Copepod Acartia Tonsa Research Articles

Validating an In-House Method for Assessing Effluent Discharge Toxicity Using Acartia tonsa in the Black Sea

The marine copepod Acartia tonsa is an important bioindicator in ecotoxicological studies due to its sensitivity to pollutants and ecological importance. This research evaluates the effects of reference toxicant on the survival of A. tonsa, aiming to validate an in-house method that assesses the sensitivity and reliability of the species for testing in the Black Sea. A. tonsa individuals were exposed in controlled laboratory conditions to varying 3,5-dichlorophenol (reference toxicant) concentrations, with their survival rates monitored over 48 h. Survival data were analyzed to determine the lethal concentration (LC50), a metric for assessing toxicity. The derived LC50 values offer important benchmarks for assessing the environmental impact of different effluent discharges in the Black Sea region. The outcomes will contribute to improving the accuracy and consistency of environmental monitoring and risk assessment practices in the Black Sea region, ensuring that variations in toxicity data are attributable to environmental factors rather than methodological discrepancies.

When the Going Gets Tough, the Females Get Going: Sex-Specific Physiological Responses to Simultaneous Exposure to Hypoxia and Marine Heatwave Events in a Ubiquitous Copepod.

The existence of sex-specific differences in phenotypic traits is widely recognized. Yet they are often ignored in studies looking at the impact of global changes on marine organisms, particularly within the context of combined drivers that are known to elicit complex interactions. We tested sex-specific physiological responses of the cosmopolitan and ecologically important marine copepod Acartia tonsa exposed to combined hypoxia and marine heatwave (MHW) conditions, both of which individually strongly affect marine ectotherms. Females and males were acutely exposed for 5 days to a combination of either control (18°C) or a high temperature mimicking a MHW (25°C), and normoxia (100% O2 sat.) or mild hypoxia (35% O2 sat.). Life-history traits, as well as sex-specific survival and physiological traits, were measured. Females had overall higher thermal tolerance levels and responded differently than males when exposed to the combined global change drivers investigated. Females also showed lower metabolic thermal sensitivity when compared to males. Additionally, the MHW exerted a dominant effect on the traits investigated, causing a lower survival and higher metabolic rate at 25°C. However, egg production rates appeared unaffected by hypoxia and MHW conditions. Our results showed that MHWs could strongly affect copepods' survival, that combined exposure to hypoxia and MHW exerted an interactive effect only on CTmax, and that sex-specific vulnerability to these global change drivers could have major implications for population dynamics. Our results highlight the importance of considering the differences in the responses of females and males to rapid environmental changes to improve the implementation of climate-smart conservation approaches.

Acartia tonsa grazing on the harmful dinoflagellate Dinophysis acuminata reduces copepod survival and increases extracellular toxin concentrations

Dinophysis spp. synthesize lipophilic toxins and form harmful algal blooms (HABs) across the globe. Zooplankton can play a role in controlling HABs and be a vector for HAB toxins; however, no study has explored the grazing and survival of copepods fed cultured Dinophysis. Here, the copepod Acartia tonsa isolated from New York, USA, was fed 3 strains of D. acuminata from the eastern USA (Massachutsetts, New York, Virginia), as well as 2 non-toxic prey (Rhodomonas salina and Gymnodinium aureolum). Grazing and survival rates of A. tonsa were quantified along with toxins. A. tonsa fed on D. acuminata at rates similar to R. salina and G. aureolum. Mixed-prey experiments suggested that D. acuminata was not acutely toxic to A. tonsa. Extracellular levels of okadaic acid (OA) significantly increased (p ≤ 0.05) and extracellular pectenotoxin (PTX2) increased by 50% upon exposure to copepods, suggesting that grazers stimulated extracellular toxin release. During 3 wk survival experiments, copepods consuming D. acuminata as a sole food source displayed significantly lower survival rates compared to those fed a control diet of R. salina (p < 0.05). This depressed survivorship was ameliorated by feeding the copepods a diet of D. acuminata mixed with G. aureolum, suggesting that nutritional deficiencies drove mortality. Since grazing on Dinophysis may be low when prey abundance is low, reduced grazing may contribute to bloom development; however, as blooms intensify, grazing may increase, potentially causing a reduction in copepod survival and continued bloom progression. Finally, grazing-induced increases in OA and PTX2 could enhance the introduction of Dinophysis-derived toxins into food webs.

