Spatial and temporal variations in phytoplankton biomass and primary productivity in the Southwest Atlantic and the Scotia Sea

Summary Two cruises of the ARA/Islas Orcadas (late winter/early spring 1978 and late summer/early fall 1979) provided data which show that temporal variability of phytoplankton biomass and productivity in the oceanic wates of the Southwest Atlantic and Scotia Sea is insignificant when compared to the influence of geographical variability. Two bloom stations sampled during the late winter/early spring cruise had chlorophyll a concentrations and productivity values an order of magnitude higher than waters sampled from the same locations the following late summer/early fall. However, a comparison of 10 paired stations from the two cruises indicated no seasonal trend, as measured values of chlorophyll a and productivity from the first cruise were randomly larger or smaller than values measured during the second cruise. Consideration of individual stations from both seasons suggests the need to re-examine widely held notions regarding the effect of the Polar Front Zone and the island-mass effect on phytoplankton abundance and productivity. Higher-than-expected standing stock and productivity values at some open-ocean stations and at some stations within the Polar Front Zone indicate that looking for specific factors which promote localized enhancement or impoverishment of phytoplankton would be more useful than continuing with attempts to generalize Antarctic productivity data into broad seasonal or geographical patterns.In memory of Mary Alice McWhinnie (1922–1980)     

Protozooplankton in the Weddell Sea,Antarctica: Abundance and distribution in the ice-edge zone

Summary Protozooplankton were sampled in the iceedge zone of the Weddell Sea during the austral spring of 1983 and the austral autumn of 1986. Protozooplankton biomass was dominated by flagellates and ciliates. Other protozoa and micrometazoa contributed a relatively small fraction to the heterotrophic biomass. During both cruises protozoan biomass, chlorophyll a concentrations, phytoplankton production and bacterial biomass and production were low at ice covered stations. During the spring cruise, protozooplankton, phytoplankton, and bacterioplankton reached high concentrations in a welldeveloped ice edge bloom 100 km north of the receding ice edge. During the autumn cruise, the highest concentrations of biomass were in open water well-separated from the ice edge. Integrated protozoan biomass was <12% of the biomass of phytoplankton during the spring cruise and in the autumn the percentages at some stations were >20%. Bacterial biomass exceeded protozooplankton biomass at ice covered stations but in open water stations during the fall cruise, protozooplankton biomass reached twice that of bacteria in the upper 100m of the water column. The biomass of different protozoan groups was positively correlated with primary production, chlorophyll a concentrations and bacterial production and biomass, suggesting that the protozoan abundances were largely controlled by prey availability and productivity. Population grazing rates calculated from clearance rates in the literature indicated that protozooplankton were capable of consuming significant portions of the daily phyto- and bacterioplankton production.     

Roles of sulfate adsorption and base cation supply in controlling the chemical response of streams of western Virginia to reduced acid deposition

Micro-organisms are vital for the functioning of all food webs and are the major drivers of the global biogeochemical cycles. The microbial community compositions and physicochemical conditions of the different water masses in the North Sea, a biologically productive sea on the northwestern European continental shelf, were studied during two summer cruises, in order to provide detailed baseline data for this region and examine its microbial biogeography. For each cruise the stations were clustered according to their physicochemical characteristics and their microbial community composition. The largest cluster, which covered most of the central and northern North Sea, consisted of stations that were characterized by a thermally stratified water column and had low chlorophyll a autofluorescence and generally low microbial abundances. The second main cluster contained stations that were dominated by picoeukaryotes and showed the influence of influxes of North Atlantic water via the English Channel and south of the Shetland Islands. The third main cluster was formed by stations that were dominated by cyanobacteria and nanoeukaryotes in the reduced salinity Norwegian Coastal and Skagerrak waters, while the fourth cluster represented the German Bight, a region with strong riverine input, high nutrient concentrations, and consequently high heterotrophic bacterial and viral abundances. Despite the complex and dynamic hydrographic nature of the North Sea, the consistent distinctions in microbiology between these different hydrographic regions during both cruises illustrate the strong links between the microbial community and its environment, as well as the possibility to use microorganisms for long-term monitoring of environmental change.     

