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Zooplankton growth and trophic linkages: Implications for fish feeding conditions in the Baltic Sea
Stockholm University, Faculty of Science, Department of Systems Ecology. (Marine Ecology)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this Thesis was to improve our understanding and assessment of feeding conditions for zooplanktivorous fish in the Baltic Sea.

We investigated (papers I, II) the usefulness of biochemical proxies for assessments of growth and metabolic rates in the dominant Baltic copepod Acartia bifilosa. A predictive model (paper I) for egg production rate (EPR), based on body size, RNA content, and water temperature, was established using females of different geographical origin. This model demonstrates the usefulness of RNA content as a proxy for growth in zooplankton and, together with abundance data, it could be used to evaluate fish feeding conditions. Further (paper II), using A. bifilosa exposed to a food gradient, we evaluated responses of physiological rates and other biochemical proxies for growth and established correlations between physiological and biochemical variables. EPR and ingestion rate were most significantly correlated with RNA content. As assayed variables saturated at different food concentrations, food availability may affect assessments of physiological rates using proxies. In paper III, we explored the effect of high EPR and ingestion rate on astaxanthin content in A. bifilosa. We found that the astaxanthin content decreased at high feeding rates, most likely due to decreased assimilation efficiency. This may impact the quality of zooplankton as prey.

The invasion of Cercopagis pengoi, a zooplanktivorous cladoceran, has altered the trophic linkages in the Baltic Sea food web. In paper IV, we evaluated the feeding of zooplanktivorous fish on C. pengoi and found that irrespective of size both herring and sprat feed on it, with large herring being more selective. In turn, C. pengoi feeds mainly on older copepods (paper V), which are acknowledged important in fish nutrition. These results indicate that C. pengoi may compete with fish due to the diet overlap.

Place, publisher, year, edition, pages
Stockholm: Department of System Ecology, Stockholm University , 2009. , 38 p.
Keyword [en]
AARS activity, biochemical markers, Clupea harengus, copepod physiology, food web interactions, non-indigenous species, RNA-based indices, Sprattus sprattus, stable isotopes
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-29485ISBN: 978-91-7155-908-1 (print)OAI: oai:DiVA.org:su-29485DiVA: diva2:233529
Public defence
2009-10-14, G-salen, Arrheniuslaboratorierna, Svante Arrhenius väg 16, Stockholm, 09:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: In progress. Paper 3: Submitted

Available from: 2009-09-22 Created: 2009-09-01 Last updated: 2012-10-31Bibliographically approved
List of papers
1. Decreased astaxanthin at high feeding rates in the calanoid copepod Acartia bifilosa
Open this publication in new window or tab >>Decreased astaxanthin at high feeding rates in the calanoid copepod Acartia bifilosa
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2009 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 31, no 6, 661-668 p.Article in journal (Refereed) Published
Abstract [en]

In marine food webs, copepods are the major producers of a carotenoid pigment astaxanthin, which is an important antioxidant. The availability of astaxanthin for higher trophic levels can be affected by changes in phytoplankton stocks and copepod feeding; however, the functional relationship between food availability and astaxanthin production is poorly understood. We hypothesized that with a given food type and quality, astaxanthin content in copepods is positively related to feeding and egg production rates. The hypothesis was tested by measuring astaxanthin accumulation in concert with ingestion and egg production rates in the copepod Acartia bifilosa exposed to different algal concentrations (Tetraselmis suecica; 0 to 1200 μg C L−1). Egg production and ingestion rates increased with increasing food availability and reached a plateau at ≥400–600 μg C L−1. In contrast, increasing accumulation of astaxanthin with increasing food availability was observed only at concentrations ≤150 μg C L−1. Contrary to our hypothesis, at 600–1200 μg C L−1 copepods had maximal ingestion and egg production rates, but low astaxanthin contents. It is suggested that this low accumulation of astaxanthin at high food concentrations results from a food-dependant decrease in assimilation efficiency. These findings are important for the understanding of astaxanthin dynamics within marine food webs, where increases in phytoplankton biomass may translate to a trade-off between zooplankton quantity and its nutritional quality for zooplanktivores.

