Hawai'i's depleted natural treasure chest: oh, what we've lost

There were many jewels in Hawai`i’s natural treasure chest, and today, the rarest of these are the land snails.

The Hawaiian archipelago's natural legacy was a splendid array—forest birds in all the colors of the rainbow, flashing reef fishes found nowhere else on the planet, and the stunning silver and crimson, gold and purple hues of the flowers.

In that array, the land snails may not stand out, although there were once hundreds of species. Today, they are recognized for their singular rarity.

(Image: One of the last remaining amastrid land snail species on O'ahu, Laminella sanguinea, in the Waianae Mountains. Credit: Kenneth A. Hayes, University of Hawai’i)

There were once 325 species of Amastridae that were unique to these islands. Today, only 15 can be found.. An extinction rate of more than 95 percent.

This tally was published in the journal "Conservation Biology" by researchers from the University of Hawai`i’s  Pacific Biosciences Research Center, Bishop Museum, and national and international teams. It is entitled “Extinction in a hyperdiverse endemic Hawaiian land snail family and implications for the underestimation of invertebrate extinction."

Of the 325, only 33 are officially listed as extinct on the International Union for Conservation of Nature (IUCN) Red List. But that’s because the paperwork can’t keep up with the rate of extinction.

“Of the 325 Amastridae species, 43 were originally described as fossil or subfossil and were assumed to be extinct. Of the remaining 282, we evaluated 88 as extinct and 15 as extant and determined that 179 species had insufficient evidence of extinction (though most are probably extinct),” the authors wrote.

When scientists write about extinction crises, they’re often mostly talking about vertebrates—the birds and mammals, fishes and reptiles. But  to miss the invertebrates is to miss a lot. 

“Invertebrates have received much less attention despite their constituting as much as 99% of animal species richness,” the authors write.

To assess the status of Amastridae, the researchers studied collections in the Bishop Museum and then went into the field, looking t 481 potential snail habitats throughout the Islands.

“At many sites, we collected leaf litter and soil, which we searched under a microscope for especially small snails. This is the most comprehensive and temporally focused land snail survey effort ever undertaken in the Islands,” they wrote.

They found just the 15. If you’re interested in the list, here it is.

“These 15  species  were  recorded  during  recent field work, including our field work specifically targeting amastrids in the Waianae Mountains of Oahu (Amastra cylindrica , Amastra micans , Amastra spirizona , Laminella sanguinea , Leptachatina cerealis , Leptachatina crystallina , Leptachatina gracilis , Leptachatina gummea , Leptachatina persubtilis, Leptachatina popouwelensis ), on Kauai (Leptachatina cuneata , Leptachatina cylindrata), on Maui (Laminella aspera , Leptachatina nitida), and on the island of Hawaii ( Leptachatina lepida),"

What could have caused this extinction catastrophe? Not just one cause. The authors make a list.

Humans (early Hawaiians) arrived and launched habitat destruction. They also brought Polynesian rats, which ate some snails but weren’t as big an issue as later introductions. 

Then came Europeans with the next big wave of extinctions, caused by pigs, goats, and other species. Polynesian rats and black rats arrived and were big predators of snails. 

Massive land clearing for ranching and plantation agriculture added to the toll, along with introduced predatory snails, and ants, and competition from introduced non-predatory snails.

Some of the same authors also participated in another paper that looked at extinction of poorly known life forms globally. Again, it suggests the extinction rate in modern times is far higher than we’ve believed. 

 

Among its points: “Mammals and birds provide the most robust data, because the status of almost all has been assessed. Invertebrates constitute over 99% of species diversity, but the status of only a tiny fraction has been assessed, thereby dramatically underestimating overall levels of extinction. Using data on terrestrial invertebrates, this study estimates that we may already have lost 7% of the species on Earth and that the biodiversity crisis is real.”

© Jan TenBruggencate 2015