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.     

Karyological Comparison between Three Sibling Species of the Tisbe reticdata Group (Copepoda, Harpacticoida)

In the Tisbe reticulata group, T. aragoi possesses n =ll, whereas T. marmorata and T. reticulata display n=12 . In relation to other species of this genus these species are characterized by relatively small dimensions of bivalents in oocytes. The discrepancy between karyological and morphological characters is discussed.     

Taxonomic Notes on Species of Tisbe (Copepoda, Harpacticoida) from a Belgian Sluice Dock

Tisbe furcata, T. gracilis, T. bulbisetosa, T. holothuriae and T. battagliai are reported from the Sluice Dock near Ostend (Flemish Coast). The latter three species are new to the Belgian fauna. A cross-breeding experiment between strains of T. holothuriae from Ostend and Venice (Italy) confirms perfect interfertility and hybrid F₁ heterosis. T. furcata , the stumbling block of the genus, is redescribed and an account is presented of the characteristics and ontogeny of its colour pattern.     

Chromosomes of two species of Tisbe (Copepoda, Harpacticoida) belonging to different groups of sibling species

Karyological investigations curried out on Tisbe marmorata and T. dobzhanskii confirmed the diploid value 2 n = 24 for the former species; on the basis of more than 200 observations it was ascertained that the diploid number of the latter species corresponds to 22, in contrast with a previous report. The karyotypes of these two species differ both in morphology and in location of satellites, not only from each other, but also from all other species so far examined. A close comparison of the two species with their respective siblings is made.     

Loureirophonte psammophila,a new species of Laophontidae T. Scott, 1904 (Copepoda: Harpacticoida) from Baja California,Mexico

Loureirophonte psammophila n. sp. was collected from coarse sediments of a beach near La Paz, Baja California, Mexico. The species belongs to the subterranea-group as defined by Fiers (1993). It differs from the other representative of the group, L. subterranea (Lang, 1965) in the presence of an outer dentiform process on 2nd segment of the antennula, the chaetotaxy of P.2–P.5 and the 1-segmented male endopodite P.4. A map with the distribution of the eleven species known so far is provided.     

Competition between the sibling species Tisbe holothuriae and T. battagliai (Harpacticoida)

The influence of salinity on the performance of the sibling species Tisbe holothuriae and T. battagliai in pure and mixed cultures was studied, using laboratory stocks adapted to 32 for over 175 generations. Cohort studies show that T. holothuriae has higher growth rates (R_o and r) at 32, T. battagliai at 20 The latter's life cycle is much less affected by the difference in salinity. De Wit replacement series were used to study competitive interactions. Without water renewal, T. holothuriae eliminates its sibling species in less than 2 generations, apparently through chemical interference. With water renewal, i.e. when exploitation competition becomes relatively more important, T. holothuriae still proves superior at 27 but the two species are competitively almost equal at 20. The two species cooccur in situ during autumn, but their differential predominance at different sites is not explained by the effect of salinity.     

Feeding of Acartia tonsa Dana (Copepoda,Calanoida): predation on nauplii of Canuella perplexa T. et A. Scott (Copepoda,Harpacticoida) in the sluice-dock at Ostend

Feeding experiments in which the zooplankton fraction of the Sluice-dock smaller than 200 μm is offered to Acartia tonsa, the dominant calanoid of this biotope, show that it feeds on the nauplii of Canuella perplexa, the dominant benthic harpacticoid. The ecological implications of this carnivorous feeding, occurring in the presence of natural phytoplankton concentrations, are briefly discussed.     

Contribution to the knowledge of the genus Phyllopodopsyllus T. Scott (Copepoda,Harpacticoida) from Africa with description of two new species

Two new species of marine, sand-dwelling harpacticoids are described: Phyllopodopsyllus pallaresae n. sp. from Namibia, and P. hartmannorum n. sp. from Tanzania. The hitherto unknown male of P. xenus (Kunz) is described from Namibia. Further remarks are made on P. furciger Sars from Tanzania.Zwei neue sandbewohnende Harpacticoiden-Arten werden beschrieben: Phyllopodosyllus pallaresae n. sp. von Namibia und Phyllopodopsyllus hartmannorum n. sp. von Tansania. Außerdem wird das bisher unbekannte Männchen von Phyllopodopsyllus xenus (Kunz) von Namibia beschrieben. Morphologische Merkmale von Phyllopodopsyllus furciger Sars werden anhand eines Fundes von Tansania ergänzt.     

