The calanoid copepods of the Nile system

At least 11 or 12 calanoid taxa occur in the Nile system. One species is typical of the river and of Lake Chad (Th. galebi); two are restricted to Lake Victoria (Th. galeboides, T. stuhlmanni), but both might be only subspecies to more widespread species. One is restricted to Lakes Edward and George (T. worthingtoni) but is a little known species. No calanoids are on record from Lakes Albert and Kyoga, while the species reported from Lake Turkana (T. banforanus) is out of range, and almost certainly represents an erroneous record. Among the remaining species, four are East-African, ranging from the southern tip of the continent to the Ethiopian plateau and the Nile valley (P. schultzei, Th. mixtus, T. kraepelini, T. cf orientalis), while two are Sahelian species that span Africa from east to west (M. mauretanicus, T. processifer et ssp.).Two new synonyms are introduced. One new subspecies (T. processifier friedae) is described from the Ethiopian plateau. It is suggested that Tropodiaptomus orientalis (Brady, 1886), the type species of its genus, should not be considered a nomen dubium, but should be redescribed on its type female(s) and on topotypical males from Sri Lanka.     

The lipid biochemistry of calanoid copepods

Calanus species, particularly those in high latitudes, can accumulate large oil reserves consisting predominantly of wax esters. These wax esters consist predominantly of 16:0, 20:1 (n–9) and 22:1 (n–11) fatty alcohols, mainly formed de novo by the animals from non-lipid dietary precursors, esterified with various fatty acids that are often polyunsaturated fatty acids and largely of dietary, phytoplanktonic origin. Wax ester formation is maximal in copepodite stages IV and V. The lipids are elaborated not primarily for buoyancy regulation but as a source of metabolic energy during overwintering, particularly for reproduction. Large quantities of wax esters are utilised for gonadal development when stage V copepodites mature to females. Development of stage V copepodites to males is not accompanied by wax ester utilisation but males consume large amounts of these lipids in physical activity during reproduction. The role of wax esters in the life history of calanoids is illustrated with particular reference to a comparison of Calanus finmarchicus and Metridia longa in Balsfjord, northern Norway.     

Mobiline peritrich riders on Australian calanoid copepods

Calanoid copepods from billabongs near Wodonga, Victoria, Australia were found to be infested with a disc-shaped mobiline peritrich ciliate belonging to the genus Trichodina. Biometrical data, including mean body diameter (43.6 m), mean adhesive disc diameter (35.9 m), mean denticle ring diameter (20.1 m), modal denticle number (17), modal number of radial pins per denticle (9), and denticle shape and dimensions, indicate that the species is T. diaptomi Basson & Van As (1991). This is the first record of T. diaptomi from Australasia. Adults of Boeckella fluvialis and B. minuta were infected, but adult Calamoecia lucasi were not. Levels of infestation were higher on B. fluvialis (67.5% of females, 54.5% of males) than B. minuta (47.4% of females, 33.3% of males). Mean numbers of Trichodina per adult B. fluvialis were 7.68 (range 0–78) for females and 4.06 (range 0–43) for males, and differed significantly between sexes. Although calanoid copepods were present in the plankton from January to early December 1991, Trichodina infestations occurred during October and November only, peaking during late November just before the copepods disappeared from the plankton. Whether the infestation was a cause of the copepod decline, developed because the copepods were rendered susceptible to infection by some other cause, or was determined by physical and/or chemical environmental factors is unknown.     

Aspects of mating, reproduction, and co-occurrence in three freshwater calanoid copepods

SUMMARY. 1. We examined the seasonal distributions and mating behaviour of Epischura lacustris, Diaptomus minutus and Diaptomus oregonensis to evaluate several proposed mechanisms for reproductive isolation. There was no divergence in onset of maturity or timing of breeding periods between sympatric diaptomid populations; size displacement between co-occurring diaptomid species did not result in concomitant reduction in mating frequency between heterospecific pairs in the laboratory.
2. Divergence in mating behaviour was supported by observations that, in conspecific mating experiments, males of both diaptomid species discriminated between females bearing ripened ovaries (gravid) and those that did not (non-gravid), and that, in heterospecific trials, males either mated indiscriminantly with all females, or engaged in mating very infrequently.
3. In mating experiments with Epischura. males did not discriminate between gravid and non-gravid females, but mated exclusively with virgins of a specific relative size. Divergence in timing of breeding seasons between Epischura and the two diaptomid species suggests that even if mating between genera is possible, it does not occur often in nature.
4. We discuss the adaptive significance of different reproductive strategies of these three copepods and speculate on mechanisms that allow for coexistence of the closely related taxa in nature.     