Ciliate diversity and distribution across an environmental and depth gradient in Long Island Sound,USA

The nature and extent of microbial biodiversity remain controversial with persistent debates over patterns of distributions (i.e. cosmopolitanism versus endemism) and the processes that structure these patterns (neutrality versus selection). We used culture‐independent approaches to address these issues focusing on two groups of ciliates, the Oligotrichia (Spirotrichea) and Choreotrichia (Spirotrichea) across an environmental gradient. We assessed SSU rDNA diversity in ciliate communities at six stations in Long Island Sound spanning the frontal region that separates the fresher Connecticut River outflow plume from the open Sound. As in previous studies, we find one abundant cosmopolitan species (Strombidium biarmatum), a few moderately abundant sequences, and a long list of rare sequences. Furthermore, neither ciliate diversity nor species composition showed any clear relationship to measured environmental parameters (temperature, salinity, accessory pigment composition and chorophyll). Overall, we observed that diversity decreased moving from nearshore to offshore. We also conducted analyses to detect clustering among the sampled communities using the software Unifrac. This approach revealed three significant clusters grouping samples from nearshore, surface and deep/well mixed stations. We find no strong fit of our communities to log series, geometric or log normal distributions, though one of the 3 clusters is most consistent with a log series distribution. However, when we remove the abundant cosmopolitan species S. biarmatum, all three clusters fit to a log series distribution. These analyses suggest that, with the exception of one cosmopolitan species, the oligotrich and choreotrich communities at these stations may be distributed in a neutral manner.     

Associated impact of inorganic fertilizers and pesticides on microbial communities in soils

This study was designed to examine the reaction of microbial communities to the associated impact of inorganic fertilizers and pesticides during laboratorial simulation for 90 days. Soils were sampled from fields in three different stations of Chinese Ecosystem Research Network (CERN). The metabolic profiles were characterized by using BIOLOG GN2 microplates. The Shannon Index (H) showed that the metabolic diversity of the three types of soil exhibited similar profiles. PCA and CLUSTER further explored the variance in community structures with the same H. There were obvious changes in the structures of microbial communities during the 90-day duration of the work and the three different types of soil showed␣similar profiles for most of the period of the experiment.     

Spatial and temporal distribution of mesozooplankton in the Gulf of Aqaba and the northern Red Sea in February/March 1999

The distribution pattern, taxonomic composition and communitystructure of mesozooplankton was studied along a transect with10 positions between the Gulf of Aqaba and the northern RedSea. Five positions were resampled two or three times duringa cruise of RV ‘Meteor’ in February/March 1999.In spite of clear differences in the density stratificationbetween the Gulf of Aqaba and the northern Red Sea, the mesozooplanktoncomposition was very similar: Copepods were by far the mostabundant taxon, contributing 76–95% to the total community.The remainder was composed largely of ostracods, chaetognaths,appendicularians and molluscs. The mesozooplankton of the deeplymixed stations was homogeneously distributed, at all other stationsthe bulk of the mesozooplankton (>70%) was concentrated inthe mixed surface layer with peaks of calanoids, cyclopoidsand appendicularians in the vicinity of the chlorophyll a (Chla) maximum layer. Ostracods and poecilostomatoids dominatedthe layers below. Standing stocks within the total water column(550–1200 m) varied between 93 and 431 x 10³ individualsm^–2 for copepods and 5–76 x 10³ individuals m^–2for other mesozooplankton with highest numbers in the northernGulf of Aqaba, where vertical mixing was deep (400–500m) and Chl a and mesozooplankton distributions homogeneous throughoutthe water column. Towards the south, the mixed depth decreasedfrom 300 m in the central Gulf of Aqaba to 50 m in the Red Sea.Cluster analysis separated three distinct groups of stations,compounding the observed differences between the northern Gulfof Aqaba (Position I) and the other positions. The analysisalso revealed temporal differences between the February andMarch sections of the cruise, indicating the winter–springtransition. The stations sampled in March are characterisedby a higher total abundance and by a higher percentage of appendiculariansand ostracods than the stations sampled in February     

