Holocene benthic foraminifera ecological succession in the Panamanian Caribbean

Benthic foraminifera assemblages from a 452 cm long sediment core (GAL18) were collected from a mangrove forest on the Caribbean coast of Panama. The core spans the last ∼5200 cal yrs. B.P. Ninety-six benthic species were recorded in the sedimentary sequence. The most frequent and abundant were the calcite hyaline species Ammonia batava, Ammonia tepida, Ammonia ariakensis, Elphidium articulatum, Elphidium cristobalense, and Cribroelphidium galeroense. The second most abundant were four porcelaneous species: Quinqueloculina cf. araucana, Quinqueloculina cf. poeyana, Quinqueloculina neocostata and Quinqueloculina seminulum. There were also scattered species of agglutinant taxa along the core and in modern sediments. Micropaleontological, sedimentological, and geochemical analyses allowed the recognition of four lithologic units that were consistent with four paleoenvironmental scenarios of ecological succession. (I) The Estuarine Zone deposited at ∼5200–3600 cal yrs. B.P. suggests the development of a mangrove ecosystem along a channeled tidal area with estuarine water exchange and dominant species from brackish waters such as Ammonia and Cribroelphidium. Isotopic (δ¹³Corg, δ¹⁵N), geochemical (C/N, Ca/Ti, K/Rd, Fe/Ca), and pollen data also show a polyhaline environment with bio-calcite production and active coastal weathering. (II) The Seaward Zone deposited between ∼3600–1250 cal yrs. B.P., closest to marine waters, with an overall increase in benthic species, like the euhaline Quinqueloculina spp., and other calcareous organisms. (III) The Transition Zone was deposited amid 1250–650 cal yrs. B.P. when the area experienced less frequent flooding by tidal waters, dominated by polyhaline Elphidium and Ammonia spp., and the establishment of a mangrove ecosystem influenced by changing salinity, as the sea level almost reached its modern position. Finally, (IV) the Landward Zone deposited over the last 650 cal yrs. B.P., where the lack of benthic foraminifera and bio-calcite deposits contrast with high amounts of organic carbon and vegetal debris, which supports that the core site was located further inland than in previous intervals. This multiproxy study features subtle but irreversible changes that a fringe mangrove community can experience over time, highlighting the complex relationship between the coastal region and the sea.