Copepod Acartia Hudsonica Research Articles

Application of Next-Generation Sequencing for the Determination of the Bacterial Community in the Gut Contents of Brackish Copepod Species (Acartia hudsonica, Sinocalanus tenellus, and Pseudodiaptomus inopinus).

Simple SummaryCopepods are important components of marine coastal food chains, supporting fishery resources by providing prey items mainly for fish. Copepods interact with small microorganisms via feeding on phytoplankton. DNA methods can determine the gut contents of copepods and provide important information regarding how copepods interact with phytoplankton and bacteria. In the present study, we designed a method for extracting the gut content DNA from small-sized copepods that are important in coastal and brackish areas. Based on DNA analyses, Rhodobacteraceae, which is common in marine waters and sediments, was most abundant in the gut contents of the three copepod species (Acartia hudsonica, Sinocalanus tenellus, and Pseudodiaptomus inopinus). However, the detailed composition of bacteria was different among species and locations. The results suggested that environmental variables and species-specific feeding behaviour can affect the gut bacterial community. The bacteria play an important role in digestion and in the overall degradation and release of metabolites to the outside water. Further analyses with advanced methods regarding DNA isolation from small microorganisms and identification skills using a DNA library for better understanding of biological interactions and matter cycling in marine food webs are required.The gut bacterial communities of copepods can affect metabolic processes, and consequently, their activity can be related to the release of organic substances to the environment. Hence, they are important for organic matter cycling in marine coast food webs. However, information regarding the variation in gut bacterial communities based on copepod species and environmental variations is limited. We analysed the differences in gut bacterial communities from dominant copepod species, i.e., Acartia hudsonica, Sinocalanus tenellus, and Pseudodiaptomus inopinus, in a brackish reservoir. The core bacteria among the copepod species and locations consisted of the following main operational taxonomic units (OTUs): Novosphingobium capsulatum and the family Rhodobacteraceae belonging to Alphaproteobacteria, which is abundant in seawater and freshwater aquatic ecosystems as a zooplankton-associated bacterial community. The bacterial community composition of each copepod (except the core species) showed high variability. The bacterial community diversity differed depending on the copepod species and the sites’ environmental conditions, especially salinity, e.g., compositional variations in the bacterial community of P. inopinus were high at sites with low salinity. Therefore, the gut bacterial community of each copepod species responds differently to the environment.

Relative importance of nitrogen sources, algal alarm cues and grazer exposure to toxin production of the marine dinoflagellate Alexandrium catenella

Dinoflagellate paralytic shellfish toxin (PST) production is mediated by several abiotic and biotic factors. This study compared the relative importance of nitrogen source and concentration, prey alarm cues and grazer presence on toxin production of the marine dinoflagellate Alexandrium catenella (Group I, strain BF-5). In separate assays run under either nutrient-replete (F/2 medium) or nutrient-depleted (filtered seawater) conditions, PST production of A. catenella was measured as a function of varying concentrations of added nitrogen sources (ammonium and urea), alarm cues from lysed conspecific (A. catenella Group I strains) and interspecific (the diatom, Thalassiosira weissflogii, and the green flagellate, Tetraselmis sp.) algae, and the presence of a grazer (the copepod Acartia hudsonica). Results showed that addition of ammonium or urea did not increase PST production. Unexpectedly, interspecific alarm cues increased toxin production but conspecific ones did not. Grazer presence dramatically induced PST production in A. catenella, irrespective of nutrient conditions, and this effect was an order of magnitude greater than any of the other variables tested. These results corroborate previous studies on grazer-induced PST production, and support the hypothesis that grazer-induced toxin production is not an experimental artifact, but rather a prey defense mechanism.

Determining the Advantages, Costs, and Trade-Offs of a Novel Sodium Channel Mutation in the Copepod Acartia hudsonica to Paralytic Shellfish Toxins (PST).

