Differential responses of populations of the copepod Acartia hudsonica to toxic and nutritionally insufficient food algae

Nutritional insufficiency and toxicity are deleterious effects of phytoplankton on grazers. We hypothesize that toxic food is likely to have stronger evolutionary selective effects on grazers than nutritionally insufficient food. We explore this hypothesis in comparative studies of egg production and egg hatching of the copepod Acartia hudsonica challenged with both a toxic and a nutritionally insufficient alga. Experiments lasting 6 days, in which mixtures of different proportions of the suspect and a control alga were offered as food to female copepods, showed that the dinoflagellate Alexandrium fundyense, which bears paralytic shellfish toxins, was toxic to A. hudsonica. In contrast, the diatom Phaeodactylum tricornutum was nutritionally insufficient to A. hudsonica. In another set of experiments, the effects of A. fundyense and P. tricornutum, respectively, as sole foods on egg production and egg hatching success of two geographically separated populations (Maine and Connecticut) of the copepod A. hudsonica were examined in common-environment experiments, after being raised under identical conditions for two generations. The location in Maine regularly experiences toxic blooms of Alexandrium sp. whereas the location in Connecticut does not. During a 6-day period, A. fundyense reduced the egg production rates of the Connecticut copepod population, but not of the Maine population. In contrast, the diatom P. tricornutum reduced the egg production of both populations. These results of this study are consistent with the hypothesis of local adaptation to toxic food, but not to nutritionally insufficient food.     

Effects of the red tide dinoflagellate, Karenia brevis, on grazing and fecundity in the copepod Acartia tonsa

Among studies of copepod grazers fed harmful algae, decreasedgrazing and fecundity are the most common results. The causesof decreased grazing (physiological incapacitation, behavioralavoidance or lack of stimulation) and decreased fecundity (toxicversus nutritional effect) vary among studies. This study useda series of controlled laboratory experiments to investigatethe cause of decreased grazing and fecundity in the copepodAcartia tonsa fed sole and mixed diets of the harmful alga,Karenia brevis. Copepods fed K. brevis mixed with the nutritionallyviable dinoflagellate Peridinium foliaceum had higher ingestionrates and offspring production than copepods fed a sole dietof K. brevis (even when K. brevis was virtually nontoxic). Copepodsfed mixtures did not discriminate between P. foliaceum and K.brevis while feeding. The results of this study suggest thatK. brevis is not toxic to A. tonsa but lacks some chemical componentresponsible for stimulating a grazing response in A. tonsa aswell as the nutritional requirements for normal offspring production.     

Ingestion of the dinoflagellate, Pfiesteria piscicida, by the calanoid copepod, Acartia tonsa

The dinoflagellate, Pfiesteria piscicida, can form harmful algal blooms in estuarine environments. The dominant copepod species usually found in these waters is Acartia tonsa. We tested the ability of A. tonsa to graze the non-toxic zoospore stage of P. piscicida and thus serve as a potential biological control of blooms of this algal species. A. tonsa grazed the non-toxic zoospore stages of both a non-inducible P. piscicida strain (FDEPMDR23) and a potentially toxic strain (Tox-B101156) at approximately equal rates. Ingestion of P. piscicida increased with cell concentration and exhibited a saturated feeding response. Both the maximum number of cells ingested (I_max) and the slope of the ingestion curve (α) of A. tonsa feeding on P. piscicida were comparable to these ingestion parameters for A. tonsa fed similar-sized phytoplankton and protozoan species. When these laboratory ingestion rates were combined with abundance estimates of A. tonsa from the Pocomoke Estuary and Chesapeake Bay, we found that significant grazing control of the non-toxic zoospore stage of P. piscicida by A. tonsa would only occur at high copepod abundances (>10 copepods L⁻¹). We conclude that under most in situ conditions the potential biological control of blooms of P. piscicida is exerted by microzooplankton grazers. However, in the less saline portions of estuaries where maximum concentrations of copepods often occur with low abundances of microzooplankton, copepod grazing coefficients can be similar to the growth rates of P. piscicida.     

