The influence of copepod and krill grazing on the species composition of phytoplankton communities from the Scotia Weddell sea

The influence of copepods (mainly Oithona sim-ilis) and krill (Euphausia superba) grazing on the species composition of plankton communities in ship board con tainers was investigated during the spring and post spring period in the Scotia Weddell Sea in the Antarctic ocean. Numbers of grazers were experimentally manipulated in containers with natural phytoplankton assemblages. With ratural levels of copepods but no krill a high (700–950 g C·l¹, ca 30 g chl a·.l¹) phytoplankton biomass developed. In these cultures large diatoms, e.g. Corethron criophilum and chains of Thalassiosira sp., made up 80% of total phytoplankton cell carbon at the end of the experiment. In cultures with elevated numbers of copepods (5X or 10X the natural level) phytoplankton biomass was somewhat reduced (ca 23 g chl a · l¹) compared to cultures with natural copepod abundance, but still high. Phytoplankton species composition was on the other hand greatly influenced. Instead of large diatoms these cultures were dominated by Phaeocystis pouchetii (70%) together with small Nitszchia sp. and Chaetoceros neogracile (20%). In containers with krill (both juveniles and adults), but without elevated numbers of copepods, phytoplankton biomass rapidly approached zero. With 10X the in situ level of copepods, krill first preyed on these before Corethron criophilum and Thalassiosira sp. were grazed. When krill were removed a plankton community dominated by flagellates (60–90%), e.g. Pyramimonas sp. and a Cryptophycean species, grazed by an unidentified droplet-shaped heterothrophic flagellate, developed. These flagellates were the same as those which dominated the plankton community in the Weddell Sea after the spring bloom. A similar succession was observed in situ when a krill swarm grazed down a phytoplankton bloom in a few hours. Our experiments show that copepods cannot control phytoplankton biomass in shipboard cultures even at artificially elevated numbers. Krill at concentrations similar to those in natural swarms have a great impact on both phytoplankton biomass and species composition in shipboard cultures. Both copepods and krill may have an impact on phytoplankton species composition and biomass in situ since the rates of phytoplankton cell division were probably artificially increased in shipboard cultures compared to natural conditions, where lower growth rates make phytoplankton more vulnerable to grazing. A similarity between phytoplankton successions in containers and in situ, especially with respect to krill grazing, supports the conclusion that grazing may structure phytoplankton communities in the Scotia-Weddell Sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Protozoan communities in chalk streams

This study assessed the individual effects of three mayflies (Paraleptophlebia sp., Ephemerella subvaria McDunnough and Epeorus sp.) and one caddisfly (Psilotreta sp.) on periphyton communities associated with clay tiles and leaves. Algal densities were estimated for leaf discs and tiles from experimental chambers (with individual grazers) and control chambers (i.e., no grazers). Scanning electron micrographs (SEM) of leaf discs and tiles also were taken for all mayfly grazing experiments. Densities of algae on leaf discs were two to five times lower than on tiles. Mouthpart morphology influenced how different insects grazed the periphyton community. Paraleptophlebia had typical collector-gatherer mouthparts and had no effect on diatom densities associated with leaves whereas diatom densities on grazed tiles were higher than densities on tiles from control chambers. Epeorus had brusher mouthparts and had little impact on diatom densities regardless of substratum type. The other two grazers had the blade-like mandibles of a scraper. Psilotreta did not reduce the numerical abundance of diatoms on either substratum, but did alter community structure by significantly reducing densities of stalked Gomphonema olivaceum and large species of Navicula and Nitzschia; densities of smaller diatoms (Achnanthes spp) increased. However, E. subvaria reduced densities of most algal species regardless of size on both substrata and also significantly altered community structure. SEMs of substrata grazed by mayflies showed reductions in fungal hyphae on all grazed leaf discs, decreases in filamentous algal forms on grazed tiles, and greatly shortened stalks of G. olivaceum (Paraleptophlebia only). Thus, periphyton communities are different on leaves versus tiles and grazers with different mouthpart morphologies have varying effects on both algal and heterotrophic microbial community structure.     

