Short term experiments on calanoid-cyclopoid-phytoplankton interactions

To investigate their potential effects on each other in nature, calanoid (Diaptomus clavipes and D. siciloides) and cyclopoid (Acanthocyclops vernalis and Mesocyclops edax) copepod populations were manipulated in 5 liter aquaria in laboratory experiments of 20–60 days duration. Diaptomus generally had a strongly negative effect on both cyclopoid species. The cyclopoids established populations more successfully when introduced to aquaria before calanoids than they did when calanoids were already present. On the other hand, whether introduced earlier or later than the cyclopoids, Diaptomus populations were unaffected by Acanthocyclops and were strongly depressed by Mesocyclops. Diaptomus effects on the phytoplankton were often strong but varied markedly among experiments. They included reduction of populations of edible algae, such as Chlamydomonas, which are essential for both calanoid and cyclopoid nauplii, and large increases in inedible algae, such as Kirchneriella. Feeding experiments revealed that under conditions of food scarcity Acanthocyclops nauplii survived less well than did Diaptomus nauplii. Competition for edible phytoplankton seemed to be a key factor in the calanoid-cyclopoid interactions, since the survival of herbivorous cyclopoid larvae determined the abundance of the predaceous adults. This indicates that the competitive effects of calanoids on cyclopoids often may exceed the predative effects of cyclopoids on calanoids.     

Inhibition of copepod feeding by exudates and transparent exopolymer particles (TEP) derived from a Phaeocystis globosa dominated phytoplankton community

We investigated if (1) dissolved compounds excreted by Phaeocystis globosa and (2) transparent exopolymer particles (TEP) formed from carbohydrates excreted into the water affect the feeding of nauplii and females of the calanoid copepod Temora longicornis during a P. globosa bloom. Copepod grazing on the diatom Thalassiosira weissflogii in the presence of these possible grazing deterrents was measured during three successive weeks of a mesocosm study, simulating the development of a P. globosa bloom. Our results demonstrate no indication for the presence of feeding deterrents in the dissolved phase, but a strong inhibitory effect of transparent exopolymer particles (TEP) on the consumption of algae by both nauplii and adult copepods. The inhibitory effect of TEP was connected to the accumulation of DOM during the progress of the bloom. We suggest that a reduction in the grazing pressure of zooplankton may increase the survival of the liberated single cells during disruption of colonies and allow seeding populations to persist. Furthermore, P. globosa reduces the trophic efficiency of the food web not only by withdrawal of its colonies from grazing but also by a relaxation of the grazing pressure on co-occurring phytoplankton and by alteration of the food web structure via TEP production.     

The influence of food concentration and container volume on life history parameters of Diaptomus dorsalis Marsh from subtropical Florida

Two experiments were conducted with a subtropical calanoid, Diaptomus dorsalis Marsh 1907, to determine the influence of food concentration and the volume of medium per copepod (one copepod in each of several containers of different volumes) on post-embryonic development rates, adult body size, clutch size, survivorship and sex ratio. Low concentrations of food (Chlamydomonas reinhardti) decreased development rates, body size, clutch size and survivorship; the sex ratio did not vary significantly from 1:1. Small container volumes had the same effects as low food concentrations, except that naupliar development time was not affected and survivorship showed greater variability. Because the copepod parameters exhibited maximum responses when food was abundant, even in the smallest container volume, it was concluded that container volume did not directly influence these parameters but exerted its effect through food availability.Larger life history stages were affected more than smaller life history stages by low food levels. In part, this was attributed to a laboratory artifact in which depletion of food by larger animals was greater than by smaller animals and, in part, to a real effect of low food concentration. A possible explanation of this real effect came from comparisons of these results to data from D. dorsalis fed phytoplankton from a Florida lake. The comparisons suggested that nauplii may be more efficient feeders on, or utilizers of, small food items such as Chlamydomonas.     