The marine copepod Acartia hudsonica was shown to be adapted to dinoflagellate prey, Alexandrium fundyense, which produce paralytic shellfish toxins (PST). Adaptation to PSTs in other organisms is caused by a mutation in the sodium channel. Recently, a mutation in the sodium channel in A. hudsonica was found. In this study, we rigorously tested for advantages, costs, and trade-offs associated with the mutant isoform of A. hudsonica under toxic and non-toxic conditions. We combined fitness with wild-type: mutant isoform ratio measurements on the same individual copepod to test our hypotheses. All A. hudsonica copepods express both the wild-type and mutant sodium channel isoforms, but in different proportions; some individuals express predominantly mutant (PMI) or wild-type isoforms (PWI), while most individuals express relatively equal amounts of each (EI). There was no consistent pattern of improved performance as a function of toxin dose for egg production rate (EPR), ingestion rate (I), and gross growth efficiency (GGE) for individuals in the PMI group relative to individuals in the PWI expression group. Neither was there any evidence to indicate a fitness benefit to the mutant isoform at intermediate toxin doses. No clear advantage under toxic conditions was associated with the mutation. Using a mixed-diet approach, there was also no observed relationship between individual wild-type: mutant isoform ratios and among expression groups, on both toxic and non-toxic diets, for eggs produced over three days. Lastly, expression of the mutant isoform did not mitigate the negative effects of the toxin. That is, the reductions in EPR from a toxic to non-toxic diet for copepods were independent of expression groups. Overall, the results did not support our hypotheses; the mutant sodium channel isoform does not appear to be related to adaptation to PST in A. hudsonica. Other potential mechanisms responsible for the adaptation are discussed.

A novel mutation from gene splicing of a voltage-gated sodium channel in a marine copepod and its potential effect on channel function

The saxitoxins (STX), a group of potent neurotoxins produced by some marine algae (dinoflagellates and cyanobacteria), block voltage-gated sodium channels, inhibiting nerve-signal transmission in consumers of STX-bearing prey. Populations of grazers (clams and copepods) persistently exposed to the STX-bearing dinoflagellate Alexandrium fundyense are less susceptible to STX than naïve ones. Adaptation to STX in clams is linked to a point mutation at the STX-binding site in the sodium channel, which dramatically lowers the sensitivity to the toxin (STX resistance). The present study tested if a similar mechanism of STX resistance occurs in the copepod Acartia hudsonica. Our cloning and sequencing results indicate that two full-length cDNA variants (AhNaV1 and AhNaV2) of the sodium channel exist in A. hudsonica, which result from alternative splicing of the single coding gene. Both variants have identical nucleotide sequences except that AhNav1 (the putative mutant isoform) contains a three-amino-acid (GRD) insertion and a single adjacent aa-substitution (A to V) close to the inactivation gate on the cytoplasmic linker between domains III and IV of the sodium channel. All individuals express both AhNaV1 and AhNaV2 in varying proportions. The functional consequences of the mutation were studied by inserting the three-amino acid codons into a rat (rNav1.2) sodium channel expressed in both Xenopus oocytes and HEK cells. Currents carried by construct rNav1.2 bearing the GRD insertion did not inactivate as completely, and recovered faster from inactivation than rNav1.2. These two rNav1.2 constructs were, however, equally sensitive to STX, suggesting that the GRD variation does not confer STX resistance on the rat sequence of Nav1.2. These results render unlikely the hypothesis that this novel mutation is responsible for the adaptation (via resistance) of A. hudsonica to STX-bearing prey.

Sodium channel expression in the copepod Acartia hudsonica as a function of exposure to paralytic shellfish toxin (PST)

