Acartia Clausii Research Articles

Effects of dredging activities and seasonal variation on coastal plankton assemblages: results from 10 years of environmental monitoring

Coastal zones support the most productive marine ecosystems, yet they are increasingly threatened by anthropogenic stressors such as dredging. In this study, we investigated how seasonal variation and dredging activities conducted during the construction of a harbor and submarine base (Sepetiba Bay, RJ, Brazil) affected the phytoplankton and zooplankton assemblages. The observed temporal variability at five different sites over 10 years revealed that dredging exceeds the expected influence of dry and rainy seasons on plankton abundance and diversity. In general, the abundance of both groups increased during dredging due to the resuspension of nutrients and benthic organisms. This increase was particularly evident in the dinoflagellate Scrippsiellaa cuminata, the diatoms Thalassiosira rotula and Nitzschia longissima, and the herbivorous zooplankton Acartia clausii and Pseudevadne tergestina. Moreover, season and dredging activities synergistically influenced plankton assemblages, resulting in larger seasonal variations during dredging activities. After the end of the harbor construction, plankton abundance decreased and remained low until the end of the monitoring, which may indicate persistent changes in the biodiversity and ecosystem functioning of impacted areas.

Kanningar av gongdini hjá fjarðarsild í Føroyum gjøgnum samdøgrið

In october 1968 investigations on plankton and 1, 2 and 3 years old herring were carried out during 24 hours in Funningsfjørður, Faroe Islands. Plankton as well as herring showed vertical migration.
 In daytime the main part of the herring and the plankton stayed from the bottom up to a level of 10 m below the surface, in the night they moved up from bottom coming to íhe surface entirely.
 The echograms showing the movements of the herring form a picture corresponding with Ball's (1951) three step movement described for middle depths in the North Sea. The only factor which the day and night migrations could be correlated with was the light intensity.
 Stomach contents was found in the afternoon, whereas a sample of herring taken at 730 GMT, at sunrise, had empty stomachs only. The herring feed was composed of Acartia sp. besides some few Temora longicornis. Acartia longiremis and Acartia Clausii were dominating in the plankton samples, ohiefly females with egg sacks.

Gene expression and epigenetic responses of the marine Cladoceran, Evadne nordmanni, and the copepod, Acartia clausi, to elevated CO2.

Characterizing the capacity of marine organisms to adapt to climate change related drivers (e.g., pCO2 and temperature), and the possible rate of this adaptation, is required to assess their resilience (or lack thereof) to these drivers. Several studies have hypothesized that epigenetic markers such as DNA methylation, histone modifications and noncoding RNAs, act as drivers of adaptation in marine organisms, especially corals. However, this hypothesis has not been tested in zooplankton, a keystone organism in marine food webs. The objective of this study is to test the hypothesis that acute ocean acidification (OA) exposure alters DNA methylation in two zooplanktonic species—copepods (Acartia clausii) and cladocerans (Evadne nordmanii). We exposed these two species to near‐future OA conditions (400 and 900 ppm pCO2) for 24 h and assessed transcriptional and DNA methylation patterns using RNA sequencing and Reduced Representation Bisulfite Sequencing (RRBS). OA exposure caused differential expression of genes associated with energy metabolism, cytoskeletal and extracellular matrix functions, hypoxia and one‐carbon metabolism. Similarly, OA exposure also caused altered DNA methylation patterns in both species but the effect of these changes on gene expression and physiological effects remains to be determined. The results from this study form the basis for studies investigating the potential role of epigenetic mechanisms in OA induced phenotypic plasticity and/or adaptive responses in zooplanktonic organisms.

Water quality assessments: A case study of plankton and macrobenthic invertebrates of Porto-Novo and parts of Gulf of Guinea

Aspects of physico-chemical characteristics, plankton and macro invertebrates of Porto-Novo and Gulf of Guinea were studied in September 2012 with a view to determine the quality of water using plankton indices. Standard methods were used to determine the physico-chemical parameters. The mean water quality parameters studied were temperature (36.71oC), pH (7.63), transparency (1.97m), total dissolved solids (10.0mg/L), dissolved oxygen (4.73mg/L) and salinity (38.58‰) for Gulf of Guinea. Five divisions; Cyanophyta, Bacillariophyta, Chlorophyta, Euglenophyta and Pyrrhophyta were recorded for both bodies of water with diatoms and dinoflagellates dominating the spectrum. The phytoplankton ofPorto-Novo recorded abundance of Gomphonema spp., Fragilaria crotonensis, Synedrasp. and Nitzschia sp.(diatoms) while that of Gulf of Guinea recorded Ceratium spp. and Gonyaulax spinifera (dinoflagellates). For the zooplankton, Acartia clausii (a copepod) and Penilla avirostris Dana (Cladocera) were the highest in both occurrence and abundance especially at Porto-Novo. The population of benthic fauna was low (20 individuals) dominated by bivalve, Tivela tripla.Keywords: Microalgae, zooplankton, benthos, Porto-Novo, Gulf of Guinea

