Simulated sequestration of industrial carbon dioxide at a deep-sea site: Effects on species of harpacticoid copepods

One proposal for alleviating global warming is to sequester large amounts of industrial carbon dioxide on the deep-sea floor, but the environmental consequences of sequestration for the animals living in the sediment are poorly known. In an earlier publication, we reported that, during an experimental sequestration off central California (36.378°N, 122.676°W, 3262 m depth), most individuals of our target taxon (the harpacticoid copepods) were killed, but ∼ 20% survived. Because knowledge of which species survived and how they did so could clarify the effects of sequestration on the fauna, we have now identified the individuals from that experiment to species. Although most were adversely affected, species differed significantly in the degree of their susceptibility. Unexpectedly, six species showed no effect and may be resistant. The hypothesis that harpacticoids could escape the effects of carbon dioxide-rich seawater by moving deeper into the seabed was not supported. Exposure to carbon dioxide-rich seawater created partially defaunated areas, but we found no evidence that disturbance-exploiting harpacticoid species invaded during the recovery of the affected area. Because the environmental effects of the carbon dioxide (e.g. unusually acidic pore water) were still present, however, the opportunity for invasion might not yet have occurred. Differences among species in susceptibility increase the complexity of the effects of carbon dioxide sequestration on the deep-sea fauna.     

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.     

Daytime grazing and assimilation rates of planktonic copepods Acanthodiaptomus denticornis and Cyclops vicinus vicinus. Comparison of spatial and resource utilisation by rotifers and cladoceran communities in a eutrophic lake

The clearance rates of ¹⁴ carbon-labelled Chlamydomonas sp. by the copepodite and adult stages of the 2 dominant species of Copepoda were studied in eutrophic Lake Aydat. They varied from 30 to 3,007 µl ind^–1 h^–1 for Acanthodiaptomus denticornis (mean = 600 µl ind^–1 h^–1) and from 20 to 1,133 µl ind^–1 h^–1 for Cyclops vicinus (mean = 340 µl ind^–1 h^–1). Their maximum assimilation efficiencies were 58% and 50%, respectively. These populations collectively could consume the available food in 4 days during September (maximum daily grazing rate = 24%). Mean individual clearance rates could be ranked Acanthodiaptomus denticornis > Ceriodaphnia quadrangula > Chydorus sphaericus > Daphnia longispina > Cyclops vicinus vicinus > Bosmina longirostris > K. cochlearis > K. quadrata and Kellicottia longispina. Like cladocerans and rotifers, the copepods living in this eutrophic lake can feed at low oxygen concentrations.     

The influence of visibility and escape ability on sex-specific susceptibility to fish predation in Eudiaptomus gracilis (Copepoda,Crustacea)

The susceptibility to fish predation in males, ovigerous, and non-ovigerous females of the freshwater copepod Eudiaptomus gracilis is investigated in the laboratory by direct observation of the predation sequence of zebrafish, and by studying mortality when confronted with zebrafish or roach. Ovigerous females had the highest encounter rate indicating that the highly visible egg-clutch is a major determinant of their susceptibility. Males were least successful in escaping, the main reason being their inability or disinclination to react fast enough when attacked. This difference in escape reaction may have evolved because of sex-specific requirements in mate encounter and mate location. Ovigerous females and males had higher mortality than non-ovigerous females in all experiments while ovigerous mortality was higher than male mortality only in the zebrafish experiments. Neither experiment showed any difference in male and overall female mortality but as a consequence of the abrupt change in susceptibility between the ovigerous and non-ovigerous condition, it follows that sex-specific mortality rates may be dependent on the reproductive condition within diaptomid populations. A consequence of the sex-specific difference in escape ability is that the sex-specific mortality may be influenced by variation in the attack efficiency within and among predator populations.     

Conjugal transfer at natural population densities in a microcosm simulating an estuarine environment

Abstract Estuarine microcosms were used to follow conjugal transfer of a broad host range IncP1 plasmid from a Pseudomonas putida donor to indigenous bacteria. Donor cells were added at a concentration similar to the natural abundance of bacteria in the water column (10⁶ cells ml⁻¹). Transfer was not detected in any of the test microcosms (calculated limit of detection of 10⁻⁷ and 10⁻⁴ transconjugants donor⁻¹ in water column and sediment, respectively), with the exception of transfer to an isogenic recipient (added at 10⁵ cells ml⁻¹) in sediments of controls that had been inoculated with both donors and recipients. The same plasmid was transferred with high efficiencies (10⁻¹ to 10⁻³) to a variety of recipients in filter and broth matings. These results suggest that if conjugal gene transfer occurred, it was at efficiencies that were not detectable in estuarine microcosms simulating natural population densities.     

