Copepod Reproduction Research Articles

Effects of physicochemical stressors on marine copepod populations: A review

Copepods are the key organisms in aquatic ecosystems; they are exposed to a variety of stressors that can significantly influence their behavior, distribution, and life cycle. Understanding how stressors influence such communities becomes a priority in marine ecology. This paper reviews the most important effects of stressors such as temperature, salinity, light, oxygen, and nutrients, and their effects on marine copepods that have been analyzed in laboratory experiments highlighting the impact of stressors on organisms. Most stressors influence the distribution and behavior of the organisms. Temperature also influences the metabolic activity, development, and reproduction of copepods; variations in salinity can affect osmotic regulation and physiological functioning, while oxygen influences the processes of respiration and metabolism. Light and nutrients also significantly impact the growth and reproduction of copepods and are essential for sustaining their populations in aquatic ecosystems. Complex interactions between multiple stressors and their effects on marine copepods are less studied. By studying the bibliography related to the experiments carried out on marine copepods and how they are influenced by the environmental factors mentioned above, I can provide a better understanding of the fact that copepods are vulnerable to environmental changes, and this information can contribute to the development of strategies effective for the conservation and management of marine ecosystems.

The marine diatom Thalassiosira rotula: chemical profile and antioxidant activity of hydroalcoholic extracts

The cosmopolitan centric diatom Thalassiosira rotula produces compounds in its natural habitat that can inhibit copepod reproduction. Moreover, it has been reported to possess compounds with therapeutic effects beneficial for health care. In this experiment, the extraction yield, total phenolic content (TPC), antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, ferric reducing/antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC), and chemical profile by gas chromatography-mass spectrometry (GC-MS) analyses of T. rotula were investigated. Extractions were performed with 50% and 70% ethanol. A higher extraction yield [0.21 ± 0.01 g extract/g dry weight (DW) diatom] was observed for 70% ethanol. In addition, higher TPC (5.80 ± 0.32 mg gallic acid equivalents (GAE)/g DW diatom) and antioxidant activity [DPPH inhibition of 17.53% ± 0.56%, FRAP of 766.67 ± 34.69 µM Trolox equivalents (TE), and ORAC of 58.87 ± 2.03 µM TE] were observed for this extract. Myristic acid, palmitelaidic acid, palmitic acid, eicosapentaenoic acid, 24-methylenecholesterol, and docosapentaenoic acid were identified as dominant compounds in both extracts, while extraction in 70% ethanol yielded a higher content of fatty acids such as myristic acid, eicosapentaenoic acid, docosapentaenoic acid, and sterol 24-methylenecholesterol. Thus, it can be concluded that extraction of T. rotula with 70% ethanol improves antioxidant activity and provides a higher yield of compounds such as polyunsaturated fatty acids and sterols. Therefore, the species T. rotula could be considered a sustainable source of essential fatty acids and other bioactive compounds for further applications.

Nanoplastics potentiate mercury toxicity in a marine copepod under multigenerational exposure

The continuous fragmentation of plastics and release of synthetic nanoplastics from products have been aggravating nanoplastic pollution in the marine ecosystem. The carrier role of nanoplastics may increase the bioavailability and toxicity effects of toxic metals, e.g., mercury (Hg), which is of growing concern. Here, the copepod Tigriopus japonicus was exposed to polystyrene nanoplastics (PS NPs) and Hg (alone or combined) at environmental realistic concentrations for three generations (F0-F2). Then, Hg accumulation, physiological endpoints, and transcriptome were analyzed. The results showed that the copepod's reproduction was significantly inhibited under PS NPs or Hg exposure. The presence of PS NPs caused significantly higher Hg accumulation, lower survival, and lower offspring production in copepods relative to Hg exposure, suggesting an increased threat to the copepod's survivorship and health. From the molecular perspective, combined PS NPs and Hg caused a graver effect on the DNA replication, cell cycle, and reproduction pathways relative to Hg exposure, linking to lower levels of survivorship and reproduction. Taken together, this study provides an early warning of nanoplastic pollution for the marine ecosystem not only because of their adverse effect per se but also their carrier role for increasing Hg bioaccumulation and toxicity in copepods.

