Copepod Populations Research Articles

Temperature effects on copepod egg hatching: does acclimatization matter?

This report investigates female sizes, egg sizes and egg hatching rates in relation to temperature for the near-shore calanoid copepod Acartia tonsa cultured at 6, 9, 14 and 24°C for several generations to achieve acclimatization. Inverse size relationships of eggs and females were revealed with increasing temperature. Eggs produced at 6°C were 85 ± 4 μm in diameter, but decreased to 80 ± 3 μm at 24°C. Female cephalothorax length was 840 ± 52 and 692 ± 39 μm at 9 and 24°C, respectively Parallel hatching experiments were performed between non-acclimatized and acclimatized cultures across a range of temperatures reflecting natural conditions in Danish waters. A greater fraction of eggs enter quiescence as temperature declines. Eggs were able to hatch at temperatures as low as 1.5°C. Final egg hatching success increased with temperature. Acclimatization of the copepods resulted in a lower maximum hatching rate, but a higher final hatching success at 9 and 6°C compared with egg hatching from non-acclimatized copepods. Eggs develop significantly better at low temperatures when compared with females in culture. This adaptation suggests that the observed annual population fluctuations in, for example, Danish waters can be explained as follows: the population of copepods in the pelagic virtually die out during the autumn―winter months; the population the following year emerges from resting eggs from the sediment and is produced by the pelagic copepods the previous year(s).

Comparison of six sewage effluents treated with different treatment technologies—Population level responses in the harpacticoid copepod Nitocra spinipes

Since conventional treatment technologies may fail in removing many micro-pollutants, there is currently a focus on the potential of additional treatment technologies for improved sewage treatment. The aim of the present study was to evaluate six different effluents from Henriksdal Sewage Treatment Plant in Stockholm, Sweden. The effluents were; conventionally treated effluent (chemical phosphorous removal in combination with an activated sludge process, including biological nitrogen removal and a sand filter), with additional treatments individually added to the conventional treatment; active carbon filtration, ozonation at 5 mg l −1, ozonation at 15 mg l −1, ozonation at 5 mg l −1 + moving bed biofilm reactor and irradiation with ultraviolet radiation + hydrogen peroxide. The evaluation was done by characterizing and comparing the effluents using a Lefkovitch matrix model based on a life cycle test with the harpacticoid copepod Nitocra spinipes, combined with analysis of juvenile development and survival over time. The conventionally treated effluent resulted in the most negative effects, leading to the conclusion that all additional treatments in the present study created effluents with less negative impacts on the copepod populations. The ozone treatments with the low dose treatment in particular, resulted in the overall least negative effects. Moving bed biofilm reactor combined with ozone did not improve the quality of the effluent in the sense that slightly more negative effects on the population abundance were seen for this treatment technology compared to ozonation alone. The active carbon treatment had more negative effects than the ozone treatments, most of which could possibly be explained by removal of essential metal ions. The effluent which was treated with ultraviolet radiation + hydrogen peroxide resulted in few developmental and survival effects over time, but still showed negative effects on the population level. Matrix population modeling proved a useful tool for biologically characterizing and comparing the effluents. Basing the assessment either on the individual level data (development and survival over time or total reproductive output) or the population level data (lambda values and projected population abundances) would not have resulted in the same conclusions as combining both analyses. The juvenile development and survival over time allowed for closer monitoring of the important molting process, whereas the population modeling provided an integrated measure of potential effects at the population level. If the dilution of the effluent in the recipient is considered, the biological effects recorded in the present study were not of substantial significance for the copepod populations, regardless of treatment technology.

Sex ratios, intersexuality and sex change in copepods

Female-biased adult sex ratios are common in copepod species, and have been observed both in wild populations and in cultures. Biased sex ratios are most commonly explained by sex- or stagespecific differences in longevity or mortality. However, neither differential longevity nor differential mortality fully explains skewed sex ratios in planktonic copepod populations. We propose that sex change is an important mechanism determining the adult sex ratio. Though sex change has been proposed for only a few copepod species, intersexuality is widespread. We review the occurrence and causation of intersexuality in planktonic copepods, which is a manifestation of late sex change during development. By way of example, we demonstrate that skewed sex ratios of Acrocalanus gracilis, a common tropical paracalanid copepod, could be explained by sex change alone. Our observations suggest that sex determination in copepods is under strong environmental control, and we argue that the food limitation is an important determinant of sex change.

