Catastrophic invertebrate extinction

Carelia turricula

The IUCN Red List contains only 733 animal species and 99 plant species listed as extinct since around 1600, a minuscule fraction of total biodiversity, commonly estimated at 5–10 million species. This extinction rate (around 2 species/year) is of the same order of magnitude as the natural background rate based on the fossil record. Such statistics are used by environmental skeptics to downplay the loss of biodiversity.

However, among animals, the focus on birds and mammals and the proportionately negligible assessment of invertebrates masks a real crisis. Although assessment of extinction for all invertebrates is impossible, it may be possible for certain, perhaps representative, groups. Such assessments might permit broad extrapolation and more realistic evaluation of true overall extinction levels.

Mollusks are such a group. Despite the relative lack of focus on invertebrates, almost as many mollusks (311) are listed as extinct by the IUCN (2014) as all chordates combined (338); most (282) are gastropods and half of these (138) Pacific island land snails. Nonetheless, almost twice as many mollusks as are listed as extinct on the IUCN Red List are considered extinct by mollusk specialists, yet the number assessed remains a tiny fraction of the 80,000–100,000 described species and perhaps up to 200,000 real species.

Hawaiʻi has been called the “extinction capital of the world.” But, with the exception of the islands’ birds, there has been no accurate assessment of the true level of this catastrophic loss. Invertebrates constitute the vast majority of the species that make up Hawaiʻi’s formerly spectacularly diverse and unique biota. A team of researchers of the US and France focused on the most diverse group of Hawaiian land snails, the family Amastridae, of which 325 species have been recognized - all known only from Hawaiʻi. They did a rigorous assessment of extinction for this group. 

The colleagues now published their alarming results. Only 15 of these species could still be found alive, and it is estimated that the rate of extinction may have been as high as 14 percent of the fauna per decade. 

In a companion study, members of the team, in collaboration with mathematics and bioinformatics specialists at the Pierre and Marie Curie University in Paris, addressed invertebrate extinction globally. Since the 1980s, many biologists have concluded that the earth is in the midst of a massive biodiversity extinction crisis caused by human activities. Yet only around 800 of the planet’s 1.9 million known species are officially recorded as extinct by the IUCN Red List. Skeptics have therefore asked, “Is there really a crisis?"

We showed, based on extrapolation from a random sample of land snail species from all over the world, and via two independent approaches, that we may already have lost 7 percent (130,000 extinctions) of all the animal species on Earth.

This loss far exceeds official numbers that are primarily based on assessments of birds and mammals and essentially excludes invertebrates, even though invertebrates constitute roughly 99 percent of known biodiversity.

Based on their findings, the researchers show that the biodiversity crisis is real and stressed the need to include assessments of invertebrates in order to obtain a more realistic picture of the current situation, known widely as the sixth mass extinction.

h/t Mario Thomas