Zooplankton community succession and trophic links during a mesocosm experiment in the coastal upwelling off Callao Bay (Peru)

Abstract. The Humboldt Current Upwelling System (HCS) is the most productive eastern boundary upwelling system (EBUS) in terms of fishery yield on the planet. EBUSs are considered hotspots of climate change with predicted expansion of mesopelagic oxygen minimum zones (OMZs) and related changes in the frequency and intensity of upwelling of nutrient-rich, low-oxygen deep water. To increase our mechanistic understanding of how upwelling impacts plankton communities and trophic links, we investigated mesozooplankton community succession and gut fluorescence, fatty acid and elemental compositions (C, N, O, P), and stable isotope (δ13C, δ15N) ratios of dominant mesozooplankton and microzooplankton representatives in a mesocosm setup off Callao (Peru) after simulated upwelling with OMZ water from two different locations and different N:P signatures (moderate and extreme treatments). An oxycline between 5 and 15 m with hypoxic conditions (<50 µmol L−1) below ∼10 m persisted in the mesocosms throughout the experiment. No treatment effects were determined for the measured parameters, but differences in nutrient concentrations established through OMZ water additions were only minor. Copepods and polychaete larvae dominated in terms of abundance and biomass. Development and reproduction of the dominant copepod genera Paracalanus sp., Hemicyclops sp., Acartia sp., and Oncaea sp. were hindered as evident from accumulation of adult copepodids but largely missing nauplii. Failed hatching of nauplii in the hypoxic bottom layer of the mesocosms and poor nutritional condition of copepods suggested from very low gut fluorescence and fatty acid compositions most likely explain the retarded copepod development. Correlation analysis revealed no particular trophic relations between dominant copepods and phytoplankton groups. Possibly, particulate organic matter with a relatively high C:N ratio was a major diet of copepods. C:N ratios of copepods and polychaetes ranged 4.8–5.8 and 4.2–4.3, respectively. δ15N was comparatively high (∼13 ‰–17 ‰), potentially because the injected OMZ source water was enriched in δ15N as a result of anoxic conditions. Elemental ratios of dinoflagellates deviated strongly from the Redfield ratio. We conclude that opportunistic feeding of copepods may have played an important role in the pelagic food web. Overall, projected changes in the frequency and intensity of upwelling hypoxic waters may make a huge difference for copepod reproduction and may be further enhanced by varying N:P ratios of upwelled OMZ water masses.

Investigation of the reproductive system in calanoid copepods: A new approach using 3D reconstructions from serial semi-thin cross-sections in Calanus glacialis and Metridia longa

The structure of the female reproductive system of the calanoid copepods Calanus glacialis and Metridia longa from the White Sea was studied using light microscopy, scanning and transmission electron microscopy, as well as confocal laser scanning microscopy. For the first time, we applied also the method of 3D reconstructions from semi-thin cross-sections to visualize the general plan of the reproductive system in both species. The application of a combination of methods provided novel and detailed information on the genital structures and muscles located in the genital double-somite (GDS) as well as structures used for the reception and storage of spermatozoa, fertilization and release of eggs. An unpaired ventral apodeme and associated muscles located in the GDS are described for the first time for calanoid copepods. The role of this structure in copepod reproduction is discussed. Stages of oogenesis and the mechanism of yolk formation in M. longa are studied using semi-thin sections for the first time. A combination of non-invasive (LM, CLSM, SEM) and invasive techniques (semi-thin sections and TEM) applied in this study substantially improves our understanding of the functioning of the genital structures in calanoid copepods and could be recommended as a standard set of methods for future research in the reproductive biology of copepods.

Nanoplastics induce epigenetic signatures of transgenerational impairments associated with reproduction in copepods under ocean acidification

Ocean acidification (OA) is one of many major global climate changes that pose a variety of risks to marine ecosystems in different ways. Meanwhile, there is growing concern about how nanoplastics (NPs) affect marine ecosystems. Combined exposure of marine organisms to OA and NPs is inevitable, but their interactive effects remain poorly understood. In this study, we investigated the multi- and transgenerational toxicity of NPs on copepods under OA conditions for ten generations. The findings revealed that OA and NPs have a synergistic negative effect on copepod reproduction across generations. In particular, the transgenerational groups showed reproductive impairments in the F1 and F2 generations (F1T and F2T), even though they were never exposed to NPs. Moreover, our epigenetic examinations demonstrated that the observed intergenerational reproductive impairments are associated with differential methylation patterns of specific genes, suggesting that the interaction of OA and NPs can pose a significant threat to the sustainability of copepod populations through epigenetic modifications. Overall, our findings provide valuable insight into the intergenerational toxicity and underlying molecular mechanisms of responses to NPs under OA conditions

