Immunohistochemical mapping of histamine, dopamine, and serotonin in the central nervous system of the copepod Calanus finmarchicus (Crustacea; Maxillopoda; Copepoda)

Calanoid copepods constitute an important group of marine planktonic crustaceans that often dominate the metazoan biomass of the world’s oceans. In proportion to their ecological importance, little is known about their nervous systems. We have used immunohistochemical techniques in a common North Atlantic calanoid to localize re-identifiable neurons that putatively contain the biogenic amines histamine, dopamine, and serotonin. We have found low numbers of such cells and cell groups (approximately 37 histamine pairs, 22 dopamine pairs, and 12 serotonin pairs) compared with those in previously described crustaceans. These cells are concentrated in the anterior part of the central nervous system, the majority for each amine being located in the three neuromeres that constitute the brain (protocerebrum, deutocerebrum, and tritocerebrum). Extensive histamine labeling occurs in several small compact protocerebral neuropils, three pairs of larger, more posterior, paired, dense neuropils, and one paired diffuse tritocerebral neuropil. The most concentrated neuropil showing dopamine labeling lies in the putative deutocerebrum, associated with heavily labeled commissural connections between the two sides of the brain. The most prominent serotonin neuropil is present in the anterior medial part of the brain. Tracts of immunoreactive fibers of all three amines are prominent in the cephalic region of the nervous system, but some projections into the most posterior thoracic regions have also been noted.     

Temperature compensation in the escape response of a marine copepod, Calanus finmarchicus (Crustacea)

Calanus finmarchicus, the dominant mesozooplankter of the North Atlantic, is an important food source for many fishes and other planktivores. This species, which has limited diel vertical migration, depends on its fast-start escape response to evade predators. It has myelinated neuronal axons, which contribute to its rapid and powerful escape response. The thermal environment that C. finmarchicus inhabits ranges from below 0 degrees C to 16 degrees C. Previous studies have shown that respiration, growth, and reproductive rates are strongly dependent on temperature, with Q10 > 2.5. A comparable dependence of the escape response could place the animal at higher risk for cold-compensated predators. Our work focused on the temperature dependence of the behavioral response to stimuli that mimic predatory attacks. We found that in contrast to other biological processes, all aspects of the escape response showed a low dependence on temperature, with Q10 values below 2. This low temperature dependence was consistent for escape parameters that involved neural as well as muscle components of the behavioral response. These findings are discussed in the contexts of the predator-prey relations of copepods and the thermal dependence of behavior in other taxa.     

Susceptibility to ultraviolet radiation in Calanus finmarchicus and Lepeophtheirus salmonis and the adaptive value of external filtering (Crustacea: Copepoda)

Copepods were exposed to UVB with a spectral irradiance maximumat 313 nm and additional visible light. In the holopelagic Calanusfinmarchicus, with a carotenoid concentration of 0.85 µgmg^-1, the LD₅₀ dose was 29 kJ m^-2 whereas in the parasitic copepodLepeophtheirus salmonis the LD₅₀ was 84 kJ m^-2. The abilityto photorepair was demonstrated for both species. The survivaldata were Weibull distributed, and this result is discussedrelative to a mechanistic ‘Weibull model’. Attenuationof UVB (306 nm) was measured in the inner Oslo fjord (K_d = 3.9m^-1). The adaptive significance of behavioural avoidance isassessed in model simulations; the results of the survival experimentsare used in connection with the Morowitz formula. Two caseswere compared; when Calanus was assumed incapable of activeexternal filtering the specimens would be safe if the depthof the mixed layer was deeper than 7 m in the inner Oslo fjord,however, with the ability of behavioural avoidance, Calanuswould be protected if they avoided the upper 1 m. The adaptivevalue associated with behavioural avoidance of toxic radiation,and the implications relative to vertical migration are discussed.     

The Yellow Sea Cold Bottom Water--an oversummering site for Calanus sinicus (Copepoda, Crustacea)

The vertical distribution and stage-specific abundance of Calanussinicus were investigated on three key transects in the southernYellow Sea and the northern East China Sea in August 1999. Theresults showed that in summer C. sinicus shrank its distributionarea to the central cold (     

The demography of Calanus finmarchicus (Copepoda: Calanoida) in the Middle Atlantic Bight, USA, 1977-2001

