A field test of temperature effects on ecophysiological responses of copepodid Calanus chilensis during coastal upwelling in northern Chile

We assessed responses of late copepodid stages of Calanus chilensis, as subject to spatial heterogeneity in oceanographic conditions, during coastal upwelling off Mejillones Peninsula, northern Chile. An oceanographic survey conducted during 26 h prior to zooplankton sampling mapped upwelling conditions. Over the next 2 d, four zooplankton stations, two inside and two outside the cold upwelling plume, were sampled twice in the day and twice at night. We then tested the effects of upwelling/non-upwelling habitat (i.e. inside/outside the upwelling plume) on body length, body weight, oil-sac volume (OSV) and a condition index (CI) of stages copepodid C5 and adult female. We also compared ovary development of females and stage distribution from both habitats. C5 and females from inside the upwelling plume were heavier, larger, had a greater CI, and females had more developed ovaries, than those located outside the plume, although there were no significant differences in the OSV. Differences in stage distribution suggested that individuals outside the plume had developed faster under a higher temperature (17∘C) than those inside the cold (14∘C) plume. Chlorophyll-a concentration was uniformly high (>4mgm-3), both outside and inside the plume. We concluded that distinct temperature regimes, persisting longer than 1 week, had caused different sized copepodids. We thus suggest that temperature alone may substantially explain variances in growth and development rates of Calanus in highly productive upwelling systems, with no need to invoke food and body size effects.