Copepod community from Arctic to Antarctic

The use of citizen science and opportunity sampling during commercial or tourist voyages can provide valuable insights into the structuring of the marine plankton community in broad biogeographic areas. With the goal of studying the distribution and abundance of smaller zooplankton using citizen science approach, plankton samples were collected at 33 stations spanning from the Arctic to Antarctic during the cruise of the S/V “Croatian Tern” (1994-1997), using vertical tows with a 53µm mesh size Nansen net in the upper epipelagic layer. In this study, we summarize the observed distribution patterns of planktonic copepods by ontogenetic stages (nauplii, copepodites, adults) and by postnaupliar assemblages (calanoids, oithonids, oncaeids, harpacticoids, corycaeids), reporting also on the numerical ratio of nauplii to postnaupliar copepods, as an important indicator of the stability of copepod reproduction. The highest abundances of total copepods were found in the northeastern and southeastern Pacific, while the lowest values were found in the Mediterranean Sea and Southern Ocean. Overall, the copepod community was dominated by naupliar stages, while most postnaupliar assemblages (calanoids, oithonids, and oncaeids) were dominated by copepodites. Spatially, nauplii and postnaupliar oithonids showed similar latitudinal patterns, with both assemblages dominating in high latitudes of temperate zones on both sides of the equator, while contributions of calanoids, oncaeids, and corycaeids increased at lower latitudes. The ratio of nauplii to postnauplii varied from 1.1 to 6.4, and only at five stations was it slightly < 1. Latitudinally, the median values of this ratio varied from 1.1 in the marginal Arctic to 3.1 in the South Pacific, with no statistically significant differences among areas. The sudden change in nauplii/ postnauplii ratio could signal disturbances in the copepod community, provided that the average values are determined for all marine areas under different productivity conditions.

Long-term effects of neonicotinoids on reproduction and offspring development in the copepod Acartia tonsa

Neonicotinoids (NEOs) are neurotoxic pesticides acting as nicotinic acetylcholine receptor agonists. NEOs' efficacy against pest insects has favoured their spreading use in agriculture, but their proven effectiveness against non-target insects in terrestrial and aquatic ecosystems also raised concern over their environmental impact. Crustaceans were often studied for the impacts of NEOs due to their economic values and nervous' system similarity with insects. However, most studies on crustaceans focused on acute effects or exposure of early-life stages, while long-term effects were seldom explored. The present study aimed to assess the potential long-term effects of four commercially available NEOs on the reproduction and offspring of the calanoid copepod Acartia tonsa, a key species in the food webs of several coastal and estuarine environments. NEOs were confirmed as potent interferents of copepod reproduction. The first-generation compound acetamiprid significantly inhibited egg production and hatching ratio at 10 ng L−1, while larval survival and development were affected at 81 ng L−1. Similarly, the first-generation compound thiacloprid significantly inhibited the hatching ratio and larval development at 9 ng L−1, while it did not affect egg production and larval survival. Second-generation compounds were less toxic than acetamiprid and thiacloprid: clothianidin affected significantly only larval development of the offspring at 62 ng L−1, while thiamethoxam was not toxic at both the tested concentrations (8 ng L−1 and 84 ng L−1). These data evidenced that effects on copepods may occur at concentrations below the chronic aquatic life benchmarks reported by USEPA for acetamiprid (2100 ng L−1) and thiacloprid (970 ng L−1), suggesting that long-term effects of NEOs have been underestimated. A comparison with environmental concentrations evidenced that NEO-mediated effects on copepods are more liable in coastal areas receiving discharge from wastewater treatment plants or diffuse inputs from agricultural land during pesticide application periods.

