Development of anchialine cave habitats and karst subterranean estuaries since the last ice age

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 21 st century sea-level rise.

Revising evidence of hurricane strikes on Abaco Island (The Bahamas) over the last 700 years

“…As discussed below, the new longer sediment cores collected from the center of TPBH do not contain B. domingensis shells, and the cores document a constant sedimentation rate in TPBH (1.3 cm yr -1 ) spanning the last 700 years using an age model built with plant macrofossils. Elsewhere, B. domingensis lives attached to reefs and underwater cave walls, and the shell experiences post-mortem detachment and incorporation into the sediment record 40,41 . Three relevant points emerge: (i) it is likely that TPBH-C1 was collected from a cave area (i.e., underneath a ceiling, Supplementary Fig.…”

Habitat Partitioning in the Marine Sector of Karst Subterranean Estuaries and Bermuda's Marine Caves: Benthic Foraminiferal Evidence

“…On the carbonate platforms of The Bahamas, for example, landmass area and mean annual rainfall alone can be used to predict meteoric lens thickness on different islands (Cant and Weech, 1986). Bermuda does have five modest meteoric lenses located in geologically-recent lithologies (Vacher, 1978), but these are not located in the primary area of cave development on the isthmus between Castle Harbor and Harrington Sound (Walsingham Formation, highest porosity: Land et al, 1967). In northeastern Bermuda where the Walsingham Formation is located, only a thin (<50 cm), seasonal and ephemeral brackish cap occurs in some cave-collapse entrances, and a limited meteoric lens can form near the "Letterbox" area of Green Bay Cave that does not directly contact the sediment-water interface, or discharge water through marine exit into Harrington Sound (see map in van Hengstum and Scott, 2011).…”

Carbon Cycling in the World's Deepest Blue Hole

“…Marine blue holes are distinguished from other onshore anchialine caves, such as sinkholes or cenotes, which are inland voids and usually contain fresh water (Bishop et al, 2015). These onshore anchialine caves are connected to an aquifer and exhibit stratification characterized by a meteoric lens in the upper layer, mixing zone, and anoxic saline groundwater (Beddows et al, 2007;Brankovits et al, 2017;Martin et al, 2012;Mylroie et al, 1995;van Hengstum et al, 2019). They can also have connections to the outer sea through lateral cave cracks (Bishop et al, 2015;Brankovits et al, 2017;Martin et al, 2012).…”

“…Marine blue holes are large water‐filled marine caverns, formed by karst processes, that is, dissolution and/or a fracture‐type collapse of carbonate rocks, under the influence of global sea level rise and fall (Bishop et al, ; Gischler, ; Martin et al, ; Mylroie et al, ; Schwabe & Herbert, ; van Hengstum et al, , ). They form as nearshore karst caves in carbonate rocks during low sea level, which can be submerged at sea level highstand, depending on proximity to shoreline and connection to the aquifer (Becking et al, ; Smith et al, ; van Hengstum et al, , ). Generally, marine blue holes are roughly circular, steep‐walled, and open to the surface.…”

“…Some prominent examples of blue holes with anoxic bottom waters are the Great Blue Hole, Belize (Gischler et al, ), South Andros Black Hole, Bahamas (Schwabe & Herbert, ), blue holes in the Great Barrier Reef of Australia (Backshall et al, ), and the Clipperton Atoll blue hole, Île de Clipperto (Sachet, ). Blue holes can also preserve scientifically significant sedimentary archives of environmental change and hurricanes (e.g., Gischler et al, ; Tamalavage et al, ; Collins et al, ; Brown et al, ; van Hengstum et al, , , , ; Wallace et al, ) and may serve as natural laboratories for studying extreme chemicophysical gradients in aquatic ecosystems.…”