Report from the Emerald Coast.

So far it seems like we have only heard numbers. The numbers describe the gallons of oil spilled from the collapsed Deepwater Horizon rig, the miles of shoreline at risk along the Gulf Coast, the volume of chemical dispersant released into the water, the length of boom laid, and the projected economic losses. I came to the Emerald Coast of Florida with a head full of numbers and no real perspective. After my first day out on the water with Skipper Tonsmeire, and Emerald Coastkeeper Chasidy Fisher Hobbs, I finally understand how catastrophic the Deepwater Horizon oil spill really is.


The barrier islands that enclose the Pensacola Bay extend for miles on either side of the Pensacola Pass as open dunes of white sand. Where other barrier islands and beach cities have been developed into a solid line of condominiums and hotels, long stretches of the Gulf Islands are preserved and protected as the Gulf Islands National Seashore. Of course there are built-out areas too - Pensacola Beach is a popular destination for locals and tourists alike. But once you enter the gates of the park, the human presence feels secondary to the natural processes at work on the island. You can still see evidence of Hurricane Ivan tearing apart the single access road in 2004, and during major weather events the Gulf pours over the island and into the Intracoastal Waterway. Closer to the Pass, Great Blue Herons silently stroll along the waterline while anglers cast their lines, waist deep in the waves.

In Skipper’s boat, we patrolled the inland waterways, inspecting boom placement and studying the pre-impact condition of the shoreline. Some lines of boom had been strategically placed to guard inlets and important ecological areas like Red Fish Point and Big Lagoon State Park. In other areas, like near the Pensacola Pass, the boom has been staged for deployment near the shore. When an oil slick enters the Pass on a flood tide, lines of boom from either side of the channel will be angled toward the middle, creating a funnel to collect and then remove the oil. The boom will then be drawn back to the shore during the ebb tide, honoring the Coast Guard’s request not to interrupt commerce on the Intracoastal Waterway.

Escambia County has done a good job so far of protecting their sensitive inland and shoreline areas with boom, but this method will only be effective at stopping oil on the surface of the water. Reports are now emerging that most of the oil is suspended in the water column, and tarballs have already been seen on Gulf Shores, 90 miles west of Pensacola. Environmental damage to the Gulf Coast from the Deepwater Horizon oil spill may be inevitable if booming is our only protective measure.

Fortunately our patrol gave us the opportunity to swim in the Gulf for what may be the last time in a while. To a person familiar with the bone-chilling water of the San Francisco Bay, the water of the Emerald Coast seems unreasonably warm. Just inside the Pass the water is clear enough to see schools of bait fish at your feet. It could have been a perfect day out on the Gulf, but swimming adjacent to lines of boom conjures up an ominous feeling that is hard to ignore. Anglers continue to fish from the shore, even though commercial fishing has been suspended. Kayakers paddle through inland waters, even though boom excludes them from the more interesting shoreline. People land their boats right on the beach and dive into the water without a second thought about its quality. Even while the Emerald Coast plays this game of sit and wait, it remains a community devoted to its beautiful shoreline and coastal resources.

The Toughest Snail on the Planet

Black smokers, a type of hydrothermal vent, create some of the harshest environmental conditions on the planet. These undersea chimneys propel superheated, sulfide-rich water from below the Earth’s crust into the deep ocean. Upon contact with the cold water of the ocean, dissolved iron sulfides precipitate out of solution and deposit onto the surrounding ocean floor. From the extreme heat (roughly 350 deg C), acidity, and suffocating chemical concentration of the water emerging from black smokers to the crushing pressure and complete darkness of the deep ocean, it’s shocking that organisms can even exist in this unforgiving abyss, let alone thrive. Yet as nature has proven time and time again, organisms adapt to exploit the conditions that we terrestrial dwellers consider most inhospitable.

Just like John Rambo, the organisms that can survive an environment as ruthless as a black smoker must be incredibly tough – even tougher than modern soldiers. For this reason MIT’s Haimin Yao has been studying the body defenses of the Scaly-foot Gastropod (Crysomalion squaminferum). The Scaly-foot Gastropod is a resourceful little snail that was discovered nine years ago at the base of black smokers near India, and it just may possess the most effective armor ever discovered.
Yao examined the shell at the nano-meter level to understand how it protects the soft body within from the extreme heat and acidity of black smoker water. It must also withstand the crushing power of predatory crabs. The shell of the Scaly-foot Gastropod is made of three layers, each composed of different materials to serve a different purpose. Together, they form a structure that's completely unlike any known armor, natural or man-made.