Comparative carbon-specific ingestion rates of phytoplankton by Acartia tonsa,Centropages velificatus and Eucalanus pileatus grazing on natural phytoplankton assemblages in the plume of the Mississippi River (northern Gulf of Mexico continental shelf)

During four cruises in continental shelf waters of the northern Gulf of Mexico in the winters of 1981–83, we performed quantitative studies on the grazing of the copepods Acartia tonsa, Centropages velificatus, and Eucalanus pileatus, on phytoplankton using natural particulate assemblages as food. Stations were in, or adjacent to the plume of the Mississippi River, thereby providing wide spectra of phytoplankton and suspended riverine particulate concentrations. Phytoplankton cell volume was converted to carbon, and this, coupled with carbon content measurements of these three copepod species, allowed comparisons of daily ingestion effort even though the copepods were of different sizes. Data were expressed in the same units (% of copepod body carbon ingested copepod ^–1 d^–1) for each species. Over similar ranges of phytoplankton carbon concentrations (0.21–92.06 gCl^–1), Acartia tonsa had higher carbon-specific ingestion rates (x = 22.31%, range = 0.08–152.37%) than C. velificatus (x = 2.8%, range = 0.00–31.09 %) or E. pileatus (x = 1.27%, range = 0.10–2.80%). Carbon-specific ingestion rates increased with increasing phytoplankton carbon concentration for A. tonsa (R² = 0.81) and there was no evidence of saturated feeding on the carbon concentrations offered. A similar, but weaker trend was evident for E. pileatus (R² = 0.71), but not C. velificatus (R² = 0.49). Over a wide range of suspended particulate concentrations (10.6–95.2 mg l^–1), there was no systematic effect of particulates on carbon-specific ingestion rate for any of the three copepod species. However, A. tonsa appeared more adept at grazing in highly turbid water than C. velificatus or E. pileatus.     

Should we expect a relationship between primary production and fisheries? The role of copepod dynamics as a filter of trophic variability

It is frequently put forward that variability in fisheries productivity is related to interannual variation in physical processes affecting phytoplankton productivity. Here, alternative views of the role of copepods as an intermediary link in North Atlantic marine food chains are discussed. Following Bainbridge & McKay (1968) and Cushing (1982), a strong link between phytoplankton and fisheries variability is proposed for some fish stocks, like cod and redfish, that spawn in spring in regions where Calanus finmarchicus dominates the plankton. Otherwise, in regions where small copepods and other microzooplankton dominate the prey field productivity for larval fish, a weak link is proposed. Experimental studies, including laboratory observations of copepod reproductive response to food concentration and incubation techniques for measuring in situ reproductive rates, are important for understanding how copepod dynamics may filter year-to-year differences in phytoplankton production cycles.     

Mesozooplankton Grazing on Picocyanobacteria in the Baltic Sea as Inferred from Molecular Diet Analysis

Our current knowledge on the microbial component of zooplankton diet is limited, and it is generally assumed that bacteria-sized prey is not directly consumed by most mesozooplankton grazers in the marine food webs. We questioned this assumption and conducted field and laboratory studies to examine picocyanobacteria contribution to the diets of Baltic Sea zooplankton, including copepods. First, qPCR targeting ITS-1 rDNA sequence of the picocyanobacteria Synechococcus spp. was used to examine picocyanobacterial DNA occurrence in the guts of Baltic zooplankton (copepods, cladocerans and rotifers). All field-collected zooplankton were found to consume picocyanobacteria in substantial quantities. In terms of Synechococcus quantity, the individual gut content was highest in cladocerans, whereas biomass-specific gut content was highest in rotifers and copepod nauplii. Moreover, the gut content in copepods was positively related to the picocyanobacteria abundance and negatively to the total phytoplankton abundance in the water column at the time of sampling. This indicates that increased availability of picocyanobacteria resulted in the increased intake of this prey and that copepods may rely more on picoplankton when food in the preferred size range declines. Second, a feeding experiments with a laboratory reared copepod Acartia tonsa fed a mixture of the picocyanobacterium Synechococcus bacillaris and microalga Rhodomonas salina confirmed that copepods ingested Synechococcus, even when the alternative food was plentiful. Finally, palatability of the picocyanobacteria for A. tonsa was demonstrated using uptake of ¹³C by the copepods as a proxy for carbon uptake in feeding experiment with ¹³C-labeled S. bacillaris. These findings suggest that, if abundant, picoplankton may become an important component of mesozooplankton diet, which needs to be accounted for in food web models and productivity assessments.     

