New book on `opae`ula and its natural habitat hopes to inspire conservation
A newly released book, “Hawaiian Anchialine Pools: Windows to a Hidden World,” describes how Hawai`i is blessed with a multitude of natural resources. “Even in some seemingly barren areas along the shoreline, there exists a unique aquatic ecosystem underfoot.”
The book’s authors, one current and two former aquatic biologists in the state Department of Land and Natural Resources' Division of Aquatic Resources (DAR) introduce readers to anchialine pools; dark, subterranean, water-filled caverns and crevices inhabited by rare shrimp and other unusual aquatic animals.
Annette Tagawa, a current DAR aquatic biologist, explains, “Anchialine pools occur worldwide, but the largest concentration of them can be found here in Hawai`i. They happen in a variety of forms, including ancient limestone sinkholes on the Ewa Plain on Oahu, a massive bomb crater on the Kaho`olawe shoreline, gold and emerald green pools at `Ahihi-Kina`u on Maui and the Kona coastline dotted with more than 600 of the State’s 700 anchialine pools on Hawai`i Island.”
The book chronicles the formation, biology and threats to anchialine pools in Hawai`i. These pools have no surface connection to the ocean, with all connections underground via cracks or crevices in limestone or lava. The focus of the book is on aquatic animals.
Author Thomas Iwai, a retired DAR aquatic biologist comments, “We included a complete chapter we call Eight Shrimp and a Crab. Readers can learn about the tiny, one-half-inch long shrimp (`opae`ula) found nowhere else in the world. We detail the distribution, lifestyle and interesting facts about these shrimp, other shrimp species, and a crab only found in anchialine pools in the `Ahihi-Kina`u Natural Area Reserve.”
As a hobby breeder of `opae`ula, I was fascinated by the book and happy to read it. I might have about 1,000 shrimp now in two tanks. It's taken me about five years to get them to breed and stabilize their populations.
What I found most interesting was a section discussing the genetic differences between shrimp populations on different islands, likely due to the geographic isolation. Quoting an Auburn University study, the book says there are a total of eight variances*: three distinct lineages on Hawaii Island, two on Maui, and three on Oahu. (*If you consider a 5% mitochindrial DNA difference enough to qualify as a new lineage.)
Tagawa says it's also the most fascinating information for her and her co-authors, too. "How did these animals get to the Hawaiian Islands? The distribution of some of these species are a real mystery as to how the same species can occur here and somewhere else as far away as the Sinai Peninsula with none of the same species found between here and there. A lot more research needs to be done on the biology and life history of each of the anchialine pool species to solve the mystery in answering some of these questions," she states.
Co-author Mike Yamamoto, also a retired DAR aquatic biologists adds, “Anchialine pools were impacted almost as soon as the first Polynesians settled in our islands more than 1,000 years ago. Low salinity pools were used as sources of drinking water, or for bathing. High salinity pools were used to hold or culture fish."
"None of these uses had long-lasting impacts on anticline pools. Today, however, the threats posted to these ecosystems by loss or degredation of habitat; introduction and spread of exotic species; and over harvesting of `opae`ula for the ornamental pet trade can be irreversible," he concludes. The book goes into enlightening- but depressing- detail on the big challenges anchilaline ponds face.
The protection of areas like `Ahihi-Kina‘u in 1973 and the addition of the Kalaeloa Unit to the U.S. Fish and Wildlife Service Pearl Harbor National Wildlife Refuge in 2001 helped protect fragile anchialine pools. At Kalaeloa, twelve sinkholes were excavated and restored. Today these anchialine pools host healthy populations of `opae`ula and other native creatures.
"Anchialine pools can be both natural and man-made. Our islands have been so developed that we may never restore a lot of the anchialine pools to their once pristine condition, but we can restore some of them to where at least they are healthy enough to sustain the aquatic life like the 'opae 'ula. Other than the natural decline or senescence of the anchialine pools, we're fortunate that the best examples of anchialine pools are preserved on Hawaii Island in the Manuka Natural Area Reserve where all of the rarer shrimp species are found, and on Maui where the most gorgeous anchialine pools are found in the Ahihi-Kinau Natural Area Reserve which also house some of the rarer species and along with the only anchialine crab ever described. On Oahu, the best complex of anchialine pools are found in the Kalaeloa area which were restored and are protected in the Pearl Harbor National Wildlife Refuge. The National Parks on Hawaii Island also provide some refuge for the anchialine pools on their properties," continues Tagawa.
"As for the rest of the anchialine pools, the ones with alien species in them such as the tilapia or topminnows would be the hardest to restore because of the heavy restrictions on the use of rotenone which is a piscicide or fish poison that would kill the fish but not the invertebrates. Before its restricted use, scientists on the Big Island of Hawaii used rotenone and successfully eradicated the alien fish in the anchialine pools, restoring them to good health for the `opae `ula. There is some work being done today on looking at some native plants that Hawaiians used to immobilize fish for capture."
The authors neither espouse or discourage people from cultivating `opae`ula as pets, and does give recommendations on how to set up your tank, should you find yourself wanting to keep them. I thoroughly enjoy mine, not least because they take absolutely no work to maintain save a monthly water top-off to my tanks.
Tagawa admits she has one tank at home "and a few jars here in the office. Sometimes we make a few jars as a donation for Aloha United Way and Hawaii Foodbank to raise funds."
"Overharvesting for the pet trade is a concern and the next step that DAR will be working on is a management plan for the anchialine animals and their ecosystem. We highly encourage businesses to culture the `opae `ula like you've been doing, to supply the pet industry with its supplies," she recommends.
If someone gives you `opae`ula as a pet and you don’t want it, biologists advise you to not release it back into an anchialine pool, as that may generate misleading data for scientists who monitor the pools and analyze the DNA of different populations of `opae`ula.
The 100-page-long book Hawaiian Anchialine Pools: Windows to a Hidden World is available at Borders and Native Books and Beautiful Things or at http://www.mutualpublishing.com/shop/index.php?l=product_detail&p=649.