Role of circulation scales and water mass distributions on larval fish habitats in the Eastern Tropical Pacific off Mexico

Abstract

On the basis of five oceanographic cruises carried out in the Eastern Tropical Pacific off Mexico, relationships between the larval fish habitats (areas inhabited by larval fish assemblages) and the environmental circulation scales (mesoscale, seasonal, and interannual) were examined. Analysis of in situ data over a grid of hydrographic stations and oblique zooplankton hauls with bongo net (505 mm) was combined with orthogonal robust functions decomposition applied to altimetry anomalies obtained from satellite. During both cool (March and June) and warm (August and November) periods, Bray-Curtis dissimilarity Index defined three recurrent larval fish habitats which varied in species composition and extent as a function of the environmental scales. The variability of the Tropical larval fish habitat (characterized by high species richness, and dominated by Vinciguerria lucetia, Diogenichthys laternatus, and Diaphus pacificus) was associated with the seasonal changes. The Transitional-California Current larval fish habitat (dominated by V. lucetia and D. laternatus, with lower mean abundance and lower species richness than in the Tropical habitat) and Coastal-and-Upwelling larval fish habitat (dominated by Bregmaceros bathymaster) was associated mainly with mesoscale activity induced by eddies and with coastal upwelling. During February 2010, the Tropical larval fish habitat predominated offshore and the Transitional-California Current larval fish habitat was not present, which we attribute to the effect of El Niño conditions. Thus, the mesoscale, seasonal, and interannual environmental scales affect the composition and extension of larval fish habitats.

Water Masses and Circulation in the Tropical Pacific off Central Mexico and Surrounding Areas

“…3) show a unimodal branch of cold and low-salinity water in the CCS corresponding to the CCW. Our data revealed that its old limits (Torres Orozco 1993; Castro et al 2006;Lavín et al 2009) were too narrow to include the complete range of the observations in the first 150 m of the water column in the CCS; therefore, we broadened the CCW temperature limits to 108-218C [the maximum temperature limit, in agreement with León-Chávez et al (2010)]. We also set the lower temperature limit of the TSW to 258C in agreement with Fiedler and Talley (2006) and the S A equal to the CCW (Table 1).…”

“…The presence of the coast (in contrast with the Transition area) and the convergence of three different circulation regimes carrying different water masses on a seasonal basis, make the TPCM a distinct transitional region, worthy of a separate designation. In addition, keeping the designation of this region as in previous recent works Cepeda-Morales et al 2013;León-Chávez et al 2010 allows comparison of the results, which improves the background for future studies in the area.…”

“…Nevertheless, the large spatial scale considered in their study missed important features of subbasin scale like the tropical Pacific off central Mexico (TPCM). Smaller-scale studies in this region used hydrographic data that covered only restricted areas (Roden 1972;Castro et al 2000Castro et al , 2006Godínez et al 2010;León-Chávez et al 2010Durazo 2015) or are not focused on water masses (Cepeda-Morales et al 2013). The scarcity of data in the TPCM, in comparison with the available amount of historical data in surrounding areas like the California Current System or the Gulf of California, has hindered the characterization of the circulation and the water masses in this region.…”

“…This current pattern, including the continuous exchanges through the entrance of the Gulf of California (Collins et al 2015), govern the spatial distribution and temporal variability of the water masses in the TPCM. In the upper layer of 1000-m depth these are Pacific Intermediate Water (PIW), Subtropical Subsurface Water [StSsW; also known as Subtropical Underwater (StUW; O'Connor et al 2002;Fiedler and Talley 2006)], California Current Water (CCW), Gulf of California Water (GCW), and Tropical Surface Water (TSW; Wyrtki 1966;Castro et al 2006;Lavín et al 2009;León-Chávez et al 2010Fiedler and Talley 2006). We preferred the name StSsW over StUW to emphasize the Southern Hemisphere origin of this water mass that reaches the TPCM with specific biogeochemical features as the minimum content of oxygen.…”

Paralarvae of the complex Sthenoteuthis oualaniensis‐Dosidicus gigas (Cephalopoda: Ommastrephidae) in the northern limit of the shallow oxygen minimum zone of the Eastern Tropical Pacific Ocean (April 2012)

“…Although the data obtained in this study cannot provide a complete description or explanation of the front, the results correspond with previous observations of strong salinity fronts in the entrance to the Gulf of California, where a southward branch of the California Current, called by Godínez et al . [] the Tropical Branch of the California Current, converges with the poleward Mexican Coastal Current in a constantly shifting zone of complex interaction [ Godínez et al ., ; Kurczyn et al ., ; Collins et al ., ; León‐Chávez et al ., ].…”