Tuesday, December 8, 2020

Nihoa Island: Conservation crucible protects the last of a genus


Swimming in the clear, 60-foot waters in the lee of Nihoa’s western cliffs, I came across a floating leafed branch blown off the island in high winds.


It was, of course, a native plant: `aweoweo, an edible amaranth that is found on all the small islands from Nihoa to Laysan and Lisianski.


Little Nihoa rises abruptly from the sea 160 miles west of Kaua’i and Niihau. It is a fragment of an old, larger volcanic island, with steep basalt cliffs on three sides, a single sandy beach, and small forests of native loulu fan palms.


The `aweoweo is in good company. Nihoa is also home to many other native species, from the Hawaiian monk seals that sometimes litter the white sand beach by the dozens, to the native Nihoa miller birds that perch in the low bushes, to the native clumping grass, Eragrostis variabilis.


And, it turns out, on the blades of the grass, known in Hawaii as kawelu, there is an exceedingly rare tiny snail found only on this little island. The snail has been known to science for a century, but has only now been given a name.


Endodonta christenseni, photo by David Sischo


It is believed to be the last survivor of the 11 species of Endodonta snails of the Hawaiian Islands.


The story of the Nihoa snail was published in the October 15 issue of the Bishop Museum Occasional Papers, under the title, “The last known Endodonta species? Endodonta christenseni sp. nov.”  


The authors are Kenneth Hayes, John Slapcinsky, David Sischo, Jaynee Kim and Norine Yeung.


They write the snail’s story with a passion many might find unusual in scientific literature:


“Here we finally give what we think is the last Endodonta species a name and describe it using an integrative taxonomic approach. 


“In describing this last Endodonta species, our hope is to inspire increased awareness and appreciation that facilitates and motivates conservation for this species and all the other undiscovered and unnamed species threatened with extinction. 


“Unless protection of this species is implemented, it may be extinct within the next decade and we will lose the last of a lineage that existed for millions of years, and the stories it could tell.”


The snail was discovered on an expedition to Nihoa in 1923, and seen again periodically since then, including by land snail expert Carl Christensen, after whom it was named. 


There’s not much to this snail. It is described as pea-sized. Viewed from the side, it is shaped like a flying saucer. The shell has a complex pattern of striped whorls in browns and tans. And when it’s traveling, the little snail’s two antennae stretch out ahead of it.


The authors say it probably spends most of its time in the moist hearts of the grass clumps, and feeds on films of fungus that form on dead leaves. 


In a press release, co-author Yeung said that there remains hope that other rare species exist and can be protected and saved. “We need to act quickly and decisively if we are to beat the extinction clock that ticks louder with each passing day,” she said.


The paper emphasizes how critical the conservation challenge is: "Despite 15 years of sampling across more than 1000 sites throughout the Hawaiian archipelago, none of the 11 previously described species of Endodonta has been observed in our studies and it is likely that all are extinct. Endodonta christenseni sp. nov. is the only known extant member of the genus and quite possibly the last."


One ray of good news is that related land snails have been raised and increased number in captivity, and it is possible that the Nihoa snail could be re-introduced to parts of the island where it has disappeared due to human-caused wildfire during the 1800s.


© Jan TenBruggencate 2020

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