Microplankton Community Structure Research Articles

Seasonal influence of intrusion from the Kuroshio Current on microplankton biomass and community structure in the northern Satsunan area, western Japan

Seasonal variations in hydrographic conditions, nutrients, and microplankton abundance and biomass were investigated inside and outside Kagoshima Bay in the northern Satsunan area. The area is a nursery ground for the migrating fish. During the mixing season from November to April, highly saline water (>34.5) originating from a branch of the Kuroshio Current, the western boundary current of the North Pacific Subtropical Gyre, intruded from the surface layer into the bay causing extrusion of coastal bottom water. This intrusion generated vertical mixing between surface water and nutrient-rich bottom water. Consequently, chlorophyll a concentrations increased (>1 μg l−1) around the bay mouth. During the stratified season from May to August, the coastal surface water was extruded due to intrusion of saline water from the bottom layer. High chlorophyll a concentrations (>1 μg l−1) were also observed in the surface layer in July during the rainy season. Such differences in hydrographic conditions between mixing and stratified seasons were due to vertical distribution of highly saline water from outside the bay, which seasonally migrated between surface and subsurface layers. Relatively distinct redundancy analysis plots and boxplots generated from a generalized linear model showed that microplankton community structure differed between mixing and stratified seasons. The mixing and stratified seasons were characterized by high diatom abundance and low microplankton abundance, respectively, suggesting that vertical mixing increases nutrient supply and consequently increases diatom abundance. Thus, microzooplankton (mainly naked ciliates and athecate dinoflagellates) abundance was related to the abundance of prey organisms, such as diatoms, thecate dinoflagellates and cryptophyte-like flagellates, rather than hydrographic conditions. Thus, saline water intrusion from a branch of the Kuroshio Current likely governs hydrographic conditions in Kagoshima Bay and consequently affects temporal variations in abundance and taxonomic composition of phytoplankton and microzooplankton communities.

Physical and Biogeochemical Factors Driving Spatially Heterogeneous Phytoplankton Blooms in Nearshore Waters of Santa Monica Bay, USA

Phytoplankton blooms in nearshore waters are difficult to predict using only biogeochemical factors known to control phytoplankton growth, yet the need to understand these events continues to grow with expanding harmful algal bloom (HAB) events. The present study investigated the spatial and temporal dynamics of phytoplankton blooms and their drivers in King Harbor, a harbor in Santa Monica Bay in the Southern California Bight. High-frequency sensor measurements of environmental variables and biomass and discrete sampling of phytoplankton community composition and nutrients over an annual cycle were obtained. Eleven distinct bloom events, nine of which were numerically dominated by dinoflagellates, were identified over the study period. Results from both regression-based and time series analyses show that these blooms were correlated with increased temperature, changes in nutrient concentrations, and decreased tidally driven mixing, revealing an opportunity for bloom initiation close to neap tides. Predictors of chlorophyll biomass and environmental factors that explained differences in microplankton community structure differed between the two basins of King Harbor, despite their close and connected nature. Biomass and HAB taxa abundances in the harbor were significantly correlated with those in Santa Monica Bay with a 1-week lag in the harbor data, suggesting possible onshore transport of organisms into the harbor. The results of this study quantify the significant influence of tidal cycle as a physical process operating locally and at timescales of hours to days and provide evidence for a high degree of spatial heterogeneity in bloom dynamics in nearshore environments.

Phytoplankton dynamics and bloom formation in the oligotrophic Eastern Mediterranean: Field studies in the Aegean, Levantine and Ionian seas

