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Subtle variation in abyssal terrain induces significant change in benthic megafaunal abundance, diversity, and community structure

Subtle variation in abyssal terrain induces significant change in benthic megafaunal abundance, diversity, and community structure
Subtle variation in abyssal terrain induces significant change in benthic megafaunal abundance, diversity, and community structure
Bathymetric gradients in the deep sea are known to affect key benthic community characteristics such as diversity. However, most studies investigate large-scale bathymetric variation, while habitat heterogeneity related to modest bathymetric variation has generally been overlooked because of limitations to sampling technology. We investigate the role of modest bathymetric variation (~10 m water depth intervals) on an abyssal hill, and horizontal variation at the 0.1–10 km scale, in the structuring of abyssal megafaunal assemblages. We assess numerical density, biomass density, diversity, and assemblage composition using seabed photographs captured with an autonomous underwater vehicle and sediment characteristics determined from cores. We detect significant differences in sediment particle size and organic carbon content, in relation to modest topographic elevation, with a greater fraction of fine particles and organic carbon on the abyssal plain than the hill. Total megafaunal numerical and biomass density, diversity, and the numerical densities of feeding groups were significantly different with modest topographic elevation; similarly, megafaunal composition varied significantly between ~10 m depth intervals. In relation to mesoscale horizontal variation, we also record significant differences between megabenthic communities in two abyssal plain areas with no significant differences in measured sedimentary characteristics and only a 2 m difference in water depth. Differences in these communities were detected in terms of dominance, assemblage composition by density and biomass, and numerical densities of feeding groups. These observations strongly indicate that previous general concepts of the abyssal environment greatly underestimate this mesoscale heterogeneity, such that beta- and gamma-diversity in the abyss may be higher than estimated. Importantly, these results also have clear implications for the design and interpretation of environmental survey and monitoring programmes in the abyss.
Abyssal plain, Deep sea, Ecology, Marine photography, Porcupine Abyssal Plain Sustained Observatory, Seabed environment
0079-6611
Durden, Jennifer M.
d7101246-b76b-44bc-8956-8ca4ae62ae1f
Bett, Brian J.
61342990-13be-45ae-9f5c-9540114335d9
Ruhl, Henry A.
177608ef-7793-4911-86cf-cd9960ff22b6
Durden, Jennifer M.
d7101246-b76b-44bc-8956-8ca4ae62ae1f
Bett, Brian J.
61342990-13be-45ae-9f5c-9540114335d9
Ruhl, Henry A.
177608ef-7793-4911-86cf-cd9960ff22b6

Durden, Jennifer M., Bett, Brian J. and Ruhl, Henry A. (2020) Subtle variation in abyssal terrain induces significant change in benthic megafaunal abundance, diversity, and community structure. Progress in Oceanography, 186, [102395]. (doi:10.1016/j.pocean.2020.102395).

Record type: Article

Abstract

Bathymetric gradients in the deep sea are known to affect key benthic community characteristics such as diversity. However, most studies investigate large-scale bathymetric variation, while habitat heterogeneity related to modest bathymetric variation has generally been overlooked because of limitations to sampling technology. We investigate the role of modest bathymetric variation (~10 m water depth intervals) on an abyssal hill, and horizontal variation at the 0.1–10 km scale, in the structuring of abyssal megafaunal assemblages. We assess numerical density, biomass density, diversity, and assemblage composition using seabed photographs captured with an autonomous underwater vehicle and sediment characteristics determined from cores. We detect significant differences in sediment particle size and organic carbon content, in relation to modest topographic elevation, with a greater fraction of fine particles and organic carbon on the abyssal plain than the hill. Total megafaunal numerical and biomass density, diversity, and the numerical densities of feeding groups were significantly different with modest topographic elevation; similarly, megafaunal composition varied significantly between ~10 m depth intervals. In relation to mesoscale horizontal variation, we also record significant differences between megabenthic communities in two abyssal plain areas with no significant differences in measured sedimentary characteristics and only a 2 m difference in water depth. Differences in these communities were detected in terms of dominance, assemblage composition by density and biomass, and numerical densities of feeding groups. These observations strongly indicate that previous general concepts of the abyssal environment greatly underestimate this mesoscale heterogeneity, such that beta- and gamma-diversity in the abyss may be higher than estimated. Importantly, these results also have clear implications for the design and interpretation of environmental survey and monitoring programmes in the abyss.

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Accepted/In Press date: 17 June 2020
Published date: 1 July 2020
Keywords: Abyssal plain, Deep sea, Ecology, Marine photography, Porcupine Abyssal Plain Sustained Observatory, Seabed environment

Identifiers

Local EPrints ID: 444451
URI: http://eprints.soton.ac.uk/id/eprint/444451
ISSN: 0079-6611
PURE UUID: ee14b806-0454-4ab3-be2a-47a8c492a00b

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Date deposited: 20 Oct 2020 16:30
Last modified: 26 Nov 2021 00:01

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Contributors

Author: Jennifer M. Durden
Author: Brian J. Bett
Author: Henry A. Ruhl

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