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.

---

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.

     

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

A total of 75 weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 0.06, 0.3, 1.5, 7.5 or 37.5 μg 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. An unusually high mortality was observed for some weeks which could not be ascribed to the added amounts of Cd⁺⁺. A change in properties of supplied water is considered responsible for the unintentional perturbation which offered a further opportunity to study the effect of compensating reactions in stress situations. The results obtained clearly indicate an effect of exploitation rate on responses to detrimental influences. A superior performance has been found in populations exploited at higher rates. The findings are discussed with respect to earlier investigations on the population dynamics ofT. holothuriae.     

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.     

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.     

Influence of three bacteria strains on the population dynamics ofTisbe holothuriae (Copepoda,Harpacticoida)

The influence of three bacteria strains (Helgo 21, NCMB 308 and NCMB 13) on the life cycle ofTisbe holothuriae Humes 1957 was investigated under constant experimental conditions (19–20°C and 38‰ S). For each of the first six experiments, females (F1), whose life history was followed, were obtained from a common mother (F0). Experiment n^o 7 was carried out with adult females (F2) obtained during exp. 4. Females were bred in 50-ml dishes and transferred to a fresh container as soon as they produced a new egg-sac. Offspring (F2: exp. 1–6; F3: exp. 7) from successive egg-layings were counted as soon as they moulted into adults. Larval mortality was estimated by enumeration of the adults issuing from a known number of nauplii that had been fed different bacteria strains. Some difficulties arose in obtaining adults with NCMB 13: it appeared to be necessary to provide this first generation with a small quantity of TetraMin (commercial fish food) in order to initiate reproduction and obtain a second generation. However, in exp. 4, F2 adult females fed NCMB 13 became ovigerous and fertile without needing TetraMin. This result is interpreted as denoting an indispensable period of adaptation to the diet, which probably requires important changes at the enzymatic level. One experiment was carried out with Helgo 21; another one with NCMB 308; two with NCMB 13 (with a unique additional meal of TetraMin to allow reproduction), two with NCMB 13 during larval development, then only tetraMin during adult stage, and one with NCMB 13 alone (with females issued from exp. 4). Data obtained regarding longevity, duration of reproduction period, number of egg-sacs and number of adult descendants show an important variability between bacteria strains. Lower results were almost always obtained with Helgo 21 and NCMB 308. An interesting result lies in the maximum number of egg-sacs: low with Helgo 21 and NCMB 308 (5), but very ample with NCMB 13 (11 in one experiment). In experiment 7, carried out with animals bearing a large coefficient of inbreeding (0.375), the results concerning the maximum number of egg-sacs are good (10) as are the mean number of descendants per female (294: the highest number of the seven experiments). These results indicate that genetic factors involved in the reduction of descendants in ageing laboratory cultures can be suppressed to a certain extent by nutritional factors. The poor results obtained with Helgo 21 and NCMB 308 alone must be considered with caution: after a period of adaptation with an alimentary complement, these strains could perhaps permit an interesting production of copepods.     

Effects of seven diets on the population dynamics of laboratory culturedTisbe holothuriae Humes (Copepoda,Harpacticoida)

The harpacticoid copepodTisbe holothuriae was collected from Saronicos Gulf (Greece) and reared under constant laboratory conditions. In order to study the effects of food on the population dynamics, seven diets were tested: the seaweedUlva; five artificial compound feeds: the liquid Fryfood^® (Waterlife), a powder ofMytilus, yeast, soya andSpirulina, respectively; and a mixed diet consisting ofUlva and Fryfood. The life cycle parameters (mortality, sex ratio, generation time, offspring production) were measured, and the demographic variables [mean generation time (T), net reproductive rate (Ro), and intrinsic rate of natural increase (r_m)] were determined. As to their efficiency regarding population dynamics, the diets ranked as follows: (1)Ulva+Fryfood, (2),Ulva, (3) Fryfood, (4)Mytilus, (5) soya, (6) yeast, and (7)Spirulina. In this order they cause a progressive increase of both larval mortality and generation time, a progressive decrease of sex ratio, number of offspring per egg sac, number of egg sacs per female and, consequently, of Ro and r_m. The observed differences between diets were most pronounced with respect to offspring production. Of the compound diets, those containing animal extracts were more efficient than those containing vegetable materials.Ulva plays an important role in the nutrition ofT. holothuriae, favouring offspring production as well as larval survival, development and pigmentation.Ulva in combination with Fryfood led to a greater copepodid survival and offspring production. This mixed diet proved to be the most favourable for rearing the Greek population oft. holothuriae, resulting in an efficient intrinsic rate of natural increase (r_m=0.304) of the population.     

