Diapause in copepods (Crustacea) from ephemeral habitats with different hydroperiods in Everglades National Park (Florida,U.S.A.)

Water management practices in the Everglades have severely stressed the natural system, particularly by reducing the hydroperiods of much of the region. During the dry season of 1999, we investigated the influence of hydroperiod on the species composition and dormancy patterns of freshwater copepod communities in seasonal wetlands of Everglades National Park, Florida, U.S.A. The habitats were characterized by an annual dry season, from December through June. We sampled at two locations: the Long Pine Key area of the Rocky Glades region (short hydroperiod, ca. 4–5 months), and western Taylor Slough (intermediate hydroperiod, ca. 8–10 months). Both areas have experienced a reduction in natural hydroperiods and an increase in the frequency of dry-down. We collected weekly plankton samples from Rocky Glades solution holes to assess the potential species pool of copepods. To document the taxa capable of surviving dry-down by resting, we performed three immersion trials in which we rehydrated, in laboratory aquaria, sediment patches from solution holes and surface soils from all stations. Only a subset of the planktonic species collected emerged from the dried sediments. The cyclopoids Microcyclops rubellus and Paracyclops poppei were dominant. This is the first record of diapause for P. poppei. Species distributions from the different hydroperiod soil patches indicated that more diapausing species occurred at the sites that dried for shorter periods. Emerging individuals of M. rubellus and P. poppei were mainly ovigerous females, demonstrating a resting strategy seldom before recorded. The cyclopoid Diacyclops nearcticushad not been previously reported to diapause, but they emerged from the dried sediments in our trials. Our collections included six new records for Florida: Diacyclops nearcticus, Megacyclops latipes, Orthocyclops modestus, Elaphoidella marjoryae, Bryocamptus sp. and Bryocamptuscf. newyorkensis. Paracyclops poppei, Macrocyclops fuscus and Arctodiaptomus floridanus are new records for Everglades National Park. Clearly, diapause is an important strategy for the persistence of copepods in short-hydroperiod wetlands. The duration of the dry period appears to be inversely related to the number of species that emerge from diapause.     

The effects of temperature and food on naupliar development,growth and metamorphosis in three species of Boeckella (Copepoda:Calanoida)

Three species of Boeckella (B. triarticulata, B. dilatata and B. hamata) were reared from hatching to copepodite I (CI) at three naturally fluctuating food levels and three temperatures in a 3 × 3 × 3 factorial design. Development times, lengths and mortality were measured for each species in nine treatments. Temperature had the major effect on development times but food level had the major effect on CI lengths. Mortality varied interspecifically with treatment. The combined effect of temperature and food on development times and lengths was species-specific. There were trade-offs between development time and growth to meet constraints imposed by naupliar metamorphosis. The three species varied in the timing of metamorphosis to CI. B. triarticulata nauplii were age determined, B. dilatata nauplii were size determined and B. hamata nauplii were flexibly age and size determined depending on treatment. Differences in life history parameters and the timing of naupliar metamorphosis are discussed in relation to the distributions of the species in ponds (B. triarticulata), glacial lakes (B. dilatata) and coastal lakes (B. hamata) in the South Island of New Zealand.     

Effects of thermal effluents from the Bergum Power Station on the zooplankton in the Bergumermeer

The influence of thermal discharge from a 640 MW steam electric power station on the Bergumermeer (shallow, eutrophic lake) was investigated. The temperature of the thermal effluent did not exceed 30 °C. The lake was sampled extensively from 1975 to 1978. Zooplankton densities at different depths in the heated and non-heated parts of the lake were compared. A vital staining technique was used to assess entrainment mortality of cladocerans. The entrainment mortalities for the most abundant cladocerans were only 2 to 3% but for Leptodora kindtii 19% and about 25% for Diaphanosoma brachyurum, Ceriodaphnia pulchella and the cyclopoid nauplii. The ecological consequences for the lake ecosystem are discussed.     

How do temperature,dissolved organic matter and nutrients influence the response of Leptodiaptomus ashlandi to UV radiation in a subalpine lake?

1. Ultraviolet radiation (UV) is an important stressor for zooplankton in alpine lake ecosystems. Multiple environmental variables such as dissolved organic matter (DOM), temperature and nutrient availability may alter how UV affects zooplankton. 2. We conducted a week‐long experiment manipulating UV, nutrients and DOM in enclosures suspended at the surface of cold and warm alpine lakes to determine the interactive effects of these variables on ovigerous Leptodiaptomus ashlandi (Marsh, 1893), a calanoid copepod. 3. UV had a negative effect on nauplii and gravid females at the colder temperature and at low, ambient DOM levels, but had no effect at the warmer temperature or when DOM was added. At the warmer temperature, fewer nauplii were produced in the +nutrient compared to ?nutrient treatment. Adult survival was not affected by UV or any other experimental variable. 4. These results demonstrate that the extent of the impact of UV radiation on zooplankton in alpine systems is altered by other environmental variables, and that these effects may not be apparent from experiments that look only at the survival of adult organisms that are better defended against UV.     

