Fecundity limitation of Calanus helgolandicus, by the parasite Ellobiopsis sp.

The effect of the parasite Ellobiopsis sp., on the fecundityof Calanus helgolandicus and Calanoides carinatus in the Bayof Biscay, was investigated in May 2003. An average of 6.8%of C. helgolandicus females were infected with Ellobiopsis sp.,whereas none of the C. carinatus were found to be infected.An objective method of estimating gonad development was appliedto quantitatively measure the effect of the parasitism on thereproduction of the copepod. Parasitism by Ellobiopsis sp. hasthe potential to reduce the fecundity of C. helgolandicus females.     

A laboratory study of the effect of non-phytoplankton diets on the reproduction of Calanus helgolandicus

The effect of five non-phytoplankton and one phytoplankton dietson reproduction is described for the copepod Calanus helgolandicusand compared to field fecundity estimates. A fecundity increasefollowed ingestion of larvae of the sea urchin Sphaerechinusgranularis (LSU) and the oyster Crassostrea gigas (OYS) by copepodfemales, whereas a decrease followed ingestion of eggs of thecopepods Acartia and Temora spp. (COP), as a function of proteinconcentration in diets. With larvae of the sea urchin Paracentrotuslividus (SSU) and the dinoflagellate Prorocentrum minimum (PM;standard phytoplankton diet), fecundity was identical. Althoughprotein concentrations differed greatly from one food treatmentto the other, mean fecundity values were rather low. For unknownreasons, and despite their very high protein concentrationsin comparison to in situ, none of these diets could improvefemale fecundity or reach maximum egg production rates reportedin C.helgolandicus. Hatching rates were >80%, stable andsimilar with both PM and COP diets. With SSU, LSU and OYS diets,egg viability was lower than in situ and with PM, showing astrong and mild decrease with time with LSU and SSU, respectively.Ingestion of zygotes of the brown alga Fucus spiralis (ZYG)led to the death of females. These results suggest that denseblooms of zygotes of macroalgae and invertebrate embryos andlarvae, occurring in the continental shelf as part of copepoddiets, could have different effects on the demographic responseof C.helgolandicus.     

Egg production and hatching success in the calanoid copepods Calanus helgolandicus and Calanus finmarchicus in the North Sea from March to September 2001

Spatial and seasonal egg production rates (E_r) and egg hatchingsuccess in the copepods Calanus finmarchicus and Calanus helgolandicuswere measured in the North Sea from March to September. Foodavailability was monitored by chlorophyll and protist concentrationsand three size fractions of seston fatty acids. Seasonal andspatial distribution and production differed between the species.Calanus finmarchicus was found only offshore of the 50-m isobath,with decreasing E_r (37–28 eggs female^–1 day^–1)from March to July. Calanus helgolandicus had two abundancepeaks, in spring and autumn, with a low in May during whichtime the highest E_r were observed (38 eggs female^–1 day^–1).At other times, E_r in C. helgolandicus remained lower than inC. finmarchicus (     

Calanus the cannibal

Recent modelling efforts have suggested that cannibalism oneggs and young nauplii is an important factor controlling thepopulation dynamics of Calanus. We measured cannibalistic feedingrates on eggs and nauplii of Calanus helgolandicus in the laboratory.Clearance rates on nauplii were     

Sources of seasonal variability in mesozooplankton aspartate transcarbamylase activity in coastal waters off Plymouth, UK

Some investigators have proposed aspartate transcarbamylase(ATCase) activity as an overall index of mesozooplankton productivity.However, seasonal changes in mesozooplankton species compositionhave never been investigated as a possible source of variationin ATCase activity. In this study, we investigate mesozooplanktoncomposition in terms of (i) developmental stages, (ii) speciesand developmental stages body mass and (iii) species composition,and their relationship to ATCase activity. In controlled laboratoryconditions, ATCase activity variability was closely relatedto changes in somatic growth rate of the copepod Calanus helgolandicus,but was not related to changes in nucleic acid concentrations.It can be argued, however, that the activity of this enzymeis partially involved in copepod somatic productivity, and shouldbe a good index of embryogenesis. In addition, changes in ATCaseactivity were not significantly influenced by variability inmesozooplankton biomass, when investigated both on inter- andintraspecific levels. Finally, when a complete seasonal cyclewas investigated at a fixed station off Plymouth (English Channel),ATCase activity was not correlated with the abundance of anymesozooplankton species apart from copepodites and adult C.helgolandicus.Furthermore, ATCase activity measured both on mesozooplanktonand female C.helgolandicus was significantly correlated (R²= 0.72, n = 33, P < 0.001) throughout the year, apart fromApril. At that particular time of the year, ATCase activitywas in phase with the peak of abundance of copepod eggs andnauplii. It is suggested that mesozooplankton peaks of ATCaseactivity reflect two periods in the life history of the copepod:embryogenesis and terminal moult. We propose further experimentsto test this hypothesis and to promote the development of molecularbiomarkers in order to characterize specific zooplankton metabolicprocesses.     