This study attempts to elucidate the dynamics of phytoplankton biomass (as Chl-a), productivity, community structure and bloom formation in different regions of the oligotrophic Eastern Mediterranean (EMed). With this scope, several chemical and phytoplankton parameters were studied along a transect of 1300 km across different pelagic environments from North (N) Aegean to South (S) Aegean, Levantine and Ionian seas during spring and summer 2008. An exceptional spring phytoplankton bloom was detected in the S Aegean Sea, dominated by large sized diatoms and spreading almost throughout the euphotic zone. This unprecedented bloom was triggered by the nutrient enrichment of surface water masses due to cyclonic formations and a strong convection event that caused deep mixing. There was a clear decreasing trend of phytoplankton biomass and productivity from the Aegean towards the Levantine and Ionian seas. The same trend was recorded for N:P ratios and increasing P limitation from the Aegean to the Levantine and Ionian seas. Si:N ratio indicated an overall deficiency of N in relation to the available Si. Picoplankton was the dominant and most productive size fraction, except for the S Aegean in spring due to the diatom bloom. Chl-a maxima in the N Aegean were constrained within the surface layer occupied by modified Black Sea water, deepening progressively towards the Levantine and Ionian seas, especially during the stratified period. Nanoflagellates and small-sized dinoflagellates were important phytoplankton components in the N Aegean inter-seasonally, whereas in the S Aegean the large diatoms associated with the spring blooming shifted to nanoflagellates and small dinoflagellates in the stratified period. Coccolithophores and small diatoms were significant components in the Levantine and Ionian seas, whereas the overall microplankton community structure did not demonstrate prominent seasonal patterns. These results confirm that oligotrophy is the main driving force for the distribution of phytoplankters, but also offer evidence of how the low nutrient-low chlorophyll EMed system can occasionally support high phytoplankton biomass and generate prominent blooms. This work will help elucidate the structure and functioning of EMed pelagic food webs and contribute to the analysis of signals related to structural and functional ecosystem changes.

Microplankton dynamics of a coastal lagoon, Chilika: interactive effect of environmental parameters on microplankton groups

Microplankton population of Asia’s largest coastal lagoon Chilika was studied for five major groups, bacillariophyceae, cyanophyceae, chlorophyceae, dinophyceae, rotifera, and tintinninae. The study reported presence of 233 species of microplankton whose average annual abundance was 1631 cells/l. The physicochemical parameters contributing to the spatio-temporal fluctuations in microplankton diversity, abundance, and community structure were identified as salinity, pH, DO, nitrate, and silicate. Salinity, transparency, depth, and silicate most explained the abundance of bacillariophyceae; nitrate, pH, and DO influenced cyanophyceae; salinity, transparency, and chlorophyll concentration influenced chlorophyceae; salinity, depth, and water temperature influenced dinophyceae; salinity, free CO2, and nitrate-influenced rotifers, whereas salinity, pH, DO, and depth influenced tintinnids. Biotic-abiotic relationships revealed particular preference of environmental conditions at species level in groups like bacillariophyceae, cyanophyceae, and dinophyceae. Although the lagoon is shallow, bacillariophyceae-environment interaction showed depth can be a critical factor for species like Aulocoseira sp., Amphipleura sp., and Rhophalodia sp. Species of dinoflagellates like Dinophysis caudata, Noctiluca scintillans, and Protoperidinium proliferated in lower level of silicate. Unlike other cyanophyceae species Streptococcus sp., Chroococcus sp., Diplococcus sp., Aphanocapsa sp., and Gloeocapsa sp. were negatively influenced by nitrate concentration. The study provides better scope for ecological management of the lagoon with respect to conserving biodiversity and hydrological quality of the ecosystem.

Microplankton biomass and diversity in the Vietnamese upwelling area during SW monsoon under normal conditions and after an ENSO event

Investigating microplankton biomass and diversity under different climatological conditions is key to the understanding of cascading effects of climate change on nutrient cycles and biological productivity. Here we have used data collected during two contrasting summers along the coast of Viet Nam to show how climatological-driven changes can have a significant influence on the distribution of microplankton communities and their biomass via its impact on nutrient concentrations in the water column. The first summer in July 2003 followed a weak El-Nino Southern Oscillation (ENSO) event and was characterized by weak coastal upwelling, in the second summer during July 2004, upwelling was normal.Very low silicate (SiO4) concentrations and SiO4:DIN ratios characterized the source water mass for upwelling in July 2004, and dynamic SiO4 to dissolved inorganic nitrogen ratios (SiO4:DIN) mainly below the Redfield-Brzezinski ratio and DIN to phosphate ratios (DIN:PO43−) below the Redfield ratio were a common feature off Viet Nam. Much higher particle concentrations and PSi/PC ratios during normal upwelling revealed major changes in the microplankton community structure among summers. Small dinoflagellates (10–20µm) prevailed ubiquitously during reduced upwelling. During normal upwelling, the diatom Rhizosolenia sp. dominated the cell-carbon biomass in the silicate poor upwelling waters. Trichodesmium erythraeum dominated in the Mekong-influenced and nutrient depleted offshore waters, where it co-occurred with Rhizosolenia sp. Both species were directly associated with the much higher primary production (PP) and N2 fixation rates that were quantified in earlier studies, as well as with much higher diversities at these offshore sites. Along the coast, the correlation between Rhizosolenia sp. and PP rates was less clear and the factors regulating the biomass of Rhizosolenia sp. in the upwelling waters are discussed. The very low silicate concentrations in the source water mass for upwelling and the offshore deflection of the Mekong river plume likely triggered the observed ecological differences in the microplankton communities off Viet Nam in the normal upwelling season compared to the post ENSO conditions.