Combined effect of salinity and temperature on copepod reproduction and oxidative stress in brackish-water environment

Climate-induced warming and increased river inflows are forcing the Baltic Sea to radical changes in the near future; organisms living in this brackish-water ecosystem are already experiencing osmotic stress, which, together with thermal stress, may have severe consequences on the ecosystem. The aim of this work was to study the combined effect of decreasing salinity and increasing temperature on reproductive success and oxidative stress in zooplankton by using a calanoid copepod Acartia sp. as a model organism. The field study was conducted during summer 2020 in the western Gulf of Finland, using three sampling sites with naturally differing salinity levels. Additionally, the copepods from these sites were experimentally exposed to ambient or 3°C elevated temperature for 72 h. The copepods derived from the deepest and the most saline sampling site suffered less oxidative damage and exhibited relatively high reproduction, while the temperature treatment itself had little effect. On the other hand, the field-based monitoring data showed otherwise; temperature increased lipid peroxidation, glutathione-s-transferase activity, or both in all three sampling sites. Meanwhile, egg production rate was negatively associated with temperature in the area with the lowest salinity. Moreover, egg production rate decreased from June to September along with increasing temperatures in the mid-salinity sampling site, while similar change occurred also in the highest-salinity site between August and September. The combined effect of salinity and sampling date on reproduction indicates the importance of even subtle salinity changes on copepods. Moreover, the data suggest that the unusually strong heatwave was responsible for increased oxidative stress during the sampling season and possibly forced a trade-off between antioxidant activity and reproductive effort.

Single substance and mixture toxicity of dibutyl-phthalate and sodium dodecyl sulphate to marine zooplankton

Several contaminants exceed their environmental thresholds in Swedish marine surface waters. We ranked the toxicity-drivers among contaminants detected near heavy industry, based on toxicity to zooplankton, and identified di-butyl phthalate and sodium dodecyl sulphate as contaminants of concern. We tested their acute individual and mixture toxicity by assessing effects on mortality, biodiversity, algal growth, and copepod reproduction in natural mesozooplankton communities. The mixture effects were compared to Independent Action mixture model predictions. Egg production and algae growth were affected at 4 µmol/l DBP, and effects on mortality, algae growth and biodiversity were observed at 12 µmol/l SDS. The mixture (1 µmol/l DBP, 3 µmol/l SDS) affected all endpoints, and the observed effects were underestimated by 21% on average compared to predictions. We found that the successional trajectory in zooplankton communities was compound dependant, and that DBP and SDS are toxic to marine zooplankton, but at levels above measured environmental concentrations.

Occurrence, characterization, partition, and toxicity of cigarette butts in a highly urbanized coastal area.

Cigarette butts (CBs) comprise one of the most relevant categories of marine litter worldwide. This study was structured as a case study simultaneously assessing (i) the occurrence of CBs in a highly urbanized coastal area, (ii) their partitioning in two environmental compartments (water column and sediments) by laboratory settling tests, and (iii) the toxicity produced by the CBs leachates (measured as copepod reproduction). Marine litter was sampled in beaches of the city of Santos (SW Brazil) and CBs were collected for analysis. The characterization showed that CBs were one of the most prevalent items (51.5% in summer and 34.4% in winter) and 22 cigarettes brands were identified at different stages of decomposition. Laboratory settling tests showed that CBs remain in the water column between 3 and 20days, subsequently reaching the sediments. The toxicity results indicated that CBs the leachates extracted from a small amount of CBs was sufficient to affect copepod reproduction (0.1 and 0.01 CBs L-1). Furthermore, the approaches adopted by the present study can serve as a preliminary assessment to estimate local impacts resulting from inadequate disposal of cigarette butts in coastal areas around the world.

The Reproduction and Development of Brackish-Water Copepods That Were Fed Microalgae of Different Species

The duration of development, survival rate, and reproductive characteristics of Calanipeda aquaedulcis (Krichagin, 1873) and Arctodiaptomus salinus (Daday, 1885) depending on a diet consisting of monospecific cultures of microalgae from three different taxonomic groups were studied in experimental conditions. The highest survival rates were recorded for the copepod C. aquaedulcis that was fed the microalga Prorocentrum cordatum (Ostenfeld) J.D. Dodge, 1975. A. salinus showed the maximum survival rate when it was fed the microalga Isochrysis galbana Parke, 1949. The duration of ontogeny in C. aquaedulcis was 14 days with each of the three diets. The shortest duration of development in A. salinus (18 days) was recorded when it fed on Rhodomonas salina (Wislouch) Hill and Wetherbee, 1989. The percentage of hatching nauplii in female C. aquaedulcis that were fed P. cordatum and I. galbana was 100%; however, when females were fed Rh. salina, it decreased to 86%. The average daily fecundity per life cycle in female C. aquaedulcis was found to be two times higher than that in A. salinus. The female A. salinus that received different diets showed significant differences in the average prosoma length and the diameter of spawned eggs; in C. aquaedulcis, these parameters did not depend on the species of food.