Prorocentrum minimum(clone Exuv) is nutritionally insufficient, but not toxic to the copepod Acartia tonsa

This study tested whether the dinoflagellate Prorocentrum minimum is nutritionally insufficient or toxic to the copepod Acartia tonsa. Experiments were carried out with adult female A. tonsa and the P. minimum clone Exuv, both isolated from Long Island Sound. Initially, the functional and numerical responses of A. tonsa feeding on exponentially growing P. minimum cells were characterized. These experiments revealed that A. tonsa readily ingested P. minimum cells, up to the equivalent of 200% of body carbon day⁻¹, but egg production was relatively low, with a maximum egg production rate of 22% of body carbon day⁻¹. Hence, the egg production efficiency (egg carbon produced versus cell carbon ingested) was low (10%). In a separate experiment, ingestion and egg production rates were measured as a function of food concentration with cells in different growth stages (early-exponential, late-exponential/early-stationary, and late-stationary growth phase) to simulate conditions during a bloom. There was no indication that cells in the stationary phase resulted in lower ingestion or egg production rates relative to actively growing cells. Egg hatching success remained high (>80%) and independent of the cell growth phase. In a third experiment specifically designed to test the hypothesis that P. minimum is toxic, ingestion, egg production and egg hatching success were measured when females were fed mixtures of P. minimum and the diatom Thalassiosira weissflogii, but in which total food concentration was held constant and the proportion of P. minimum in the mixed diet varied. A. tonsa readily ingested P. minimum when it was offered in the mixed diet, with no detrimental effects on egg production or egg hatching observed. Supplementing P. minimum with T. weissflogii increased both the egg production rate and the egg production efficiency. It is concluded that P. minimum is nutritionally insufficient, but not toxic to A. tonsa. Finally, it is estimated that in the field grazing by A. tonsa is approximately equivalent to 30% of the maximum daily growth rate of P. minimum. Hence, copepod grazing cannot be ignored in field and modeling studies of the population dynamics of P. minimum.     

Zooplankton interactions with toxic phytoplankton: Some implications for food web studies and algal defence strategies of feeding selectivity behaviour, toxin dilution and phytoplankton population diversity

This study focuses on the interactions between toxic phytoplankton and zooplankton grazers. The experimental conditions used are an attempt to simulate situations that have, so far, received little attention. We presume the phytoplankton community to be a set of species where a population of a toxic species is intrinsically diverse by the presence of coexisting strains with different toxic properties. The other species in the community may not always be high-quality food for herbivorous zooplankton. Zooplankton populations may have developed adaptive responses to sympatric toxic phytoplankton species. Zooplankton grazers may perform a specific feeding behaviour and its consequences on fitness will depend on the species ingested, the effect of toxins, and the presence of mechanisms of toxin dilution and compensatory feeding. Our target species are a strain of the dinoflagellate Alexandrium minutum and a sympatric population of the copepod Acartia clausi. Mixed diets were used with two kinds of A. minutum cells: non-toxic and toxic. The flagellate Rhodomonas baltica and the non-toxic dinoflagellate Alexandrium tamarense were added as accompanying species. The effect of each alga was studied in separate diets. The toxic A. minutum cells were shown to have negative effects on egg production, hatching success and total reproductive output, while, in terms of its effect on fitness, the non-toxic A. minutum was the best quality food offered. R. baltica and A. tamarense were in intermediate positions. In the mixed diets, copepods showed a strong preference for toxic A. minutum cells and a weaker one for A. tamarense cells, while non-toxic A. minutum was slightly negatively selected and R. baltica strongly negatively selected. Although the level of toxins accumulated by copepods was very similar, in both the diet with only toxic A. minutum cells and in the mixed diet, the negative effects on fitness in the mixed diet could be offset by toxin dilution mechanisms. The implications of these findings are the fact that mesozooplankton may not play an important role in phytoplankton blooms development. Phytoplankton endotoxin production does not seem to be an evolutionary stable strategy as a defence against some herbivores.     