Particulate matter stoichiometry driven by microplankton community structure in summer in the Indian sector of the Southern Ocean

AbstractMicroplankton community structure and particulate matter stoichiometry were investigated in a late summer survey across the Subantarctic and Polar Front in the Indian sector of the Southern Ocean. Microplankton community structure exerted a first order control on PON:POP stoichiometry with diatom‐dominated samples exhibiting much lower ratios (4–6) than dinoflagellate and ciliate‐dominated samples (10–21). A significant fraction of the total chlorophyll a (30–70%) was located beneath the euphotic zone and mixed layer and sub‐surface chlorophyll features were associated to transition layers. Although microplankton community structure and biomass was similar between mixed and transition layers, the latter was characterized by elevated Chl:POC ratios indicating photoacclimation of mixed layer communities. Empty diatom frustules, in particular of Fragilariopsis kerguelensis and Pseudo‐nitzschia, were found to accumulate in the Antarctic Zone transition layer and were associated to elevated BSi:POC ratios. Furthermore, high Si(OH)4 diffusive fluxes (>1 mmol m2 d−1) into the transition layer appeared likely to sustain silicification. We suggest transition layers as key areas of C and Si decoupling through (1) physiological constraints on carbon and silicon fixation (2) as active foraging sites for grazers that preferentially remineralize carbon. On the Kerguelen Plateau, the dominant contribution of Chaetoceros Hyalochaete resting spores to microplankton biomass resulted in a three‐fold enhancement of POC concentration at 250 m, compared to other stations. These findings further highlight the importance of diatom resting spores as a significant vector of carbon export through the intense remineralization horizons characteristing Southern Ocean ecosystems.

Effects of an Acute Hypoxic Event on Microplankton Community Structure in a Coastal Harbor of Southern California

Fish mortality and hypoxic events occur in many coastal and inland systems and may result from natural or anthropogenically mediated processes. The effects of consequent changes in water biogeochemistry have been investigated for communities of benthic invertebrates and pelagic metazoans. The responses of micro-plankton assemblages, however, have remained largely unstudied. The northern basin of King Harbor, a small embayment within Santa Monica Bay, CA, USA, suffered a massive fish kill in March 2011 as a consequence of acute hypoxia. Dissolved oxygen concentrations < 0.1 ml l−1 were measured in the northern basin of the harbor for several days following the mortality event, and a strong spatial gradient of oxygen was observed from the northern basin to waters outside the harbor. The microplankton community within King Harbor differed significantly from a diatom-dominated community present in neighboring Santa Monica Bay. The latter region appeared unaffected by physicochemical changes, induced by the fish kill, that were observed within the harbor. A trophic shift was observed throughout King Harbor from a photoautotrophic-dominated assemblage to one of heterotrophic forms, with relative abundances of bacterivorous ciliates increasing by more than 80 % in the most impacted part of the harbor. Significant changes in community structure were observed together with dramatically reduced photosynthetic yield of the remaining phytoplankton, indicating severe physiological stress during the extreme hypoxia.

High diversity of microplankton surrounds deep-water coral reef in the Norwegian Sea

Coral reefs that exist in the depths of the oceans are surrounded by Eukarya, Archaea and bacterial communities that may play an important role in the nutrition and health of the reef. The first interdomain community structure of planktonic organisms in seawater from a deep-water coral reef is described. Community profiling and analysis of ribosomal RNA gene sequences from a coral reef system at 350m depth in the Norwegian Sea revealed a rich diversity of Eukarya and Bacteria and a moderate diversity of Archaea. Most sequences affiliated with marine microplankton from deep-sea to cold-surface regions, with many sequences being similar to those described in studies of mesopelagic and oxygen minimum zones. Dominant phylotypes belonged to the Alveolata (group I, II, dinoflagellates), Stramenopiles (silicoflagellates), Alphaproteobacteria (Pelagibacter ubique), Gammaproteobacteria (ARCTIC96BD-19), Bacteroidetes (Flavobacteria) and mesophilic Crenarchaeota (Nitrosopumilus maritimus). Several rare and novel members of the community fell into distinct phylogenetic groups. The inferred function of dominant community members suggested autotrophs that utilise light, ammonium or sulphide, and lifestyles based on host associations. The high diversity reflected a microplankton community structure, which is significantly different from that of microplankton collected at the same depth at a pelagic station away from reefs.

