Unique Habitat for Benthic Foraminifera in Subtidal Blue Holes on Carbonate Platforms

Abstract

Dissolution of carbonate platforms, like The Bahamas, throughout Quaternary sea-level oscillations have created mature karst landscapes that can include sinkholes and off-shore blue holes. These karst features are flooded by saline oceanic waters and meteoric-influenced groundwaters, which creates unique groundwater environments and ecosystems. Little is known about the modern benthic meiofauna, like foraminifera, in these environments or how internal hydrographic characteristics of salinity, dissolved oxygen, or pH may influence benthic habitat viability. Here we compare the total benthic foraminiferal distributions in sediment-water interface samples collected from <2 m water depth on the carbonate tidal flats, and the two subtidal blue holes Freshwater River Blue Hole and Meredith’s Blue Hole, on the leeward margin of Great Abaco Island, The Bahamas. All samples are dominated by miliolid foraminifera (i.e., Quinqueloculina and Triloculina), yet notable differences emerge in the secondary taxa between these two environments that allows identification of two assemblages: a Carbonate Tidal Flats Assemblage (CTFA) vs. a Blue Hole Assemblage (BHA). The CTFA includes abundant common shallow-water lagoon foraminifera (e.g., Peneroplis, Rosalina, Rotorbis), while the BHA has higher proportions of foraminifera that are known to tolerate stressful environmental conditions of brackish and dysoxic waters elsewhere (e.g., Pseudoeponides, Cribroelphidium, Ammonia). We also observe how the hydrographic differences between subtidal blue holes can promote different benthic habitats for foraminifera, and this is observed through differences in both agglutinated and hyaline fauna. The unique hydrographic conditions in subtidal blue holes make them great laboratories for assessing the response of benthic foraminiferal communities to extreme environmental conditions (e.g., low pH, dysoxia).

More Frequent Hurricane Passage Across the Bahamian Archipelago During the Little Ice Age

“…Based on a qualitative local survey, sediment around LDBH and TURT on the tidal flats are primarily inorganic calcite and aragonite mud, fragmented organic matter (OM) from surrounding dwarf red mangroves ( Rhizophora mangle ), and coarser sediment (>63 μm) composed primarily of skeletal material and peloids. These textures are consistent with similar environments in Andros (Maloof & Grotzinger, 2012; Milliman et al., 1993; Rankey, 2002; Rankey et al., 2004; Shinn et al., 1969; Wallace et al., 2019), Crooked Island (Berkeley & Rankey, 2012), Turks and Caicos (Kaczmarek & Hasiuk, 2008; Tedesco & Aller, 1997; Trower et al., 2018, 2019; Wanless et al., 1988a, 1988b), and Abaco (Little et al., 2021; van Hengstum et al., 2020). Holocene sediment accumulation on Bahamian carbonate tidal flats is typically <3 m, and consists of thin transgressive facies (paleosols, mangrove peat, limnetic faces) overlain by aragonitic mud that is produced by calcareous green algae (e.g., Halimeda , Penicillus , and Udotea ).…”

First insights into an exceptionally deep blue hole in the Western Caribbean: The Taam ja’ Blue Hole

“…Blue holes, submarine caves, and sinkholes are common features on coastal karst platforms around the world, including the Caribbean Sea and the Yucatań Peninsula, that they contain unique environments (Mylroie, 2008;Mylroie, 2013;van Hengstum et al, 2011;Little et al, 2021). Karstic systems are formed from the dissolution of limestone.…”

“…Blue holes in The Bahamas (Mylroie and Mylroie, 2007;Tamalavage et al, 2018;Little et al, 2021) and in the western Caribbean are also notable due to their remarkable structures, such as Dean's Blue Hole in The Bahamas (~202 m deep) (Vimpere, 2017) or the Great Blue Hole off the coasts of Belize (~125 m deep) (Jones and Dill, 2002;Gischler et al, 2013;Schmitt et al, 2021). These karst features are relevant to marine scientific research as they represent repositories of paleoenvironmental and paleoclimate information that enhance the understanding of environmental (Husson et al, 2018) and geologic processes (van Hengstum et al, 2020), provide support for modeling the mixing zone (Bottrell et al, 1991), the connectivity of aquifers (Martin et al, 2012) and the water origin of these hydrogeologic systems (Smith et al, 2021).…”

“…These karst features are relevant to marine scientific research as they represent repositories of paleoenvironmental and paleoclimate information that enhance the understanding of environmental (Husson et al, 2018) and geologic processes (van Hengstum et al, 2020), provide support for modeling the mixing zone (Bottrell et al, 1991), the connectivity of aquifers (Martin et al, 2012) and the water origin of these hydrogeologic systems (Smith et al, 2021). They offer windows into regional hydroclimate variability (Winkler et al, 2020;Wallace et al, 2021) and are galleries to observe subfossil benthic meiofauna and modern biodiversity (van Hengstum et al, 2011;Gonzalez et al, 2020;Baremore et al, 2021;Little et al, 2021).…”