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Absorption efficiencies and basal turnover of C, N and fatty acids in a marine Calanoid copepod

Mayor, Daniel J., Cook, Kathryn, Thornton, Barry, Walsham, Pamela, Witte, Ursula F. M., Zuur, Alain F. and Anderson, Thomas R. (2011) Absorption efficiencies and basal turnover of C, N and fatty acids in a marine Calanoid copepod Functional Ecology, 25, (3), pp. 509-518. (doi:10.1111/j.1365-2435.2010.01791.x).

Record type: Article

Abstract

1. Marine copepods of the genus Calanus can reproduce prior to the spring bloom in the absence of sufficient food. Their starvation physiology, and hence the factors limiting their pre-bloom population growth (egg production), remain poorly understood.

2. Stoichiometric theory can provide insights into the factors controlling an organism’s growth and the fate of elements in an ecosystem. It is underpinned by substrate utilization efficiencies that relate to key physiological processes such as absorption efficiencies (AEs) and biomass turnover. These parameters are seldom investigated, particularly in the case of essential ‘micronutrients’ such as the polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

3. Calanus spp. were fed briefly and subsequently starved for 5 days to determine basal turnover rates of biomass carbon, nitrogen and essential PUFAs. The effect of short-term fasting on nitrogen isotope signatures was also examined. The elemental, fatty acid and isotopic composition of their faecal pellets were compared to that of their food, providing insights into AEs and digestive isotopic discrimination.

4. Gut AEs typically followed the sequence: PUFA > nitrogen > carbon, although low AE for DHA was a notable exception. Starvation-induced losses of carbon, nitrogen, EPA and DHA demonstrate that homeostatic organisms must ingest all of these substrates in substantial quantity to achieve positive net growth.

5. Egested material was significantly depleted in 13C and 15N relative to the ingested food. We attribute this to isotopic discrimination at the macromolecular level, indicating that food quality contributes to the isotopic signature of a consumer organism. Values of d15N in the copepods’ tissues did not increase during starvation, despite significant losses of bulk nitrogen. This supports the suggestion that dissimilatory protein pathways in marine crustaceans are non-discriminating.

6. The significant basal turnover rates and variable AEs for essential PUFAs and nitrogen presented herein demonstrate that organisms cannot be assumed to utilize all nutritious substrates with the same, high efficiency, even when scarce in the diet. Our data highlight the need for a more detailed understanding of organismal physiology before isotopic and stoichiometric models can be meaningfully constructed and parameterized.

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More information

Accepted/In Press date: 7 October 2010
Published date: 1 June 2011
Keywords: absorption efficiency, Calanus, docosahexaenoic acid, ecological stoichiometry, eicosapentaenoic acid, essential polyunsaturated fatty acids, isotope fractionation, basal biomass turnover
Organisations: Marine Systems Modelling, National Oceanography Centre,Southampton

Identifiers

Local EPrints ID: 167287
URI: http://eprints.soton.ac.uk/id/eprint/167287
ISSN: 0269-8463
PURE UUID: e0404231-a586-44de-b3fd-fb4a20038eea

Catalogue record

Date deposited: 10 Nov 2010 13:06
Last modified: 18 Jul 2017 12:24

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Contributors

Author: Daniel J. Mayor
Author: Kathryn Cook
Author: Barry Thornton
Author: Pamela Walsham
Author: Ursula F. M. Witte
Author: Alain F. Zuur
Author: Thomas R. Anderson

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