Etude de la respiration chez des copépodes de niveaux bathymétriques variés dans la région sud marocaine et canarienne

The results of 281 respiration analyses of pelagic copepods sampled in the South Moroccan and Canarian area are described. The copepods used in experimentation were collected from various bathymetric levels: hyponeustonic species (Anomalocera patersoni, Pontellopsis villosa, P. regalis, Labidocera wollastoni, Pontella lo biancoi), epipelagic species (Centropages typicus, Temora stylifera, Calanus helgolandicus, Acartia clausi), meso and bathypelagic species (Pleuromma xiphias, P. abdominalis, Euchaeta acuta, Undeuchaeta plumosa and some other rare species). Analysis of the metabolismtemperature curve makes it possible to describe different modes of adaptation in relation to geographical distribution, altitudinal repartition, and dietary characteristics. When all species are studied together, a strong correlation exists between the log of respiration and the log of weight. The regression coefficient varies with temperature; it is strongest at a temperature near that of the natural thermic conditions.     

Relationship between mouthpart structures and in situ feeding habits of species of the family Pontellidae (Copepoda: Calanoida)

Pontellid copepods were collected from the surface waters of a tidal front region in the Bungo Channel (the Inland Sea of Japan) in June 1986 to examine the relationship between the morphology of cephalic appendages and gut contents. In particular, two dominant species,Labidocera japonica Mori andPontellopsis yamadae Mori, were compared in detail. Large setae on the second maxillae ofL. japonica possessed two rows of setules at right angles to each seta along its inner margin except a terminal part which was serrated, whereas the inner margin of those setae ofP. yamadae was entirely serrated. Judging from the structure of the mouthparts, especially the second maxillae, the former species seems to employ both suspension and raptorial feeding modes, in contrast to the latter, which may use only the raptorial mode of feeding. InP. yamadae, the first maxilla and the maxilliped are also modified for carnivory. Gut content analysis supported the morphological evidence for feeding differences, and revealed thatP. yamadae is a carnivore preying mainly on copepodids whileL. japonica feeds omnivorously on copepod nauplii and phytoplankton particles. Since the mouthpart structures of congeners are quite similar to each other, the feeding behavior and habits might also be similar. Within the family Pontellidae, the generaAnomalocera, Calanopia, Epilabidocera, andPontella have mouthpart structures similar to those ofLabidocera, whereas the genusPontellina resemblesPontellopsis. Morphological similarities would suggest that the first group of genera employs both suspension and raptorial feeding modes, and thatPontellina is a carnivore likePontellopsis.     

Subitaneous, diapause, and delayed-hatching eggs of planktonic copepods from the northern Gulf of Mexico: morphology and hatching success

Experiments were conducted to examine the morphology and hatching success of eggs, either spawned by freshly caught planktonic copepods or recovered from bottom sediments in the northern Gulf of Mexico. Collections were made between August 1992 and September 1995. Eggs of nine species were described and these differed in their diameter, color and surface attributes. Three types of eggs were distinguished: subitaneous, diapause, and delayed-hatching. Three species, Labidocera aestiva Wheeler, Acartia tonsa Dana, and Centropages velificatus (Oliveira) produced only subitaneous eggs. Hatching success varied greatly among these species. Two species, Labidocera mirabilis Fleminger and Centropages hamatus (Lilljeborg) produced diapause eggs and subitaneous eggs. The length of the refractory phase of the diapause eggs differed greatly both within and between these two species. A third type of dormant egg, delayed-hatching, was recognized in Labidocera scotti Giesbrecht and Pontella meadi Wheeler. The existence of delayed-hatching eggs may be an adaptive response of subtropical species to less seasonal fluctuation. Based upon morphological characteristics of the eggs and rearing of nauplii to an identifiable stage, benthic dormant eggs of eight species of calanoid copepods were also identified. Received: 9 September 1996 / Accepted: 1 October 1996     

Plankton community dynamics of the central Great Barrier Reef Lagoon: Analysis of data from Ikeda et al.

