Postembryonic development ofParalabidocera antarctica (I. C. Thompson) (Copepoda,Calanoida) from the fast ice near Syowa Station,Antarctica

Six nauplius and five copepodid stages as well as adults ofParalabidocera antarctica (I. C. Thompson, 1898) (Copepoda:Calanoida) are described based on specimens obtained from fast ice and collected by a plankton net near Syowa Station (69°00 S, 39° 35 E), Antarctica. The adult male and female are redescribed in detail. Nauplius stages ofP. antarctica are very similar to the previously describedAcartia species. Sexual dimorphism becomes apparent from copepodid IV onwards in the morphology of antennule and leg 5. The copepodid stages of this species retain certain characteristics not only of Acartiidae but also of Pontellidae and Parapontellidae.     

A calanoid copepod Gladioferens imparipes,holding to surfaces

Gladioferens imparipes, a calanoid copepod from estuaries in Western Australia, displays behaviour and associated morphology which is unusual among calanoids. Adult and copepodid stages make temporary attachment to underwater surfaces using fine hair sensillae on the surface of the prosome. A clear pattern can be seen in the number and arrangement of hair sensillae in early copepodid stages. Line drawings, photomicrographs and an S.E.M. are used to illustrate the structures. Laboratory studies with live copepods in a flow chamber show that adult animals may hold position against water currents. It is hypothesized that this behaviour influences the distribution pattern in an estuary where low velocity tidally induced water movement occurs, and may be of value in enabling the copepod to exist beyond the distribution of a major predator.     

Ontogenetic niches of a planktonic copepod in Lake Biwa studied on a fine temporal scale

Eodiaptomus japonicus was collected in the north basin of Lake Biwa, Japan, on six dates from 11 to 25 June 1987. Temporal changes in its vertical distribution and reproduction indices were small, but those in its abundance were large. Mortality was high in the naupliar stage I and from copepodid stage III to adult stage. The latter fact and low proportion of females in adulthood suggest heavy predation by fishes which prefer larger prey.Eodiaptomus japonicus showed ontogenetic vertical migration within the epilimnion. The direction of the migration was upward in the early naupliar stages and downward in the late naupliar and early copepodid stages. Both migrations resulted in raising mortality in the corresponding or succeeding stages, probably expressing the behavioral constraints ofE. japonicus.     

Taxonomic analysis of species characters for copepodid instars 4 and 5 of the subfamily Eucyclopinae of European Russia

Morphological characters useful for taxonomic identification of older copepodid instars of the subfamily Eucyclopinae were studied among 14 species of Eucyclops, Macrocyclops, Ectocyclops, Paracyclops and Tropocyclops known from European Russia. For taxonomic analysis, the following elements of copepodid morphology were chosen: armament and proportion of furcal rami; morphology of swimming legs and reduced 5th and 6th legs; antennule segmentation; and relative body length of copepodid instars in comparison with the female length. Changes in morphology of major copepodid instars of the subfamily Eucyclopinae during ontogenetic development are traced and noticeable differences among five genera and 14 species are described. These differences among major copepodid stages may be important for both taxonomic and ecological analysis. For taxonomy, they provide information on development of sexes and species during maturation. For ecology they allow identification of the specimens at 4–5 copepodid instars in diapause. A key to major copepodid instars of the species from the subfamily Eucyclopinae which are known from limnetic habitats of the European part of Russia is presented.     

Distribution of <Emphasis Type="Italic">Calanus</Emphasis> populations in a glaciated fjord in the Arctic (Hornsund,Spitsbergen)—the interplay between biological and physical factors

The distribution and diversity of copepods of the genus Calanus were investigated in Hornsund Fjord (on the southwest coast of Spitsbergen) in summer 2001. The Bhattacharya method was used to sort individuals by species based on their prosome length. The established prosome length boundary values for the Calanus copepodid stages coincided with those defined for the Calanus species from Kongsfjorden (on the northwest coast of Spitsbergen). The predominant species in the main and inner fjord basins was Calanus glacialis, whereas Calanus finmarchicus was the prevailing species outside Hornsund. Younger copepodid stages (CI–CIII) of both species concentrated in the surface water layers (0–50∼70 m), while older copepodids (CIV–CVI females) that were ready for wintering stayed in deep layers (50∼70 m to bottom). Calanus hyperboreus was present in low numbers, predominantly as CIV, and in Hornsund deep water layers. The distribution and diversity of Calanus species complied with the notion that the marine fauna in Hornsund is of a more Arctic character than in Kongsfjorden, a fjord 260 km to the north on the west coast of Spitsbergen.     