National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-29484 (URN)10.1093/plankt/fbp016 (DOI)000265741700006 ()
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2017-12-13Bibliographically approved
2. Assessing diet of the non-indigenous predatory cladoceran Cercopagis pengoi using stable isotopes
Open this publication in new window or tab >>Assessing diet of the non-indigenous predatory cladoceran Cercopagis pengoi using stable isotopes
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:su:diva-29480 (URN)
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2010-01-14Bibliographically approved
3. Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
Open this publication in new window or tab >>Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
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2009 (English)In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 7, 785-794 p.Article in journal (Refereed) Published
Abstract [en]

Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0–1200 µg C L–1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-32862 (URN)000273294600007 ()
Available from: 2009-12-17 Created: 2009-12-17 Last updated: 2017-12-12Bibliographically approved
4. Relationships between RNA content and egg production rate in Acartia bifilosa (Copepoda, Calanoida) of different spatial and temporal origin
Open this publication in new window or tab >>Relationships between RNA content and egg production rate in Acartia bifilosa (Copepoda, Calanoida) of different spatial and temporal origin
2008 (English)In: MARINE BIOLOGY, ISSN 0025-3162, Vol. 153, no 3, 483-491 p.Article in journal (Refereed) Published
Abstract [en]

To evaluate factors regulating RNA content (RNA, mu g RNA female(-1)) -egg production rate (EPR, eggs female(-1) day(-1)) relationship and to develop a model for in situ egg production rate estimates for Acartia bifilosa, we (1) measured EPR and RNA in females sampled at geographically distant areas at varying temperature (T, degrees C), (2) determined environmental (station, season, and T), endogenous (prosome length (PL), mm and EPR) variables that influence RNA levels, and (3) explored a set of multiple regression models to predict EPR from RNA, PL, station, season, and T. Egg production experiments were carried out in spring and summer 2005 in the Gulf of Finland and in the western part of the northern Baltic proper. We found that up to 88% of the RNA variation could be explained by variations in PL, EPR, and season/T. In explaining the RNA variability, PL played a major role followed in order of importance by EPR and season/T. Further, PL, RNA, and season/T explained up to 53% of the variation in EPR, nearly half of which is explained by RNA alone. The effect of spatial origin was never significant, suggesting that the derived relationships are general for A. bifilosa inhabiting northern Baltic proper.

National Category
Ecology
Identifiers
urn:nbn:se:su:diva-15629 (URN)doi:10.1007/s00227-007-0838-2 (DOI)000251488200023 ()
Note
There is an Erratum available for this publicationAvailable from: 2008-12-07 Created: 2008-12-07 Last updated: 2009-09-01Bibliographically approved
5. Erratum to: Relationships between RNA content and egg production rate in Acartia bifilosa (Copepoda, Calanoida) of different spatial and temporal origin
Open this publication in new window or tab >>Erratum to: Relationships between RNA content and egg production rate in Acartia bifilosa (Copepoda, Calanoida) of different spatial and temporal origin
2008 (English)In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 153, no 5, 1007-1008 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-29479 (URN)10.1007/s00227-007-0887-6 (DOI)
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2017-12-13Bibliographically approved
6. Predation by herring (Clupea harengus) and sprat (Sprattus sprattus) on Cercopagis pengoi in a wastern Baltic Sea bay
Open this publication in new window or tab >>Predation by herring (Clupea harengus) and sprat (Sprattus sprattus) on Cercopagis pengoi in a wastern Baltic Sea bay
2004 (English)In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 61, no 6, 959-965 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-29483 (URN)10.1016/j.icesjms.2004.06.016 (DOI)
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2017-12-13Bibliographically approved

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