The environmental setting and microfauna of the oligohaline Timsah pond, Israel: The last remnant of the Kabara swamps

Abstract

Abstract Enot Timsah is a spring-fed wetland ecosystem at the foot of the Carmel Mountain, a relict of the much larger Holocene Kabara swamps, at the northern outlet of the Yarqon-Tanninim mountain aquifer. This groundwater-surface water interaction zone supports a unique living foraminiferal and ostracod fauna. Sampling of water and sediment was carried out approximately monthly in 2002/3 as part of a study of the species richness and history of this distinctive ecosystem. Enot Timsah is nearly isothermal (23.98 ± 0.4 °C) and oligohaline with total dissolved solids (TDS) of 3,213 ± 118.5 mg/l. The water column is transparent and highly oligotrophic, with very low phosphate concentration. Living ostracods and Rose Bengal stained benthic foraminifera occur in low numbers. A monospecific population of the ostracod Cyprideis torosa lives at the surface, with a reproductive peak in April, 2002. Foraminifera occur throughout the topmost 0–4 cm. Extreme oligotrophy of this ecosystem means that there is a low flux of phytoplankton, limiting abundance of surface-dwelling ostracods and foraminifera. Microbial decomposition of vascular plant debris was the food source for infaunal foraminifera. The low salinity means that living conditions are marginal explaining low numerical abundance of foraminifera. However, foraminiferal diversity is exceptionally high at Enot Timsah compared with other oligohaline environments, with 15 living benthic taxa and three additional species found in the dead assemblage. The living assemblage is composed of cosmopolitan agglutinants known to live in brackish environments, together with some calcareous hyaline and miliolid taxa. The exceptional foraminiferal diversity is attributed to four factors: the very stable conditions of salinity and temperature; the high Ca2+ and HCO3− concentrations derived from the karstic aquifer (promoting mineralization of calcareous tests), the maturity of the Kabara ecosystem dating from the early Holocene; and the repetitive reintroduction of cosmopolitan brackish foraminifera by avian transport. Increased numbers of living foraminifera with abnormal morphologies testify to stress conditions. Dead foraminifera are more abundant than living ones, with agglutinated foraminifera dominating the living assemblage, and calcareous forms dominating the dead assemblage. This taphonomic reversal is attributed to microbial decomposition of organic cement of the agglutinants, while the calcareous forms are resistant to dissolution because of the high Ca2+ and HCO3− of the aquifer-derived spring waters. The Holocene fossil record of the predecessors of the Kabara swamps therefore represents an estimated 10–40% of the information found in the living foraminiferal assemblage at Timsah.