Local adaptation of the copepod Acartia hudsonica to toxic Alexandrium spp. is associated with degree of historical co-exposure. Recently, a novel mutation in the sodium channel in A. hudsonica was hypothesized to be the mechanism of adaptation to toxic Alexandrium; all copepods express both types of sodium channels. We tested the hypothesis that mutant sodium channel expression in A. hudsonica individuals corresponded to historical co-exposure to A. fundyense. Female A. hudsonica were sampled from historically exposed (Maine) and naïve (Connecticut and New Jersey) populations to A. fundyense, throughout the 2011 season of growth of A. hudsonica. There were no consistent differences in wild-type: mutant isoform ratios nor in the relative abundance of individuals that predominately express one type of isoform, either through time within a population or among populations or over time within each location. We also tested the hypothesis that expression of the mutant sodium channel isoform in A. hudsonica should increase during the progression of a toxic Alexandrium bloom. Sodium channel expression was compared before, during, and after the 2011 toxic Alexandrium spp. bloom in Northport Harbor, NY. Moreover, the relative expression of the mutant isoform increased slightly after the peak of the toxic Alexandrium spp. bloom; however, there was no simultaneous increase in individuals that predominately express mutant channel isoforms. Overall, there was little evidence in support of our hypotheses. Other mechanisms must be responsible for the observed geographic differences in adaptation of copepods to toxic Alexandrium.

An improved method for achieving high-quality RNA for copepod transcriptomic studies

An efficient RNA-extraction method is crucial for transcriptomic studies of ecologically important organisms like copepods. In this study, we used the copepod Acartia hudsonica as a test species to evaluate existing methods, and formulated several improved protocols to consistently and efficiently isolate high-quality RNA from both pooled and individual copepod samples. Our protocols recommend copepod preservation in a phenol/guanidine thiocyanate reagent, followed by bead-beating or micropestle homogenization. To obtain high-quality RNA from pooled samples, one initial chloroform extraction followed by multiple phenol/chloroform extractions are needed before the raw RNA samples are further purified with the Qiagen RNeasy Mini Kit. When analyzing individual samples, one chloroform extraction followed by purification using the Zymo Research Direct-zol™ MiniPrep Kit gives the best results. Using these protocols, we isolated RNA from pooled and individual A. hudsonica samples with consistent recovery rate (individual samples: 95±12ng/male; 272±57ng/female). The cDNAs synthesized using these RNAs were proven to be of high quality by successful amplification of transcripts including the >7kb alpha subunit of the voltage-gated sodium channel gene (SCG). For individual A. hudsonica samples, our protocols yielded significantly higher success rates (95%, n=456) in reverse transcription quantitative PCR of SCG compared to existing methods (0–85%, n=150). Applications of these protocols to nine other copepod species from seven families have led us to achieve high-quality RNAs and cDNAs from pooled and/or individual samples. As a result of testing the protocols, we obtained cDNA sequences of various genes in ten copepod species, some of which are the first record in copepods. Our protocols can easily be adopted by laboratories to facilitate molecular work on copepods.

Impact of improved bottom hypoxia on zooplankton community in shallow eutrophic lake

We followed changes in the abundance of meso- and microzooplankton after an existing bottom hypoxia improved by the introduction of water with high oxygen content into the bottom. Mesozooplankton, calanoid copepod Acartia hudsonica showed ten times higher abundance under high oxygen condition at the bottom than under control where there was less oxygen at the bottom. On the other hand, during summer when microzooplankton such as rotifers and small cyclopoid species Oithona spp. were dominant, no difference in their distribution pattern and abundance was observed. Results have suggested that oxygen concentration at the bottom is one important factor determining the abundance and distribution of mesozooplankton even in local-scale probably by providing bottom refuge, but not for microzoooplankton. Since spring season is important for recruitment of many commercial fish juveniles, the distribution of oxygen in the lake seems very important for the fish stock in the lake.

A novel approach to identifying PST tolerant copepods: An individual ingestion assay

Phenotypic tolerance of individual copepods to paralytic shellfish toxins (PSTs), as determined by fecundity, has recently been reported. In the present study, we tested whether similar phenotypic tolerance related to ingestion also exists. In short-term feeding assays, ingestion rates of individual females of the copepod Acartia hudsonica were measured on a sole diet of toxic Alexandrium fundyense as well as on a sole diet of nontoxic Alexandrium tamarense. When copepods fed on A. fundyense, the frequency distribution of ingestion rates was polymodal, consistent with the hypothesis of levels of phenotypic tolerance associated with toxin ingestion. Four distinct groups of ingestion rates on toxic algae were observed. Mean rates ranged from near zero to more than 100 cells copepod −1 h −1. In contrast, when the same individuals fed on the nontoxic A. tamarense diet, the polymodal distribution of ingestion rates was not apparent. Furthermore, group-specific mean ingestion rates, for two ingestion-defined groups, were always significantly greater on the toxic diet than they were on the nontoxic diet. These results support the hypothesis that discrete groups of grazer ingestion of toxic A. fundyense are related to PST tolerance.

