Phenological changes of blooming diatoms promoted by compound bottom-up and top-down controls

GUINDER V. A.; MOLINERO J. C.; LÓPEZ ABBATE M. C.; BERASATEGUI A.; POPOVICH C. A; SPETTER C.V.; MARCOVECCHIO J. E.; FREIJE R. H.

ESTUARIES AND COASTS

SPRINGER

Lugar: Berlin; Año: 2017

1559-2723

Understanding phytoplankton species-specific responsesto multiple biotic and abiotic stressors is fundamental to assess phenologicaland structural shifts at the community level. Here we present the case of Thalassiosira curviseriata, a winterblooming diatom in the Bahía Blanca Estuary, Argentina, which displayed anoticeable decrease in the past decade along with conspicuous changes inphenology. We compiled interannual field data to assess compound effects ofenvironmental variations and grazing by the invasive copepod Eurytemora americana. The two species displayedopposite trends over the period examined. The diatom decreased towards the last years, mainly during the winters, and remainedrelatively constant over the other seasons, while the copepod increased towardsthe last years, with an occurrence restricted to winter and early spring. Aquantitative assessment by structural equation modeling unveiled that theobserved long term trend in T.curviseriata resulted from synergistic effects of environmental changesdriven by water temperature, salinity and grazing. These results allowhypothesizing that the shift in the abundance distribution of T. curviseriata towards higher annualranges of temperature and salinity ?as displayed by habitat association curves-constitutes a functional response to avoid seasonal overlapping with itspredator in late winters. The observed changes in timing and abundance of the bloomingspecies resulted in conspicuous shifts in primary production pulses. Ourresults provide insights on mechanistic processes shaping the phenology andstructure of phytoplankton blooms.