Microcystin-LR toxicity on dominant copepods Eurytemora affinis and Pseudodiaptomus forbesi of the upper San Francisco Estuary

This study investigates the toxicity and post-exposure effects of dissolved microcystin (MC-LR) on the dominant copepods of the upper San Francisco Estuary (SFE), where blooms of the toxic cyanobacteria Microcystis aeruginosa coincide with record low levels in the abundance of pelagic organisms including phytoplankton, zooplankton, and fish. The potential negative impact of Microcystis on the copepods Eurytemora affinis and Pseudodiaptomus forbesi has raised concern for further depletion of high quality fish food. Response of copepods to MC-LR (MC) was determined using a 48-h standard static renewal method for acute toxicity testing. Following exposure, a life table test was performed to quantify any post-exposure impacts on survival and reproduction. The 48-h LC-50 and LC-10 values for MC were 1.55 and 0.14 mg/L for E. affinis; and 0.52 and 0.21 mg/L for P. forbesi. Copepod populations recovered once dissolved MC was removed and cultures returned to optimal conditions, suggesting no post-exposure effects of MC on copepod populations. Dissolved microcystin above 0.14 mg/L proved likely to have chronic effects on the survival of copepods in the SFE. Since such high concentrations are unlikely, toxicity from dissolved microcystin is not a direct threat to zooplankton of the SFE, and other mechanisms such as dietary exposure to Microcystis constitute a more severe risk.

Life history traits and spatiotemporal distributional patterns of copepod populations in the Gulf of Maine-Georges Bank region

Life history traits play a significant role in determining the spatiotemporal distributional patterns of marine zooplankton, but biological-physical mechanisms controlling the population dynamics need to be further examined. In the present study, we used a coupled biological-physical model to examine the processes controlling the observed distributional patterns of 3 representative copepod populations in the Gulf of Maine-Georges Bank region including Pseudocalanus spp., Cen- tropages typicus and C. hamatus. The model reveals that the shorter generation time of Pseudo- calanus spp. at cold temperatures, together with their egg-carrying strategy, allows an earlier popu- lation development compared to Centropages spp. The model further reveals that predation mortality plays an important role in the decline of Pseudocalanus spp. in the warm season, and that the resting egg strategy is crucial for the persistence of the C. hamatus population in the Gulf of Maine-Georges Bank region. Analyses of observational data and model results suggest that temper- ature- and food-dependent egg production and development rates, temporally and spatially varying mortality rates and physical transport are important contributors to the formation of characteristic distributional patterns for the copepod populations in the system.

Macrophytes as refuge or risky area for zooplankton: a balance set by littoral predacious macroinvertebrates

Summary1. Zooplankton use macrophytes as day‐time refuge areas when trying to escape from pelagic predators. But macrophytes can also host a diverse and abundant macroinvertebrate assemblage and zooplankton are also likely to face predacious macroinvertebrates once they enter the littoral zone. This study aimed to elucidate the role of macroinvertebrates in determining the refuge capacity of macrophytes.2. We conducted a field enclosure experiment using plastic bags and complementary laboratory feeding trials to test how macroinvertebrates counteract the benefits to zooplankton of the macrophyte refuge. The field experiment consisted of three treatments with different macroinvertebrate assemblages: without predators (WP), low abundance and diversity (LAD) and high abundance and diversity of predators (HAD – which represents lake conditions).3. Populations of Diaphanosoma brachyurum, Bosmina huaronensis and Moina micrura (Cladocera) and of both male and female Notodiaptomus incompositus (Copepoda, Calanoida) declined (by nearly 80%) in the presence of HAD in comparison to WP and LAD treatments.4. Feeding trials revealed that Buenoa sp. (backswimmer), adults of Palaemonetes argentinus (grass shrimp) and Cyanallagma interruptum (damselfly) had a significant negative impact on cladocerans (D. brachyurum, B. huaronensis) and the calanoid copepod population (males, females and copepodites). These predators showed a strong predation effect ranging from 75% to 100% reductions of zooplankton populations.5. The refuge effect offered by macrophytes to zooplankton depends on and is balanced by the predacious macroinvertebrate assemblage that plants host. The risk of confronting littoral predators is high and macroinvertebrate presence can turn the macrophytes into risky areas for zooplankton.