Colonization of the pelagic realm by calanoid copepods

The evolution of calanoid copepods probably extends back into the mid-Paleozoic. Environmental change from the Paleozoic through to the Tertiary is reviewed. Turbidity, water clarity, oxygen, pelagic primary production, and tectonically induced changes in the morphology of the oceans are probably all important drivers of calanoid evolution and their invasion of the pelagic realm. Current views of the phylogeny of the Calanoida are presented as well as a review of some recent work on metabolic potential, female genital system, and nervous system. It is hypothesized that ancestors of the Arietelloidea and Diaptomoidea invaded the water column in the Devonian at a similar time to the Ostracoda and that the ancestors of the Calanoidea–Clausocalanoidea, with their myelinated axons, arose in the Permian during the major deep ventilation of the ocean. Present day distributions of some Diaptomidae, Centropagidae, and Calanidae suggest that these families successfully came through the Jurassic/Cretaceous expansion of the oxygen minimum zone and the K-T boundary event. Some Arietelloidea and Clausocalanoidea became secondarily benthic and may have survived the K-T boundary event in this environment. It is postulated that some Clausocalanoidea reinvaded the water column (e.g. Clausocalanidae, Aetideidae, Phaennidae, Scolecitrichidae) in the Tertiary after finding refuge in deep, low oxygen water away from the sea surface. It is possible that these hypotheses may be testable using genetic information in the near future.     

Sublethal effects of three ectoparasites on fish

Vulnerability to predation, resistance to high temperature, weight-length relationships, and fecundity were compared for fish with and without or with light and heavy infestations of three ectoparasites. The fish and parasites were fathead minnow ( Pimephales promelas ) with anchor worm ( Lernaea cyprinaceae); brook trout ( Salvelinus fontinalis ) with gill lice ( Salmincola edwardsii); and yellow perch ( Perca flavescens ) with black-spot ( Neascus of Crassiphiala bulboglossa). The only sublethal effect found was that of gill lice, which reduced resistance of brook trout to high temperature. None of the three ectoparasites increased vulnerability offish to predation by piscivorous fish.     

Perceptive performance and feeding behavior of calanoid copepods

The goal of this study was to determine variables associatedwith calanoid feeding behavior, and thus, to improve our understandingof the basics of calanoid feeding rates. These variables includedperiods and frequency of appendage motion, rates of cell clearance,distance at which a copepod first reacts to a cell which iseventually captured, and rate of water flow through the areacovered by the motions of a copepod's feeding appendages. Theeffects of these variables on feeding rates were determinedfor copepodids and adult females of the calanoid copepod Eucalanuspileatus at phytoplankton concentrations covering the rangeencountered by this species on the south-eastern shelf of theUSA. Our results indicate that the distance at which E.pileatusperceives phytoplankton cells increases {small tilde}2-foldas food concentrations decrease from 1.0 to 0.1 mm³ l^–1.These results lead us to hypothesize that this is due to increasedsensitivity of chemosensors on the copepods' feeding appendages.This 2-fold increase in perceptive distance amounts to a near4-fold increase in perceived volume which is close to the 6-foldincrease in volume swept clear (VSC) from 1.0 to 0.1 mm³ l^–1of Thalassiosira weissflogii. We assume that the increases inVSC by planktonic copepods, when food levels are below satiation,are largely a function of the sensory performance of the individualcopepod.     

