Abstract
Extinction models generally predict that coastal and neritic fauna benefit during sea-level rise (transgression), whereas sea-level retreat (regression) diminishes their suitable habitat area and promotes evolutionary bottlenecks. Sea-level change also impacts terrestrial island biogeography, but it remains a challenge to evidence how sea-level rise impacts aquatic island biogeography, especially in the subterranean realm. Karst subterranean estuaries (KSEs) occur globally on carbonate islands and platforms, and they are populated by globally-dispersed, ancient ecosystems (termed anchialine). Anchialine fauna currently exhibit a disjunct biogeography that cannot be completely explained by plate tectonic-imposed vicariance. Here we provide evidence that anchialine ecosystems can experience evolutionary bottlenecks caused by habitat reduction during transgression events. Marine-adapted anchialine fauna benefit from habitat expansion during transgressions, but fresh- and brackish-adapted fauna must emigrate, evolve to accommodate local habitat changes, or are regionally eliminated. Phanerozoic transgressions relative to long-term changes in subsidence and relief of regional lithology must be considered for explaining biogeography, evolution, local extirpation or complete extinction of anchialine fauna. Despite the omission of this entire category of environments and animals in climate change risk assessments, the results indicate that anchialine fauna on low-lying islands and platforms that depend upon meteoric groundwater are vulnerable to habitat changes caused by 21st century sea-level rise.
Highlights
Sea-level oscillations during the last 500 million years (Phanerozic Eon) have impacted marine and terrestrial island biogeography and evolution by modifying habitat availability and opportunities for organismal gene flow[1,2,3]
Subterranean estuaries are analogous to other coastal estuaries by having an upper meteoric water mass of varying salinity buoyed on a saline groundwater mass below[14,15]
In the late 20th century did technical scuba diving procedures allow human exploration of Karst subterranean estuaries (KSEs) through flooded caves, which lead to the discovery of their unique ecosystems, fauna, and habitats that are prefaced with the adjective ‘anchialine’[21]
Summary
Was dominant at first, but the high sedimentation rate at this site indicates these assemblages rapidly transitioned to Entzia-dominated assemblages In modern settings, these benthic foraminifera dominate subtidal anchialine habitats that are flooded by a low salinity (oligohaline) meteoric lens on the Yucatan Peninsula (Tiphotrocha, Entzia)[42,57], and subtidal marine settings in Bermuda dominated by terrestrial organic carbon (Bolivina)[58]. The Iron-rich carbonate deposits provide evidence for benthic habitats becoming flooded with saline groundwater, whereby upwelling anoxic saline groundwater was mixing with the overlying freshwater in a paleo mixing zone [base of cores 3, 15 and 9, and intercalated within cores 4,10, 11 and 9 (Fig. 3)] These deposits were not recovered from shallower sampling locales (Supplementary Table S1). Unlike the terra rosa paleosols, these iron-rich carbonate sediments have a distinctive orange-hue
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
