World Wetlands Day too late for spray toad?

02 February 2010

Today is World Wetlands Day, and the Natural History Museum’s Species of the day highlights a species whose survival is so closely linked to a specific wetland that changes in its habitat mean it is now extinct in the wild.

As its name suggests, the Kihansi spray toad lived only in very small areas that are covered by spray from the Kihansi waterfall in Tanzania. Over time it has evolved to live in this very specific habitat and has even evolved flaps over its nostrils to help it thrive.

Impact of dam
Kihansi Fall in Tanzania

Kihansi Fall in Tanzania © Alan Channing

In 2000, the water flow in the area was drastically reduced after a large hydroelectric dam was built. As well as changing the type of vegetation that thrived there, the resulting massive drop in the volume of spray meant conditions were no longer suitable for the toad.

Drop in numbers

The highest counts of individual Kihansi spray toads found around 20,000 on dates before and shortly after the dam was constructed. Then in January 2004 only 3 were seen, with the calls of 2 males heard. In 2005, there was one unconfirmed sighting and since then there have been no sightings in the wild. It has therefore been declared extinct in the wild by the IUCN (International Union for Conservation of Nature).

Wet spray zone at Kihansi Fall with sprinkler system

Wet spray zone at Kihansi Fall with sprinkler system © Alan Channing

'I was one of four authors who wrote the original description of the Kihansi spray toad in 1998,' says Natural History Museum frog expert Barry Clarke, who chose the amphibian for Species of the Day.

'We knew then about the hyrdroelectric power scheme putting the toad under threat. 

'In a mere 7 years, the toad’s numbers have gone from an estimated 20,000 to a probable 0 due to human activities (power generation and pesticides) and disease (chytrid fungus). 

'The American ecologist Rachel Carson predicted that pesticide use would bring about "Silent Springs" among birds in the States. 

'The Kihansi spray toad’s Silent Spring arrived in 2005 in the Kihansi Gorge - no male toad has been heard calling since then.'

Tiny toad and toadlets
Kihansi spray toad adult and juvenile

Kihansi spray toad adult and juvenile © Alan Channing

The Kihansi spray toad, Nectophrynoides asperginis, is a tiny amphibian with adults typically growing to about 15-20mm in length. Most people think toads produce eggs that hatch into tadpoles, but the spray toad hatches froglets that are about 5mm long.

Vulnerable species

The Kihansi spray toad highlights how vulnerable different species can be to changes in habitat. Humans are the main cause of habitat change, which is a major threat to biological diversity (biodiversity).

Current rates of biodiversity loss, some scientists say, are on a level with the mass extinctions of the dinosaurs, and this year biodiversity is highlighted in the UN’s International Year of Biodiversity.

Irreversible changes?

The Kihansi spray toad also highlights how difficult it can be to try and bring back species after they are extinct in the wild. After the dam construction, an artificial sprinkler system was introduced to the area. However, the toad’s numbers never recovered.

A few hundred individuals were taken into captivity and are now bred in the USA. It is hoped that some may be introduced back into the wild.

Wetlands

As well as providing essential eco-services like coastal protection and nurseries for fish, wetlands are home to a huge variety of biodiversity.

Humans as well as plants and animals depend on wetland habitats and the annual World Wetlands Day aims to raise awareness of their value.

Ahmed Djoghlaf, Executive Secretary of the Convention on Biological Diversity, in his message for World Wetlands Day 2010, talks about how caring for wetlands will also help us tackle the effects of climate change.

Species of the day

The Museum is celebrating the UN's 2010 International Year of Biodiversity with its Species of the day. All 365 species are chosen and written by Museum scientists, highlighting the world-class research and collections at the Museum.

Share this