Marine copepod culture as a potential source of bioplastic-degrading microbiome: The case of poly(butylene succinate-co-adipate)

The poly(butylene succinate-co-adipate) (PBSA) is emerging as environmentally sustainable polyester for applications in marine environment. In this work the capacity of microbiome associated with marine plankton culture to degrade PBSA, was tested. A taxonomic and functional characterization of the microbiome associated with the copepod Acartia tonsa, reared in controlled conditions, was analysed by 16S rDNA metabarcoding, in newly-formed adult stages and after 7 d of incubation. A predictive functional metagenomic profile was inferred for hydrolytic activities involved in bioplastic degradation with a particular focus on PBSA. The copepod-microbiome was also characterized in newly-formed carcasses of A. tonsa, and after 7 and 33 d of incubation in the plankton culture medium. Copepod-microbiome showed hydrolytic activities at all developmental stages of the alive copepods and their carcasses, however, the evenness of the hydrolytic bacterial community significantly increased with the time of incubation in carcasses. Microbial genera, never described in association with copepods: Devosia, Kordia, Lentibacter, Methylotenera, Rheinheimera, Marinagarivorans, Paraglaciecola, Pseudophaeobacter, Gaiella, Streptomyces and Kribbella sps., were retrieved. Kribbella sp. showed carboxylesterase activity and Streptomyces sp. showed carboxylesterase, triacylglycerol lipase and cutinase activities, that might be involved in PBSA degradation. A culturomic approach, adopted to isolate bacterial specimen from carcasses, led to the isolation of the bacterial strain, Vibrio sp. 01 tested for the capacity to promote the hydrolysis of the ester bonds. Granules of PBSA, incubated 82 d at 20 °C with Vibrio sp. 01, were characterized by scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, showing fractures compared to the control sample, and hydrolysis of ester bonds. These preliminary results are encouraging for further investigation on the ability of the microbiome associated with plankton to biodegrade polyesters, such as PBSA, and increasing knowledge on microorganisms involved in bioplastic degradation in marine environment.

Comparative assessment of microplastics and microalgae as vectors of mercury and chlorpyrifos in the copepod Acartia tonsa

Microplastics (MPs) raise concerns not only as pollutants themselves, but also due to their ability to act as vectors of pollutants adsorbed from seawater, transferring them to marine organisms. However, the relevance of MPs as carriers of pollutants compared to microalgae needs further exploration. This study compared the role of MPs (2–10 μm non-oxidized and 10–15 μm oxidized high-density polyethylene) and natural organic particles (Rhodomonas lens microalgae, MA) as carriers of mercury (Hg, 2.3 μg Hg/L) and chlorpyrifos (CPF, 1.0 μg CPF/L) to adult Acartia tonsa copepods, after 24–48 h exposure. Dose-response experiments were first performed with adult female copepods exposed to oxidized MPs (0.25–4.0 mg/L), waterborne Hg (0.01–10.0 μg/L) and Ox MPs + Hg (0.25–4.0 mg oxidized MPs/L + 0.50–8.0 μg Hg/L) for 48 h, to complement previous studies that focused on the pesticide CPF. Effects were evaluated with four replicates for physiological and reproductive responses (6 females/replicate), biochemical techniques (40 individuals/replicate) and Hg/CPF bioaccumulation measurements (1000 individuals/replicate). Copepods accumulated Hg/CPF similarly from dissolved pollutants (6204 ± 2265 ng Hg/g and 1251 ± 646 ng CPF/g) and loaded MPs (3125 ± 1389 ng Hg/g and 1156 ± 266 ng CPF/g), but significantly less from loaded MA (21 ± 8 ng Hg/g and 173 ± 80 ng CPF/g). After 24–48 h, copepods exposed to MPs + Hg/CPF showed generally greater biological effects than those exposed to dissolved Hg/CPF or to MA + Hg/CPF, although differences were not statistically significant. MA + CPF had significantly lower AChE inhibition (1073.4 nmol min−1 mg−1) and MA + Hg lower GRx induction (48.8 nmol min−1 mg−1) compared to MPs + Hg/CPF and dissolved Hg/CPF (182.8–236.4 nmol min−1 mg−1 of AChE and 74.1–101.7 nmol min−1 mg−1 of GRx). Principal component analysis suggested different modes of action for Hg and CPF.

