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The trophic ecology of key megafaunal species at the Pakistan Margin: Evidence from stable isotopes and lipid biomarkers

The trophic ecology of key megafaunal species at the Pakistan Margin: Evidence from stable isotopes and lipid biomarkers
The trophic ecology of key megafaunal species at the Pakistan Margin: Evidence from stable isotopes and lipid biomarkers
The Arabian Sea is subject to intense seasonality resulting from biannual monsoons, which lead to associated large particulate fluxes and an abundance of organic carbon, a potential food source at the seafloor for benthic detritivores. We used the stable isotopes of carbon and nitrogen alongside lipid analyses to examine potential food sources (particulate and sedimentary organic matter, POM and SOM respectively) in order to determine trophic linkages for the twelve most abundant megafaunal species (Pontocaris sp., Solenocera sp., Munidopsis aff. scobina, Actinoscyphia sp., Actinauge sp., Echinoptilum sp., Pennatula aff. grandis, Astropecten sp. Amphiura sp. Ophiura euryplax, Phormosoma placenta and Hyalinoecia sp.) at the Pakistan Margin between 140 and 1400 m water depth. This transect spans a steep gradient in oxygen concentrations and POM flux. Ranges of ?13C and ?15N values were narrow in POM and SOM (4‰ and 2‰ for ?13C and ?15N, respectively) with little evidence of temporal variability. Labile lipid compounds in SOM originating from phytoplankton did exhibit seasonal change in their concentrations at the shallowest sites, 140 and 300 m. Benthic megafauna had broad ranges in ?13C and ?15N (>10‰ and >8‰ for ?13C and ?15N, respectively) suggesting they occupy several trophic levels and utilize a variety of food sources. There is evidence for feeding niche separation between and within trophic groups. Lipid biomarkers in animal tissues indicate a mixture of food sources originating from both phytoplankton (C20:5(n-3) and C22:6(n-3)) and invertebrate prey (C20:1 and C22:1). Biomarkers originating from phytodetritus are conserved through trophic transfer to the predator/scavengers. Six species (Pontocaris sp., Solenocera sp., Actinoscyphia sp., Echinoptilum sp., Amphiura sp. and Hyalinoecia sp.) showed a significant biochemical response to the seasonal supply of food and probably adapt their trophic strategy to low food availability. Biotransformation of assimilated lipids by megafauna is evident from polyunsaturated fatty acid distributions, for example, Echinoptilum sp. converts C20:5(n-3) to C24:6(n-3).

Benthos, Megafauna, Oxygen minimum zone, Stable isotopes, Lipids, Pakistan Margin, Seasonality
0967-0637
1816-1833
Jeffreys, Rachel M.
00be4640-1d07-4f82-964a-0a61b50322c4
Wolff, George A.
6b29d886-06f9-4405-8fab-33cfb436acaa
Murty, Sarah J.
5b2d7c42-4634-4d20-adc4-94cb77f54ec2
Jeffreys, Rachel M.
00be4640-1d07-4f82-964a-0a61b50322c4
Wolff, George A.
6b29d886-06f9-4405-8fab-33cfb436acaa
Murty, Sarah J.
5b2d7c42-4634-4d20-adc4-94cb77f54ec2

Jeffreys, Rachel M., Wolff, George A. and Murty, Sarah J. (2009) The trophic ecology of key megafaunal species at the Pakistan Margin: Evidence from stable isotopes and lipid biomarkers. Deep Sea Research Part I: Oceanographic Research Papers, 56 (10), 1816-1833. (doi:10.1016/j.dsr.2009.05.001).

Record type: Article

Abstract

The Arabian Sea is subject to intense seasonality resulting from biannual monsoons, which lead to associated large particulate fluxes and an abundance of organic carbon, a potential food source at the seafloor for benthic detritivores. We used the stable isotopes of carbon and nitrogen alongside lipid analyses to examine potential food sources (particulate and sedimentary organic matter, POM and SOM respectively) in order to determine trophic linkages for the twelve most abundant megafaunal species (Pontocaris sp., Solenocera sp., Munidopsis aff. scobina, Actinoscyphia sp., Actinauge sp., Echinoptilum sp., Pennatula aff. grandis, Astropecten sp. Amphiura sp. Ophiura euryplax, Phormosoma placenta and Hyalinoecia sp.) at the Pakistan Margin between 140 and 1400 m water depth. This transect spans a steep gradient in oxygen concentrations and POM flux. Ranges of ?13C and ?15N values were narrow in POM and SOM (4‰ and 2‰ for ?13C and ?15N, respectively) with little evidence of temporal variability. Labile lipid compounds in SOM originating from phytoplankton did exhibit seasonal change in their concentrations at the shallowest sites, 140 and 300 m. Benthic megafauna had broad ranges in ?13C and ?15N (>10‰ and >8‰ for ?13C and ?15N, respectively) suggesting they occupy several trophic levels and utilize a variety of food sources. There is evidence for feeding niche separation between and within trophic groups. Lipid biomarkers in animal tissues indicate a mixture of food sources originating from both phytoplankton (C20:5(n-3) and C22:6(n-3)) and invertebrate prey (C20:1 and C22:1). Biomarkers originating from phytodetritus are conserved through trophic transfer to the predator/scavengers. Six species (Pontocaris sp., Solenocera sp., Actinoscyphia sp., Echinoptilum sp., Amphiura sp. and Hyalinoecia sp.) showed a significant biochemical response to the seasonal supply of food and probably adapt their trophic strategy to low food availability. Biotransformation of assimilated lipids by megafauna is evident from polyunsaturated fatty acid distributions, for example, Echinoptilum sp. converts C20:5(n-3) to C24:6(n-3).

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More information

Published date: October 2009
Keywords: Benthos, Megafauna, Oxygen minimum zone, Stable isotopes, Lipids, Pakistan Margin, Seasonality

Identifiers

Local EPrints ID: 67566
URI: http://eprints.soton.ac.uk/id/eprint/67566
ISSN: 0967-0637
PURE UUID: ec7ac833-1952-4b70-918f-91893b4dd9d8

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Date deposited: 25 Aug 2009
Last modified: 13 Mar 2024 18:53

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Contributors

Author: Rachel M. Jeffreys
Author: George A. Wolff
Author: Sarah J. Murty

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