Roles of tidal and wind-generated currents in transporting white shrimp (Penaeus setiferus) postlarvae through a South Carolina (USA) inlet

The temporal and spatial abundance of postlarval Penaeus setiferuswas studied from plankton samples in oceanic and estuarine watersnear the North Edisto Inlet, South Carolina (USA), during threecruises in 1993 and 1994 (May 1993, August/September 1993 andJune 1994). Each covered a full cycle of neap-spring tides.On each cruise, bongo nets were towed at three stations acrossthe inlet throat on nightly flood tides. During the first twocruises, tows were made at surface and near-bottom depths inthe inlet, while sampling was confined to surface depths duringthe last cruise. Plankton tows were also made outside the inletalong transects extending in a cross-shelf direction and alongan arcuate transect around the inlet mouth. Stations along thearcuate transect were intensively sampled over a full tidalcycle during the last cruise. Extensive oceanographic and meteorologicalobservations were obtained from moored instrument arrays andshipboard sampling in order to relate fluctuations in tidal,lunar and wind phenomena to temporal changes in postlarval density.Densities of postlarvae were greater in the inlet throat thanat stations offshore. A significant interaction of postlarvaldensity among inlet stations and depth was noted in May. Forother cruises, no significant differences in density were notedamong stations across the inlet, but postlarvae were concentratedat the surface. The lack of a consistent horizontal salinitygradient and obvious pattern in water masses across the inletmay explain why postlarval densities did not consistently differlaterally in the inlet. Greater densities generally occurredduring the first quarter moon, although a clear relationshipof larval density to the spring-neap cycle was not observed.Highest mean densities of ingressing postlarvae in surface floodtide collections from the inlet were generally associated withdownwelling onshore winds which generate onshore flow near thesurface. The similarity between the time series curves of postlarvaldensity and the tidal component of currents just offshore ofthe inlet suggests that tidal transport may facilitate movementinto the estuary. Based on increased postlarval density at thesurface during early strong flood tides and a reduced densityat depth in the inlet, we hypothesize that postlarval P setiferusare utilizing selective tidal stream transport.     

Fragilariopsis cylindrus (Grunow) Krieger: The most abundant diatom in water column assemblages of Antarctic marginal ice-edge zones

Summary Planktonic diatoms were sampled in the ice-edge zone of the Bellingshausen Sea during the early austral spring of 1990 and of the Weddell Sea during the late spring of 1983, the autumn of 1986, and the winter of 1988. The four cruises in the Antarctic marginal ice edge zones, combined with the summer cruise in Prydz Bay during a brief ice-free period (1988) provided us with opportunities for spatial and seasonal studies of diatom abundance and distribution in the water column. Cells from discrete water samples from 73 stations near the marginal ice-edge zones during all seasons were counted to gain quantitative information on the composition, abundance, and distribution of diatoms. Diatom abundance was dominated by the pennate diatom, usually nanoplanktonic, Fragilariopsis cylindrus (Grunow) Krieger, during all five cruises. The highest integrated numbers of F. cylindrus were found during the summer cruise with 7.9 × 10¹⁰ cells m^–2 and the lowest numbers were found during the winter cruise with 1.1 × 10⁸ cells m^–2. The average integrated abundance of F. cylindrus from the five cruises was about 35% of the total diatom abundance. The overall spatial pattern of F. cylindrus near the marginal ice-edge zones during the five seasonal cruises were similar with the highest number of cells in open waters compared to ice-covered waters. When all 73 stations during the five cruises were included in the correlation analysis, the abundance of total diatoms was positively correlated with the abundance of F. cylindrus, suggesting that the ice-edge pulses of diatom assemblages in the water column largely reflected its abundance. Cluster analysis revealed that the stations in marginal ice-edge zones were not only separated by seasons and locations, but they also separated based on location of stations in relation to the ice edge (open water stations vs. ice-covered stations).     

