Abstract
Recent reports have shown an increase in potentially harmful phytoplankton in Santos bay (Southeastern Brazilian Coast), located in a highly urbanised estuarine complex. Prediction of blooms is, thus, essential but the phytoplankton community structure in very dynamic regions is difficult to determine. In the present work, we discriminate bloom forming microphytoplankton dominance and their relationship to physical and meteorological variables to look for patterns observed in different tides and seasons. Comparing 8 distinct situations, we found five scenarios of dominance that could be related to winds, tides and rainfall: i) Surfers, diatoms occurring during high surf zone energies; ii) Sinkers, represented by larger celled diatoms during spring tide, after periods of high precipitation rates; iii) Opportunistic mixers, composed of chain forming diatoms with small or elongate cells occurring during neap tides; iv) Local mixers, microplanktonic diatoms and dinoflagellates which occurred throughout the 298 sampling stations; and v) Mixotrophic dinoflagellates, after intense estuarine discharges. Results suggest alterations in the temporal patterns for some bloom-forming species, while others appeared in abundances above safe limits for public health. This approach can also illustrate possible impacts of changes in freshwater discharge in highly urbanised estuaries.
Highlights
Understanding how changes in environmental conditions are capable of driving phytoplankton dominance is key for comprehending coastal dynamics and to develop environmental monitoring programmes
The individual surveys will be identified as their respective months and years, followed by neap tides (NT) or Scrippsiella trochoidea (ST) to discriminate between neap and ST
Precipitation rates were low during the March surveys, except for the ST survey of 2007, when values were closer to the summer climatology (DAEE, 2009)
Summary
Understanding how changes in environmental conditions are capable of driving phytoplankton dominance is key for comprehending coastal dynamics and to develop environmental monitoring programmes. The relationships between increase in both input and residence times of anthropogenic nutrients in estuarine systems and enhancements of phytoplankton biomass are well documented (e.g., Pinckney et al, 2001). Studies in costal regions, influenced by estuaries, show that inputs of nutrients drive changes on the frequency of local algal blooms (Glibert et al, 2006), with occasional changes in taxa that may even include potential harmful species (harmful algal blooms- HABs - Hallegraeff, 2004; Zingone and Enevoldsen, 2000; Heil et al, 2005), but in many regions of the coastal oceans, the available information is not enough to link the occurrence of HABs and anthropogenic effects (Anderson, 2008)
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