Ethnobotany of seaweeds: clues to uses of seaweeds

Extensive uses of fresh and dried seaweeds by coastal populations over the world can furnish clues to potential food and other uses of seaweeds, just as the first extraction of a seaweed gelatin now used for bacteriological purposes was discovered by a housewife in search of a pudding. Ethnic uses as food depend heavily on closely related species suitable for making cool, gelatinous dishes or concoctions, or on species suitable for adding to soups or stews. Rarely, single species like cochajugo (Durvillea antarctica) in Chile and rimu (Durvillea antarctica) in New Zealand point to different kinds of food preparation. Oriental cuisine incorporates many different species of seaweeds in a wide variety of ways, whereas commercial western uses depend upon extracts of wall materials to suspend, emulsify or stabilize a broad variety of foods and products.     

The systematics of Porphyra: character evolution in closely related species

Isozymes, vegetative and reproductive morphology, seasonality, vertical and geographic distributions and chromosomes were compared for six pairs of putative sibling species of Porphyra (P. abbottae/P. torta, P. fallax subsp. fallax/P. fallax subsp. conwayae, P. amplissima/P. cuneiformis, P. fucicola/P. leucostica, P. miniata/P. variegata, P. umbilicalis/P. umbilicalis) and among five species in a complex (P. brumalis, P. kurogii, P. linearis, P. pseudolinearis, and P. purpurea.) Geographic distribution and zymograms for certain proteins showed the greatest change between species pairs: only one pair of species had identical distributions, and most species pairs were disjunct; every species had a different allozyme for GOT-1, whereas all species had apparently identical proteins for phycoerythrin. Seasonality and habitat exhibited moderate differentiation: Northeast Pacific sibling species were characterized by a high intertidal winter species pairing with a mid intertidal spring species, whereas all but one of the other species pairs exhibited nearly identical vertical distributions and seasonalities. There were few changes in morphology: most species pairs had essentially identical morphologies and coloration and the same arrangement of reproductive cells. Chromosome numbers and karyotypes were identical for species pairs and in the species complex. These results provide evidence for different rates of evolution of different characters in the genus Porphyra.     

Species diversities analyzed by density and cover in an early volcanic succession

To evaluate alpha diversities, various variables such as density, cover, volume, and weight have been used. However, density is often a distinct variable from the remaining three. To clarify differences in diversity measured by those two kinds of variables, the data collected in fourteen 2×5 m permanently-marked plots on Mount Usu, Japan, which erupted during 1977 and 1978 in growing seasons from 1983 to 1989 was analyzed, using Shannon's species diversity (H) that is represented as a result of combination of species richness and evenness (J). H and J were evaluated by density (density H and J) and cover (cover H and J). Cover H and J were significantly lower than density H and J, indicating that cover H has different characteristics from density H. Those differences are due to differences in evenness, because species richness is the same. The rank orders of species density are different from those of cover. The predominance of a few perennial herbs greatly decreases cover evenness, while seedling establishment success influences density evenness. Therefore, I propose that, during the early stages of succession on harsh environments such as volcanoes, density diversity represents seedling establishment success rate while cover diversity expresses vegetative reproduction success rate.     

Optimal foraging by a suspension-feeding copepod: responses to short-term and seasonal variation in food resources

Laboratory radioisotope experiments were used to investigate the effects of phytoplankton seasonal succession on the selectivity and clearance rates of a suspension-feeding copepod in two Indiana lakes. Responses to particle size and quality were tested by allowing adult female Diaptomus birgei feeding in natural seston to select between a small (6×7 m) flagellate (Chlamydomonas reinhardii) and a large, poor quality food (heat-killed Carteria olivieri, 22×25 m). Short-term responses were tested in one lake by additional treatments in which copepods were acclimated for 5–6 h in filtered lake water (starved) or natural seston with added Chlamydomonas (enriched). Copepods from both lakes fed selectively on the small live flagellate during the spring bloom of edible phytoplankton but fed selectively on the larger, poor quality particle during the clear water phase when food was scarce. These results are interpreted as an interaction between the concentration-dependent selectivity for high quality foods predicted by optimal diet theory and a perceptual bias for large-sized particles. Selectivity for high-quality food was intermediate and clearance rates were depressed when total phytoplankton abundance was high but dominated by filamentous cyanobacteria. In each experiment copepods also responded to the short-term manipulations by exhibiting weaker discrimination against the poor quality particle in the starvation treatment and stronger discrimination in the enriched treatment. A two-way mixed model ANOVA revealed substantial short term (37%) and seasonal (53%) components to the total variance in selectivity. Clearance rates were also influenced by both phytoplankton succession and the short-term resource manipulations. As expected, clearance rates on the poor quality food were more sensitive to the abundance of alternative foods. These results show how the feeding behavior of a freshwater copepod is modulated by both seasonal and short-term variation in natural food.     