Development, growth and egg production of the two copepod species Centropages hamatus and Centropages typicus in the laboratory

Laboratory experiments were set up in order to determine andcompare developmental rates, growth rates, generation timesand egg production rates for the two calanoid copepod speciesCentropages typicus and Centropages hamatus. The nauplii showeda higher developmental rate than the copepodites for both specieswith quite different individual stage durations, which gaveno indication of isochronal development. For C typicus equiproportionaldevelopment was found. The growth rates were exponential andhighest for the largest species C typicus, and for both speciesthe juvenile growth rates were very similar to the egg productionrates of the adults.     

Prey capture capabilities by juveniles of the false percula clownfish (Amphiprion ocellaris) fed calanoid nauplii vs. adults

The reaction field of juvenile false percula clownfish (Amphiprion ocellaris) were studied when fed two different developmental stages (nauplii and adults) of the calanoid copepod Pseudodiaptomus annandalei. As the copepods undergo ontogenetic development, their morphologic and kinematic traits changes and may therefore influence the ability of the clownfish to identify and capture prey. The fish reacted to nauplii at shorter distances (15.2 ± 7.1 mm) compared to adult copepods (28.0 ± 9.8 mm). However, the fish reaction angle was significantly wider when offered nauplii (?25.3° to 64.4°) compared to adult copepods (?14.2° to 36.7°). This resulted in an equivalent attack rate on both prey items. Hence, even though nauplii are less apparent at greater distances, the fish counteract this partly by reacting to smaller prey items at a wider range. However, the carbon-specific ingestion rate was higher when offered adult copepods, which suggests adult copepods are a more rewarding prey.     

Context-dependent effects of bluegill in experimental mesocosm communities

Most knowledge of direct and indirect effects of zooplanktivorous fish has come from studies in which a treatment with a zooplanktivore is compared to a fishless control. However, effects of a zooplanktivore may be different in the presence of other fish species because the other fish have direct and indirect effects that may alter the effects of the zooplanktivore in question. To test this hypothesis, we conducted a tank mesocosm experiment of 2×2 factorial design in which the presence and absence of bluegill (Lepomis macrochirus) were cross-classified with the presence and absence of a fish assemblage composed of western mosquitofish (Gambusia affinis) and common carp (Cyprinus carpio). The presence of bluegill decreased Daphnia, Ceriodaphnia, cyclopoid copepodids, calanoid copepodids, copepod nauplii, amphipods, gastropods, and notonectids. Daphnia, Ceriodaphnia, cyclopoid copepodids, copepod nauplii, gastropods, notonectids, Najas, and Chara were decreased and herbivorous rotifers, turbidity, chlorophyll a, total nitrogen and total phosphorus were increased in the presence of the fish assemblage. Significant bluegill×fish assemblage interaction effects were detected for Daphnia, Ceriodaphnia, cyclopoid copepodids, copepod nauplii, gastropods, and notonectids. Analysis of simple effects for these response variables revealed that all significant bluegill effects in the absence of the fish assemblage were not significant in the presence of the fish assemblage. Our results indicate that the effects of bluegill may be context dependent, or dependent upon the presence of other trophically similar fish species. Received: 3 November 1998 / Accepted: 24 September 1999     

Early life history of kitsune-mebaru,sebastes vulpes (scorpaenidae), in the sea of japan

The larval and juvenile stages of kitsune-mebaru,Sebastes vulpes, based on 50 wild specimens collected in, the Sea of Japan, are described and illustrated, and some ecological aspects of the early life history (feeding, horizonal distribution and habitat shift) included. Preflexion larvae became extruded between 3.9–4.6 mm body length (BL) and notochord flexion occurred between 4.7–7.1 mm BL. Transformation from postflexion larvae to pelagic juventiles occurred between 13–17 mm BL. Compared with other rockfish species,S. vulpes is deep-bodied, throughout both larval and, juvenile stages. Larval and juvenileS. vulpes inhabit mainly coastal water surface layer (usually on the continental shelf), but do not occur offshore region (northwest of Oki Islands). Although someS. vulpes juveniles are associated with drifting seaweed, such clumps are not indispensable habitats for any stages. Surface-to-benthie migration of juveniles occurs at about 25 mm BL. Preflexion and flexion larvae feed mainly on copepod nauplii, and postflexion, transforming larvae and pelagic juveniles mainly on calanoid copepodites (Parracalanus parvus).     