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.

Comparative dynamics of paralytic shellfish toxins (PST) in a tolerant and susceptible population of the copepod Acartia hudsonica

In common-environment experiments, we measured the uptake, accumulation, retention, transformation and depuration of paralytic shellfish toxins (PSTs) of the dinoflagellate Alexandrium fundyense in adult females of two geographically separated populations (Maine and New Jersey, USA) of the copepod Acartia hudsonica. These populations were previously shown to differ in their history of exposure to Alexandrium blooms, and in their degree of adaptation to this dinoflagellate. Toxin accumulation was measured at several times in incubations lasting up to 72 h. Toxin depuration was assessed after a 60 h incubation of females with toxic A. fundyense and subsequent 60 h incubation in a sole diet of the non-toxic green flagellate Tetraselmis sp. As previously observed, the Maine population had significantly higher toxin ingestion rates. By contrast, both toxin accumulation (up to ∼2.5 ng STX eq. female −1) and the depuration rate (∼0.73 d −1) were not significantly different between populations. Hence, faster depuration is ruled out as a tolerance mechanism in the Maine population. Some toxin transformation during both accumulation and depuration was evident in both populations. However, differential toxin transformation does not appear to be a tolerance mechanism either. In contrast to these results, toxin retention (ratio of accumulation/cumulative ingestion) was significantly lower in the Maine population. The retentions of gonyautoxin 3 (GTX3) and of two of the most potent toxins, neosaxitoxin (NEO) and saxitoxin (STX), were also significantly lower in that population. At steady state, toxin absorption efficiency was estimated to be 6% for the Maine population and 9% for the New Jersey population. These results suggest that lower toxin absorption is a possible tolerance mechanism for the Maine population. The results of the present study also suggest that copepod adaptation to toxic dinoflagellates does not necessarily lead to higher toxin transfer up the food web.

Phylogeography of the copepod Acartia hudsonica in estuaries of the northeastern United States

Copepods of the genus Acartia dominate zooplankton assemblages in northwestern Atlantic estuaries, many of which originated after the last glacial maximum 10,000–18,000 years ago. Acartia hudsonica occurs, at least seasonally, in estuaries from Chesapeake Bay to Labrador/Newfoundland. We sequenced the mitochondrial gene Cytochrome B (CytB) of 75 individuals of A. hudsonica from 26 estuaries from New Jersey to Maine, covering four biogeographic regions, and 11 individuals of Acartia tonsa from four of these estuaries in the southern part of the sampling range. A. hudsonica exhibited exceptionally high intraspecific DNA sequence variation. Uncorrected p-distances between sequences ranged from 0.3 to 31%. Five highly divergent sequence groups differed in frequencies across populations and biogeographic regions. One sequence group dominated northern localities, and two sequence groups were found at intermediate to high frequencies in two southern biogeographic regions. Ages of the sequence groups were estimated to be 11, 13, 30, and 37 million years, by applying a molecular clock calibrated by divergence in Alpheus snapping shrimps across the Isthmus of Panama. These ages were compared with independent biogeographic paleoceanographic data, and may have coincided with periods of global climate change over the past 40 MY.