Vertical stratification of microbial communities in the Red Sea revealed by 16S rDNA pyrosequencing

The ecosystems of the Red Sea are among the least-explored microbial habitats in the marine environment. In this study, we investigated the microbial communities in the water column overlying the Atlantis II Deep and Discovery Deep in the Red Sea. Taxonomic classification of pyrosequencing reads of the 16S rRNA gene amplicons showed vertical stratification of microbial diversity from the surface water to 1500 m below the surface. Significant differences in both bacterial and archaeal diversity were observed in the upper (2 and 50 m) and deeper layers (200 and 1500 m). There were no obvious differences in community structure at the same depth for the two sampling stations. The bacterial community in the upper layer was dominated by Cyanobacteria whereas the deeper layer harbored a large proportion of Proteobacteria. Among Archaea, Euryarchaeota, especially Halobacteriales, were dominant in the upper layer but diminished drastically in the deeper layer where Desulfurococcales belonging to Crenarchaeota became the dominant group. The results of our study indicate that the microbial communities sampled in this study are different from those identified in water column in other parts of the world. The depth-wise compositional variation in the microbial communities is attributable to their adaptations to the various environments in the Red Sea.     

Community structure and species diversity of Harpacticoida (Crustacea: Copepoda) at two sites in the deep sea of the Angola Basin (Southeast Atlantic)

The aim of this study was to evaluate compositional differences between harpacticoid (Crustacea, Copepoda) assemblages at two widely separated abyssal locations. During the DIVA 1 cruise of RV METEOR (July/August 2000) to the Angola Basin (Southeast Atlantic), two deep-sea stations, approximately 300 nautical miles apart (Stations 325 and 346), were sampled repeatedly by Multicorer (MUC). For quantitative analyses, 5 MUC samples were selected at random from each of 15 deployments at both stations, totalling 75 cores. Across the study, 7,081 Harpacticoida specimens were encountered and of these 31.4 % were adults and could be analysed to species level: 682 species were identified, with 99.3 % new to science. At northern Station 346, a total of 600 species were recorded—the highest harpacticoid species number ever recorded for a single deep-sea locality. Most species (56 %) were represented by singletons. Multivariate tests identified significant differences between community compositions at the two stations. Diversity, species richness and species density were higher at Station 346, whilst taxonomic distinctness, evenness, and rarefaction were similar between stations. Regression and correlation analyses showed that the difference in species diversity was best explained by species densities rather than species richness. Under-sampling due to low densities was an issue at the southern Station 325. Nevertheless, our study demonstrated significant differences in regional-scale harpacticoid community structures within a single deep-sea basin that would usually be considered a uniform and stable habitat. These observed differences are thought to reflect differences in food availability at the two stations.     

Characterization of Microbial Community Structure in the Surface Sediment of Osaka Bay, Japan, by Phospholipid Fatty Acid Analysis

Twenty-eight sediment samples collected from Osaka Bay, Japan, were analyzed for phospholipid ester-linked fatty acids (PLFA) to determine regional differences in microbial community structure of the bay. The abundance of three major groups of C₁₀ to C₁₉ PLFA (saturated, branched, and monounsaturated PLFA), which accounted for 84 to 97% of the total PLFA, indicated the predominance of prokaryotes in the sediment. The distribution of six clusters obtained by similarity analysis in the bay revealed a marked regional distribution in the PLFA profiles. Total PLFA concentrations (0.56 to 2.97 μg/g [dry weight] of the sediment) in sediments also showed marked variation among the stations, with higher concentrations of total PLFA in the central part of the bay. The biomass, calculated on the basis of total PLFA concentration, ranged from 0.25 × 10⁸ to 1.35 × 10⁸ cells per g (dry weight) of the sediment. The relative dominance of microbial groups in sediments was described by using the reported bacterial biomarker fatty acids. Very small amounts of the characteristic PLFA of microeukaryotes in sediments indicated the restricted distribution of microeukaryotes. By examining the distribution of clusters and groups of microorganisms in the bay, there were two characteristics of the distribution pattern: (i) the predominance of anaerobic bacteria and gram-positive prokaryotes, characterized by the high proportions of branched PLFA in the eastern and northeastern sides of the bay, where the reported concentrations of pollutants were also high, and (ii) the predominance of aerobic prokaryotes and eukaryotes, except for a few stations, in the western and southwestern sides of the bay, as evidenced by the large amounts of monounsaturated PLFA. Such significant regional differences in microbial community structure of the bay indicate shifts in microbial community structure.     

