Surface Water Population Research Articles

A multicenter genomic epidemiological investigation in Brazil, Chile, and Mexico reveals the diversity and persistence of Salmonella populations in surface waters.

This study examined the diversity and persistence of Salmonella in the surface waters of agricultural regions of Brazil, Chile, and Mexico. Research groups (three in 2019-2020 and five in 2021-2022) conducted a long-term survey of surface water across 5-8 months annually (n = 30 monthly). On-site, each team filtered 10-L water samples with modified Moore Swabs to capture Salmonella, which were then isolated and identified using conventional microbiological techniques. Salmonella isolates were sequenced on Illumina platforms. Salmonella was present in 1,493/3,291 water samples (45.8%), with varying isolation rates across countries and years. Newport, Infantis, and Typhimurium were the most frequent among the 128 different serovars. Notably, 22 serovars were found in all three countries, representing almost half of the 1,911 different isolates collected. The resistome comprised 72 antimicrobial resistance (AMR) genes and six point mutations in three genes. At least one AMR determinant was observed in 33.8% (646/1,911) of the isolates, of which 47.4% (306/646) were potentially multidrug resistant. Phylogeny based on core genome multilocus sequence typing (cgMLST) showed that most isolates clustered according to sequence type and country of origin. Only 14 cgMLST multi-country clusters were detected among the 275 clusters. However, further analysis confirmed that close genetic relatedness occurred mostly among isolates from the same country, with three exceptions. Interestingly, isolates closely related phylogenetically were recovered over multiple years within the same country, indicating the persistence of certain Salmonella in those areas. In conclusion, surface waters in these regions are consistently contaminated with diverse Salmonella, including strains that persist over time.IMPORTANCESalmonella is a leading foodborne pathogen responsible for millions of illnesses, hospitalizations, and deaths annually. Although Salmonella-contaminated water has now been recognized as an important contamination source in the agrifood chain, there is a lack of knowledge on the global occurrence and diversity of Salmonella in surface water. Moreover, there has been insufficient research on Salmonella in surface waters from Latin American countries that are major producers and exporters of agricultural products. Incorporating genetic profiling of Salmonella isolates from underrepresented regions, such as Latin America, enhances our understanding of the pathogen's ecology, evolution, antimicrobial resistance, and pathogenicity. Moreover, leveraging genomic data derived from pathogens isolated from diverse geographical areas is critical for assessing the potential public health risk posed by the pathogen and expediting investigations of foodborne outbreaks. Ultimately, global efforts contribute significantly to reducing the incidence of foodborne infections.

Evaluation of Microbiological Quality of Agricultural Water and Effect of Water Source and Holding Temperature on the Stability of Indicator Organisms' Levels by Seven U.S. Environmental Protection Agency–Approved Methods

The Food Safety Modernization Act Produce Safety Rule requires covered produce growers to monitor the quality of their agricultural water on a regular basis by some U.S. Environmental Protection Agency (EPA)-approved methods recognized by the U.S. Food and Drug Administration. In this study, we evaluated the changes in the population of indicator organisms in surface water up to 6 months, and the effects of water source and holding temperature on the survival of indicator organisms by seven EPA-approved methods (five methods for Escherichia coli and two methods for Enterococcus). The levels of E. coli and Enterococcus in the surface water were variable with sampling month, ranging from 1.61 ± 0.04 to 2.68 ± 0.15 log most probable number (MPN)/100 mL and from undetectable level to 1.19 ± 0.29 log MPN/100 mL, respectively. At 25°C (holding temperature), there were significant reductions (P < 0.05) in E. coli and Enterococcus populations in surface water after 48 and 24 h, respectively, whereas at 4°C, no significant changes in the bacterial populations were observed up to 48 h. Methods 1603, 1604, 1103.1, 10029, and Colilert showed a comparable sensitivity in quantifying E. coli, whereas method 1600 and Enterolert showed a variable sensitivity with the type of water. The results indicated that regular monitoring of agricultural water is essential to examine whether the microbial quality of water is appropriate for its intended use. Water samples should be maintained at 4°C to minimize the changes in microbial populations between sampling and testing. The comparison of the sensitivity of EPA methods for quantifying indicator organisms could provide growers with useful information for choosing the method for their water quality analysis.