The life-cycle of Ergasilus briani Markewitsch, 1993 (Copepoda: Poecilostomatoida)

The life cycle of Ergasilus briani is shown to consist of six nauplius stages, five copepodid stages and the adults. Only the adult female is parasitic. The free-living stages are described in detail. The presence of three aesthetascs on the antennules of all copepodid stages and the adult is noted for the first time. Unusual aspects of E. briani development include: the antennule is sexually dimorphic from copepodid IV onwards, the dimorphism being expressed in the numbers of setae present on the more proximal segments, and the first appearance of the male maxilliped is at the copepodid II stage. The endopodal setation of the male maxilliped is the maximum known within the Poecilostomatoida. The striking pigmentation of the developmental stages of ergasilids is noted and discussed.     

The effect of temperature on the development time and brood size of diaptomus pallidus herrick

Diaptomus pallidus individuals were raised in the laboratory at three temperatures (15, 20, and 25°C) and fed an alfalfa and trout-food diet ad libitum. Data were taken on the development times of the egg, naupliar, and each copepodid stage and the brood sizes of field animals acclimated to the test conditions.The results indicated D. pallidus does not have a temperature range over which its development rate is nearly constant as earlier reported. Rather, the development rate is temperature dependent within the experimental range. Broods produced at 20°C and 25°C were significantly smaller than those produced at 15°C but not significantly different from each other.     

Postembryonic development of Drescheriella glacialis Dahms & Dieckmann (Copepoda,Harpacticoida) reared in the laboratory

Summary All 6 naupliar and 5 copepodite stages of Drescheriella glacialis, a tisbid from Antarctic fast ice, are described. A key for the identification of the naupliar stages is given. Sexual dimorphism makes its first appearance in the copepodid IV. The setae configuration of the exopod of the second antenna in copepodid I is considered to be an ancestral state, and subsequent ontogenetic reductions are proposed to be apomorphic processes.     

Post-embryonic development of Psammopsyllus maricae Cottarelli,Saporito & Puccetti, 1983 (Copepoda,Harpacticoida)

The post-embryonic development of Psammopsyllus maricae Cottarelli, Saporito & Puccetti, 1983 has been described for the first time. Six morphologically distinct naupliar and five copepodid stages were discerned and studied using light microscopy. Some features were also examined by scanning electron microscopy.     

Copepod post-embryonic durations: pattern,conformity, and predictability. The realities of isochronal and equiproportional development,and trends in the opepodid-naupliar duration ratio

A collation of post-embryonic durations for freshwater and marine calanoid, cyclopoid and harpacticoid copepods is provided, and examined for patterns and conformities which may be of predictive value. Most of the analysis concerns calanoids. Only the genus Acartia exhibits evidence of equal stage duration (isochronality). Accordingly, isochronal development must be rejected as a general pattern in copepods — with various implications to the study of their production. Conversely, relative stage durations are surprisingly comparable in a wide range of copepods across a broad range of temperatures and food levels. A loose consistency is evident among copepod species generally, (interspecific equiproportionality), but within given genera, a striking regularity, here termed intergeneric equiproportionality (IGE) is evident. Patterns of IGE are consistent with selectively adaptive life-history traits, and IGE thus offers predictive prospects which are of both quantitative and qualitative (heuristic) value. Empirical support which exists for IGE among marine calanoids suggests that in contrast to isochronality and interspecific equiproportionality, IGE is indeed a real, and ultimately quantifiable feature of copepod development. Within calanoids, the ratio of total copepodid to total naupliar duration (Dc/Dn) appears independent of temperature, shows little relationship to adult body mass, but is inversely related to food supply, markedly so in freshwater forms. In this context, changes in the ratio are attributable largely to influences of food supply upon copepodid development times: naupliar durations appear relatively independent of food concentrations during development. Considerably higher Dc/Dn ratios in freshwater than in marine calanoids conceivably arise from selective influences of different nutritional conditions and size-selective predation pressures in freshwater and marine environments. In the generally high predation environment of freshwaters, acceleration of naupliar development potentially reduces the vulnerability of these smaller stages to size-selective tactile predation, while larger copepodid instars are able to reduce the opposing size-selective influences of visual planktivores by virtue of their escape responses to suction attack. Within the spectrum of copepod life histories and development schedules, ecologically consistent trends of this nature await formal recognition. The present recognition of IGE is a modest initiative in this quest. Both naupliar and copepodid durations are inverse monotonic functions of temperature. Several mathematical expressions which account for this temperature-duration response are provided. The response envelope is much tighter for naupliar than copepodid durations. Predictability of temperature-duration responses accordingly declines ontogenetically from egg to naupliar to copepodid stages.     

