Dormancy, dispersal and the survival of cyclopoid copepods (Cyclopoida, Copepoda) in a lowland floodplain

1. The survival of cyclopoid copepods was investigated in a floodplain for 2 years where flooding occurred during the cold season. The cyclopoid community was studied in three waterbodies with distinct hydroperiods: a permanent pond connected to the flooded area during inundation, a temporary pool that is part of the flooded area and an isolated temporary pool.
2. Field studies, including data obtained from samples of water, sediment and soil, showed the overall predominance of species with a summer diapause over those with a winter diapause or without diapause. Emergence of cyclopoid copepods at the onset of flooding, examined using emergence traps and data from recently filled or still isolated temporary pools, showed that some species can survive several months of drying.
3. The ability of the diapausing fourth copepodid stages of Cyclops strenuus and C. insignis , the two cyclopoids most abundant during winter and spring flooding, to survive terrestrial conditions was tested in laboratory experiments. Both species survived for several months, but rates differed among the species. A higher percentage of C. strenuus survived for a longer period, possibly explaining why this species was relatively more abundant in more temporary habitats.
4. Both dormancy and dispersal facilitated survival of cyclopoid copepods in transient habitats connected to each other during flood periods. Dormancy was the most important survival strategy, whereas dispersal could be more important following prolonged periods without flooding.     

Diapausing fertilized adults

Summary A lake population of the cyclopoid copepod Cyclops strenuus Fischer had a 1-year life cycle including a diapause from June to January. Dormant stages consisted of fertilized females, not previously described as a diapause stage, and a small fraction of cop V. The longevity of the sperm in a diapausing female was at least 6–7 months. Pre-fertilization is assumed to be an adaptive mechanism to assure fertilization when male abundance is low. This life cycle pattern also gives a shorter time-lag between diapause break and offspring development, and also the low total adult population exerts a lower predation pressure on their offspring. The flexibility of life cycle patterns of copepods is emphasized.     

Finding copepod footprints: a protocol for molecular identification of diapausing eggs in lake sediments

Even though calanoid copepods produce diapausing eggs that stay alive in lake sediments, these eggs have rarely been used paleolimnologically, as they lack diagnostic morphological features. In this study, we developed a method to identify copepod diapausing eggs in Japan as a clue toward reconstructing past plankton populations. We first determined a 28S ribosomal DNA (rDNA) (i.e., nc28S) regional sequence library (240 bp) of various calanoid copepod species using ethanol-fixed plankton samples collected from across the Japanese archipelago. Then we applied the UltraSHOT method to extract DNA from an individual diapausing egg. Finally, the nc28S region of diapausing eggs collected from various lakes was sequenced and compared with the regional library for species identification. In total, 21 haplotypes of the nc28S region were recovered from planktonic samples of 11 Japanese freshwater calanoid copepod species. Despite the short length of this region, no identical haplotypes were shared among the species analyzed, including the Acanthodiaptomus pacificus complex treated as a species. Even different lineages of A. pacificus could be separated. These results indicate that the nc28S region can be used as a barcode in Japan. A total of 112 diapausing eggs collected from various lakes and ponds was processed, and the nc28S region of each was successfully sequenced. All of these egg sequences matched one or the other of the nc28S haplotypes in the regional library mentioned above. The set of protocols we applied (i.e., preparing a comprehensive regional sequence library and sequencing egg DNA) is thus useful for involving copepod diapausing eggs in paleolimnological studies in lakes. The nc28S region treated in this study has a strong potential to uncover the paleodiversity of copepods, at least in Japan.     

Zooplankton interactions in an enclosure experiment: insights from stable isotope analyses

