Inland blue holes of The Bahamas – chemistry and biology in a unique aquatic environment

Abstract

While lake systems in temperate regions have been extensively studied, tropical and subtropical systems have received less attention. Here, we describe the water chemistry and biota of ten inland blue holes on Andros Island, The Bahamas, representative of the morphological, abiotic, and biotic variation among Androsian inland blue holes. The majority of the studied blue holes were vertically stratified with oxic freshwater overlying anoxic saline groundwater of marine origin. Water chemistry (e.g.total phosphorus and nitrogen) in shallow waters was similar among blue holes, while turbidity and water color varied. Presence of hydrogen sulfide and reduced iron in and below the halocline indicate reducing conditions in all stratified blue holes. The biota above the halocline was also similar among blue holes with a few taxa dominating the phytoplankton community, and the zooplankton community consisting of copepods and rotifers. The Bahamas mosquitofish (Gambusia hubbsi) was present in all investigated blue holes, often accompanied by other small planktivorous fish, while the piscivorous bigmouth sleeper (Gobiomorus dormitor) was only present in some of the blue holes. Our field study reinforces that inland blue holes are highly interesting for biogeochemical research, and provide naturally replicated systems for evolu- tionary studies.

Changes in Organic Matter Deposition Can Impact Benthic Marine Meiofauna in Karst Subterranean Estuaries

“…Although the proportion of 13 C-depleted OM has decreased over time, its sources continued to contribute to the sediments throughout the record (Figure 4). These patterns are most likely a result of mixed OM supply from the mangroves or other vegetation surrounding the terrestrial opening, similar to observations in the Yucatán Peninsula (van Hengstum et al, 2010;Collins et al, 2015), The Bahamas (Tamalavage et al, 2018;Björnerås et al, 2020), andBermuda (van Hengstum et al, 2011;Little and van Hengstum, 2019). Globally, mangrove ecosystems are important carbon reservoirs (Donato et al, 2011) and a major source of organic carbon to the oceans (Dittmar et al, 2006;Maher et al, 2013), and they clearly contribute considerable organic carbon to tropical KSEs.…”

Predation and Resource Availability Interact to Drive Life-History Evolution in an Adaptive Radiation of Livebearing Fish

“…Inland blue holes (water-filled, vertical caves) on Andros Island, The Bahamas were colonized by Bahamas mosquitofish during the past ∼15,000 years, harbor relatively simple fish and plankton communities (e.g., typically 1-3 fish species, 1-3 dominant zooplankton species), appear very stable through time, and are quite isolated from one another in most cases (Fairbanks, 1989;Langerhans and Gifford, 2009;Heinen-Kay and Langerhans, 2013;Riesch et al, 2013;Björnerås et al, 2020;Sha et al, 2021). The post-Pleistocene radiation of Bahamas mosquitofish in these blue holes is largely characterized by predator-driven multi-trait adaptation (e.g., Langerhans et al, 2007;Heinen-Kay and Langerhans, 2013;Anderson and Langerhans, 2015;Heinen-Kay et al, 2015;Fowler et al, 2018;Langerhans, 2018), although resource availability appears to also play some role in phenotypic differentiation (e.g., Martin et al, 2014;Riesch et al, 2020).…”

“…These small, livebearing fish inhabit blue holes that differ considerably in predation risk (presence/absence of predatory fish) and resource availability (continuous variation in density of zooplankton resources)both factors are temporally consistent but do not covary with one another in this system . Moreover, no known environmental factor should obscure the effects of these two agents on phenotypic evolution because previous research has investigated numerous environmental features of blue holese.g., temperature, salinity, turbidity, dissolved oxygen, pH, total phosphorus, total nitrogen, total organic carbon, surface area, water depth, and densities of chlorophyll a, phycocyanin, and phytoplankton-and documented a lack of covariation between these variables and either the presence of predatory fish or zooplankton density (e.g., Langerhans et al, 2007;Björnerås et al, 2020). The fish are also highly amenable to laboratory rearing under common-garden conditions, enabling us to test for evolutionary divergence of life-histories in response to these ecological agents while minimizing direct environmental effects on the phenotypes (i.e., phenotypic plasticity).…”

Consuming Costly Prey: Optimal Foraging and the Role of Compensatory Growth

“…In other blue holes, G. hubbsi are heavily preyed upon by the much larger bigmouth sleeper (Gobiomorus dormitor) and have much lower population densities (e.g., Langerhans et al, 2007;Heinen et al, 2013;Martin et al, 2015). Because these two categories of blue holes do not systematically differ in abiotic environmental variables (Langerhans et al, 2007;Heinen et al, 2013;Riesch et al, 2013;Björnerås et al, 2020), this system provides a remarkable opportunity to test for the role of altered predatory and competitive environment on diet.…”