A simple method for fitting Bělehrádek's equation to embryonic development data of zooplankton

A method is described whereby a Bělehrádek function is fitted to experimentally derived data for embryonic development duration at a range of temperatures. The method is applied to data for the freshwater copepods Cyclops abyssorum and Eudiaptomus gracilis from Lough Neagh, Northern Ireland. Differences in duration of embryonic development of Lough Neagh populations and that of previously published data for these species are discussed.     

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.     

Individual and combined toxicity of three heavy metals,Cu, Cd and Cr for the marine copepod Tisbe holothuriae

The acute toxicity of Cu, Cd and Cr to the marine copepod Tisbe holothuriae, Humes, was estimated by static bioassays and the LC _inf50 ^su48h (in mg/l) was calculated. Copper proved to be the most toxic (LC _inf50 ^su48h = 0,08 ± 0,01 mg/l) and chromium the least toxic (LC _inf50 ^su48h = 8,14 ± 0,05 mg/l), while cadmium showed an intermediate toxicity (LC _inf50 ^su48h = 0,97 ± 0,04 mg/l).In mixtures of the two metals an obvious synergism of the effects was observed in all cases. In all three combinations with two metals (Cu + Cd, Cu + Cr, and Cd + Cr) the mortality was higher than that expected on a purely additive basis. The mixture of the three metals presented a higher toxicity than that of the individual metals acting separately, but lower than that of all two metals mixture.     

PLASTICITY OF OXYLIPIN METABOLISM AMONG CLONES OF THE MARINE DIATOM SKELETONEMA MARINOI (BACILLARIOPHYCEAE)1

Diatom oxylipins have been observed to deleteriously impact copepod reproductive success. However, field studies have revealed very variable and case‐dependent results. Therefore, the plasticity of diatom oxylipin metabolism was studied among four clones of the marine diatom Skeletonema marinoi Sarno et Zingone. Diatom oxylipin metabolism was studied by two lipoxygenase (LOX) activity assays carried out at different pH values and by oxylipin quantification. The four clones showed no major metabolic differences in terms of protein content or growth rate. However, two of the clones produced significantly higher levels of oxylipins than the other two. LOX activity measurements also indicated clonal variability in fatty acid oxidative metabolism. The presence of clone‐specific differences in oxylipin metabolism may play a role in shaping diatom population dynamics by conferring selective advantages to certain clones.     

The predictability of biological populations and communities: an example from the meiobenthos

The predictability of temporal changes was analysed in the population density of three meiobenthic copepod species, and for three parameters characterizing this community. For Paronychocamptus nanus and Tachidius discipes a large part of the variation in time scales longer than 1 year is explainable as cyclic factors. In P. nanus clear cyles with periods of 2 years and 1.5 years were found. These cyclic factors can be extrapolated for prediction. In Canuella perplexa almost all the variation was due to unpredictable long-term drift. Community parameters are generally better predicted than population densities. In our data set total density of the copepods was the best parameter to monitor. Monitoring does not necessitate a strict sampling scheme; irregular quarterly sampling from the P. nanus series showed that the essential features of the series were still discernible.     

Assessing the diversity of New Zealand freshwater harpacticoid copepods (Crustacea: Copepoda) using mitochondrial DNA (COI) barcodes

Taxonomic and ecological studies of freshwater harpacticoid copepods are limited globally by the ability to easily and accurately identify specimens. Here, we test the use of the mitochondrial cytochrome c oxidase subunit I (COI) gene locus as a tool for assessing the diversity of freshwater Harpacticoida. We obtained sequences from New Zealand harpacticoid copepods, representing two families, five genera and nine species, including the non-indigenous Elaphoidella sewelli. All species were delineated by the COI gene. However, high intraspecific diversity was evident among populations of Elaphoidella bidens (>12%), and between North and South Island populations of Bryocamptus pygmaeus (>18%), potentially indicating the presence of morphologically cryptic taxa. We suggest that mitochondrial DNA (COI) sequences can provide a useful tool for the routine identification of freshwater harpacticoid copepods. Applications of these data will include assessing species diversity and biogeography as well as assisting with the detection of non-indigenous species.