1. Density gradients of cladocerans and copepods were generated in an enclosure experiment to compare the impact on the plankton of a filter feeder (Daphnia hyalina × galeata) with that of more selective feeders (calanoid and cyclopoid copepods). The experiment was conducted in situ over 25 days during spring in a mesotrophic lake, Schöhsee, Germany. 2. The plankton community was monitored regularly. Daphniids were able to graze on the phytoplankton present, which mainly consisted of small (<1000 μm³) species, whereas copepods did not show any impact on algae. 3. At the end of the experiment, Daphnia and remaining cyclopoid copepods were harvested and sorted manually, prior to analyses for stable isotopes of carbon and nitrogen. Daphniids from mesocosms stocked purely with differing densities of Daphnia showed little variability in stable isotope values, whereas those that thrived in enclosure bags together with copepods exhibited lower δ¹³C values. 4. The change in Daphniaδ¹³C indicates a change of food sources, modified by the presence of the copepods: the higher the mean abundance of copepods in the enclosures, the more ¹³C‐depleted the daphniids. Increasing abundance of high nucleic acid (HNA) bacteria in the copepod bags may account for the trend in Daphniaδ¹³C via increased grazing on the bacteria themselves, or via grazing on phytoplankton utilising isotopically light CO₂ from respiratory release. 5. Cyclopoid copepod stable isotope signatures were related to Daphnia and copepod abundances in copepod bags, suggesting that cyclopoids preyed on the available zooplankton.     

Life-history traits of lake plankton species may govern their phenological response to climate warming

A prominent response of temperate aquatic ecosystems to climate warming is changes in phenology – advancements or delays in annually reoccurring events in an organism's life cycle. The exact seasonal timing of warming, in conjunction with species-specific life-history events such as emergence from resting stages, timing of spawning, generation times, or stage-specific prey requirements, may determine the nature of a species' response. We demonstrate that recent climate-induced shifts in the phenology of lake phytoplankton and zooplankton species in a temperate eutrophic lake (Müggelsee, Germany) differed according to differences in their characteristic life cycles. Fast-growing plankton in spring (diatoms, Daphnia ) showed significant and synchronous forward movements by about 1 month, induced by concurrent earlier ice break-up dates (diatoms) and higher spring water temperature ( Daphnia ). No such synchrony was observed for slow-growing summer zooplankton species with longer and more complex life cycles (copepods, larvae of the mussel Dreissena polymorpha ). Although coexisting, the summer plankton responded species specifically to seasonal warming trends, depending on whether the timing of warming matched their individual thermal requirements at decisive developmental stages such as emergence from diapause (copepods), or spawning ( Dreissena ). Others did not change their phenology significantly, but nevertheless, increased in abundances. We show that the detailed seasonal pattern of warming influences the response of phyto- and zooplankton species to climate change, and point to the diverse nature of responses for species exhibiting complex life-history traits.     

Predation by juvenile roach on the calanoid copepod Eudiaptomus gracilis and the cyclopoid copepod Cyclops vicinus: a laboratory investigation with mixed and single prey

We tested the outcome of predation by juvenile roach on the calanoid copepod Eudiaptomus gracilis and the similar sized cyclopoid copepod Cyclops vicinus in laboratory experiments with mixed and single-prey. When ovigerous females and adult non-ovigerous females of the calanoid copepod and the cyclopoid copepod were offered in equal numbers to the fish in the mixed-prey experiments, the cyclopoid copepods were significantly more heavily preyed upon than the calanoids. Between 14 and 16 females of the cyclopoid copepod and only between 2 and 4 calanoids had been consumed after the observation period of two hours. The single-prey experiments revealed that the conspicuousness of the calanoid vs the cyclopoid depended on sex and gravidity. Ovigerous females of the cyclopoid copepod were slightly earlier detected by the fish than ovigerous females of the calanoid, probably a result of the highly visible egg-sacs carried by the cyclopoid females. Females without eggs and males of the cyclopoid copepod were recognized later by the predator than females without eggs or males of the calanoid, probably a result of the different behaviours of the different copepod taxa. Cyclopoids frequently congregated near the aquarium bottom while calanoids were closer to the water surface where they were better visible. The calanoid copepod could better escape the fish's attacks than the cyclopoid copepod. Egg-bearing females of both the calanoid and the cyclopoid copepod could significantly better escape than non-ovigerous females or males. Probably ovigerous females react very early to water disturbances caused by the predator. Activity measurements showed that the cyclopoid copepod displayed 2 to 4 times more hops per time unit than the calanoid. Probably the high number of jerky movements displayed by the cyclopoid attracted attention of the predator and contributed to its greater vulnerability.     

