Seasonal variation of astaxanthin production in a changing pelagic ecosystem
(English)Manuscript (preprint) (Other academic)
The carotenoid pigments of mesozooplankton communities in the Baltic Sea area were investigated in a large-scale survey. Ninety-nine percent of the zooplankton carotenoid concentrations consisted of astaxanthin and only 1% of canthaxanthin. We recorded large seasonal differences in astaxanthin concentrations, but no apparent patterns in the regional distribution within the Baltic Sea proper. Astaxanthin levels were lowest in summer when zooplankton feeding and growth rates are highest. In the cold season astaxanthin concentrations were three to four times higher than in summer and the proportions of astaxanthin esters were much higher than in summer. This suggests that astaxanthin is necessary especially in winter for the antioxidant protection of storage lipids. The seasonal cycles of astaxanthin was strongly intertwined with seasonal environmental conditions and changes in zooplankton community composition. Large differences between cladoceran- and copepod-dominated communities were were discovered. The abundances of the cladoceran genera Bosmina, Evadne and Podon were strongly negatively correlated with community concentrations of all forms of astaxanthin. Among the copepods, Temora longicornis and Pseudocalanus acuspes had the highest affinities with astaxanthin and Acartia spp. the lowest. The proportion of astaxanthin esters in the mesozooplankton of the Baltic Sea proper was on average 35%, which is lower than normally reported for pelagic crustaceans. This may indicate starvation of zooplankton and low nutritional value as astaxanthin source for predators in the Baltic Sea proper. Climate change scenarios for the area predict developments towards higher water temperature and lower salinity in the near future and this may lower the food quality for planktivorous fish if the abundances of Bosmina spp. and Acartia spp. increase at the cost of more nutritious copepods with higher astaxanthin concentrations. Because of their small size these taxa are normally avoided as prey by the major planktivorous fish, herring and sprat, in the Baltic Sea proper. However, when the abundances of larger zooplankton decrease by the ongoing bottom-up and top-down pressures on the zooplankton community, which already has happened in the case of Pseudocalanus acuspes, this may have consequences for the transport of astaxanthin to higher trophic levels.
Baltic Sea, pelagic, phytoplankton regime shift, zooplankton
IdentifiersURN: urn:nbn:se:uu:diva-130141OAI: oai:DiVA.org:uu-130141DiVA: diva2:346644