Sex‐related differential mortality of a marine copepod exposed to a toxic dinoflagellate

In this study we hypothesized that the sexes of the copepod Acartia hudsonica experience different mortalities when exposed to the toxic dinoflagellate Alexandrium fundyense. In laboratory experiments, we manipulated toxin dose and measured sex‐specific mortality. We also used a split‐family design to determine whether there were genetic influences on sex determination, and therefore on sex ratio. When the dose of the toxic alga was high (25% of diet by carbon content), population mortality was high, and the fraction of males surviving to adulthood was low (20‐30% of the adult population). No such effect was observed when A. fundyense comprised only 10% of the diet. Adult male copepods were also more susceptible to the toxic alga, though prior selection for resistance to toxins also had an effect on mortality. No genetic variation for sex ratio was detected in the split‐family experiment. Males of A. hudsonica are more sensitive to the toxins of A. fundyense than are females. Resistance may be sex‐linked, and copepod populations exposed to a bloom of toxic Alexandrium sp. may experience shifts in sex ratios away from males and toward females. Differential mortality and skewed sex ratios are feedback mechanisms potentially affecting both the population dynamics of grazers and the development of toxic algal blooms.

Mate limitation in an estuarine population of copepods

We determined the probability of mating as a function of population density in the estuarine copepod Acartia hudsonica by combining experimental measurements with a simple model. Pairs of unmated copepods were confined in containers of various volumes to simulate variable population density, and experiments were run for 8, 16, and 24 h. Mating frequencies indicated that males search for females at an effective search volume rate of 0.34 ± 0.15 L h−1 or 8.2 ± 3.5 L d−1 and that males become ready to mate only after ~15 h exposure to the females. We applied these parameters in a simple population model to determine the critical density for zero population growth. With high egg production, zero mortality, and residence time of 60 d, the critical density for A. hudsonica was 0.01 m−3, at the low end of the range of observed population densities. Critical densities for less favorable conditions were well within the range of observed population densities, even allowing for the effects of aggregation. Thus, mate limitation in sexually reproducing organisms, or Allee effects, can cause negative density dependence in growth rate of these populations at low but realistic population densities. We applied these results to the introduction of exotic zooplankton via ships’ ballast water under various scenarios of initial dilution in harbors and subsequent conditions for reproduction and survival. Inocula resulting from the discharge of post‐exchange ballast water were often high enough to establish new resident populations.

Comparison of the functional and numerical responses of resistant versus non-resistant populations of the copepod Acartia hudsonica fed the toxic dinoflagellate Alexandrium tamarense

The functional and numerical responses of grazers are key pieces of information in predicting and modeling predator–prey interactions. It has been demonstrated that exposure to toxic algae can lead to evolved resistance in grazer populations. However, the influence of resistance on the functional and numerical response of grazers has not been studied to date. Here, we compared the functional and numerical responses of populations of the copepod Acartia hudsonica that vary in their degree of resistance to the toxic dinoflagellate Alexandrium tamarense. In common environment experiments carried out after populations had been grown under identical conditions for several generations, female copepods were offered solutions containing different concentrations of either toxic A. tamarense or the non-toxic green flagellate Tetraselmis sp. ranging from ∼25 to 500 μgC L −1, and ingestion and egg production rates were measured. Throughout most of the range of concentrations of the toxic diet, copepod populations that had been historically exposed to toxic blooms of Alexandrium exhibited significantly higher ingestion and egg production rates than populations that had little or no exposure to these blooms. In contrast, there were no significant differences between populations in ingestion or egg production for the non-toxic diet. Hence, the between population differences in functional and numerical response to A. tamarense were indeed related to resistance. We suggest that the effect of grazer toxin resistance should be incorporated in models of predator and toxic prey interactions. The potential effects of grazer toxin resistance in the development and control of Alexandrium blooms are illustrated here with a simple simulation exercise.

Induction of embryonic dormancy in the calanoid copepod Acartia hudsonica: heritability and phenotypic plasticity in two geographically separated populations

The planktonic copepod Acartia hudsonica apparently requires summer diapause or dormancy to persist in Narragansett Bay, RI. In estuaries to the north, however, active A. hudsonica populations are present year-round and may not express dormancy. Using a full-sibling rearing design and analysis of variance (ANOVA), I assessed the importance of phenotypic and genetic sources of variation in two geographically separate populations, one from Maine and one from Rhode Island. Both populations showed phenotypic plasticity in the percentage of dormant eggs produced. Moreover, experiments revealed significant sibship–environment interactions in both populations, indicating that the phenotypic plasticity has a genetic component. Both populations also revealed a significant amount of genetic variation in the percentage of dormant eggs produced. For the Maine population, broad sense heritability was high (0.91, 1.10) in two short-day (12L:12D) treatments and near zero (0.08) in the long-day treatment (15L:9D). For a Rhode Island population, broad sense heritability was higher (0.95) in a low-temperature short-day treatment (13.5 °C, 12L:12D) than in a high-temperature short-day treatment (17.5 °C, 12L:12D; h 2=0.25).