Microcrustacean communities in streams from two physiographically contrasting regions of Britain

ABSTRACT. Benthic microcrustaceans were sampled from forty-three streams in two physiographically contrasting regions of Britain: lowland southern England and upland Wales. Lowland streams had a significantly higher species richness than upland streams and, of the forty-three copepod and cladoceran species identified, only fourteen (33%) were found in both the lowlands and uplands. Canonical correspondence analysis revealed large differences in community structure between regions and between streams within regions. Differences within regions were related to pH, the distance downstream of a site and the presence of upstream impoundments. Variables underlying the large biological differences between regions are also discussed, including differences in chemistry (ionic content), physical parameters (e.g. flow), habitat availability and the influence of species biogeography. The importance of understanding species ecology and biogeography when assessing pollution impacts on stream communities is emphasized and a model is proposed for predicting the composition of microcrustacean communities in temperate European streams.     

Experimental whole‐lake increase of dissolved organic carbon concentration produces unexpected increase in crustacean zooplankton density

The observed pattern of lake browning, or increased terrestrial dissolved organic carbon (DOC) concentration, across the northern hemisphere has amplified the importance of understanding how consumer productivity varies with DOC concentration. Results from comparative studies suggest these increased DOC concentrations may reduce crustacean zooplankton productivity due to reductions in resource quality and volume of suitable habitat. Although these spatial comparisons provide an expectation for the response of zooplankton productivity as DOC concentration increases, we still have an incomplete understanding of how zooplankton respond to temporal increases in DOC concentration within a single system. As such, we used a whole‐lake manipulation, in which DOC concentration was increased from 8 to 11 mg L^?1 in one basin of a manipulated lake, to test the hypothesis that crustacean zooplankton production should subsequently decrease. In contrast to the spatially derived expectation of sharp DOC‐mediated decline, we observed a small increase in zooplankton densities in response to our experimental increase in DOC concentration of the treatment basin. This was due to significant increases in gross primary production and resource quality (lower seston carbon‐to‐phosphorus ratio; C:P). These results demonstrate that temporal changes in lake characteristics due to increased DOC may impact zooplankton in ways that differ from those observed in spatial surveys. We also identified significant interannual variability across our study region, which highlights potential difficulty in detecting temporal responses of organism abundances to gradual environmental change (e.g., browning).     

Ecological roles of saprotrophic Peronosporales (Oomycetes,Straminipila) in natural environments

The fungus-like Peronosporales are composed of several lineages of mainly biotrophic and hemibiotrophic representatives. Saprotrophic species of Peronosporales are limited to the genera Halophytophthora and Salisapilia, and to some species in Phytopythium and Phytophthora Clades 6 and 9, which inhabit terrestrial and all types of aquatic ecosystems. The recent discovery of species of Phytophthora in marine habitats and of Halophytophthora in freshwater indicated that these genera are not only morphologically but also ecologically poorly delineated. In addition, half of these genera are not monophyletic. They play key ecological roles by upgrading nutrients to higher trophic levels through colonization of plant debris, which makes substrata more palatable for detritivores or through zoospore grazing by zooplankton, although their role as saprotrophs is still largely neglected. Some species of Phytophthora can be aggressive opportunistic pathogens of riverine forests in the presence of susceptible hosts and favourable environmental conditions and, as a consequence, most studies have focused on their role as pathogens. Identification of species is challenging due to hybridization and species complexes that harbour multiple cryptic species and, therefore, is not reliable without DNA sequencing tools.     

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.     

Comparative carbon-specific ingestion rates of phytoplankton by Acartia tonsa,Centropages velificatus and Eucalanus pileatus grazing on natural phytoplankton assemblages in the plume of the Mississippi River (northern Gulf of Mexico continental shelf)

During four cruises in continental shelf waters of the northern Gulf of Mexico in the winters of 1981–83, we performed quantitative studies on the grazing of the copepods Acartia tonsa, Centropages velificatus, and Eucalanus pileatus, on phytoplankton using natural particulate assemblages as food. Stations were in, or adjacent to the plume of the Mississippi River, thereby providing wide spectra of phytoplankton and suspended riverine particulate concentrations. Phytoplankton cell volume was converted to carbon, and this, coupled with carbon content measurements of these three copepod species, allowed comparisons of daily ingestion effort even though the copepods were of different sizes. Data were expressed in the same units (% of copepod body carbon ingested copepod ^–1 d^–1) for each species. Over similar ranges of phytoplankton carbon concentrations (0.21–92.06 gCl^–1), Acartia tonsa had higher carbon-specific ingestion rates (x = 22.31%, range = 0.08–152.37%) than C. velificatus (x = 2.8%, range = 0.00–31.09 %) or E. pileatus (x = 1.27%, range = 0.10–2.80%). Carbon-specific ingestion rates increased with increasing phytoplankton carbon concentration for A. tonsa (R² = 0.81) and there was no evidence of saturated feeding on the carbon concentrations offered. A similar, but weaker trend was evident for E. pileatus (R² = 0.71), but not C. velificatus (R² = 0.49). Over a wide range of suspended particulate concentrations (10.6–95.2 mg l^–1), there was no systematic effect of particulates on carbon-specific ingestion rate for any of the three copepod species. However, A. tonsa appeared more adept at grazing in highly turbid water than C. velificatus or E. pileatus.