Every year, thousands of people suffer from thousands of people year, Every n a tropical island vacation, one of the last island vacation, n a tropical want to worrythings you about is food poison- includes a trip to the tropics for many, Yet ing. a painful education in a mysterious food-borne or CFP. Poisoning, illness called Ciguatera Fish On some small islands in the Caribbean and On in St. Thomas, diving in here why I’m That’s by Katie Pitz SCIENTIST EXPLORES MYSTERIOUS SCIENTIST EXPLORES MYSTERIOUS CIGUATERA ILLNESS: FOOD-BORNE CFP, a poisoning syndrome caused by eating toxic caused by syndrome a poisoning CFP, and both gastrointestinal fish. CFP symptoms are reef - bringing on bouts of nausea, vomit neurological, in someing, diarrhea, headaches, muscle aches, and and cold sensations. Some of hot cases, the reversal symptoms can persist for days to monthsneurological test is no quick way to There after exposure. to years and unless action is taken within hoursfor the toxins, sick. once you’re of the poisoning, no cure that CFP can affect estimated it’s Pacific, South of the population. Ciguatera than 50 percent more these communi- through runs like an undercurrent ties, not always visible at the surface but having vast economic and public health impacts. CFP is consis- because of both misdiagnosis tently underreported of local people to go to the hospital and a reluctance or local clinic when sick. water the color of an unclouded sky for a near-in- fish Amid the coral and seaweeds, visible quarry. and light. appear like bright flashes in the shadows the algae and dead They tear and scrape food from in and enclose some seaweed down corals. I reach but a plastic bag, collecting not only the seaweed, O Tropics

the Illustrations by E. Paul Oberlander, WHOI Illustrations by E. Paul Oberlander, in Trouble

Phytoplankton also thousands of tiny hitchhikers. I’m hoping to fish caught in a safe area could have just traveled from find elusive cells sticking to that seaweed. a prime Gambierdiscus habitat. These microscopic cells, called Gambierdiscus, Low levels of ciguatoxins probably permeate the produce the toxins that cause CFP. By learning more entire tropical food web, so that even if people avoid about their genetics, I hope to find out how they high-risk fish, they can still consume low levels of grow in different environments and how that affects toxin. Unfortunately, even if a fish isn’t toxic enough the risk of CFP around the globe. to make you sick in one sitting, eating fish with low levels of toxin can lead to chronic effects that are still Up the food chain largely unknown. Gambierdiscus likes warm water. It’s a tropical If patients are able to get to the hospital soon dinoflagellate, which is a type of phytoplankton. after they have consumed a poisonous fish, they may Phytoplankton use photosynthesis, harnessing the be given an intravenous dose of mannitol, a drug sun’s energy to make food. They are named plank- that greatly alleviates the symptoms of CFP. How- ton because they “drift” through the world’s oceans. ever, after a certain period of time, mannitol has no However, this can be misleading, since dinofla- effect. Locals also use several herbal and traditional gellates, as implied in their name, possess two flagel- folk remedies, but these have not been scientifically la—whiplike appendages that they use to make proved effective. small movements in their underwater environment. Gambierdiscus lead a benthic existence, attaching A better world … for Gambierdiscus themselves to seaweed, sand, and dead coral on the Understanding the ecology and growth pat- ocean floor. When herbivorous, or plant-eating, fish terns of Gambierdiscus species can help us predict a bite or scrape seaweed to feed, they also coinciden- region’s potential risk of CFP. As water temperatures tally consume many Gambierdiscus cells. The toxins increase because of global warming, Gambierdiscus’ in those cells accumulate in the fish. Gambiertoxins range has expanded to new environments—from the produced by Gambierdiscus are biotransformed by fish Caribbean, for example, to the Gulf of Mexico and into ciguatoxins, which can cause disease in humans. up the coast of Florida. Ciguatoxins can accumulate not only in fish But it also may be diminishing in other areas if that directly eat Gambierdiscus cells, but also in the temperatures rise higher than Gambierdiscus’ growth predators that eat those fish. When carnivorous threshold. Furthermore, coral reefs are declining, fish consume toxic herbivorous fish, the toxins can creating environments that allow seaweeds to accumulate in them as well, allowing the toxins to take over corals—and providing perfect habitats biomagnify up the coral reef food chain. By the for Gambierdiscus. time a barracuda, snapper, or grouper is caught on Corals are being damaged in many ways: physi- a fishing line, it often has levels of toxin many times cally, chemically, and biologically. They are torn up higher than in the herbivorous fish it consumed. by ship anchors, damaged by blast fishing tech- niques, suffocated by sedimentation, or bleached by To eat or not to eat? high temperatures. They are affected by pollution Currently there is no reliable, quick test for cig- and acidification of the world’s oceans, and they are uatera toxicity in fish, and heat from cooking doesn’t harmed by overfishing and marine diseases. inactivate the toxins. Consumers must rely on the A trend toward warmer, more seaweed-rich en- trustworthiness of fishermen and their knowledge vironments may drastically change the map of CFP of local CFP risk. Fishermen generally have learned risk, potentially introducing CFP to new regions which locations and fish are likely to be safe to eat and jeopardizing the current method of using fish- through long experience of catching, selling, and ing histories to find safe catch locations. hearing back from customers about which fish made them sick. Often a certain region or side of an island The Gambierdiscus community Me H H OH will be more toxic than anotherO because of differenc- Back on the beach, I process the samples I’ve H Me HO Me O O H es in winds and water turbulence.O collected. Brown gunk settles to the top of the fil- H O H H H H H Certain reef fish speciesH do tendMe O to settle and stay ter’s membrane. “This is going to be good,” I think, H O O O OH Me in the sameH place forH their whole adult lives, and as I admire its muddy color and viscous consisten- H O H HO H O choosingO theseH “homebodies” to fish offers a better cy. Careful not to lose any of the sample, I wash the HO H CCT

