Marine Copepod Research Articles

Protoraphis Simonsen, a newly recorded marine epizoic diatom genus for China

Epizoic diatoms on marine copepods are common in nature and may have a special ecological relationship with their hosts. However, this special ecological group is not well known, and it has only rarely been studied in the China seas. To address this knowledge gap, the species diversity and classification of epizoic diatoms on planktonic copepods were studied with samples collected from the East China Sea. In the present study, a marine araphid diatom genus Protoraphis and its type species, Pr. hustedtiana, were observed and identified by light and electron microscopy, thus representing the first record of this genus and its type species in China. This genus is characterized by a median sternum strongly bent to opposite sides and terminate in two transapical grooves at the valve ends. Protoraphis hustedtiana was found to be epizoic on the posterior body appendages and segments of the marine calanoid copepod Candacia bradyi. An internal view shows a complex, ear-shaped process that is close to the apical slit field. The ecological habitats and geographical distributions of Protoraphis were also discussed, and, together with complementary morphological studies, our results have increased the number of records for marine epizoic diatoms to three genera with three species in China, including Pseudohimantidium and Pseudofalcula.

Impact of increases in heat stress frequency associated with climate change on lifespan in different thermally adapted populations of an inter‐tidal marine invertebrate

Climate change is expected to change temperature regimes though multiple avenues such as increasing maximal environmental temperatures as well as frequency of daily maximum temperatures, which has been relatively understudied to the former. This study examines the chronic effect of heat stress due to higher frequencies of current daily maximum temperature on lifespan of two populations the intertidal marine copepod Tigriopus californicus with vastly different thermal tolerances. This study applied different heat stress regimes to the two populations and monitored their survival for the entirety of their lifespan. Our results show that frequency of heat stress impacts lifespan.

The Hidden Dimension: Context-Dependent Expression of Repeatable Behavior in Copepods.

In ecotoxicology and aquatic ecology, we often ignore responses of individuals and focus on average responses. However, both terrestrial and aquatic animals display consistent behavioral differences between individuals. The distribution of behavioral differences within a population contains vital information for predicting population responses to novel environmental challenges. Currently, individual data for behavioral and physiological traits of small marine invertebrates are few, partly because such variation is lost within published group means and assumed normality. We tested the combined effects of an inorganic contaminant (copper) and a biological stressor (i.e., chemical cues of a fish predator) on activity in a marine copepod. Although direct stress effects were weak, individuals behaved consistently differently, depending on the context. Individual differences in behavior were only expressed under the influence of kairomones, but not by copper exposure alone. This finding indicates that copepods express repeatable and context-dependent behavior. We also demonstrate how large variations in behavioral data can hide consistent differences between individuals. Environ Toxicol Chem 2020;39:1017-1026. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Draft Genome Sequence of Marinobacter hydrocarbonoclasticus NCT7M, Obtained from the Microbiome of a Marine Copepod.

The gammaproteobacterium Marinobacter hydrocarbonoclasticus NCT7M was cultivated from the copepod Acartia tonsa, collected from the coastal western North Atlantic Ocean. The genome was assembled into 45 contigs for a total of 4,128,590 bp, a GC content of 57.3%, and 3,890 protein-coding genes. The genome contains the full gene cluster for denitrification.

Fuzzy clustering and dynamic tables for knowledge discovery and decision-making: Analysis of the reproductive performance of the marine copepod Cyclopina sp.

The objective of this study was to evaluate the main reproductive aspects of the marine cyclopoid copepod Cyclopina sp. under laboratory conditions and to design, to implement, and to validate a framework for the development of decision system support based on a fuzzy set theory using clusters and dynamic tables. To validate the proposed framework, a fuzzy inference system was developed with the aim to estimate reproductive performance (Juvenile infertility period - JIP, Generational time – GT, Average fertility – AF, Reproductive frequency – RF, Reproductive events number – REN and Longevity - Long) of the marine copepod cyclopina sp. submitted to different thermal water and pH values conditions and compared with other computational intelligence techniques (Artificial Neural Networks models and Adaptive Neuro-Fuzzy Inference System - ANFIS). The results show that the determination coefficients (R2) for the six output variables for the Fuzzy Inference System – FIS were 0.991, 0.996, 1.0, 1.0, 0.999 and 1, respectively. The mean values of the standard deviations were 0.054 days, 0.047 days, 0.037 eggs, 0.061 h, 0.027 reproductive events, and 0.027 days respectively, representing mean percentage errors of 0.782, 0.583, 0.240, 0.181, 1.039, and 0.091%, showing a better accuracy, allowing the prediction of the reproductive performance to be more realistic. The Fuzzy Model produced more accurate predictions than other techniques (ANN and ANFIS). The proposed framework may provide an effective means to draw a pattern to the development of fuzzy systems.