Plankton data collected by Ikeda et al. (1980) from the central region of the Great Barrier Reef, and spanning two years (1976 through 1978) of zooplankton records, have been analyzed extensively for spatial and temporal patterns. Estimates of net zooplankton (including chaetognaths, copepods, and larvaceans) and microzooplankton (juvenile copepods, encompassing nauplii and copepodites, and ciliates) were assessed at three stations across the 60 km lagoon. Temperature, salinity, and chlorophyll a were also measured. A cross-lagoonal gradient was identified in the plankton, concurring with results of related surveys of benthic taxa, such as scleractinian corals, soft corals, macro-algae, fish, sponges, crinoids, etc. Two associations of net zooplankton were identified. The first was associated primarily with the inner lagoon; the second with the outer lagoon. The inshore association was characterized by higher abundances of almost all net zooplankton taxa, particularly chaetognaths, copepods, polychaetes, decapods, and meroplanktonic larvae as well as higher concentrations of chlorophyll a. This inshore association wove back and forth across the lagoon through time, dominating the lagoon entirely during periods of high river discharge, reaching the mid-shelf platform reefs in this region, and sometimes being entirely absent during dry periods. Both seasonal and annual peaks in plankton abundance were generally linked with degree of runoff. Summer/autumn peaks of abundance were evident in chaetognaths, copepods, and larvaceans while annual variation was detected in the former two as well as in chlorophyll a concentrations. Depth stratification was noted in juvenile copepods and chlorophyll a concentrations at the center of the lagoon, with higher abundances recorded in deeper waters. The central Great Barrier Reef lagoon was found to be typical of other tropical coastal waters where plankton community dynamics are controlled primarily by physical factors. We suggest that any substantial changes in river discharge in this area will affect plankton production.A.I.M.S. Contribution No. 242     

Composition biochimique des copépodes de l'hyponeuston de Méditerranée Nord occidentale. Poids sec et analyse élémentaire du carbone,de l'hydrogène et de l'azote

Dry weight, total carbon, hydrogen and nitrogen contents were studied in Anomalocera patersoni, Pontella mediterranea, P. lo biancoï and Labidocera wollastoni as a function of sex and developmental stage. 629 individuals were analysed over the year. Protein content was calculated from the nitrogen values, and results are presented as percent dry weight. C:H and C:N ratios were also determined. The lowest contents of carbon (32.4%) and nitrogen (9.3%) were determined for female L. wollastoni, the highest carbon content (43.3%) for female P. lo biancoï, and the highest nitrogen content (11.5%) for female P. lo biancoï and male A. patersoni. This range agrees with the data in the literature for marine copepods. According to available data on biochemical composition of zooplankton in relation to depth, the Pontellidae contain a high amount of proteins. The carbon:nitrogen ratio displays great stability within a species, indicating a constant elementary composition during development from copepodite to adult. Nevertheless, there is a statistically significant discrepancy between the C:N ratios for A. patersoni and P. mediterranea which is due to a higher rate of increase in carbon content in A. patersoni. As a whole, interspecific variations were small (C:N ranged between 3.4 and 3.8) compared to those recorded in true planktonic species. This appears to be an important characteristic of the Pontellidae, in contrast with other, more widely distributed copepods, and probably is related to the peculiarities of their biotope, the ultrasuperficial layer.     

New patterns of diurnal vertical migration of some deep-water copepods in the Tyrrhenian and Adriatis Seas

The diel vertical migration of copepods from intermdiate water layers of the Tyrrhenian and Adtiatic Seas has been studied on the basis of plankton samples made from depths down to 1000 m, with a Nansen net, mesh size 250 , diameter 113 cm. The species considered display two different patterns of migration: (1) nocturnal ascent, e.g. Pleuromamma abdominalis and Euchaeta acuta; (2) nocturnal descent, e.g. species of the genera Spinocalanus, Scaphocalanus, Temoropia, Mormonilla and Oncaea. These two patterns are compared on the pasis of the dimensions of the species and of their different capacities for active movement. Ililumination is considered to be the most important factor influencing vertical movements. The behaviour of Pleuromamma gracilis is also described, the adult population of which is divided in two discrete sections, each one showing a different pattern of migration.     

