Reproductive performance of small-sized dominant copepods with a highly variable food resource in the coastal upwelling system off the Chilean Humboldt Current

Abstract

Small-sized copepods represent a major contribution to the bulk of zooplankton biomass in highly productive coastal upwelling systems, and they are potentially the key link for channelling autotrophic C towards higher trophic levels, mainly via a heterotrophic food web. Here, we show how these small-sized copepods may efficiently exploit both autotrophic and heterotrophic components of the nanoplankton and microplankton size fractions throughout the year in the upwelling zone off Chile. The nutritional value of these food resources, in terms of C, N and lipid content, may vary extensively. However, copepods can successfully adjust their reproductive performance, measured as egg production and hatching success, in order to maintain high growth rates. This apparent flexibility enables copepod populations to sustain high production rates despite a strongly heterogeneous and variable food resource in the coastal upwelling zone. These findings provide further support to the hypothesis that those small-sized omnivorous copepods, not larger-sized, are the major organisms mediating the flux of phytoplankton C towards higher trophic levels in coastal upwelling systems.

Egg production and hatching success of Calanus chilensis and Acartia tonsa in the northern Chile upwelling zone (23°S), Humboldt Current System

“…Vargas et al (2006) found higher A. tonsa EPR (50-10 eggs female −1 day −1 ) in central-southern Chile (36°S) than other studies on the reproductive performance of A. tonsa in the HCS. EPR values for A. tonsa range between 4 and 6 eggs female −1 day −1 (Aguilera et al, 2011) in northern and southern Chile. Aguilera et al (2013) showed that A. tonsa EPR ranged from 39 and 5 eggs female −1 day − 1 from coastal to estuarine waters (Aguilera et al, 2013).…”

Upwelling modulation of functional traits of a dominant planktonic grazer during “warm-acid” El Niño 2015 in a year-round upwelling area of Humboldt Current

“…Upwelling areas are characterized by a high temporal variability, from hours to months, in consequence, upwelling driven pH-changes might constitute a significant environmental factor affecting short-term but ecologically functional plankton processes, such as growth and reproduction [13,14,15]. In the plankton system of these productive upwelling zones, short life-cycle (e.g.…”

Antagonistic interplay between pH and food resources affects copepod traits and performance in a year-round upwelling system

“…In this highly productive coastal upwelling system (gross primary production = 20 g C m −2 d −1 50 ) the contribution to the secondary production and biomass of microzooplankton like ciliates is relatively low (<100 mg C m −2 d −1 ) for the upper 40 m depth 47 . Further, previous studies have shown the temporal dominance of small sized diatoms on the diet of A. tonsa 48,49 . Thus, in this system A. tonsa likely derives the bulk of its carbon ration from an herbivorous diet.…”

“…Along with temporally variable heterotrophic components 29,47 , chlorophyll-a is a valuable index of phytoplankton upon which A. tonsa efficiently preys 48 to maintain continuous reproductive output 49 . In this highly productive coastal upwelling system (gross primary production = 20 g C m −2 d −1 50 ) the contribution to the secondary production and biomass of microzooplankton like ciliates is relatively low (<100 mg C m −2 d −1 ) for the upper 40 m depth 47 .…”

“…To measure egg production rates (EPR), groups of 25-30 A. tonsa females were gently pipetted individually into 200 mL closed acid-washed crystallizing dishes filled with natural seawater filtered on 200 μm mesh. Females were incubated at in situ temperature and EPR (egg fem −1 d −1 ) was the average (±SD) number of eggs produced over 18-20 h 49 . After counting, eggs were preserved (90% ethanol) and the egg diameter (µm) was measured on 20-30 eggs using an inverted microscope Olympus IX-51 within 30 days after preservation.…”