Temporal and Spatial Coexistence of Archaeal and Bacterial amoA Genes and Gene Transcripts in Lake Lucerne

Despite their crucial role in the nitrogen cycle, freshwater ecosystems are relatively rarely studied for active ammonia oxidizers (AO). This study of Lake Lucerne determined the abundance of both amoA genes and gene transcripts of ammonia-oxidizing archaea (AOA) and bacteria (AOB) over a period of 16 months, shedding more light on the role of both AO in a deep, alpine lake environment. At the surface, at 42 m water depth, and in the water layer immediately above the sediment, AOA generally outnumbered AOB. However, in the surface water during summer stratification, when both AO were low in abundance, AOB were more numerous than AOA. Temporal distribution patterns of AOA and AOB were comparable. Higher abundances of amoA gene transcripts were observed at the onset and end of summer stratification. In summer, archaeal amoA genes and transcripts correlated negatively with temperature and conductivity. Concentrations of ammonium and oxygen did not vary enough to explain the amoA gene and transcript dynamics. The observed herbivorous zooplankton may have caused a hidden flux of mineralized ammonium and a change in abundance of genes and transcripts. At the surface, AO might have been repressed during summer stratification due to nutrient limitation caused by active phytoplankton.

(Table 2) Fatty acid profile of blubber from harp seals and hooded seals from the Greenland Sea and Denmark Strait

Sub-Arctic marine ecosystems are some of the most productive ecosystems in the world's oceans. The capacity of herbivorous zooplankton, such as Calanus, to biosynthesize and store large amounts of lipids during the short and intense spring bloom is a fundamental adaptation which facilitates the large production in these ecosystems. These energy-rich lipids are rapidly transferred through the food chain to Arctic seals. The fatty acids and stable isotopes from harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) off East Greenland as well as their potential prey, were analysed. The results were used to describe the lipid dynamics and energy transfer in parts of the East Greenland ecosystem. Even if the two seal species showed considerable overlap in diet and occurred at relatively similar trophic levels, the fatty acid profiles indicated that the bases of the food chains of harp and hooded seals were different. The fatty acids of harp seals originate from diatom-based food chain, whereas the fatty acids of hooded seals originate from dinoflagellate and the prymnesiophyte Phaeocystis pouchetii-based food chain. Stable isotope analyses showed that both species are true carnivores on the top of their food chains, with hooded seal being slightly higher on the food chain than harp seal.

Dietary analysis of the herbivorous hemiramphid Hyporhamphus regularis ardelio: an isotopic approach

The stable isotope values for a range of size classes of Hyporhamphus regularis ardelio from Moreton Bay, south-east Australia were determined. There was a positive linear relationship between 613 C and standard length (L-s) (delta(13)C = 0.034 Ls - 16-23; r(2) = 0.78). delta(13)C ranged from -8.48 to - 17.29 parts per thousand with the smallest size class (50 mm Ls) being on average 1.04 parts per thousand enriched with respect to that of zooplankton (Temora turbinata) and 7.97 parts per thousand depleted compared to Zostera capricorni. delta(13)C was positively correlated with Ls (P 0.0 1) with delta(15) N, ranging from 9.18 to 11.00 parts per thousand. Fish of all size classes were on average 2.32 and 7.63 parts per thousand more enriched than zooplankton and seagrass, respectively. Carbon isotope data indicate that H. r. ardelio commence life as carnivores and change to a diet in which seagrass is the primary carbon source. The dependence on animal matter, however, is always present. Due to the low percentage of nitrogen in Z. capricorni (2.5%) compared to zooplankton (9.1%) it appears that nitrogen from zooplankton is necessary throughout their life history with the carbon requirements for these fish coming chiefly from Z. capricorni. (c) 2005 The Fisheries Society of the British Isles.

Structure of the tegument and ectocommensal microorganisms of Gyliauchen nahaensis (Digenea : Gyliauchenidae), an inhabitant of herbivorous fish of the Great Barrier Reef, Australia

The ultrastructure of the tegument and tegument-associated microorganisms of the gyliauchenid digenean Gyliauchen nahaensis is described by transmission and scanning electron microscopy. The tegument is devoid of surface spines and is characterized by a moderately folded apical membrane, abundant vesicles, basal mitochondria, a folded basal plasma membrane, and a thick basal matrix. Microorganisms form a dense biofilm on the tegument of the posterodorsal surface and the excretory papilla. At least 7 microbial morphotypes were identified, including eubacteria, spirochaetes, and nanobacteria.