Effects of anoxia on the viability of subitaneous eggs of planktonic copepods

The effect of anoxia on the viability (as evidenced by hatching) of newly spawned and fully developed subitaneous eggs of three species of copepods, Acartia tonsa (Dana), Centropages hamatus (Lilljeborg), and Labidocera aestiva (Wheeler) was determined for eggs produced in the laboratory by adults collected from inshore waters of the northeastern Gulf of Mexico between January and August 1992. Hatching success decreased to 50% or less when eggs were exposed to oxygen concentrations <0.06 mll^-1 for more than 12 d, except for newly spawned eggs of L. aestiva, which still showed 50% survival after 32 d of exposure to anoxia. For all three species, newly spawned eggs survived exposure to anoxia longer than fully developed eggs. The results indicate that the increasing occurrence of anoxia in estuarine and coastal waters could have a major impact on the population growth of these important food web organisms.     

Effects of low oxygen concentrations on the hatching and viability of eggs of marine calanoid copepods

Hatching of the eggs of four species of copepods, Acartia tonsa, Labidocera aestiva, Tortanus discaudatus, and Centropages hamatus was suppressed at oxygen concentrations less than 0.02 ml O₂/l. When such eggs were subsequently exposed to normal oxygen concentrations, hatching varied among the species, indicating variability in the capacity of eggs to survive exposure to low oxygen. Incubation of eggs at low oxygen concentrations resulted in an increase in the duration of embryonic development. Experiments were conducted in closed systems and oxygen concentration was determined by thermal conductivity using gas chromatography.     

Annual life cycle of the copepod<Emphasis Type="Italic"> Eucalanus inermis</Emphasis> at a coastal upwelling site off Mejillones (23°S), northern Chile

Eucalanus inermis is an abundant species in the eastern tropical and subtropical South Pacific, including the oceanic and coastal waters off Chile and Peru. Its annual life cycle was studied through a time-series sampling (weekly intervals) during 2002, at a fixed coastal station at an upwelling site (Mejillones Bay, 23°S) off northern Chile. The more-or-less continuous occurrence and abundance of naupliar and copepodid stages indicated that the species reproduces during most of the year, with two peaks: one during the austral spring and the other during the summer. Thereafter, an abrupt decline in the population was observed during winter. The abundances of E. inermis copepodids and nauplii were positively correlated with sea surface temperature, suggesting temperature-dependent development and growth during the spring–summer period. Three cohorts could be distinguished during one annual cycle, with generation times >30 days. The estimate of mean weight-specific daily growth (0.12 day^–1) is lower than that of other species in the area, but it is consistent with a slower development rate. The distribution of this copepod is associated with the equatorial subsurface waters characterized by low-oxygen content (<0.5 ml l^–1). The ascent of this water mass to the near-surface during coastal upwelling in the spring–summer period and the presence of E. inermis adults favor their reproduction and the development of cohorts in the food-rich upwelling environment. The wintertime disappearance of E. inermis from shallow waters is, thus, interpreted as a movement to deep waters (>200 m depth), probably in a lethargic mode, within the oxygen minimum zone in the adjacent oceanic area.Communicated by P.W. Sammarco, Chauvin     

Vertical distribution and feeding patterns of midwater fish in the central equatorial Atlantic

Fishes and zooplankton were obtained (March–April 1979 and partly in August 1974) from 45 hauls taken during the day and at night in the central equatorial Atlantic between Latitude 3°N and 2°S from the surface to 1250-m depth, using the RMT 1+8, a combined opening-closing plankton and micronekton trawl. The vertical distribution of 30 myctophid species is described. All species migrate in a diel pattern, Ceratoscopelus warmingii and Lampanyctus photonotus down to at least 1250 m. During daytime most species aggregated at 400-to 700-m depth, therefore only partly occupying the depth of the Deep Scattering Layer (400 to 500 m at 15 kHz). The feeding patterns of seven of the most abundant species were compared, with a total of 1 905 stomach contents being analysed. All seven species are regarded as opportunistic predators, which feed predominantly during the night on calanoid copepods. A total of 66 species of calanoid copepods were identified among the prey items, with smaller species definitely being in the minority. Stomachs of C. warmingii (700 to 1 250 m depth) and Lepidophanes guentheri (500 to 900 m depth) from daytime samples contained copepod species restricted to the upper 150 m of the water column, including Undinula vulgaris, Nannocalanus minor, and Euchaeta marina, thereby confirming an extended vertical migration of predators. Differences in diet and preferences between species in their total food spectrum are described.     

