Bottom Water Characteristics and Their Influence on Temporal Distribution of Benthic Foraminifera from off Manapad, Gulf of Mannar, South East Coast of India

Abstract

To understand the influence of bottom water characteristics on temporal distribution of benthic foraminifera, sediment and bottom water samples were collected at 18 stations ranging in depth from 2.3 m to 17.4 m, from off Manapad, Gulf of Mannar. The collections were carried out, once in four months starting from May 2016, for a period of one year - representing summer (May), period between SW and NE monsoons (September) and winter/post monsoon (January). Thus, the collections amounted to a total of 54 samples. Faunal analysis led to the recognition of 99 foraminiferal species belonging to 47 genera, 33 families, 17 super families of suborders Textulariina, Miliolina, Lagenina and Rotaliina. The population size both as living and total (living + dead) in each of the stations during different seasons have been found out. It was observed that the fauna is in living condition in all the samples of all the collections and the living population was found to be maximum in summer (May) and in winter (January). Among the 99 foraminiferal species identified, six species were found to be significant and abundant viz. Ammonia beccarii, A. tepida, Asterorotalia inflata, Noninoides boueanum, Quinqueloculina seminulum and Spiroloculina communis. The various bottom water parameters of all the 54 samples have been estimated and correlated with foraminiferal population. The water parameters do not show marked variation among different stations of a collection, but a distinctive variation was seen between seasonal collections. The temporal distribution of assemblages was found to be closely associated with sea bottom environments and bathymetry. Temporally, the increase in temperature, salinity, dissolved oxygen and pH content of the bottom water are suggested for an abundance of living population. Abundant and widespread foraminiferal population was also found to have a positive correlation with that of temperature, salinity and dissolved oxygen of the bottom water. In the present area, spatially depth is the controlling factor for the abundance of population in all seasons.