Life cycle traits of two transatlantic populations of Eurytemora affinis (Copepoda: Calanoida): salinity effects

While the populations of the copepod Eurytemora affinis are often morphologically (i.e. taxonomy) indistinguishable, the species complex is composed of genetically distinct clades, representing divergent evolutionary histories. The most distant clades, genetically and morphologically (i.e. phylogeny), are transatlantic clades: North American and European (Lee, 2000). The study of the life cycle strategies of two populations from St. Lawrence salt-marshes (Canada) and from the Seine estuary (France) at three salinities (5, 15 and 25) revealed differences in their salinity tolerance. Individuals from the Seine exhibited high mortality under the highest salinity suggesting that the St. Lawrence population tolerated a wider salinity range. At the lowest salinity, the development time of St. Lawrence individuals was longer than that of individuals from the Seine suggesting that the Seine population was more adapted to low salinity. The clutch size and the longevity of St. Lawrence adults were on average two times higher compared to Seine adults. Thus, the St. Lawrence population exhibited a higher fitness relative to the Seine population. Such differences could be due to genetic differences resulting from divergent evolutionary history, to phenotypic plasticity and/or to the acclimation to culture conditions. We confirmed that a gamma density function is an appropriate fitting function for copepod development time, based on a large data set on development time. It can therefore be integrated into individual-based models of copepod population dynamics.

Aldehyde-induced insidious effects cannot be considered as a diatom defence mechanism against copepods

The last 2 decades have seen much controversy concerning the negative impacts that consumption of diatoms may have upon copepods. Because diatoms have traditionally been consid- ered a major food item for copepods, this controversy has raised fundamental questions concerning our understanding of the marine food chain. The mode of operation of this negative impact is via so- called insidious effects on the survival of early-stage copepod progeny, caused for example by polyunsaturated aldehydes (PUA), with the mechanism proposed as a defence evolved by diatoms. Here the effects of diatoms on copepod reproduction rates are evaluated using a stoichiometric weight- or age-stage copepod model coupled with variable stoichiometric descriptions of prey. We show that, considering different combinations of copepod population age structure and diet compo- sition (diatoms, non-diatoms, microzooplankton and copepods), the concept of an 'insidious' effect of diatom consumption upon copepods cannot be sustained as a defence mechanism, as it does not con- fer any advantage to the diatoms. While metabolites that deter grazing can be advantageous, slowly killing a predator (via the death of juvenile copepods) responsible for consuming competitor primary producers, and also consuming another predator (microzooplankton), is not advantageous to the diatoms. Indeed it is shown to be counterproductive on occasion. While PUA (or compounds that act in a similar fashion) have the potential to adversely affect copepod production, alternative explana- tions for their production need consideration. Such alternatives include the potential impact of PUA against microzooplankton, or simply that PUA represent secondary metabolites of no evolutionary selective advantage.

A multi-generation Schmakeria poplesia culturing system for use in ecotoxicological study

Crustacean zooplankton form the keystone link between primary producers and fish stocks in marine and estuary ecosystems. We have established a multi-generation cultivation system for zooplankton with which future experiments on the biological effects of pollutants in marine and estuary environments can be better performed. A population of calanoid copepod, Schmakeria poplesia, was collected in December 2003 and maintained in a static system through all stages (eggs to adults). The population exhibited an average developmental time of 13.6 d in conditions corresponding to the natural environment (water temperature 20°C, salinity 15). A series of experiments were performed to examine copepod egg production and hatching success as functions of food type and feeding concentration. Results in our study showed that Isochrysis galbana was more favored for the reproduction of copepods than Phaeodactylum tricornutum, and 10×104cells mL−1 was the most practical algae concentration. We have demonstrated that the Schmakeria poplesia population can be maintained in the laboratory through multiple generations. In addition, methods to control egg production through changes in food concentration have been established, making it feasible to control the start date of exposure experiments or the timing of the collection of offspring to initiate a new generation.