An individual-based model for evaluating post-exposure effects of UV-B radiation on zooplankton reproduction

Solar ultraviolet (UV) radiation, and UV-B (280–320 nm) in particular, has been shown to be partially responsible for adverse effects on zooplankton throughout the world, from damaged DNA to altered population dynamics. To cope with these effects, copepods have developed several protective systems, including avoiding extended and intense periods of exposure. How much UV-B exposure a cohort of thousands of spawners can withstand remains unknown. To evaluate the post-exposure effects of UV-B radiation on reproduction in egg-carrying copepods, we developed an individual-based model (IBM) that integrates in vivo data. We calibrated the IBM for a small cyclopoid copepod species, Paracyclopina nana, which is a biological model used in both ecotoxicology and aquaculture. Our findings improve our understanding of the species’ response to UV-B radiation. Significant radiative effects include decreased reproductive success (at ≥ 0.7 kJ.m − 2) and offspring production (at 0.6 ≥ kJ.m − 2). The model predicted fewer than 500 females from an original cohort of 1000 would survive for five days after exposure to 1 kJ/m2, and 50% offspring suppression eight days after exposure to 1 kJ.m − 2. This integrative model highlighted the importance of female longevity in maintaining a viable population at doses below 2 kJ.m − 2 and that of hatching success for radiation levels exceeding 2 kJ.m − 2. P. nana appeared to be a sensitive species at 25 °C but improvements in the model, such as incorporation of temperature variation effects and recovery mechanisms, should provide better estimates of the species’ sensitivity to UV-B.

De novo Transcriptome of the Non-saxitoxin Producing Alexandrium tamutum Reveals New Insights on Harmful Dinoflagellates.

Many dinoflagellates species, especially of the Alexandrium genus, produce a series of toxins with tremendous impacts on human and environmental health, and tourism economies. Alexandrium tamutum was discovered for the first time in the Gulf of Naples, and it is not known to produce saxitoxins. However, a clone of A. tamutum from the same Gulf showed copepod reproduction impairment and antiproliferative activity. In this study, the full transcriptome of the dinoflagellate A. tamutum is presented in both control and phosphate starvation conditions. RNA-seq approach was used for in silico identification of transcripts that can be involved in the synthesis of toxic compounds. Phosphate starvation was selected because it is known to induce toxin production for other Alexandrium spp. Results showed the presence of three transcripts related to saxitoxin synthesis (sxtA, sxtG and sxtU), and others potentially related to the synthesis of additional toxic compounds (e.g., 44 transcripts annotated as “polyketide synthase”). These data suggest that even if this A. tamutum clone does not produce saxitoxins, it has the potential to produce toxic metabolites, in line with the previously observed activity. These data give new insights into toxic microalgae, toxin production and their potential applications for the treatment of human pathologies.

Remediation criteria for gasworks-impacted sediments: Assessing the effects of legacy hydrocarbons and more recent metal contamination

Historical contamination of sediments from industries that commenced before environmental regulations were commonplace is prevalent in many large cities. This contamination is frequently overlain and mixed with more recent urban contamination. The remediation of contaminated sites is often a very expensive exercise and the final remediation criteria often reflect a trade-off between protecting human and ecological health and the finances of those deemed responsible for the site clean-up. In this study, we describe an assessment of estuarine sediments impacted historically by contamination from a gasworks site. The major historical sediment contaminants included polycyclic aromatic hydrocarbons (PAHs) and other petroleum-related hydrocarbons (TRHs). Elevated concentrations of metals exist throughout the city region due to historical pollution and ongoing urban stormwater discharges. Equilibrium partitioning models were used to consider the influence on the bioavailability of PAHs of both natural sedimentary organic carbon and forms of black carbon (pyrogenic carbon - coal tars, charcoal). The strongest predictor of the observed sublethal toxicity to amphipod and copepod reproduction was a combination of total PAHs and metals (primarily Cu, Pb and Zn). Total PAHs was the strongest predicting variable for toxicity to organism survival. While high total PAH concentrations were attributed to the former gas works, high background concentrations of metals existed throughout much of this region of the estuary. Thus, without remediation at the estuary-scale, resuspension of the surrounding sediments by tidal currents and boat movements is predicted to re-contaminate remediated areas with sediments that may continue to cause chronic toxicity due to metals. The assessment indicated that remedial actions that remove or isolate sediments that caused toxicity to benthic organism survival would lead to significant improvements in ecosystem health, but toxicity to organism reproduction may remain at similar levels that exist throughout much of this region of the estuary due to high metal concentrations.

