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The role of hydrostatic pressure in constraining the bathymetric distribution of marine ectotherms

The role of hydrostatic pressure in constraining the bathymetric distribution of marine ectotherms
The role of hydrostatic pressure in constraining the bathymetric distribution of marine ectotherms
A hyperbaric and thermal physiological bottleneck at bathyal depths is thought to contribute to bathymetric zonation of marine benthic invertebrates and demersal fishes on deep continental margins. The focus of this thesis was to investigate hyperbaric tolerance in the lithodid crab Lithodes maja as a case study for the effects of hydrostatic pressure on upper bathyal marine ectotherms. Experimental hyperbaric exposures revealed that hyperbaric tolerance is oxygen- and capacity-limited. Hyperbaric tolerance appears proximately oxygen-limited, but ultimately limited by cardiac capacity: adverse hyperbaric impacts on cardiac capacity appear mediated by the effects of pressure on membranes and membrane related functions. However, bathymetric range appears constrained by increased metabolic cost at elevated hydrostatic pressure. Hyperbaric limitation of bathymetric range supports a role for hydrostatic pressure in structuring bathymetric zonation in the deep sea, and lineage-specific physiological tolerances appear to contribute to global phylogenetic bottlenecks. Further, physiological effects of high hydrostatic pressure and low temperature at bathyal depths, acting on shallow-water taxa at the lower limits of their distribution, may invoke a stress–evolution mechanism. The resulting bathymetric variation in speciation rates could drive a unimodal diversity–depth pattern, typically peaking at bathyal depths, over time.

Marine ectotherms’ thermal tolerance is also oxygen- and capacity-limited, and functionally associated with hypoxia tolerance. Comparing hypoxia thresholds and hyperbaric thresholds of taxonomic groups of shallow-water fauna revealed significant correlation, supporting the proposition that hydrostatic pressure tolerance is oxygen- limited. Consequently, it appears that the combined effects of temperature, pressure, and oxygen concentration constrain the fundamental ecological niches of marine invertebrates and fishes. Including depth in a conceptual model of oxygen- and capacity-limited fundamental ecological niches’ responses to ocean warming and deoxygenation confirms that polar taxa are most vulnerable to the effects of climate change, but reveals for the first time that temperate fauna as well as tropical fauna may experience substantial fundamental ecological niche expansion with ocean warming and deoxygenation.
University of Southampton
Brown, Alastair Edward
909f34db-bc9c-403f-ba8f-31aee1c00161
Brown, Alastair Edward
909f34db-bc9c-403f-ba8f-31aee1c00161
Thatje, Sven
f1011fe3-1048-40c0-97c1-e93b796e6533

Brown, Alastair Edward (2015) The role of hydrostatic pressure in constraining the bathymetric distribution of marine ectotherms. University of Southampton, Ocean & Earth Science, Doctoral Thesis, 197pp.

Record type: Thesis (Doctoral)

Abstract

A hyperbaric and thermal physiological bottleneck at bathyal depths is thought to contribute to bathymetric zonation of marine benthic invertebrates and demersal fishes on deep continental margins. The focus of this thesis was to investigate hyperbaric tolerance in the lithodid crab Lithodes maja as a case study for the effects of hydrostatic pressure on upper bathyal marine ectotherms. Experimental hyperbaric exposures revealed that hyperbaric tolerance is oxygen- and capacity-limited. Hyperbaric tolerance appears proximately oxygen-limited, but ultimately limited by cardiac capacity: adverse hyperbaric impacts on cardiac capacity appear mediated by the effects of pressure on membranes and membrane related functions. However, bathymetric range appears constrained by increased metabolic cost at elevated hydrostatic pressure. Hyperbaric limitation of bathymetric range supports a role for hydrostatic pressure in structuring bathymetric zonation in the deep sea, and lineage-specific physiological tolerances appear to contribute to global phylogenetic bottlenecks. Further, physiological effects of high hydrostatic pressure and low temperature at bathyal depths, acting on shallow-water taxa at the lower limits of their distribution, may invoke a stress–evolution mechanism. The resulting bathymetric variation in speciation rates could drive a unimodal diversity–depth pattern, typically peaking at bathyal depths, over time.

Marine ectotherms’ thermal tolerance is also oxygen- and capacity-limited, and functionally associated with hypoxia tolerance. Comparing hypoxia thresholds and hyperbaric thresholds of taxonomic groups of shallow-water fauna revealed significant correlation, supporting the proposition that hydrostatic pressure tolerance is oxygen- limited. Consequently, it appears that the combined effects of temperature, pressure, and oxygen concentration constrain the fundamental ecological niches of marine invertebrates and fishes. Including depth in a conceptual model of oxygen- and capacity-limited fundamental ecological niches’ responses to ocean warming and deoxygenation confirms that polar taxa are most vulnerable to the effects of climate change, but reveals for the first time that temperate fauna as well as tropical fauna may experience substantial fundamental ecological niche expansion with ocean warming and deoxygenation.

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Submitted date: 5 August 2014
Published date: 2015
Organisations: University of Southampton, Ocean and Earth Science, Southampton Marine & Maritime Institute

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Local EPrints ID: 377296
URI: https://eprints.soton.ac.uk/id/eprint/377296
PURE UUID: d073dbe2-38fb-43cb-b21d-d9c322851f26

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Date deposited: 21 May 2015 10:29
Last modified: 25 Jan 2018 17:30

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