Ecology of Foraminifera and Habitat Variability in an Underwater Cave: Distinguishing Anchialine Versus Submarine Cave Environments

Abstract

Seventy-five surface «4 cm) sediment samples were collected throughout Green Bay Cave System, Bermuda to investigate foraminiferal ecology and habitat variability in underwater coastal caves. This cave is ideal for studying different cave environments because it consists of an anchialine cave environment connected to a submarine cave environment. Each sediment sample was analyzed for foraminifera, 1) 13 C org , C:N, organic matter content, CaC0 3 , and granulometry. Measurements of pH, salinity, dissolved oxygen, and temperature in the coastal aquifer distinguished the meteoric lens and saline groundwater. Q-mode cluster analysis on the foraminifera produced a dendrogram that segregates the anchialine and submarine cave environments, and subdivides each environment into distinct habitats consistent with local hydrogeology and sedimentology. The anchialine cave environment near the sinkhole is characterized by two groups of foraminifera: 1) the Meteoric Lens Assemblage living in the brackish meteoric lens within 60 cm of sea level, and 2) the Anchialine Cave Assemblage living in the saline groundwater. Helenina anderseni, Discorinopsis aguayoi, and other marsh foraminifera can persist in the brackish meteoric lens, which transitions into a more diverse assemblage dominated by Bolivina striatula and Rosalina globularis below the halocline. The boundary between the anchialine (terrestrially dominated) and submarine cave (marine-dominated) environments is demarcated by gross foraminiferal and sedimentary changes (1)13Corg from -24%0 to -18%0, C:N from 11.2 to 8.3) that correspond to the m~ximum point where terrestrial influences routinely impact the cave benthos. Three assemblages of foraminifera inhabit the submarine cave environment: 1) the Entrance Assemblage in the first -60 m of the submarine cave, dominated by Quinqueloculina; 2) the Circulated Submarine Cave Assemblage dominated by Spirillina vivipara' and Triloculina oblonga, and 3) the Isolated Submarine Cave Assemblage dominated by Spirophthalmidium emaciatum. Planktic tintinnids suggest that tidally forced saline groundwater circulation is transporting more nutrients and particulate organic matter to the Circulated Submarine Cave Assemblage than the Isolated Submarine Cave Assemblage. These results indicate that coastal caves are partitioned into specific environments that can be further subdivided into habitats by groundwater masses, sediment fluxes (terrestrial versus marine), and groundwater circulation. This implies that that cave foraminifera can be useful paleohydrogeologic, paleoclimatic, and Quaternary sea-level proxies.

Benthic foraminifera as proxies of marine influence in the Orosei marine caves, Sardinia, Italy

“…The identification of ecozones was carried out only in the BM cave because of the very low number of foraminifera recovered in the BT cave in 2015. In 2014, studies were conducted on the BT and BM caves, and these studies were based on the quantitative data of the total (living plus dead) assemblage, while also considering possible postmortem processes (van Hengstum & Scott, ), which allowed the reliable definition of ecozones (Bergamin et al, ; Romano, Bergamin, et al, ). Additionally, in this research, the total foraminiferal assemblage was considered a proxy for the definition of reliable ecozones, corresponding to the average conditions during the deposition of the sediment analysed (Fontanier et al, ; Frezza & Carboni, ; Jorissen et al, ; Leorri, Cearreta, Irabien, & Yusta, ).…”

“…To prevent the inclusion of reworked or transported specimens, only well‐preserved tests, without breakages or abrasion signs, were picked, counted, and classified. Moreover, according to Van Hengstum and Scott (), one species was considered as autochthonous in one sample and was included in the multivariate analysis only when at least one stained specimen of the same species was found. The classification of foraminifera at the genus level was made according to the most commonly used taxonomical study on foraminiferal genera (Loeblich & Tappan, ), whereas the species were determined according to some important studies on the Mediterranean area (Cimerman & Langer, ; Sgarrella & Moncharmont‐Zei, ) and according to the World Modern Foraminifera Database (Hayward, Cedhagen, Kaminski, & Gross, ).…”

“…Fossil foraminifera have also been used as palaeo‐environmental indicators of Quaternary sea‐level changes in the tropical karst systems of Bermuda (Van Hengstum, Scott, & Javaux, ) and the Yucatan peninsula (Van Hengstum, Reinhardt, Beddows, Schwarcz, & Gabriel, ). On the other hand, recent foraminifera were successfully applied as environmental tools for ecological zonation in Mexican cenotes (van Hengstum, Reinhardt, Beddows, Huang, & Gabriel, ) and in the Green Bay cave system of Bermuda (vVan Hengstum & Scott, ), where different foraminiferal assemblages were recognized in the marine‐dominated sector of the cave. Based on these results, the authors deduced that, in cave environments, benthic foraminifera can be useful as palaeo‐hydrogeologic, palaeo‐climatic, and Quaternary sea‐level proxies.…”

Xibalbanus cozumelensis, a new species of Remipedia (Crustacea) from Cozumel, Mexico, and a molecular phylogeny of Xibalbanus on the Yucatán Peninsula

“…and Bahadzia sp., and the isopod Metacirolana mayana Bowman, 1987; in addition to the starfish Asterinides pompom (Clark, 1983) (Yañez-Mendoza et al 2007). Sediment occurring along the cave floor in these localities also included benthic foraminifera Spirophthalmidium emaciatum Haynes, 1973, a foraminifer widely distributed in coastal caves in Bermuda that are also flooded by saline groundwater ( Van Hengstum & Scott 2011). The material of Xibalbanus cozumelensis sp.…”

Baseline physicochemical investigations on waters from three blue holes, San Salvador Island, Bahamas

“…Connectivity can be surmised, in the blue hole (Davis and Johnson, 1989;Martin et al, 2012). The mixing of freshwater with seawater results in the formation of the two waters creates a sharp interface with a steep gradient 1989; van Hengstum and Scott, 2011;Martin et al, 2012). Mixing zones within carbonate islands have been recognized as the primary locations for dissolution of carbonates (Back et al, 1986;Mylroie and Carew, 1990;Carew and Mylroie, 1995;Mylroie, 2008).…”