Weight and chemical composition of some important oceanic zooplankton in the North Pacific Ocean

Wet and dry weight, total carbon, nitrogen, hydrogen, and ash contents were determined on 33 species of zooplankton distributed predominantly in the open sea region of the North Pacific. Sampling covered the waters from 44°N to the equator. Average percentage of dry weight to wet weight was about 19% of all samples from the whole area. Percentage dry weight of carbon in copepods was on an average 51.5%. The highest value, 66.6%, was obtained in eggs of the copepod Pareuchaeta sarsi. Mixed zooplankton was assumed to contain carbon comprising about 35 to 45% of the dry weight. Carbon contained in the zooplankton biomass existing in the upper 200 m in the western parts of the northern North Pacific and Bering Sea during spring and summer was estimated to range from 20 to 85 mg C/m³. Nitrogen content varied considerably with localities. Average ratio of carbon to nitrogen was 8.5 in subarctic copepods, and 4.1 in subtropic-tropic copepods. This ratio also varied with season. In the copepod Calanus cristatus the ratio was highest (10.0) in May, immediately after the spring bloom of phytoplankton, when the animals contained much fat. The ratio fell to 5.1 in December. There seemed to be a large seasonal variation in boreal zooplankton due to great fluctuations of environmental conditions, especially the amount of food available; in tropical species the range was small because of environmental uniformity. Average hydrogen content was about 6 to 10%. The percentage of ash to dry weight amounted to 39.3% in pteropods and 3.4% in copepods.     

Geographical patterns in reproductive biology of the Pan-American sandy beach isopod<Emphasis Type="Italic"> Excirolana braziliensis</Emphasis>

Eleven populations of the Pan-American sandy beach isopod Excirolana braziliensis, distributed from tropical (9°N) to temperate (39°S) sandy beaches in Atlantic and Pacific Oceans, were analyzed to determine latitudinal variations in: breeding and recruitment patterns, sex ratios, size of ovigerous females and of juveniles and length–fecundity relationships. E. braziliensis exhibited strong latitudinal patterns in all reproductive traits throughout its distribution range. Breeding and recruitment shifted from continuous to seasonal from tropical to temperate beaches, having a predominance of females at higher latitudes. In agreement with the latitudinal gradient hypothesis, ovigerous females inhabiting tropical sandy beaches (low latitudes) were smaller, became sexually mature at smaller sizes and had lower individual fecundity than on temperate beaches. Juveniles were also smallest at low latitudes. Between-ocean comparisons showed very similar reproductive characteristics for roughly the same latitude. These linked reproductive parameters suggest that the intensity of breeding effort is associated with the duration of the breeding season and geographically size-related characteristics of the species. Geographic variations in the breeding and recruitment seasons, as well as in individual fecundity, size structure of mature females and sex ratios, are proposed to have major consequences in explaining local variations in population demography. Our paper also reinforces the notion that sandy beach animals are highly plastic.Communicated by O. Kinne, Oldendorf/Luhe     

Etude de la respiration chez des copépodes pélagiques méditerranéens (bassin occidental et Mer Ionienne) et de ses variations en fonction de la bathymétrie des espèces et de leur origine géographique

A shipboard experimental study was conducted on the respiratory rate of pelagic copepods from two Mediterranean stations (Ionian Sea and Occidental Basin). In each sampling area, copepods were collected from different depths (0 to 2500 m) by horizontal net hauls. Selected copepod species included bathypelagic, lower mesopelagic, upper mesopelagic and epipelagic species. Respiration rates were determined at 4 different temperatures (10°, 14°, 18°, 22°C). The metabolism-temperature curves revealed varying degrees of thermal sensibility of copepod respiration related to their respective habitats. During experiments employing a large range of temperatures, bathypelagic species proved most sensitive. By contrast, vertically migrating species appeared to be more tolerant to temperature variation. The relationship between respiratory rate and copepod dry weight was investigated for the 4 temperatures used. A strong correlation emerged between log of respiration and log of weight. The equation of regression lines varied with experimental temperature and with geographic origin of the copepods studied. Comparison of the relation respiration-weight of specimens from the two Mediterranean stations and from a previously studied Atlantic station (Canarian and south Moroccan region), indicated that observed differences are related to the average temperature of the mesopelagic waters in each sampling area. The pressure effect on metabolic rate is discussed. It is suggested that hydrostatic pressure does not affect the characteristics of temperature sensibility of copopods' respiration under the temperature conditions prevailing in their natural habitat.     

