Non-limiting food conditions for growth and production of the copepod community in a highly productive upwelling zone

• This work provides first estimates of copepod production for a highly productive eastern boundary current.
• The study also tests whether food conditions can indeed control growth and production in this upwelling zone.
• Findings suggest the absence of bottom-up control on copepods.
• Lack of food limitation must be assessed over an annual basis, thus spatial and temporal variation needs to be integrated.

Zooplankton production is critical for understanding marine ecosystem dynamics. This work estimates copepod growth and production in the coastal upwelling and coastal transition zones off central-southern Chile (~35 to 37°S) during a 3-year time series (2004, 2005, and 2006) at a fixed shelf station, and from spring-summer spatial surveys during the same period. To estimate copepod production (CP), we used species-biomasses and associated C-specific growth rates from temperature dependent equations (food-saturated) for the dominant species, which we assumed were maximal growth rates (gmax). Using chlorophyll-a concentrations as a proxy for food conditions, we determined a size-dependent half-saturation constant with the Michaelis-Menten equation to derive growth rates (g) under the effect of food limitation. These food-dependent C-specific growth rates were much lower (<0.1 d−1) than those observed in the field for the dominant species, while gmax for same species, in the range of 0.19–0.23 d−1 better represented the necessary growth to attain observed adult sizes of at least two copepods, Paracalanus cf. indicus and Calanus chilensis. Copepod biomass (CB) and rates of maximal copepod production (CPmax) obtained with gmax were higher in the coastal upwelling zone (<50 km from shore), and correlated significantly to oceanographic variables associated with upwelling conditions. Both CPmax and gmax exhibited negative trends at the fixed station from 2004 to 2006 in association with increased duration of upwelling in the latter year. Annual CPmax ranged between 24 and 52 g C m−2 y−1 with a mean annual P/B ratio of 7.3. We concluded that interannual variation in copepod production resulted from factors and processes regulating copepod abundance and biomass in the absence of bottom-up control, allowing copepods to grow without limitation due to food resources.