Calanoid–cyclopoid interactions: evidence from an 11-year field study in a eutrophic lake

1. The interactions between calanoid and cyclopoid copepods were examined in an 11-year field study of a eutrophic lake (Heiligensee, Berlin, Germany).
2. A diminishing ratio of calanoids to cyclopoids was observed. The responses, however, were species specific. While two cyclopoid species responded with increased populations ( Cyclops vicinus, Thermocyclops oithonoides ), one species exhibited marked declines ( C. kolensis ). Other species extended the duration of their pelagic phase ( Mesocyclops leuckarti, Diacyclops bicuspidatus, T. oithonoides, C. vicinus ), leading to higher population overlaps. Eudiaptomus graciloides and E. gracilis, which used to be present throughout the year, were more frequently absent.
3. These changes coincided with a series of mild winters during which prey availability (algae and rotifers) was high.
4. Enhanced prey availability, in conjunction with a flexible diapausing strategy, are hypothesized to underly the increased success of C. vicinus . Predatory losses due to early occurrence and enhanced abundances of C. vicinus, rather than competition for the same food resources, are hypothesized to be responsible for the declines of C. kolensis and Eudiaptomus .
5. Summer species tended to develop higher abundances early in the season, which led to enhanced seasonal means during spring. These changes cannot be explained by the interaction between calanoids and cyclopoids alone, but were probably a result of changes in fish predation.     

Phenology of dormancy in a Virginia population ofMesocyclops edax (Crustacea: Copepoda)

The abundance and age structure of a Virginia, USA population ofMesocyclops edax that undergoes dormancy in an eutrophic lake was investigated from October 1988 through March 1989. During the fall all instars ofM. edax were present in the water column. By early December, only CI-CIV instars were found. M. edax was not found in the water column in January, but sediment cores in February revealed the presence of CIV's and adult females distributed predominantly at 0–3 cm and in lesser abundance at 3–6 cm. NoM. edax were found below 6 cm. By early March animals in the sediments emerged from dormancy and colonized the water column; CIV's and adult females predominated while CV's and adult males were present in small numbers. Dormancy of both juvenile and adult instars within one population is unusual among animal species. Life histories including multiple dormant stages may be more important for the adaptive evolution of cyclopoid copepods than calanoid copepods in freshwater habitats.     

Feeding dynamics of the copepod Diacyclops thomasi before, during and following filamentous cyanobacteria blooms in a large, shallow temperate lake

Cyanobacteria blooms are an increasing problem in temperate freshwater lakes, leading to reduced water quality and in some cases harmful effects from toxic cyanobacteria species. To better understand the role of zooplankton in modulating cyanobacteria blooms, from 2008 to 2010 we measured water quality and plankton abundance, and measured feeding rates and prey selectivity of the copepod Diacyclops thomasi before, during and following summertime cyanobacteria blooms in a shallow, eutrophic lake (Vancouver Lake, Washington, USA). We used a combined field and experimental approach to specifically test the hypothesis that copepod grazing was a significant factor in establishing the timing of cyanobacteria bloom initiation and eventual decline in Vancouver Lake. There was a consistent annual succession of zooplankton taxa, with cyclopoid copepods (D. thomasi) dominant in spring, followed by small cladocerans (Eubosmina sp.). Before each cyanobacteria bloom, large cladocerans (Daphnia retrocurva, Daphnia laevis) peaked in abundance but quickly disappeared, followed by brief increases in rotifers. During the cyanobacteria blooms, D. thomasi was again dominant, with small cladocerans abundant in autumn. Before the cyanobacteria blooms, D. thomasi substantially consumed ciliates and dinoflagellates (up to 100% of prey biomass per day), which likely allowed diatoms to flourish. A shift in copepod grazing toward diatoms before the blooms may have then helped to facilitate the rapid increase in cyanobacteria. Copepod grazing impact was the highest during the cyanobacteria blooms both years, but focused on non-cyanobacteria prey; copepod grazing was minimal as the cyanobacteria blooms waned. We conclude that cyclopoid copepods may have an indirect role (via trophic cascades) in modulating cyanobacteria bloom initiation, but do not directly contribute to cyanobacteria bloom decline.     