Isolation and Diversity of Actinomycetes in the Chesapeake Bay

Chesapeake Bay was investigated as a source of actinomycetes to screen for production of novel bioactive compounds. The presence of relatively large populations of actinoplanetes (chemotype II/D actinomycetes) in Chesapeake Bay sediment samples indicates that it is an eminently suitable ecosystem from which to isolate actinomycetes for screening programs. Actinomycetes were isolated from sediment samples collected in Chesapeake Bay with an isolation medium containing nalidixic acid, which proved to be more effective than heat pretreatment of samples. Actinomycete counts ranged from a high of 1.4 × 10⁵ to a low of 1.8 × 10² CFU/ml of sediment. Actinomycetes constituted 0.15 to 8.63% of the culturable microbial community. The majority of isolates from the eight stations studied were actinoplanetes (i.e., chemotype II/D), and 249 of these isolates were obtained in a total of 298 actinomycete isolates. Antimicrobial activity profiles indicated that diverse populations of actinoplanetes were present at each station. DNA hybridization studies showed considerable diversity among isolates between stations, but indicated that actinoplanete strains making up populations at nearby stations were more similar to each other than to populations sampled at distant stations. The diversity of actinoplanetes and the ease with which these organisms were isolated from Chesapeake Bay sediments make this a useful source of these actinomycetes.     

Characterization of a deep-sea microbial mat from an active cold seep at the Milano mud volcano in the Eastern Mediterranean Sea

A white, filamentous microbial mat at the Milano mud volcano in the Eastern Mediterranean Sea was sampled during the Medinaut cruise of the R/V Nadir in 1998. The composition of the mat community was characterized using a combination of phylogenetic and lipid biomarker methods. The mat sample was filtered through 0.2 and 5-microm filters to coarsely separate unicellular and filamentous bacteria. Analyses of 16S rRNA gene sequences amplified from the total community DNA from these fractions showed that similar archaeal populations were present in both fractions. However, the bacterial populations in the fractions differed from one another, and were more diverse than the archaeal ones. Lipid analysis showed that bacteria were the dominant members of the mat microbial community and the relatively low delta(13)C carbon isotope values of bulk bacterial lipids suggested the occurrence of methane- and sulfide-based chemo(auto)trophy. Consistent with this, the bacterial populations in the fractions were related to Alpha-, Gamma- and Epsilonproteobacteria, most of which were chemoautotrophic bacteria that utilize hydrogen sulfide (or reduced sulfur compounds) and/or methane. The most common archaeal 16S rRNA gene sequences were related to those of previously identified Archaea capable of anaerobic methane oxidation. Although the filamentous organisms observed in the mat were not conclusively identified, our results indicated that the Eastern Mediterranean deep-sea microbial mat community might be sustained on a combination of methane- and sulfide-driven chemotrophy.     

Microbial functioning and community structure variability in the mesopelagic and epipelagic waters of the subtropical northeast atlantic ocean

