Bermuda’s Walsingham Caves: A Global Hotspot for Anchialine Stygobionts

Abstract

Bermuda is an Eocene age volcanic island in the western North Atlantic, entirely capped by Pleistocene eolian limestone. The oldest and most highly karstified limestone is a 2 km2 outcrop of the Walsingham Formation containing most of the island’s 150+ caves. Extensive networks of submerged cave passageways, flooded by saltwater, extend under the island. In the early 1980s, cave divers initially discovered an exceptionally rich and diverse anchialine community inhabiting deeper sections of the caves. The fauna inhabiting caves in the Walsingham Tract consists of 78 described species of cave-dwelling invertebrates, including 63 stygobionts and 15 stygophiles. Thus, it represents one of the world’s top hotspots of subterranean biodiversity. Of the anchialine fauna, 65 of the 78 species are endemic to Bermuda, while 66 of the 78 are crustaceans. The majority of the cave species are limited in their distribution to just one or only a few adjacent caves. Due to Bermuda’s high population density, water pollution, construction, limestone quarries, and trash dumping produce severe pressures on cave fauna and groundwater health. Consequently, the IUCN Red List includes 25 of Bermuda’s stygobiont species as critically endangered.

Global Subterranean Biodiversity: A Unique Pattern

“…What was accessible for sampling in these four sites was quite different. Movile Cave is only 240 m long but connected to a much larger, deeper aquifer of between 50 and 100 km 2 [21]; Walsingham Caves comprise a large number of small caves located in a 4 by 0.5 km isolated band of limestone-the Walsingham Tract [22]. The San Marcos Artesian Well samples the 900,000 km 2 Edwards/Trinity Aquifer, and the two Robe River wells (about 1 km apart) sample the iron-rich Robe alluvial aquifer (of unknown size) [23].…”

“…There is no completely satisfactory terminology for troglomorphic cave populations of species with non-troglomorphic populations outside of caves, like those of Astyanax mexicanus [55]. The statuses of species that have deep-soil species facies, those in Robe River boreholes [23], and of species with deep sea populations, those from Walsingham Caves [22] are disputable because their connection with soil (Robe River) or marine environment (Walsingham Caves) is unknown. These and other problems have led some researchers to reject the terminology or at least reduce its usage [57,58].…”

“…Among aquatic species, these include parasites and commensals, Protista, Rotifera, Nematoda, Nemertea, Oligochaeta and water mites. For example, subterranean-limited Protista have been reported from Planina Postojna Cave System [40] and Walsingham Caves [22], but have been searched for in few of the other caves (but see [66]). Only three contributions report on subterranean rotifers-Ojo Guareña [32], Robe Valley [23] and Cent Fonts [12,67]-and only for the Robe Valley is it claimed that the rotifers are stygobiotic.…”

A new species of Eupelte (Copepoda: Harpacticoida: Peltidiidae) from Anchialine caves in Bermuda

“…1). Cherry Pit is adjacent and likely connected to the Palm Cave System, a complex series of submerged caverns and collapsed entrances (Iliffe & Calderón-Gutiérrez, 2021). It is located midway across the isthmus separating Harrington Sound and Castle Harbour.…”

“…Bermuda represents an exceptional global hotspot for anchialine cave biodiversity (Iliffe & Calderón-Gutiérrez, 2021) with the Walsingham Cave System containing 78 described anchialine species of which 20 are copepods and five harpacticoids. It is not clear why Bermuda has the highest level of anchialine species, although possible explanations include the island's isolated mid-Atlantic location, Pleistocene age limestone, and fluctuating sea levels which alternately submerged and exposed the anchialine caves.…”