The present study records small and large benthic foraminifera with endosymbionts distributed in the shelf sediments of the western continental shelf and continental slope (5-1333 m) of eastern Arabian Sea, with reference to climate change and coral reef monitoring. The larger benthic foraminifera (LBF) include Alveolinella quoyii, Amphistegina lessonii, Amphistegina gibbosa, Operculina granulosa, Heterostegina depressa and Amphisorus hemprichii which have symbiotic associations with diatoms, dinoflagellates, green algae, red algae and chrysophytes. The symbionts make these very efficient in utilising a wide range of the light spectrum and water depths. The size of species Alveolinella quoyii and Amphistegina lessonii recorded from water depths of 30 m to 1333 m showed intraspecific variations in size, those collected from deeper waters were larger than those found in shallow waters. It is evident that the presence of endosymbionts probably attributed to the intraspecific variations in size. The species belonging to these genera have evolved strategies like phenotypic plasticity and local adaptation of the concerned photosymbionts which have helped them tolerate thermal variations. The finding that the number of tests of LBFs decreased from shelf to slope areas may be indicative of the relation between oxidative stress, reduced light levels that affect the growth
rate of these species. It is confirmed that LBFs have longer lifespan than the smaller forms. 

Larger benthic foraminifera, endosymbionts, Amphistegina