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.     

Population genetics of drifting (Calanus spp.) and resident (Acartia clausi) plankton in Norwegian fjords

Kaartvedt distinguished between drifting and resident planktonand hypothesized that the latter were distinguished by theirability to maintain their horizontal position in desired habitats(Kaartvedt, 1993). In this study, we examined the populationgenetic consequences of these two lifestyles for copepods infour fjords of western Norway (Lurefjorden, Masfjorden, Sognefjordenand Sørfjorden) and one fjord in eastern Norway (Oslofjorden).Based on DNA sequence variation of a region of mitochondrial16S rRNA, we contrasted population genetic diversity and structurein drifting populations of Calanus spp. with that of residentpopulations of Acartia clausi. With the exception of Sørfjorden(where Calanus spp. were rare), two or three species of Calanusco-occurred in significantly different proportions in the fjords.Based on a 350 base-pair region of mitochondrial 16S rRNA, Calanusspp. varied in molecular genetic diversity, with the highestvalues for C.helgolandicus. There was no evidence of significantgenetic structure of fjord populations for either C.finmarchicusor C.helgolandicus; the population structure of C.glacialiscould not be evaluated as the species was only abundant in Lurefjorden.Acartia clausi was abundant in all five fjords sampled for thisstudy. Molecular genetic diversity of A.clausi, based on a 220bp region of mt 16S rRNA, was within the range of Calanus spp.values. Populations of A.clausi showed significant genetic structure(i.e. haplotype frequencies differed markedly) among the fjords.The results of this study indicated that little exchange (geneflow) occurs between populations of A.clausi in different fjords,and suggested that the populations are long-term residents ofa fjord. In contrast, most Calanus spp. fjord populations maybe replaced periodically, as they drift with currents flowingto and from coastal and fjord environments.     

Food ingestion and digestive transit time in the euphausiid Meganyctiphanes norvegica as a function of animal size

Laboratory experiments with Meganyctiphanes norvegica of differentsizes (7 to 70 mg dry) fed on Artemia salina show that the dailyspecific ingestion rate varies with animal weight accordingto a power law with a negative exponent of -0.58. This relationis used to calculate the production rate of faeces which ishigher in the smaller individuals when expressed as a percentageof animal weight; a comparison of the M. norvegica data withpublished data for Calanus helgolandicus indicates that thisrate is higher for the smaller species. Under the experimentalconditions used the digestive transit time of food in M. norvegicais appreciably shorter in smaller animals (15 minutes versus30 minutes). The data, combined with other data previously obtainedfor the same ipecies, show that the metabolism of active, well-fedindividuals is about three times higher than the standard metabolism.     

Ecologie alimentaire de Cyclothone braueri Jespersen et Taning, 1926 (Gonostomatidae) en mer Ligure, Mediterranee occidentale

Stomach contents of 4557 specimens of Cyclothone braueri wereanalyzed. Specimens were captured between 300 and 900 m depth,during November 1980 through December 1981. Results showed thatthis species is a carnivore that feeds mainly on zooplanktonorganisms, of wide vertical distribution, comprising about 38prey items. Most important preys were Copepods' (80%) and Ostracods(12%). Other minor items were euphausid larvae, amphipods anddecapod crustaceans. Dominant prey species was Pleuromamma gracilis,and in minor proportion, Euchaeta marina, Chiridius poppei,and Calanus helgolandicus. The emptiness coefficient was quitehigh (V = 72.6%), with significant differences (P < 0.05)between sexes: V(males) = 81%, V(females) = 71%; between depths:V(at 400 m) = 63%, V(at 900 m) = 79%, and between seasons: V(autumn)= 80%, V(winter) = 60%. Nous avons analysé les contenus stomacaux de 4557 spécimensde Cyclothone braueri capturés entre 300 et 900 m deprofondeur, pendant la période comprise entre novembre1980 et décembre 1981. Le contenu stomacal montre quele régime alimentaire de cette espéce est carnivoreconstitué par 38 sortes de proies, appartenant fondamentalementaux copépodes (80%) et ostracodes (12%). En mondre proportionon trouvait de larves d'euphausiacés, amphipodes et crustacésdécapodes. L'espèce-proie dominante fut Pleuromammagracilis, suivi de loin par Euchaeta marina, Chiridius poppeiet Calanus helgolandicus. La plupart des espèces proiessont des organismes zooplanctoniques d'une vaste distributionverticale. Le coefficient de vacuité est tres élevé(V = 72.6%), présentant des variations significatives(p << 0.05) en fonction du sexe (V mâles = 81% etV femelles = 71%), de la profondeur de pêche (V = 63%à 400 m et V = 79% à 900 m), et de la saison del'année (V = 80% en automne et V = 60% en hiver).     