We analyzed the regional distribution of bulk heterotrophic prokaryotic activity (leucine incorporation) and selected single-cell parameters (cell viability and nucleic acid content) as parameters for microbial functioning, as well as bacterial and archaeal community structure in the epipelagic (0 to 200 m) and mesopelagic (200 to 1,000 m) subtropical Northeast Atlantic Ocean. We selectively sampled three contrasting regions covering a wide range of surface productivity and oceanographic properties within the same basin: (i) the eddy field south of the Canary Islands, (ii) the open-ocean NE Atlantic Subtropical Gyre, and (iii) the upwelling filament off Cape Blanc. In the epipelagic waters, a high regional variation in hydrographic parameters and bacterial community structure was detected, accompanied, however, by a low variability in microbial functioning. In contrast, mesopelagic microbial functioning was highly variable between the studied regions despite the homogeneous abiotic conditions found therein. More microbial functioning parameters indicated differences among the three regions within the mesopelagic (i.e., viability of cells, nucleic acid content, cell-specific heterotrophic activity, nanoflagellate abundance, prokaryote-to-nanoflagellate abundance ratio) than within the epipelagic (i.e., bulk activity, nucleic acid content, and nanoflagellate abundance) waters. Our results show that the mesopelagic realm in the Northeast Atlantic is, in terms of microbial activity, more heterogeneous than its epipelagic counterpart, probably linked to mesoscale hydrographical variations.     

Patterns in the benthic communities on the shelf of the sub-Antarctic Prince Edward Islands

Summary Benthic communities at the sub-Antarctic Prince Edward Islands were sampled qualitatively with an epi-benthic sled at 57 stations over a five year period. Additional information on these communities was obtained from replicate underwater photographs. In total, 546 macrofaunal species were found. Despite the extreme isolation and geological youth of the islands, there seems to have been a diverse colonisation. A cluster-analysis based on species abundance aggregated most stations into 8 groups. Each of these groups had a unique depth and substratum combination. Thourella variabilis (Octocoralea), and Cabarea darwinii (Bryozoa) characterised deep rocky assemblages and Serpula vermicularis, Lanice conchilega (Polychaeta) and Magellania kerguelenensis (Brachiopoda) characterised soft substrata. Indicator species separating each of the 8 clusters are given. Trends in percentage cover and densities of major taxa with respect to depth and substratum, as shown by photographs, are described. Deep, rocky substrata were dominated by Porifera, Bryozoa and Cnidaria, while soft-substrata were dominated by Polychaeta, Bivalvia and Brachiopoda. Errant forms consisted predominantly of Echinodermata, with Crustacea being important in shallower habitats. Filter-feeders dominated the benthos of the islands in all habitats.     

Microplankton distribution in the Strait of Gibraltar: coupling between organisms and hydrodynamic structures

In this paper we present microplankton distribution patternsin the Strait of Gibraltar obtained during a cruise carriedout in September 1997. Chlorophyll, microplankton abundanceand biovolume increase from southwest to northeast, a tendencythat coincides with a gradual elevation of the interface depthin the same direction. The vertical distribution of biomassat the different stations shows deep maxima associated withthe pycnoclines. The generation of internal waves and eventualintrusion of deep water on the sill can be decisive in the enrichmentof surface water and plankton dynamics. The taxonomic structureagrees with the expected pattern, with a predominance of diatomsin the richer Mediterranean stations (especially in the north)and a predominance of dinoflagellates and microzooplankton atthe Atlantic side. Phytoplankton distribution and salinity valuesfound in the Strait of Gibraltar can be explained by a preliminarymodel that assumes a coupling between diatom life cycles andhydrodynamic features. Thus, the cells in the surface watersof the eastern side of the Strait would aggregate and sink belowthe interface, moving westwards and returning to the surfacewaters coupled with the rising and mixing of deep Mediterraneanwater at the sill.     

Spatial changes in the concentrations and activities of amylase and trypsin in Euphausia superba. A comparison between activity measurement and immunoquantitation

Summary Two digestive enzymes: alpha amylase and trypsin were purified by affinity chromatography from the antarctic euphausiid Euphausia superba and the corresponding antibodies developed in male New-Zealand rabbits. Electrophoresis of purified enzymes yielded 4 isozymes for amylases and 6 for trypsin. The purification level was relatively low for amylase because of a high molecular weight contaminant with a low level of activity. Rocket immunoelectrophoresis of amylase showed three precipitin lines; a single line was obtained for trypsin. The antiserum obtained at a dilution of 1% presented a good linearity of the response between 60 to 1000 ng of pure trypsin. Both enzyme concentrations were measured by the quantitative method of rocket immunoelectrophoresis for different stations of the FIBEX cruise. Enzyme activities and concentration displayed significant spatial changes and a certain degree of association with the developmental stages sampled. Several inconsistencies in the relationships between growth stages and enzyme rates or quantities suggested that the spatial variations were not solely related to specific growth requirements but to combine effects of both physiological and environmental factors. Comparison of the spatial changes in concentration and activity showed that the changes in enzyme concentration were in a large part (60% of the total variance) responsible for the activity changes. The results strongly suggest that enzyme synthesis and degradation ensured the gross regulation of activity while modifications of the kinetic properties could be implicated in the fine tuning.     

