Effects of prey trophic mode on the gross-growth efficiency of marine copepods: the case of mixoplankton

Abstract

Copepod reproductive success largely depends on food quality, which also reflects the prey trophic mode. As such, modelling simulations postulate a trophic enhancement to higher trophic levels when mixotrophy is accounted in planktonic trophodynamics. Here, we tested whether photo-phagotrophic protists (mixoplankton) could enhance copepod gross-growth efficiency by nutrient upgrading mechanisms compared to obligate autotrophs and heterotrophs. To validate the hypothesis, we compared physiological rates of the copepod Paracartia grani under the three functional nutrition types. Ingestion and egg production rates varied depending on prey size and species, regardless of the diet. The gross-growth efficiency was variable and not significantly different across nutritional treatments, ranging from 3 to 25% in the mixoplanktonic diet compared to autotrophic (11–36%) and heterotrophic (8–38%) nutrition. Egg hatching and egestion rates were generally unaffected by diet. Overall, P. grani physiological rates did not differ under the tested nutrition types due to the large species-specific variation within trophic mode. However, when we focused on a single species, Karlodinium veneficum , tested as prey under contrasting trophic modes, the actively feeding dinoflagellate boosted the egestion rate and decreased the copepod gross-growth efficiency compared to the autotrophic ones, suggesting possible involvement of toxins in modulating trophodynamics other than stoichiometric constraints.

Mixotrophy upgrades food quality for marine calanoid copepods

“…This observation does not come as a surprise. In fact, lower C‐GGE in P. grani fed mixotrophic K. veneficum (0.15) in nutrient starvation in comparison to nutrient‐depleted (0.29) and replete (0.26) autotrophic cultures had already been reported (Traboni et al 2020), in agreement with the decrease observed in this study between N‐limited mixotrophic and autotrophic treatments in P. grani (39%) and C. typicus (32%).…”

The effect of short-term temperature exposure on vital physiological processes of mixoplankton and protozooplankton

“…24 h. Vi, on the other hand, depicts the average volume of a cell (μm 3 ) before exposure to the target temperature. Carbon values for all species were obtained from the pg C:μm 3 ratio provided by Traboni et al (2020) and used to determine C-specific rates.…”

Mixoplankton interferences in dilution grazing experiments

“…S2 ), from where the dilution series began. Carbon concentrations for all species were obtained from the average volume and Carbon: µm 3 ratio provided by Traboni et al 67 . All predators were allowed to deplete their co-occurring prey before starting the experiment, to reset their feeding history.…”