Oceanographic variability and copepod traits in two coastal ecosystems in the Southeast Pacific

Temperature, salinity, and pH, along with copepod traits were measured inter-daily (i.e., on average each 4 days) in an upwelling and temperate estuary in the coastal Southeast Pacific. The purpose of the study was to evaluate the phenotypic plasticity of local copepod populations to natural extreme low pH conditions. Temperature and salinity were measured with CTD (Ocean Seven 305 Plus in the estuary system, and SeaBird SBE19 Plus in the upwelling location). Samples for pH measurements were collected with an oceanographic bottle. pH was measured potentiometrically, and calibrated with Tris buffer at 25 °C. Adult females of the copepod species Acartia tonsa (Copepoda, Calanoidea) were sampled with a WP2 plankton net. Cephalothorax length was measured under a stereomicroscope. Egg production was estimated individually over 24 h incubation.