Marine Copepods, The Wildebeest of the Ocean

Marine Copepods, The Wildebeest of the Ocean

Comparison of artificially weathered Macondo oil with field samples and evidence that weathering does not increase environmental acute toxicity

Macondo source oils and artificially weathered oil residues from 150 °C+ to 300 °C+, including artificially photo oxidized oils, were prepared and used for generating low energy water accommodated fractions (LE-WAFs) in order to assess the impact of oil weathering on WAF chemistry composition and toxicity to marine organisms. Two pelagic species representing primary producers (the marine algae Skeletonema pseudocostatum) and invertebrates (the marine copepod Acartia tonsa) were tested. Obtained acute toxicity levels, expressed as EC/LC50 values, were in the same range or above the obtained maximum WAF concentrations for WAFs from most weathering degrees. Based on % WAF dilutions, reduced toxicity was determined as a function of weathering. The chemical compositions of all WAFs were compared to compositions obtained from water samples reported in the GRIIDC database using multivariate analysis, indicating that WAFs of photo oxidized and two field weathered oils resembled the field data the most.

Low microalgae availability increases the ingestion rates and potential effects of microplastics on marine copepod Pseudodiaptomus annandalei

Microplastics have aroused great concern for their potential threats to marine organisms. This study investigated the interaction between three sizes of microplastics (0.5, 2, and 10 μm) and the marine copepod Pseudodiaptomus annandalei under two different microalgae concentrations (1 × 103 and 1 × 105 cells/mL). The results revealed that low microalgae supply increased microplastic ingestion through enhancing the encounter rates, and moreover increased the retention time of 0.5 μm microplastics. When the microalgae concentration was 1 × 103 cells/mL, 0.5 μm microplastics could be observed in the copepods after depuration in clear seawater for 24 h, but almost totally excreted at 1 × 105 cells/mL of microalgae. In addition, 0.5 μm microplastics induced significant effects on the ingestion of microalgae by P. annandalei both after 24 h of exposure and depuration. These results suggest that low microalgae availability may increase the ingestion and retention of microplastics in marine copepods, which might increase the ecological risk of microplastics.

Interspecific biotransformation and detoxification of arsenic compounds in marine rotifer and copepod

The toxicity of arsenic (As) has been reported to be different depending on their chemical forms. However, its toxicity mechanisms largely remain unknown. In this study, to investigate toxicity mechanism of As in marine zooplanktons, namely, the rotifer Brachionus plicatilis and the copepod Paracyclopina nana, metabolites of As were analyzed by using a high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry with in vivo toxicity and antioxidant responses in response to inorganic As, including arsenate (AsV) and arsenite (AsIII). While AsIII was more toxic than AsV in both organisms, the rotifer B. plicatilis exhibited stronger tolerance, compared to the copepod P. nana. The As speciation analysis revealed differences in biotransformation processes in two species with B. plicatilis having a more simplified process than P. nana, contributing to a better tolerance against As in the rotifer B. plicatilis compared to P. nana. Moreover, the levels of GSH content and the regulation of omega class glutathione S-transferases were different in response to oxidative stress between B. plicatilis and P. nana. These results suggest that the rotifer B. plicatilis has a unique survival strategy with more efficient biotransformation and antioxidant responses, compared to P. nana, conferring higher tolerance to As.

Polyethylene microplastics increase the toxicity of chlorpyrifos to the marine copepod Acartia tonsa

Ingestion of microplastics by marine organisms has been well documented, but their interaction with chemical pollutants has not been sufficiently addressed. The aim of this study was to determine the individual and combined effects of chlorpyrifos (CPF) and polyethylene microplastics (MP) on the survival, fecundity, feeding and egg viability of Acartia tonsa, a calanoid copepod widely distributed in planktonic communities. The median lethal concentration obtained for CPF was higher (LC50 = 1.34 μg/L) than for the combination with MP (LC50 = 0.37 μg/L), or CPF-loaded MP (LC50 = 0.26 μg/L). Significant effects were also observed for feeding and egg production (EC50 = 0.77 and 1.07 μg/L for CPF, 0.03 and 0.05 μg/L for CPF combined with MP, 0.18 and 0.20 μg/L for CPF-loaded MP). No significant effects were observed in the exposure to ‘virgin’ MP. This study confirms the role of MP as vectors of pollutants to marine organisms and supports the increased availability of certain toxicants carried out by MP. The effects observed in fitness-related responses suggest potential damage to A. tonsa populations. The comparison of the results obtained here with environmental concentrations indicates that the combined exposure to CPF and MP could constitute a risk to A. tonsa in the natural environment.

