They're innocent looking enough. Just some marine snails in conical hats, clamped to the rocks in the intertidal zone, and doing their part for the ecosystem by keeping the fuzzy algae in check. But the saying, He ia make ka opihi - the opihi is the fish of death, serves as a reminder that picking 'opihi for their tasty flesh is a risky business. While their shape and strong muscular foot allows them to hold fast through pounding surf, the tidal surge can be downright frightening for the 'opihi harvester. There are three species of 'opihi here: the blackfoot, 'opihi makaiauli; the yellowfoot, 'opihi alinalina; and the kneecap 'opihi, or koele. The blackfoot inhabits areas closest to shore, the kneecap likes it a bit deeper, and the yellowfoot prefers it where the surf is roughest. Despite the difficulties for the collector, 'opihi numbers have declined significantly due mainly to overharvesting. A gallon of 'opihi can go for as much as $200. Presently, the 'Opihi Partnership, spearheaded by the Nature Conservancy, is working to gather baseline data about 'opihi populations near Maui and Kaho'olawe. Others are attempting to raise 'opihi using aquaculture techniques to relieve pressure on this humble limpet. On a side note, genetic studies have been underway by researchers at the Hawaii Institute of Marine Biology. They have determined that each island has it's own unique populations of 'opihi.
'Opihi are similar to other marine snails in that they have gills, a mouth tube, a head with tentacles, and a strong muscular foot. They are known to create shallow depressions in the rock which becomes their "base camp." After venturing out for feeding, they return to the snugly-fitting base camp for extra gripping power. Though they do not permanently attach themselves like barnacles do, they are the "super gluers" of the snails and may be near impossible to pry off once a failed attempt to pluck them has been made. Their low profile also helps them to remain steadfast through wave action and the ribbing of the shell allows water to drain off easily. Traditionally, 'opihi were also used as scrapers for taro, and for jewelry.
From the life-sustaining oceans, the ancients found many gifts. One was this, the Triton's Trumpet. The shell, beautiful and large, could produce a rich sound when its tip was filed down. Resounding out across the land and water, the blowing of the pu was used in various forms of communication, and often signified events of importance; for example, the arrival of royalty, or the beginning of the Makahiki season. Sacred protocols guided the use of the pu and the much cherished shells were passed down from generation to generation. In Hawaiian waters, pu were often made from the Horned Helmet (Cassis cornuta) and the Triton's Trumpet (Charonia tritonis), both large marine gastropod molluscs. Today's post features the Triton's Trumpet, the largest snail in our waters, reaching sizes up to twenty inches.
Like many sea snails, it has a shell that is spirally coiled (some snails have conical shells, and are generally referred to as limpets). The shell is ribbed and is a mottled brown and white in color. Locomotion is achieved by a strong, muscular foot, which this snail uses to pursue such prey as sea urchins and seastars. The triton's trumpet is one of the few organisms that prey on the crown-of-thorns seastar, which is notorious for feeding on and destroying corals, making our snail and important player in the marine ecosystem. Once the seastar has been captured, the triton holds it down with its strong foot. A saliva is injected which paralyzes its victim, then the snail gains easy access to the seastar's soft insides with its serrated radula, a tongue-like organ with scraping teeth. Though many sea snails are hermaphroditic, the tritons are either male or female. After internal fertilization, a cluster of eggs are laid. The buoyant young hatch and become part of the free-drifting plankton. Tritons can be found in waters from fairly shallow to about seventy-five feet deep, which makes them vulnerable to collectors. If you are lucky enough to spot this treasure, best to simply admire and leave it be, as they are becoming rarer across the globe. The corals will thank you for it.
Hihiwai, Neretina granosa, is an endemic snail that inhabits cool, clean freshwater streams. And though snails have a slow reputation, these guys are quite the travelers. They lay capsules of eggs during the summer months, which hatch and get washed downstream into the ocean. They'll spend a good part of the year at sea before recruiting back up the stream, pulling themselves along single-file with their strong, muscular foot. They have a distinctive shell: about an inch and a half in length, with a dark top dotted in red, and an orangish operculum (the lid-like structure the snail uses to close the opening of the shell when it is retracted inside). The texture and shape of the shell may vary a bit, depending on what part of the stream they inhabit; those at the lower elevations tend to have rougher shells than those further upstream. They're algae grazers, but do most of their feeding at night when they are less likely to be gobbled up by 'auku'u (night heron) and other waders. Because their life cycle requires clear, well oxygenated waters and unimpeded access from the streams to the ocean, they are now uncommon on Oahu, which has had most of it streams modified.
Today's post is intended to give voice to the native tree snails of Oahu, genus Achatinella. I hope you become as enamored as I am with these "jewels of the forest." Once abundant throughout Oahu, this genus of forty-one species of endemic, nocturnal snails has suffered from a "perfect storm" of events that has caused the loss of at least half to extinction, with the rest endangered or critically endangered. Those that remain cling to life on isolated ridges in the Ko‘olau and Wai‘anae ranges. They are small wonders indeed; all species are just around two centimeters long, with beautiful coloration and patterning that varies from species to species. As their name suggests, they are arboreal, but do little damage to the native trees that they prefer. Instead, they dine on a fungus that grows on the leaves, which may actually help the trees to photosynthesize. Achatinella young develop in eggs inside the mother, then are born live. They live for as many as ten years, but their reproductive capacity is low. For example, Achatinella mustelinadoes only produces four to seven offspring a year, and this occurring only after sexual maturity is reached, between ages three to five.
As you can imagine, their slow growth rate and fecundity would make them a vulnerable species. Recovery would be extra tough after any event that would reduce their numbers. And there have been several. For years they were over-collected for their beautiful shells. Add to that the loss of much of their native habitat to farming and other human activities. If that isn't enough, we opened the door to one of their most dreaded predators: the carnivorous rosy wolf snail. Introduced in 1955 to combat the Giant African snail, the rosy wolf snail decided that the smaller, native snails tasted a lot better. Rats have also taken their toll on the population. But instead of throwing their hands up in the air, some have come to the snail's rescue, including The Hawaiian Tree Snail Conservation Lab, whose main goal is to care for rare Hawaiian tree snails and breed them in captivity. Nine species of Achatinella are under their loving care. Also fighting the good fight is the U.S. Fish and Wildlife Service and the Oahu Army Natural Resources Program (OANRP), who are involved with the effort to build snail refuges with elaborate "exclosure" systems to keep predators out. I, for one, am grateful for their efforts to save these jewels, and for the important lesson that sometimes, big things come in small packages.
welcomes you to visit with the all the wonderful flora and fauna that we share this lovely aina with.