Long-term monitoring of benthic foraminiferal assemblages from Asia's largest tropical coastal lagoon, Chilika, India

Abstract

The present study undertaken in the largest coastal lagoon of Asia, Chilika, deals with monthly monitoring of benthic foraminifera assemblages in terms of distribution pattern, diversity and variations in taxonomic composition spanning over a period of 20 months. In total, 13 species of benthic foraminifera represented by eight families were identified in the lagoon. The stations in the Southern sector of the lagoon showed relatively low foraminifera abundance yet high diversity whereas higher abundance and lower diversity were observed in stations located in the Central sector which indicates the spatial patterning of the assemblage. Live foraminifera abundance was sparse in the study area indicating the stressed nature of the lagoon environment. The dissolved nutrient concentration of bottom water reflected significant seasonal variation. The stressed nature of the lagoon is further indicated by the dominance of the genus Ammonia across the inner sectors of the lagoon, a genus known to inhabit impacted habitats. Overall these data can serve as a baseline proxy for understanding palaeontological assemblages of foraminifera in similar shallow-water settings globally.

Foraminiferal assemblage structure from Brazilian tropical urbanized beaches (~7°S)

“…Debenay et al 2001, Vilela et al 2004 and in several places around the world (e.g. Samir & El-Din 2001, Gupta et al 2019, being typical of sandy beaches where the presence of most species commonly is due to post-mortem transport (Murray 1973, Haslett et al 2000. Previous comparisons of fauna of dead and alive Foraminifera demonstrated various degrees of correspondence between the two assemblages (Debenay et al 2005).…”

“…Staining with rose bengal, used here, is the most common method used to differentiate among living and dead individuals (e.g. De Stigter et al 1998, Bernhard 2000, Eichler et al 2001, Tapia et al 2008, Gupta et al 2019). There are, however, a number of negative aspects regarding its use (Bernhard et al 2006): it can stain bacteria attached to or located inside the test (Martin & Steinker 1973); staining is difficult to visualize in opaque specimens such as certain agglutinant or miliolid foraminiferans (Bernhard 2000), likewise Quinqueloculina lamarckiana, Sorites marginalis and Textularia agglutinans, abundant in the present study (see below).…”

“…This is particularly true in polluted regions or under high anthropic stress (e.g. Vilela et al 2004, Gupta et al 2019, since it is tolerant to thermic and chemist pollution like fertilizers, heavy metals and hydrocarbons (e.g. Seiglie 1975, Setty 1976, Setty & Nigam 1984, Yanko & Flexer 1991.…”

“…Foraminifera is a diversifi ed taxon, with more than 60.000 described species, and with high ecological and bioindicator importance of both current and past conditions (Horne et al 2002, Gupta et al 2019. Once dead, their tests settle in the sediment and begin to behave like sedimentary particles indicating or paleoindicating the environmental conditions during their deposition (Debenay et al 1996, Gupta et al 2019. Physical-chemical parameters of the environment can be evaluated through the taphonomic analysis of the test coloring and abrasion.…”

“…Thus, beyond the diversity abundance and taxonomic composition, important features of Foraminifera assemblages are proportion of living and dead organisms and their taphonomic characteristics. The study of total community of Foraminifera (alive and dead) allows a deeper and longer-term view, since the changes in community composition due to taphonomic processes are also incorporated (Goldstein & Watkins 1999, Walker & Goldstein 1999, Gupta et al 2019.…”