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.     

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.     

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.     

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.     

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.     

Precopulatory mate guarding in Harpacticella inopinata Sars (Copepoda: Harpacticoida) from Lake Baikal

Precopulatory mate guarding is reported for the first time from a freshwater harpacticoid, Harpacticella inopinata. Adult males were observed grasping onto juvenile females from the third copepodid stage onwards, but most commonly with the fifth copepodid. This behaviour is interpreted as a plesiomorphic trait of the family Harpacticidae.     

The Role of the Predaceous Copepod Parabroteas Sarsi in the Pelagic Food Web of a Large Deep Andean Lake

Parabroteas sarsi is a predaceous calanoid copepod that inhabits both shallow temporary fishless ponds and deep fish lakes of Patagonia and Antarctica. The aim of this study was to analyse the effect of P. sarsi on the plankton structure of a deep Andean lake (>100 m depth) and the zooplankton vertical distribution in order to asses a possible vertical refuge of the predatory copepod against visual fish predation. We tested the extent to which the trophic cascade effect of this predator propagates through the food web. We carried out a vertical sampling in Lake Rivadavia (Patagonia, Argentina) in order to assess zooplankton distribution. P. sarsi showed a vertical distribution towards deeper layers of the water column both at midday and at night, indicating that the copepod had an effective refuge against visual predation. Additionally, we carried out both field and laboratory experiments with the presence of P. sarsi. The predator was observed to affect significantly the survival of the copepod Boeckella michaelseni both in laboratory and field experiments. On the contrary, rotifers and adults of Daphnia cf. commutata were not substantially affected by the predator. B. michaelseni mouthparts revealed an omnivorous diet; therefore a broad phytoplanktonic size spectrum could be affected by this copepod. However, no cascade effect was observed due to the presence of P. sarsi despite the decrease of B. michaelseni abundance.     

桉小卷蛾触角感器的超微结构

[目的] 桉小卷蛾是桉树、番石榴等林木和果树的一种重要害虫。为确定桉小卷蛾成虫触角上的感器对寻找生存环境及对外界环境的各种刺激所起的作用,研究了桉小卷蛾触角感器的种类、形态和分布。[方法] 利用扫描电镜对桉小卷蛾成虫触角感器进行了详细观察和研究。[结果] 桉小卷蛾雌、雄蛾触角由柄节、梗节和鞭节组成,触角的外侧面覆盖有鳞片;雄性触角略短于雌虫,且鞭节近1/4处有一凹陷。共发现7种感器,即鳞形感器、毛形感器、锥形感器、腔锥形感器、耳形感器、刺形感器和Böhm氏鬃毛,其中以毛形感器数量最多。[结论] 桉小卷蛾雌雄成虫触角的感器种类、分布、数量有一定的规律但又有差异。建议应用气相-触角电位联用技术GC-EAD和触角电位EGA等技术进一步解析触角感器的功能。     

New evidence for the involvement of Paracartia grani (Copepoda,Calanoida) in the life cycle of Marteilia refringens (Paramyxea)

The dynamics of the protozoan parasite Marteilia refringens was studied in Thau lagoon, an important French shellfish site, for 1 year in three potential hosts: the Mediterranean mussel Mytilus galloprovincialis (Mytiliidae), the grooved carpet shell Ruditapes decussatus (Veneriidae) and the copepod Paracartia grani (Acartiidae). Parasite DNA was detected by PCR in R. decussatus. In situ hybridisation showed necrotic cells of M. refringens in the digestive epithelia of some R. decussatus suggesting the non-involvement of this species in the parasite life cycle. In contrast, the detection of M. refringens in mussels using PCR appeared bimodal with two peaks in spring and autumn. Histological observations of PCR-positive mussels revealed the presence of different parasite stages including mature sporangia in spring and autumn. These results suggest that the parasite has two cycles per year in the Thau lagoon and that mussels release parasites into the water column during these two periods. Moreover, PCR detection of the parasite in the copepodid stages of P. grani between June and November supports the hypothesis of the transmission of the parasite from mussels to copepods and conversely. In situ hybridisation performed on copepodites showed labeling in some sections. Unusual M. refringens cells were observed in the digestive tract and the gonad from the third copepodid stage, suggesting that the parasite could infect a copepod by ingestion and be released through the gonad. This hypothesis is supported by the PCR detection of parasite DNA in copepod eggs from PCR-positive females, which suggests that eggs could contribute to the parasite spreading in the water and could allow overwintering of M. refringens. Finally, in order to understand the interactions between mussels and copepods, mussel retention efficiency (number of copepods retained by a mussel) was measured for all P. grani developmental stages. Results showed that all copepod stages could contribute to the transmission of the parasite, especially eggs and nauplii which were retained by up to 90%.     