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.

Optimal development time in pelagic copepods

According to life history theory, development times have evolved to an optimum solu- tion of the trade-offs between rapid development and high fecundity: rapidly developing individuals have a higher chance of surviving to maturity than do slowly developing ones, but they mature at a smaller size and, thus, have lower fecundity. Here we develop a model to predict egg-to-adult times in marine pelagic marine copepods that maximizes fitness, quantified either as lifetime reproductive output or population growth rate. The model is tested against global data sets of development time as a function of temperature. The optimum development time increases when the enhancement of fecundity with delayed maturation increases, and it decreases with increasing juvenile mortality. Our predictions match the patterns in nature for broadcast spawners, for which most data are available, but appear to underpredict development times for sac-spawning copepods. The partial uncoupling of growth and development rates in copepods demonstrated in laboratory experiments, the substantial variation in age at maturity observed in copepod field populations, as well as the fair match of pre- dicted and observed development times together suggest that development rates in marine pelagic copepods are tuned to the prevailing predation mortality. Observations in freshwater zooplankton suggest that life histories may be adapted to local conditions of growth and predation mortality. The striking lack of similar observations in marine zooplankton calls for work to explore the significance of environmental modulation of life histories of marine zooplankton. Possible future research avenues are proposed, including studies of the effects of seasonal environments, variable presence of preda- tors and the effects of sexual selection on life histories of marine planktonic copepods.

Environmental regulation of the estuarine copepods Acartia tonsa and Eurytemora americana during coexistence period

The seasonal dynamics of Acartia tonsa and the invader Eurytemora americana were analysed in relation to the environmental variability occurring from April to November in the Bahía Blanca Estuary. Twice a month, the abundance of eggs, nauplii, copepodites and adults was examined and some environmental variables were recorded. Multivariate statistics (CCA) was applied to analyse the data of variables. Acartia tonsa eggs and nauplii diminished from April–May and they were almost absent between June and September, although a small larval peak could be detected from the end of July to October. All the stages of this species increased in number through spring. Eurytemora americana was registered as from June and only nauplii larvae were observed, with a peak increase during September. Copepodites and adults were observed as from July, increasing in number until peaking at the end of September. The number of all stages of this species decreased abruptly, the whole population disappearing from the plankton. The A. tonsa developmental stages were most positively correlated with temperature, photoperiod and other light variables whereas those of E. americana showed positive correlations with chlorophyll-a and salinity. The gradients of the main environmental factors likely give rise to a certain niche separation facilitating the coexistence of the two copepod populations within the period studied.

The role of inflow magnitude and frequency on plankton communities from the Guadalupe Estuary, Texas, USA: Findings from microcosm experiments

Changes in magnitude and frequency of inflow results in subsequent alterations in the delivery of nutrients essential for phytoplankton growth and competition producing variations in community composition and nutritional value of phytoplankton. Zooplankton demographics are likely directly influenced by pulsed inflows due to flushing losses, whereas they are also indirectly affected by changes in prey quality. In this study, we report the potential effect of pulsed inflows on the plankton community of the Guadalupe Estuary. Microcosms were used that allowed control of light intensity and photoperiod, turbulence, temperature, nutrient loading, and flushing magnitude and periodicity. Our microcosm experiments were novel as they utilized natural plankton communities, thereby allowing the simultaneous interaction between hydrology, resource availability and grazing. Results show differences in microcosms according to magnitude and frequency of flushing. For example, copepod population density was greatest at the annual mean inflow magnitude. At half the annual mean inflow a decline in prey quality likely resulted in poorer grazer performance, and at double the annual mean inflow magnitude increased flushing losses prevented the incidence of higher copepod densities. Similarly, pulsed inflows resulted in greater copepod population densities, higher overall phytoplankton biomass, and dominance of centric diatoms (known to be faster growing and more edible). While reduced freshwater inflow associated with increasing anthropogenic demands often strains the needs of estuarine systems, the effects of reduced river input may be alleviated with several management options including manipulation of the timing, frequency, and magnitude of freshwater inflows. Before implications for management can be discerned from these findings, however, larger scale experiments are needed focus on the roles of inflow magnitude and frequency.