Seasonal succession of phytoplankton in a lake of the Paraná river floodplain,Argentina

Phytoplankton biomass, morphological and taxonomic composition, species diversity and productivity were analyzed in a shallow lake of the Middle Paraná River floodplain (El Tigre, 31 ° 41 S and 60° 42 W), between November 1986 and July 1988. Lake inundation (filling and through-flow phases) constituted an intense long-term perturbation in the physical and chemical environment. As the lake filled with river water, K-selected species (netplanktonic filamentous bluegreens, > 37 µm, with low surface area/volume (SA/V) ratios) that had existed prior to filling (late spring 1986) were replaced in summer-fall by r-selected species (nannoplanktonic chlorophytes and cryptophytes, < 37 µm, mainly stout forms with high SA/V ratios). During the through-flow phase, lentic phytoplankton was replaced by lotic flagellate populations due to the direct flushing by river water. During the period of falling water (drainage and isolation phases), nanoplanktonic algae with similar characteristics to those of the filling phase dominated in late winter-spring. Later in the isolation phase, these were succeeded by K-selected species (netplanktonic algae, mainly motile spherical dinoflagellates and filamentous bluegreens with low SA/V ratios). Simultaneously, primary production per unit biomass decreased and total biomass and specific diversity increased. Seasonal changes of phytoplankton in floodplain lakes can be interpreted as the interaction between true successional development (as observed in the drainage and isolation phases) and intermediate disturbance. Using Reynolds' terminology, short-term disturbance (slight inflow of nutrient-rich river water) caused reversion to an earlier stage in the former succession, and long-term disturbance (lake inundation) truncated the successional progression and a new (or shifted) succession was initiated.     

An experimental study of the effects of fish zooplanktivory on the phytoplankton of a Brazilian reservoir

Two short-term (4–5 week) sets of enclosure experiments were conducted during winter periods (1982, 1983) in Americana Reservoir near Sao Paulo to test effects of fish predation reducing grazing pressure by large cladoceran zooplankton (mainlyDaphnia gessneri) on phytoplankton density, cell size distribution, biomass, species composition and richness. Two enclosures were stocked with the zooplanktivorous characin fishAstyanax whereas two others remained fishless during each set of experiments. Within two weeks or less, phytoplankton cell density and biomass were significantly reduced in the fishless enclosures, particularly in the small cell size (< 15 µm) fraction. Changes also occurred in species composition and richness. These shifts generally were maintained or intensified during the course of the experiments.     

Fatty Acid Patterns in <Emphasis Type="Italic">Chlamydomonas</Emphasis> sp. as a Marker for Nutritional Regimes and Temperature under Extremely Acidic Conditions

Fatty acid profiles were used to characterize nutritional pathways in Chlamydomonas sp. isolated from an acidic mining lake (pH 2.7). Surprisingly, profiles of Chlamydomonas sp. grown in the lab under photoautotrophic, mixotrophic, and heterotrophic conditions at in situ deep strata lake water temperatures (8°C) were very similar, polyunsaturated fatty acids including -linolenic acid (18:33) and 16:43 along with palmitic acid (16:0) being most abundant. Therefore, heterotrophic growth of Chlamydomonas sp. at low temperatures can result in high concentrations of polyunsaturated fatty acids, as previously only described for some psychrophilic bacteria. By contrast, the cultivation of isolated Chlamydomonas sp. at 20°C, reflecting surface water temperatures, provided fatty acid patterns characteristic of the nutrition strategy applied: the concentration of polyunsaturated fatty acids decreased when the growth pathway changed from photoautotrophic via mixotrophic to heterotrophic. Total fatty acid concentration also diminished in this order. Principal component analysis confirmed the significance of FA profiling to mirror nutritional pathways. Lake-water analysis revealed low concentrations of dissolved organic carbon, mainly consisting of polymeric fulvic acids that are unable to support heterotrophic growth of Chlamydomonas sp. Polymeric fulvic acids present in the deeper strata of the lake turned out to be formed in situ on the basis of organic monomers including reduced sulfur-containing ones, as revealed by thermochemolysis and pyrolysis. Growth of Chlamydomonas sp. in the deep chlorophyll maximum is therefore assumed to mainly result from photosynthesis, despite very low photon densities. Phytol-including metabolites proved to be significant biomarkers to indicate the nutritional pathway of Chlamydomonas sp. , -Dicarboxylic acids—light-induced degradation products of unsaturated fatty acids—appeared to be good indicators of photooxidative alterations to the algal species under study.     

