Ontogenetic changes in the elemental composition and stoichiometry of marine copepods with different life history strategies

2022

Front. Microbiol.

Self Cite

Proper thermal adaptation is key to understanding how species respond to long-term changes in temperature. However, this is seldom considered in protozooplankton and mixoplankton experiments. In this work, we studied how two heterotrophic dinoflagellates (Gyrodinium dominans and Oxyrrhis marina), one heterotrophic ciliate (Strombidium arenicola), and one mixotrophic dinoflagellate (Karlodinium armiger) responded to warming. To do so, we compared strains adapted at 16, 19, and 22°C and those adapted at 16°C and exposed for 3 days to temperature increases of 3 and 6°C (acclimated treatments). Neither their carbon, nitrogen or phosphorus (CNP) contents nor their corresponding elemental ratios showed straightforward changes with temperature, except for a modest increase in P contents with temperature in some grazers. In general, the performance of both acclimated and adapted grazers increased from 16 to 19°C and then dropped at 22°C, with a few exceptions. Therefore, our organisms followed the “hotter is better” hypothesis for a temperature rise of 3°C; an increase of >6°C, however, resulted in variable outcomes. Despite the disparity in responses among species and physiological rates, 19°C-adapted organisms, in general, performed better than acclimated-only (16°C-adapted organisms incubated at +3°C). However, at 22°C, most species were at the limit of their metabolic equilibrium and were unable to fully adapt. Nevertheless, adaptation to higher temperatures allowed strains to maintain physiological activities when exposed to sudden increases in temperature (up to 25°C). In summary, adaptation to temperature seems to confer a selective advantage to protistan grazers within a narrow range (i.e., ca. 3°C). Adaptation to much higher increases of temperatures (i.e., +6°C) does not confer any clear physiological advantage (with few exceptions; e.g., the mixotroph K. armiger), at least within the time frame of our experiments.

Section: Methodsmentioning

confidence: 99%

“…Adaptation). Error propagation, when necessary, was calculated using the square root law ( Saiz et al, 2020 ).…”

Section: Methodsmentioning

confidence: 99%

Thermal Acclimation and Adaptation in Marine Protozooplankton and Mixoplankton

2022

Front. Microbiol.

Self Cite

“…Copepod ingestion rates (cells ind −1 d −1 ) were calculated using Frost's equations (Frost 1972) and converted to C, N, and P intakes using the volumetric prey content determined in this study. Egg production rate (EPR, eggs ind −1 d −1 ) was converted into carbon units assuming egg content of 38 ng C egg −1 and 29 ng C egg −1 for respectively P. grani (Saiz et al 2020) and C. typicus (Saiz unpubl.). Hatching success, estimated after 48 h incubation, was expressed as the percentage of nauplii hatched relative to the total offspring.…”

Section: Methodsmentioning

confidence: 99%

Mixotrophy upgrades food quality for marine calanoid copepods

Traboni

Limnology & Oceanography

2021

Self Cite

Inorganic nutrient limitation affects the stoichiometry and nutritional quality of marine phytoplankton. Mixoplankton, able to photosynthesize and feed simultaneously in the one cell, can compensate shortage of nutrients by phagotrophy, theoretically upgrading their nutritional quality for their predators: the zooplankton. Yet, the additional value that phagotrophy in mixoplankton may provide to support zooplankton growth and recruitment has been poorly explored. Therefore, we investigated the feeding and reproductive performances of the copepods Paracartia grani and Centropages typicus on mono-diets of the dinoflagellate Karlodinium veneficum grown as strict autotroph and as mixotroph, both under N and P depletion, and in nutrient-balanced conditions (f/2 medium; only as autotroph). Feeding and reproduction outputs were generally higher in P. grani than in C. typicus. Both copepod species ingested the mixotrophic K. veneficum at similar rates than the autotrophic ones in either nutrient-limited scenario. However, egg production and recruitment rates generally increased when feeding on mixotrophs, in P. grani on both N-and P-limited diets, and in C. typicus under P limitation. In general, P limitation influenced copepod physiology more than N depletion. Our results show that phagotrophy upgrades nutritional quality in nutrientlimited mixotrophs as prey for copepods compared to the strict autotrophic ones. These findings are among the first reported cases of copepod ingestion in the laboratory on actively feeding mixoplankton, and they highlight the importance of considering the trophic mode of the protist and the response by various zooplanktonic predators when attempting to understand the functioning of marine planktonic food webs.

“…Hatching success was estimated as percentage of nauplii hatched after 48 h, based on the initial egg number. Ingestion and egg production rates were converted into µg C prey ind −1 d −1 using respectively the prey carbon contents analysed in this study (see below) and the P. grani egg content provided by Saiz et al 68 . Gross-growth efficiency (as %) was calculated as the quotient between egg production rates and ingestion rates, both expressed in carbon terms.…”

Section: Methodsmentioning

confidence: 99%

“…For the mixotrophic and heterotrophic protists, when small amounts of their own cryptophyte prey had remained at the time of preparing the experimental suspensions, their contribution to the elemental content of the copepod prey was subtracted after analysis. Stoichiometric ratios were calculated as molar ratios and propagation of error was taken into account due to independency between CN and P samples 68 .…”

Section: Methodsmentioning

confidence: 99%

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

Traboni

2020

Sci Rep

Self Cite

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.