O H chanceH of avoiding a toxic catch. But the problem is soupy mess into a plastic tube, sealing it tight and O H that fish don’t necessarily stay in one place, and even a packing it away from the hot sun. I’ve just captured the benthic community living on the and enumerate the different Gambierdiscus species in the envi- surface of a collection of seaweeds. Many different types of cells ronment. We can then look at how the community of Gambier- inhabit the algae’s surface, but I’m most interested in which discus changes over time and in different locations. species of Gambierdiscus are there. Since Gambierdiscus lives on a variety of substrates, from There are more than ten different species within the ge- seaweed to dead coral rubble, it’s difficult to measure how nus Gambierdiscus. Most are impossible to distinguish from one many cells are in a specific location. A big research question is another under the light microscope. However, these species can how the abundance of Gambierdiscus changes over the year and vary widely in their production of toxins and their optimum if we can link these changes to the timing of illness in humans. growth conditions. Distinguishing among these species can Traditionally, researchers have used the number of cells per help us determine the overall gram wet weight of seaweed toxicity present in a location. Melissa Moulton, WHOI to quantify Gambierdis- A high abundance of cells cus densities. This measure- with low toxicity may mean ment is used to compare the the same risk of CFP to local abundance of Gambierdis- populations as a lower abun- cus over time and between dance of highly toxic cells. locations. Unfortunately, Furthermore, by identify- the relationship between ing different species, we can cells and the host seaweed is see if they respond differently complicated: The abundance to changes in their environ- of seaweed can vary season- ment. As overall temperatures ally, and not all seaweeds are increase and natural con- equally good hosts. ditions change, one species An important question has MIT-WHOI Joint Program graduate student Katie Pitz is on the hunt for may be favored over another, invisible yet dangerous organisms in the tropical ocean. She is con- emerged from the research: affecting the amount of toxin ducting research on a microscopic phytoplankton that produce toxins How has this variability on a reef. that cause Ciguatera Fish Poisoning, a food-borne illness that harms affected estimates of Gam- thousands of people each year. bierdiscus’ abundance over Fluorescent probes time? If there is less seaweed, do the same number of Gambier- I am developing a way to apply fluorescent labels to different discus cells just pile on the seaweed surface in a more crowded species of Gambierdiscus based on their genetic code, using a configuration, or do the toxic cells move to another substrate in technique called fluorescence in situ hybridization, or FISH. the environment? FISH use synthetic DNA probes with genetic sequences Furthermore, Gambierdiscus can be choosy in where it likes tailored to pair specifically with the genetic material in cells of to live. Different species of Gambierdiscus prefer to live on individual species. different species of seaweed. The picture gets complicated, so These probes also have an attached fluorophore, a chemical recently we have tried using artificial substrates to get around compound that glows under certain wavelengths of light. In these difficulties. this way, we can target species of Gambierdiscus by their par- We deployed small ceramic tiles under water for monthlong ticular genetic sequences and identify them in samples using a periods. Gambierdiscus settle on these tiles, and when we harvest fluorescence microscope. This technique will help us to identify them, we can record their abundance and density. This way,

