Brackish Foraminifera Research Articles

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

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.

Foraminiferal assemblages response to anthropogenic influence and parallel to decadal sea-level changes over the last 70 years in Lake Kugushi, Fukui Prefecture, southwest Japan

Foraminiferal assemblages in Lake Kugushi in the Sea of Japan coast of Southwest Japan responded to both human activity and sea-level changes over the last 70 years. Human modifications in and around this lake were mainly related to the dredging and widening of the Urami River in 1935 and to shore protection projects that removed aquatic plants around the lake in the middle 1970s. About 60% of the natural shoreline was replaced by artificial ones. Marine foraminifera migrated into the southern part of the lake after the modifications of 1935. Brackish foraminifera preferring phytodetritus became dominant from the middle 1970s, while the original assemblage, preferring low-salinity and probably land-derived organic matter, decreased. The sea-level rise over the last 70 years is clearly indicated by two kinds of foraminiferal assemblages: the appearance of marine species in the 1950s and 1970s, and the development of a brackish assemblage preferring eutrophic water from the 1980s onward. The latter is an assemblage dominated by Trochammina hadai, which is common in coastal lagoons with a well developed halocline and highly eutrophied argillaceous substrates. Based on the different response of these foraminiferal assemblages to sea-level rise, the most recent sea-level rise is driven by a mechanism unlike those in the 1970s and 1950s. The thermal expansion of seawater will lead to coastal lagoons that will be more stagnant and eutrophic, with little exchange of coastal marine water.

Foraminifera in elevated Bermudian caves provide further evidence for +21 m eustatic sea level during Marine Isotope Stage 11

Two hypotheses have been proposed to explain the origin of marine isotope stage (MIS) 11 deposits in small Bermudian caves at +21m above modern sea level: (1) a +21m MIS 11 eustatic sea-level highstand, and (2) a MIS 11 mega-tsunami event. Importantly, the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments. After statistically comparing foraminifera in modern Bermudian littoral caves and the MIS 11 Calonectris Pocket A (+21m cave) to the largest available database of Bermudian coastal foraminifera, the assemblages found in modern littoral caves – and Calonectris Pocket A – cannot be statistically differentiated from lagoons. This observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone, where typical coastal processes (waves, storms) homogenize and rework lagoonal, reefal, and occasional planktic taxa. Fossil protoconchs of the Bermudian cave stygobite Caecum caverna were also associated with the foraminifera. These results indicate that the MIS 11 Bermudian caves are fossil littoral caves (breached flank margin caves), where the total MIS 11 microfossil assemblage is preserving a signature of coeval sea level at +21m. Brackish foraminifera (Polysaccammina, Pseudothurammina) and anchialine gastropods (∼95%, >300 individuals) indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase. The onset of sea-level regression following the +21m highstand would first lower the ancient brackish Ghyben-Herzberg lens (<0.5m) and flood the cave with brackish water, followed by drainage of the cave to create a permanent vadose environment. These interpretations of the MIS 11 microfossils (considering both taphonomy and paleoecology) are congruent with the micropaleontological, hydrogeological and physical mechanisms influencing modern Bermudian coastal cave environments. In conclusion, we reject the mega-tsunami hypothesis, concur with the +21m MIS 11 eustatic sea-level hypothesis, and reiterate the need to resolve the disparity between global marine isotopic records and the physical geologic evidence for sea level during MIS 11.

京都府久見浜湾における最近６０年間の有孔虫群集の変化が示す海面水位変動の意義

Brackish foraminifera were investigated from surface sediments and cores collected in Kumihama Bay, northern Kyoto Prefecture, to clarify the impact on brackish organisms of sea-level changes and recent global warming. Foraminifera increased in the 1950s and the early 1970s, corresponding to periods of higher sea levels around the Japanese Islands. Despite continuous sea-level rises from the 1980s, however, they began to decrease and became eutrophic fauna as represented by Trochammina hadai, preferring highly fertilized water. This change may be related to annual changes in sea level and lake water circulation, which become more intense during periods with wider annual ranges of sea-surface atmospheric pressure. Sea-level changes observed in Maizuru Bay during the 1950s and 1970s are intimately related to long-term changes in the Aleutian Low Pressure system called the Pacific Decadal Oscillation (PDO), but this has not been the case since the late 1980s. Thus, the mechanism of modern sea-level rises since the 1980s is probably not the same as that of the pre-1980s, and is caused by modern lake water conditions with less circulation and an abundance of T. hadai. In addition, the widening and deepening of the channel opening to the Sea of Japan between 1972 and 1975 are also found to contribute to the modification of brackish foraminiferal fauna in the lake.

Brackish Foraminifera in New Zealand: A Taxonomic and Ecologic Review

Approximately one third (11 species) of the world obligate brackish foraminiferal taxa occur in New Zealand's estuaries and upper reaches of enclosed harbours, inlets and lagoons. The previously confused local taxonomy of New Zealand's obligate (11 species) and common facultative (9 species) brackish foraminifera is integrated with current overseas usage. Nineteen of the 20 brackish species in New Zealand have a world-wide distribution. All 20 species occur in northern New Zealand (lat 35?S) with a progressive decrease in diversity to 13 species in the south (lat 47?S). Cluster analysis based on the quantitative faunal counts of 68 samples from 5 study areas results in the recognition of nine brackish foraminiferal associations. Within brackish settings, salinity and secondly tidal exposure, are the two environmental factors having the strongest influence on foraminiferal distribution. With increasing salinity, brackish faunas increase in diversity, decrease in abundance of agglutinated taxa and increase in abundance of calcareous taxa. The associations exhibit the following general trend correlated with increasing salinity: a. Trochamminita (least saline); b. Haplophragmoides wilberti, Miliammina; c. Ammonia Miliammina; d. Elphidium excavatum, Ammonia Elphidium, Ammonia; e. Marginal Marine (most saline). Five associations are apparently restricted to the intertidal zone: a. Trochammina inflata (above mean high water); b. Trochamminita, Haplophragmoides wilberti (above mean sea level); c. Elphidium excavatum (predominantly mid-tidal); d. Ammonia Elphidium (between mean low and mean high water). Tidal current transport of foraminiferal tests produces mixed assemblages in the mouths and lower channels of New Zealand estuaries (diurnal microtidal and low mesotidal ranges).