Impact of fish cage-culture on the community structure of zooplankton in a tropical reservoir

We investigated the impact of fish cage culture on the zooplankton community structure in a tropical reservoir. We hypothesized that community abundance is greater near cages and increases over time due to the increase in food availability. Samplings were performed near, upstream and downstream from net cages, and before and after net cage installation. The abundance of zooplankton increased 15 days after the experiment was set up, followed by a reduction and finally increased. Rotifer abundance showed significant differences among sites (p<0.05) and sampling periods (p<0.001). Significant differences were also observed in total zooplankton and cladoceran abundance (p<0.001). The spatial and temporal variation of the physical and chemical variables were indirectly correlated with the structure and dynamic of the zooplankton community, as they indicated the primary production in the environment. Our hypothesis was rejected, since the zooplankton was abundant at the reference site. Only rotifers showed higher abundance near cages, due to the influence of food availability. Community dynamics during the experiment was also correlated to food availability. Our results suggest an impact of fish farming on the zooplankton community.

Daily variation of zooplankton abundance and evenness in the Rosana reservoir, Brazil: biotic and abiotic inferences

The zooplankton community presents stochastic temporal fluctuation and heterogeneous spatial variation determined by the relationships among the organisms and environmental conditions. We predicted that the temporal and spatial zooplankton distribution is heterogeneous and discrete, respectively, and that the daily variation of most abundant species is related to environmental conditions, specifically the availability of resources. Zooplankton samples were collected daily at three sampling stations in a lateral arm of the Rosana Reservoir (SP/PR). The zooplankton did not present significant differences in abundance and evenness among sampling stations, but the temporal variation of these attributes was significant. Abiotic variables and algal resource availability have significantly explained the daily variation of the most abundant species (p<0.001), however, the species distribution makes inferences on biotic relationships between them. Thus, not only the food resource availability is influential on the abundance of principal zooplankton species, but rather a set of factors (abiotic variables and biotic relationships).

Diel vertical migration of predators (planktivorous fish larvae) and prey (zooplankton) in a tropical lagoon

ABSTRACT Based on the hypothesis that diel vertical migration (DVM) is a mechanism of predator avoidance, the objective of the present study was to test for the occurrence of DVM in planktivorous fish larvae of Hypophthalmus edentatus (Spix, 1829) (Siluriformes, Pimelodidae) and Plagioscion squamosissimus (Heckel, 1840) (Perciformes, Sciaenidae), and zooplankton (rotifers, cladocerans and copepods) in an isolated tropical lagoon in the floodplain of the Upper Paraná River, Brazil (region of Parque Nacional de Ilha Grande). We investigated spatial overlap between predators (planktivorous fish larvae) and prey (zooplankton), and tested which physical and chemical variables of the water are related to the DVM of the studied communities. We performed nocturnal (8:00 pm and 4:00 am) and diurnal sampling (8:00 am and 4:00 pm) in the limnetic region of the lagoon for six consecutive months, from October 2010 to March 2011, which comprises the reproductive period of the fish species analyzed. During the day the larvae tried to remain aggregated in the bottom of the lagoon, whereas at night they tried to disperse in the water column. Especially for cladocerans, the diel vertical migration is an important behavior to avoid predation larvae of H. edentatus and P. squamosissimus once decreased spatial overlap between secured and its potential predators, which corroborates the hypothesis that DVM is a mechanism of predator avoidance. Although significant correlations were observed between the abiotic factors and WMD of microcrustaceans at certain times of day, the effect of predation of fish larvae on zooplankton showed more important in this environment, because the small depth and isolation not allow great variation of abiotic factors seasonally and between strata the lagoon.

Development of specific ITS markers for plant DNA identification within herbivorous insects

DNA based techniques have proved to be very useful methods to study trophic relationships 17 between pests and their natural enemies. However, most predators are best defined as omnivores, 18 and the identification of plant-specific DNA should also allow the identification of the plant 19 species the predators have been feeding on. In this study, a PCR approach based on the 20 development of specific primers was developed as a self-marking technique to detect plant DNA 21 within the gut of one heteropteran omnivorous predator (Macrolophus pygmaeus) and two 22 lepidopteran pest species (Helicoverpa armigera and Tuta absoluta). Specific tomato primers 23 were designed from the ITS 1-2 region, which allowed the amplification of a tomato DNA 24 fragment of 332 bp within the three insect species tested in all cases (100% of detection at t = 0) 25 and did not detect DNA of other plants nor of the starved insects. Plant DNA half-lives at 25ºC 26 ranged from 5.8h, to 27.7h and 28.7h within M. pygmaeus, H. armigera and T. absoluta, 27 respectively. Tomato DNA detection within field collected M. pygmaeus suggests dietary mixing 28 in this omnivorous predator and showed a higher detection of tomato DNA in females and 29 nymphs than males. This study provides a useful tool to detect and to identify plant food sources 30 of arthropods and to evaluate crop colonization from surrounding vegetation in conservation 31 biological control programs.