Acanthodiaptomus denticornis another omnivorous calanoid copepod: description of its mouth appendages and feeding experiments on animal prey

The mouthpart morphology of the freshwater calanoid copepod Acanthodiaptomus denticornis was examined with optical microscopy. The mouthparts have sharp teeth and stout appendages with clawlike setae, typical of omnivorous calanoid mouthpart morphology. Observation of the buccal aperture with Scanning Electron Microscopy shows a large opening permitting feeding on prey as large as Keratella cochlearis. These observations agree with our feeding experiments which show that A. denticornis feed on K. cochlearis.     

Projected marine climate change: effects on copepod oxidative status and reproduction

Zooplankton are an important link between primary producers and fish. Therefore, it is crucial to address their responses when predicting effects of climate change on pelagic ecosystems. For realistic community‐level predictions, several biotic and abiotic climate‐related variables should be examined in combination. We studied the combined effects of ocean acidification and global warming predicted for year 2100 with toxic cyanobacteria on the calanoid copepod, Acartia bifilosa. Acidification together with higher temperature reduced copepod antioxidant capacity. Higher temperature also decreased egg viability, nauplii development, and oxidative status. Exposure to cyanobacteria and its toxin had a negative effect on egg production but, a positive effect on oxidative status and egg viability, giving no net effects on viable egg production. Additionally, nauplii development was enhanced by the presence of cyanobacteria, which partially alleviated the otherwise negative effects of increased temperature and decreased pH on the copepod recruitment. The interactive effects of temperature, acidification, and cyanobacteria on copepods highlight the importance of testing combined effects of climate‐related factors when predicting biological responses.     

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.     

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.     

Life cycle of Boeckella poppei Mrazek and Branchinecta gaini Daday (King George Island, South Shetlands)

In Lake Wujka, a shallow, polymictic Antarctic lake situated at 15 m from the seashore, several yearly cohorts occur of the copepod Boeckella poppei and one of the fairy shrimp Branchinecta gaini. There is circumstantial evidence that the two species compete for food, and perhaps adult fairy shrimp feed on the nauplii of the copepod. Both species are positively influenced by a measure of salinity. However, when autumn storms massively sweep seawater into the lake, all fairy shrimp are wiped out; no hatching occurs until next spring. In B. poppei, some nauplii and copepodites survive or hatch after the salt flows out of the lake. This is an advantage to the copepod that may balance its coexistence with the shrimp. Its cycle is, however, aborted by the freezing of the lake. In contrast to many other Antarctic lakes, the life cycle of the crustaceans is therefore controlled by salinity rather than freezing.     

Patterns of prey selectivity in the cyclopoid copepod Mesocyclops thermocyclopoides