A simple method for maintaining a laboratory supply of limnetic cyclopoid copepods

The following method is used for maintaining a laboratory supply of freshwater cyclopoid copepods with intervening diapause phase. Animals are collected with a core sampler from the upper sediment surface just after initiation of diapause, i.e. during early summer for summer resting species and mid autumn for winter resting species. The method makes it possible at all times of the year to keep a variety of cyclopoid copepod species ready for experimental work. The following widespread species have been used: Mesocyclops leuckarti, Thermocyclops oithonoides, Diacyclops bicuspidatus, Cyclops vicinus, C. strenuus and C. abyssorum. Probably all cyclopoid copepods with a diapause phase could be stored according to the present method.     

Control of Diapause by Acidic pH and Ammonium Accumulation in the Hemolymph of Antarctic Copepods

Life-cycles of polar herbivorous copepods are characterised by seasonal/ontogenetic vertical migrations and diapause to survive periods of food shortage during the long winter season. However, the triggers of vertical migration and diapause are still far from being understood. In this study, we test the hypothesis that acidic pH and the accumulation of ammonium (NH₄ ⁺) in the hemolymph contribute to the control of diapause in certain Antarctic copepod species. In a recent study, it was already hypothesized that the replacement of heavy ions by ammonium is necessary for diapausing copepods to achieve neutral buoyancy at overwintering depth. The current article extends the hypothesis of ammonium-aided buoyancy by highlighting recent findings of low pH values in the hemolymph of diapausing copepods with elevated ammonium concentrations. Since ammonia (NH₃) is toxic to most organisms, a low hemolymph pH is required to maintain ammonium in the less toxic ionized form (NH₄ ⁺). Recognizing that low pH values are a relevant factor reducing metabolic rate in other marine invertebrates, the low pH values found in overwintering copepods might not only be a precondition for ammonium accumulation, but in addition, it may insure metabolic depression throughout diapause.     

桡足类滞育规律研究

首次提出用滞育指数对桡足类滞育能力进行相对量化处理 ,并对 10 2种桡足类的滞育能力同迁移能力、体长、栖息地之间的关系进行了数学分析 ,初步得出了滞育在桡足类中的分布规律 :在桡足类中滞育与迁移呈负相关 ,两者之间存在一定程度的置换 ;个体较小的桡足类一般具有较强的滞育能力和较弱的迁移能力 ,个体较大的桡足类一般具有较弱的滞育能力和较强的迁移能力 ;淡水桡足类一般比海洋桡足类具有较强的滞育能力。最后探讨了这种分布模式的成因     

Calanoid copepod grazing on phytoplankton: seasonal experiments on natural communities

Calanoid copepods are major components of most lacustrine ecosystems and their grazing activities may influence both phytoplankton biomass and species composition. To assess this we conducted four seasonal, in situ, grazing experiments in eutrophic Lake Rotomanuka, New Zealand. Ambient concentrations of late stage copepodites and adults of calanoid copepods (predominantly Calamoecia lucasi, but with small numbers of Boeckella delicata) were allowed to feed for nine days on natural phytoplankton assemblages suspended in the lake within 1160 litre polyethylene enclosures. The copepods reduced the total phytoplankton biomass of the dominant species in all experiments but were most effective in summer (the time of highest grazer biomass) followed by spring and autumn. In response to grazing pressure the density of individual algal species showed either no change or a decline. There were no taxa which increased in density in the presence of the copepods. The calanoid copepods suppressed the smallest phytoplankton species (especially those with GALD (Greatest Axial Linear Dimension) < µm) and there appeared to be no selection of algae on the basis of biovolume. Algal taxa which showed strong declines in abundance in the presence of the copepods include Cyclotella stelligera, Coelastrum spp., Trachelomonas spp., Cryptomonas spp., and Mallomonas akrokomos. Calanoid copepods are considered important grazers of phytoplankton biomass in this lake. The study supports the view that high phytoplankton:zooplankton biomass ratios and large average algal sizes characteristic of New Zealand lake plankton may, at least partly, be caused by year round grazing pressure on small algae shifting the competitive balance in favour of larger algal species.     