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.

A simplified age-stage model for copepod population dynamics

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 360:179-187 (2008) - DOI: https://doi.org/10.3354/meps07314 A simplified age-stage model for copepod population dynamics Qiao Hu*, Cabell S. Davis, Colleen M. Petrik Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA *Email: qiao_hu@alum.mit.edu ABSTRACT: Complex 3D biological-physical models are becoming widely used in marine and freshwater ecology. These models are highly valued synthesizing tools because they provide insights into complex dynamics that are difficult to understand using purely empirical methods or theoretical analytical models. Of particular interest has been the incorporation of concentration-based copepod population dynamics into 3D physical transport models. These physical models typically have large numbers of grid points and therefore require a simplified biological model. However, concentration-based copepod models have used a fine resolution age-stage structure to prevent artificially short generation times, known as numerical ‘diffusion.’ This increased resolution has precluded use of age-stage structured copepod models in 3D physical models due to computational constraints. In this paper, we describe a new method, which tracks the mean age of each life stage instead of using age classes within each stage. We then compare this model to previous age-stage structured models. A probability model is developed with the molting rate derived from the mean age of the population and the probability density function (PDF) of molting. The effects of temperature and mortality on copepod population dynamics are also discussed. The mean-age method effectively removes the numerical diffusion problem and reproduces observed median development times (MDTs) without the need for a high-resolution age-stage structure. Thus, it is well-suited for finding solutions of concentration-based zooplankton models in complex biological-physical models. KEY WORDS: Plankton · Copepods · Modeling · Marine ecology · Oceanography · Limnology · Methodology · Mean age Full text in pdf format PreviousNextCite this article as: Hu Q, Davis CS, Petrik CM (2008) A simplified age-stage model for copepod population dynamics. Mar Ecol Prog Ser 360:179-187. https://doi.org/10.3354/meps07314 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 360. Online publication date: May 22, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Seasonal variation in abundance and feeding rates of the first stages of copepods in a temperate sea

An understanding of the role of copepod populations in marine ecosystems and carbon fluxes is limited by the scarcity of information on small copepods and developmental stages (nauplii and copepodites). Here, we present a study that includes the whole copepod population in the Cantabrian Sea, with special emphasis on copepodites and copepods <200 µm and nauplii. Total copepod abundance and feeding rates of phytoplankton by nauplii, copepods and copepodites belonging to the size fraction < 200 µm were measured during an annual cycle in 3 stations off Cud- illero (southern Bay of Biscay). Nauplii were the most abundant group in the metazooplankton, with densities ranging between 1 and 48 ind. l -1 . The highest abundances were found during late summer and autumn. Feeding rates on phytoplankton showed a significant increase with chlorophyll a con- centration in the water, and a saturation response at around 240 µg C l -1 . Specific ingestion rates ranged from 0.04 to 2.05 µg C µg -1 nauplii C d -1 and 0.04 to 3.38 µg C µg -1 copepod C d -1 . Nauplii and copepods < 200 µm, respectively, ingested 0.2 to 7.1% and 0.1 to 4.9% of total chlorophyll a in the water column daily.

Copepod mating: chance or choice?

Mate choice is common in most animals, but the issue has largely been ignored in regard to pelagic copepods-the most abundant zooplankton group in the oceans. Contemporary demographic models of copepods assume that all encounters lead to successful copulation and viable egg production. We revisit the subject of copepod mating biology in the framework of sexual selection theory. We discuss, and point to, examples that suggest mate choice in both sexes. Sexual selection theory may add an important dimension for understanding copepod population dynamics and potentially lead to renewed interpretations of the diverse copepod behaviours and life histories. In addition, the range of mating strategies in copepods represents a rich, but unexplored, source of information for general behavioural ecologists.