Diel and seasonal vertical distribution of meiobenthic copepods in muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay)

The vertical distribution of meiobenthic copepods was investigated within muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay, France). The aim of the study was to determine if in muddy sediments, as previously established in sandy sediments, meiobenthic copepods migrate vertically according to the seasons or diel periods. Two experimental approaches were used, viz: a three-season comparison was made of the diel vertical distribution of the harpacticoid Canuella perplexa T. & A. Scott (1893) and secondly the depth distribution of a meiobenthic copepod assemblage was followed for a 24 h period, in shallow water subtidal locations. The harpacticoid C. perplexa vertically migrated through the top three centimeters of the sediment, showing diel and seasonal variations in depth distribution. The differential vertical distributions shown by the dominant meiobenthic populations suggest that emergence into the water column may mainly concern surface dwelling copepods. The physical and biological factors affecting seasonal and diel changes in the copepod assemblage of the fish ponds are discussed.     

Biological cycle of a population of subantarctic copepod,Drepanopus pectinatus (Clausocalanidae), Kerguelen Archipelago

Summary Depending on seasons, 73% to 99% of the copepod number in the subantarctic ecosystem of the Kerguelen Archipelago consists of Drepanopus pectinatus. All developmental stages from copepodid 1 to 5 and adults are found all year through. The annual population cycle fluctuates between a maximum abundance during the summer (150×10³ individuals per m²) and a minimum during the winter (80 individuals per m²). A succession of 4 generations a year is discussed, based on the percentages of the various developmental stages in the population and changes in size of specimens in the various stages.     

Copepod life cycle adaptations and success in response to phytoplankton spring bloom phenology

In a seasonal environment, the timing of reproduction is usually scheduled to maximize the survival of offspring. Within deep water bodies, the phytoplankton spring bloom provides a short time window of high food quantity and quality for herbivores. The onset of algal bloom development, however, varies strongly from year to year due to interannual variability in meteorological conditions. Furthermore, the onset is predicted to change with global warming. Here, we use a long-term dataset to study (a) how a cyclopoid copepod, Cyclops vicinus , is dealing with the large variability in phytoplankton bloom phenology, and (b) if bloom phenology has an influence on offspring numbers. C. vicinus performed a two-phase dormancy, that is, the actual diapause of fourth copepodid stages at the lake bottom is followed by a delay in maturation, that is, a quiescence, within the fifth copepodid stage until the start of the spring bloom. This strategy seems to guarantee a high temporal match of the food requirements for successful offspring development, especially through the highly vulnerable naupliar stages, with the phytoplankton spring bloom. However, despite this match with food availability in all study years, offspring numbers, that is, offspring survival rates were higher in years with an early start of the phytoplankton bloom. In addition, the phenology of copepod development suggested that also within study years, early offspring seems to have lower mortality rates than late produced offspring. We suggest that this is due to a longer predator-free time period and/or reduced time stress for development. Hence, within the present climate variability, the copepod benefited from warmer spring temperatures resulting in an earlier phytoplankton spring bloom. Time will show if the copepod's strategy is flexible enough to cope with future warming.     