PH and other upwelling hydrographic drivers in regulating copepod reproduction during the 2015 El Niño event: A follow-up study

The combined upwelling-El Niño (EN) event regulation of the numerically dominant Acartia tonsa (Crustacea, Copepoda) reproduction was examined in a year-round upwelling system (23°S) of the Humboldt Eastern Boundary Upwelling System (EBUS) during the EN 2015. A previous analysis of the environmental regulation of this system is extended here by considering complementary oceanographic information (sea level, stratification indexes) and additional reproductive traits, such as maximum (MaxEPR), median (MedianEPR) and prevalence of egg producing females over a period of six months. Furthermore, field minimum-maximum pH levels were reproduced in three 96-h incubation experiments conducted under variable salinity conditions to evaluate copepod mean EPR, egg size and hatching success. Supporting previous assertions, the warm-high salinity EN 2015 was observed in the study site separately from hydrographic conditions associated with upwelling to non-upwelling regimes. Analysis of similarity-distance (Distance based Linear Model (DistLM)) and normalized data (separate-slope comparison under a General Linear Model (GLM)) showed that reproductive traits were regulated by specific combinations of ambient conditions, and that this regulation was also sensitive to the prevailing hydrographic regime. Thus, upwelling to non-upwelling transitions changing the pH, and EN-associated salinity and stratification shifts, were significantly and strongly linked to almost all reproductive traits (DistLM). Slope comparison (GLM) indicated MaxEPR and MedianEPR variations also underlie the phenology, highlighting the relationship between pH and salinity with biological variations. In conjunction with experimental observations, the current study consistently suggests that pH-variations in the upwelling realm, and EN hydrographic perturbations might underpin responses of plankton populations to climate change in productive EBUS.

Lipoxygenase Pathways in Diatoms: Occurrence and Correlation with Grazer Toxicity in Four Benthic Species.

Oxygenated derivatives of fatty acids, collectively called oxylipins, are a highly diverse family of lipoxygenase (LOX) products well described in planktonic diatoms. Here we report the first investigation of these molecules in four benthic diatoms, Cylindrotheca closterium, Nanofrustulum shiloi, Cocconeis scutellum, and Diploneis sp. isolated from the leaves of the seagrass Posidonia oceanica from the Gulf of Naples. Analysis by hyphenated MS techniques revealed that C. closterium, N. shiloi, and C. scutellum produce several polyunsaturated aldehydes (PUAs) and linear oxygenated fatty acids (LOFAs) related to the products of LOX pathways in planktonic species. Diploneis sp. also produced other unidentified fatty acid derivatives that are not related to LOX metabolism. The levels and composition of oxylipins in the benthic species match their negative effects on the reproductive success in the sea urchin Paracentrotus lividus. In agreement with this correlation, the most toxic species N. shiloi revealed the same LOX pathways of Skeletonema marinoi and Thalassiosira rotula, two bloom-forming planktonic diatoms that affect copepod reproduction. Overall, our data highlight for the first time a major role of oxylipins, namely LOFAs, as info-chemicals for benthic diatoms, and open new perspectives in the study of the structuring of benthic communities.

Nitric oxide mediates oxylipin production and grazing defense in diatoms.