Littoral microcrustacea in Lake 302S in the Experimental Lakes Area of Canada: acidification and recovery

• 1 The littoral microcrustacean community (Cladocera and Copepoda) was examined from 1989 to 1991 in a lake experimentally acidified to pH 4.5, and from 1992 to 1997 during the early stages of pH recovery.
• 2 Cladoceran abundance declined significantly from 1989 to 1991 (pH 4.5), but species richness did not change. Acantholeberis curvirostris, Simocephalus serrulatus, Latona spp. (Latona setifera, L. parviremis), and all species of chydorid Cladocera declined markedly in abundance while at pH 4.5. The abundance of cyclopoid copepods was low and Ceriodaphnia and calanoid copepods were absent.
• 3 Recovery of the community was subsequently monitored as pH was incrementally changed to a target pH 5.1 in 1992 and 1993, and to 5.8 in 1994–97. Species richness remained unchanged. Chydorid cladocerans remained at low abundance in 1992, and only Chydorus cf. brevilabris increased substantially from 1993 to 1996. Non‐chydorid Cladocera increased in abundance in 1992, declined again in 1993, then gradually increased (mainly due to Ophryoxus gracilis) in 1994–96. All species declined in 1997 as minnows recolonized the lake. The calanoid copepod Leptodiaptomus minutus was present in low numbers in 1997.
• 4 The microcrustacean community in the littoral zone of Lake 302S has not yet shown consistent signs of recovery from acidification.

     

Spatial and temporal abundance patterns for the late stage copepodites of Metridia lucens (Copepoda: Calanoida) in the US northeast continental shelf ecosystem

The annual cycle of abundance for the calanoid copepod Metridialucens and its interannual variability are described from 17611 samples collected on 193 broad-scale plankton surveys ofthe US northeast continental shelf region from 1977 to 1999.The copepod’s seasonal distribution is illustrated withbi-monthly geographic abundance plots. Abundance of M. lucensis compared with various environmental variables, abundanceof the copepod Calanus finmarchicus, density of potential predatorsand the North Atlantic Oscillation (NAO) index. Metridia lucensabundance increased throughout the ecosystem during spring warmingand usually reached peak levels in late spring. The highestmean densities were measured in the Gulf of Maine (GOM), wherethe copepod is usually found year round and exhibits a weak,decreasing west to east abundance gradient. The less dense populationslocated on Georges Bank and within the Middle Atlantic Bightare characterized by year-round onshore to offshore gradientsthat strengthen during the summer months when the copepod concentratesoffshore where there is a cool layer of subthermocline water,the region often referred to as the cold pool. Interannual variabilityin abundance showed two persistent periods: above average valuesfrom 1979 to 1982, followed by very low levels from 1983 toat least 1987. Metridia lucens abundance in the 1990s has usuallybeen at or above time series means. None of the environmentalvariables measured during the surveys could be correlated tothis variability. The copepod’s abundance in the GOM wasnot related to variation in the NAO index or to changes in predatorabundance found in the region. The seasonal abundance cycleand interannual variability of M. lucens in the GOM were foundto be very similar to those found for the dominant copepod,Calanus finmarchicus. Reasons for this coupling are discussed.     

The food of adult copepods from Lake Kainji, Nigeria

SUMMARY. Gut contents of adult copepods from Lake Kainji were analysed. The calanoid copepod Tropodiaptomus banforanus was exclusively herbivorous with Melosira and Peridinium forming a large proportion of the diet. Of the cyclopoid copepods, Mesocyclops leuckarti was mainly carnivorous while the smaller Thermocyclops neglectus was mainly herbivorous. Experiments with Diplocystis (Microcystis) showed that it was not ingested by these three copepod species even after starvation and possible explanations for the results are discussed.     

Zooplankton of the lagoons of the Laccadives: diel patterns and emergence

Zooplankton populations in the water column increased substantiallyat night in four lagoons of the Laccadives. Epibenthic formsemerging into the water column during night, as well as non-epibenthicforms such as calanoid and cyclopoid copepods, were responsiblefor this. Unsealed traps were found subject to contaminationand hence less reliable in estimating densities of emergingfauna compared with sealed traps. Direct sampling of the substratumduring daytime showed that the actual densities of epibenthicforms are much higher than those observed in traps. Densitiesof emerging plankton varied geographically. Most of the zooplanktonorganisms which contribute to the lagoon fauna are residentin the lagoons and rarely occurred in the surrounding sea     