Spatial mismatch between phytoplankton and zooplankton biomass at the Celtic Boundary Front

Thermohaline fronts are present globally and have been identified as biodiversity hotspots, encouraging enhanced primary productivity and attracting dense aggregations of higher trophic level organisms. The Celtic Boundary Front (CBF) sits in an important zone of economic activity yet no contemporary studies describing the meso-zooplankton community exist for this region. High-frequency sampling during June 2009 revealed three distinct areas on the mixed (Irish Sea) and stratified (Celtic Sea; Celtic Deep) sides of the front, each exhibiting distinct physical and biological characteristics. Low zooplankton abundance was found above the Celtic Deep, despite apparent optimal phytoplankton conditions, conflicting with observations made at other frontal locations. Although zooplankton assemblages were generally distinct within areas, the copepod Acartia clausii was ubiquitous across all three areas and accounted for almost 60% of all counted individuals. The long-term variation of zooplankton during the seasonal front development was examined using samples from the Continuous Plankton Recorder. The results of this analysis suggest that low abundance is a recurring feature over the Celtic Deep. Possible explanations for the observed patterns may be top-down effects on zooplankton from pelagic fish; alternatively, these patterns may be a consequence of the strong density and stratification gradients in the Celtic Deep.

A molecular and co-evolutionary context for grazer induced toxin production in Alexandrium tamarense.

Marine dinoflagellates of the genus Alexandrium are the proximal source of neurotoxins associated with Paralytic Shellfish Poisoning. The production of these toxins, the toxin biosynthesis and, thus, the cellular toxicity can be influenced by abiotic and biotic factors. There is, however, a lack of substantial evidence concerning the toxins' ecological function such as grazing defense. Waterborne cues from copepods have been previously found to induce a species-specific increase in toxin content in Alexandrium minutum. However, it remains speculative in which context these species-specific responses evolved and if it occurs in other Alexandrium species as well. In this study we exposed Alexandrium tamarense to three copepod species (Calanus helgolandicus, Acartia clausii, and Oithona similis) and their corresponding cues. We show that the species-specific response towards copepod-cues is not restricted to one Alexandrium species and that co-evolutionary processes might be involved in these responses, thus giving additional evidence for the defensive role of phycotoxins. Through a functional genomic approach we gained insights into the underlying molecular processes which could trigger the different outcomes of these species-specific responses and consequently lead to increased toxin content in Alexandrium tamarense. We propose that the regulation of serine/threonine kinase signaling pathways has a major influence in directing the external stimuli i.e. copepod-cues, into different intracellular cascades and networks in A. tamarense. Our results show that A. tamarense can sense potential predating copepods and respond to the received information by increasing its toxin production. Furthermore, we demonstrate how a functional genomic approach can be used to investigate species interactions within the plankton community.

Effects of nitrogen stressed algae on different Acartia species

We studied the reproductive response of two copepod species, Acartia tonsa and Acartia clausii, fed algae with different C:N ratios (4.5 and 9.1 molar ratios respectively) in order to investigate the influence of nutritional imbalances on calanoid copepods egg production. Adult females were incubated with the cryptophyte Rhodomonas sp. at saturating concentrations. The algae were cultured under nitrogen depleted and sufficient conditions. Ingestion rates of the animals fed with different algae and their response in terms of egg production and hatching success of the eggs were quantified. Both species produced more egg when fed with nitrogen-limited algae. Ingestion rates and egg hatching differed between species, but were not significantly affected by the quality of the food. The only difference between the two species in their reaction to food quality was that A. tonsa increased the number of resting eggs, whereas no resting egg production was observed in A. clausii when fed with nitrogen limited algae. These results support the recent suggestion that a moderately high prey C:N ratio (10–15) supports a higher egg production than a C:N ratio substantially <10.