Molecular evidence for a new endemic species of Acartia (Copepoda, Calanoida) from the Southeast Pacific coast

The loss of biodiversity in marine populations is one of the consequences of the increased events of extreme environmental conditions in the oceans, which can condition the persistence of populations to future scenarios of climate change. Therefore, it is extremely necessary to explore and monitor the genetic diversity of natural populations. In the Southeast Pacific Ocean (SEPO), specifically on the coast of Chile, the presence of the copepod Acartia tonsa has been indicated solely using morphological evidence, due to the absence of genetic information. In the present work, the genetic diversity, population structure and phylogenetic position within the genus Acartia, of populations identified morphologically as A. tonsa, was evaluated by amplification of the mitochondrial cytochrome c oxidase subunit I and nuclear marker 18 s. Our results showed that the populations identified as A. tonsa correspond to a new monophyletic group endemic to SEPO (GMYC = 1.00; PTP = 0.95). The populations showed moderate to high genetic diversity with an incipient structuring between populations and biogeographic zones. Our results suggest that despite the homogenizing effect of the Humboldt Current, isolation by distance and contrasting environmental conditions at different geographic scales have an important influence on the genetic diversity of zooplankton in the SEPO region.

Ecotoxicological Assays with the Calanoid Copepod Acartia tonsa: A Comparison between Mediterranean and Baltic Strains

The use of marine invertebrates in ecotoxicology is important for an integrated approach which takes into consideration physiological responses and chemical levels in environmental matrices. Standard protocols have been developed and organisms belonging to different trophic levels are needed as model organisms to evaluate toxicant bioavailability and assess their impact on marine biota. The calanoid copepod Acartia tonsa is commonly used in ecotoxicology due to its widespread distribution and well-studied biology. However, different strains coming from various geographical areas are available, and possible variations in physiological characteristics raise concerns about the comparability of ecotoxicological results. This study compares the life cycle assessment and sensitivity of Adriatic and Baltic strains of A. tonsa exposed to nickel (Ni2+) in standardized acute and semi-chronic tests. Life cycle assessments revealed differences in egg production, egg-hatching success, and naupliar viability between the strains. The acute toxicity test demonstrated the significantly higher sensitivity of Adriatic strain nauplii to Ni2+ compared to the Baltic strain, whereas the semi-chronic test showed no significant difference in sensitivity between the strains. These findings suggest that while strain-specific differences exist in different geographical populations, responses to toxicants are not significantly different. Particularly, the semi-chronic assessments with both A. tonsa strains emphasized the robustness of this species as a model organism in ecotoxicology.

Effects of ocean warming on the fatty acid and epigenetic profile of Acartia tonsa: A multigenerational approach

The effects of climate change are becoming more prevalent, and it is important to know how copepods, the most abundant class in zooplankton, will react to changing temperatures as they are the main food source for secondary consumers. They act as key transferers of nutrients from primary producers to organisms higher up the food chain. Little is known about the effects of temperature changes on copepods on the long term, i.e., over several generations. Especially the epigenetic domain seems to be understudied and the question remains whether the nutritional value of copepods will permanently change with rising water temperatures. In this research, the effects of temperature on the fatty acid and epigenetic profiles of the abundant planktonic copepod Acartia tonsa were investigated, since we expect to see a link between these two. Indeed, changing methylation patterns helped copepods to deal with higher temperatures, which is in line with the relative abundance of the most important fatty acids, e.g., DHA. However, this pattern was only observed when temperature increased slowly. A sudden increase in temperature showed the opposite effect; Acartia tonsa did not show deviant methylation patterns and the relative abundance of DHA and other important fatty acids dropped significantly after several generations. These results suggest that local fluctuations in temperature have a greater effect on Acartia tonsa than an elevation of the global mean.

A simple protocol for estimating the acute toxicity of unresolved polar compounds from field-weathered oils

