Role of across‐shelf currents in the dynamics of harmful dinoflagellate blooms in the northwestern Iberian upwelling

Abstract

Harmful dinoflagellate blooms are frequent in the Rías Baixas, which are made up of four open bays on the northwest part of the Iberian Peninsula. The relationship between surface currents resulting from wind forcing and the microplankton composition on the shelf offshore of the Rías Baixas was studied from May 2001 to April 2002. The aim was to assess the role of shelf currents in the dynamics of harmful dinoflagellate blooms in the Rías Baixas shelf system. In summer, upwelling-favorable northerly winds forced a variable but persistent southwestward flow on the shelf, which reverted to an onshore flow following the change to downwellingfavorable southwesterly winds in autumn. During winter and spring, there was an intense alongshore flow to the north. Diatoms and dinoflagellates were common components of the microplankton community in summer. Although diatoms increased their abundance during summer upwelling events, a dinoflagellate assemblage was also present on the shelf. This dinoflagellate assemblage acquired higher importance during the intermediate periods of upwelling relaxation and during the autumn downwelling in particular, when satellite images revealed the accumulation of phytoplankton in a narrow band close to the coast. A dinoflagellate bloom of Prorocentrum minimum (10,564 cells mL 21 ) and Karenia cf. mikimotoi (3,022 cells mL 21 ) developed in the interior section of the Ría de Vigo coincident with the onshore flow imposed by the autumn downwelling. As these two species were components of the dinoflagellate assemblage present on the shelf in summer, it is inferred that downwelling caused their accumulation in the interior section of the Ría de Vigo.

Dynamics of Alexandrium fundyense blooms and shellfish toxicity in the Nauset Marsh System of Cape Cod (Massachusetts, USA)

“…Although this possibility has to be examined through the genetic analysis of samples collected in the marsh and in offshore waters, it appears that the driving force was a downwelling-favorable wind pattern that carried cells to shore from the coastal bloom, allowing them to enter the marsh. This type of downwelling-driven delivery of cells has been described before for this area (Keafer et al, 2005) and for other ecosystems (Crespo et al, 2006; 2007). This second bloom was short-lived, disappearing one week after it was initially observed (Fig.…”

The physical oceanography of upwelling systems and the development of harmful algal blooms

“…19b). During this reverse circulation, especially important during the transition to seasonal downwelling in autumn (Figueiras et al, 2002; Crespo et al, 2007), the outflow towards the ocean in the outer circulation cell takes place in the bottom layer, while the inner cell maintains a positive circulation, forced by runoff. The driving force of the two-layered circulation in the inner cell during winter is the high runoff, which also causes salinity stratification of the water column and the consequent formation of two layers.…”

“…Dinophysis acuminata also causes regular outbreaks of Diarrhetic Shellfish Poisoning, typically in summer in association with periods of stratification between moderate pulses of upwelling (Reguera et al, 1993, 1995), which favours the in situ growth of D. acuminata (Reguera et al, 2003). Other harmful dinoflagellates include Karenia mikimotoi and Prorocentrum minimum , which bloom in late summer and early autumn (Crespo et al, 2007). There are conflicting opinions on the origins of these dinoflagellate blooms.…”

“…These differences tend therefore to be associated with temporal and spatial transitions from turbulent to stratified water columns, in which there is often a shift in the control of production dynamics from a dependence on new nitrogen to regenerated nitrogen (Hutchings et al, 1995), and the resulting patterns of succession afford some degree of predictability. The incidence and distribution of HABs within upwelling systems is therefore related to the dynamics of the surface boundary layer in that the upper mixed layer is important in effecting the composition of phytoplankton communities and in that fields of flow determine bloom transport and concentration (Trainer et al, 2002; Pitcher and Nelson, 2006; Crespo et al, 2007). Surface boundary-layer characteristics are in turn modified by the interaction of varying windforcing cycles with changes in coastline configuration and orientation, bottom topography, and buoyant freshwater plumes.…”

Patterns and Scales of Phytoplankton Variability in Estuarine–Coastal Ecosystems

“…For example, pulses of freshwater inflow can remove phytoplankton from small systems (de Madariaga et al 1992) or promote phytoplankton growth in large retentive systems by delivering land-derived nitrogen and phosphorus (Paerl et al 2009). Upwelling in coastal boundary currents can be a source of phytoplankton biomass or nutrients to fuel blooms within rías (Crespo et al 2007) or estuaries (Brown and Ozretich 2009). Heat waves promote surface blooms in nutrient-rich estuaries by establishing strong thermal stratification (Cloern et al 2005), and seasonal wind mixing triggers blooms in nutrient-poor bays by mixing high-nutrient bottom waters to the surface (Iverson et al 1974).…”