Population dynamics of exploited cultures of calanoid copepods

En laboratoire, cultures des copépodes calanoides,Acartia tonsa (Dana) etEurytemora affinis (Poppe) étaient exposées à différents taux de déprédation, allant de 10 à 24% des populations par jour, suivant les espèces et les températures. Les densités des populations variaient considérablement, ce qui provenait probablement des évènements intermittents (la nourriture et les récoltes) habituelles de la procédure en laboratoire. La bibliographie, ainsi que mes propres observations avancent deux mécanismes homéostatiques. Le cannibalisme aide à régulariser la population d'A. tonsa quand la nourriture devient rare par suite de la haute densité des populations. La proportion des femelles adultes augmente durant les densités basses des populations d'A. tonsa. La proportion sexuelle génésique de ces populations était de 1:1. L'augmentation proportionnelle des femelles paraisse provenir de mâles génotypiques changeant en femelles phénotypiques au cours de leur croissance. Cette proportion plus élevée des femelles augmente le taux de la reproduction quand les populations étaient peu denses.     

Escape reaction performance of myelinated and non-myelinated calanoid copepods

Calanoid copepods from seven families in three superfamilies were exposed to a controlled near-field hydrodynamic stimulus and their escape reactions were recorded using high-speed videographic techniques. Copepod species have two distinct mechanisms for increasing conduction speed of neural signals: larger diameter nerve axons and insulated axons, i.e., myelination. Myelinated axons have been found in certain species of the more recently-evolved calanoid superfamilies. Copepod representatives from these superfamilies were expected to have shorter response latencies than species from more ancestral superfamilies due to the increased conduction speed of nerve impulses in myelinated neurons. Using frame-by-frame playback and computerized motion analysis techniques, response latency, jump speed, and acceleration were measured. Kinetic performance of copepods was highly variable, with mean escape speeds ranging between 100-250 mm s^− 1 and accelerations of 9-230 m s^− 2. Minimum behavioral response latencies of 2 ms were recorded for both myelinated and non-myelinated calanoids. There was no significant difference between the response latencies of copepods from the myelinated and non-myelinated superfamilies. Furthermore, no relationships were found between copepod latency and size for either myelinated or non-myelinated species. Previous research may suggest that myelin may shorten the response latencies of certain calanoid species. However, our results show that non-myelinated copepods are also capable of responding rapidly, within as few as 2 ms, to hydrodynamic stimuli and produce similar kinetic performance to myelinated species. The main advantage of myelination over giant nerve axons is their more efficient transfer of nerve impulses resulting in a metabolic energy savings. Although this energetic reward would be important for copepods in food-limited environments, for coastal copepods, in food-rich habitats, either mechanism is a viable solution.     

Photophobic responses of calanoid copepods: possible adaptive value

A genual pattern of photophobic responses has been observedwhich differs for calanoid copepods from freshwater, estuarineand oceanic environments. Using a video-computer system formotion analysis, the photophobic responses of light and darkadapted calanoid copepods were compared. Dark-adapted copepodswere exposed to 600 ms flashes of dim blue light at 5 s intervalswhich simulated the flashes of biolumines-cent marine zooplankton.Light-adapted copepods were exposed to 600 ms intervals of darknessat 5 s intervals to simulate the shadows of organisms passingoverhead. Four species of coastal marine copepods (Acartia hudsonica,Centropages hamatus, Pseudocalanus minutus and Temora longicornis)all showed photophobic responses to both flashes and shadows.These responses may have adaptive value to the copepods sincethey live in an environment with predators that are bioluminescentat night and cast shadows on their prey during the day (e.g.ctenophores and cnidarian medusae). Two species of oceanic copepods(Euchaeta marina, Pleuromamma abdominalis) showed strong photophobicresponses to flashes but no response to shadows. This may correspondto the abundance of bioluminescent predators on copepods inthe oceanic environment (fish, ctenophores, siphonophores, etc.)and their lack of exposure to the shadows of predators, sinceboth these species are rarely found in the euphoric zone duringthe day. Two species of freshwater copepods (Diaptomus sanguineus,Epishwa massachusettsensis) showed no similar photophobic responseto flashes of light. This lack of startle response may relateto the lack of bioluminescence in the freshwater environment.Freshwater copepods showed a weak photophobic response to shadows.The adaptive value of this behavior is unclear, however, sincethe responses seem to be too weak to function for escape, andthe dominant predators large enough to cast shadows (fish) tendto approach their prey laterally. ¹Present address: Marine Science Institute, University of Texasat Austin, Port Aransas, TX 78373–1267, USA     

