Search

Q-mode and R-mode cluster analyses have been carried out on the census counts data of 68 genera and one ‘other genera’ of benthic foraminifera from 32 stations off Mangalore-Cochin sector, west coast of India, to study the ecological preferences, especially the effect of depth on external test morphology of benthic foraminifera. We report that benthic foraminiferal distribution in the central western continental margin of India, can be grouped into three clusters. Cluster A is predominantly represented by angular-asymmetrical forms, cluster B is dominated by rounded-symmetrical forms, whereas cluster C includes both rounded-symmetrical and angular-asymmetrical forms. From the spatial distribution of cluster A-C-B, we report that with decreasing depth, there is a gradual tendency among benthic foraminifera to become more symmetrical from angular-asymmetrical. The observed morphological changes in benthic foraminifera are attributed to the sediment turbulence. The spatial distribution of benthic foraminifera indicates that the angular-asymmetrical morpho-group indicates relatively deeper water while rounded-symmetrical forms suggest shallow environment. Therefore, the temporal variation in the relative abundance of these benthic foraminiferal morpho-groups, can be used for paleo-depth reconstruction. [ABSTRACT FROM AUTHOR]

Being sensitive to environmental changes, foraminifera have been extensively used to monitor pollution level in the marine environment, including the effect of mining in coastal areas. In the Goa state of India, the rejects from opencast mining on land largely find their way to the estuaries, as washout during monsoon. Additionally, the Mormugao Port at the mouth of the Zuari estuary is the hub of activities due to the transport of ore from hinterland areas by barges and its subsequent loading for export. On the directive of the Supreme Court of India, all the mining-related activities abruptly stopped throughout India, including that in Goa in 2012, and got reinstated in 2015. Therefore, it provided a fit case to test the effectiveness of benthic foraminifera as an indicator of environmental impact due to mining activities. A total of ten surface sediment samples from five locations in Zuari estuary were collected from a depth range of 4.5-8.5 m in the years of 2013 and 2016 and were analyzed for both the living (stained) and dead benthic foraminifera. The year 2013 represents a time interval immediately after the closure of extensive mining activity, and the sampling during 2016 represents minimal mining. The living benthic foraminiferal abundance was higher (19-54/g sediment) during 2013 and decreased substantially during 2016 (3-22/g sediment), suggesting an adverse effect of activities associated with mine closure on benthic foraminifera. Additionally, the relative abundance of Ammonia was also significantly low during the year 2016. The temporal variation in dead foraminifera was, however, different than that of the living foraminifera. The differential response was attributed to the terrigenous dilution as a result of change in sedimentation rate. Therefore, we conclude that living foraminifera correctly incorporate the changes in mining pattern and may be used as an effective tool to monitor the impact of mining. We further suggest that the potential counter effect of terrigenous dilution on total and living benthic foraminiferal population should be considered while interpreting temporal variations in foraminiferal abundance in marginal marine settings. [ABSTRACT FROM AUTHOR]

Abstract: The seawater temperature is an important physical parameter that affects marine benthic community. The effect of seawater temperature however is not consistent throughout various groups of marine benthos. Here, juvenile specimens of marginal marine species Rosalina globularis were subjected to different temperatures (20°C, 25°C, 27°C, 30°C and 35°C), to understand the effect of temperature on growth and reproduction in benthic foraminifera. The growth of the specimens was recorded till the specimens matured and reproduced. It was observed that out of five different temperatures, optimum growth took place at 30°C. The growth in rest of the specimens subjected to either higher or lower temperatures was comparatively less. However, the highest percentage of reproduction was reported in the specimens subjected to 27°C temperature. None of the specimens kept at 20°C reproduced whereas only one specimen reproduced at 35°C temperature. Based on this experiment, it is concluded that R. globularis can tolerate temperature variations from 20°C to 35°C and further that the optimum temperatures for growth and reproduction are different. The study shows that the ambient seawater temperature affects the growth, survival and reproduction in benthic foraminifera. The study further indicates that variation in morphology and abundance of benthic foraminifera, might reflect different climatic conditions. [Copyright &y& Elsevier]

Abstract: Laboratory culture experiments were carried out to understand the response of benthic foraminifer Rosalina leei to gradual as well as sudden addition of heavy metal mercury into the media. When mercury was added suddenly, specimens did not show any change in morphology during the initial 40days. However, later on, out of all the specimens subjected to mercury concentrations up to 150ng/l, 75% developed deformities, whereas all the specimens subjected to 150–275ng/l Hg concentrations, had deformed chambers. All specimens kept at 300ng/l Hg concentration died within 20days. In addition to this, irregularities were also observed in the rate of reproduction, number of juveniles produced and the survival rate of the juveniles. Where as in an earlier experiment where Hg concentration was increased gradually, irregularities in the newly added chambers were noticed only in case of specimens subjected to very high (180ng/l) Hg concentration. However, during this experiment, growth was found to be inversely proportional to the mercury concentration. [Copyright &y& Elsevier]

