Spatial distribution of Calanus chilensis off Mejillones Peninsula (northern Chile): ecological consequences upon coastal upwelling

Abstract

The Mejillones Peninsula upwelling system (northern Chile) appears to be a natural laboratory, suitable to test hypotheses concerning variability of copepod growth in nature. In this zone, in January 2000, we collected zooplankton samples inside and outside of an upwelling plume to assess differential responses of copepodid Calanus chilensis to spatial distribution of temperature, chlorophyll a (chl a), current field and dissolved oxygen (DO). We studied variability of prosome length (PL), dry weight (DW), oil sac volume (OSV), ovary development (GI) and a condition index (CI) of females, and PL and OSV of Copepodid Stage C5. The sea temperature ranged between 14 and 20°C in the upper 10 m, whereas chl a varied between 3 and 14 mg m -3. We distinguished 2 zones according to temperature and the current field: a cold retention area coinciding with the upwelling plume, and a warmer highly advective zone, outside the plume. Abundance of most copepodids was associated with cold and chl a-rich waters, and positively correlated to current speeds. DW and CI of females and PL of Stage C5 were negatively correlated to temperature, but not to chl a. Within the cold retention zone, copepodids were more abundant, females and C5 copepodids were larger and heavier, and females had more developed ovaries, but there were no differences in lipid content or CI. We concluded that resulting circulation may act as an efficient mechanism to maintain copepodids within the chl a-rich upwelling center, but this also implies spatial heterogeneity in temperature and food, giving rise to variability in growth and development of copepods, which is then reflected in different-sized individuals in the late stages of development.

Sublittoral soft bottom communities and diversity of Mejillones Bay in northern Chile (Humboldt Current upwelling system)

“…This pattern may reXect the availability of food since primary production is at maximum in a depth of 15 m (Giraldo et al 2002). Furthermore, the oxygen concentration measured during the present 7-year study always exceeded 1 ml l ¡1 at the 10 m stations, whereas lower oxygen concentrations at 20 m depth might have reduced abundances and limited the distribution of some species (FAO 1975), leading to a virtual absence of macrobenthos at deeper bottoms forming part of the OMZ.…”

“…Several studies have shown the existence of cold upwelled water in nearshore zones (e.g. Fonseca 1989;Escribano 1998;Marín et al 2001;Giraldo et al 2002), sustaining large biomasses of small pelagic Wsh (Alheit and Bernal 1993).…”

“…Chlorophyll-a concentrations of 10 (November 1983; Rodríguez et al 1986) and 14 mg m ¡3 (January 2000; Giraldo et al 2002) were measured at the surface of Mejillones Bay.…”

“…The oxygen minimum layer is typically shallow in the coastal area oV northern Chile (Morales et al 1996;Escribano et al 2002Escribano et al , 2004 with an upper boundary, e.g. at 42 m during the austral summer 2000 (Giraldo et al 2002) and between 20 and 40 m during spring 1996 (Escribano and Hidalgo 2000). Due to the lack of oxygen here invertebrate biomass is very low (0.17 g m ¡2 wet mass; Gallardo 1963;Neira et al 2001;Arntz et al 2006).…”

Epipelagic copepod distributions in the eastern equatorial Pacific during the weak La Niña event of 2001

“…This species occupied the largest part of this area and was highly influenced by subtropical waters with low temperatures and salinity. This species is typical of the Humboldt Current System (Giraldo et al, 2002;Escribano et al, 2004;Hidalgo and Escribano, 2007;Ayón et al, 2008) and location of catches in this area indicates a displacement from the coast of Chile-Peru to Ecuador, coinciding with the proposal of Arcos and Fleminger (1986). However, in this study, C. chilensis distribution extended farther northward than in normal years (Arcos and Fleminger, 1986), offering evidence that the influence of the Humboldt Current reached farther north in the equatorial Pacific during the cold event of 2001.…”