The spatial distribution and annual cycle of abundance for thelate-stage copepodites of the calanoid copepod Calanus finmarchicusare described for the shelf and slope waters of the Middle AtlanticBight (MAB), a subregion of the US Northeast large marine ecosystem.Samples were collected with bongo nets from 1977 to 2001 onbroad-scale surveys of the region and from a continuous planktonrecorder (CPR) towed at 10-m depth along a route that traversedthe area. The copepod’s abundance in shelf waters increasedrapidly in early spring and reached maximum levels in May–June.It declined slowly thereafter, until a minor secondary pulseoccurred in late autumn, which was followed by the annual winterlow. Slope water abundance of C. finmarchicus peaked in Apriland was virtually absent there at 10-m depth from July throughthe following February. The two samplers, both portrayed similarhigh interannual abundance variability with no long-term trendevident for the 25-year period. Cluster analysis pinpointedthree shelf areas with similar abundance patterns, one of whichwas a region of high density located in the northeastern offshorewaters. Evidence is presented that indicates the source of thishigh abundance is likely from the populations that overwinterin deep water basins of the Gulf of Maine (GOM). The copepod’sinterannual abundance variability was found to be negativelycorrelated with water temperature and unrelated to fluctuationsof the North Atlantic oscillation (NAO) index.     

Effect of the parasitic dinoflagellate Ellobiopsis chattoni (Protozoa: Mastigophora) on the winter mortality of the calanoid copepod Calanus finmarchicus (Crustacea: Copepoda) in the Norwegian Sea

We studied the effects of the parasitic dinoflagellate Ellobiopsis chattoni on the winter mortality of natural population of the calanoid copepod Calanus finmarchicus in the Norwegian Sea (materials was collected in March-April 1989 and September 1990). Dinoflagellate infection occurred during autumn (the infection rates of copepods with E. chattoni was 15%, as average). Average mortality rate in C. finmarchicus was about 0.08% per day, or about one-tenth of total mortality in winter period.     

Physiology and population structure of Calanus finmarchicus (Copepoda: Calanoida) during a Lagrangian tracer release experiment in the North Atlantic

A population of Calanus finmarchicus was followed in the opensea for a period of 10 days at the end of June 1996 using atracer release method. Gut fluorescence, egg production, carboncontent and stage specific abundance, together with phytoplanktonconcentration and composition, were measured during this period.Chlorophyll levels were less than 1 µg l^–1 and thephytoplankton population was dominated by coccolithophorids.Gut fluorescence decreased during a period with strong winds,whereas egg production remained constant. Estimated phytoplanktoningestion was too low to cover egg production requirements.However, the microzooplankton concentration seemed to be highenough to complement phytoplankton ingestion, enabling egg productioncarbon requirements to be covered. C/N ratios of adult femalesand stage CV were low, indicating low levels of lipid storage.The population was dominated by stage CIV, but shifted to adominance of younger stages during the study. Mortality calculatedfrom population structure indicates that higher death ratesoccurred at stage CV.     

The occurrence of Calanus finmarchicus (Gunnerus) and Calanus helgolandicus (Claus) in the western Irish Sea

The seasonal abundance of Calanus finmarchicus and Calanus helgolandicusin the North Channel and stratified region of the western IrishSea is reviewed using data collected between 1992 and 1996.Both species occur in the western Irish Sea, but were more abundantin the stratified region during spring. Increased abundanceduring May/June was attributed to an increase in copepoditestages. Calanus helgolandicus dominated in both regions, exhibitingspring and autumn peaks in abundance in the stratified region.It is argued that the presence of ripe females and naupliarstages in the stratified region is evidence of an in situ breedingpopulation, rather than advection of individuals from populationcentres outside the Irish Sea. The lack of geographical separationof the two species in the western Irish sea, and reports thatboth species occur in the Celtic Sea and Malin Shelf, limitthe use of either species as indicators of exchange processesbetween the Irish Sea and neighbouring waters.     

Local variations in size and activity among Calanus finmarchicus and Metridia longa (Copepoda, Calanoida) overwintering on the west coast of Norway

Vertical net hauls were taken at thirteen stations between latitude6008'N – 6120'N and longitude 0304'E – 0700'Ein late November 1980. Size and activity characteristics ofCalanus finmarchicus and Metridia longa were studied. Significantdifferences were noted between C. finmarchicus from differentstations. Average body length, dry weight, protein and lipidcontents, gonad development, and ainylase and trypsin activitiesvaried but average gut fullness and trypsin/amylase ratio appearedconstant. M. longa from different stations showed significantdifferences in average body length, dry weight, protein content,amylase and trypsin activities and gut fullness, but there wereno apparent variations in lipid content and trypsin/ainylaseratio. Those animals inhabiting the most seaward station tendedto show the most specific local charactenstics. M. longa hadconsistently lower lipid proportion with higher gut fullnessand digestive-enzyme activities than C. finmarchicus. The resultstherefore indicate that C. finmarchicus had assumed a winterstate of low activity with dependence on stored energy, whileM. longo relied more upon utilization of available food.     

