Abstract
Temporal variability of physicochemical parameters and phytoplankton primary productivity, abundance and composition were investigated at Babitonga Bay, southern Brazil, using a hierarchical sampling design on the scales of months, weeks and days during spring 2012 and summer 2013. Only temperature, respiration rates and concentrations of dissolved oxygen and silicate exhibited significant differences in the greatest timescale (seasons: spring; summer). In contrast, most physicochemical parameters, such as salinity and the concentration of nitrogen compounds, varied mainly among weeks and days. This short-scale variability was similarly observed for the microphytoplankton abundance, ranging from 0.04 to 1.7.106 cells L–1 during a bloom of the diatom Skeletonema costatum. Two major phytoplankton assemblages were associated with high primary production rates: > 30 μm centric diatoms such as Cyclotella spp. and Cymatodiscus sp., in spring; and a summer assemblage dominated by smaller, bloom-forming diatoms (S. costatum and Eucampia cornuta). Primary production ranged from 10.5 to 1793 mg C m–2 d–1 and varied significantly between days and months, being associated with the photosynthetic active radiation level and weather conditions on the sampling day. Abundance of specific plankton taxa appeared controlled by trophic interactions, as revealed for the mixotrophic, toxic dinoflagellate Dinophysis acuminata complex and its prey, the ciliate Mesodinium rubrum.
Highlights
Phytoplankton primary production (PP) is one of the main sources of organic carbon sustaining the pelagic food webs in coastal ecosystems such as estuaries (Lalli and Parsons 1997, Chen and Borges 2009)
The NWSE axis, known as Linguado Channel, was blocked in 1935 during the construction of a road leading to the island of São Francisco do Sul
We have demonstrated that the main physicochemical characteristics of the water column vary on different timescales in a subtropical estuary, Babitonga Bay, which explains the high variability in phytoplankton production, abundance and composition commonly reported in this type of environment
Summary
Phytoplankton primary production (PP) is one of the main sources of organic carbon sustaining the pelagic food webs in coastal ecosystems such as estuaries (Lalli and Parsons 1997, Chen and Borges 2009). Located at the interface between the continental and oceanic environments, estuaries are influenced by both and are dynamic ecosystems with high complexity and marked variability in their physicochemical characteristics, which directly affect the rates of primary productivity and the composition and abundance of phytoplankton This variability is determined by seasonal cycles of solar irradiance, rainfall, winds and tides, which act together in different temporal and spatial scales (Jouenne et al 2005, Abreu et al 2010, Kimmerer et al 2012). The determination of the different scales of variability in environmental parameters and biological associations is an essential component in ecological studies, especially in highly dynamic and complex environments such as estuaries They represent a small portion of the water masses compared with the oceans, estuaries exhibit high rates of primary production and remineralization of organic matter, and play an important role in biogeochemical cycles (Chen and Borges 2009). Small-scale variability may be related to weather events, such as fronts and episodes of heavy rainfall, as well as variations in the tidal level, local currents, concentration of dissolved nutrients and the rates of grazing and competition
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