Myctophid and pelagic shrimp assemblages in the oxygen minimum zone of the Andaman Sea during the winter monsoon

Abstract

Stratified samples were collected with a Multiple Plankton Net for assessing the myctophid and pelagic shrimps composition from the Andaman Sea during the winter monsoon. Andaman Sea has a fair representation of mesopelagic micronektonic fauna such as the myctophids and pelagic shrimps in the upper 1000 m depth. Among the myctophids, Benthosema fibulatum had the maximum biomass followed by Diaphus lucidus and Benthosema pterotum. Among the pelagic shrimps Sergestus seminudus and Oplophorus types were the dominant species. Sergestes seminudus was present at all depths [up to 1000 m] and its distribution pattern suggested the co-occurrence of a strong diurnal vertical migration. Temperature decreased from the mixed layer depth downwards. Salinity did not show any significant variation. Dissolved oxygen ranged between 2.8 and 4.8 mL.L sup(-1) in the upper 75 m and from 0.05 to 0.2 mL.L sup(-1) in the 150-650 m column, with a gradual increase in the bottom layers [>0.8 mL.L sup(-1)]. Majority of myctophids and shrimps occurred in abundance in the oxygen minimum zone [150-650 m]