Proteomic fingerprinting enables quantitative biodiversity assessments of species and ontogenetic stages in Calanus congeners (Copepoda,Crustacea) from the Arctic Ocean

Species identification is pivotal in biodiversity assessments and proteomic fingerprinting by MALDI-TOF mass spectrometry has already been shown to reliably identify calanoid copepods to species level. However, MALDI-TOF data may contain more information beyond mere species identification. In this study, we investigated different ontogenetic stages (copepodids C1–C6 females) of three co-occurring Calanus species from the Arctic Fram Strait, which cannot be identified to species level based on morphological characters alone. Differentiation of the three species based on mass spectrometry data was without any error. In addition, a clear stage-specific signal was detected in all species, supported by clustering approaches as well as machine learning using Random Forest. More complex mass spectra in later ontogenetic stages as well as relative intensities of certain mass peaks were found as the main drivers of stage distinction in these species. Through a dilution series, we were able to show that this did not result from the higher amount of biomass that was used in tissue processing of the larger stages. Finally, the data were tested in a simulation for application in a real biodiversity assessment by using Random Forest for stage classification of specimens absent from the training data. This resulted in a successful stage-identification rate of almost 90%, making proteomic fingerprinting a promising tool to investigate polewards shifts of Atlantic Calanus species and, in general, to assess stage compositions in biodiversity assessments of Calanoida, which can be notoriously difficult using conventional identification methods.     

On the ecology of marine cyclopoid copepods (Crustacea, Copepoda)

The goal of these studies was to improve our understanding ofhow Oithonidae and Oncaeidae can exist in nearly every partof the ocean. In particular, it was intended to obtain quantitativeinformation on reproduction rates and the longevity of adultfemales, and on feeding and growth rates of Oncaeidae. Whenfeeding at relatively high food levels, early copepodids ofOncaea mediterranea ingested     

Anomalies morphologiques chez le genre Acartia (Crustacea, Copepoda): description et essai de quantification

We have found morphological anomalies in the fifth pair of thoraciclegs of female Acartic clausi and A. discaudata, sampled inthe harbour at Dunkirk (France), in the eastern English Channeland in the North Sea. The percentage of anomalies in A. clausi(<1%) is not significantly different between polluted andnon-polluted sites. The frequency of anomalies is on the otherhand clearly higher in A. bilfilosa (>20%) than in A. clausi.     

Molecular phylogeny of the Calanoida (Crustacea: Copepoda)

The order Calanoida includes some of the most successful planktonic groups in both marine and freshwater environments. Due to the morphological complexity of the taxonomic characters in this group, subdivision and phylogenies have been complex and problematic. This study establishes a multi-gene molecular phylogeny of the calanoid copepods based upon small (18S) and large (28S) subunits of nuclear ribosomal RNA genes and mitochondrial encoded cytochrome b and cytochrome c oxidase subunit-I genes, including 29 families from 7 superfamilies of the order. This analysis is more comprehensive than earlier studies in terms of number of families, range of molecular markers, and breadth of taxonomic levels resolved. Patterns of divergence of ribosomal RNA genes are shown to be significantly heterogeneous among superfamilies, providing a likely explanation for disparate results of previous studies. The multi-gene phylogeny recovers a monophyletic Calanoida, as well as the superfamilies Augaptiloidea, Centropagoidea, Bathypontioidea, Eucalanoidea, Spinocalanoidea and Clausocalanoidea. The phylogeny largely agrees with previously-published morphological phylogenies, including e.g., enlargement of the Bathypontioidea to include the Fosshageniidae.     

Energy budget of the female harpacticoid Tisbe carolinensis (Copepoda,Crustacea)

Partitioning of the ingested energy in harpacticoid Tisbe carolinesis was investigated with ¹⁴C labelled diatom Cylindrotheca sp. (Strain N-1) as food source under laboratory conditions (salinity 30 ppt, 24 ± 1.5°C). Over a 24 hr period, egg sacs and fecal pellets produced per T. carolinesis were 0.64 and 1.19, respectively. Radioactivity measured in the body accounted for 49.1% of the ingested radioisotope, whilst 42.3% of the energy was channneled into reproduction. Respiration and excretion took up 4.9% of the energy and the rest, 3.7%, went into fecal pellets.