Filtering and feeding rates of cyclopoid copepods feeding on phytoplankton

The algal biomass ingested by omnivorous cyclopoid copepods (Cyclops kolensis and C. vicinus) was measured by two methods in the hypertrophic Heiligensee in Berlin (West Germany). The clearance and ingestion rates inferred from measurements of natural populations of ¹⁴C labelled phytoplankton were compared with those obtained from chlorophyll a determinations using the presence/absence method (observed chlorophyll a content of natural lake phytoplankton with and without addition of cyclopoids). Both methods gave similar results. Nevertheless, the radio tracer method is preferred, mainly because the short feeding duration excludes high variations in both the food composition and food concentration that limit the presence/absence method.     

Food and growth relations of the marine microzooplankter,Synchaeta cecilia (Rotifera)

The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species; a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1⁻¹, the population growth constant increased from 0.17 to 0.60 d⁻¹ at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 10⁴ cells ml⁻¹, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1⁻¹ (0.3 to 1.9 individuals 1⁻¹), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod⁻¹ day⁻¹.     

Do Inactivated Microbial Preparations Improve Life History Traits of the Copepod <Emphasis Type="Italic">Acartia tonsa</Emphasis>?

We have tested a microbial preparation with probiotic effects (PSI; Sorbial A/S DANISCO) on the calanoid copepod Acartia tonsa (Dana) development time and reproduction effectiveness in culture. The hypotheses were that PSI increases the productivity and quality of copepods in culture (increased egg production and hatching success, HS). This was carried out because the use of copepods as live prey in aquaculture could increase the number of fish successfully raised through their entire life cycle. However, the availability of copepods is limited by their difficulty to be effectively raised. Our results show that the addition of PSI to the algal food increased the individual size of the adult females and their egg production. The PSI, together with Rhodomonas salina, also increased the HS of the eggs produced by PSI-treated females. These effects were observed despite that the biochemical analysis of the PSI revealed that it is a nutritionally poor food lacking essential fatty acids, and hence it cannot be used alone to raise copepods but instead as a food additive. This is the first demonstration that the effectiveness of copepod culturing can be improved using microbial preparations as a food additive.     

Induction of toxin production in dinoflagellates: the grazer makes a difference

The dinoflagellate Alexandrium minutum has previously been shown to produce paralytic shellfish toxins (PST) in response to waterborne cues from the copepod Acartia tonsa. In order to investigate if grazer-induced toxin production is a general or grazer-specific response of A. minutum to calanoid copepods, we exposed two strains of A. minutum to waterborne cues from three other species of calanoid copepods, Acartia clausi, Centropages typicus and Pseudocalanus sp. Both A. minutum strains responded to waterborne cues from Centropages and Acartia with significantly increased cell-specific toxicity. Waterborne cues from Centropages caused the strongest response in the A. minutum cells, with 5 to >20 times higher toxin concentrations compared to controls. In contrast, neither of the A. minutum strains responded with significantly increased toxicity to waterborne cues from Pseudocalanus. The absolute increase in PST content was proportional to the intrinsic toxicity of the different A. minutum strains that were used. The results show that grazer-induced PST production is a grazer-specific response in A. minutum, and its potential ecological importance will thus depend on the composition of the zooplankton community, as well as the intrinsic toxin-producing properties of the A. minutum population.     

Toxicity of blooms of the cyanobacterium Trichodesmium to zooplankton

The marine filamentous bloom-forming cyanobacteria Trichodesmium thiebautii and T. erythraeum were collected at locations in the Carribean during Jan.–Feb. 1991. They were screened for toxicity using Artemia salina and several species of copepods, which were harpacticoid grazers, filter-feeding calanoids, or cyclopoid copepods. Approximately 50% of the 89 T. thiebautii samples caused> 50% lethality of A. salina, though none of the 16 T. erythraeum samples caused> 25% lethality. The T. thiebautii bloom samples were toxic to the calanoid and cyclopoid copepods and non-toxic to the harpacticoid grazers. In contrast the T. erythraeum bloom samples were not toxic to any copepods tested.     