Branchinecta belki n. sp. (Branchiopoda: Anostraca), a new fairy shrimp from Mexico,hybridizing withB. packardi Pearse under laboratory conditions

A new fairy shrimp,Branchinecta belki n.sp., endemic to the south of Coahuila state is described and figured. A total of nine species of phyllopods, including the new species, occur in ponds in the type area.The laboratory hybridization ofB. belki andB. packardi through no-choice mating tests in reciprocal crosses is discussed. A mixture of characteristics of parental species is present in male F1 and F2 hybrids. This may provide a biological tool, or search image (sensu Wiman, 1979a), for detecting male hybrids, should such exist, between theBranchinecta species of this study in nature. In addition to the reported interspecific hybridizations inStreptocephalus (Wiman, 1979a & 1979b) and inArtemia (Bowenet al., 1985) under laboratory conditions, the new evidence inBranchinecta suggests that absence of efficient premating mechanisms may be common in Anostraca.     

Microhabitat location and niche segregation in two sibling species of Drosophilid parasitoids: Asobara tabida (Nees) and A. rufescens (Foerster) (Braconidae: Alysiinae)

Summary Olfactometer tests with Asobara tabida (Nees 1834), a larval endo-parasitoid of frugivorous Drosophilidae showed that females are attracted to the odour of host food: a suspension of living yeast. This attraction decreased as the fermenting medium grew older and became less likely to contain suitable host stages. Olfactometer tests with — what was considered to be — A. tabida from two different microhabitats (fermenting fruits and decaying plants) showed a genetically determined difference in microhabitat odour preference between the two microhabitat strains. Each strain preferred the odour of its own microhabitat. This odour preference was not modified by larval conditioning. Hybridization tests indicated that we were dealing with two sibling species: A. tabida and A. rufescens (Foerster 1862), reproductively isolated by a pre-mating isolation mechanism only. Enforced matings resulted in fertile female offspring. Some small morphological differences were detected. The two species live sympatrically, although each inhabits and is most attracted to its own microhabitat.     

Nutrient-induced competition between two species of marine diatoms

Competition experiments betweenPhaeodactylum tricornutum andSkeletonema costatum showed that even at temperatures higher than 10°C (i.c. 14°C), the development ofSkeletonema can be favoured by adjusting nutrient levels and nutrient ratios. Low NSi ratios were found to favourSkeletonema. Additionally, high NP ratios further enhanced the ability ofSkeletonema to dominate the cuftures. Contrary to some statements in literature, it seems that high concentrations of silicates are more important for the dominance ofSkeletonema costatum in large-scale cultures than just low temperatures. This finding is important with regard to stimulating the blooming ofSkeletonema costatum in natural phytoplankton populations as food for bivalve molluscs.     