Postembryonic development of Phyllodiaptomus blanci (Guerne & Richard, 1896) (Copepoda,Calanoida)

All the postembryonic developmental instars of Phyllodiaptomus blanci (Guerne & Richard, 1896), reared in the laboratory, are described and illustrated. The larval affinities of this species vis-a-vis certain other diaptomid species are mentioned.     

Zur Biologie vonParamphiascella fulvofasciata (Copepoda,Harpacticoida)

The benthic harpacticoid copepodParamphiascella fulvofasciata Rosenfield & Coull was collected from holdfasts ofLaminaria hyperborea from a subtidal area of Helgoland (North Sea). All developmental stages ofP. fulvofasciata are raptorial feeders. The feeding of the nauplii is advanced by a marginal setule-crest of the labrum which prevents food-particles from being swept away. The oral appendages of the copepodites circumscribe a frustal space ventral to the mouth which facilitates uptake of food-particles. The nauplii are not able to swim and perform stalking movements with their antennal endopodites. Good swimming ability as well as digging-in-behaviour and negative phototaxis of the copepodites indicate epi- as well as inbenthic mode of life. Several life-cycle characters are described. Precopula lasts ca. one day. The mean egg-number is 27, and mean egg-diameter is 87 × 75 µm. The number of nauplii per egg (double)-sac amounts to 25–30. Developmental time at 19°C is 6–9 days (nauplii) and 20–24 days (copepodites). The whole developmental period lasts 28 days. The maximal lifespan in the laboratory is 193 days. Sex-ratio is almost balanced. Females produce egg-sacs more than 3.5 times during their life period. Seasonal effects on reproductive activity have not been detected in laboratory cultures.     

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.     

Peltidiidae (Copepoda, Harpacticoida) from the Weddell Sea (Antarctica)

Alteutha polarsternae sp.n. is described and Eupelte villosa (Brady, 1910) is redescribed in detail. The distribution of both these species in the Weddell Sea is recorded.     

Zur Dynamik exploitierter Populationen vonTisbe holothuriae (Copepoda,Harpacticoida)

