrow stretch of the Sacramento River, the elimination of the remaining spawning ground would mean the extinction of this genetically distinct Green Sturgeon population. The National Marine Fisheries Services (NMFS) is strengthening protective measures of the Southern DPS by proposing the same take prohibitions that are applied to species listed as endangered. Take prohibitions will make it illegal to hunt, harass, or otherwise harm the fish, including any action that degrades its critical habitat.

Unfortunately this step may not be enough to ensure the long-term survival of the population. A combination of human-influenced factors, now woven into the ecological fabric of the San Francisco Bay and Delta, has turned this estuary into a toxic environment where animals are actually poisoned by their food web. The Green Sturgeon feeds on invertebrates that it finds bottom of the Bay, including the invasive Overbite Clam (Potamocorbula amurensis). This prolific bivalve, which can be found in densities as great as 50,000 per square meter in some areas of San Francisco Bay, is likely to compose the better portion of the Green Sturgeon’s diet. The Overbite Clam itself has a voracious appetite, and it rapidly filters food particles out of the water column with amazing efficiency. Although it may be seeking tiny organisms and detritus, the clam inadvertently consumes the contaminants that pollute the water column including selenium, a bioaccumulative element that comes from oil refineries and Central Valley agriculture. The efficiency with which it incorporates selenium into its tissues makes the Overbite Clam a toxic meal for any predator it succumbs to.

The impact of selenium may not be immediately apparent in the individual adult fish, but it can cause massive reproductive failure. Selenium from a diet of contaminated Overbite Clams will bioaccumulate in fish tissues over the course of its lifetime. Although it may not harm the adult fish, selenium is transferred from a female fish to her eggs, which can cause embryonic death or fatal deformities upon hatching. These reproductive impacts can be severe enough to devastate a population. All fish species in the San Francisco Bay that feed on the Overbite Clam are at risk; however, the unique life history of the Green Sturgeon makes it more vulnerable to this poisonous prey.

In many ways the life of the Green Sturgeon is similar to that of a human. It has a remarkably long lifespan of up to 70 years, and it does not reach sexual maturity until it is at least 15 years old. As an adult it has an iteroparous reproductive strategy, meaning it allocates energy to multiple spawning efforts over the course of its lifetime as opposed to a “big bang” spawning effort once before death. The Southern DPS of the Green Sturgeon, which spends the majority of its adult life in the ocean, returns to the Sacramento River every 2 to 5 years to spawn. Even though it spends more time in the ocean than other sturgeon species, Southern DPS adults may live in the estuary for seven months of the year and juveniles can live here year-round, all the while exposed to dietary selenium.

Given its late age of sexual maturity, the Green Sturgeon will accumulate selenium in its body for at least fifteen years before it first spawns. The level of bioaccumulated selenium imparted to eggs will then increase for all subsequent reproductive efforts as the sturgeon ages. As a result the reproductive impacts of selenium are likely to be more severe for the Green Sturgeon than for a fish with a shorter lifespan and quicker maturation. This reproductive challenge can greatly reduce recruitment within the Southern DPS, meaning that fewer individuals are surviving to reproduce and maintain the size of the population. With this obstacle to the population’s survival so deeply rooted in the ecology of the San Francisco Bay and Delta, the actions that result in the take of an individual animal seem relatively easy to avoid. The proposed take prohibitions are a necessary step in slowing the decline of the Southern DPS, but they are by no means the solution. The elimination of selenium discharges to the San Francisco Bay and Delta may be the only way to ensure the population’s long-term survival.

(Photo credit: David Gotschall)