Influence du mode de conservation sur la composition chimique élémentaire de Pontella mediterranea (Copepoda: pontellidae)

A comparative study of the elementary chemical composition (C, H, N) of Pontella mediterranea (males, females and copepodites) was carried out in two series: in Series 1, live copepods were briefly rinsed with distilled water, dried for one night (12 h) at 60°C, and then stored in a desiccator; in Series 2, the copepods were preserved in a 5% formalin-freshwater solution neutralized with borax; they were then rinsed with distilled water, and subsequently dried and stored in a desiccator as in Series 1. The results reveal that the dry weight of preserved copepods (Series 2) is 20 to 25% less than that of fresh, dried individuals. Carbon loss was estimated as about 10% in males and 17% in females, hydrogen loss as 14% in males and 23% in females, and nitrogen loss as 20% in males and 21% in females. The organic compounds lost seem to be mainly proteinaceous. Nevertheless, relative carbon content expressed as percent dry weight, and C:N and C:H ratios were all significantly higher in the preserved specimens. These results are compared with literature data on two other crustancean species.     

Vertical distribution,abundance and community structure of oncaeid copepods in the Oyashio region,western subarctic Pacific

The vertical distribution, abundance and community structure of oncaeid copepods were investigated in the Oyashio region, western subarctic Pacific. Samples were collected with a 0.10 mm mesh closing type net from five discrete layers down to a maximum depth of 2,000 m in September and December 1996 and in April and October 1997. The copepods were widely distributed from epipelagic to bathypelagic zones, and showed prominent peaks of abundance above the thermocline and/or between 250 and 1,000 m depth. Standing stocks of total oncaeid copepods ranged from 1.5 to 2.5×10⁵ inds m^–2 at 0–2,000 m in the water column, which are the same order of magnitudes as those reported in tropical, subtropical and polar regions by previous workers. A total of 38 species and two forms belonging to the genera Oncaea, Triconia, Spinoncaea, Conaea and Epicalymma, and two provisionally classified species of the family Oncaeidae were identified in this study. Of these, 14 species have already been recorded from the eastern subarctic Pacific. Several warm-water species were also found in December 1996 and/or October 1997, when the effect of warm-core rings originating from the Kuroshio Current was evident in the epipelagic zone. Dominant species throughout the whole water column were T. borealis, T. canadensis, O. grossa, O. parila, O. rimula, O. lacinia, Epicalymma spp. and Oncaea sp. A, and these eight species together always made up about half of the total oncaeid numbers. Community analysis revealed that species composition in epipelagic and upper mesopelagic zones varied temporally due to the changes of hydrographic conditions, whereas those in lower mesopelagic and bathypelagic zones were relatively stable, reflecting the constancy of deep environments.Communicated by O. Kinne, Oldendorf/Luhe     

Fatty acid signature analysis documents the diet of five myctophid fish from the Southern Ocean

Fatty acid (FA) and fatty alcohol (FAlc) compositions of both total lipid and neutral lipid fractions were studied for five myctophid species sampled in Kerguelen waters. Both qualitative and quantitative FA signature analyses were then performed to investigate their diet over longer time scales than the conventional stomach content analysis. Regarding their lipid class, FA and FAlc compositions, the five species could be discriminated into two groups: wax-ester-rich species (Electrona antarctica, Krefftichthys anderssoni) characterised by large amounts of monounsaturated FAs (>73% of total FAs) and triacylglycerol-rich species (Electrona carlsbergi, Gymnoscopelus nicholsi, Protomyctophum bolini) with major amounts of saturated and monounsaturated FAs (>29 and >46% of total FAs, respectively). Qualitative and quantitative FA analyses showed that K. anderssoni mainly preyed upon copepods, E. antarctica upon copepods and more euphausiids and P. bolini and E. carlsbergi mainly upon euphausiids with some copepods, while G. nicholsi had a more diverse diet. This study shows the usefulness of quantitative statistical analysis to determine the diet of Antarctic and sub-Antarctic predators and stresses the need of increasing the lipid and FA analyses of more zooplanktonic and micro-nektonic marine species.     