Mediterranean marine copepods: basin-scale trends of the calanoid Centropages typicus

The Mediterranean Sea is located in a crossroad of mid-latitude and subtropical climatic modes that enhance contrasting environmental conditions over both latitudinal and longitudinal ranges. Here, we show that the large-scale environmental forcing is reflected in the basin scale trends of the adult population of the calanoid copepod Centropages typicus. The species is distributed over the whole Mediterranean basin, and maximal abundances were found in the north-western basin associated to oceanic fronts, and in the Adriatic Sea associated to shallow and semi enclosed waters. The peak of main abundances of C. typicus correlates with the latitudinal temperature gradient and the highest seasonal abundances occurred in spring within the 14–18°C temperature window. Such thermal cline may define the latitudinal geographic region where C. typicus seasonally dominates the >200 μm-sized spring copepod community in the Mediterranean Sea. The approach used here is generally applicable to investigate the large-scale spatial patterns of other planktonic organisms and to identify favourable environmental windows for population development.     

The distribution of calanoid copepods in the plankton of Wisconsin Lakes

Zooplankton communities from 499 lakes were examined for calanoid copepod species. Limnocalanus macrurus and Senecella calaloides are confined to Lakes Michigan, Superior and one inland lake each. Eurytemora affinis has recently become established in the coastal waters of Lakes Michigan and Superior. Epischura lacustris is present in the summer plankton of a wide variety of lake types. Aglaodiaptomus leptopus is sensitive to fish predation and confined to small lakes without fish. Leptodiaptomus ashlandi is restricted to Lakes Michigan and Superior, but L. sicilis is also found in some inland lakes. Leptodiaptomus minutus is a boreal species found mostly in lakes of the far north. Skistodiaptomus oregonensis is the most commonly occurring calanoid and seems well adapted to lakes of the meso-to low eutrophic types. Skistodiaptomus pallidus is also generally distributed throughout the state, but less common than oregonensis and adapted to more eutrophic lakes. Leptodiaptomus siciloides and A. clavipes are western species, adapted to eutrophic lakes, which are expanding their ranges eastward, aided by cultural eutrophication.     

Population dynamics of calanoid copepods in the subtropical mesohaline Danshuei Estuary (Taiwan) and typhoon effects

We studied the populations of the dominant calanoid copepods Pseudodiaptomus annandalei and Acartia spp. in the mesohaline Danshuei Estuary for two successive springs and summers. We analyzed environmental factors (i.e., temperature, salinity, chlorophyll a, light attenuation coefficient, and suspended particulate matter) and the population densities and structures at the surface and near the estuarine bed. The population of P. annandalei dominated the zooplankton community from surface to bottom, except during a medusa bloom in 2009 and during the post-typhoon period, when Acartia spinicauda dominated. The relationships between environmental factors and densities differed between and within populations of P. annandalei and Acartia spp. We concluded that the primary determinants of the P. annandalei population are predation and the typhoon-related freshwater runoff, which can strongly influence the copepod succession in this part of the estuary.     

Decreased cupric ion uptake as the mechanism for cupric ion resistance in Escherichia coli

Abstract Plasmid-encoded copper (Cu²⁺) resistance in Escherichia coli was due to decreased uptake of Cu²⁺. The Cu²⁺-resistant E. coli Rtsl strain contained a 60 MDa plasmid which is known to encode for both Cu²⁺ and kanamycin resistance. A plasmid-free derivative of the same organism exhibited a greater uptake of Cu²⁺, and sensitivity to Cu²⁺ in both respiration and growth studies than the E. coli Rtsl strain.     

Spatio-temporal distribution and production of calanoid copepods in the central Baltic Sea

The aim of our study was the exploration of species-specificdistribution and production patterns of dominant copepods inthe Central Baltic Sea (Bornholm Basin). Spatio-temporal distribution,egg and secondary production were studied by means of net-samplingand egg production experiments from April to August 1999. Verticaland horizontal distribution patterns appeared to be linked witheach other and were primarily species-dependent. Both Acartiaspp. and Temora longicornis preferentially inhabited the upper30 m of the water column and the shallower marginal regionsof the Bornholm Basin. In contrast, the C4–5 and C6 ofPseudocalanus spp. preferentially inhabited the halocline region(50–70 m) and the deep central part of the area. Observeddifferences in horizontal distribution among these three copepodsappear to result from different depth preferences and depth-dependentwater circulation patterns. Egg production rates (EPR) clearlyexhibited seasonal differences with maximum EPR in May and minimumEPR in July. Mean EPR was significantly different between species,being highest in Acartia spp. and lowest in Pseudocalanus spp.The variability in EPR was related to differences in hydrographyand modelled food environment.     

