Sink or swim, accumulation of biomass at fronts

Abstract

The dense concentrat~ons of blomass colnmonly seen at fronts are often explalned by a phys~olog~cal response of the oiganlsms to the frontal environment However, some fractlon of the enhanced b~o m a s s may be explalned through purely phys~cal processes the interaction of floating sinking or swlmmlng w~t h the flows at a front To explore this hypothesis, I present a model of steady, 2-dlmenslonal cross-frontal circulat~ons, whlch I combine ~1 1 t h a vanety of swlrnming behaviors The models show how patchmess may arise at fronts through retention and accumulat~on zones, and the patterns which evolve glven vanous flow and swimmlng characterlst~cs The ecological slgnlficance of the results 1s discussed

Cross-frontal variation in growth rate and prey availability of larval North Sea cod Gadus morhua

“…These areas are characterised by large spatial variability in key physical parameters such as temperature and salinity (Fortier et al 1992, Lochmann et al 1997, Lee et al 2005, and here we often observe enhanced primary production, due to upwelled nutrients, and enhanced concentrations of zooplankton and fish larvae, partly due to converging currents and concentration of non-passive organisms (LeFevre 1986, Franks 1992, Franks & Chen 1996, Aretxabaleta et al 2005. Specific physical and biological measures vary markedly within relatively short distances across frontal zones (< 5 km), and both field observations (e.g.…”

“…Differential growth and thereby differential mortality has implications for the interpretation of larval concentrations in frontal zones. The frequently observed aggregations of plankton organisms are mainly attributed to localised spawning behaviour of adults and accumulation due to an interplay of converging currents and vertically migrating behaviour of plankton organisms (Fortier et al 1992, Franks 1992. However, no firm conclusion has been reached on the influence of differential mortality (e.g.…”

Comunidades microplanctônicas no Oceano Atlântico Sul Ocidental: biomassa e distribuição em novembro de 1992

“…Estes. gradientes tendem a manter as células do fitoplâncton concentradas na zona fótica, favorecendo o desenvolvimento de "blooms" (Lutjeharms et aI., 1985;Franks, 1992;Franks & Walstad, 1997;Gayoso & Podestá, 1996;.…”

Mesoscale subduction at the Almeria–Oran front

“…Owen (1981) and Wishner and Allison (1986) (Heywood, 1996). In addition the coincident abundance of phytoplankton tends to suggest the increase in zooplankton is a result of behaviourally mediated concentration in the presence of convergence zones and increased food abundance (as seen by Okubo, 1978;Gorsky et al, 1991 and modelled by Franks, 1992;.…”

“…behaviourally mediated concentration in the presence of convergence zones (Okubo, 1978;Olson and Backus, 1985;Franks 1992;Govoni and Grimes, 1992); close association with thermal gradients (Ortner et al, 1980;1981;Magnuson et al, 1981); orientation to density discontinuities (Murav'yev and Shirshov, 1984) or abundance of food (Bowman and Esaias, 1978;Crowder and Magnuson, 1983). Interpreting zooplankton distributions can be further complicated by zooplankton behaviour such as diel migration (e.g.…”