Relevant scales in zooplankton ecology: Distribution, feeding, and reproduction of the copepod Acartia hudsonica in response to thin layers of the diatom Skeletonema costatum

We investigated the interaction of the copepod Acartia hudsonica in relation to thin layers of the diatom Skeletonema costatum. Thin layers have recently received much attention, since they are common and persistent features in the water column, often overlooked by traditional sampling methods. Their frequent abundance in coastal oceans and the high biomass associated with them has led to the assumption that they are important grazing sites of calanoid copepods. We employed 2‐m tall tower tanks that allowed us to simulate thin layers. Three variables representative of three time scales were considered: the distribution of copepods in the tanks (time scale of minutes), fecal pellet production as a proxy for ingestion rate (time scale of hours), and egg production rate (time scale of >12 h). A. hudsonica responded significantly but very little to the thin layers in terms of their distribution. Given a choice, there was a slightly higher tendency to swim through a patch of diatoms than to swim around it. Fecal pellet production was slightly lower in the thin‐layer treatments than in the homogeneous controls. Egg production was not influenced by differential distribution of diatoms in the tanks, which indicated that the copepods dealt equally well with patchy food as when the same numbers of cells were available in a homogeneous distribution. Time series experiments showed that ingested carbon is integrated over time scales of >12 h. Therefore, small scale fluctuations of food in space and time do not necessarily translate into small‐scale fluctuations in reproductive output.

Effects of the toxic dinoflagellate Alexandrium fundyense on the copepod Acartia hudsonica: a test of the mechanisms that reduce ingestion rates

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 248:55-65 (2003) - doi:10.3354/meps248055 Effects of the toxic dinoflagellate Alexandrium fundyense on the copepod Acartia hudsonica: a test of the mechanisms that reduce ingestion rates Sean P. Colin1,2,*, Hans G. Dam1 1Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340-6097, USA 2Present address: Biology Department, Roger Williams University, One Old Ferry Road, Bristol, Rhode Island 02809, USA *Email: scolin@rwu.edu ABSTRACT: Reduced grazing on harmful algal bloom species has been attributed to both the feeding deterrence and toxicity of the algae. Both toxic and deterrent effects of dinoflagellates of the genus Alexandrium, which contain toxins that cause paralytic shellfish poisoning, have been reported on different copepod species. We examined how toxin-containing Alexandrium fundyense affected ingestion rates of 2 geographically distinct Acartia hudsonica (Copepoda: Calanoida) populations over short timescales. The copepod population from Great Bay, New Jersey, has never been exposed to blooms of toxic A. fundyense, whereas the population from Casco Bay, Maine, has experienced regular blooms of the highly toxic dinoflagellate for decades. Our goals were to examine the mechanisms by which toxin-containing Alexandrium reduced the ingestion rates of copepods and determine whether the mechanisms were related to the exposure history of copepod populations. Copepods were fed, for 48 h durations, sole diets of toxin-containing A. fundyense, non-toxin containing Alexandrium tamarense and the green flagellate Tetraselmis sp. (not known to have toxic effects) and different mixtures of each (70% Alexandrium/30% Tetraselmis sp., 40/60, 20/80). Changes in ingestion rates over time were determined by measuring ingestion at different time intervals (3, 6, 12, 24, 48 h) over the 48 h period using 3 h incubations. The naïve copepods from New Jersey initially ingested toxin-containing A. fundyense, in both sole and mixed diets, at high rates followed by decreases in ingestion over time. By 24 h, their total ingestion rates were near zero. The decreases in ingestion rates, which were not due to prey selection, were also accompanied by reduced respiration rates. In contrast, none of these effects were observed when the New Jersey copepods fed on non-toxic A. tamarense. Additionally, feeding rates of historically exposed copepods from Maine were not affected by the toxin-containing A. fundyense diets. These observations are consistent with the hypothesis that toxic A. fundyense physiologically incapacitated the copepods from New Jersey but not those from Maine. Such toxic effects, as opposed to deterrence effects, can have profound implications on the grazers¹ ability to control harmful algal blooms. KEY WORDS: Copepod · Toxic dinoflagellate · Toxicity · Resistance · Ingestion rate · Physiological incapacitation · Feeding deterrence Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 248. Online publication date: February 20, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Latitudinal differentiation in the effects of the toxic dinoflagellate Alexandrium spp. on the feeding and reproduction of populations of the copepod Acartia hudsonica