Differential effectiveness of microbially induced resistance against herbivorous insects in Arabidopsis.

Rhizobacteria-induced systemic resistance (ISR) and pathogen-induced systemic acquired resistance (SAR) have a broad, yet partly distinct, range of effectiveness against pathogenic microorganisms. Here, we investigated the effectiveness of ISR and SAR in Arabidopsis against the tissue-chewing insects Pieris rapae and Spodoptera exigua. Resistance against insects consists of direct defense, such as the production of toxins and feeding deterrents and indirect defense such as the production of plant volatiles that attract carnivorous enemies of the herbivores. Wind-tunnel experiments revealed that ISR and SAR did not affect herbivore-induced attraction of the parasitic wasp Cotesia rubecula (indirect defense). By contrast, ISR and SAR significantly reduced growth and development of the generalist herbivore S. exigua, although not that of the specialist P. rapae. This enhanced direct defense against S. exigua was associated with potentiated expression of the defense-related genes PDF1.2 and HEL. Expression profiling using a dedicated cDNA microarray revealed four additional, differentially primed genes in microbially induced S. exigua-challenged plants, three of which encode a lipid-transfer protein. Together, these results indicate that microbially induced plants are differentially primed for enhanced insect-responsive gene expression that is associated with increased direct defense against the generalist S. exigua but not against the specialist P. rapae.

Factors influencing zooplankton size structure at contrasting temperatures in coastal shallow lakes: Implications for effects of climate change

We assessed the importance of temperature, salinity, and predation for the size structure of zooplankton and provided insight into the future ecological structure and function of shallow lakes in a warmer climate. Artificial plants were introduced in eight comparable coastal shallow brackish lakes located at two contrasting temperatures: cold-temperate and Mediterranean climate region. Zooplankton, fish, and macroinvertebrates were sampled within the plants and at open-water habitats. The fish communities of these brackish lakes were characterized by small-sized individuals, highly associated with submerged plants. Overall, higher densities of small planktivorous fish were recorded in the Mediterranean compared to the cold-temperate region, likely reflecting temperature-related differences as have been observed in freshwater lakes. Our results suggest that fish predation is the major control of zooplankton size structure in brackish lakes, since fish density was related to a decrease in mean body size and density of zooplankton and this was reflected in a unimodal shaped biomass-sizespectrum with dominance of small sizes and low size diversity. Salinity might play a more indirect role by shaping zooplankton communities toward more salt-tolerant species. In a global-warming perspective, these results suggest that changes in the trophic structure of shallow lakes in temperate regions might be expected as a result of the warmer temperatures and the potentially associated increases in salinity. The decrease in the density of largebodied zooplankton might reduce the grazing on phytoplankton and thus the chances of maintaining the clear water state in these ecosystems

Patterns and processes of littoral zooplankton composition in relation to the trophic state of the environment

Avhandlingen handlar om hur kompositionen hos litoralt djurplankton varierar med omgivningens trofiska nivå (m.a.o. eutrofieringsgrad). Arbetets inledande mål är att beskriva hur mängden och artmångfalden hos djurplankton i strandnära vattnen och de omgivande organismsamhällen ändras med närsaltshalter. Huvudsyftet är att utreda allmänna mekanismer som styr dessa mönster och som på så sätt kan vara viktiga i att reglera samhällen även i andra ekologiska system. Undersökningarna gjordes i åländska flador över flera tillväxtsäsonger samt i laboratorier där omgivningsförhållanden i fladorna kunde simuleras och manipuleras. Djurplankton i dessa lagunlika vikar är lägliga modellsystem. Flador är lämpligt avgränsade från det omgivande havet och förekommer allmänt i norra Östersjöregionen. Således kan de inom ett litet område som Åland representera hela regionala gradienten från näringsfattiga till näringsrika förhållanden. De små kräft- och hjuldjuren som djurplankton består av befinner sig i mitten av näringsväven. De sammankopplar olika typer av mikrobiell produktion vidare till högre konsumenter och är på så sätt centrala för organismsamhällens struktur och funktion i nästan alla akvatiska miljöer. I likhet med primärproducenterna (d.v.s. växter och alger som direkt påverkas av närsaltshalterna, och som bl.a. utgör föda och habitat för djurplankton) samvarierar kompositionen hos djurplankton tydligt med omgivningens trofiska nivå tills den blir hög. Sedan börjar hela samhällskompositionen utveckla sig åt två skilda håll. Dessa mönster kan för djurplanktonets del förklaras med att dess komposition ingalunda styrs endast av primärproducenterna, utan av ett komplicerat samspel mellan dessa resurser samt konkurrerande och högre konsumenter (d.v.s. predatorer på flera högre trofinivåer). Detta kom fram speciellt i laboratorieförhållanden då kompositionen hos dessa samhällskomponenter manipulerades. Både deras sammansättning och relativa tätheter i sig, samt en kombination av båda visade sig styra djurplanktonkompositionen. Lokala processer (inom fladorna) och synnerligen förändringar hos olika fundament- (speciellt vass, borstnate och rödsträfse), kärn- (speciellt yngel av a bborre och mört) och nyckelarter (stora predatorer som gädda) verkar kunna avgöra till vilken grad djurplanktonkompositionen samvarierar med omgivningens trofiska nivå. Inte bara samhällen utan också de mekanismer som styr dem ändras med omgivningens trofiska nivå. Flador är ypperliga naturliga laboratorier för att studera dessa och även andra allmänekologiska mönster och mekanismer. De är också oerhört viktiga miljöer för hela kustregionens natur.