Evaluation of Size Structure in Freshwater Cyanobacterial Populations: Methods to Quantify Risk Associated with Changes in Biomass and Microcystin Concentrations

Cyanobacterial populations in surface waters, including drinking water supplies and recreational waters, represent an ever present challenge for resource managers. As communities continuously respond to external and internal processes, dynamic profiles of composition, dominance, growth and toxigenicity emerge. In this study measures of size structure and biomass, quantified using light microscopy and fluorometry, were used to estimate microcystin concentrations through linear regression analysis. Toxigenic profiles using cyanobacterial biomass were developed for lakes dominated by Microcystis spp. and Dolichospermum spp., influenced by both genus-specific pigment concentrations as well as microcystin concentrations. Community composition (Log %MIC) and biomass were used to describe microcystin concentrations in mixed assemblages, where composition was the first input variable. The accessory photopigment phycocyanin was used to describe the linear relationship between the daily growth and net microcystin production rates in the bloom-forming Microcystis spp. samples, suggesting that this size-fractionated sample may provide indications of potential toxigenicity in the whole lake water sample. Future investigations using fluorometric evaluation of cyanobacterial populations could provide additional applications and metrics for use by resource managers to quantify risk association with elevated cyanotoxin concentrations.

Prevalence and genetic variability of Plesiomonas shigelloides in temperate climate surface waters of the Pannonian Plain

Plesiomonas shigelloides, a Gram-negative bacterium and the causative agent of intestinal diseases and extraintestinal infections in humans and animals, is most frequently found in aquatic environments in tropical or subtropical areas. The present study was designed to establish the prevalence and genetic variability of P. shigelloides in surface waters (lakes, rivers, ponds, inlets and canals) located in a temperate climate zone, namely the Pannonian Plain of the northern part of Serbia and southern part of Hungary. The strains were isolated directly by plating samples on inositol-brilliant green-bile agar with neutral red or phenol red as indicators. Our results indicate that phenol red effectively facilitates differentiation of P. shigelloides from other bacteria. A number of samples were enriched using alkaline peptone water broth, peptone inositolbile broth and tetrathionate broth. The recovery of the isolates was more successful with the first medium. Out of a total of 51 water samples collected from 28 different locations, 22 samples (43.1%) were found positive for P. shigelloides. Among the 37 isolated strains, 34 were from lakes (Satrinci, Ludas, Panonija, Krivaja, Pecs, Kapetanski rit, Pavlovci, Kovacsszenaja, Dobrodol, Vranjas, Borkovac, Hermann Otto, Sot, Selevrenac, Zobnatica, Palic, Orfui, Jarkovci, Conoplja) and 3 were from rivers (Danube, Sava). The strains were identified by phenotypic characteristic or by the VITEK2 system and confirmed by PCR using 23S rRNA species-specific oligos. The strains showed a high genetic variability, displaying a variety of RAPD profiles. Our results reveal for the first time a high prevalence of genetically diverse P. shigelloides populations in surface waters located in the temperate climate of central and southeastern Europe.

Metagenomic analysis reveals unusually high incidence of proteorhodopsin genes in the ultraoligotrophic Eastern Mediterranean Sea.

Sunlight can be directly harvested by photoheterotrophic bacteria to create a pH gradient across the membrane, which can then be utilized to produce ATP. Despite the potential importance of this trophic strategy, when and where such organisms are found in the seas and oceans is poorly described. Here, we describe the abundance and taxonomy of bacteria with different trophic strategies (heterotrophs, phototrophs and photoheterotrophs) in contrasting water masses of the ultra-oligotrophic eastern Mediterranean Sea. These water bodies, an anticyclonic eddy and a high-chlorophyll patch resulting from transport of nutrient-rich coastal waters into offshore oligotrophic waters, each supported different microbial populations in surface waters. Based on infrared microscopy and metagenomics, aerobic anoxygenic photoheterotrophic (AAP) bacteria represented up to 10.4% of the microbial community. In contrast, the proteorhodopsin (PR) gene was found in 78.6%-118.8% of the bacterial genome equivalents, the highest abundance reported to date. These results suggest that PR-mediated photoheterotrophy may be especially important in oligotrophic, potentially phosphate-limited conditions.