Zusammenfassung 1. An wöchentlich mit Raten von 0,10; 0,30; 0,50; 0,70 oder 0,90 exploitierten Populationen des harpacticoiden CopepodenTisbe holothuriae Humes wurde unter konstanten Bedingungen (22° C, 30 S) die Abhängigkeit der Reproduktionsleistung, des Geschlechtsverhältnisses, der Entwicklungsdauer und der Überlebenszeit von der Exploitationsrate untersucht.2. Es lassen sich drei Klassen von Eisäcken unterscheiden: (a) Eisäcke mit Entwicklung aller Eier bis zum schlüpfenden Nauplius, (b) Eisäcke mit Entwicklung nur eines Teils der Eier und (c) Eisäcke, aus denen keine Nauplien hervorgehen. Eine Abhängigkeit von der Entnahmerate besteht bei den Anteilen an Eisäcken, bei denen aus allen Eiern oder aus keinem Ei Nauplien hervorgehen.3. Der Anteil an Eisäcken, aus denen keine adulten Individuen hervorgehen, ist bei allen Entnahmeraten größer als der Anteil, aus dem keine Nauplien schlüpfen. Der Unterschied entsteht durch Eisäcke, bei denen unmittelbar nach dem Schlupf sämtliche Nauplien sterben.4. Die Zahl der pro 100 Eisäcke im Mittel produzierten Eier, Nauplien und adulten Individuen ist abhängig von dem Mittel der mittleren Populationsdichten zwischen den Entnahmen.5. Bei allen Befunden wird die durch die Exploitationsrate beeinflußte mittlere Populationsdichte zwischen den Entnahmen als die unmittelbarer wirkende Einflußgröße angesehen.6. Bei höherer Entnahmerate beziehungsweise geringer mittlerer Populationsdichte zwischen den Entnahmen werden im Mittel pro Eisack mehr Eier, Nauplien und adulte Individuen produziert als bei geringer Entnahmerate beziehungsweise höherer mittlerer Populationsdichte zwischen den Entnahmen. Es scheint die Tendenz zu bestehen, unabhängig von der Entnahmerate einen durch die Kulturbedingungen als Führungsgröße vorgegebenen Sollwert der Biomasse zu erreichen und konstant zu halten.7. Die Sterberate der Nauplien ist bei der Entnahmerate von 0,90 herabgesetzt. Das Reproduktionspotential wird allerdings selbst bei dieser Entnahmerate nur etwa zur Hälfte ausgenutzt.8. Außer bei der Entnahmerate von 0,90 werden im Mittel pro Eisack mehr Embryonen gefunden als Nauplien schlüpfen. Die relative Häufigkeit der Eier und Eisäcke, in denen keine Embryonen gefunden werden, zeigt keine Anhängigkeit von der Entnahmerate beziehungsweise der mittleren Populationsdichte zwischen den Entnahmen.9. Bei isolierten zeigt sich unmittelbar nach der Isolierung eine Abhängigkeit der Frequenz der Eisackbildung von der Entnahmerate beziehungsweise der mittleren Populationsdichte zwischen den Entnahmen. Es scheint, als erführen die Individuen durch die Populationen, aus denen sie stammen, eine Prägung, die in der Isolation allerdings bald verlorengeht.10. Das Geschlechtsverhältnis ist abhängig von der Entnahmerate beziehungsweise der mittleren Populationsdichte zwischen den Entnahmen. Bei der Entnahmerate von 0,90 überwiegt die Zahl der , bei der Entnahmerate von 0,10 die der .11. Bei isolierten Brutsätzen konnte eine Abhängigkeit der embryonalen Entwicklungsdauer von der Entnahmerate beziehungsweise der mittleren Populationsdichte zwischen den Entnahmen beobachtet werden. Eine Beeinflussung der Überlebenszeit adulter sowie der Geschwindigkeit der Entwicklung vom geschlüpften Nauplius bis zum adulten Individuum konnte bei den isolierten Brutsätzen nicht festgestellt werden.12. Das mittlere Gewicht eines Individuums im adulten oder Copepoditstadium und die mittlere Länge des adulten stehen in inverser Beziehung zur mittleren Populationsdichte zwischen den Entnahmen.

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On the dynamics of exploited populations ofTisbe holothuriae (Copepoda, Harpacticoida)III. Reproduction, sex ratio, rate of development and survival time

In weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes, effects of exploitation rate on production of eggs, embryos, nauplii and adults, as well as frequency of egg-sac formation, rate of development of embryos and nauplii and survival time of adult females were studied under conditions of surplus food supply at 22° and 30 S. Three classes of egg sacs could be distinguished: (a) Egg sacs in which all eggs developed until hatching of the nauplii, (b) egg sacs in which only part of the eggs developed, and (c) egg sacs with eggs that did not hatch at all. The fraction of egg sacs giving rise to no adult individual is larger at all exploitation rates than the fraction of egg sacs giving no nauplius. This difference is caused by the fact that some egg sacs produce nauplii, all of which die shortly after hatching. The mean number of eggs, nauplii and adults produced per egg sac depends on the mean average population densities between exploitations. In general, the mean average population densities between exploitations are considered to be a more immediate causal agent than the removal rate. At a higher removal rate or a lower density between exploitations, more eggs, nauplii and adults are produced per egg sac than at a lower removal rate or at a higher density. There seems to be a tendency to reach and to keep constant a set point of biomass, rather than population size, the culture conditions being the controlling variable. Death rate of nauplii is lowered at the exploitation rate of 0.90, and even at this highest removal rate only half of the eggs gave rise to adult individuals. Except at the exploitation rate of 0.90, more embryos per egg sac are found on the average than hatched nauplii, implying death of a certain number of embryos during development. The relative frequency of eggs and egg sacs in which no embryos could be detected shows no dependency upon the removal rate or mean population density between exploitations. In isolated females, an inverse relationship has been found between the frequency of egg-sac formation and the average population density between exploitations shortly after isolation. There seems to be some imprinting by the populations in which the specimens are living. Sex ratio is influenced by the removal rate or the average population density between exploitations in such a way that at the removal rate of 0.90 there is a surplus of males while at the rate of 0.10 a surplus of females is found. In isolated broods an inverse relationship between embryonic developmental rate and average population density between exploitation could be established. No influence of population density on rate of development of juvenile stages and survival time of adult females could be observed in equally isolated broods. The average weight of an individual in the adult or copepodid stage, and the average length of an adult female are inversely related to the average population density between exploitations.