Sublethal effects of the toxic dinoflagellate Karenia brevis on marine copepod behavior

Apart from grazing interactions, little is known regarding thesublethal effects of Karenia brevis cells on copepod behavior.We conducted grazing and mortality experiments with K. breviscells and brevetoxins (PbTx-2), establishing routes of toxicityfor the copepods Acartia tonsa, Temora turbinata and Centropagestypicus. Subsequent behavioral experiments determined whethercopepod swimming and photobehavior, both behaviors involvedin predator avoidance, were impaired at sublethal K. brevisand PbTx-2 levels. Copepods variably grazed toxic K. brevisand non-toxic Prorocentrum minimum at bloom concentrations.Although copepods accumulated brevetoxins, significant mortalitywas only observed in T. turbinata at the highest test concentration(1 x 10⁷ K. brevis cells L^–1). Acartia tonsa exhibitedminimal sublethal behavioral effects. However, there were significanteffects on the swimming and photobehavior of T. turbinata andC. typicus at the lowest sublethal concentrations tested (0.15µg PbTx-2 L^–1, 1 x 10⁵ K. brevis cells L^–1).Although physiological incapacitation may have altered copepodbehavior, starvation likely played a major role as well. Thesedata suggest that sublethal effects of K. brevis and brevetoxinon copepod behavior occur and predicting the role of zooplanktongrazers in trophic transfer of algal toxins requires knowledgeof species-specific sublethal effects.     

Loss of waterborne brevetoxins from exposure to phytoplankton competitors

We tested whether interactions among phytoplankton competitors affect toxin dynamics involving the red tide dinoflagellate Karenia brevis, whose brevetoxins incapacitate and kill coastal wildlife. The addition of a live diatom, Skeletonema costatum, led to decreased concentrations of brevetoxin B (PbTx-2) associated with K. brevis cells in co-culturing experiments and with two of three natural bloom samples containing K. brevis. Similar decreases in PbTx-2 concentration, but not PbTx-3 concentration, occurred when a mixture of brevetoxins (without live K. brevis cells) was exposed to S. costatum, indicating that S. costatum metabolizes waterborne PbTx-2. Liquid chromatography–mass spectrometry (LC–MS) and ELISA analyses indicated that PbTx-2 is probably not transformed into other brevetoxins or into known brevetoxin metabolites, and instead is biotransformed by a previously unrecognized mechanism. Four different S. costatum strains from around the world caused similar loss of PbTx-2, suggesting that evolutionary experience with K. brevis is not a pre-requisite for the ability to metabolize PbTx-2. Additionally, phytoplankton-associated bacteria were found to play no role in the loss of PbTx-2, as bacteria-free S. costatum strains metabolized PbTx-2. Finally, loss of waterborne PbTx-2 caused by exposure to a dinoflagellate, a cryptophyte, and two additional diatom species indicates that this phenomenon is widespread among phytoplankton. Our results unexpectedly suggest that competing phytoplankton species present during K. brevis blooms, and possibly other red tides, could mediate bloom toxicity and therefore ecosystem-level consequences of red tides.     

Feeding rates and productivity of the copepod Acartia bifilosa in a highly turbid estuary; the Gironde (SW France)

Acartia spp. are the dominant copepod species in the Gironde estuary, seaward of the turbidity maximum area. Acartia bifilosa develop a large population in spring and early summer whereas Acartia tonsa appear in late summer. High values and high variability of chlorophyll a/suspended particulate matter ratio are found seaward of the turbidity maximum area. Feeding rates of A. bifilosa were measured by fluorometry. Phytoplankton ingestion was found to be highly variable, between 8 to 80% of copepod carbon body weight. Except for adult females, copepods were heavier in summer than in winter. PB ratios, estimated by the instantaneous growth rate method, varied from 0.03 d^–1 to 0.14 d^–1. The gut contents and P/B ratios of Acartia bifilosa were related to chl a/SPM ratio. From those data, and a few obtained for A. tonsa, it is concluded that only in summer months phytoplankton ingestion is enough to maintain secondary production.     

