'Spineless' animals under threat of extinction
A fifth of animals without backbones could be at risk of extinction, say scientists.
Almost 80% of the world's species are invertebrates, meaning they lack a spinal column.
Reviewing over 12,000 species known to be threatened, biologists found that freshwater ones are most at risk.
Researchers urged for comprehensive studies of those vulnerable, to help inform conservation and protect species.
A bug's life
Insects make up a huge proportion of the living organisms on the planet; so you do not have to go far to find them yourself.
Human pressures, ranging from habitat disruption to increased temperatures, were key concerns according to the report published by the Zoological Society of London.
"We knew that roughly one fifth of vertebrates and plants were threatened with extinction, but it was not clear if this was representative of the small spineless creatures that make up the majority of life on the planet," said Professor Jonathan Baillie, ZSL's director of conservation.
"The initial findings in this report indicate that 20% of all species may be threatened.
"This is particularly concerning as we are dependent on these spineless creatures for our very survival," he said.
The majority of the world's estimated 126,000 freshwater species are invertebrates including molluscs and insects, such as dragonflies.
Of those included on the International Union for the Conservation of Nature's (IUCN's) Red List of Threatened Species, 35% are considered threatened and 131 species are listed as Extinct.Continue reading the main story
According to the ZSL review, a major issue for threatened freshwater species is water pollution from agricultural run-off, domestic sewage and industrial waste.
Damming and the removal of water, in addition to human settlements disrupting habitat, are also adding pressure for the freshwater crabs, crayfishes, molluscs, dragonflies and damselflies included in the assessment.
"They're important because they play a number of roles in eco-systems that provide humans with great benefits," said Dr. Ben Collen, head of the Indicators and Assessments unit at ZSL.
"Invertebrates are particularly good at providing things like water filtration and nutrient recycling."
The picture for marine invertebrates however is less clear. Of the species assessed by the IUCN, 25% are said to be at risk of extinction but the list only covers 1% of all described species.
"Our marine system is the least well-known system, so there's lots more work to be done in terms of discovering what's out there let alone what's happening to it," said Dr Collen.
"It's plausible that threat levels could be higher, particularly with threats that have no real boundaries like ocean acidification."
According to Dr Collen, this ongoing process, where the pH levels of the ocean rise in response to increases in atmospheric CO2, could be particularly harmful for species with external skeletons that can be eroded.
Complete global assessments of reef-building corals, lobsters, and cuttlefish have been achieved and comprehensive work on squids, octopuses, cone snails, reef building oysters and sea cucumbers is nearing completion.
But the report urged studies on other groups, including the iconic living fossils known as nautiluses.
Having survived relatively unchanged for millions of years, the animals are now the subject of concern for some as they are commonly collected for both shell curios and the pet trade.
According to ZSL, nautiluses could be particularly vulnerable to this pressure due to their low populations and slow rates of reproduction.
Chamber of secrets
Nautiluses move through the water by pumping air into and out of gas filled chambers within their shells
"From the marine species that we assessed, the ones that we're most concerned about are the ones which are exploited - things like lobsters and crabs and species of shellfish," said Dr Collen.
On land, invertebrates such as insects, molluscs and worms make up 96% of all known species.
The ZSL report describes many as having "bizarre" appearances due to their specialist adaptations to live in a particular habitats.
But scientists said that this extreme attention to habitat also heightens many species' sensitivity to change.
Forty-two percent of the species currently listed by the IUCN are considered under threat but, again, the assessed animals only represent a tiny proportion (0.3%) of the total described species.
"Invertebrates tend to go under the radar, people don't realise just how integral they are," said Dr Collen.
"All of the flowers that we see around us, many of the crops that we grow and eat are pollinated for free by insects."
"Invertebrates form quite a big part of people's diets in certain parts of the world, they form parts of systems that recycle nutrients [and] they're part of the forest systems that stores carbon."
"They are very much the architects of a lot of these eco-system services."
He told BBC Nature that the role of terrestrial invertebrates was "more immediately obvious" to us because of their proximity.
In the report, scientists have included calculations of the rarely recognised economic worth of the animals.
For example, in 2007 honeybees' role as pollinators was worth £200m to the UK economy according to The National Audit Office.
"The things that [invertebrates] do are worth billions of dollars per year to the global economy and at the moment those costs aren't factored into decisions," said Dr Collen.
"We're not genuinely thinking about what the environment provides for us so putting a monetary value on eco-system services is one way [conservationists] can help to do that."
"While the cost of saving [invertebrates] will be expensive, the cost of ignorance to their plight appears to be even greater," said Dr Collen.