The role of copepod grazing in phytoplankton bloom dynamics : a species-based approach

Mahadik, Gauri A (2014). The role of copepod grazing in phytoplankton bloom dynamics : a species-based approach. PhD thesis The Open University.



Seasonal phytoplankton blooms characterize the pelagic communities in temperate oceans and in coastal regions of the Mediterranean Sea. The present study was aimed at understanding the role of trophic interactions in the dynamics of phytoplankton blooms in a long-term time series in the inner Gulf of Naples (LTER-MC) where phytoplankton and mesozooplankton are dominated by diatoms and copepods, respectively. The abundant calanoids Acartia clausi, Centropages typicus, Paracalanus parvus, and Temora stylifera peak in different seasons and interact with different co-occurring phytoplankton communities, of which the diatoms Chaetoceros socialis, Leptocylindrus spp. and Pseudo-nitzschia spp. are the most abundant. By following a species-specific approach, the feeding performances and behaviour of the four copepod species on selected bloom-forming diatoms were analyzed by incubation experiments using the food removal method and video recordings of individuals at small scale. Significant differences appeared in the feeding responses of the copepods to the different diatom species, which can be attributed to the species-specific traits of both the predator and prey. Copepods showed behavioral plasticity in presence of different diets, with changes in the duration of feeding bouts and proportion of time allotted to different behaviors, which can in turn affect the feeding rates. Finally, the estimated impact of copepod grazing at st. LTER-MC showed that the copepods can remove a significant portion of the bloom-forming diatoms but have a limited impact on total standing stock of a diversified diatom assemblage. The impact also varies depending on the phases of the blooms with respect to the abundance and composition of the plankton communities. This study discloses the role of key copepod species in the dynamics of phytoplankton blooms for a better understanding of the seasonal and long-term patterns of plankton communities in marine coastal ecosystems.

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