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 scaling and structure of aquatic animal wakes

Animal generated water movements are visualized and quantifiedusing two-dimensional particle image velocimetry (PIV). Theresulting vector flow fields allow for the study of the distributionof velocity, vorticity and vortices. Structural and temporalaspects of animal-induced flows covering a range of Reynolds(Re) numbers between less than 1 to more than 10⁴ are presented. Maps of flow induced by continuous foraging and intermittentescape responses of tethered nauplius and copepodid stages ofthe marine copepod Temora longicornis offer insight in viscosity-dominatedflow regimes. Fast escape responses of the equally sized largestnauplius stage and the smallest copepodid stage are compared.The nauplius moves by generating a viscous flow pattern withhigh velocities and vorticity; the copepodid moves by usinginertial effects to produce a vortex ring with a rearward jetthrough the center. Larvae and small adult fish (zebra danio) use a burst-and-coast-swimmingmode at Re numbers up to 6,000, shedding a vortex ring withthe associated jet at the tail during the burst phase. Flowpatterns during the coasting phase differ between the smalllarvae and larger adults due to the changes in importance ofviscosity. A 12 cm long mullet swimming in a continuous mode generatesa chain of vortex rings with a backward undulating jet throughthe centers of the rings at Re numbers of 4 x 10⁴ in inertia-dominatedregimes. Our empirical results provide realistic insight in the scaleeffects determining the morphology of the interactions betweenanimals and water.     

Direct evidence of tidally oriented behavior of the copepod <Emphasis Type="Italic">Eurytemora affinis</Emphasis> in the Seine estuary

The calanoid copepod Eurytemora affinis dominates the zooplankton communities in most northern hemisphere estuaries. A recurrent behavior noticed in several estuaries suggests that this species maintains its horizontal position through vertical migration. In order to investigate this behavioral strategy in detail, we sampled E. affinis nauplii, copepodids and adults at high frequency at a fixed point in the low salinity zone of the Seine estuary. We took water samples in sub-surface and near bottom during a 12- and 50-h tide cycle, in May 2002 and May 2004, respectively. Since nauplii have weak swimming capabilities compared to copepodid and adult stages, we proposed here to consider them as passive particles. The variation of the relative abundances of nauplii to older stages regarding the vertical position was therefore viewed as direct evidence of the behavior of later stages. We showed that copepodids and adults tried to stay close to the bottom during the ebb, were re-suspended in the water column 1 h after the low tide during the maximum current velocity, and then vertically migrated back to the bottom layer when current velocity decreased. We also showed that copepodids behaved as adults, with only a lower velocity, taking more time to go near the bottom.     

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.     

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.     

A light and electron microscopic study of tissue interactions between a parasitic copepod, Scolecodes huntsmani (Henderson), and its host ascidian, Styela gibbsii (Stimpson)