Crude oil spilled at sea is chemically altered through environmental processes such as dissolution, biodegradation, and photodegradation. Transformation of hydrocarbons to oxygenated species increases water-solubility. Metabolites and oxidation products largely remain uncharacterized by common analytical methods but may be more bioavailable to aquatic organisms. Studies have shown that unresolved (i.e. unidentified) polar compounds (‘UPCs’) may constitute > 90% of the water-accommodated fraction (WAF) of heavily weathered crude oils, but still there is a paucity of information characterizing their toxicological significance in relation to other oil-derived toxicants. In this study, low-energy WAFs (no droplets) were generated from two field-weathered oils (collected during the 2010 Deepwater Horizon incident) and their polar fractions were isolated through fractionation. To allow establishment of thresholds for acute toxicity (LC50) of the dissolved and polar fraction of field collected oils, we concentrated both WAFs and polar fractions to beyond field-documented concentrations, and the acute toxicity of both to the marine copepod Acartia tonsa was measured and compared to the toxicity of the native WAF (non-concentrated). The difference in toxic units (TUs) between the total of the mixture and of identified compounds of known toxicity (polycyclic aromatic hydrocarbons [PAHs] and alkyl phenols) in both WAF and polar fractions was used to estimate the contribution of the UPC to overall toxicity. This approach identified that UPC had a similar contribution to toxicity as identified compounds within the WAFs of the field-weathered oils. This signifies the relative importance of polar compounds when assessing environmental impacts of spilled and weathered oil.

Life stage-specific effects of tire particle leachates on the cosmopolitan planktonic copepod Acartia tonsa

Tire wear particles (TWP) are a major source of microplastics in the aquatic environment and the ecological impacts of their leachates are of major environmental concern. Among marine biota, copepods are the most abundant animals in the ocean and a main link between primary producers and higher trophic levels in the marine food webs. In this study, we determined the acute lethal and sublethal effects of tire particle leachates on different life stages of the cosmopolitan planktonic copepod Acartia tonsa. Median lethal concentration (LC50, 48 h) ranged from 0.4 to 0.6 g L−1 depending on the life stages, being nauplii and copepodites more sensitive to tire particle leachates than adults. The median effective concentration (EC50, 48 h) for hatching was higher than 1 g L−1, indicating a relatively low sensitivity of hatching to tire particle leachates. However, metamorphosis (from nauplius VI to copepodite I) was notably reduced by tire particle leachates with an EC50 (48 h) of 0.23 g L−1 and the absence of metamorphosis at 1 g L−1, suggesting a strong developmental delay or endocrine disruption. Leachates also caused a significant decrease (10–22%) in the body length of nauplii and copepodites after exposure to TWP leachates (0.25 and 0.5 g L−1). We tested a battery of enzymatic biomarkers in A. tonsa adult stages, but a sublethal concentration of 50 mg L−1 of tire particle leachates did not cause a statistically significant effect on the measured enzymatic activities. Our results show that tire particle leachates can negatively impact the development, metamorphosis, and survival of planktonic copepods. More field data on concentrations of TWPs and the fate and persistence of their leached additives is needed for a better assessment of the risk of tire particle pollution on marine food webs.

Local scale extreme low pH conditions and genetic differences shape phenotypic variation in a broad dispersal copepod species

Extreme low pH events in estuaries and upwelling areas can modulate the phenotypic and genetic diversity of natural populations. To test this hypothesis, we explored the linkage between local scale extreme low pH events, genetic diversity, and variation in fecundity-related traits (body size, egg size, and egg production rate) in the broad-dispersal copepod Acartia tonsa. We assessed genetic and phenotypic characteristics of populations by contrasting extreme low pH environments (upwelling and temperate estuary) in the coastal Southeast Pacific, under natural and experimental conditions. These populations showed significant genetic differentiation with higher diversity in mitochondrial and nuclear loci (encoding mtCOI and 18S rRNA) in the estuarine population. Copepods from this population are exposed to more frequent extreme low pH events (< 7.7), and the adult females exhibit consistent phenotypic variation in body size, egg size, and egg production rate across different cohorts. Experimental acclimation to extreme low pH conditions revealed no significant differences in fecundity-related traits between A. tonsa populations. Although these results partially support our hypothesis, the experimental findings suggest other drivers might also influence phenotypic differences in the local environments.

Short-term impact assessment of ocean liming: A copepod exposure test

Ocean liming (OL) is a potential carbon dioxide removal (CDR) method that aims to increase the ocean's capacity to absorb atmospheric CO2 by adding hydrated lime to the surface ocean. Modeling studies indicate that OL may cause temporary pH spikes lasting several minutes, depending on the lime sparging rate. Little is known about the short-term effects of these spikes on marine organisms. Aim of the present study is to investigate these effects on the copepod Acartia tonsa. Copepods were exposed to different pH conditions (9, 10, 11, 12) by dosing different hydrated lime solutions. Copepod mortality, movements, and behavior were recorded. At pH 9 for short exposure times (<6 h), no negative effects were observed indicating a potential tolerable threshold for OL applications. At longer exposure times (>6 h) and pH higher than 9, negative effects (mortality and sublethal effects) were found significantly higher than in the control.

