Hawaii is the ultimate destination for a vacation in a tropical climate. Kayaking on a gentle river or wading in secret ponds are great activities, yet so is visiting farmers’ markets. There, cottage-style growers bring produce from gardens tucked in nature. Among them is taro (kalo in Hawaiian) used for the traditional poi. Yet, water activities and taro plantations are subjected to the destructive apple snails.
The Renewable Taro Plant from the Hanalei Valley of Kauai
Known as the Garden Isle, Kauai is the oldest island of the State of Hawaii. Its pristine pastures, warm regular rainfalls, isolation from pollution, and fertile soil are ideal conditions for the organically-grown and renewable taro plant.
Taro (Colocasia esculenta) is sold in bunches of dark green leaves on long stems. It grows in the moist soil of backyard gardens, and is commercially cultivated below Princeville, in the monochromatic green patches of the Hanalei Valley. There, a narrow road leads to a one-way bridge and to verdant glossy leaves deployed in glistening ponds irrigated by the Hanalei River.
Taro is part of the Hawaiian genesis story and a traditional staple food. The plant is bountiful with edible roots, leaves, stems, and renewable as any part can be replanted for a new crop. The Hanalei Valley produces 75% of Hawaii taro and its culture is encouraged. But, the invasive apple snail challenges production and threatens the livelihood of taro farmers.
How Introducing an Alien Species Created an Agricultural Pest
The apple snail ((Pomacea canaliculata) is categorized internationally as one of the 100 global invasive alien species. Its habitat is in the shallow waters of aquatic crops, rivers, and ponds. Because of their pink/orange colour the eggs could be mistaken as flowers, or clusters of seeds.
In 1970, allowing the apple snail for the aquatic pet industry was the first encounter with the species. DNA attributed the origin of this particular genera to the Philippines where it is habitually consumed as food (kuhol), and the Filipino community in Hawaii (bisocol).
In 1989, it was categorized as an invasive species. In a control attempt, the Hawaiian Department of Agriculture (HDOA) considered a pest-for-profit program and Maui Economic Opportunity (MEO) sponsored “the escargot project” for the food industry. According to conservation planner Penny Levin, backyard prolific snail-farming might have found its way to taro ponds.
Pest Control Techniques
By 1992, the apple snail had invaded all the Hawaiian Islands, except Nihau, Molokai, and Kahoolawe. Other than hand-picking and ducks as management control, all other techniques failed, from solarization, copper sulfate, mugwort, yucca compound, neem and papaya extracts, to underwater electric shocks. Considerations for effects on eco-systems ended the attempts.
But, control also failed due a defensive "door" that seals the animal in its shell and protects it from any aggression. Saltwater was considered as it would eventually kill the somewhat salt-tolerant snails, but would also destroy soil productivity. So far, removal with mesh bags, screens, and posts has been a labor intensive solution, whereas a necessary increase in ducks would affect other species. Is self-depredation an option? Snails will cannibalize each other when food is scarce.
The Economic Impact
After the eggs hatch on the stems, the snails head for the water and hide in the base of the plants where they devour everything including the corms (bulbs harvested for poi). An entire crop can be decimated in a few days.
By 2006, the snail infestation had raised the cost of a crop by 50%, a disastrous situation for farmers who spend as much time “harvesting” the pest and unclogging pipes as they do actual farming. Also impacted are taro-related businesses such as taro milling and related food products. Furthermore, decreased corm size and quality have resulted in a higher number of corms filling the usual 80 lbs. bags.
Kawika Winter, Director at Limahuli Garden and Preserve in Kauai, indicates in an email, "This is a plague for our taro farmers as many had to give up taro farming." In 2005, it was estimated that families who rely on it as a staple food would experience a 64% food budget increase if availability was jeopardized. Farmers lost an average of 32 days of work due to snail-related injuries.
Health Risk from Leptospirosis
Furthermore, the apple snail is linked to two health risks. First, it carries the parasite known as rat lungworm (Angiostrongylus cantonensis) potentially harmful after snail consumption. Second, rat urine carries leptospirosis which contaminates wetlands. Hawaii has the highest rate of the disease, mostly among taro farmers, after cuts from crushed snail shells come in contact with contaminated water. Leptospirosis can affect ocular fluids, spinal cord, brain, renal tubes, and cause fatigue and psychological problems.
The Hawaiian Trails & Mountain Club lists leptospirosisas a hazard when visitors swim, wade, or drink water in a natural environment. Therefore, water sports and secret ponds could be potentially risky in the presence of cuts or abrasions, often the result of walking or snorkeling around coral reefs.
Cultural Implications
Kalo is part of the Hawaiian spiritual notion of caring between land and people in the whole encompassing Haloa (Aloha). The complete demise of huli (the parent plant) would be seen as a loss of identity and a point of no return to what was. Farmers share huli among each other to spread sustainance and abundance. Already, the apple snail has altered their connection to the land since they now wear rubber boots to work in the paddies. Traditionally, bare feet took the pulse of the land as feet and legs "massaged" the fertile mud “like the hands of a lomilomi (Hawaiian massage practioner).”
Sources
- HTMC Mountain Guide: Hazard: Hawaii Trails & Mountain Club.
- 100 of the World Most Invasive Alien Species. Global Invasive Species Database.
- Penny Levin. Statewide Strategic Control Plan for Apple Snail in Hawaii. September 2006. Request report at National Tropical Gardens, Kauai.
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Marie-Claude Arnott - Marie-Claude Arnott writes about topics that interest her, from experience and with passion.
