Onshore advection of warm water, larval invertebrate settlement, and relaxation of upwelling off central Chile

Abstract

Observations from several places around the world suggest that periods of relaxation of winds tha drive upwelling favor the onshore transport of larvae entrained in shoreward movement of warm surface waters. However, the generality of this process has not yet been appropriately evaluated. We examined the frequency, intensity, spatial extent, and inter-annual variability of sea surface temperature fluctuations associated with the relaxation of equator-ward winds and their influence on invertebrate settlement in central Chile (33°30' S, 71°40' W). Our results showed that there were marked differences in the intensity and structure of temperature increases following the relaxation of upwelling favorable winds. While most temperature increases were small (0.5 to 1°C) and preserved the stratification of the water column, large 'warming events' (> 3°C) led to a breakdown of stratification for periods of 3 to 9 d at least twice during each spring-summer season. These large warming events occurred in association with downwelling-favorable (northerly) winds, and their formation might have required certain conditions in terms of mesoscale eddy features and local topography. Settlement of invertebrates occurred during these events as well at other times, and was not quantitatively correlated with relaxation or downwelling conditions. However, during specific large warming events, we observed significant synchrony in the settlement of several marine invertebrate taxa (e.g. decapods, gastropods, polychaetes, mussels, and sea urchins). Thus, at this site in central Chile and during our period of study, relaxation events did not dominate settlement, and it appeared that the upwelling-relaxation model did not adequately represent the larval transport mechanism for any taxa examined. However, large warming events (which produced synchrony in the settlement of several different taxa) could be important in that they may result in uniform settlement along the shore and deliver larvae from distant origins, increasing long-distance demographic and genetic connectivity. Thus, these infrequent events are likely to be a critical factor in settlement distribution along the shore.

Influence of intermittent-upwelling on Mytilus galloprovincialis settlement patterns in the Ría de Ares-Betanzos

“…The study of spatial and temporal settlement patterns is a widely accepted indirect method for inferring pre-settlement processes (Wing et al 1995, Ladah et al 2005, Narváez et al 2006, Pfaff et al 2011) despite some limitations due to differences in the temporal span of both processes (Pineda et al 2010, Pan et al 2011. Combined studies of settlement patterns and local oceanography are essential to infer larval dispersal patterns and potential connectivity pathways between populations (Dudas et al 2009a).…”

Onshore transport of plankton by internal tides and upwelling-relaxation events

“…In addition, it has been hypothesized that zooplankton (holo-and meroplankton) in surface waters may be advected offshore by upwelling and accumulate at the upwelling (Parrish et al 1981, Roughgarden et al 1988, Shanks 1995. When upwelling winds weaken (relax) or reverse, the upwelling front moves shoreward and can transport larvae (Shanks et al 2000, Narváez et al 2006 as well as phytoplankton (Tilstone et al 1994, Adams et al 2006) associated with the front shoreward. Thus, episodic settlement of invertebrates and the arrival of HABs at the coast have been hypothesized to be due to onshore transport during upwelling-relaxation events (Yoshioka 1982, Roughgarden et al 1988, Farrell et al 1991.…”

Restricted gene flow in Chilean barnacles reflects an oceanographic and biogeographic transition zone

“…Chile and Peru) shares many broad characteristics with the northeastern Pacific (Strub et al 1987, Halpin et al 2004, Thiel et al 2007. A dominant equatorward offshore circulation (Humboldt Current) sets the stage for the seasonally variable wind-driven upwelling, which is modulated by coastal topography and represents the main source of variation in oceanographic conditions in nearshore waters (Narváez et al 2006, Aiken et al 2007, Thiel et al 2007, Wieters et al 2009). The biogeography of coastal taxa is relatively well studied (Brattström & Johanssen 1983, Camus 2001, and major transitions in faunal distribution and recruitment that are associated with both paleoglacial environments (up tõ 42°S;Hulton et al 2002) and shifting oceanographic regimes have been described (Navarrete et al 2008).…”