Diatom blooms are important features of productive marine ecosystems and are known to support higher trophic levels. However, when stressed or wounded, diatoms can produce oxylipin molecules known to inhibit the reproduction and development of copepods and decrease microzooplankton growth rates. Using oxylipin chemical treatments, lipidomic analysis and functional genomic approaches, we provide evidence that nitric oxide (NO) and oxylipin signalling pathways in diatoms respond to protist grazers, resulting in increased defence fitness and survival. Exposure of the diatom Phaeodactylum tricornutum to the dinoflagellate Oxyrrhis marina resulted in NO production by P. tricornutum and pronounced change in its dissolved oxylipin profile. Experimentally elevating levels of NO also resulted in increased oxylipin production, and lower overall grazing rates. Furthermore, O. marina preferentially grazed on P. tricornutum prey with lower levels of NO, suggesting that this molecule and its effect on oxylipin pathways play a key role in prey selection. Exposure of O. marina grazing on P. tricornutum to exogenous oxylipins also decreased grazing rates, which is consistent with a grazing deterrence role for these molecules. These results suggest that NO and oxylipin production help to structure diatom communities, in part by modulating interactions with microzooplankton predators.

Effect of ocean acidification on the nutritional quality of marine phytoplankton for copepod reproduction.

Phytoplankton are the oceans’ principal source of polyunsaturated fatty acids that support the growth and reproduction of consumers such as copepods. Previous studies have demonstrated ocean acidification (OA) can change the availability of polyunsaturated fatty acids to consumer diets which may affect consumer reproduction. Two laboratory experiments were conducted to examine the effects of feeding high-pCO2-reared phytoplankton on copepod egg production, hatching success, and naupliar survival. Marine phytoplankton Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans, and Isochrysis galbana were exponentially grown in semi-continuous cultures at present (control) (400 ppm CO2, pH~8.1) and future (1,000 ppm CO2, pH~7.8) conditions and provided to Acartia tonsa copepods over 4 consecutive days as either nitrogen-limited (Exp. I) or nitrogen-depleted (Exp. II) mixed assemblage of phytoplankton. The composition of FAs in the phytoplankton diet was affected by pCO2 concentration and nitrogen deficiency; the ratio of essential fatty acids to total polyunsaturated fatty acids decreased in phytoplankton grown under high pCO2 and the mass of total fatty acids increased under nitrogen depletion. Additionally, total concentrations of essential fatty acids and polyunsaturated fatty acids in the diet mixtures were less under the high-pCO2 compared to the control-pCO2 treatments. Median egg production, hatching success, and naupliar survival were 48–52%, 4–87%, and 9–100% lower, respectively, in females fed high-pCO2 than females fed low-pCO2 phytoplankton, but this decrease in reproductive success was less severe when fed N-depleted, but fatty acid-rich cells. This study demonstrates that the effects of OA on the nutritional quality of phytoplankton (i.e., their cellular fatty acid composition and quota) were modified by the level of nitrogen deficiency and the resulting negative reproductive response of marine primary consumers.

Upwelling modulation of functional traits of a dominant planktonic grazer during "warm-acid" El Niño 2015 in a year-round upwelling area of Humboldt Current.

Climate change is expected to exacerbate upwelling intensity and natural acidification in Eastern Boundaries Upwelling Systems (EBUS). Conducted between January-September 2015 in a nearshore site of the northern Humboldt Current System directly exposed to year-round upwelling episodes, this study was aimed at assessing the relationship between upwelling mediated pH-changes and functional traits of the numerically dominant planktonic copepod-grazer Acartia tonsa (Copepoda). Environmental temperature, salinity, oxygen, pH, alkalinity, chlorophyll-a (Chl), copepod adult size, egg production (EP), and egg size and growth were assessed through 28 random oceanographic surveys. Agglomerative clustering and multidimensional scaling identified three main di-similitude nodes within temporal variability of abiotic and biotic variables: A) “upwelling”, B) “non-upwelling”, and C) “warm-acid” conditions. Nodes A and B represented typical features within the upwelling phenology, characterized by the transition from low temperature, oxygen, pH and Chl during upwelling to higher levels during non-upwelling conditions. However, well-oxygenated, saline and “warm-acid” node C seemed to be atypical for local climatology, suggesting the occurrence of a low frequency oceanographic perturbation. Multivariate (LDA and ANCOVA) analyses revealed upwelling through temperature, oxygen and pH were the main factors affecting variations in adult size and EP, and highlighted growth rates were significantly lower under node C. Likely buffering upwelling pH-reductions, phytoplankton biomass maintained copepod reproduction despite prevailing low temperature, oxygen and pH levels in the upwelling setting. Helping to better explain why this species is among the most recurrent ones in these variable yet productive upwelling areas, current findings also provide opportune cues on plankton responses under warm-acid conditions, which are expected to occur in productive EBUS as a consequence of climate perturbations.