Host and site selection by larval stages and adults of the parasitic copepod Lernaeenicus sprattae (Sowerby) (Copepoda,Pennellidae) in the Oslofjord

Sprat caught by beach seining during the period 1977–1980 were examined for adult Lernaeenicus, and both sprat and herring caught in 1981–1983 were examined for all parasitic stages. Lernaeenicus was never found on herring. Adult L. sprattae were always found in the sprat's eye, usually (89%) in the upper rear quadrant of the eye. Double and triple infection of one or both eyes were found. Infection experiments support results from field work. The sprat is the only intermediate and final host of L. sprattae. In laboratory experiments, copepodites showed no preference for particular size groups of sprat. The infective stages, copepodid and adolescent female, are both initially randomly distributed on the host before the copepodites move towards the fins and the gravid females to the eye.     

Copepod biomass in an estuarine and a stagnant brackish environment of the S. W. Netherlands

In the mesohaline zone of the Westerschelde estuaryEurytemora affinis is the dominant copepod, demonstrating large biomass values nearly throughout the year. In the meso-polyhaline Lake VeereAcartia tonsa is abundant, mainly during summer. In spring a small population ofEurytemora americana is found. The tidal estuary harboured far denser copepod populations throughout the year than the stagnant brackish lake water. The average yearly copepodid+adult biomass in the Westerschelde estuary was approx. 850 mg/m³ (wet weight), in Lake Veere approx. 130 mg/m³. Temporarily low oxygen values did not influence negatively the copepod populations in the Westerschelde estuary. The seasonal distribution of the dominant copepods in both areas is explained in the light of recent litterature data. PerennialEurytemora affinis abundance in the Westerschelde estuary must be mainly caused by large concentrations of nannodetritus particles, bacteria included, throughout the year.Acartia tonsa in Lake Veere has to thrive mainly on nannophytoplankton. Communication no. 141 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherland.     

Life cycle of Calanus chilensis Brodsky in Bay of San Jorge,Antofagasta, Chile

The copepod Calanus chilensis is an endemic component of the zooplankton community in northern Chile. Size distributions of adult females, relative frequency of copepodid stages and relative numbers of adult males and nauplii, suggest the presence of at least 6 generations during the year, although the species seems to continuously reproduce through all seasons. Temperature profiles from 0 to 175 m indicated the presence of the El Niño current during March and April. Surface temperature ranged between 21.1 and 13.1 °C. Warm waters during the El Niño event seemed to affect the body size of adult females and the normal course of cohort development, although the population tended to recover rapidly through the subsequent months. We discuss the role of oceanographic conditions in controlling the life cycle of this species, as well as its continuous growth through the year compared to other Calanus species.     

Diel distribution of copepods across a channel of an overwash mangrove island

The distribution of copepod species and their nauplii was studied in a narrow, blind channel on an overwash mangrove island offshore of Belize. Copepodids were sampled with a pump at five stations across the channel during a diel cycle. Diel changes of copepodid stages II – VI were marked by horizontal dispersal of Dioithona oculata, the dominant species, from swarms in the prop roots along the shore during the day to the edge of the prop root habitat at night. Migration of copepodids back to the prop roots appeared to be controlled endogenously because change from a night to a daytime age structure began before first light. Mean copepodid stage at subsurface depths in the channel and prop root edge decreased from 4.2 (with 6.0 = all adults) to 2.9 at predawn to 1.1 during day. The oceanic Oithona nana and O. simplex, and the coastal zone O. fonsecae were evenly distributed with depth and distance from shore during day and night, with avoidance of prop root shoreline during day. These species were much less abundant than Dioithona oculata in the prop roots, but of comparable or greater abundance in the channel. Coastal zone Acartia spinata exhibited evidence of swarming. Nauplii, sampled with a 25m plankton net, were dominated by harpacticoid (50%) and cyclopoid (34%) nauplii, which generally were more abundant at 1m than at the surface and more abundant at night than the day. Lagrangian current measurements indicated velocities at ebb tide twice those of flood tide (1.9 vs. 0.8 cm s^–1) and a minimal residence time of 5 days, which could result in advection of D. oculata nauplii out of the Lair Channel before their recruitment into swarms as copepodid stage II. Previously reported maximum swimming speeds of swarming D. oculata copepodid stages (2.0 cm s^–1) and greater densities in prop roots and near the benthos may help copepodids avoid advection. The swarming behavior and diel horizontal migration (or dispersal) reported for D. oculata appears analogous to that of limnetic zooplankton, which may swarm among macrophytes along shorelines during the day to avoid visual predators and disperse or migrate away from the shoreline at night.     