Live Microalgae-Based Diets as Enrichment to Improve the Nutritional Profile of the Calanoid Copepod Acartia tonsa (Dana, 1849) Nauplii

Most emerging species in marine aquaculture and the aquarium industry have a sensitive and small-mouthed larval stage, and their culture is very challenging due to a lack of appropriate early feeding protocols. The use of copepods has been widely recognized as a good alternative to traditional fish live feeds (rotifers and Artemia spp.), especially for new species targeted for the multibillion-dollar marine aquarium trade. However, most copepod culture trials are focused on biomass production, while their nutritional requirements and enrichment protocols remain scarcely known. The main objective of this study was to determine the dietary contribution of three microalgae-based diets, provided as a mono R (Rhodomonas salina) or binary I–R (Isochrysis galbana + R. salina) and T–R (Tetraselmis suecica + R. salina), on the biochemical composition (proximate and fatty acids (FAs)) and survival of the calanoid copepod Acartia tonsa (nauplii) versus the conventional rotifer Brachionus plicatilis throughout 96 hr exposure. Both live preys were characterized by the highest protein and total n-3 long-chain polyunsaturated FAs (LC-PUFAs) content when fed with the binary diet I–R compared to other treatments, although the nutritional value of A. tonsa nauplii was always much higher compared to B. plicatilis. In general, there was a wide difference in proximate and FAs composition between the two preys, denoting A. tonsa as better live feed in terms of capacity to retain n-3 LC-PUFAs, especially eicosapentanoic acid (20 : 5n-3) and docosahexanoic acid (22 : 6n-3). The present study highlights the nutritional profile of enriched A. tonsa nauplii and contributes to the production of high-quality live feeds, which may be able to reach the nutritional needs of new marine fish species during their larval development, as well as contributing to the improvement of A. tonsa culture.

The effect of copepod Acartia tonsa during the first days of larval rearing in skeleton ontogeny and skeletal deformities in greater amberjack (Seriola dumeliri Risso, 1810)

The effect of feeding greater amberjack (Seriola dumerili) with copepod nauplii (Acartia tonsa) on osteological development was observed until 35 days after hatching (DAH). The skeletal deformities were observed at the end of the trial. Copepods are the natural food of marine fish larvae, and they are rich in highly unsaturated fatty acids and free amino acids. In a commercial marine fish hatchery in Greece (Galaxidi Marine Farm S.A.), four 2700 l cylindroconical tanks were stocked with amberjack yolk-sac larvae at a density of about 55 larvae/l. The larvae were initially fed from 3 to17 DAH in two tanks with copepod nauplii and rotifers (Brachionus sp.) (Copepods group), while in the other two tanks, only with rotifers (Control group). After 12 DAH, all the tanks were also fed with rotifers (3–27 DAH), Artemia nauplii (12–22 DAH), enriched Artemia metanauplii (20–30 DAH), and formulated diet (25–30 DAH). Fish samples were taken every three days, fixed in phosphate-buffered 5% formalin (pH = 7.2). Bone and cartilage were stained with alizarin red and alcian blue, respectively. Specific meristic characters were chosen to compare the first appearance and the completion of the formation of a structure as well as the completion of the calcification between the two rearing protocols (Copepods - Control), correlated with total length data. These meristic characters included replacement and membranous bones from the vertebral column and all the fins. The ontogeny of the meristic characters was observed earlier in fish larvae from the Copepods group compared with the Control, and for most of the meristic characters, these differences were significant (p < 0.05). TL50 data analysis was performed, and the results were similar. At the end of the trial, 35 DAH sixty fish from each tank were sampled for the analysis of skeletal deformities. A higher number and more significant deformities were observed in the Control group compared with the Copepods group (p < 0.05). In conclusion, the use of copepod nauplii during the first feeding period of greater amberjack had a positive effect on the osteological development and skeletal deformities of the larvae.

