Retention of plankton within ocean eddies

Abstract

Aim Mesoscale ocean eddies (closed circular currents typically 100-300 km in diameter) are ubiquitous features of the world's oceans. They form partially isolated environments with distinct physical and chemical conditions capable of supporting and transporting whole plankton communities. The productivity and biodiversity of these communities is ultimately dependent on an eddy's ability to retain planktonic organisms. Our aim was to estimate eddy retention time-scales across a range of oceanic environments and larval behaviours, with implications for both distributions and future changes in plankton communities.Location The Pacific Ocean, Indian Ocean, Southern Ocean and Mediterranean Sea.Methods A particle-tracking model was forced using ocean currents from a number of validated hydrodynamic models covering environments ranging from shelf seas to the open ocean and equatorial to high-latitude waters. Eddies were seeded with large numbers of particles and their rate of loss from the eddy was used to estimate retention times. The influences of common plankton swimming behaviours were explicitly captured in the model.Results Eddy retention times of modelled plankton ranged from 5 to 67 days, with a median of 19 days. Retention times were not correlated with latitude or eddy size. However, plankton residing near the surface of eddies rotating cyclonically (anticlockwise in the Northern Hemisphere) had significantly shorter retention times than those residing in the same eddy at depth, and vice versa for eddies rotating anticyclonically.Main conclusions We show that ocean eddies have the potential to retain and support planktonic (and even nektonic) communities over many generations and are likely to enhance larval survival for many invertebrate and fish species. Differences in retention with depth suggest that cyclonic and anticyclonic eddies will support differing plankton communities. If their relative geographical distributions change with global climate, then the relative proportions of diatom-based and dinoflagellate-based communities may also change, with potential implications for higher trophic animals.

Distribution and abundance of the ichthyoplankton assemblages and its relationships with the geostrophic flow along the southern region of the California Current

“…The dispersive property of cyclonic eddies (Condie & Condie, 2016) explained the lowest SST, the shallowest MLD as well as the high density of photosynthetic pigments and ZB compared with the surrounding areas of each eddy. In contrast, warm core anticyclonic eddies were associated with the deepest MLD and lowest density of Chl-a and ZB.…”

Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

“…Once NO − 3 is in the mixed layer the eddy retention (D'Ovidio et al, 2013;Condie and Condie, 2016) will trap a fraction of the upwelling waters. The AOU : NO − 3 ratio of the eddy core is altered high (16) when compared with the classical Redfield ratio (8.625) or the background ratio (8.1).…”

“…A key role is played by the vertical flux of nutrients into the euphotic zone, either by advection along outcropping isopycnals or by mixing. Moreover, eddies are retention regions (d'Ovidio et al, 2013) and the upwelled nutrients are kept in the eddy and utilized for new production (Condie and Condie, 2016).…”

Modelling the differences between El Niño and La Niña years and planktonic larval duration on dispersal across the southeast Australian biogeographic barrier

“…These eddies help retain (Condie & Condie, 2016), and may move larvae of rocky-shore taxa, as documented for fish larvae, further down the SE Australian coast and into Tasmania, albeit in an irregular fashion (Booth et al, 2007). These eddies help retain (Condie & Condie, 2016), and may move larvae of rocky-shore taxa, as documented for fish larvae, further down the SE Australian coast and into Tasmania, albeit in an irregular fashion (Booth et al, 2007).…”