Aspects of the biodiversity of brackish water foraminifera

Abstract

Foraminiferal fauna of the Chilka lake situated between 19 degrees 25 minutes and 19 degrees 54 minutes N and 85 degrees 6 minutes and 85 degrees 38 minutes E in Orissa state on the east coast of India during different seasons was studied using Pielou's, Simpson's, Margalef's, Shannon-Wiener's, and Heip's evenness indices of diversity. Mean diversity levels were low during the postmonsoon period (November) when there is heavy rainfall followed by the diluting effects of the river systems of the area; however, levels were high during the premonsoon season (March and May) due to prevalence of marine conditions in the lake. Furthermore, the evaluation of different sectors in the study area showed somewhat poor diversity within the lagoon and rich diversity in the outer channel, the fauna of which was similar to the nearshore foraminiferids of Bay of Bengal. The spatial pattern of species diversity was predictable and was related to environmental features of the areas in the lake. Regarding the spatial community structure, outer channel showed highly stable environment due to its proximity to the sea whereas northern sector showed highly fluctuating environment being away from the oceanic region and highly affected by variations in the salinity. Seasonal comparison showed postmonsoon season as the most consistent period, whereas early premonsoon was the least consistent period. Bray-Curtis group linkage cluster analysis showed that none of the clusters of foraminiferal species present during post-monsoon occurred during pre-monsoon. In contrast to this observation, approximately 30% of the species were always clustered together during early premonsoon and late premonsoon, indicating the possibility of succession of species during November. An interesting observation was that a species replacement takes place in the case of foraminiferal fauna over a seasonal cycle. This finding could be an indication of the seasonality of this community through species succession.