First assessment of flux rates of jellyfish carcasses (jelly-falls) to the benthos reveals the importance of gelatinous material for biological C-cycling in jellyfish-dominated ecosystems

There is accumulating evidence that jellyfish contribute significantly to biological carbon cycling and that their carcasses can have controversial effects on seafloor ecosystems. Moreover, changes in the thermal properties of the ocean, ocean chemistry and direct anthropogenic effects can seriously modify jellyfish populations in surface waters and potentially alter the importance of jellyfish in the biological pump relative to other forms of detritus. However, no studies have ever quantified the flux rate of jellyfish carcasses (jelly-falls) to the seafloor, or quantified how jelly-fall C and N fluxes compare to phytodetrital fluxes. In this study, we documented the seafloor abundance of jelly-falls over a 1-year period in the jellyfish-dominated Lurefjord, western Norway. A total of 9 jelly-falls were documented from 768 seafloor images over the course of the study, equivalent to 0-13.4 mg C m-2 and 0-2.1 mg N m-2 of jellyfish material being deposited in the deep fjord basin. Assuming that jellyfish removal rates and phytodetrital flux rates from nearby fjord environments are similar to Lurefjorden, we estimate that the jellyfish C and N fluxes to the seafloor were 0-72.8 mg C m-2 d-1 and 0-11.2 mg N m-2 d-1 at the time of sampling. In addition, we estimate that the maximum jellyfish carcass flux rates were equivalent to 96 and 160% of the phytodetrital C and N flux that would arrive at the seafloor where the jelly-falls were recorded. These results imply that jelly-falls most likely contribute significantly to detrital C and N fluxes in at least one jellyfish-dominated environment, despite often being recorded in low abundances. If more fjord environments become jellyfish hotspots as a result of water column darkening, the contribution of jellyfish C and N in the biological pump will potentially increase, necessitating the conceptual inclusion of a jelly-pump in future fjord biogeochemical cycling studies.

Role of temperature in growth, feeding, and vertical distribution of the mixotrophic chrysophyte Dinobryon

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 71:155-163 (2013) - DOI: https://doi.org/10.3354/ame01673 Role of temperature in growth, feeding, and vertical distribution of the mixotrophic chrysophyte Dinobryon Adam W. Heinze1,2,*, Corinne L. Truesdale1, Sarah B. DeVaul1, Jonathan Swinden1, Robert W. Sanders1 1Department of Biology, Temple University, Philadelphia, Pennsylvania 19122, USA 2Present address: Alvernia University, 3104 Bernardine Hall, Reading, Pennsylvania 19607, USA *Email: adam.heinze@alvernia.edu ABSTRACT: Dinobryon spp. are common components of the phytoplankton in temperate lakes. While these chrysophytes link bacterial carbon as well as primary production to the larger food web, few studies have examined their vertical distribution over a season. Data were collected over a 2.5 yr period in mesotrophic Lake Lacawac in eastern Pennsylvania (USA) to examine water column attributes relating to seasonality of the mixotrophic alga D. cylindricum, and specifically to address a hypothesis that abundance and vertical distribution in the genus are associated with temperature. This information was used to guide laboratory experiments examining temperature and light effects on growth, feeding, and vertical migration of cultured Dinobryon. Data from Lake Lacawac and the literature indicated that high abundances of Dinobryon were associated with a narrow range of temperature (9-18°C) relative to temperatures where they were present (3-26°C). High abundances of several species of Dynobryon were associated with this temperature range, and occurred from late winter to late spring, depending on latitude and depth in the water column. Although high Dinobryon abundances were not tied directly to levels of photosynthetically active radiation in Lake Lacawac, a UV-exclusion experiment in a nearby oligotrophic lake indicated a temperature-dependent negative effect of UV radiation. UV may limit the occurrence of Dinobryon populations in surface waters of clear oligotrophic lakes. Laboratory experiments showed that both light and temperature affected growth and feeding rates of Dinobryon, and that maximum feeding and growth rates occurred within the temperature range where high Dinobryon abundances were observed in field studies. KEY WORDS: Phytoplankton · Lake bloom · Succession · Ultraviolet radiation · Seasonality Full text in pdf format PreviousNextCite this article as: Heinze AW, Truesdale CL, DeVaul SB, Swinden J, Sanders RW (2013) Role of temperature in growth, feeding, and vertical distribution of the mixotrophic chrysophyte Dinobryon . Aquat Microb Ecol 71:155-163. https://doi.org/10.3354/ame01673 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 71, No. 2. Online publication date: December 16, 2013 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2013 Inter-Research.

