By Alison Copeland, 25th February 2021
Bermuda is an archipelago of 200 islands in the subtropical western Atlantic. Around 64,000 people inhabit the 54 km2 landmass. Like many isolated islands around the world, Bermuda has relied on imported commodities throughout its 400-year history. Numerous animals and plants have been imported, intentionally and accidentally, changing Bermuda’s habitats and food chains irreversibly. It is within this context that the Department of Environment and Natural Resources endeavours to manage the recovery of Bermuda’s most threatened species, including two surviving species of the endemic land snail genus Poecilozonites.
The greater Bermuda land snail Poecilozonites bermudensis has a beautiful shell with fine stripes and chestnut bands. When fully grown, it is about the size of a UK penny. Poecilozonites bermudensis suffered a well-documented decline in the late 20th century, and was considered extinct by the mid 1990s. In 2014 it was rediscovered in the service alley behind an ice cream store. In 2017 another relict subpopulation was discovered on Port’s Island, a 6.7 ha camping ground in the Great Sound. Both of these subpopulations were isolated from introduced predators such as the rosy wolf snail Euglandina rosea.
Poecilozonites bermudensis from the alleyway were sent to the UK for breeding, with 166 sent to the Zoological Society of London in 2014 and 60 descendants of these sent to Chester Zoo in 2016. Over the last 6 years, this collaboration has resulted in the breeding of thousands of snails. The goal of this life-boat programme was always to maintain a small ex situ population, returning the majority of captive-bred snails to the wild. One goal of our study was examining how the wild snails on Port’s Island used their habitat, to guide placement of zoo-reared snails and hopefully improve the success of their reintroduction.
Another of our goals was to inform searches for other wild subpopulations. Given the incredibly unlikely location of the relict subpopulation in the urban alleyway, it is possible there are other snails waiting to be discovered. Since 2018, we have searched islands within the Great Sound and other parts of Bermuda but have not found additional live P. bermudensis.
Our work on Port’s Island showed P. bermudensis has no obvious affinity for native or introduced plant species, but it does avoid the dry needle litter beneath invasive Australian whistling pines Casuarina equisetifolia. Unfortunately, we were not able to conduct feeding observations, but we would like to conduct nocturnal feeding observations on Port’s Island to note which plant types and species the snails are eating. A recent feeding study by high school student Noah Da Silva confirmed that captive P. bermudensis did not choose the offered endemic plants over invasive ones. Knowing the food preferences of these snails will help us choose the best reintroduction sites, and allow us to plant favoured native plants where snails have already been released.
Our study on Port’s Island is a small contribution to research, monitoring and husbandry activities over the last 5 years. This ongoing collaboration between the Department of Environment and Natural Resources, Zoological Society of London, Chester Zoo and Kristiina Ovaska at Biolinx Environmental Research Ltd. has resulted in 30,250 zoo-bred Poecilozonites bermudensis being released at nine sites, mostly in 2019 and 2020. Only two sites were on mainland Bermuda, with the other seven on offshore islands in locations such as unused limestone quarries, dry stone walls, and rubble piles. The plant communities at the release sites ranged from relict Bermuda palmetto forests, to coastal woodlands dominated by broadleaf invasive trees and islands undergoing restoration with mixed invasive and indigenous woodlands.
All photos: Alison Copeland
The article Habitat preferences of the Critically Endangered greater Bermuda land snail Poecilozonites bermudensis in the wild is available in Oryx—The International Journal of Conservation.