Demystifying the Mythical Seahorse
Norah Saarman, Conservation and Resource Studies '06, explains how genetic sleuthing led her to the medicinal herb shops of Chinatown and beyond.
When Dr. Healy Hamilton invited Norah Saarman, to do an undergraduate research project on seahorse genetics, she felt a tingle of excitement. "I've always had a crush on Syngnathidae, the family of fishes including pipefish, pipehorses, seadragons and
The appearance of seahorses is exciting enough. As their scientific name Hippocampus implies, seahorses have the head of a horse (hippo = horse, campus = head). This, combined with a curvy prehensile tail and a series of armor like body rings, complete a mythical image. Exotic stripe-ringed eyes move independently to scope out tiny floating prey.
The uses of seahorses
Seahorses have an astonishing and endearing reproductive strategy. A male seahorse receives between 5 and 2,000 eggs directly into his brood pouch. The eggs are fertilized and then nourished as they develop in this internally regulated environment. His stomach becomes distended just like a pregnant woman until he gives birth to the young, which emerge fully formed at the end of gestation, and rise to the surface to disperse on ocean currents. The appreciative female performs courtship dances daily to exhibit her loyalty.
As Saarman began her research, she became aware that she had stumbled upon a group that is not only unique and captivating, but also understudied, overexploited and in grave danger of extinction. In 2004, seahorses were added to Appendix II of the Convention on International Trade of Endangered Species agreement to protect them from exploitation. The 167 nations who have signed the agreement are responsible for controlling cross-boarder trade and regulating fishing practices so that sustainable populations of all 35 seahorse species can persist. One might say that seahorses are the charismatic ambassador of the coral reef and mangrove forest.
Seahorses are found in various marine habitats close to the coast. Because the coastal areas that seahorses call home are some of the most threatened marine ecosystems of the world, protecting seahorses will ensure the continued vitality of the whole ocean floor community.
These communities provide many services to humans including invaluable nutrition, lumber, fuel wood, carbon sequestration and medicinal ingredients. Seahorses are not only endangered because of their ecological fragility, they are also threatened by their overexploitation in trade for traditional Chinese medicine.
Seahorses as medicinal ingredients
An estimated 24.5 million or 70 tons of seahorses are sold annually for use in Chinese medicine. Most seahorses on the market are caught accidentally by shrimp trawlers who later handpick them from the net and sell them for additional income on the international market. In some countries, seahorses are targeted by lantern fishers who fish by night when seahorses are most active.
Seahorses are reputedly high in yang, the active male force, and are a respected treatment for many ailments associated with a cold kidney system. As a source of fire energy, seahorse can be used to treat many symptoms including impotence, urinary incontinence, wheezing, abdominal pain, toxic swelling and debility in the elderly.
But seahorses are a fragile species that respond quickly to habitat destruction and overfishing and may not be able to survive the current rate of harvest. Seahorses are sparsely distributed and don't travel much, so once they're removed from an area they don't return easily. They also remain faithful to their mate and don't reproduce quickly, making them exceptionally vulnerable to population reduction when too many are caught at sexual maturity.
The international seahorse trade
Why does trade continue despite the negative impacts? The seahorse trade is widespread and affects millions of people whose income is so low that the economic value cannot be represented effectively in US dollars.
Some of the world's poorest fishermen target seahorses. Because the average income in some poor countries is just one or two dollars a day, seahorses can greatly increase a fisherman's income. Even though most fishermen sell their catch to distributors at the low price of $0.10 to $1.56 USD per kilo, the profit is a strong incentive. Desiccated seahorses sell for between $333 and $666 USD per kilo in San Francisco.
Enforcement of fishing regulations are expensive, and management plans are difficult to implement. With such a high incentive driving the seahorse market the challenge of maintaining seahorse populations will require extensive research, more careful documentation and international cooperation.
Trade is well documented for species such as H. trimaculatus, which originate in Asia. However the 'giant' Pacific seahorse, H. ingens, the only species which occurs along the Pacific coast of North and South America, remains an unrecognized component of Chinese medicine. If Saarman could prove that giant Pacific seahorses were being traded often for Chinese medicine, it might provide incentive for more careful documentation.
Journey to Chinatown
Saarman's research quickly snowballed into different disciplines, and she made a trip to Chinatown, San Francisco. There she interviewed seahorse specialists and acupuncturists alike to answer her questions about the cultural and economic value of seahorses.
Two years after placement on Appendix II of CITES, Saarman found large jars and trays of seahorses available in almost every herbal supply shop in Chinatown, San Francisco. There are usually two different types of whole, dried seahorses, sold in pairs to be used in home made formulas: "dark" seahorses and "light" seahorses. According to storeowners, the dark seahorses were bought from providers in South America, and the light seahorses were bought from providers in China. Dark seahorses were priced at about $15 to $25 per pair, and light seahorses were priced at about $3 per pair.
Saarman wasn't able to talk freely with storeowners, because they fear repercussions for illegally obtained seahorses, and are unwilling to risk their business to provide information to researchers. Instead, she sent representatives into shops to purchase seahorses for various hypothetical illnesses. Saarman then sampled the dried seahorses and identified the species. The wildlife trade monitoring network, TRAFFIC, provides a seahorse guide - using this key she was able to identify the seven specimens collected from the shops. The small white seahorses were of three different species (H. kelloggi, H. spinosissimus, and H. trimaculatus) all found in the indo-Pacific. The large dark seahorses were in fact the 'giant' Pacific seahorse or H. ingens. It was interesting to find that the 'giant' Pacific Seahorse is significantly more valuable in San Francisco than the Asian species.
Tracking down H. ingens
Although H. ingens is frequently sold for Chinese medicine, no one knows where they are harvested. The population size, how different populations interact, and how genetically diverse the populations are, is also unknown. Taking a tiny step toward better understanding of seahorses, Saarman completed a new research project using genetic markers to examine the relationship between giant pacific seahorses in different parts of their range.
Saarman looked at genetic diversity in a small part of the H. ingens mitochondrial DNA in the hopes that patterns of variation found in the DNA could be enough to tell her where the seahorses come from. She looked at 86 different specimens from five different eastern Pacific locations (California, Mexico, Guatemala, Ecuador, and Peru). For each seahorse she analyzed the same 438 base pair fragment of mitochondrial DNA.
Unfortunately, the differences in DNA between seahorses in different locations were small, suggesting either movement of individuals between populations (contrary to expectations), or that the differences were too small to show up in the analysis. Only seahorses from California and Mexico were different enough to distinguish between the two. It is possible that very recent separation of populations created changes in DNA profiles that were unrecognizable in the mitochondrial DNA fragment she looked at.
Although the fragment of DNA Saarman studied wasn't able to tell her where undocumented seahorses were coming from, there are other even smaller bits of DNA with more genetic diversity that could help find the answer. These are called microsatellites. Because microsatellites change rapidly, two populations separated for even a small amount of time will result in detectable differences. As a contracted technician at the California Academy of Sciences, Saarman is now working on developing microsatellite markers that she believes will elucidate the true evolutionary story of the 'giant' Pacific seahorse.