Mass density contrast in relation to the feeding currents in calanoid copepods

Theoretical analyses show that positively buoyant copepods areable to generate feeding currents by adopting upside-down bodypositions and pushing water upward. Thus, the excess buoyancyacting on the copepods will be balanced and cone-shaped feedingcurrents generated to transport water to the capture areas.The intensities of the feeding currents, which can be measuredin the present modeling study by calculating the volumetricflux going through the capture areas, are proportional to themass density contrasts between the copepods and the ambientseawater. The mass density contrasts may vary spatially andtemporally depending on copepod body contents and on the propertiesof the seawater immediately surrounding them. We focus on thecase where the mass density contrast between a wax ester-richcopepod and its ambient seawater can vary strongly with depthbecause wax esters are more compressible and 6–10 timesmore thermally expansible than seawater. These theoretical analysesshow that the intensities of the feeding currents generatedby wax ester-rich copepods vary strongly with depth. Our conclusionsfrom these theoretical analyses need to be tested by directobservations. This paper is one of six on the subject of the role of zooplanktonpredator–prey interactions in structuring plankton communities.     

Foraging tactics and prey-selection patterns of omnivorous and carnivorous calanoid copepods

The foraging tactics and prey-selection patterns of omnivorous and carnivorous calanoid copepods are reviewed. Calanoid foraging tactics are envisioned as falling along several closely coupled continua reflecting swimming behavior, feeding behavior, and dietary habit. The consequences of these foraging tactics on prey-selection patterns are explored in the context of a graphical model. It is hypothesized that the prey-selection patterns of calanoid copepods are determined, to a large extent, by calanoid foraging tactics and the size relationships of predator and prey.     

Birth, growth and death rates for enclosed populations of calanoid copepods

Rates of birth, growth and death are inferred for enclosed populationsof the marine copepods Pseudocalanus elongates, Acartia clausiand Temora longicomis. The rates are determined by fitting apopulation dynamics model to the time series of developmentalstage abundances observed over 87 days in four 310 m³ enclosures.Two enclosures were treated with ‘produced’ waterfrom North Sea oil production platforms and two were untreatedcontrols. The pollutant mainly affected recruitment to the populations.Development times varied considerably between enclosures, thoughnot in any apparent relation to the pollutant. Mortality wasmost strongly related to the population size of herring larvaeintroduced to all four enclosures. Levels of secondary productionderived from the model were compared with those calculated directlyfrom population densities.     

Feeding behavior of newly settled winter flounder (Pseudopleuronectes americanus) on calanoid copepods

Field and laboratory investigations were conducted to examine feeding by newly settled winter flounder (Pseudopleuronectes americanus) on two co-occurring calanoid copepods, Eurytemora affinis and Acartia hudsonica. During the spring, these prey are present when winter flounder initiate their demersal lifestyle in estuaries of the northeastern United States. Epibenthic zooplankton were collected concurrently with winter flounder in the Navesink River estuary, NJ, in May 1998 and 1999. Although both calanoid species were in the estuary during the 2-year survey, E. affinis was consumed nearly to the exclusion of A. hudsonica by newly settled winter flounder. Annually, E. affinis and A. hudsonica had similar size distributions in field collections, indicating that species choice was not size selective. However, when preying on E. affinis, winter flounder preferred the larger sized organisms. In single species laboratory experiments, E. affinis and A. hudsonica were consumed equally by newly settled winter flounder (19-23 mm TL), but there were more strikes made toward E. affinis. Despite the lower catch efficiency, E. affinis was selected over A. hudsonica when the prey species were offered together in equal numbers. The selection for E. affinis over A. hudsonica by newly settled winter flounder may be the result of behavioral and/or morphological differences in the prey species.