Harpacticoid copepod respiration: Enhydrosoma propinquum and Longipedia helgolandica

Oxygen consumption rates of 2 harpacticoid copepods, one benthic, Enhydrosoma propinquum (Brady) and one benthopelagic, Longipedia helgolandica (Klie), were determined and compared with those of the pelagic harpacticoid Euterpina acutifrons. The respiratory rates of the 3 species differed significantly and could be correlated with activity patterns and habitat preferences. E. propinquum consumed the least oxygen, E. acutifrons an intermediate amount, and L. helgolandica the most per unit dry weight. Gravid L. helgolandica had a lower metabolic rate than the non-gravid females. The lower values for the gravid females most likely reflected the metabolic activity of the developing egg mass. Harpacticoids may be important contributors to total meiobenthic metabolism, since they respire more per unit weight than do nematodes.Supported by NSF Grant GB-8189 to Duke University Cooperative Program in Biological Oceanography (BCC) and NSF Grant 7435 (WBV).     

Nutrient regeneration by zooplankton during a red tide off Peru,with notes on biomass and species composition of zooplankton

During March and April 1976, a red tide, dominated by the dinoflagellate Gymnodinium splendens Lebour, developed in the vicinity of 15°06'S and 75°31'W off Peru. At the height of the bloom, the euphotic zone was 6 m deep and the chlorophyll a at the surface was 48 g l^-1. A daily collection of zooplankton at 09.00 hrs showed large fluctuations of biomass, from 0.2 to 3.84 g dry weight m^-2 in a water column of 120m. Copepodids and nauplii dominated the collections. During a period of reduced wind, the adult copepods were a mixture of the species characteristic of the coastal upwelling system and the neritic species associated with more northerly, tropical waters. Nitrogen regeneration by the zooplankton varied with the development of the bloom, the type of zooplankton dominating the experiment, and biomass fluctuations, but never accounted for more than 25% of the nitrogen uptake by phytoplankton.     

Zooplankton growth rates: the influence of female size and resources on egg production of tropical marine copepods

Egg production was measured in 17 species of copepods from the genera Acartia, Calanopia, Centropages, Clausocalanus, Corycaeus, Eucheata, Euterpina, Oithona, Oncaea, Paracalanus, Parvocalanus, Temora and Undinula in Jamaican waters. At the high local temperatures (∼28 °C), mean egg production ranged from 3.2 to 88 eggs female^–1 d^–1, and instantaneous female growth (g, as egg production) ranged from 0.04 to 0.87 d^–1. Female growth was positively related to ambient chlorophyll concentration (r ² = 0.44) and negatively to female body size (r ² = 0.29). Together these two variables explained 60% of the variation in growth. When quadratic terms for chlorophyll and a term for interaction of body size and chlorophyll were introduced, 82% of the variance in growth rate was explained. Egg production rates represent an extension of the resource and size-dependent relationship established for copepodites. In smaller species (<3.5 μg), egg production was comparable to prior copepodite somatic growth; in larger species (>3.5 μg), egg production is compromised at lower resource concentrations than copepodite somatic growth. Thus, it appears that egg production in tropical copepods may be frequently limited by resources in a size-dependent manner. Under conditions where growth is resource limited, we caution against the application of egg production rates for the calculation of total copepod production. Received: 30 May 1997 / Accepted: 13 May 1998     

Occurrence,viability and significance of resting eggs of the calanoid copepod Labidocera aestiva

Field and laboratory observations on the occurrence and viability of eggs of Labidocera aestiva Wheeler show that eggs of this temperate species which are laid in late fall remain viable on the bottom and hatch in late spring. These eggs thereby provide the means of repopulating temperate areas with this species after its winter disappearance from the plankton.