In the shallow and eutrophic subtropical aquatic ecosystems, which it generally inhabits, the omnivorous copepod Mesocyclops thermocyclopoides encounters a wide variety of animal prey types including ciliates, rotifers, and cladocerans. We studied prey selectivity in laboratory-reared adult females of this species given a choice of (i) prey types belonging to different taxa (ciliates, rotifers, cladocerans, and cyclopoid nauplii), and (ii) different prey species within a taxonomic group differing in body size, morphology or behaviour. We also tested the effect of different proportions of prey species on its selectivity. Prey type proportion had no significant effect on selectivity of the copepod, nor was there any evidence of switching based on the relative abundance of prey. Among the ciliate prey species tested, the largest species, Stylonychia mytilus was positively selected regardless of its relative abundance, while the smallest, S. notophora was selected only when its density was higher. Offered a choice of three species of a brachionid rotifer differing in size, the copepod selected the largest of them, Brachionus calyciflorus, and avoided the smallest B. angularis. The evasive rotifer Hexarthra mira was also avoided. When prey choice included three cladoceran species Daphnia similoides, Moina macrocopa and Ceriodaphnia cornuta, the copepod selected the intermediate-sized M. macrocopa regardless of the abundance of the other two species. Although it fed on Mesocyclops nauplii when there was no choice, M. thermocyclopoides avoided them when alternative food was available. In a multispecies prey choice test, the copepod selected predominantly the rotifer B. calyciflorus and the cladoceran M. macrocopa. We suggest that the prey selectivity patterns shown by M. thermocyclopoides are adaptive in that they lead to ingestion of the most profitable prey.     

Salinity tolerance of the copepod Apocyclops dengizicus (Lepeschkin, 1900), a key food chain organism in the Salton Sea,California

The copepod Apocyclops dengizicus is a key item in the food chain of the Salton Sea where the salinity is currently 45 g 1^–1. The salinity of the Salton Sea may reach 90 g 1 ^–1 within the next 20 years. This study examined the salinity tolerance of this copepod.Large copepodite and adult A. dengizicus were introduced into various salinities with and without acclimation. The 96 h LC₅₀ without acclimation was 101 g 1^–1. Mortality (at 96 h) without acclimation was low at salinities of 90 g 1 ^–1 or less.Copepod cultures were maintained, with successful reproduction of at least one new generation, at salinities of from 0.5 to 68 g 1 ^–1 for at least 120 days. Copepods maintained at higher salinities, up to 79 g 1 ^–1, remained alive up to 90 days, but a new generation was not produced. In laboratory studies of larval production and survivorship, few nauplii were released at salinities of 68 g 1 ^–1 or higher, and none survived to the copepodite stage.     

Long-term development of the crustacean plankton in the Saidenbach Reservoir (Germany) – changes,causes, consequences

The rates of development and food intake of the copepod Temora longicornis (Müller) were studied using artificial blooms of Phaeocystis globosa Scherffel under different conditions of nutrient limitation. Mesocosms with 800 l of natural seawater were manipulated by inoculation with cultured P. globosa and by addition of nitrogen and/or phosphorus, to obtain N- or P-limited blooms of P. globosa. During development and ageing of these blooms, water from the mesocosms was used as medium for incubation of nauplii of T. longicornis. Only moderate rates of naupliar development as well as high rates of mortality were observed, irrespective of major differences of nutrient conditions and density of P. globosa. Grazing by the nauplii on P. globosa seemed to be low, suggesting a low food quality of this alga at all physiological conditions studied. The results of this study indicate a low capability of T. longicornis nauplii for control of nuisance algal blooms caused by P. globosa.     

Selective grazing of Temora longicornis in different stages of a Phaeocystis globosa bloom—a mesocosm study

Selective grazing of a calanoid copepod Temora longicornis was measured during different stages of a Phaeocystis globosa bloom, in order to reveal (1) if T. longicornis feeds on single cells and/or colonies of P. globosa in the presence of alternative food sources, (2) if copepod food selection changes during the initiation, maintenance, collapse and decay of a P. globosa bloom and (3) if P. globosa dominated food assemblage provides a good diet for copepod egg production. Our results show low but constant feeding on small colonies of P. globosa, irrespective of the type or concentration of alternative food sources. In contrast, feeding on single cells was never significant, and the total contribution of P. globosa to carbon ingestion of T. longicornis was minor. T. longicornis fed most actively on the decaying colonies, whereas during the peak of the bloom copepods selected against P. globosa. Mostly, T. longicornis fed unselectively on different food particles: before the bloom, the major part of the diet consisted of diatoms, whereas during and after the bloom copepod diet was dominated by dinoflagellates and ciliates. Egg production was highest during the decay of the bloom, coinciding with highest proportional ingestion of heterotrophic organisms, but was not seriously reduced even during the peak of the bloom. We conclude that P. globosa blooms should not threaten survival of copepod populations, but the population recruitment may depend on the type (and concentration) of the dominant heterotrophs present during the blooms. Due to relatively unselective grazing, the impact of T. longicornis to the initiation of a Phaeocystis bloom is considered small, although grazing on decaying colonies may contribute to the faster termination of a bloom.     