Food selectivity and grazing impact on toxic Dinophysis spp. by copepods feeding on natural plankton assemblages

Food selectivity and grazing impact by Acartia bifilosa, Temora longicornis and Centropages typicus on Dinophysis spp. plankton assemblages were experimentally investigated in the Baltic Sea. Toxin analyses were carried out on phyto- and zooplankton-dominated size fractions from field-collected samples to assess if toxins produced by Dinophysis spp. would end up in the zooplankton. All copepod species fed actively on toxic Dinophysis spp. (Dinophysis acuta and Dinophysis norvegica). Despite the non-selective feeding behaviour by T. longicornis and C. typicus, selectivity coefficients on D. acuta progressively decreased as food availability increased. Similar response was not observed for A. bifilosa, which displayed an even less selective behaviour. A. bifilosa had no significant negative effect on the net growth of D. norvegica at the lowest food concentration offered, whereas T. longicornis and C. typicus had significant negative effects on the net growth of D. acuta at low concentrations, similar to those observed in situ. Both species could potentially contribute as a substantial loss factor for Dinophysis spp. provided they are abundant at the onset of the blooms. The estimated grazing impact by the copepod populations was only considerable when C. typicus abundance was high and D. acuta population in sharp decline. Our results suggest that when high abundance of grazers and poor growth condition of prey populations prevail, grazing impact by copepods can contribute considerably to prevent Dinophysis spp. populations to grow or to cause the populations to decline. Okadaic acid was detected in the zooplankton size fraction at one occasion, but the concentration was far lower than the one expected from the ingested toxins. Thus, even if copepods may act as vectors of DSP-toxins to higher trophic levels, the amount of these toxins transported in the food web by copepods seems limited.     

Growth of dominant zooplankton species feeding on plankton microflora in Lake Shira

Batch cultures and continuous flow cultures were used to study the growth rates of zooplankton species from Shira lake, the rotifer Brachionus plicatilis Muller and calanoid copepod Arctodiaptomus salinus Daday, which were fed on phytoplankton and bacterioplankton from the lake. Analyses of the birth and survival rates were used to demonstrate that the lake phytoplankton, consisting mostly of cyanobacteria and diatomaceous algae, is inadequotes for optimal realisation of the reproductive potential of B. plicatilis when compared with the bacterial diet. The study revealed that the kinetic growth characteristics of the two zooplankters were similar: B. plicatilis r _max, 0.120 d^–1; S ₀, 0.253; and K _s, 0.114 mg dry mass l^–1; and for A. salinus r _max, 0.129 d^–1; S ₀, 0.240; and K _s, 0.171 mg dry mass l^–1. Fluctuations in natural food concentration reduced the growth rate of both species. Even though the threshold concentration of food for B. plicatilis and A. salinus were quite similar, the copepods were less sensitive to food limitation.     

Different Nutritional Histories Affect the Susceptibility of Algae to Grazing

We hypothesize that algae with different cell compositions are differently perceived by their predators and consequently subjected to selective grazing. Five populations of the diatom Phaeodactylum tricornutum that differed in organic and elemental composition, but were otherwise identical, were generated by acclimation to distinct growth regimes. The different populations were then mixed in pairs and subjected to predation by either the rotifer Brachionus plicatilis or the copepod Acartia tonsa. The presence of rotifers had no impact on the ratio between any two algal populations. The presence of copepods, however, affected the ratio between algae previously acclimated to a medium containing 1 mM NH₄⁺ and algae acclimated to 0.5 mM NO₃^?, and to either a lower irradiance or a higher CO₂ concentration. We discuss the possible reason for the influence of different nutritional histories on the vulnerability of algae to predators. The differential impact of grazers on the growth of algae with different nutritional histories may result from direct selective grazing (i.e., grazers can detect algae with the most palatable cell composition), alone or combined to an asymmetric utilization of the nutrients regenerated after predation by co‐existing algal populations. Our results strongly suggest that the nutritional history of algae can influence the relationships between phytoplankton and grazers and hint at the possibility that algal cell composition is potentially subject to natural selection, because it influences the probability that algae survive predation.