The functional response of copepodid stages to adult of Parabroteas sarsi (copepoda,calanoida)

P. sarsi is a carnivorous calanoid commonly found in South Andes lakes. Feeding experiments were carried out in order to analyze the functional response of P. sarsi (copepodid IV to adult) on different cladoceran prey. Predation rates increased with increasing prey density up to maximum (type II) in almost cases. The highest attack coefficients were obtained when P. sarsi adults were fed with the smaller prey (C. dubia juvenile and B. longirostris). The ingestion rates of copepodid IV and CV were smaller than for the adults. The ingested biomass as a proportion of predator biomass (B_e/B_p) showed an inversal relationship with the predator length. The maximum B_e/B_p ratio, in both sex of P. sarsi, was achieved with C. dubia adult, the intermediate-sized prey.     

Nutritional suitability of some uni-algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others

• 1 Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono-specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl^?1).
• 2 All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development.
• 3 Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen-fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.

     

Geographical variation in dormancy in a copepod: evidence from population crosses

Populations of the freshwater copepod Mesocyclops edax inhabiting Michigan lakes are dormant during winter, whereas populations inhabiting Florida lakes develop and reproduce continuously throughout the year. A Michigan and a Florida population were exposed to dormancy inducing conditions (low temperature and short photoperiod) in the laboratory and observed for indications of dormancy. All Michigan individuals and a small percentage of the Florida individuals entered dormancy as indicated by prolonged duration of the fourth copepodid instar and cessation of feeding. I suggest that in these population these observations represent diapause, rather than quiescence. The two populations were crossbred to examine the nature of inheritance of dormancy. The F₁ hybrids exhibited an incidence of diapause approximately intermediate between the Florida and Michigan parental stocks. The backcrosses of F₁ individuals to the Michigan and Florida stocks, respectively, exhibited a high and an intermediate incidence of diapause. Survival of the F₂ crosses was very low. The present study presents evidence of genetic differentiation between the Michigan and Florida populations of M. edax with respect to ability to diapause.     

Experimental studies on the development of Lernaeocera branchialis (Copepoda: Pennellidae): population processes from egg production to maturation on the flatfish host

Quantitative population dynamical information derived from laboratory- and field-based experiments is provided for the fish-parasitic copepod, Lernaeocera branchialis, infecting flounder (Platichthys flesus) and whiting (Merlangius merlangus). Adult, post-metamorphosis females from whiting can produce more than one set of egg-strings. The mean number of eggs in each egg-string pair was 1445. At 10 °C these eggs took about 12.7 d after extrusion before hatching of NI nauplii began. Hatching took up to 12 days to be completed with an exponentially declining pattern of output over this period. In the laboratory about 44% of the egg-string egg population successfully passed through the NI to NII nauplius moult and the NII to copepodid moult to produce infective copepodids, a process lasting about 2 d. The non-feeding copepodids had a maximum survival time at 10 °C of 18 d, with a time to 50% survival of 7.5 d. In laboratory infection experiments at 10 °C, copepodids infected flounder and passed through all their developmental stages to adulthood and copulation in a minimum of 25 d. Field experiments on the seabed off Lowestoft in June 1987 with a sea temperature of about 16 °C suggested that the developmental period in those conditions could be as short as 11 d. Previously uninfected flounder in the field experiments became naturally infected with copepodids at a mean rate of not less than 30 parasites per fish d^–1.     

The first nauplius and the copepodite stages ofThalestris longimana Claus, 1863 (Copepoda,Harpacticoida, Thalestridae) and their bearing on the reconstruction of phylogenetic relationships

The first nauplius and 5 copepodite stages ofThalestris longimana Claus, 1863 are described. Sexual dimorphism makes its first appearance in the copepodid IV. Brief remarks are given on cultivation and on ecology of the species. The significance of both the naupliar and the copepodite development for the reconstruction of phylogenetic relationships of Thalestridae is discussed.     

The host specificity of Lepeophtheirus pectoralis (Müller, 1776) (Copepoda: Caligidae)

The host specificity of Lepeophtheirus pectoralis (Müller) was examined experimentally by exposing different fish species to infection by artificially reared copepodid larvae. Copepodids which were hatched from eggs of adults parasitic on plaice ( platessae copepodids) preferred plaice to all other fishes tested, whereas copepodids which were hatched from eggs of adults parasitic on flounder ( flesi copepodids) preferred flounder to all other fish species. These behavioural differences suggest that two strains of L. pectoralis exist, one ( platessae ) adapted to plaice as its host and the other ( flesi ) to flounder. Comparison of an experimentally derived order of host preference with a table of occurrence obtained from the literature, suggests that a third strain of L. pectoralis , adapted to dab as its host, might also occur.
The process of infection by L. pectoralis copepodids is also described. It comprises a host location phase, during which the copepodid enters the habitat of its flatfish hosts and locates a host individual, and an attachment phase. The host location phase appears to be governed by changes in the activity of the copepodid and by its positively rheotactic response to water currents produced by the host. The attachment phase is probably based on the response of the copepodid to chemical factors produced by the host.