Facultative feeding in a marine copepod: effects of larval food and temperature on performance

Most marine invertebrate larvae either feed or rely on reserves provisioned by parents to fuel development, but facultative feeders can do both. Food availability and temperature are key environmental drivers of larval performance, but the effects of larval experience on performance later in life are poorly understood in facultative feeders. In particular, the functional relevance of facultative feeding is unclear. One feature to be tested is whether starved larvae can survive to adulthood and reproduce. We evaluated effects of larval temperature and food abundance on performance in a marine harpacticoid copepod,Tisbesp. In doing so, we report the first example of facultative feeding across the entire larval stage for a copepod. In a series of experiments, larvae were reared with ad libitum food or with no food, and at 2 different temperatures (20 vs. 24°C). We found that higher temperatures shortened development time, and larvae reared at higher temperature tended to be smaller. Larval food consistently improved early performance (survival, development rate and size) in larvae, while starvation consistently decreased survival, increased development time and decreased size at metamorphosis. Nonetheless, a small proportion (3-9.5%, or 30-42.7% with antibiotics) of larvae survived to metamorphosis, could recover from a foodless larval environment, reach maturity and successfully reproduce. We recommend that future studies of facultative feeding consider the impact of larval environments on adult performance and ability to reproduce.

Response of the copepod Acartia tonsa to the hydrodynamic cues of small-scale, dissipative eddies in turbulence.

This study quantifies the behavioral response of a marine copepod (Acartia tonsa) to individual, small-scale, dissipative vortices that are ubiquitous in turbulence. Vortex structures were created in the laboratory using a physical model of a Burgers vortex with characteristics corresponding to typical dissipative vortices that copepods are likely to encounter in the turbulent cascade. To examine the directional response of copepods, vortices were generated with the vortex axis aligned in either the horizontal or vertical direction. Tomographic particle image velocimetry was used to measure the volumetric velocity field of the vortex. Three-dimensional copepod trajectories were digitally reconstructed and overlaid on the vortex flow field to quantify A. tonsa's swimming kinematics relative to the velocity field and to provide insight into the copepod behavioral response to hydrodynamic cues. The data show significant changes in swimming kinematics and an increase in relative swimming velocity and hop frequency with increasing vortex strength. Furthermore, in moderate-to-strong vortices, A. tonsa moved at elevated speed in the same direction as the swirling flow and followed spiral trajectories around the vortex, which would retain the copepod within the feature and increase encounter rates with other similarly behaving Acartia While changes in swimming kinematics depended on vortex intensity, orientation of the vortex axis showed minimal significant effect. Hop and escape jump densities were largest in the vortex core, which is spatially coincident with the peak in vorticity, suggesting that vorticity is the hydrodynamic cue that evokes these behaviors.

Sorption of PAHs to microplastic and their bioavailability and toxicity to marine copepods under co-exposure conditions

Organic chemical pollutants associated with microplastic (MP) may represent an alternative exposure route for these chemicals to marine biota. However, the bioavailability of MP-sorbed organic pollutants under conditions where co-exposure occurs from the same compounds dissolved in the water phase has rarely been studied experimentally, especially where pollutant concentrations in the two phases are well characterized. Importantly, higher concentrations of organic pollutants on ingested MP may be less bioavailable to aquatic organisms than the same chemicals present in dissolved form in the surrounding water. In the current study, the sorption kinetics of two model polycyclic aromatic hydrocarbons (PAHs; fluoranthene and phenanthrene) to MP particles in natural seawater at 10 and 20 °C were studied and the bioavailability of MP-sorbed PAHs to marine copepods investigated. Polyethylene (PE) and polystyrene (PS) microbeads with mean diameters ranging from 10 to 200 μm were used to identify the role of MP polymer type and size on sorption mechanisms. Additionally, temperature dependence of sorption was investigated. Results indicated that adsorption dominated at lower temperatures and for smaller MP (10 μm), while absorption was the prevailing process for larger MP (100 μm). Monolayer sorption dominated at lower PAH concentrations, while multilayer sorption dominated at higher concentrations. PE particles representing ingestible (10 μm) and non-ingestible (100 μm) MP for the marine copepod species Acartia tonsa and Calanus finmarchicus were used to investigate the availability and toxicity of MP-sorbed PAHs. Studies were conducted under co-exposure conditions where the PAHs were also present in the dissolved phase (Cfree), thereby representing more environmentally relevant exposure scenarios. Cfree reduction through MP sorption was reflected in a corresponding reduction of lethality and bioaccumulation, with no difference observed between ingestible and non-ingestible MP. This indicates that only free dissolved PAHs are significantly bioavailable to copepods under co-exposure conditions with MP-sorbed PAHs.