Tracking differential incorporation of dissolved organic carbon types among diverse lineages of Sargasso Sea bacterioplankton

Bacterioplankton are the primary trophic conduit for dissolved organic carbon (DOC) and linking community structure with DOC utilization is central to understanding global carbon cycling. We coupled stable isotope probing (SIP) with 16S rRNA pyrosequencing in dark seawater culture experiments on euphotic and mesopelagic communities from the Sargasso Sea. Parallel cultures were amended with equimolar quantities of four DO(13) C substrates to simultaneously evaluate community utilization and population-specific incorporation. Of the substrates tested - two cyanobacterial products (exudates or lysates from a culture of Synechococcus) and two defined monosaccharides (glucose or gluconic acid) - the cyanobacterial exudates were incorporated by the greatest diversity of oligotrophic bacterioplankton populations in surface waters, including taxa from > 10 major subclades within the Flavobacteria, Actinobacteria, Verrucomicrobia and Proteobacteria (including SAR11). In contrast, the monosaccharide glucose was not incorporated by any taxa belonging to extant oligotrophic oceanic clades. Conversely, proteobacterial copiotrophs, which were rare in the ambient water (< 0.1% of sequences), grew rapidly on all DOC amendments at both depths, but with different substrate preferences among lineages. We present a new analytical framework for using SIP to detect DOC incorporation across diverse oligotrophic bacterioplankton and discuss implications for the ecology of bacterial-DOC interactions among populations of diverging trophic strategies.

Genetic Diversity and Antimicrobial Resistance of Escherichia coli from Human and Animal Sources Uncovers Multiple Resistances from Human Sources

Escherichia coli are widely used as indicators of fecal contamination, and in some cases to identify host sources of fecal contamination in surface water. Prevalence, genetic diversity and antimicrobial susceptibility were determined for 600 generic E. coli isolates obtained from surface water and sediment from creeks and channels along the middle Santa Ana River (MSAR) watershed of southern California, USA, after a 12 month study. Evaluation of E. coli populations along the creeks and channels showed that E. coli were more prevalent in sediment compared to surface water. E. coli populations were not significantly different (P = 0.05) between urban runoff sources and agricultural sources, however, E. coli genotypes determined by pulsed-field gel electrophoresis (PFGE) were less diverse in the agricultural sources than in urban runoff sources. PFGE also showed that E. coli populations in surface water were more diverse than in the sediment, suggesting isolates in sediment may be dominated by clonal populations.Twenty four percent (144 isolates) of the 600 isolates exhibited resistance to more than one antimicrobial agent. Most multiple resistances were associated with inputs from urban runoff and involved the antimicrobials rifampicin, tetracycline, and erythromycin. The occurrence of a greater number of E. coli with multiple antibiotic resistances from urban runoff sources than agricultural sources in this watershed provides useful evidence in planning strategies for water quality management and public health protection.

