The influence of diel vertical migration on zooplankton transport and recruitment in an upwelling region: estimates from a coupled behavioral‐physical model

Abstract

Diel vertical migration (DVM) is a common zooplankton behavior in which organisms reside in surface or near-surface waters at night and at deeper depths during the day. In many upwelling regions, DVM reduces the transport of organisms away from the region. It is unclear, however, what role DVM plays in recruitment (the arrival of larvae or juveniles to locations where they will become reproducing adults) to upwelling regions. In this study, we estimate the influence of DVM on zooplankton transport, the level of recruitment of locally produced propagules (self-recruitment), and sources of recruits in the upwelling region near Monterey Bay, California, by simulating the trajectories of fixed-depth and vertically migrating organisms with a drifter-tracking algorithm driven by climatological velocity fields from a three-dimensional hydrodynamic model. Our simulations suggest that DVM into subsurface poleward and onshore currents during the day does not fully compensate for equatorward and offshore transport in the surface Ekman layer at night and does not retain zooplankton in the Monterey Bay region. Our simulations also suggest that DVM decreases the ability of zooplankton to return to the region after being transported away and shifts source regions for recruits closer to the bay. While DVM does not appear to substantially increase the potential for self-recruitment to the region, this study indicates that other mechanisms, such as transport during non-upwelling periods, continuous transport below the surface, increases in mean transport depth over time, or seasonal changes in hydrography, may still enable relatively high levels of self-recruitment to this highly advective region.

Constructing end-to-end models using ECOPATH data

“…Usually, the problems of retention of plankton in upwelling systems are regarded as part of the closure conditions on NPZD models (Lamb and Peterson, 2005, Batchelder et al, 2002, Peterson, 1998Carr et al, 2008). We show here that this relatively unknown factor will affect significantly the fish production.…”

“…For larger organisms, the potential rate of loss can equal or be greater than the growth rate, making the populations unsustainable. It is generally accepted that diel and ontogenetic vertical migration minimize the time these populations spend in the surface layer and reduce (or reverse) offshore transport (Lamb and Peterson, 2005, Batchelder et al, 2002, Peterson, 1998Carr et al, 2008). But increased time at depth may also decrease recycling of NH4 to the upper layer.…”

A Lagrangian study tracing water parcel origins in the Canary Upwelling System

“…The tracking code is ROMS Offline (Roff, version 2.0.1; Capet et al 2008, Carr et al 2008. Similar approaches using Roff have been taken by Carr et al (2008) for the US West Coast, and Montes et al (2010) for Peru/ Chile. At the Canary Islands, Brochier et al (2011) use a Lagrangian model to study pelagic egg and larval transport from the coast to the islands.…”

Shoreward swimming boosts modeled nearshore larval supply and pelagic connectivity in a coastal upwelling region

“…The resulting drop in sea level near the coast is associated with an alongshore, equatorward surface jet, often with substantial speeds, embedded within a chaotic eddy field (Strub et al, 1991;Strub and James, 2000;Kurian et al, 2011). The combined near-surface currents should flush larvae from the shelf and away from their home populations in several days (Carr et al, 2008;Mitarai et al, 2008;Drake et al, 2013). Nevertheless, benthic larvae in these regions are consistently retained near the coast, typically within a few kilometers of shore.…”