Untangling the effect of organic matter and dissolved oxygen on living benthic foraminifera in the southeastern Arabian Sea.

We studied the relationship between organic carbon in sediments (%Corg), bottom water dissolved oxygen and living benthic foraminifera in a marginal marine upwelling setting from the southeastern Arabian Sea to develop proxy indicator for marine productivity as well as oxygen deficient zones. The surface sediments from 43 stations covering a depth range of 25 to 2980 m were used. The relationship between living benthic foraminifera and ambient environmental parameters (seawater temperature, salinity, dissolved oxygen, organic carbon and Corg/TN and depth) was assessed by multivariate analysis. A majority of the living benthic foraminifera were significantly affected by several ambient parameters. We report that the living benthic foraminiferal assemblage comprising of Epistominella umbonifera, Uvigerina auberiana, Reophax longicollis and Osangularia bengalensis is significantly affected only by %Corg in the sediment. Additionally, we also found that the assemblage including Bolivina obscuranta, Bulimina arabiensis, Bulimina pseudoaffinis and Cancris penangensis is significantly affected only by the bottom water dissolved oxygen. The living benthic foraminifera assemblages can be used to reconstruct marine productivity and dissolved oxygen concentration in the past.

Effects of sudden stress due to heavy metal mercury on benthic foraminifer Rosalina leei: laboratory culture experiment.

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 40 days. However, later on, out of all the specimens subjected to mercury concentrations up to 150 ng/l, 75% developed deformities, whereas all the specimens subjected to 150-275 ng/l Hg concentrations, had deformed chambers. All specimens kept at 300 ng/l Hg concentration died within 20 days. 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 (180 ng/l) Hg concentration. However, during this experiment, growth was found to be inversely proportional to the mercury concentration.

Application of foraminifers in ecotoxicology: retrospect, perspect and prospect.

In view of the extensive use of foraminifers for the pollution monitoring especially their unmatched utility in deciphering the temporal variation in the type and concentration of pollutants at a given location, the literature dealing with the application of foraminifers for pollution studies has been reviewed. The pollution monitoring through foraminifers started with attribution of peculiar foraminiferal features at any location to the circumstantial presence of pollutants at that site. These peculiar features of the foraminifers in polluted areas included, variation in the abundance of total, calcareous and agglutinated foraminifers, species diversity, abnormal tests, etc. The abnormalities of tests included stunted growth, abraded margins, dissolved ornamentations, etc. Initially, much attention was paid to the effects of sewage pollution on the foraminifers but later on all kinds of human induced as well as natural pollutants came under the preview of foraminiferologists working on pollution aspects. The advantage of application of foraminifers, over other chemical and biological techniques, for pollution monitoring lies in their potentiality to decipher temporal variation in type and concentration of pollutants at any site even in the absence of pre-pollution studies, based on the recovery of foraminifers from the sediment core samples. Realizing the potential application of characteristic foraminiferal features from the polluted areas to decipher the variation in introduction and concentration of pollutants at any given location with time, efforts were made to characterize the specific types of foraminiferal features to the specific pollutants. It was at this point that the need of culture studies was widely felt which resulted in numerous lab and field culture studies where foraminifers were subjected to specific pollutants in order to document their response to these pollutants and to develop effective foraminiferal proxies for pollution monitoring through time. Such studies are still going on and it is felt that culture studies need to be supplemented with advanced crystallographic and molecular studies in order to find the mechanism through which foraminifers respond to the pollutants.

Foraminifers as indicators of marine pollution: a culture experiment with Rosalina leei.

In order to develop a viable foraminiferal proxy for heavy metal pollutants, juvenile specimens of Rosalina leei were subjected to different mercury concentrations (0-180 ng/l). Initially considerable growth was observed in specimens kept in saline water having a mercury concentration up to 100 ng/l. But with the gradual increase in concentration of mercury the growth rate started decreasing. Total growth achieved was significantly lower in case of specimens kept at relatively higher mercury concentrations then those maintained in normal saline water. The most significant result of this experiment was the addition of abnormal chambers in the specimens kept at higher mercury concentration. Later the specimens kept at highest concentration (180 ng/l) were subjected to progressively increasing concentration of mercury to see the further effects and it was found that the specimens were still living at as high a mercury concentration as 260 ng/l although there was no growth.