Population Dynamics of Escherichia coli in Surface Water1

Bucci, Vanni, Marin Vulić, Xiaodan Ruan, and Ferdi L. Hellweger, 2011. Population Dynamics of Escherichia coli in Surface Water. Journal of the American Water Resources Association (JAWRA) 47(3):611-619. DOI: 10.1111/j.1752-1688.2011.00528.x Abstract: Present models of the fate of enteric bacteria in surface water usually assume simple first-order decay. However, observed decay kinetics are typically biphasic and there is increasing evidence for growth in the ambient environment. These features are similar to the stationary phase of long-term batch cultures, where the dynamics are the result of repeated cycles of population takeovers by Growth Advantage in Stationary Phase (GASP) mutants able to scavenge nutrients released from dead cells. We investigated the possible role of this mechanism (i.e., growth of an adapted subpopulation) in surface water using laboratory experiments with various strains of Escherichia coli in different types of water. Addition of ampicillin (which only kills dividing cells) to these cultures caused a decrease in the total cell density, demonstrating the presence of a growing subpopulation. Furthermore, long-term survivors from surface water cultures outcompete naïve cells and take over the population in surface water. This growth advantage is heritable (i.e., aged strains were isolated from a single cell) and consistent with the GASP mechanism, although the responsible loci were not identified. Our results show that E. coli populations in surface water are dynamic and consist of dying naïve cells and growing surface water adapted cells. These results can explain the apparent biphasic decay pattern observed in laboratory experiments. This mechanism may also be important in the ambient environment.

Antibiotic Resistance Characteristics of Environmental Bacteria from an Oxytetracycline Production Wastewater Treatment Plant and the Receiving River

We characterized the bacterial populations in surface water receiving effluent from an oxytetracycline (OTC) production plant. Additional sampling sites included the receiving river water 5 km upstream and 20 km downstream from the discharge point. High levels of OTC were found in the wastewater (WW), and the antibiotic was still detectable in river water downstream (RWD), with undetectable levels in river water upstream (RWU). A total of 341 bacterial strains were isolated using nonselective media, with the majority being identified as Gammaproteobacteria. The MICs were determined for 10 antibiotics representing seven different classes of antibiotics, and the corresponding values were significantly higher for the WW and RWD isolates than for the RWU isolates. Almost all bacteria (97%) from the WW and RWD samples demonstrated multidrug-resistant (MDR) phenotypes, while in RWU samples, these were less frequent (28%). The WW and RWD isolates were analyzed for the presence of 23 tetracycline (tet) resistance genes. The majority of isolates (94.2% and 95.4% in WW and RWD, respectively) harbored the corresponding genes, with tet(A) being the most common (67.0%), followed by tet(W), tet(C), tet(J), tet(L), tet(D), tet(Y), and tet(K) (in the range between 21.0% and 40.6%). Class I integrons were detected in the majority of WW and RWD isolates (97.4% and 86.2%, respectively) but were not associated with the tet genes. We hypothesize that the strong selective pressure imposed by a high concentration of OTC contributes to the wide dissemination of tetracycline resistance genes and other antibiotic resistance genes, possibly through mobile genetic elements.

Comparison of Fecal Indicator Bacterial Populations in Surface Waters of the Kalamazoo River, USA

Surface waters along the Kalamazoo River, USA, were examined for occurrence and population trends of fecal indicator bacteria (FIB) with culture-based and culture-independent methods. The two methods recorded discrepancies in FIB counts, with the culture-independent method revealing more consistent numbers between the river sites. FIB cells that hybridized with the ECO1482 probe were highest in the downstream site, while the upstream site recorded higher ENF343 hybridized cells. Spatial and temporal differences in FIB populations were probably attributable to contrasting fecal pollution influences, vegetation type, varying environmental conditions as well as several in-stream factors between the two river sites.

