The University of Southampton
University of Southampton Institutional Repository

Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna

Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna
Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna
The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150–1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140–1850 m water depth) across the OMZ during the 2003 intermonsoon (March–May) and late/post-monsoon (August–October) seasons. All groups exhibited some drop in abundance in the OMZ core (250–500 m water depth; O2: 0.10–0.13 mL L?1=4.46–5.80 ?M) but to differing degrees. Densities of foraminiferans >63 ?m were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 ?m were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O2 <0.14–0.15 mL L?1=6.25–6.69 ?M) but were represented by a huge, ophiuroid-dominated abundance peak at 1000 m (O2 0.15–0.18 mL L?1=6.69–8.03 ?M). Gromiid protists were confined largely to depths below 1150 m (O2 >0.2 mL L?1=8.92 ?M). The progressively deeper abundance peaks for foraminiferans (>63 ?m), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136–300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mL L?1(=5.80 ?M). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side.
Hypoxia, Oxygen minimum zone, Benthos, Arabian Sea, Biodiversity, Deep sea
0967-0645
488-502
Gooday, A.J.
d9331d67-d518-4cfb-baed-9df3333b05b9
Levin, L.A.
e7b34e8b-4aae-475f-abf6-6da85b313cdf
Aranda da Silva, A.
72acff95-3c27-4084-bb29-68183e74d5a1
Bett, B.J.
61342990-13be-45ae-9f5c-9540114335d9
Cowie, G.L.
3d3d9adf-b235-4a2b-919d-8c883beab0da
Dissard, D.
0c48b59f-c095-4d29-b4b3-72dca30fb6a7
Gage, J.D.
05b32e98-9bc2-4110-bec7-1d815c85c7b0
Hughes, D.J.
bfdc68bb-0efc-4b54-9401-865c68ee325a
Jeffreys, R.
5e8b9a45-d613-4e2f-939a-85a88cec25bf
Lamont, P.A.
0d73ccc1-bfef-4229-84f6-449db7f07bf3
Larkin, K.E.
f359bbaa-8a50-4972-9a01-2a9d4c428ba6
Murty, S.J.
866a06cc-68b6-4abc-9ff6-f3629984334f
Schumacher, S.
4287be7b-e112-403d-84e5-c4d3a6546437
Whitcraft, C.
2ac283a2-5aa7-423f-bdc7-5c764dec6330
Woulds, C.
4e4a8faf-aecb-4768-a6d5-6cbef7a4a4a2
Gooday, A.J.
d9331d67-d518-4cfb-baed-9df3333b05b9
Levin, L.A.
e7b34e8b-4aae-475f-abf6-6da85b313cdf
Aranda da Silva, A.
72acff95-3c27-4084-bb29-68183e74d5a1
Bett, B.J.
61342990-13be-45ae-9f5c-9540114335d9
Cowie, G.L.
3d3d9adf-b235-4a2b-919d-8c883beab0da
Dissard, D.
0c48b59f-c095-4d29-b4b3-72dca30fb6a7
Gage, J.D.
05b32e98-9bc2-4110-bec7-1d815c85c7b0
Hughes, D.J.
bfdc68bb-0efc-4b54-9401-865c68ee325a
Jeffreys, R.
5e8b9a45-d613-4e2f-939a-85a88cec25bf
Lamont, P.A.
0d73ccc1-bfef-4229-84f6-449db7f07bf3
Larkin, K.E.
f359bbaa-8a50-4972-9a01-2a9d4c428ba6
Murty, S.J.
866a06cc-68b6-4abc-9ff6-f3629984334f
Schumacher, S.
4287be7b-e112-403d-84e5-c4d3a6546437
Whitcraft, C.
2ac283a2-5aa7-423f-bdc7-5c764dec6330
Woulds, C.
4e4a8faf-aecb-4768-a6d5-6cbef7a4a4a2

Gooday, A.J., Levin, L.A., Aranda da Silva, A., Bett, B.J., Cowie, G.L., Dissard, D., Gage, J.D., Hughes, D.J., Jeffreys, R., Lamont, P.A., Larkin, K.E., Murty, S.J., Schumacher, S., Whitcraft, C. and Woulds, C. (2009) Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna. Deep Sea Research Part II: Topical Studies in Oceanography, 56 (6-7), 488-502. (doi:10.1016/j.dsr2.2008.10.003).

Record type: Article

Abstract

The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150–1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140–1850 m water depth) across the OMZ during the 2003 intermonsoon (March–May) and late/post-monsoon (August–October) seasons. All groups exhibited some drop in abundance in the OMZ core (250–500 m water depth; O2: 0.10–0.13 mL L?1=4.46–5.80 ?M) but to differing degrees. Densities of foraminiferans >63 ?m were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 ?m were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O2 <0.14–0.15 mL L?1=6.25–6.69 ?M) but were represented by a huge, ophiuroid-dominated abundance peak at 1000 m (O2 0.15–0.18 mL L?1=6.69–8.03 ?M). Gromiid protists were confined largely to depths below 1150 m (O2 >0.2 mL L?1=8.92 ?M). The progressively deeper abundance peaks for foraminiferans (>63 ?m), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136–300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mL L?1(=5.80 ?M). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side.

Text
Gooday_et_al._final1.pdf - Accepted Manuscript
Download (908kB)

More information

Published date: March 2009
Keywords: Hypoxia, Oxygen minimum zone, Benthos, Arabian Sea, Biodiversity, Deep sea
Organisations: Ocean and Earth Science, National Oceanography Centre,Southampton

Identifiers

Local EPrints ID: 66598
URI: http://eprints.soton.ac.uk/id/eprint/66598
ISSN: 0967-0645
PURE UUID: d6493247-fd18-467d-a4da-0327583fea30

Catalogue record

Date deposited: 30 Jun 2009
Last modified: 13 Mar 2024 18:26

Export record

Altmetrics

Contributors

Author: A.J. Gooday
Author: L.A. Levin
Author: A. Aranda da Silva
Author: B.J. Bett
Author: G.L. Cowie
Author: D. Dissard
Author: J.D. Gage
Author: D.J. Hughes
Author: R. Jeffreys
Author: P.A. Lamont
Author: K.E. Larkin
Author: S.J. Murty
Author: S. Schumacher
Author: C. Whitcraft
Author: C. Woulds

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×