Lipids at the plant–animal interface: a stable isotope labelling method to evaluate the assimilation of essential fatty acids in the marine copepod Calanus finmarchicus

AbstractLinking production, transfer and subsequent bioavailability of nutritionally significant matter from phytoplankton to higher trophic levels is a fundamental aspect in understanding marine food webs. The plant–animal interface is of interest because of the highly variable transfer between producers and consumers, and the myriad of factors that influence it. Essential fatty acids (EFAs) are dietary nutrients that are necessary for normal function in all consumers, yet it remains unclear how efficiently they are transferred through marine food webs. We introduced a 13C-labelled carbon source to the cryptophyte Rhodomonas salina to quantify primary production of two omega-3 long-chain polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We investigated transfer and assimilation efficiencies of these EFAs from phytoplankton to the calanoid copepod Calanus finmarchicus in an 8-day feeding experiment. We found low production of both EFAs in R. salina. Assimilation efficiencies of both EFAs ranged from 5 to 15% throughout the experiment, remaining slightly higher on average for DHA. This was mirrored in more efficient trophic transfer of DHA (up to 28%, compared to 13% for EPA). These results add to previously scarce experiments empirically quantifying the assimilation and transfer efficiency of EFAs in a basic marine planktonic food chain.

Efflux behavior of inorganic mercury and methylmercury in the marine copepod Tigriopus japonicus

Marine copepods play an important role in transferring mercury to higher trophic levels in aquatic ecosystems. Exposure time is an important environmental parameter that potentially influences the bioaccumulation and biomagnification of Hg in copepods, which increases the uncertainty in risk assessments of Hg in food chains. In the present study, we employed the radiotracer technique to evaluate the efflux behavior of inorganic mercury [Hg(II)] and methylmercury (MeHg), and the effects of exposure time in a population of Tigriopus japonicus copepods. Exposure treatments were compared to understand the effects of exposure time (1 d, 3 d, and 7 d) on the release routes and efflux rate constants (ke) of Hg in copepods. During a depuration period of 5 d, the ke value of Hg(II) in the three exposure treatments ranged from 0.190–0.330 d−1, while the ke of MeHg was generally slower and ranged from 0.031–0.051 d−1. The exposure time significantly affected the efflux rates of Hg(II), i.e., a longer exposure time caused a higher retained Hg(II) burden in copepods, while no significant changes were observed in the MeHg treatments. The release routes of Hg in T. japonicus included excretion, feces production, and reproduction. In all the treatments, the excretion of Hg was the most important release route. The relative contribution of reproduction significantly increased in the MeHg exposure treatments, while the contribution of water excretion decreased with exposure time. Our study demonstrated that the retention of Hg(II) and the maternal transfer of MeHg were time-dependent and significantly affected by exposure time. Long-term exposure caused a decrease in the ke of Hg(II) and increase in the contribution of MeHg transfer to nauplii, thereby indicating an increasing risk of biological transmission of Hg under long-term exposure.

Evaluation of microplastic toxicity in accordance with different sizes and exposure times in the marine copepod Tigriopus japonicus

The indiscriminate use of plastic has greatly increased microplastic contamination risk in the marine environment. Microplastics can affect all marine life via the food web, from primary producers (e.g., microalgae) to final consumers (e.g., carnivorous fish). Thus, several studies have attempted to evaluate microplastic toxicity, but information about the underlying mechanisms of their effect is limited. Therefore, in this study, we examined multiple factors that could contribute to microplastic-induced toxicity. We investigated the potential molecular effects of microplastic size and exposure time. We exposed the marine copepod Tigriopus japonicus to 50 nm and 10 μm polystyrene microbeads. We found that both size and exposure time increased intracellular levels of reactive oxygen species. In addition, antioxidant-related gene expression was modulated and antioxidant enzyme activities were changed significantly. The results of this study provide important insights into the molecular mechanisms of microplastic-induced toxicity in a marine organism.

Draft Genome Sequence of Vibrio cyclitrophicus NCT10V, Cultivated from the Microbiome of a Marine Copepod.