VIBRIO AND PHYTOPLANKTON DYNAMICS DURING THE SUMMER OF 2004 IN A EUTROPHYING ESTUARY

Bacterioplankton response to eutrophication is a critical part of the transition from phytoplankton blooms to bottom‐water hypoxia in estuaries. This topic is of particular concern when endemic bacterial populations, such as Vibrio sp., may pose a health risk to local human populations using estuaries for recreation and food. The purpose of this study was to observe the dynamics of both Vibrio and phytoplankton in the Neuse River Estuary (NRE) in North Carolina, USA, during the summer of 2004. Vibrio concentrations, particle suspension characteristics, and chlorophyll a were measured in surface water collected at a series of stations along the estuarine gradient. Consistent with previous studies, a strong positive relationship between Vibrio concentration and salinity was found. Both Vibrio sp. and phytoplankton concentrations increased moving downstream, but beyond the salt front, phytoplankton declined while Vibrio sp. concentrations continued to increase. In surface waters, a large portion of suspensions was comprised of phytoplankton cells. The fraction of Vibrio cells attached to phytoplankton increased with phytoplankton concentration and decreased with increasing salinity. These observations of Vibrio dynamics in the NRE provide evidence that populations interact with phytoplankton populations in surface waters. This information may prove critical for models of estuarine bacterial dynamics in response to eutrophication.

Relationship between conductivity and analysed composition in a large set of natural surface-water samples, Queensland, Australia

The relationship between Total Dissolved Ions (TDI) and conductivity is established in around 34000 samples collected from rivers, streams and dams in Queensland since the 1960s. These data are extremely variable in content, reliability and periodicity of sampling. The data were sorted into useable modules, and their statistical distribution was examined. The median ratios of TDI/Conductivity obtained for different salinity ranges were between 0.59 and 0.72, with normal variability ranging from below 0.35 to greater than 1.00, particularly at lower salinities. The data set used has sufficient sample numbers and areal distribution per increment to give reasonable reliability within the conductivity range of 50–1000 μScm–1. A table has been developed that enables selection of conversion factors from conductivity to salinity (as TDI) which could be used to predict TDI from future conductivity measurements from the same surface water population.

Avoidance of aluminum by rainbow trout

AbstractAluminum is the principal toxicant in fish in acid waters. The ability to avoid Al, particularly at low concentrations, would confer a considerable ecological advantage, but previous research into avoidance of Al has produced mixed results. I used a cylindrical perspex tank, 150 cm in length, to study avoidance of Al by rainbow trout fry. The fish avoided Al, and their response was dependent on pH. Avoidance that was demonstrated at pHs of 5.00, 5.50, and 5.75 was abolished at a pH of 6.00. Fry avoided very low Al concentrations, being sensitive to [Al] &gt; 1.00 μmol L−1 at a pH of 5.00. This unequivocal demonstration of avoidance by rainbow trout fry of Al may have important implications for the ecology of indigenous fish populations in surface waters impacted by acidic deposition.

AVOIDANCE OF ALUMINUM BY RAINBOW TROUT

Aluminum is the principal toxicant in fish in acid waters. The ability to avoid Al, particularly at low concentrations, would confer a considerable ecological advantage, but previous research into avoidance of Al has produced mixed results. I used a cylindrical perspex tank, 150 cm in length, to study avoidance of Al by rainbow trout fry. The fish avoided Al, and their response was dependent on pH. Avoidance that was demonstrated at pHs of 5.00, 5.50, and 5.75 was abolished at a pH of 6.00. Fry avoided very low Al concentrations, being sensitive to [Al] > 1.00 μmol L−1 at a pH of 5.00. This unequivocal demonstration of avoidance by rainbow trout fry of Al may have important implications for the ecology of indigenous fish populations in surface waters impacted by acidic deposition.