Effect of crowding on nauplii production during mating time inTisbe clodiensis andT. holothuriae (Copepoda,Harpacticoida)

Tisbe clodiensis andT. holothuriae females and males were maintained at different densities, from sexual maturity to the extrusion of the first egg sac, in order to study the effect of crowding on the number of nauplii produced by the first egg sac. They were tested in pure cultures at densities of 1, 2, 4, 6 and 8 couples per 20 ml of sea water, and in mixed cultures (half of the individuals belonging to each of the two species) with 2, 4, 6 and 8 couples per 20 ml, without food limitation. At the highest crowding level, and forT. holothuriae only, the effect of daily renewal of the culture water was examined. The mean number of nauplii per female decreases with increased density. A significant linear regression of number of nauplii on number of couples was found. The regression slopes appear to be the same for both species, regardless of whether they are cultured singly or together. The daily renewal of water diminishes the effect of crowding. The possibility that a complex chemical compound, produced by the animals, which enables the latter to perceive and to react to crowding, is discussed.     

Dry weight and chemical composition (CHN) in relation to population density of cultivatedTisbe holothuriae (Copepoda,Harpacticoida)

The harpacticoid copepodTisbe holothuriae was cultivated at different densities in a running-water system. Dry weight and chemical composition (CHN) of both females and egg-sacs have been determined. Dry weight decreased significantly with increasing density from 3,48 to 1.94μg in egg-sacs, and from 10.80 to 6.58μg in females. Increasing density in both egg-sacs and females results in decrease of carbon, nitrogen and hydrogen contents, expressed as a percentage of dry weight of egg-sacs and females, respectively. Carbon decreases from 52.56 to 50.57% (egg-sacs) and 45.80 to 39.95% (⧫), nitrogen from 12.63 to 11.94% and 10.72 to 9.73% and hydrogen from 9.08 to 7.78% and 7.47 to 6.17%. The dry weight and elemental compositions of the egg-sacs varied in accordance with that of the females, however, a higher percentage of elemental content was observed in egg-sacs. The energy equivalents were calculated from the carbon content. This indicates that more energy was transferred from the maternal body into egg-sacs. The ratio of carbon to nitrogen did not show any marked variations; no clear relation appeared between C:N and density, indicating a relatively constant chemical composition in both females and egg-sacs.     

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.     

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

A total of 90, weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148, 222, 333, 500, 750 or 1125µg 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. All populations exposed to concentrations down to 500µg Cd⁺⁺ l^–1 and 3 populations (out of 15) exposed to 333µg l^–1 became extinct within the experimental period of 30 weeks. Survival time significantly depended on concentration. A recovery phase from an initially high mortality preceded eventual population extinction after adding 500µg Cd⁺⁺ l^–1. In the initial phase, higher nauplii mortality prevailed. During these experiments on acute intoxication, no relationship could be established between survival and exploitation rate. However, experiments on the effects of stepwise increases in Cd concentration (results not yet published) produced evidence of such a relationship. In spite of increased mortality, no significant numbers of dead copepods were detected in weekly samples because of their rapid decomposition and cannibalism, which depends on the amount of food available. Sampling regimes of 5 times per week yielded significant numbers of dead individuals.     

Postembryonic development of Tisbe gracilis (T. Scott) (Copepoda, Harpacticoida)

All six naupliar and five copepodite stages of Tisbe gracilis (T. Scott, 1895) are described. A key for the identification of the nauplius stages is given. The oral appendages of all copepodite stages are described. Sexual dimorphism is visible from the copepodite IV stage on.     

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.     

Effects of light (photoperiod,spectral composition) on the population dynamics of Tisbe holothuriae Humes (Copepods,Harpacticoida)

The harpacticoid copepod Tisbe holothuriae Humes was reared for several generations under different photoperiods (white light) and spectral quality (continuous illumination). The main life cycle parameters were measured and demographic variables were determined. Development time was retarded under green wavelengths and at photoperiods different from LD 12:12, especially under continuous white light. Total body length of females and males was shortest under LD 12:12 and longest under constant dark. Photoperiods different from LD 12:12 prolonged the interval between broods of egg sacs. Short photoperiods caused higher abortion rate, while long photoperiods retarded the maturation time of the egg sacs. Red wavelengths stimulated the abortion rate. Photoperiod LD 12:12 and blue wavelengths increased the production of offspring and the life span of females. Highest intrinsic rates of natural increase were estimated under LD 12:12 (rm =0.304) and blue wavelengths (rm = 0.254). These light conditions proved the most favourable for rearing Tisbe holothuriae.     