Thermocyclops ouadanei n. sp. (crustacea: copepoda) from Mauretania (North-West Africa)

Thermocyclops ouadanei n. sp. from Mauretania is described and figured. This new species is characterized by the structure of the receptaculum seminis, the uniting lamella of the P₄ which bears no marginal denticles on the rounded prominences, the length of the apical spines on the endopodite 3 of the P₄ and by the length of the furcal setae. Its relationship with other Thermocyclops species is discussed.Contribution no 16 from project Limnology of the Sahara under contract n° 2.0009.75 with the Fonds voor Kollektief Fundamenteel Onderzoek, Belgium     

Using multiviriate analyses for separating spatial and temporal effects within species-environment relationships

We present a multiviriate approach for the analysis of contigency tables involved in the study of species-environment relationships. The first table (species x sample) contains the abundance of p species collected in n samples. The second table (environment variables x sample) contains values for q environmental variables measured in the n samples. The third table contains the indication of where and when samples were taken.In this paper we demonstrate: (1) how to match an environmental table and a faunistic table using co-inertia analysis; (2) how to take into account a spatial effect using between-class analyses; and (3) how to combine point (1) and (2) to determine the spatial structure shared by fauna and habitat.We illustrate such an approach by using a set of hydrobiological data concerning 13 Ephemeroptera species and ten physical and chemical variables which were collected in the same site at the same dates in a small river of the Prealps.     

Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis

Summary The mean stable-carbon isotope ratios (¹³C) for polar bear (Ursus maritimus) tissues (bone collagen –15.7, muscle –17.7, fat –24.7) were close to those of the same tissues from ringed seals (Phoca hispida) (–16.2, –18.1, and –26.1, respectively), which feed exclusively from the marine food chain. The ¹³C values for 4 species of fruits to which polar bears have access when on land in summer ranged from –27.8 to –26.2, typical of terrestrial plants in the Arctic. An animal's ¹³C signature reflects closely the ¹³C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.     

Using stable hydrogen and oxygen isotope measurements of feathers to infer geographical origins of migrating European birds

Successful application of stable-hydrogen isotope measurements (D_f) of feathers to track origins of migratory birds and other wildlife requires a fundamental understanding of the correlation between D_f and deuterium patterns in rainfall (D_p) over continental scales. A strong correlation between D_p and D_f has been confirmed for birds and insects in North America, but not yet for other continents. Here, we compare D_f data from resident European birds to new D_p basemaps for Europe. Three maps, representing growing-season and mean annual D_p estimates from an elevation-explicit, detrended interpolation model and growing-season D_p estimates from simple Kriging, all indicate that strong isotope gradients occur across Europe with a general depletion occurring in a northeast direction. The feather data, representing 141 individuals of 25 avian species from 38 sites, ranged from –131 to –38. Regression analysis showed that strong correlations existed between both mean annual and growing-season D_p estimated by detrended interpolation and D_f of non-aquatic and non-corvid birds (r²=0.66 and 0.65, respectively). We also examined mean annual and growing-season ¹⁸O_p vs. ¹⁸O_f for our samples. Both oxygen regressions were similar (r²=0.56 and 0.57, respectively) but poorer than for deuterium. Our study reveals that D measurements of feathers from migratory birds in Europe may be used to track their origin and movements, and so provide a powerful investigative tool for avian migration research in Europe.     

Identification and chromosomal locations of aconitase gene loci in Triticeae species

Summary Two systems of monomeric aconitase (ACO) isozymes, designated ACO-1 and ACO-2, were identified in Triticum aestivum and in five diploid Triticeae species. The gene loci Aco-A1, Aco-B1, and Aco-D1 were located in T. aestivum cv. Chinese Spring chromosome arms 6Aq, 6Bq, and 6Dq, respectively, and the gene loci Aco-A2, Aco-B2, and Aco-D2 in 5 Aq, 5 Bq, and 5Dq, respectively. Aco-1 gene loci were also identified in 6E of Elytrigia elongata, 6HL of Hordeum vulgare cv. Betzes, 6RL of Secale cereale PI 252003, 6S¹ of T. longissimum, and CSU-31 of T. umbellulatum. Other Aco-2 gene loci were identified in 5RL of S. cereale cv. King II and 4EL of E. elongata. Conservation of synteny relationships is indicated among the species studied for the genes identified, with the exception of Aco-E2; the presence of this gene in 4EL suggests that E. elongata differs from Chinese Spring and King II by a translocation involving 4E and 5E.Adapted from a thesis submitted to the Graduate College, Texas A&M University, by K.J.C. in partial fulfillment of the requirements for the M.S. degree in Genetics     