Long-term changes in the diel vertical migration behaviour of zooplankton

Samples historically collected and analysed by the Continuous Plankton Recorder survey were used to examine long-term (1958 to 1994) patterns in the normal diel vertical migration (NDVM) behaviour of 7 copepod taxa in the North Sea: Calanus finmarchicus C5-C6; Calanus spp. C1-C4; Centropages typicus; Centropages hamatus; Temora longicornis; Acartia clausii and Para-Pseudocalanus (this last group included all Paracalanus and Pseudocalanus species). The ratio of night:day abundance near the surface was used as a measure of the extent of NDVM. For all 7 taxa, the extent of NDVM between 1958 and 1994 co-varied with the abundance of herring Clupea harengus in the North Sea. Fisheries data show that during this period the herring stock was a good indicator of the overall abundance of planktivorous fish in the North Sea. These results suggest that changes in the abundance of planktivorous fish in the North Sea over recent decades have resulted in modifications in the NDVM behaviour of many zooplankton taxa.

Survival and sex ratios of the intertidal copepod, Tigriopus californicus, following ultraviolet-B (290?320 nm) radiation exposure

The marine harpacticoid copepod, Tigriopus californicus (Baker), is a successful colonizer of supralittoral splash pools from Torch Bay, Alaska, to Baja California, Mexico. As these pools are subject to abundant amounts of direct solar radiation, it was of interest to determine the sensitivity of T. californicus to ultraviolet-B (UV-B, 290 to 320 nm) radiation. During 1980, copepods were raised under diurnal conditions in the laboratory and fed a mixture of unicellular algae and bacteria. Larval and adult stages were irradiated for 0 to 26 h on a rotating turntable under enhanced ultraviolet radiation. Following irradiation, the copepods were maintained in the culture area and checked daily for survival. All life stages of T. californicus tolerated enhanced UV-B radiation irrespective of exposure period; in contrast, survival of an irradiated planktonic copepod, Acartia clausii (Giesbrecht), was significantly lower. Additionally, there appeared to be asex ratio shift in adults that developed from the youngest naupliar stages (N1/N2) of T. californicus that were irradiated. Extraction and tentative identification of the pigment(s) responsible for the bright orange color of the carapace of T. californicus were performed. These pigments may function to absorb UV radiation and protect internal structures from photochemically induced damage.

Foraging Behavior and Prey Selection by the Ambush Entangling Predator Pleurobrachia Bachei

Ctenophores and other gelatinous predators in the ocean are ephemeral in their spatial and temporal distributions, but often have a dramatic impact on the dynamics of their prey populations. Considerable information is currently available on the functional and numerical responses of several nearshore ctenophore species; however, an understanding of their potential for shaping the structure of natural zooplankton assemblages requires further information on the selective nature of their predation. Prey selection by the tentaculate ctenophore Pleurobrachia bachei was examined in the laboratory with predation experiments and videotaped observations of predator and prey behavior. Prey types offered to the ctenophore included each of the developmental stages of Calanus pacificus, adult Acartia clausii, and adult Pseudocalanus sp. Pleurobrachia exhibited an unusual, bimodal pattern of prey selection on the different developmental stages of Calanus. Calanus' vulnerability increased through the naupliar stages, dropped at the first copepodid stage, and then rose again throughout the subsequent copepodid stages prior to another decline at the adult stage. Adult Acartia and Pseudocalanus were found to be among the most vulnerable of the prey types offered to Pleurobrachia. We conclude that Pleurobrachia's diet is determined by the relative availability and vulnerability of prey, and that vulnerability to the ctenophore can be predicted from prey swimming speeds and the susceptibility of prey after encounter.

Impact of UV-B radiation on the fecundity of the copepod Acartia clausii

It has recently been demonstrated that acute midultraviolet irradiation (UV-B, 290 to 320 nm) of the marine copepod Acartia clausii results in reduced survival and fecundity. In the present study, immature late copepodites were separted by sex and exposed to three UV-B exposure levels (0, 25, and 50 effectiveDNA Jm-2). The irradiated copepods were then reared to sexual maturity, and adult virgin survivors were mated according to prior exposure, supplying 7 different types of mating crosses (M0F0, M0F25, M25F0, M25F25, M0F50, M50F0, M50F50). Six replications of each cross were maintained for the duration of an experiment. Two experiments are documented. There was a significant effect of UV-B radiation on the survival of the parents as well as a reduction in the number of eggs and the number of living nauplii produced. For each experiment, 30 nauplii from each type of cross were separated, reared to maturity and counted, providing information on the survival capability of non-irradiated offspring from the 7 different mating types. Previous exposure of parental stock did not significantly affect the survival, and development to maturity, of these nauplii 15 d after separation.

Midultraviolet (UV‐B) sensitivity of Acartia clausii Giesbrecht (Copepoda)1

The sensitivity of all life stages of laboratory‐cultured Acartia clausii to various fluences of UV‐B radiation was evaluated. Organisms were irradiated on a rotating turntable beneath FS40 sunlamps and “deluxe white” fluorescent lamps. Copepods were randomly assigned to treatments utilizing a randomized complete block design. Least‐squares regression analysis was performed between surviving fraction and fluence for all treatments administered to each age group and also between the offspring:survivor ratio and fluence for treatments administered to the oldest age group, which was composed of equal numbers of males and females. Results indicated an inverse relationship between surviving fraction and UV‐B exposure. Reproductive capability of the surviving organisms was also negatively affected.