The structure of the cellular cyst which encapsulates the parasitic copepod, Scolecodes huntsmani, in the subendostylar blood vessel of the ascidian, Styela gibbsii, is described from light and electron microscopic studies. The cells comprising the cyst are contributed by the ascidian. The cells are columnar, contain large central reservoirs of glycogen and lipid, and have a conspicuous Golgi apparatus, many small cisternae of smooth endoplasmic reticulum and peripheral mitochondria. The cells are held together by complex basal interdigitations and a short apical zonula occludens. Long cilia emerge in circular clusters from the cell apices and beat in the lumen of the cyst. As atypical of a columnar epithelial layer, the nuclei are staggered in position in the cells and there is no basal lamina. One end of the cyst is blind, but the other end, which may be either anterior or posterior with respect to the longitudinal axis of the host, narrows to a profusely ciliated duct which opens through the wall of the blood vessel to the atrium of the ascidian by a ciliated funnel. The effective beat of the cilia of the duct and the funnel is outward toward the atrium. The first nauplii of the copepod emerge from the incubatory pouch of the adult and pass to the exterior sea water through the cyst funnel and the atrium and atrial siphon of the ascidian. As in other notodelphyid copepods, the life cycle of this incarcerated form also involves free-living naupliar stages followed by two free-living copepodid stages. The provision of an egress for the first nauplii is, therefore, important to the survival of the species. The adult females of Scolecodes, which range in length from 2 to 14.6 mm, are sluggish when removed from the cyst and fail to survive in sea water for more than 24 hours. The males, which have only been obtained when parasitic fifth copepodids molt in culture, are much smaller, averaging 0.8 mm, and are very active. Since one dead male has been found inside the cyst of an adult female and females are often found with attached spermatophores, it is suggested that the funnel of the cyst may also serve as an entrance for the males. Evidence is presented for the formation of the cyst as an accumulation of totipotent lymphocytes around the copepod. Cysts of parasitic developmental stages (third through fifth copepodids) are also described. All of these cysts and those of immature adult females lack funnels to the atrium. The funnel of the cyst of mature females is formed, in part, by modified cells of the wall of the blood vessel, but is induced after the major portion of the cellular cyst has been formed. Cells in the general circulation of the ascidian and those inside the lumen of the cyst are compared. The cells in the lumen of the mature cyst do not arise by diapedesis of blood cells from the subendostylar blood vessel, but by conversion and migration of cells composing the cyst proper. These cells have been found in the guts of the copepods and they may serve as a nutritive source. The ascidian appears not to be harmed by the association, but the copepod gains in many ways.     

Impact of warm water advection on the winter zooplankton community in an Arctic fjord

The west coast of Spitsbergen is influenced by water masses of Atlantic and Arctic origin. During the winter of January–April 2006, water temperatures on the West Spitsbergen Shelf were ∼3°C warmer than typical winter conditions, leading to a coastal sea ice cover of reduced thickness, extent and duration. A sediment trap deployed from September 2005 to May 2006 in the outer basin of Kongsfjorden (NW Spitsbergen) at a depth of 115 m has provided a continuous winter time-series of zooplankton during a period of rapid increase in water temperatures. Prior to an anomalous and prolonged influx of warm Atlantic water (AW) starting at the end of January, the trap samples were dominated by the boreo-Arctic copepod Metridia longa. Species that increased in abundance during the influx included late stages of Calanus finmarchicus, C. glacialis, C. hyperboreus and Paraeuchaeta norvegica. The early introduction of shelf populations into the fjord, and thus increased copepod biomass relative to typical winter conditions with little advection, has implications for the marine pelagic food web and pelagic-benthic coupling.     

Late postnaupliar development of Monstrilla sp. (Copepoda: Monstrilloida), a protelean endoparasite of benthic polychaetes

Polychaete specimens from Hawaii were infected by the copepod Monstrilla. The development of these protelean parasites has remained unstudied for more than a century. Three postnaupliar endoparasitic stages were obtained: copepodids CIII, CIV, and CV, the latter stage found previous to and during emergence. Copepodid development, including the body and appendages (antennules, legs 1–4, caudal rami), is described and analyzed. The feeding tubes and the exiting from the host are also described. In light of the recently proposed inclusion of monstrilloids among caligiform copepods, it was found that monstrilloid copepodid development diverges from caligiforms and other copepod groups in: (1) the segmentation of the urosome at CIII, (2) the early formation of a genital complex, (3) early completion of swimming legs setation, at CIII; (4) delayed segmentation of rami of leg 3 at CIII (vs. the usual two-segmented pattern), (5) loss of one exopodal seta of leg 1 at CIV, (6) full development of leg 1 endopod vs. usually vestigial condition in caligiforms; (7) earlier segmentation of leg 4 rami, and (8) stable interstage (CIII–CV) setation pattern of legs 3 and 4. Overall, monstrilloid development appears to have unique characters and their phylogenetic relations deserve further study.