     

Zur Dynamik exploitierter Populationen vonTisbe holothuriae (Copepoda,Harpacticoida)

In weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes, effects of exploitation rate on population density, age distribution, growth, as well as numerical and biomass yields were studied under conditions of surplus food supply at 22° C and 30 ‰ S. Increase of exploitation rate lowered the adult plus copepodid density and raised the density of nauplii, thus shifting the age distribution in favour of the nauplii. Total population density was almost equal at exploitation rates of 0.10, 0.50 and 0.70, but lower at rates of 0.30 and 0.90. Experiments, which have not yet been completed, have shown a higher resistance against the toxic effect of cadmium in populations exploited at rates of 0.30 or 0.90; populations exploited at the lower rate displayed a lesser degree of resistance than populations exploited at the rate of 0.90. Variability of densities was least at intermediate exploitation rates, whereas the variability of the age structure and the intrinsic rate of natural increase was less at higher rates, indicating smaller fluctuations in the ratio of the regulating variables mortality and fecundity with increasing exploitation. The assumption is made that an appropriate exploitation rate contributes to the achievement of favourable culture conditions for copepods, which are subjected to intense predation in natural populations. Within the range of the exploitation rates selected, biomass yields of nauplii and adults plus copepodids were approximately proportional to exploitation rate; therefore, the maximum rate sustainable by aTisbe holothuriae population cannot be established. From data on adult numerical yield, however, it may be concluded that exploitation rates exceeding 0.90 will not result in increased productivity.     

A revision of Leptopontia T. Scott (Gopepoda: Harpacticoida) with description of six new species

The presumed amphiatlantic distribution of Leptopontia cwmicauda T. Scott, 1902 (Copepoda: Harpacticoida) is reviewed and the species being redescribed on the basis of a single male from the Isle of Sylt. Examination of other material previously attributed to L. curvicauda , collected in South Carolina and a wide range of localities in northwestern Europe, resulted in the discovery of four new, morphologically similar species: L. dovpori sp. no v., L. flandrica sp. no v., L. punctata sp. nov. and L. americana sp. Nov . In addition, two new species, L. mediterranea sp. Nov . and L. breviarticulata sp. Nov . are described from the Mediterranean and the Galapagos archipelago, respectively. L. curvicauda sensu Marinov (1971) and sensu Apostolov (1973) from the Black Sea and sensu Klie (1950) from Helgoland are regarded as species inquirendae. A revised diagnosis of the genus Leptopontia T. Scott is presented.     

On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoida)

A total of 30 weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148 or 222µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22 °C and 30 S. During the observation period, most populations exhibited distinct U-shaped density trends. Addition of Cd⁺⁺ prolonged and reinforced the downward trends present in the initial periods of the experiments. If population densities, both in control and test populations, fell short of a certain value, the age structures shifted in favour of the nauplii. More pronounced reductions in population densities of the test populations did not result in increased elevations of the nauplius fraction. Within 23 weeks (or 20 generations), the effect of Cd⁺⁺ on population density was counteracted by an acclimation process. No relationship could be established between exploitation rate and observed effects. Erroneous assumptions on the adaptability of parametric methods had led to invalid statements on the dispersion of data published in previous papers of this series. These statements have been revised. Possible limitations of the significance of the results obtained are discussed in some detail.     

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.