Larval fish distribution and retention in the Canary Current system during the weak upwelling season

Abstract

The spatial distribution of fish larvae was studied in the Canaries‐African Coastal Transition Zone, outside the strong upwelling season. An onshore–offshore transition in the larval fish community structure was observed, from a coastal assemblage dominated by small pelagics (sardine, anchovy, mackerel), bounded by the upwelling front, to an offshore assemblage dominated by mesopelagic species (mainly Myctophidae, Phosichthydae, Gonostomatidae). Distribution of the neritic larvae was deeply influenced by the intense mesoscale activity found in the area, both horizontally (larvae were advected offshore but were always retained within the upwelling area) and vertically (larvae were deepened in the vicinity of two anticyclonic eddies). A combined effect of the upwelling front and a cyclonic–anticyclonic eddy dipole is likely the successful retention mechanism for these larvae. These results support the current belief that retention may be higher than previously thought in upwelling areas. Oceanic larvae were also collected in higher abundances near the front and an anticyclonic eddy. Neritic and oceanic larvae frequently showed a differentiated position in the water column, although they sometimes coexisted. Finally, larval connectivity between Islands within the Canary archipelago is suggested. The present study thus contributes to the understanding of the complex dispersal and retention processes in the Canaries‐African Coastal Transition Zone. However, results also highlight the poor knowledge of this region compared with the other three main Eastern Boundary Upwelling Systems in terms of ichthyoplankton dynamics. The importance of routine monitoring programs of commercial and non‐commercial species in the area is emphasized.

Population genetic structure of Calanoides natalis (Copepoda, Calanoida) in the eastern Atlantic Ocean and Benguela upwelling system

“…In the Benguela system, the northwestward drift of the active surface population in the Ekman layer may be compensated by the southward flow of diapause stages within the poleward undercurrent (Timonin, 1997;Peterson, 1998;Auel and Verheye, 2007). Diel or ontogenetic vertical migrations and their linkage to coastal currents are believed to support the retention of planktonic organisms within upwelling systems (Verheye and Field, 1992;Johnson, 2007;Parada et al, 2008;Harkins et al, 2013;Morgan, 2014;Moyano et al, 2014). Phylogeographic studies in other zooplankton species suggest that retention strategies also promote genetic differentiation (Papetti et al, 2005;Nuwer et al, 2008).…”

Seasonal-Dial Shifts of Ichthyoplankton Assemblages and Plastic Debris around an Equatorial Atlantic Archipelago

“…At Rottnest Island (Western Australia), recruitment pulses of fish larvae were recorded in La Nina and El Nino years related with stronger and weaker Leeuwin Current, respectively (Pearce and Hutchins, 2009). These results show that in some areas, seasonal oceanic processes or even small-scale temporal events can be stronger factors driving the formation of larval fish assemblages than do spatial distribution of habitats around the oceanic islands (Pearce and Hutchins, 2009;Moyano et al, 2014).…”

“…In contrast, the dry period was very important for larval Myctophidae C. warmingii and C. maderensis, although pulses were not observed. In the Gran Canaria Island (Northeast Atlantic), seasonality also showed a strong influence on the annual larval assemblages than sampling site, resulting in two seasonal larval assemblages: a mixed and a stratified assemblage (Moyano et al, 2014). At Rottnest Island (Western Australia), recruitment pulses of fish larvae were recorded in La Nina and El Nino years related with stronger and weaker Leeuwin Current, respectively (Pearce and Hutchins, 2009).…”

“…In the present study, the northwest and southwest winds reaching the west side of the islands and the South Equatorial Current flowing eastward seems to be responsible for the nearshore retention of fish larvae due to the creation of surface eddies around the archipelago. Although upwelling is likely to be responsible by the dispersion of larvae toward the open ocean, at SPSPA these events seem to have a combined effect with eddies for the retention of fish larvae near the archipelago, such as observed in the Canary Current System during a weak upwelling season (Moyano et al, 2014). Areas of retention of pelagic larvae of island related taxa maybe due to the combination of current flow, topography and formation of eddies and upwelling, as reported at Johnston Atoll FIGURE 6 | Total mean (+S.E.)…”

“…However, larvae of some species are able to remain near adult habitat by mechanisms that evolved to avoid dispersal or advection to unfavorable areas (Boehlert et al, 1992;Vigliola et al, 1998;Sabatés et al, 2003;Moyano et al, 2014). Around oceanic islands these mechanisms include "winter cascading" (Boden and Kampa, 1953), retention in island eddies (Sale, 1970;Emery, 1972), flow-topography interactions (Hamner and Hauri, 1981;Wolanski and Hamner, 1988) and behavioral patterns such as ontogenetic migration (Leis and Trnski, 1989).…”