Ecological interactions between zooplankton and photosynthetic bacteria in Crawford Lake, Ontario

The present study was carried out to test the hypothesis that photosynthetic bacteria contribute a large portion of the food of filter feeding zooplankton populations in Crawford Lake, Ontario. The temporal and spatial variations of both groups of organisms are strongly dependent on one another. 14 By using C-Iabelled photosynthetic bacteria. the ingestion and clearance rates of Daphnia pulex, ~. rosea, and Keratella spp were estimated during summer and fall of 1982. These quantitative estimations of zooplankton ingestion and clearence rates on photosynthetic bacteria comprised an original addition to the literature. Photosynthetic bacteria comprised a substantial portion of the diet of all four dominant zooplankton species. The evidence for this is based on the ingestion and clearance rates of the dominant zooplankton species. Ingestion rates of D. pulex and D. rosea ranged 5 5 -1 -1 - -- 5 - -- 5 from 8.3X10 -1 to 14.6XlO -1 cells.ind. hr and 8.1X10 to 13.9X10 cells.ind. hr • Their clearance rates ranged from 0.400 to 1.000 -1 -1 -1 -1 ml.ind. hr. and 0.380 to 0.930 ml.ind. hr • The ingestion and clearance -1 -1 -1 -1 rates of Keratella spp were 600 cell.ind. hr and 0.40 ul.ind. hr respectively. Clearance rates were inversely proportional to the concentration of food cells and directly proportional to the body size of the animals. It is believed that despite the very short reg~neration times of photosynthetic bacteria (3-8 hours) their population densities were controlled in part by the feeding rates of the dominant zooplankton in Crawford Lake. By considering the regeneration times of photosynthetic bacteria and the population clearance rates of zooplankton, it was estimated that between 16 to 52% and 11 to 35% of the PHotosynthetic bacteria were' consumed· by Daphnia· pulex. and Q.. rosea per day. The temporal and spatial distribution of Daphnia pulex, !.. rosea, Keratella quadrata, K. coChlearis and photosynthetic bacteria in Crawford Lake were also investigated during the period of October, 1981 to December, 1982. The photosynthetic bacteria in the lake, constituted a major food source for only those zooplankton Which tolerate anaerobic conditions. Changes in temperature and food appeared to correlate with the seasonal changes in zooplankton density. All four dominant species of zooplankton were abundant at the lake's surface (O-4m) during winter and spring and moved downwards with the thermocline as summer stratification proceeded. Photosynthetic bacteria formed a 2 m thick layer at the chemocline. The position of this photosynthetic bacterial J-ayer changed seasonally. In the summer, the bacterial plate moved upwards and following fall mixing it moved downwards. A vertical shift of O.8m (14.5 to 15.3m) was recorded during the period of June to December. The upper limit of the photosynthetic bacteria in the water column was controlled by dissolved oxygen, and sulfide concentrations While their lower limit was controlled by light intensity. A maximum bacterio- 1 chlorophyll concentration of 81 mg Bchl.l was recorded on August 9, 1981. The seasonal distribution of photosynthetic bacteria was controlledinpart' by ·theg.-"z1ai'_.Q;~.zoopl. ank:tCm;-.Qther -ciactors associated with zooplankton grazing were oxygen and sulfide concentrations.