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Copepods in Skeletonema-dominated food webs: Toxicity and nutritional quality as factors controlling copepod-diatom interactions
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

My thesis focuses on copepod-diatom interactions, specifically on the effects of food quality and toxicity on copepod feeding, reproductive success and behavior but as a frame, also includes a quantitative evaluation of copepod carbon requirements compared to other trophic plankton groups. My aim was to evaluate the function of copepods in diatom-dominated spring blooms. I thereby used a series of mesocosm and laboratory experiments. For a realistic extrapolation of the results to natural environments I used different strains of a diatom species, Skeletonema marinoi, which is a common spring blooming species in the Baltic Sea. This species is known to produce polyunsaturated aldehydes (PUA; mainly heptadienal, octadienal and decadienal), which have previously been identified as the potential reasons for the detrimental effects of diatoms on copepod reproduction. All strains varied in size, mineral and biochemical content, and PUA production. I tested the effects on different dominant copepod species from northern temperate waters; Acartia sp. (A. clausi and A. tonsa), Calanus finmarchicus, Pseudocalanus elongatus, and Temora longicornis, as well as the dominant species in the northern Baltic Sea, Eurytemora affinis.

The specific contributions of respiratory carbon requiment of mesozooplankton and lower size fractions to carbon cycling during PUA-producing diatom blooms are poorly documented. My results show that nanoplankton and microzooplankton dominated the carbon cycling (> 50% of primary production) whereas the contribution of bacterioplankton varied. Mesozooplankton was always of minor importance with contribution of <6% of primary production.  This illustrates the importance of lower size fractions during a phytoplankton spring bloom.

Irrespective of their small contribution to the total community carbon cycling, copepods displayed non-selective and typically high feeding rate on different PUA-producing S. marinoi strains, indicating that there was no feeding deterrence. The effect of feeding on copepod reproductive success, however, varied between different strains, and depending on copepod species. In experiments with monospecific diatom diets reduced egg production rate and hatching success were mainly related to food quality measured as fatty acids and sterols, or algae growth rate, low assimilation efficiency or PUA production / ingestion. On the other hand, copepod reproduction and population development in the diverse diet, including a high concentration of S. marinoi and PUA (both particulate and dissolved), increased with increasing food concentration and was unaffected by the presence of toxic diatoms. I conclude that although a negative correlation between different reproductive variables and PUA production / ingestion may sometimes be observed in laboratory incubations, this is highly dependent on the strain / species used, and the effect of the algal strain can be stronger than the effect of the e.g., growth-stage dependent PUA production. Although copepod grazing might not be very important during a diatom spring bloom, even a highly PUA-producing S. marinoi can be considered an appropriate food source for copepods when occurring among the natural food assemblage, inducing a high reproductive output. 

Place, publisher, year, edition, pages
Umeå: Department of Ecology & Environmental Science, Umeå University , 2011. , 25 p.
Keyword [en]
Copepod-diatom interaction, toxicity, nutritional quality, Skeletonema
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:umu:diva-49411ISBN: 978-91-7459-297-9 (print)OAI: oai:DiVA.org:umu-49411DiVA: diva2:455872
Public defence
2011-12-05, Naturvetarhuset, Natural Science Building, N420, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-11-14 Created: 2011-11-11 Last updated: 2011-11-14Bibliographically approved
List of papers
1. Partition of planktonic respiratory carbon requirements during a phytoplankton spring bloom
Open this publication in new window or tab >>Partition of planktonic respiratory carbon requirements during a phytoplankton spring bloom
2012 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 451, 15-29 p.Article in journal (Refereed) Published
Abstract [en]

We studied the effect of variable phytoplankton biomass and dominance of the diatom Skeletonema marinoi on the planktonic community respiratory carbon requirement over a period of 14 days (14-28 April, 2008) in 3 different mesocosms filled with natural water at Espegrend marine biological field station by Raunefjord, Norway. The carbon requirement was measured on mesozooplankton (the calanoid copepod Calanus finmarchicus) and three different size fraction; <200 µm (dominated by microzooplankton), <15 µm (dominated by nanoplankton including most of the phytoplankton) and particles passing GF/C (dominated by bacterioplankton) by measuring oxygen consumption with an optode system with two SensorDish Readers. The respiratory carbon requirement showed no clear trend over time for any of the four groups. The mesozooplankton contributed the least to the total community carbon requirement, corresponding to less than 6% of primary production. In contrast, microzooplankton and nanoplankton consistently dominated the community carbon requirement, corresponding to > 50% of the primary production, while bacterioplankton showed an intermediate and variable contribution (ca <20% with a max of 50%). Feeding experiments on mesozooplankton (C. finmarchicus) two days before the peak in phytoplankton biomass, showed that the copepods ingested 2.4-4.3 times their respiratory carbon requirements, thus giving a high potential for growth. Respiratory carbon requirements of mesozooplankton were not significantly related to dominance or quantity of food available, whereas the respiratory carbon requirements of other groups were all related to the production of 22:6(n-3) fatty acid. The study confirms the important role of microorganisms in the biological carbon transformation through the food web during a phytoplankton spring bloom.

Place, publisher, year, edition, pages
Inter-research, 2012
Keyword
Plankton community, respiratory carbon requirement, Skeletonema marinoi, mesozooplankton, Calanus
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-49415 (URN)10.3354/meps09564 (DOI)000303908000002 ()
Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-10-24Bibliographically approved
2. Strain-related physiological and behavioral effects of Skeletonema marinoi on three common planktonic copepods
Open this publication in new window or tab >>Strain-related physiological and behavioral effects of Skeletonema marinoi on three common planktonic copepods
2011 (English)In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 158, no 9, 1965-1980 p.Article in journal (Refereed) Published
Abstract [en]

Three strains of the chain-forming diatom Skeletonema marinoi, differing in their production of polyunsaturated aldehydes (PUA) and nutritional food components, were used in experiments on feeding, egg production, hatching success, pellet production, and behavior of three common planktonic copepods: Acartia tonsa, Pseudocalanus elongatus, and Temora longicornis. The three different diatom strains (9B, 1G, and 7J) induced widely different effects on Acartia tonsa physiology, and the 9B strain induced different effects for the three copepods. In contrast, different strains induced no or small alterations in the distribution, swimming behavior, and turning frequency of the copepods. 22:6(n-3) fatty acid (DHA) and sterol content of the diet typically showed a positive effect on either egg production (A. tonsa) or hatching success (P. elongatus), while other measured compounds (PUA, other long-chain polyunsaturated fatty acids) of the algae had no obvious effects. Our results demonstrate that differences between strains of a given diatom species can generate effects on copepod physiology, which are as large as those induced by different algae species or groups. This emphasizes the need to identify the specific characteristics of local diatoms together with the interacting effects of different mineral, biochemical, and toxic compounds and their potential implications on different copepod species.

Place, publisher, year, edition, pages
Berlin: Springer-Verlag, 2011
Keyword
patchy food environments, fatty-acid-composition, acartia-tonsa dana, egg-production, hatching success, reproductive success, temora-longicornis, polyunsaturated aldehydes, laboratory observations, calanus-helgolandicus
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-46677 (URN)10.1007/s00227-011-1706-7 (DOI)
Available from: 2011-09-14 Created: 2011-09-09 Last updated: 2017-10-24Bibliographically approved

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