The outer layer is the thinnest and toughest, composed of iron sulfide particles extracted from the water surrounding the black smoker. This layer is designed to be sacrificed. When it is crushed by a crab claw (simulated in the lab by a diamond-tipped probe), the outer layer breaks but only into tiny cracks. By allowing these slight cracks, the outer layer dissipates the energy of the attack, and prevents the shell from shattering completely. The tough iron minerals of the shell can also wear down the crab's claw.

The middle layer is thick and soft. It is composed of organic matter rather than minerals. Its spongy consistency also absorbs the force of the crab’s claw, protecting the integrity of the inner layer. The outer and middle layers meet at a wavy junction rather than a flat one. This design keeps the two layers stuck together, preventing them from sliding apart.

Below the first two layers, the Scaly-foot Gastropod resembles the snails we’re familiar with. The inner layer of the shell is composed of calcium carbonate, the most common material for snail shells. If an ordinary snail were exposed to the acidic water of the black smoker, however, its calcium carbonate shell would rapidly dissolve. With the two outer layers, the Scaly-foot Gastropod can protect its inner shell, which provides structural support and prevents the shell from bending under the grip of a crab claw.

The three-layered armor makes this soft, vulnerable creature nearly invincible, even in the most extreme environment. Yao believes that this natural design could help to inspire the next generation of man-made defenses – from body armor to vehicles and sporting equipment. Perhaps we’ll see Scaly-foot Gastropod armor on Sylvester Stallone in the next installment of Rambo – Badass in a Mollusk Suit.

Learn more about the defenses of the Scaly-foot Gastropod in Yao’s article, published in the Proceedings of the National Academy of Sciences.

Photo: Our friend, the Scaly-foot Gastropod, courtesy of Anders Waren.

Species Profile: Bay Pipefish

Interesting fact from Baykeeper's upcoming Winter Newsletter: San Francisco's Seahorses are not limited to those plastered on the walls in the Powell Street BART Station.

What is a Pipefish?
The Bay Pipefish (Sygnathus leptohynchus) is a member of Syngnathidae – a family of fish that includes Seahorses and Sea Dragons. The Bay Pipefish shares many characteristics with its enigmatic cousins, including plates of bony armor, small tubular mouths, cryptic coloration, and secretive behavior. Like other Pipefish, however, the Bay Pipefish has a long, straight body.

What do they look like?
The Bay Pipefish is a long, thin fish that grows to about a foot in length. Its coloration varies between shades of green and brown. It may be possible that the Bay Pipefish changes its color to match its surroundings, but this is not known for sure. Just like Seahorses and Sea Dragons, the Bay Pipefish has a long tubular mouth formed by fused jaw-bones.


Where are Bay Pipefish found?
The Bay Pipefish inhabits eelgrass beds and shallow estuaries along the Pacific Coast from Baja California to Alaska. Hidden among blades of eelgrass, the long slender fish is almost completely concealed. The eelgrass beds also support an abundance of prey, allowing the Bay Pipefish to thrive. In the Bay Area, the Bay Pipefish can be spotted in eelgrass beds in San Francisco Bay, Suisun Bay, Drakes Estero, and Tomales Bay.

What do they eat?
The Bay Pipefish uses its tubular mouth to suck plankton prey out of the water like a vacuum cleaner, rather than biting it. When it is hunting, the Bay Pipefish remains completely still beneath its prey. Its eyes are capable of binocular vision, allowing it to determine the distance to its prey. When the position is just right, the Bay Pipefish will quickly snap its head up, placing its tiny mouth about an inch from the prey and delivering suction to capture its meal.

How do they reproduce?
Bay Pipefish reproduction begins in the early spring when eelgrass grows and plankton density increases in the water column. Like other male Syngnathids, the male Pipefish has a well-developed brood pouch on the underside of its tail. After the female deposits her eggs within the male's brood pouch, a layer of tissue grows to seal the eggs inside. The male Pipefish carries the embryos for several weeks, providing them with the nutrients, oxygen, and water they need to develop. When ready to hatch, hundreds of Pipefish young split the pouch and emerge into the water, resembling miniature versions of the adults.

What are the threats to Bay Pipefish in the Bay?
The greatest potential threat to the Bay Pipefish in the Bay Area would be the loss of habitat. Luckily for the Bay Pipefish and other eelgrass dependent species, the extent of eelgrass beds in the San Francisco Bay has actually been expanding in recent years. Although there is no commercial fishery for Pipefish species, they are collected for the Chinese medicine trade. At this time Pipefish are abundant, but if the demand for Pipefish by alternative health care markets increases, Pipefish might become as scarce as their Seahorse relatives.

Photo credit: Aquarium of the Bay

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