Infaunal macrobenthos of the oxygen minimum zone on the Indian western continental shelf

Abstract

The Arabian Sea is characterized by a mid-depth layer of reduced dissolved oxygen (DO) concentration or oxygen minimum zone (OMZ -DO concentration <0.5 mlÁl À1 ) at~150-1000 m depth. This OMZ results from the flux of labile organic matter coupled with limited intermediate depth water ventilation. Generally, benthic animals in the OMZ have morphological and physiological adaptations that maximize oxygen uptake in the limited oxygen availability. Characteristics of OMZ benthos have been described from only a few localities in the Arabian Sea. We measured the bottom water DO and studied the characteristics of infaunal macrobenthos of the Indian western continental shelf by collecting samples at 50, 100 and 200 m in depth from 7°to 22°N. The DO values observed at 200 m (0.0005-0.24 mlÁl À1 ) indicated that this area is lying within an OMZ. Five major taxa, namely Platyhelminthes, Sipunculoidea, Echiuroidea, Echinodermata and Cephalochordata were absent from the samples collected from this OMZ. In general, declines in total macrobenthic density and biomass and polychaete species richness and diversity were observed in this OMZ compared with the shallower depths above it. Community analyses of polychaetes revealed the dominance of species belonging to families Spionidae, Cirratulidae and Paraonidae in this OMZ. Low oxygen condition was more pronounced in the northern continental shelf edge ( 0.03 mlÁl À1 ), where the majority of spionids including Prionospio pinnata and cirratulids were absent; whereas amphipod, isopod and bivalve communities were not impacted. 22 Marine Ecology 35 (2014) 22-35 ª

Macrobenthic composition of the southeast continental shelf of India

“…In the present study the second dominant group was crustaceans, as found in previous works (Jayaraj et al 2007;Joydas & Damodaran 2009, 2013Musale & Desai 2011) and in other areas (Johnson et al 2007;Sellanes et al 2007;Mamouridis et al 2011;Naser 2011). Hoey et al (2004 reported 65 species (34%) of crustaceans, which constituted the second most dominant group among macrobenthos.…”

“…Joydas & Damodaran (2009) also observed the dominance of polychaetes (56.97%) in the macrofauna of the west coast of India, followed by crustaceans (28.05%). The dominance of polychaetes in the shelf region of the India has been reported by various workers (Vizakat et al 1991;Prabhu et al 1993;Ganesh 2003;: Jayaraj et al 2007;Ganesh & Raman 2007;Joydas & Damodaran 2013).…”

“…In the present study the second dominant group was crustaceans, as found in previous works (Jayaraj et al . ; Joydas & Damodaran , ; Musale & Desai ) and in other areas (Johnson et al . ; Sellanes et al .…”

Macrobenthos relative to the oxygen minimum zone on the East Indian margin, Bay of Bengal

“…On the west coast of India, sediment organic matter levels were appreciably higher within the OMZ areas, coinciding with depleted DO (Ingole et al . ; Joydas & Damodaran ). Our observations in the Bay of Bengal are in conformity with the generalised models – falling DO levels coincided with depths that promoted organic matter accumulation within the OMZ.…”

“…The recently concluded Deep Gulf of Mexico Benthos program on the continental slope and abyssal plain of Mexico is one example of a program aimed at understanding how oil and gas exploration and production might affect the ecosystem and its inhabitants even at such great depths (Rowe & Kennicutt 2008). In the Indian Ocean region, deep-sea macrobenthos investigations in relation to the OMZ have been carried out on the Oman margin in the NW Arabian Sea (Levin et al 2000) and more recently on the Pakistan slope Hughes et al 2009;Levin et al 2009b;Murty et al 2009) and the West Indian shelf in the Arabian Sea Hunter et al 2011Hunter et al , 2012Levin et al 2013;Joydas & Damodaran 2014). At present, macrobenthic studies on the E Indian margin in the Bay of Bengal are limited to mid-shelf depths (30-200 m;Ganesh & Raman 2007).…”