Thin layers in the coastal zone of Ubatuba, Brazil: Mechanisms of formation and dissipation

Abstract

Thin layers are vertically compressed, horizontally extensive, highly concentrated features comprised of plankton and/or particles. They are critical components of the marine ecosystem, likely playing a key role in the life histories and evolutionary trajectories of species found in, or, interacting with them. These structures have been reported in diverse marine environments around the globe. However, the mechanisms of thin layer formation/dissipation in the southwestern Atlantic Ocean were unknown until this contribution. To assess the temporal evolution of thin phytoplankton layers on the inner shelf off Ubatuba, Brazil, we conducted two oceanographic fixed station cruises, including optics, acoustics, and imaging techniques. Over a period of 2 days, three thin layers were observed: within the pycnocline close to the maximum stratification, and below the pycnocline where phytoplankton were affected by enhanced nutrient supply provided by the South Atlantic Central Water (SACW). Changes in regional wind patterns influenced the presence of SACW, which directly affected shear and stratification: the primary physical mechanisms we attribute to thin layer formation in this region. The associated biological mechanisms contributing to thin layer formation were biomass accumulation (in situ growth) and likely the mobility of dinoflagellates. The dominant organisms in the thin layer depths and surroundings, by our in situ imaging system, were cyanobacteria, diatoms, dinoflagellates, and crustaceans. Thin Layers likely have crucial importance for meso‐oligotrophic environments, representing important feeding resources for higher trophic levels.

Gyrotactic trapping of micro-swimmers in simple shear flows: a study directly from the fundamental Smoluchowski equation

“…Thin phytoplankton layers are highly vertically compressed structures of photosynthetic micro-organisms (Durham & Stocker 2012) as found occasionally in coastal water bodies (Steinbuck et al 2009;Penninck et al 2020) and stratified lakes (Fee 1976;Jones 1988;Latasa et al 2017;Lofton et al 2020). Of significant importance to the ecology of aquatic systems, mechanisms underlying the formation, persistence and dissipation of thin phytoplankton layers are hot-spots in marine science (Durham & Stocker 2012).…”

“…2009; Penninck et al. 2020) and stratified lakes (Fee 1976; Jones 1988; Latasa et al. 2017; Lofton et al.…”

Influence of environmental drivers on the plankton distribution on the inner shelf off Ubatuba, southeastern Brazil

“…However, the average winds for the observation period indicated a predominance of northeasterly winds, with greater intensities than those observed in winter. This wind pattern, acting parallel to the shoreline, favours coastal upwelling phenomena that lead to the subsurface intrusion of the cold, nutrient-rich waters of SACW onto the Ubatuba inner shelf (BRAGA; MÜLLER, 1998;PENNINCK et al, 2021), as observed during the study period (Fig. 3.4 D).…”

“…SCMs are associated with thermoclines due to the accumulation of cells at neutral density depths along a vertical temperature gradient (DURHAM; STOCKER, 2012), and due to thermal stratification regulating the mixing of nutrients from deeper waters in the euphotic zone, being an important factor in determining nutricline (CULLEN, 2015;LEACH et al, 2018). Penninck et al, (2021), using an imaging system, found a great abundance of diatoms (microphytoplankton) in the SCM region, which developed in the form of a thin layer, on the inner shelf of Ubatuba. Our results indicate a great contribution of pico-and nanoplankton populations to the SCM, mainly Syne, PicoEuk, and NanoEuk.…”

“…The increase in current shear in the bottom layer, due to tidal flow and SACW intrusion, may be related to the increase in the diatom population in this layer during the summer. SACW onshore intrusions have been related to current shear (PENNINCK et al, 2021), the transport of diatoms in resting stages to coastal areas (BRANDINI et al, 2014), and the resuspension of nutrients accumulated in the sediment (AIDAR et al, 1993;BRAGA;MÜLLER, 1998), contributing to the variability in plankton abundance and diversity.…”