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Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic Meridional Transect (AMT) programme

Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic Meridional Transect (AMT) programme
Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic Meridional Transect (AMT) programme
Coccolithophore species composition was determined in 199 samples collected from the upper 300 m of the Atlantic Ocean, spanning temperate, tropical and subtropical waters in both hemispheres during four Atlantic Meridional Transect (AMT) cruises over the period 2003 to 2005. Of the 171 taxa observed, 140 consistently represented less than 5% of total cell numbers, and were classed as rare. Multivariate statistical techniques were used on the common taxa to assess variability in community composition vertically in the water column, horizontally across hydrographic provinces (subtropical gyres, equatorial waters, temperate waters), and temporally between cruises. Sharper gradients of statistical dissimilarity in species composition occurred vertically over a few tens of metres than horizontally over hundreds of kilometres. Three floral groups were identified from analysis of the depth of normalised abundance maxima in the subtropical gyres and equatorial waters: the upper euphotic zone (UEZ, >10% surface irradiance); the lower euphotic zone (LEZ, 10-1% surface irradiance); and the sub-euphotic zone (SEZ, <1% surface irradiance). The LEZ includes the deep chlorophyll maximum (DCM) and nutricline, and was characterised by species such as Emiliania huxleyi and Gephyrocapsa ericsonii which were also abundant at higher latitudes. It is suggested that this pattern reflects similarities in the light (and inorganic nutrient) conditions between the LEZ and temperate waters. The SEZ is below the depth where light is thought to be sufficient to support photosynthesis, suggesting that deep-dwelling species such as Florisphaera profunda and Gladiolithus spp. may be mixotrophic or phagotrophic, although conclusive proof will need to be gained experimentally. Mixotrophy could also be an important nutritional strategy for species abundant (Umbellosphaera spp., holococcolithophores) in the UEZ where inorganic nutrient concentrations are depleted and limiting to growth, although other nutritional strategies, such as the use of organic nutrients, are also possible. Statistical differences were also found in the species composition between the different cruises, with high levels of similarity for similar timed cruises (May or September-October). Few individual taxa showed significant variability in abundance over the time-span of sampling, except species such as E. huxleyi and G. ericsonii at higher latitudes. In subtropical and equatorial waters, high levels of species richness and low levels of species dominance remained throughout the sampling period indicating that seasonal fluctuations reflected differences in the whole coccolithophore community rather than in just one or a few species. Multivariate analyses of the taxa classified as rare also indicated some level of temporal, as well as vertical, zonation. Such insights into coccolithophore ecology and community composition provide important new perspectives that require innovative research to fully understand their impact on ocean biogeochemistry.
Coccolithophores, euphotic zone, biogeography, physiology, mixotrophy, Atlantic Ocean, subtropical, tropics, equatorial waters, temperate waters
0079-6611
150-170
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Holligan, Patrick M.
4c1d9d64-dfa7-49bf-9e15-37f891d59b7c
Charalampopoulou, Anastasia
2b5d63cd-be8f-45d2-95cd-68cb591d7407
Adey, Tim R.
5737a6f0-844e-4c7c-b695-b941a5a6f887
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Holligan, Patrick M.
4c1d9d64-dfa7-49bf-9e15-37f891d59b7c
Charalampopoulou, Anastasia
2b5d63cd-be8f-45d2-95cd-68cb591d7407
Adey, Tim R.
5737a6f0-844e-4c7c-b695-b941a5a6f887

Poulton, Alex J., Holligan, Patrick M., Charalampopoulou, Anastasia and Adey, Tim R. (2017) Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic Meridional Transect (AMT) programme. Progress in Oceanography, 158, 150-170. (doi:10.1016/j.pocean.2017.01.003).

Record type: Article

Abstract

Coccolithophore species composition was determined in 199 samples collected from the upper 300 m of the Atlantic Ocean, spanning temperate, tropical and subtropical waters in both hemispheres during four Atlantic Meridional Transect (AMT) cruises over the period 2003 to 2005. Of the 171 taxa observed, 140 consistently represented less than 5% of total cell numbers, and were classed as rare. Multivariate statistical techniques were used on the common taxa to assess variability in community composition vertically in the water column, horizontally across hydrographic provinces (subtropical gyres, equatorial waters, temperate waters), and temporally between cruises. Sharper gradients of statistical dissimilarity in species composition occurred vertically over a few tens of metres than horizontally over hundreds of kilometres. Three floral groups were identified from analysis of the depth of normalised abundance maxima in the subtropical gyres and equatorial waters: the upper euphotic zone (UEZ, >10% surface irradiance); the lower euphotic zone (LEZ, 10-1% surface irradiance); and the sub-euphotic zone (SEZ, <1% surface irradiance). The LEZ includes the deep chlorophyll maximum (DCM) and nutricline, and was characterised by species such as Emiliania huxleyi and Gephyrocapsa ericsonii which were also abundant at higher latitudes. It is suggested that this pattern reflects similarities in the light (and inorganic nutrient) conditions between the LEZ and temperate waters. The SEZ is below the depth where light is thought to be sufficient to support photosynthesis, suggesting that deep-dwelling species such as Florisphaera profunda and Gladiolithus spp. may be mixotrophic or phagotrophic, although conclusive proof will need to be gained experimentally. Mixotrophy could also be an important nutritional strategy for species abundant (Umbellosphaera spp., holococcolithophores) in the UEZ where inorganic nutrient concentrations are depleted and limiting to growth, although other nutritional strategies, such as the use of organic nutrients, are also possible. Statistical differences were also found in the species composition between the different cruises, with high levels of similarity for similar timed cruises (May or September-October). Few individual taxa showed significant variability in abundance over the time-span of sampling, except species such as E. huxleyi and G. ericsonii at higher latitudes. In subtropical and equatorial waters, high levels of species richness and low levels of species dominance remained throughout the sampling period indicating that seasonal fluctuations reflected differences in the whole coccolithophore community rather than in just one or a few species. Multivariate analyses of the taxa classified as rare also indicated some level of temporal, as well as vertical, zonation. Such insights into coccolithophore ecology and community composition provide important new perspectives that require innovative research to fully understand their impact on ocean biogeochemistry.

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Accepted/In Press date: 7 January 2017
Published date: 1 November 2017
Keywords: Coccolithophores, euphotic zone, biogeography, physiology, mixotrophy, Atlantic Ocean, subtropical, tropics, equatorial waters, temperate waters
Organisations: Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 404647
URI: https://eprints.soton.ac.uk/id/eprint/404647
ISSN: 0079-6611
PURE UUID: f172543e-5c6f-4d81-a3a3-1c52076b02e6

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Date deposited: 12 Jan 2017 14:40
Last modified: 03 Dec 2019 06:22

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Contributors

Author: Alex J. Poulton
Author: Patrick M. Holligan
Author: Anastasia Charalampopoulou
Author: Tim R. Adey

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