Ciguatera Fish Poisoning causes severe gastrointestinal and neurological symptoms in

people. It is caused by toxins Me H H OH O made by phytoplankton. H Me HO Me O O H O H O H H H H H H Me O H O O O OH Me H H H O H HO H O O H HO H CCT

O H H O H Gambierdiscus phytoplankton attach Fish that eat seaweed or scrape themselves to seaweed, sand, and dead coral coincidentally consume dead coral on the ocean floor. Gambierdiscus. we have a standard surface area to sample, and Gambierdiscus’ habitat preferences don’t bias the results. Ideally, we hope to obtain a more balanced view of what species are abundant in the environment at any given time.

Diverse cultures Back in the lab at the Woods Hole Oceanographic Institu- tion, I look at my filtered field samples under the microscope, searching for the characteristic Gambierdiscus cells, which look like little brown UFOs flitting about amid the muck. Taking a glass pipette, I carefully reach in to pick up a cell, chasing it around the slide and finally cornering it behind a green blob of sloughed-off seaweed cells and bacteria.

Somewhat reluctantly, the cell releases its hold on the slide’s Melissa Moulton, WHOI surface, and I happily place it into a well inside a plastic plate filled with filtered seawater. I’ll give this cell light and food, letting it multiply and provide me with another culture of cells to use to investigate the genetic diversity of Gambierdiscus.

Funding for this research was provided by the U.S. Food and Drug Adminis- tration, the National Oceanic and Atmospheric Administration, the National Science Foundation, and the National Institutes of Environmental Health Science through the Woods Hole Center for Oceans and Human Health.

Katie Pitz collects specimens of dead coral rubble that harbor the toxic phytoplankton Gambierdiscus. She is investigating many facets of Gambierdiscus in an effort to combat the serious food-borne illness they inflict on people. Pitz is developing a way to apply fluorescent probes to the several different species of Gambierdiscus, based on their genetic code, using a technique called fluorescence in situ hybridization, or FISH. FISH probes have an attached fluorophore that glows under certain wavelengths of light. Here the cells are seen using a species-specific probe designed by Pitz. Katie Pitz, WHOI

Growing up in California, Katie Pitz was happiest surrounded by a post-college appointment at Lawrence Livermore nature, whether it was scrambling over rocks in the intertidal National Laboratory and carried it into her studies in zone of Monterey Bay, hiking to the top of Yosemite Falls, or just the MIT-WHOI Joint Program with her Ph.D. advisor searching for insects in her own backyard. As an undergraduate Don Anderson. She also enjoys ceramics and makes majoring in molecular cell biology at the University of California, a mean dinoflagellate-themed coffee mug. Her Berkeley, she discovered an interest in genetics. She cultivated mentor on this article was Kate Madin, a writer and Katie Pitz Biology that interest during an internship at Sangamo Biosciences and editor for Oceanus magazine. Penny Johnson

Illustrations by E. Paul Oberlander, WHOI

The Gambierdiscus toxins are Carnivorous fish eat smaller ones, Ciguatoxins continue to accumulate By the time a barracuda, snapper, biotransformed by fish into and the ciguatoxins move up the in fish at the top of the food chain. or grouper is caught, it potentially ciguatoxins. food chain. has accumulated high levels of ciguatoxins.