A new species of Phyllodiaptomus Kiefer (Copepoda,Calanoida) from South India

Phyllodiaptomus sasikumari, a new species of calanoid copepod is described from the material collected in several ephemeral ponds and pools in the Palghat District of Kerala State, South India.     

Seasonal vertical distribution and diel migration of zooplankton in a temperate stratified lake

The investigation of the vertical distribution of the zooplankton community in the temperate Lake Trichonis during four seasons in 2005, showed the existence of vertical segregation among species, ontogenetic stages and sexes within and between the major groups. In each season, the two or three more abundant rotifer species distributed at separate depth layers, while this feature was maintained during the entire 24 h period, since no diel vertical migrations (DVM) were performed. In contrast, the crustacean community, comprised mainly by the calanoid copepod Eudiaptomus drieschi and the cladoceran Diaphanosoma orghidani, showed various patterns of DVM, being more pronounced in spring and summer. Females of E. drieschi distributed deeper than males, while the copepod nauplii were found mainly in the surface layer in all four seasons. Temperature was the most important abiotic factor affecting directly and indirectly the vertical distribution and migration of various species. During stratification, the metalimnion was the most productive layer in Lake Trichonis, having maximum values of dissolved oxygen and low transparency due to high concentration of organic matter and phytoplankton. The DVM patterns of the crustaceans indicate that the metalimnion acts probably as a daylight refuge against predation by Atherina boyeri, which is the dominant planktivorous fish in the lake.     

Possible involvement of microcystins in the unexplained mass mortalities of Lesser Flamingo (<Emphasis Type="Italic">Phoeniconaias minor</Emphasis> Geoffroy) at Lake Manyara in Tanzania

We examined the effects of food and light on the swimming behavior of nauplii of the cyclopoid Apocyclops royi (Lindberg, 1940) (Copepoda: Cyclopoida) and the calanoid Pseudodiaptomus annandalei Sewell, 1919 (Copepoda: Calanoida). Several behavioral parameters such as swimming patterns, speed, and trajectories exhibited distinct ontogenetic differences between the two species. When algae Isochrysis galbana (Haptophyta: Isochrysidales) were offered as food to the nauplii of A. royi, they showed fast circle swimming behavior, while nauplii of P. annandalei never exhibited such behavior, neither with, nor without algae. The different behavioral patterns between the nauplii of both species suggest they both have different foraging strategies in detecting and capturing food.     

Clearance rates and prey selectivity of the predaceous cladoceran Polyphemus pediculus

Littoral plankton communities have rarely been included in food web dynamics and predator/prey behavior studies of planktonic communities of fresh water ecosystems. Polyphemus pediculus, a typically littoral predaceous cladoceran, is common in lakes and ponds throughout the northern temperate zone.Diel clearance rates of Polyphemus were studied with a differential count method. A multi-chambered in situ feeding trap manipulated Polyphemus densities at three levels above the control ambient densities. Polyphemus generally selected small prey (Vorticella and Keratella) over large prey (nauplii) and more vulnerable prey (Conochilus and Polyarthra) over smaller prey with long protective structures (Kellicottia). Polyphemus clearance rates were inversely correlated with body volume of prey. Polyphemus clearance rates ranged from 4.2 to 4.5 ml h^–1 for Keratella and Vorticella respectively to <1 ml h^–1 for copepod nauplii. Selectivity coefficients were highest for small species, Vorticella and Keratella.