Live specimens of benthic foraminiferal species Rosalina leei were subjected to a combination of temperature (25°C, 30°C and 35°C) and salinity (25‰, 30‰ and 35‰) to assess its differential response to the annual range of seawater temperature and salinity reported at the sampling site. A total of 216 specimens were used for the experiment. Within the range of temperature and salinity, to which R. leei specimens were subjected as part of the present experiment, growth increased with increasing salinity, whereas increase in seawater temperature resulted in retarded growth. Maximum growth was reported in the specimens kept at 25°C temperature and 35‰ salinity while the rest of the specimens maintained in 30‰ and 25‰ saline water, showed comparatively less growth. The specimens kept at 30°C and 35°C temperature and different salinities showed much less growth as compared to the specimens maintained at 25°C temperature. However, none of the R. leei specimens subjected to the present experiment reproduced during the course of the experiment. The absence of reproduction under the present set of temperature and salinity conditions, probably indicates that R. leei reproduces at a very narrow range of temperature and salinity which is different from the temperature and salinity conditions in the present experiment. It is further inferred that under the present set of temperature–salinity conditions, 25°C temperature and 35‰ saline water is most suitable for the growth of R. leei. Results are significant as the responses of benthic foraminifera to different temperatures and salinity are being used for palaeoclimatic reconstruction. [ABSTRACT FROM PUBLISHER]

Despite being located at the same latitudes, the Bay of Bengal oxygen deficient zone (ODZ) is markedly different than the Arabian Sea ODZ. The uptake of oxygen in the Bay of Bengal does not lead to denitrification as in the Arabian Sea. This difference in ODZ of the Bay of Bengal and the Arabian Sea is expected to support different benthic fauna. We report that the living benthic foraminifera in the Bay of Bengal ODZ are markedly different than that in the Arabian Sea ODZ. Only four species (Brizalina spathulata , Eubuliminella exilis , Uvigerina peregrina and Rotaliatinopsis semiinvoluta) dominant in the Bay of Bengal ODZ have also been reported from the Arabian Sea oxygen deficient waters. The difference in living benthic foraminifera dominant in the ODZ of the Bay of Bengal and the Arabian Sea, is attributed to the lack of denitrification and associated processes in the Bay of Bengal. • Comparison of foraminifera of low oxygen zones of the Bay of Bengal and Arabian Sea • Total 20 species are positively correlated with low oxygen in the Bay of Bengal. • B. spathulata , E. exilis , U. peregrine , R. semiinvoluta are common in both basins. • The difference is attributed to the lack of denitrification in the Bay of Bengal. [ABSTRACT FROM AUTHOR]

Agglutinated benthic foraminiferal morphogroups have often been used as a proxy in paleoecological studies. The response of various agglutinated morphogroups may, however, vary regionally. Here we report the ecological preferences of agglutinated morphogroups from the fresh-water influx dominated western Bay of Bengal. The abundance of both living (rose-Bengal stained) as well as dead agglutinated benthic foraminifera and their morphogroups, has been studied in a total of 42 core-top samples from the depth range of 25–2540 m, covering the entire shelf and slope. Agglutinated foraminifera are divided into four morphogroups (A–D). Out of these, two morphogroups, namely B and C are sub-grouped into (B1–B4) and (C1–C2), respectively. We report exceptionally high agglutinated benthic foraminiferal abundance on the slope of the western Bay of Bengal. The depth and temperature affect the total abundance of agglutinated benthic foraminifera. Morphogroups A (tubular), B1 (globular), and B3 (planispiral/trochospiral, only dead) are positively correlated with water depth and negatively correlated with the ambient temperature, suggesting its preference for deeper waters. Both the dead and living assemblages of morphotype B2 as well as C1, are negatively correlated with dissolved oxygen (DO) and positively correlated with organic carbon (%C org) suggesting its preference for depleted oxygen environment. The morphotype B4 prefers relatively deeper depths. The morphotype C2 (quinqueloculine/milioline forms) is positively correlated with DO, temperature, coarse fraction and organic carbon/nitrogen, and negatively correlated with %C org and water depth, thus indicating that species belonging to this morphotype prefer shallow water, oxic, coarse-grained environment. The relative abundance of morphogroup D (dead) is negatively correlated with ambient salinity, thus suggesting its preference for hyposaline conditions in the shallow marine environment. The study suggests a clear ecological preference of a majority of the agglutinated morphotypes and morphogroups and thus their potential application in paleoecological interpretations. [ABSTRACT FROM AUTHOR]