Here, we report the draft genome sequence of Vibrio cyclitrophicus NCT10V, cultivated from the copepod Acartia tonsa, collected from coastal surface waters of the western North Atlantic Ocean. The assembly is 5,638,575 bp long and has 44 contigs, a GC content of 43.2%, and 5,044 protein coding sequences.

Recent advances of marine ornamental fish larviculture: broodstock reproduction, live prey and feeding regimes, and comparison between demersal and pelagic spawners

AbstractMarine ornamental fish are a key component of the multimillion‐dollar marine aquarium trade industry, a controversial industry due to current heavy reliance on wild‐collected specimens. Aquaculture of marine ornamental fish is considered as a sustainable alternative, but it is still in the early stage of development. This review focuses on the current state of marine ornamental fish aquaculture, by covering topics on reef fish reproductive biology in captivity, traditional and novel live feeds, feeding regimes and visual environment in larviculture. Where possible, major differences between demersal and pelagic spawners are compared and discussed. Overall, for many ornamental fish species, natural spawning can be achieved in a captive environment without the use of hormone induction; however, sex identification and successful pairing for reef fish species could be a challenge. With the use of both traditional (rotifers and Artemia) and novel live feeds (e.g. marine copepods and ciliates), a range of breakthroughs in larval rearing of both demersal and pelagic spawning ornamental fish species have been achieved in recent years, although larval survival varies. To further improve the larval rearing success of marine ornamental fish, this review suggests that future research should focus on optimizing the use of live feed in terms of both quality and quantity, and establishment of well‐defined species‐specific larval feeding regime, as well as providing appropriate rearing condition through improved manipulation of light conditions and the ‘greenwater’ techniques in larval rearing.

An experimental test of mate choice for red carotenoid coloration in the marine copepod Tigriopus californicus

AbstractColorful ornaments are hypothesized to have evolved in response to sexual selection for honest signals of individual quality that provide information about potential mates. Red carotenoid coloration is common in diverse groups, and in some vertebrate taxa, red coloration is a sexually selected trait whereby mates with the reddest ornaments are preferred. Despite being widespread among invertebrates, whether red carotenoid coloration is assessed during mate choice in these taxa is unclear. The marine copepod Tigriopus californicus displays red coloration from the accumulation of the carotenoid astaxanthin. Previous research on copepods has shown that astaxanthin provides protection from UV radiation and xenobiotic exposure and that carotenoid production is sensitive to external stressors. Because of the condition dependency of the red coloration, we hypothesized that Tigriopus would use it as a criterion during mate choice. To test this hypothesis, we conducted trials in which males chose between females that were wild‐type red (carotenoid‐rich algae diet) or white (carotenoid‐deficient yeast diet). To control for dietary differences and to isolate the effect of carotenoid coloration, we also presented males with restored‐red females fed a carotenoid‐supplemented yeast diet. We found that wild‐type red females were weakly preferred over white females. After controlling for diet, however, we found that restored‐red females were avoided. Our observations do not support the hypothesis that male copepods prefer the carotenoid coloration of females during mate choice. We hypothesize that algal‐derived compounds other than carotenoids play a role in mate choice. Red coloration in copepods appears to be a condition‐dependent trait that is not assessed during mating.

Genotoxic Response and Mortality in 3 Marine Copepods Exposed to Waterborne Copper.

Copper (Cu) is an essential trace metal, but may also be toxic to aquatic organisms. Although many studies have investigated the cytotoxicity of Cu, little is known about the in vivo genotoxic potential of Cu in marine invertebrates. We investigated the genotoxicity of Cu in 2 pelagic calanoid copepods, Acartia tonsa and Temora longicornis, and the intertidal harpacticoid copepod Tigriopus brevicornis by exposing them for 6 and 72 h to waterborne Cu (0, 6, and 60 µg Cu/L). A subsequent 24-h period in filtered seawater was used to investigate delayed effects or recovery. Genotoxicity was evaluated as DNA strand breaks in individual copepods using the comet assay. Copper did not increase DNA strand breaks in any of the species at any concentration or time point. The treatment did, however, cause 100% mortality in A. tonsa following exposure to 60 µg Cu/L. Acartia tonsa and T. longicornis were more susceptible to Cu-induced mortality than the benthic harpacticoid T. brevicornis, which appeared to be unaffected by the treatments. The results show major differences in Cu susceptibility among the 3 copepods and also that acute toxicity of Cu to A. tonsa is not directly associated with genotoxicity. We also show that the comet assay can be used to quantify genotoxicity in individual copepods. Environ Toxicol Chem 2019;38:2224-2232. © 2019 SETAC.