Integrating conventional microscopy and molecular analysis to analyse the abundance and distribution of four Calanus congeners in the North Atlantic

Analysis of the demographic structure of Calanus species inthe North Atlantic presents particular difficulties due to theoverlapping spatial distributions of four main congeneric species(Calanus finmarchicus, Calanus helgolandicus, Calanus glacialisand Calanus hyperboreus). These species have similar morphologies,making microscopic discrimination only possible between someof the species at late copepodite or adult stages. However,molecular techniques now offer the possibility of screeningsignificant numbers of specimens and unambiguously identifyingthem to species, regardless of developmental stage. Unfortunately,the processing rate of specimens by molecular methods is stilltoo low to offer a realistic alternative to microscopy for analysisof samples from large field surveys. Here, we outline and testan approach involving the use of molecular methodology in conjunctionwith conventional microscopy to assess the species assignmentof developmental stage abundances of Calanus congeners. Ourstudy has highlighted many important methodological issues.First, it cannot be assumed that the species composition ishomogeneous across the development stages; applying proportionalspecies composition of adults to morphologically undistinguishableearlier development stages can result in error. The second importantconclusion is that prosome length may be a highly unreliablediscriminator of C. finmarchicus and C. glacialis.     

The production and ingestion of faecal pellets by nauplii of marine calanoid copepods

The downward transport of organic matter as zooplankton faecalmaterial is influenced by copepods which fragment, ingest andrecycle some of the pellet contents. Most of this activity hasbeen attributed to the later copepodite stages and the adults,but little is known about the role of nauplii. Stage-relateddefaecation rates during the naupliar development of two speciesof copepod, Calanus helgolandicus and Pseudocalanus elongatus,were quantified in a series of laboratory experiments. The productionof faecal material commenced soon after the appearance of theNIII in both species and increased throughout naupliar development.The causes of the increase were the formation of larger pelletsby later stages in Calanus and an increased rate of productionby Pseudocalanus. Calanus nauplii, when supplied with algalfood at concentrations that would support full naupliar development,ingested or broke up the pellets of the smaller Pseudocalanusspecies at rates of 1.15 pellets nauplius^–1 h^–1This consumption increased to 2.96 pellets nauplius^–1h^–1 when the concentration of algal food was reduced toa limiting level. Pseudocalanus was not able to consume thepellets of Calanus. Ingestion of Pseudocalanus faecal pelletsby Calanus could supply a nutritional benefit to a food-limitednauplius.     

Discontinuite hydrobiologique dans le detroit du Pas-de-Calais

Hydrobiological studies in the Straits of Dover show a differencebetween the characteristics of the French coastal water andthe open sea water. A cruise between Boulogne-sur-mer and Dover(October 15, 1985) confirms the existence of a frontal area(4 miles off the French coast). This area is characterized byan increase of the salinity (1%) and decrease of the suspendedmatter content (from 27 to 20 mg l^–1), of primary production(from 15 to 3 mg C m^–3h^–1) and of chlorophyll aconcentration (from 4.5 to 1.5 mg m^–3). The presence ofdifferent zooplanktonic species in the two water masses alsocharacterizes this discontinuity. Oncaea sp., Corycaeus anglicus,Centropages typicus and Calanus helgolandicus are indicatorspecies of open sea water, while Cyciopina littoralis and ‘Saphirella’are only present in coastal water.     