Analysis of the transcriptional pathways associated with the induction of quiescent embryonic arrest in the calanoid copepod Acartia tonsa

The copepod species Acartia tonsa (Dana)(Crustacea) have the unique ability to induce quiescent embryonic dormancy if adverse environmental conditions occur; a characteristic shared by 41 other species belonging to the superfamily Centropagoida in the Calanoida order. However, the transcriptional changes characterizing this process are not known. Here, we compare the transcriptome of embryos in arrested quiescence with the normal development to identify pathways and differentially regulated transcripts involved in quiescent embryogenesis. Quiescence was induced by incubating eggs at 4 °C with anoxia for 26 h(hr), while eggs undergoing normal immediate development were incubated at 16.9 °C in normoxia for 7 h (where gastrulation occurs) or 14 h (where organogenesis occurs) before collecting for RNA extraction and analysis by RNA-sequencing. Results indicate that the expression profile of the quiescent embryo is not as different from the normal embryonic gastrulation as initially expected: None of the mapped transcripts is uniquely expressed in quiescence. Moreover, in quiescence a large proportion of the annotated transcripts display expression values halfway in-between the normal, immediate developmental stages of gastrulation and organogenesis. In depth comparison between the organogenesis stage and quiescent samples, reveal a high degree of divergence, confirming that a developmental arrest has been induced through quiescence. Specifically: Stress response transcripts are prominent in the quiescent phase with a transcript like the mammalian autophagy gene Sequestosome-1/p62 (SQSTM) being upregulated. The present analysis provides a better understanding of the molecular mechanisms characterizing the quiescent embryonic state of A. tonsa.

Parasitism does not reduce thermal limits in the intermediate host of a bopyrid isopod

Parasitism has strong effects on community dynamics. Given the detrimental effects parasites have on host health, infection or infestation might be expected to reduce upper thermal limits, increasing the vulnerability of host species to future climate change. Copepods are integral components of aquatic food webs and biogeochemical cycles. They also serve as intermediate hosts in the life cycle of parasitic isopods in the family Bopyridae. As both copepods and isopod parasites play important roles in aquatic communities, it is important to understand how the interaction between parasite and host affects thermal limits in order to better predict how community dynamics may change in a warming climate. Here we examined the effect of infestation by larvae of a bopyrid isopod on the cosmopolitan copepod Acartia tonsa to test the hypothesis that infestation reduces thermal limits. To aid with this work, we developed an affordable, highly portable system for measuring critical thermal maxima of small ectotherms. We also used meta-analysis to summarize the effects of parasitism on critical thermal maxima in a wider range of taxa to help contextualize our findings. Contrary to both our hypothesis and the results of previous studies, we observed no reduction of thermal limits by parasitism in A. tonsa. These results suggest that life history of the host and parasite may interact to determine how parasite infestation affects environmental sensitivity.

Interactive effects of salinity, temperature and food web configuration on performance and harmfulness of the raphidophyte Heterosigma akashiwo

The cosmopolitan raphidophyte Heterosigma akashiwo commonly forms harmful algal blooms (HABs) in diverse estuaries discharging into Algoa Bay, South Africa, potentially leading to hypoxia, fish kills and a decline in key primary consumers. Despite the high environmental variability in these estuaries, little is known about how abiotic factors such as temperature and salinity constrain bloom formation and harmfulness of H. akashiwo. The present study therefore investigates growth, competition, and grazing interactions of H. akashiwo in laboratory experiments in response to two naturally relevant levels of salinity (15, 30) and temperature (16, 22°C), respectively. Experiments were set up with the naturally co-occurring dinoflagellate competitor Heterocapsa rotundata and two estuarine microzooplankton consumers, i.e., nauplii of the copepod Acartia tonsa and the rotifer Brachionus plicatilis. In monoculture, H. akashiwo growth was promoted at high temperature – low salinity conditions, while H. rotundata thrived under low temperature – high salinity conditions. In polyculture, H. akashiwo dominated at high temperature irrespective of the salinity regime, while at low temperature, it only dominated at low salinity and was suppressed by H. rotundata at high salinity. Grazing assays revealed highly negative effects of H. akashiwo on copepod nauplii survival and growth as well as mucus-induced immobilization, especially at high temperatures in combination with low salinity, while the estuarine adapted rotifers showed highest mortalities at the higher salinity level. The presence of H. rotundata significantly alleviated the harmful effects of H. akashiwo on both grazers, and the selectively feeding copepod nauplii actively avoided H. akashiwo when non-harmful prey was present. Overall, this study demonstrates that population dynamics and harmful effects of H. akashiwo are interactively determined by both abiotic conditions and food web configuration, implying competitor and consumer specific tolerances to the abiotic environment and their susceptibility to the harmful alga H. akashiwo.