A new genus of Cletopsyllidae (Copepoda,Harpacticoida) from Gulf of Mexico

A new genus and new species of the family Cletopsyllidae Huys & Willems, 1989 from deep-sea sediment in the Gulf of Mexico, are reported and fully described and illustrated. The new genus Pentacletopsyllus (type species: P. montagnisp. n.) can be distinguished from the four known genera of the family by antennule segmentation, length ratio of first and second endopodal segments of P1, and armature pattern on P5 exopod. It also differs from its sister genera by the rostrum being bifid at the tip, third segment of the female antennule having a smooth posterior margin, the baseoendopod of P5 with biarticulate outer setophore bearing basal seta, and female caudal rami without lobate expansion. A revised key to species of the family Cletopsyllidae Huys & Willems, 1989 is provided.     

A new genus (Copepoda,Harpacticoida, Laophontidae) from Jeju Island of Korea

A survey on the harpacticoid copepods from an intertidal zone in Hyeopjae sandy beach, Jeju Island, Korea, resulted in the discovery of an unusual laophontid, Jejulaophonte hyeopjaeensis sp. n., which cannot be placed in any extant genus within the family. To accommodate the species, a new genus of the family Laophontidae T. Scott, 1905 is proposed and fully described here. The new species is closely related to the lineage of the five primitive genera, Carraroenia McCormack, 2006, Coullia Hamond, 1973, Hemilaophonte Jakubisiak 1933, Psammoplatypus Lee & Huys, 1999, and Robustunguis Fiers, 1992 (the CCHPR-lineage) by the reduced P2 endopod, ovate shape of the female P5 exopod and sexual dimorphism in the P3 endopod. However, it displays discrepancies from the species of the CCHPR-lineage in the presence of an inner seta on P3 and P4 exp-2, four setae on P4 enp-2, and an inner seta on P3 and P4 enp-2 in the female. Furthermore, no other species within the family Laophontidae has three setae on P2 exp-3 and a seta on P2 enp-2 at the same time. The new species has sexual dimorphism in the antennule, genital segmentation and the legs from P2 to P5. The terminal seta on the second endopodal segment of P2 in the male is longer than that in the female. The endopod of P3 is 3-segmented and displays a short inner apophysis on the second segment in the male. The outer setae on the exopod of P3 and P4 are distinctly thicker and stronger in the male than in the female. Mitochondrial cytochrome oxidase subunit I (mtCOI) sequencing of the new species has been realized in order to be used in future phylogenetic analysis.     

On sperm ultrastructure,spermiogenesis and the spermatophore of Heterolaophonte minuta (Copepoda,Harpacticoida)

Summary The spermatophore, mature spermatozoon and spermiogenesis of Heterolaophonte minuta have been investigated by light and electron microscopy. The spermatophore contains three different secretions which are responsible for the discharge of the contents of the spermatophore, the formation of the fertilization tube and the storage of the spermatozoa. The spermatozoon represents a type new for the Copepoda. It is a filiform cell about 25 m in length, ellipsoid in transverse section and tapered at the posterior end. The elongated nucleus contains chromatin fibrils and does not possess a nuclear envelope. Posterior to the nucleus, six mitochondria are placed one after the other. The posterior part of the spermatozoon contains parallel pseudomembranes. The gamete is not helically twisted and is without a flagellum and centrioles. The most remarkable feature of the spermatozoon is an osmiophilic cap in front of the nucleus. This cap corresponds to the acrosome of the spermatozoon. Early stages of spermiogenesis take place in the testis, where the spermatids are incorporated into accessory cells. The origin of the chromatin fibrils and the glycocalyx, as well as the breakdown of the nuclear envelope and centrioles, represent the final steps of spermiogenesis which occur in the vas deferens.     

A new genus of Canuellidae (Copepoda, Harpacticoida) associated with Atlantic bathyal sea-urchins

Both sexes of Echinosunaristes bathyalis gen. ct sp. n. are described from the rectum of a deepwater spatangoid sea-urchin Palaeopneustes sp. taken off San Salvador Island, Bahamas. The new genus displays strong sexual dimorphism in body form, size, antennules and caudal rami. E. bathyalis can also be readily distinguished from the other members of the family by the specialized geniculation mechanism of the male antennule, the atypical reductions in the mouthparts and the unusual facies of the swimming legs. On the basis of the structure of the genital field in both sexes, Echinosunaristes is placed in the Sunaristes lineage which groups species that arc primarily associated with crustacean hosts. A ncw genus Intersunaristes is established to accommodate Sunaristes curticaudata Thompson & A. Scott, 1903 and S. dardani Humes & Ho, 1969. Canuella paenelanitica Fiers, 1992 is formally transferred to the genus Elanella Por, 1984. Records of Canuellidae associated with other invertebrates arc compiled and a key to the 17 genera of the family is presented.