Comparison of zooplankton sampling performance of Longhurst-Hardy Plankton Recorder and Bongo nets

Data on the abundance and biomass of zooplankton off the northwesternPortuguese coast, separately estimated with a Longhurst–HardyPlankton Recorder (LHPR) and a Bongo net, were analysed to assessthe comparative performance of the samplers. Zooplankton wascollected along four transects perpendicular to the coast, deploymentsalternating between samplers. Total zooplankton biomass measuredusing the LHPR was significantly higher than that using theBongo net. Apart from Appendicularia and Cladocera, abundancesof other taxa (Copepoda, Mysidacea, Euphausiacea, Decapoda larvae,Amphipoda, Siphonophora, Hydromedusae, Chaetognatha and Fisheggs) were also consistently higher in the LHPR. Some of thesedifferences were probably due to avoidance by the zooplanktonof the Bongo net. This was supported by a comparative analysisof prosome length of the copepod Calanus helgolandicus sampledby the two nets that showed that Calanus in the LHPR sampleswere on average significantly larger, particularly in day samples.A ratio estimator was used to produce a factor to convert Bongonet biomass and abundance estimates to equate them with thosetaken with the LHPR. This method demonstrates how results fromcomplementary zooplankton sampling strategies can be made moreequivalent.     

Comparative study of the reproduction of Calanus helgolandicus in well-mixed and seasonally stratified coastal waters of the western English Channel

Field estimates of the production and viability of eggs of thecopepod Calanus helgolandicus were conducted weekly during 1993and 1994 at two fixed stations in the western English Channel.The stations were located in the coastal zone off Roscoff (NWFrance) and Plymouth (SW England). These areas are characterizedby homogeneous and seasonally stratified waters, respectively.In these two different environments, the egg production ratevaried seasonally and was significantly correlated with chlorophylla concentration, but not with surface temperature. Significantcorrelations between fecundity and particulate carbon and nitrogenwere found only off Plymouth. The seasonal pattern of fecunditydiffered between the two sites. Off Plymouth, spawning occurredearlier, lasted longer and was significantly higher than inRoscoff waters. In both localities, fecundity was generallybelow the maximum specific egg production rate (     

Copepod feeding behaviour and egg production during a dinoflagellate bloom in the North Sea

Feeding strategies of copepods were studied during a dinoflagellate-dominated bloom in the North Sea in August 2001. The aim of this study was to evaluate the importance of mesozooplankton grazing as a biological loss factor of harmful algal blooms under natural conditions. Therefore, ingestion, egestion and egg production experiments were performed with the most abundant copepod species Calanus helgolandicus, Temora longicornis and Acartia sp. feeding on the natural phytoplankton community. Dinophysis norvegica and Ceratium furca were the most abundant dinoflagellate species at the time of the experiments. Grazing experiments as well as examination of fecal pellet content revealed C. helgolandicus fed efficiently on D. norvegica. Ingestion rates up to 47 cells female⁻¹ h⁻¹ were measured and a large proportion of the C. helgolandicus fecal pellets contained intact D. norvegica cells. Dinophysis cells were rarely seen in fecal pellets produced by T. longicornis, and never observed in pellets produced by Acartia sp. The ingestion rate of C. furca, which was the dominating Ceratium species, mimicked that of D. norvegica. C. helgolandicus grazed significantly on C. furca (16 cells female⁻¹ h⁻¹), while the ingestion rate of T. longicornis was low and Acartia sp. was not able to graze on C. furca. Egg production experiments revealed that 92% of the C. helgolandicus females produced eggs. The specific egg production rate and the proportion of females producing eggs among T. longicornis were low. This field experiment clearly shows that some copepod species feed efficiently on D. norvegica and C. furca under natural conditions, which may affect the bloom development of these dinoflagellates.     

Potential toxicity of chrysophytes affiliated with Poterioochromonas and related 'Spumella-like' flagellates

The chrysophyte genera Poterioochromonas and Ochromonas andtheir heterotrophic analogons, i.e. the ‘Spumella-like’flagellates, account for a significant and often dominatingfraction of the pelagic nanoplankton. Even though several osmotrophicallyand autotrophically grown strains of Ochromonas and Poterioochromonasare assumed to produce toxins, the potential toxicity has beeninvestigated neither for its association with bacterivorousnutrition nor within the related exclusively heterotrophic ‘Spumella-like’flagellates. We investigated the toxic potential of severalflagellate strains using cultures of flagellates, cell extractsand filtrate of flagellate cultures. The effect on potentialpredators was exemplarily tested for the cladoceran Daphniamagna and the rotifer Platyias sp. All tested heterotrophicand mixotrophic flagellate strains were toxic to zooplanktonat abundances exceeding 10⁴ flagellates mL^–1. For therotifers, survival on any of the flagellate strains was significantlylower than that in the control treatment (P < 0.001) alreadyafter 24 h. We conclude that (i) ‘Spumella-like’flagellates can be toxic to zooplankton, (ii) all tested flagellates,i.e. heterotrophic and mixotrophic flagellates, feeding phagotrophicallycan be toxic to zooplankton and (iii) sublethal effects maybe observed at typical field abundances, even though acute toxicityseems to be restricted to flagellate abundances observed onlyat peak events.     