Naupliar exposure to acute warming does not affect ontogenetic patterns in respiration, body size, or development time in the cosmopolitan copepod Acartia tonsa.

Short-term, acute warming events are increasing in frequency across the world's oceans. For short-lived species like most copepods, these extreme events can occur over both within- and between-generational time scales. Yet, it is unclear whether exposure to acute warming during early life stages of copepods can cause lingering effects on metabolism through development, even after the event has ended. These lingering effects would reduce the amount of energy devoted to growth and affect copepod population dynamics. We exposed nauplii of an ecologically important coastal species, Acartia tonsa, to a 24-hour warming event (control: 18°C; treatment: 28°C), and then tracked individual respiration rate, body length, and stage duration through development. As expected, we observed a decrease in mass-specific respiration rates as individuals developed. However, exposure to acute warming had no effect on the ontogenetic patterns in per-capita or mass-specific respiration rates, body length, or development time. The lack of these carryover effects through ontogeny suggests within-generational resilience to acute warming in this copepod species.

Decreased feeding rates of the copepod Acartia tonsa when exposed to playback harbor traffic noise

IntroductionCopepods present the largest and most diverse group of zooplankton and their feeding behavior can affect top-down and bottom-up processes. Thus, how efficient feeding is executed determines the abundance of copepods’ prey and their predators and, with that, carbon transfer and storage in ecosystems. The rise of anthropogenic underwater noise from shipping, oil exploration and exploitation, wind farm construction and operation, and more, is increasingly changing the marine acoustic environment. This acoustic pollution can have detrimental effects on biological life. Studies on this topic increasingly indicate that anthropogenic underwater noise adversely affects primary producers, marine mammals, fish, and invertebrates. However, little data exist on the effects of anthropogenic underwater noise on the feeding behavior of zooplankton.MethodsHere, we investigated the ingestion and clearance rates of the copepodAcartia tonsaon a motile phytoplankton as a function of prey density under ambient aquarium sound conditions and, when exposed to playback, harbor traffic noise.ResultsWe measured significantly decreased ingestion rates and clearance rates ofA. tonsawhen exposed to harbor noise compared to ambient conditions. The negative impact of noise on the ingestion rates was found at all given phytoplankton cell densities between 1k to 10k cells ml−1. Clearance rates were fitted to the Rogers random predator equation which revealed significantly decreased capture rates on phytoplankton under the exposure of harbor noise while handling times remained the same in both sound treatments.DiscussionOur results call for follow-up studies to focus on noise driven community-effects in field experiments to confirm laboratory results and to predict the outcome of a changing world with multiple stressors. Further, the underlying mechanism on how noise affects the feeding behavior of copepods is still unknown. Noise may distract copepods or mask hydromechanical cues of the prey. Noise may also adversely affect copepod physiology or morphology that would lead to changes in the feeding behavior. All potential mechanisms need to be investigated rigorously in future experiments.

Effects of airgun discharges used in seismic surveys on development and mortality in nauplii of the copepod Acartia tonsa

Seismic surveys are conducted worldwide to explore for oil and gas deposits and to map subsea formations. The airguns used in these surveys emit low-frequency sound waves. Studies on zooplankton responses to airguns report a range of effects, from none to substantial mortality. A field experiment was conducted to assess mortality and naupliar body length of the calanoid copepod Acartia tonsa when exposed to the discharge of two 40-inch airguns. Nauplii were placed in plastic bags and attached to a line at a depth of 6 m. For each treatment, three bags of nauplii were exposed to one of three treatments for 2.5 h: Airgun array discharge, a boat control, or a silent control. After exposure, nauplii were kept in filtered seawater in the laboratory without food. Immediate mortality in the nauplii was approximately 14% compared to less than 4% in the silent and boat control. Similarly, there was higher mortality in the airgun exposed nauplii up to six days after exposure compared to the control treatments. Nearly all of the airgun exposed nauplii were dead after four days, while >50% of the nauplii in the control treatments were alive at six days post-exposure. There was an interaction between treatment and time on naupliar body length, indicating lower growth in the nauplii exposed to the airgun discharge (growth rates after 4 days: 1.7, 5.4, and 6.1 μm d−1 in the airgun exposed, silent control, and boat control, respectively). These experiments indicate that the output of two small airguns affected mortality and growth of the naupliar stages of Acartia tonsa in close vicinity to the array.