Minimal sampling requirements for a precise assessment of soft-bottom macrobenthic communities, using AMBI

Since AMBI was published originally in 2000, it has been used in an increasing number of investigations with monitoring purposes, or to analyse impacts on soft-bottom macrobenthic communities. Some guidelines for its correct use were published in 2005; however, a main issue remained without an answer — which are the minimal area and number of replicates necessary, to obtain a precise estimate for AMBI? In this study, new methodologies such as bootstrap techniques have been applied to this particular problem.Data were obtained from sampling carried out in 1995, within the framework of the Littoral Water Quality Monitoring and Control Network of the Basque Country (northern Spain). The sampling strategy consisted of 11 intertidal estuarine sampling stations (0.25m², sampled for each of six replicates) and 17 subtidal estuarine and coastal sampling stations (0.125m², sampled for each of six replicates).Two replicates have been established as being sufficient, both for intertidal and subtidal sampling stations, to classify 80% of the pseudosamples into the same disturbance level, in terms of AMBI, for 64% of the stations.For the minimal area, it has been determined also (for both intertidal and subtidal sampling stations) that 0.25m² is sufficient to classify 80% of the iterations into the same disturbance level, for 64% of the stations.     

Seasonal evolution of blood levels of thyroxine and triiodothyronine in the post-pubertal bull in France and Iraq. Concomitant variations of LH and testosterone

An inquiry was conducted in 2 performance testing stations, A and B located in France and Iraq, respectively. In both stations, at solstice and equinox, thirty 15 month-old Holstein bulls were blood sampled for plasma LH, testosterone, thyroxine and triiodothyronine determination. For LH, no coherent seasonal effect was found. As regards testosterone, maximal mean values were obtained in December in both stations (3.4 ng/ml). In A as well as in B, thyroxine peaked in December reaching 64.6 ng/ml and 77.8 ng/ml, respectively, and falling down to 49.4 ng/ml and 65.6 ng/ml, respectively in June. The difference was significant for A (P less than 0.001). For T3, the fall from December (1.42 ng/ml in A and 1.68 ng/ml in B) to June (1.09 ng/ml in A and 1.26 ng/ml in B) resulted in about the same relative value and was significant (P less than 0.005) in both stations. The detrimental effect of high temperatures on semen quality does not seem to be mediated by an alternation of thyroid function.     

Zooplankton sampling strategies for environmental studies

This study characterizes sources of variation in total zooplankton abundance estimates at seven stations within the 5–10 m depth contour of southeastern Lake Michigan which were sampled monthly, April through October, for the 1975 to 1979 period. Month, year, and station were statistically significant factors affecting abundance estimates as were all interactions. Month was the largest source of variance either as a main effect or interaction. Smallest coefficients of variation were associated with subsampling (mean 6.1%) and replicate sampling (mean 15.1%). The between-station coefficient of variation averaged 39.0% and tended to be highest during the summer. For a given station and month, the between-year coefficient of variation averaged 73.4% while the between-month coefficient of variation for a single station in a given year averaged 95.1%. A table shows the estimated number of replications necessary to detect a true difference in two population means as a function of coefficient of variation. Environmental studies designed to detect spatial alterations should conduct such analyses on a cruise-by-cruise basis. Cruises should consist of a large number of stations and be conducted at least once during each season. Studies designed to detect temporal alterations require more frequent sampling because of the greater variability associated with temporal data sets. Because spatial variability adds little to the overall variability of such data sets, only a few representative stations need be sampled during each cruise.