Toxicity of coastal coccolithophores (Prymnesiophyceae, Haptophyta)

Over the last decade, certain coccolithophores have been thesubject of extensive multidisciplinary research. Several speciesof coccolithophore, belonging mainly to the families Pleurochrysidaceaeand Hymenomonadaceae, inhabit inshore coastal waters where theymay occasionally bloom and hence impact aquaculture resources.The toxicity to Artemia salina larvae of 11 species of coccolithophore(nine coastal and two oceanic members of the order Coccolithales)was tested. For the nine coastal species, tests were conductedwith rapidly growing and stationary phase cultures at a rangeof cellular concentrations and for two different exposure times(24 and 48 h). Five of the coastal species (four in the genusPleurochrysis as well as Jomonlithus littoralis) were foundto be toxic to A. salina nauplii. Allelopathic effects of acell-free filtrate of a culture of a toxic coccolithophore werealso tested on three flagellate microalgal species: Scrippsiellatrochoidea, Tetraselmis sp. and Isochrysis galbana. Negativeeffects of the filtrate on growth rates and motility of S. trochoideaand Tetraselmis sp. were recorded, suggesting that the toxinof the coccolithophore tested could be an exotoxin similar tothat produced by other non-calcifying members of the Prymnesiophyceae.The fact that certain coccolithophores were found to be toxicto invertebrates and were shown to exhibit allelopathic activitycould imply negative effects at different trophic levels incoastal areas.     

棉蚜和七星瓢虫对紫茎泽兰挥发物的行为反应及挥发物化学成分初步分析

田间调查 发现紫茎泽兰Eupatorium adenophorum Spreng上有一定数量的棉蚜Aphis gossypii寄生。从棉蚜是否可为紫茎泽兰的生物防治提供新思路的角度出发,研究了紫茎泽兰挥发性气味物质的化学组成及其对棉蚜和七星瓢虫Coccinella septempunctata行为的影响。棉蚜选择性试验结果表明：紫茎泽兰饲养的棉蚜对紫茎泽兰的趋向率为62.5%,对棉花的趋向率为37.5%。棉花饲养的棉蚜对紫茎泽兰的趋向率为30%,对棉花的趋向率为70%。在七星瓢虫对感染蚜虫植株的选择性实验中,七星瓢虫对感染蚜虫的紫茎泽兰植株气味趋向率为29.2%,对感染蚜虫的棉花植株气味趋向率为70.8%;七星瓢虫对除去植株的两种蚜虫气味选择率没有显著差异,对取食紫茎泽兰的蚜虫气味选择率为46.7%,对取食棉花植株的蚜虫气味选择率为53.3%。通过GC-MC分析了紫茎泽兰挥发性化学物质的组分及相对含量,其主要挥发物的成分是α-蒎烯、莰烯、β-蒎烯、2-蒈烯和α-水芹烯等。     

Cyanidium caldarium as a bridge alga between Cyanophyceae and Rhodophyceae: Evidence from immunodiffusion studies

The primer-independent phosphorylase isozyme, a₂, of Cyanidiumcaldarium was used for immunization of rabbits. The immune serumwas tested against pure a₂ isozymes from blue-green, red, andgreen algae. Double immunodiffusion in agar indicated that therewas structural similarity in the isozyme from Cyanidium caldarium,the blue-green algae, Oscillaloria princeps, Pleclonema nostocorumand the red alga, Rhodymenia pertusa. Complete fusion of theprecipitin lines was obtained with these algae. However, onlypartial fusion was observed with the a₂ isozymes from Chlorophyceaesuch as Chlorella pyrenoidosa and Spirogyra setiformis. Spurformation on the precipitin lines occurred when the isozymesfrom these algae were tested against the immuneserum. The results were interpreted as indicative of the possible transitionstatus of Cyanidium caldarium between prokaryotic blue-greenalgae and eukaryotic red algae. It would appear that the Chlorophyceaeevolved along different lines from Cyanophyceae than did theRhodophyceae. (Received November 25, 1975; )