The effect of the crossability loci Kr1 and Kr2 on fertilization frequency in hexaploid wheat x maize crosses

Summary Dominant alleles of the Kr1 and Kr2 genes reduce the crossability of hexaploid wheat with many alien species, including rye and Hordeum bulbosum, with Kr1 having the greater effect. However, a cytological study of wheat ovaries fixed 48 h after pollination showed that the wheat genotypes Highbury (kr1, Kr2) and Chinese Spring (Hope 5B) (kr1, kr2) were crossable with Seneca 60 maize, fertilization occurring in 14.4 and 30.7% of embryo sacs respectively. The latter figure was similar to the 29.7% fertilization found in Chinese Spring (kr1, kr2). Most embryo sacs in which fertilization occurred contained an embryo but lacked an endosperm and where an endosperm was formed it was usually highly aberrant. All three wheat x maize combinations were karyotypically unstable and rapidly eliminated maize chromosomes to produce haploid wheat embryos.     

Maximisation of reproductive success by European orchidaceae under conditions of infrequent pollination

Summary The pollination biology of a group of European orchids (Dactylorhiza, Ophrys, Orchis, Platanthera, Goodyera, andSerapias species) are investigated, and their anthecological characteristics considered in relation to natural levels of reproductive success. Pollen ovule (P O) ratios of the European orchids surveyed range from 10 1 (Goodyera repens) to 24 1 (Platanthera chlorantha). Average pollen-load ovule ratios are consistently lower than P O ratios. Naturally occurring pollen loads range from 1 massula to >1 pollinium. Even the smallest pollen load is sufficient to stimulate embryogenesis in experimentally pollinatedDactylorhiza purpurella flowers, although more seeds are set with larger loads. Pollen tubes grow rapidly through the stylar canal and into the top of the ovary within 2 or 3 days of pollination, and grow down either side of the 3 parietal ridges in the ovary. Fertilisation occurs throughout the length of the ovary but its distribution is non-random, especially when pollen loads are limiting, with more seeds being set at the stylar end. All species ofDactylorhiza, Ophrys, andOrchis studied are highly self-compatible. In the absence of pollination,Ophrys andOrchis flowers remain open and fertile for at least 3 weeks. Pollinated flowers remain receptive to further pollinations for at least 8 days. Some fruits can even be obtained on selfing 20-day-old unpollinatedOrchis morio flowers. Excised pollinia retain germinability for a long time, up to 51 days inDactylorhiza purpurella. The arrival of pollen on the stigma hastens floral senescence, but post-pollination changes are relatively slow when compared with those reported for tropical orchid species. It is concluded that characteristics of the pollination biology of European orchids act to maximise reproductive success by (1) prolonging the opportunity for effective pollen deposition both pre- and post-pollination, (2) increasing the likelihood of widespread dispersal, (3) reducing pollen wastage, and (4) increasing seed quality by promoting some pollen competition. As most European orchids are xenogamous and require pollen to arrive on the stigma before seed can be set, reproductive maximisation is of particular adaptive advantage because many of them are infrequently visited by insects so that the probability of successful pollination can be very low.Abbreviations P O pollen ovule ratio - PL O pollen-load ovule ratio - FCR fluorochromatic reaction test     

Isolation,sequence and expression in Escherichia coli of the nitrite reductase gene from the filamentous,thermophilic cyanobacterium Phormidium laminosum

The nitrite reductase (NiR) gene (nirA) has been isolated and sequenced from the filamentous, thermophilic non-N₂-fixing cyanobacterium Phormidium laminosum. Putative promoter-like and Shine-Dalgarno sequences appear at the 5 end of the 1533 bp long nir-coding region. The deduced amino acid sequence of NiR from P. laminosum corresponds to a 56 kDa polypeptide, a size identical to the molecular mass previously determined for the pure enzyme, and shows a high identity with amino acid sequences from ferredoxin-dependent NiR. This cyanobacterial NiR gene has been efficiently expressed in Escherichia coli DH5 from the E. coli lac promoter and probably from the P. laminosum NiR promoter.Abbreviations IPTG isopropyl--D-thiogalactopyranoside - NiR nitrite reductase - NR nitrate reductase - NT nitrate transport - SiR sulfite reductase