A matter of timing: heat wave impact on crustacean zooplankton

1. Climate change has affected zooplankton phenology and abundance in many freshwater ecosystems. The strong temperature anomalies that characterise summer heat waves make these events particularly suitable to study the effects of different seasonal warming patterns on zooplankton. Since heat waves are expected to occur more frequently under continuing climate change, they may also allow us to investigate how freshwater systems will be affected in the future. 2. Using a long‐term data set (1991–2007) from a shallow, eutrophic lake in Germany, we identify time periods in spring and summer during which cyclopoid copepods and bosminids are particularly sensitive to changes in water temperature. Based on this knowledge, we consider why summer populations responded differently to recent heat wave events that occurred at different times in the season. 3. Linear regressions of moving averages suggested that water temperatures shortly before and shortly after the clear‐water phase (CWP) were crucial for summer development of bosminids and cyclopoid copepods, respectively. Algal food availability (diatoms and cryptophytes) in the first weeks after the CWP also strongly influenced the summer populations of the two zooplankton groups. 4. Inter‐annual differences in water temperature during the critical time periods at least partly explained the contrasting responses of cyclopoid copepods and bosminids to heat wave events. 5. Our findings indicate that the zooplankton response to climate warming, particularly to heat wave events, is critically dependent on the temporal pattern of elevated water temperatures. Beyond that, we show that the summer zooplankton populations react to periods of warming in relation to events in the plankton annual cycle (such as the CWP in eutrophic lakes) rather than to warming at a fixed time in the season.     

Species-specific changes in the phenology and peak abundance of freshwater copepods in response to warm summers

SUMMARY 1. Climate warming is now widely recognised as a major factor influencing ecological processes in terrestrial, marine and freshwater habitats. Here, we investigated how a recent period of warm springs and summers has affected the population dynamics of various cyclopoid copepods in a central European lake. We compared (i) the duration of the period when the species were present in the water column, and (ii) their annual peak density in a period dominated by cool summers (1980–91) and one dominated by warm summers (1992–99). 2. The copepods under investigation were (i) Thermocyclops oithonoides, (ii) Mesocyclops leuckarti and (iii) Acanthocyclops robustus. These species differ in their thermal demand and seasonal phenology. Therefore, we hypothesised that enhanced summer warming would produce species‐specific responses. 3. The active phase of the copepods was usually prolonged both in spring and autumn. The earlier emergence of T. oithonoides (May in the warm years, July in the cool years) was probably related to high water temperature in late spring. The later onset of winter diapause in all species may have been coupled to raised temperature in late summer and autumn. 4. The annual peak abundance of the two thermophiles M. leuckarti and T. oithonoides increased significantly in the warm period. In the latter case, the increase was probably because of the early start to population growth. In contrast, M. leuckarti probably responded primarily to mid‐summer heat waves, in that its development time was likely to be short. We speculate that the increase in population size of both species resulted from the development of an additional generation (three instead of two cohorts per year). In contrast to these thermophiles, the coexisting A. robustus, which is adapted to a broader temperature range, did not respond noticeably to the warming trend. 5. In general, the nature of these responses to summer warming varied substantially among species, and depended on the detailed seasonal patterning of the warming. Our findings thus support the hypotheses that single species are sensitive indicators of climate change, and that the seasonal timing of warming is crucial in the context of climate–ecosystem relationships. 6. Moreover, our results add to the body of evidence that climate warming produces shifts in the seasonal phenology of aquatic and terrestrial organisms.     

Dissolved solids do not induce diapause in the calanoid copepod Aglaodiaptomus leptopus

The effect of different total dissolved solid levels (TDS) was investigated as a predictor of diapause induction in the calanoid copepod Aglaodiaptomus leptopus. We collected adult copepods in the field and monitored seasonal changes in diapause egg production. We determined total dissolved solid levels, conductivity and temperature values from five ponds. In experimental work, females bearing clutches, collected from the field, were monitored under laboratory conditions to determine the extent of diapause induced. Females without clutches were placed with males and then subjected to low, medium and high TDS levels. After six days, females bearing clutches were isolated to determine the proportion of clutches that were diapausing. The relationship between TDS and food levels was calculated using Williamson and Butlers food limitation index (f). We concluded that neither TDS nor temperature are predictors of the induction of diapause in this study. The obtained results suggest, however, that density possibly plays a role in predicting diapause induction.