A study of the effects of migratory zooplankton on microbial populations in surface waters of the N.W. Mediterranean

We examined the hypothesis that metazoan zooplankton may directly influence on microbial populations in an oligotrophic marine system. Diel variations of microbial populations, relative to changes in the biomass and feeding activity of metazoan zooplankton, were studied at an offshore station in the North Western Mediterranean Sea. Two different parts of the water column, representing relatively low, 0.05 μg l −1, and high, 0.12 μg l −1, chlorophyll zones were repeatedly sampled. At 3 h intervals, samples were obtained from 5 m and 40 m for estimates of microbial population abundances, size-fractions of chlorophyll and bacterial production; metazoan zooplankton were sampled concurrently with vertical net hauls between 0 and 50 m. Overall, there were no large day/night differences or clear diel rhythms in parameters of microbial populations. Bacterial concentrations peaked in the early evening at 40 m and later at 03:00 h at 5 m depth. Cell specific thymidine incorporation rates showed a distinct peak in the early morning hours at 5 m and were nearly constant at 40 m. Photosynthetic and heterotrophic nanoflagellates showed dissimilar temporal trends both relative to one another and between the two sampling depths. Chlorophyll, in the <10 μm or <3 μm size-fractions, increased at both 5 m and 40 m over the study period. Chlorophyll >10 μm was a negligible part of the chlorophyll crop at 5 m but represented about 50% of the chlorophyll at 40 m and showed considerable variability. In contrast to parameters of microbial populations, we found clear and large day/night differences in both abundances and feeding activities of metazoan zooplankton. Abundances of total zooplankton were higher by about a factor of 4 during nightime hours. Metazoan zooplankton peak abundances occurred from midnight to 03:00 h corresponding with peak activities of the digestive enzymes amylase and trypsin in total zooplankton as well as gut fluorescence in the most abundant copepod, Centropages typicus. There were few significant relationships detectable between parameters of microbial populations and metazoan zooplankton. The link between metazoan zooplankton and microbial populations, even in low-chlorophyll surface waters was apparently weak.

Nocturnal synthesis and diurnal degradation of phytoplankton biomass in surface waters

Natural populations of phytoplankton were collected near the Bay of Bourgneuf, France, in spring 1982, and were subjected to natural surface irradiance outdoors. They exhibited exponential growth on time scales of a week, but significant decreases in biomass indicators such as chlorophyll a and particulate nitrogen were observed during daytime. At night, these decreases were more than compensated by increases in the same biomass variables, which could double over 12 h of darkness. These features are characteristic of phytoplankton populations in surface waters which cannot escape high irradiances, and may be representative of situations in incubation bottles held at fixed depths near the surface. Under such conditions, a decrease in biomass during daytime should not necessarily be interpreted as irreversible damage unless growth measurements are carried out over the following night hours to check for possible recovery.

Effects of Pharmaceutical Wastes on Microbial Populations in Surface Waters at the Puerto Rico Dump Site in the Atlantic Ocean

A series of cruises during 1979 and 1980 to the pharmaceutical dump site located 64 km north of Arecibo, Puerto Rico, in the Atlantic Ocean, was carried out to evaluate effects of wastes on the ecology of the microflora of surface waters of the dump site. In addition to bacteriological monitoring of the waste plume created by the release of wastes from the disposal barge, stations along a series of transects, extending north from coastal waters through and beyond the dump site, were sampled. Largest numbers of culturable bacteria on marine agar were found at stations closest to shore and in the vicinity of the dump site. Bacteria recovered on marine agar were predominantly Vibrio and Aeromonas spp., with the relative abundance of these organisms decreasing as gram-positive organisms (staphylococci, micrococci, and bacilli) became dominant in areas immediately affected by waste dumping. Total numbers of bacteria (determined by acridine orange direct counts [AODC]), which were relatively stable throughout the region, and a direct estimate of viable cells (DVC), i.e., those cells responsive to additions of yeast extract and nalidixic acid, were determined by acridine orange staining and epifluorescence microscopy. Heterotrophic bacterial activity, measured by the uptake (V(max)) of C-labeled amino acids, declined relative to distance from land. Increases in specific activity indices (DVC/AODC and V(max)/AODC) were observed near the dump site. The composite results of this study, i.e., increased specific activities (determined by two methods), increased numbers of culturable marine bacteria, and marked alteration of the taxonomic composition of the culturable bacterial community in waters within and surrounding the Puerto Rico dump site, indicate demonstrable changes in the marine microbial community in the region used for waste disposal.