Normal versus gamma: stochastic models of copepod molting rate

Communicating editor: K.J. Flynn Molting rate is a key life history parameter in copepods. Since copepod population growth is an inherently exponential process, accurate formulation of molting rate is of critical importance. Many experiments have been conducted to culture different copepod species under varying temperatures and food concentrations. Probability density functions (PDFs) then were used to estimate the median development time (MDT) of different copepod stages from the experimental data. These MDTs are used in copepod population models. Asymmetrical PDFs are widely used to model molting rate, because the shapes of these curves are similar to laboratory data on cohort development. In this paper, we developed an individual stochastic model (ISM) to simulate the molting rate with different PDFs. We showed that there was no connection between the asymmetry of cohorts and the asymmetry of the molting PDF. Although age-within-stage models have been widely used to simulate copepod population dynamics, we found that none had used the correct formulation of molting rate. The population model requires the probability of molting at each time step, whereas the laboratory-derived PDF is the frequency distribution of stage duration. Therefore, the PDF cannot be applied directly to the population model. We present here a corrected formula based on the PDF for use in copepod population models, termed the probability of molting for remaining individuals (PMR). Despite emphasis on use of the gamma function for copepod molting, we found simpler functions work equally well, but that prior use of incorrect molting rate functions in copepod models can seriously overestimate generation time.

Do benthic and planktonic diatoms produce equivalent effects in crustaceans?

Hippolyte inermis Leach 1814 is a benthic shrimp characterized by a peculiar mechanism of sex reversal influenced by diatom foods. In fact, the appearance of primary females in spring is due to an apoptotic early disruption of the androgenic gland and of the male gonad, triggered by still unknown compounds present in diatoms of the genus Cocconeis. The influence of diatoms on the reproductive ecology and life cycle of planktonic crustaceans has been demonstrated previously: some planktonic diatoms produce aldehydes inducing apoptosis in the embryos and in the larvae of marine copepods, reducing their viability. Both benthic and planktonic diatoms therefore produce compounds having an apoptotic effect on some tissues of target crustaceans, although the ecological significance of the two processes is different: deleterious for copepod populations, regulative for shrimps associated with Posidonia oceanica. In the present article we experimentally administered specific planktonic diatoms, their fractions and compounds known to induce apoptosis in planktonic copepods, to H. inermis postlarvae, to check whether the apoptotic effect is due to an identical family of diatom compounds, and to establish whether the processes observed in the plankton and in the benthos, respectively, are analogous or homologous, from an ecological point of view. Our results indicated that diatom compounds acting in the two systems are different, since both planktonic diatoms and their aldehydes had negligible effects on the sex ratios of cultured shrimps.

Photoprotective compounds in weakly and strongly pigmented copepods and co‐occurring cladocerans

Summary1. The prevalence of mycosporine‐like amino acids (MAAs) – a group of potential ultraviolet (UV)‐photoprotective compounds – was surveyed across 11 species of freshwater copepods from 20 lakes of varying ultraviolet radiation (UVR) transparency in North America, New Zealand and Argentina. Co‐occurring cladocerans were also analysed (seven species from 12 lakes). Many of the calanoid copepod populations were red with carotenoid pigmentation, allowing comparison of MAA and carotenoid accumulation as photoprotective strategies.2. In two Pennsylvania (U.S.A.) lakes, MAA and carotenoid contents were followed during the early spring to mid‐summer period of lake warming. A pronounced seasonal pattern of higher carotenoid/low MAA content in spring, shifting to low carotenoid/higher MAA content in summer, was observed in calanoids from the more UV transparent lake.3. All copepod samples contained MAAs. Visibly red calanoids, especially southern Hemisphere Boeckella, often had moderate to high concentrations (2.5–11 μg MAA mg−1 dw), but low concentrations (0.04–1 μg MAA mg−1 dw) in some N. American red calanoids show that high carotenoid pigmentation (e.g. 5–10 μg carotenoid mg−1 dw) does not necessarily imply high MAA content.4. No cladoceran sample had more than trace amounts of MAAs (&lt;0.05 μg mg−1 dw). Therefore, MAA accumulation does not seem to be a photoprotective strategy utilized by Daphnia (five species from nine lakes) or other cladocerans.5. Seven identifiable MAAs were widely distributed among both calanoids and cyclopoids. Shinorine was ubiquitous and was usually the most abundant MAA in N. American samples. In contrast, porphyra‐334 was the predominant MAA in the southern Hemisphere Boeckella.6. Copepods from higher UVR lakes tended to have a higher MAA content, but this relationship was statistically weak overall and taxon‐specific when found.