Zonation and maintenance of copepod populations in the Oregon upwelling zone

Oregon has one of the smaller and best known coastal upwelling systems. It is about 50 km wide, but upwelling is most intense within 15 km of the shore, and episodes of active upwelling primarily affect the circulation and hydrography of the upper 20 m. It is in this nearshore, surface zone that phytoplankton and zooplankton are most abundant. Phytoplankton biomass is 5 to 20 mg chl- am −3, and zooplankton 50 to 200 mg dry weight m −3. Vertically stratified sampling along transects perpendicular to the shore has produced a new picture of the upwelling process and suggests relationships between circulation and the population biology of planktonic animals. The zooplankton is dominated by five species of copepod. Each is distributed in a different pattern: Acartia clausii is almost completely restricted to the upper 5 to 10 m of the water column and the first 5 km from shore. Pseudocalanus sp. is abundant from 0 to 15 km and between 10 and 20 m depth, but it reproduces only within a few kilometers of the shore. Acartia longiremis lives and reproduces offshore (10 km) in the surface (0 to 10-m) mixed layer. Oithona similis is abundant offshore (10 km) between 10- and 20-m depths. Calanus marshallae lives offshore as older copepodite stages, but the females return shoreward and lay their eggs at about 10 km offshore. The nauplii and younger copepodites develop in the very nearshore zone. The patterns of animal distribution together with data on salinity, temperature, and chlorophyll- a lead to the following conclusions about the circulation in the Oregon upwelling zone: First, during active upwelling, the Ekman layer within 0 to 10 km is less than 5 m deep. Offshore of the frontal region, this layer is 10 to 15 m thick. Second, when upwelling is active, the surface layer offshore of the frontal region is not continuously transported offshore. Instead, this mass is moved offshore some fixed distance, no more than 20 to 40 km. During relaxation, this surface water returns shoreward to its former location. Third, we propose a two-cell zonal circulation scheme during initiation of active upwelling: Looking north in vertical section, a divergence is located 10 km from shore, with a clockwise rotating cell on the landward side and a counterclockwise cell on the seaward side. The population of each zooplankton species appears to be maintained within the upwelling zone by a specific relationship between its distribution and the circulation.

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 μg carbon l-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 μg C l-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 μm to 10 μm diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.

Brackish-water plankton and their environment in the Werribee River, Victoria.

A plankton and water sample were taken at each of 10 stations on 7 April, 22 September, and 30 October 1970. Surface chlorophyll a values as high as 1220 mg/m³ were recorded, although normally they were less than 100 mg/m³. The horizontal and temporal distribution of 16 species of calanoid and cyclopoid copepods is presented, together with their observed salinity tolerances. Four major species-Sulcanus conflictus, Gladioferens pectinatus, Gippslandia estuarina (all estuarine), and Acartia clausii (marine) -accounted for most of the copepod numbers. Evidence is outlined suggesting that the males of A. clausii can penetrate upstream more readily than the females. Zooplankton numbers varied markedly with time, the influence of river flow being quite evident. Variation in egg number and body size in G. pectinatus was studied, and the importance of rate of water renewal on egg number in an estuarine population is discussed. The results are compared with those obtained from two other Victorian ecological studies. Aspects of the Australasian genus Gladioferens are discussed.

Further studies on some saline lakes of south-east Australia

A series of closed saline lakes located between Beachport and Robe in South Australia are discussed in more detail than previously. The following taxa are reported for the first time: the polychaete Capitella capitata (Fabricius), the dipteran Culicoides, the turbellarian Mesostoma, and the copepod Acartia clausii Giesbrecht. New taxa that will be described by other workers wholly or partially from material collected in this region are as follows: a new species and genus of hydrozoan probably belonging to the order Limnomedusae, and three new copepod species belonging to the genera Mesochra, Robertsonia, and Heterolaophonte. Previously recorded taxa which have now been more closely identified are as follows: "Nereidae" (earlier paper) → Ceratoneereis erythraeensis Fauvel (present paper), "Onychocamptus sp." → O. bengalensis (Sewell), and "Halicyclops sp. nov." → H. Ambiguus Kiefer. The cladoceran Daphniopsis pusilla Serventy is recorded from a salinity of 57‰. The significance of resistant stages, and the biological status of closed saline lakes located close to the sea, are discussed.