Effects of plankton community structure on energy pathways and tropic efficiency (PATH)
Final Report Abstract
The goal of this project was to use CSIA to investigate energy transfer from phytoplankton to mesozooplankton in marine food webs. We used both 513C of fatty acid (FA) and 51SN of amino acid (AA) to test and apply this tracing applicability in a diverse set of studies to improve our understanding of ecosystem functioning and response to climate change. A meta-anlysis of 51SN-AA revealed that this approach provides improved estimation of trophic position and feeding relationships in diverse organisms, as shown from measurements from 276 marine species covering 4 trophic levels. We found that the trophic enrichment factor was consistent across the trophic levels, however significantly lower than the commonly applied value. Modelling the trophic position using CSIA data revealed that the addition of multiple 51SN values from source and trophic AAs improves trophic position estimation, and thus it is recommended to use multiple AA in food web studies. Advantages and limitations of the application of individual 51SN AA values as tools in trophic ecology are discussed and guidelines for future food web studies presented. In a mesocosm experiment with 13C labeling we aimed to measure carbon transfer in a coastal pelagic food web under increased temperature and CO2 levels, and their interactive effects with gelatinous zooplankton (appendicularians). Our study showed that coastal communities are relatively resistant to high CO2 levels and mainly affect the grazing community. In specific, we found that gelatinous zooplankton are favored with climate warming, which can mediate climate affects on phytoplankton and affect carbon cycling. In addition, CSIA of FA showed that temperature increased growth rates of certain algal taxa, whereas food quality in terms of essential FA was not affected by climate warming. Overall, this study showed that climate warming affects carbon cycling within marine systems by favouring specific grazer communities. An ongoing challenge in marine systems is to estimate how shifts at the base of the food web propagate up the food chain as many zooplanktons consumers constantly alter between preferred food sources and level of omnivory resulting in seasonally variable trophic position and nutrient pool utilization. Natural tracers, such as stable isotopes are valuable tools for assessing trophic structures and consumer dietary uptake are fundamental to accurately study energy flow alterations in aquatic ecosystem. To better understand feeding ecology of a key zooplankton species, we applied bulk IA and CSIA analysis to seston and a copepod species over a seasonal cycle in the Baltic Sea. A clear link between changes in bulk 513C, 51SN values, 513C E-AA values and changes in Acartia N and C bulk isotopic composition indicate that changes in apparent dietary sources consequently have major influence on the nutritional state of zooplankton. Finally, the clear mismatch between Acartia and seston 513C E-AA values stresses the importance of critically evaluating isotopic baseline information such as bulk 51SN values prior to inferring trophic information, as seston isotope values may not always be an appropriate isotopic baseline for preferentially feeding zooplankton. Overall, this project showed that complimentary to common bulk isotopes, the application of CSIA provides an advanced tool to improve our understanding ecosystem functioning and it's response to future climate change.
Publications
- Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms. Oecologia July 2015, Volume 178, Issue 3, pp 631–642
Nielsen JM, Popp BN, Winder M
(See online at https://doi.org/10.1007/s00442-015-3305-7) - Increased appendicularian zooplankton alter carbon cycling under warmer more acidified ocean conditions. Limnology and oceanography, Vol 62 Issue 4, July 2017, Pages 1541-1551
Winder M, Bermudez JR, Bouquet JM, Hansen T, Brandes J, Berger S, Sazhin A, Jens C. Nejstgaard, Ulf Båmstedt, Hans H. Jakobsen, Jörg Dutz, Frischer ME, Troedsson C, Thompson E
(See online at https://doi.org/10.1002/lno.10516)
