Multiple Ecological Parameters Affect Living Benthic Foraminifera in the River-Influenced West-Central Bay of Bengal

Abstract

The huge riverine influx and associated processes decrease the ambient salinity, stratify the water column, modulate the oxygen-deficient zone, and are also responsible for the recent acidification in the Bay of Bengal. Here, we have studied the effect of these riverine influx-dominated ecological parameters on living benthic foraminifera in the west-central Bay of Bengal. We report that the pH below 7.6 in front of the Krishna river, reduces the diversity and the richness of living benthic foraminifera on the adjacent shelf and the slope. A similar decreased diversity and richness is also observed in front of the Godavari River. We delineate three prominent assemblages, representing different depth zones with associated distinct physico-chemical conditions. The shallow water assemblage (∼27–100 m) is represented by Nonionella labradorica, Hanzawaia nipponica, Brizalina dilatata, Ammonia tepida, and Nonionella limbato-striata. These species are adapted to relatively warmer temperatures and more oxygenated waters. The deepwater assemblage (∼1,940–2,494 m) includes Bulimina cf. delreyensis, Bulimina marginata, Hormosinella guttifera, Cassidulina laevigata, and Gyroidinoides subzelandica and can tolerate a relatively colder temperature. The intermediate-depth assemblage (∼145–1,500 m) dominated by Eubuliminella exilis, Bolivinellina earlandi, Fursenkoina spinosa, Bolivinellina lucidopunctata, Globobulimina globosa, Fursenkoina spinosa, Eubuliminella cassandrae, Uvigerina peregrina, Rotaliatinopsis semiinvoluta, and Cassidulina laevigata, represents oxygen-deficient and organic carbon-rich environment. Besides the pH, temperature, dissolved oxygen and organic matter, we also report a strong influence of bathymetry, coarse fraction (CF) and the type of organic matter on a few living benthic foraminifera. The ecological preferences of 40 such dominant living benthic foraminifera, each representing a specific environment, have also been reported for site-specific proxy. We conclude that although the huge riverine influx affects living benthic foraminifera on the shelf, the dissolved oxygen and organic carbon mostly control benthic foraminiferal distribution in the deeper west-central Bay of Bengal.

Large salinity gradient and diagenetic changes in the northern Indian Ocean dominate the stable oxygen isotopic variation in Globigerinoides ruber

“…The multicore samples were also collected at regular intervals in transects running perpendicular to the coast, from the western BoB during the cruise SK308, onboard Research Vessel Sindhu Sadhana (cruise SSD067) and Research Vessel Sindhu Sankalp (cruise SSK35). A total of 84 surface samples (including 71 multicore samples and 13 grab samples from sandy sediments) were collected from the inner shelf to outer slope region of the eastern margin of India during the cruise SK308 (Suokhrie et al, 2021a;Saalim et al, 2022).…”

Response of inner shelf benthic foraminiferal community to different concentrations of dissolved oxygen under laboratory culture experiment

“…The grain size, temperature and salinity were similar for all the sets, thus ruling out any differential influence of these parameters on living benthic foraminifera in the experiment. The estimation of benthic foraminiferal abundance in sediments is strongly influenced by the coarse fraction percentage (Suokhrie et al, 2021). The coarse fraction abundance in the field changes with the terrestrial supply.…”

“…Oxygen is vital for marine organisms, especially benthic organisms. The unicellular benthic foraminifera constitute a substantial fraction of the benthic community on the shelf and slope (Alves Martins et al, 2019; Lei et al, 2014; Suokhrie et al, 2021; Yamashita et al, 2020). Foraminifera play a largely unquantified but potentially significant role in carbon cycling (Gooday et al, 1992; Kurbjeweit et al, 2000).…”

Understanding Role of Foraminifera in Environmental Studies: A Review

“…In the following section, we summarize current understanding of foraminifera and ecological parameters. Many environmental factors such as food, oxygen, temperature, pH, salinity and substrate influence species abundance and composition of foraminifera (Suokhrie et al 2021). According to Martins (2016), environmental stress is mostly induced due to variations in physicochemical parameters, rather than metal contamination and organic matter enrichment.…”