Retention and dispersal of shelf waters influenced by interactions of ocean boundary current and coastal geography

Abstract

Retention and dispersal of shelf waters under the influence of ocean boundary currents is crucial to recruitment processes of many coastal species. In this study, a Lagrangian particle tracking method based on an eddy-resolving, data-assimilating, hydrodynamic model is used to study spatial variations of local retention rates and alongshore dispersal of surface waters on the continental shelf off the west coast of Australia. The circulation on the shelf off the west coast of Australia is dominated by the southward-flowing eastern boundary current, the Leeuwin Current, which is interrupted by episodic wind-driven, northward, inshore surface transport during the austral summer, and by mesoscale eddy formations during the austral winter. Low-retention shelf regions tend to experience high alongshore currents, owing to the near-shore influence of the Leeuwin Current, protruding coastal geography, or formation of mesoscale eddies, whereas high-retention regions are sheltered from the direct influence of the Leeuwin Current by coastal geographic features. Alongshore dispersal also exhibits spatial as well as seasonal heterogeneity, with predominantly southward dispersal during the austral winter, and more symmetrical dispersal during the austral summer. Shelf retention and seasonal dispersal are linked with recruitment processes of invertebrate and fish species off the west coast of Australia.

Pelagic early life stages promote connectivity in the demersal labrid Choerodon rubescens

“…Both of these water flows probably influence the dispersal of the ELS in C. rubescens, which spawns mainly in spring and early summer (Fairclough et al, 2011). The results of hydrodynamic modelling of passive particles released in water around the Houtman Abrolhos Islands, and further south off Perth, suggest that the prevailing water movements could transport 28-day pelagic ELS in multiple directions, sometimes over hundreds of kilometres, particularly during the peak spawning period of C. rubescens (see Feng et al, 2010;Penton and Pattiaratchi, 2013). Some areas, including one south of the Houtman Abrolhos Islands, may, however, have higher retention rates than others (Feng et al, 2010).…”

“…The latter dominates in late-autumn and winter, while the former are predominant in summer, although the strength and peak flow of each vary from year to year (Cresswell et al, 1989;Feng et al, 2010). Both of these water flows probably influence the dispersal of the ELS in C. rubescens, which spawns mainly in spring and early summer (Fairclough et al, 2011).…”

“…The results of hydrodynamic modelling of passive particles released in water around the Houtman Abrolhos Islands, and further south off Perth, suggest that the prevailing water movements could transport 28-day pelagic ELS in multiple directions, sometimes over hundreds of kilometres, particularly during the peak spawning period of C. rubescens (see Feng et al, 2010;Penton and Pattiaratchi, 2013). Some areas, including one south of the Houtman Abrolhos Islands, may, however, have higher retention rates than others (Feng et al, 2010). Overall the data imply that the hydrology of the broader environment may facilitate widespread mixing of the pelagic ELS of C. rubescens (also see Kennington et al, 2013).…”

Larval fish assemblages and particle back-tracking define latitudinal and cross-shelf variability in an eastern Indian Ocean boundary current

“…Recruitment variability of coastal teleost species has been linked to variability of the Gulf Stream (Hare et al 1999), the Florida Current (Graber & Limouzy-Paris 1997, Cowen 2002, Sponaugle et al 2005) and the East Australian Current (Booth et al 2007). Interannual variability of the anomalously poleward-flowing eastern boundary Leeuwin Current off the coast of Western Australia (Pearce 1991, Feng et al 2003, Ridgway & Condie 2004) is also linked to recruitment variability in several marine populations (Lenanton et al 1991, Caputi et al 1996, Caputi 2008, Feng et al 2010, although the mechanism(s) driving this relationship are less well understood.…”

Climate-driven regime shift of a temperate marine ecosystem

“…However, the transition in community structure and subsequent persistence of the new regime would have been augmented by the low and high availability of temperate and tropical propagules and immigrants, respectively, as well as changes in competitive interactions following the loss of kelp canopies (21). The oceanography of the region is dominated by the poleward flowing Leeuwin Current, which delivers warm nutrient poor water and tropical species into the temperate region, while limiting the supply of propagules including kelp zoospores from higher latitude kelp forests (22,23). …”