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A recent study has revealed that elevated salt levels in water are likely a significant barrier to the recovery of one of the UK’s rarest amphibians, the natterjack toad. The research points out that salinity in former breeding ponds may render these habitats inhospitable, thus threatening the toad’s survival and growth. This issue is of particular concern, as the natterjack toad now occupies only a few isolated locations.
In Scotland, the natterjack toad’s last known populations are found along the Solway Coast, notably at the RSPB’s Mersehead Reserve near Southerness. Scientists examined water samples from various sites across southwest Scotland, including areas where the toads had previously bred but have since disappeared. Their findings showed that increased salt concentrations were associated with poor hatching success, stunted development, and reduced toad size.
Leading the investigation, Dr Frances Orton, an environmental biologist at Edinburgh’s Heriot-Watt University, explained the motivation behind the study. She said, “Natterjack toads have declined across the UK, not just in Scotland. We wanted to find out why these tiny toads were surviving in the nature reserve in Dumfries and Galloway, but had disappeared from sites along that coast.” By gathering anecdotal evidence from local farmers and wildlife groups, the team identified abandoned breeding ponds for further analysis.
The research included measuring temperature, pH, and salinity in waters from sites such as Mersehead, where toads still exist, and other locations where they no longer do. The toad embryos were then exposed to water from each site. Dr Orton reported, “Some of the former breeding sites had such a high level of salinity that no embryos survived to hatching.” In cases where the salt levels were lower but still elevated, the toads were smaller. She highlighted the importance of size, stating, “That doesn’t sound like a big deal, but when you’re a frog, size really does matter. 95% of tadpoles are eaten by predators. For the 5% that make it to the next stage of development, they need to be as big as possible for a chance at survival.”
The study’s outcomes have important implications for conservation strategies. Dr Orton emphasized that traditional restoration efforts focusing mainly on improving terrestrial habitats such as scrub clearance or vegetation control, although still necessary, will not be sufficient unless salinity issues in the water are addressed. She warned, “Until now, a lot of natterjack toad restoration efforts have focused on improving terrestrial habitat, like clearing scrub or controlling vegetation … That’s still important, but now we know that unless the salinity of the water is tackled, the tiny toads will have no chance of survival.”
Highlighting the urgency of the matter, Dr Orton commented on the broader significance of amphibian declines worldwide. “Amphibians are the fastest-declining vertebrate group globally,” she said. “They’ve been around for 350 million years, but now species like the natterjack toad are disappearing, quickly.” She noted their vital role in ecosystems, both as predators and prey, and added, “Natterjack toads are on the verge of extinction and it’s vital we understand ways to protect and boost the populations that remain.” The study was conducted with support from the Carnegie Trust and NatureScot and involved seven sites in Dumfries and Galloway
Read the full article from The BBC here: Read More
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