Blooms of the dinoflagellate Alexandrium spp. increase in their frequency, toxicity and historical presence with increasing latitude from New Jersey (USA) to the Gaspé peninsula (Canada). Biogeographic variation in these blooms results in differential exposure of geographically separate copepod populations to toxic Alexandrium. We hypothesize that the ability of copepods to feed and reproduce on toxic Alexandrium should be higher in copepods from regions that are frequently exposed to toxic Alexandrium blooms. We tested this hypothesis with factorial common environment experiments in which female adults of the copepod Acartia hudsonica from five separate populations ranging from New Jersey to New Brunswick were fed toxic and non-toxic strains of Alexandrium, and the non-toxic flagellate Tetraselmis sp. Consistent with the hypothesis, when fed toxic Alexandrium we observed significantly higher ingestion and egg production rates in the copepods historically exposed to toxic Alexandrium blooms relative to copepods from regions in which Alexandrium is rare or absent. Such differences among copepod populations were not observed when copepods were fed non-toxic Alexandrium or Tetraselmis sp. These results were also supported by assays in which copepods from populations both historically exposed and naı̈ve to toxic Alexandrium blooms were fed mixtures of toxic Alexandrium and Tetraselmis sp. Two-week long experiments demonstrated that when copepods from populations naı̈ve to toxic Alexandrium were fed a toxic strain of Alexandrium they failed to acclimate, such that their ingestion rates remained low throughout the entire two-week period. The differences observed among populations suggest that local adaptation of populations of A. hudsonica from Massachusetts (USA) to New Brunswick (Canada) has occurred, such that some populations are resistant to toxic Alexandrium.

Escape behavior of Acartia hudsonica copepods during interactions with scyphomedusae

Calanoid copepods possess remarkable abilities to detect and escape from hydrodynamic disturbances, such as those created by approaching predators. At the same time, a number of studies in coastal ecosystems have suggested that gelatinous predators, including medusae in the Class Scyphozoa, exert top-down control on copepod populations. Although prey escape behavior plays a critical role in predation models, we have relatively little empirical data on how copepods respond to encounters with scyphomedusae. In this study, I used video to quantify encounter rates and escape behaviors of the copepod Acartia hudsonica during interactions with two scyphomedusae, Aurelia aurita and Cyanea sp., in two flow regimes. Escapes were complex, variable and effective. Fewer than 1% of encounters resulted in ingestion. Typically, A.hudsonica avoided contact by responding when predators remained several body lengths (4 to 10 mm) distant and stringing together many escape jumps at submaximum velocities (33 to 59 mm s -1 ). In addition, copepodite stages behaved passively-or failed to respond-following encounters with medusae more often than did adults. Because escape behavior exhibited by A.hudsonica was so variable, it is unlikely that medusae capture copepods using a single, quantifiable mechanism. A range of responses within populations and individuals may be the best strategy for zooplankton faced with strong predation pressure from a variety of predators.

Chemical, mechanical and visual cues in the vertical migration behavior of the marine planktonic copepod Acartia hudsonica

Chemical, mechanical and visual cues in the vertical migration behavior of the marine planktonic copepod <i>Acartia hudsonica</i>