Diversity and community dynamics of protistan microplankton in Sagami Bay revealed by 18S rRNA gene clone analysis

The diversity and short-term changes in the protistan microplankton community from April to June 2006 in Sagami Bay were revealed by 18S rRNA gene clone analysis. A total of 1,076 clones consisted of 68 phylotypes of dinoflagellates, 96 phylotypes of diatoms and 27 phylotypes of other protists affiliated with Ciliophora, Prymnesio- monada, Chlorophyta, Cercozoa, Chytridiomycota, and Heterokonta. Approximately half of all dinoflagellate phylo- types were affiliated with the following genera: Ceratium, Gonyaulax, Gymnodinium, Gyrodinium, Lepidodinium, Neoceratium, Prorocentrum, and Woloszynskia. The other half was classified into seven uncultured groups. These di- noflagellate clones were mostly detected in May, in contrast to the diatom clones, which were detected frequently throughout the study period. Diatoms were diverse and consisted of 14 genera and three uncultured groups. The gen- era Discostella, Thalassiosira and Skeletonema were dominant in April, May and June, respectively. Species richness (number of phylotypes) and diversity (Shannon-Weiner) of the whole protistan microplankton community were high- est in May. This is the first example of a comprehensive molecular biological analysis of protistan microplankton community structure, and the results clearly showed a dynamic shift in the protistan community in coastal waters from April to June in Sagami Bay. The results of a direct comparison between the clone analysis and microscopic ob- servations indicated that the clone analysis had the great advantage of enabling identification of plankton that were morphologically indistinguishable, and to reveal detailed information on the biodiversity of protistan microplankton. This advancement in molecular biological analysis will assist in our understanding of the biodiversity of protistan mi-

Responses of microplankton community structure to iron addition in the Scotia Sea

The Southern Ocean is largely a High Nutrient Low Chlorophyll (HNLC) region where macronutrient concentrations are high and phytoplankton productivity is low. However, there are productive ‘hot spots’ that sustain large phytoplankton blooms. These areas, maintained by natural iron (Fe) fertilization, are important for the Southern Ocean ecosystem and for driving carbon export. Fe addition on-deck bioassay experiments were conducted on two cruises to the Scotia Sea region of the Southern Ocean (austral spring 2006 and summer 2008) to better understand how Fe controls the microplankton (20–200 μm) community structure on a seasonal basis. Light microscopy and fast-repetition rate fluorometry were used to examine changes in the species composition and physiological status of the microplankton community. Bioassays were carried out in three contrasting regions of the Scotia Sea: (1) a naturally Fe-fertilized, high chlorophyll area downstream (north and northwest) of the Islands of South Georgia (DSG); (2) a low Fe, low chlorophyll area upstream (south) of the Islands of South Georgia (USG); and (3) a naturally Fe-fertilized area north of the South Orkney Islands (SOI). Multivariate statistics were applied to the light microscopy results, showing significant differences between the initial microplankton communities for each of the bioassays. These differences were primarily spatial (between regions) and secondarily temporal (between seasons). Significant microplankton community shifts occurred in three of five bioassays, those in spring and summer USG and in summer DSG only. In summer, USG community responses increased significantly in medium (100–1000 pg C cell −1) and large (>1000 pg C cell −1) diatom species in response to Fe addition. Such a response was consistent with relief from in situ Fe limitation, which favours larger microplankton species with higher Fe requirements and subject to lower grazing pressures. The largest biomass increase in Fe-treated bioassay bottles was in Pseudonitzschia spp., which suggests that this genus may be a particularly important member of the microplankton community in the Scotia Sea.

Harmful algal blooms (HABs), dissolved organic matter (DOM), and planktonic microbial community dynamics at a near-shore and a harbour station influenced by upwelling (SW Iberian Peninsula)

The surface microalgal community, including harmful species, dissolved organic matter (DOM), and bacterial and viral populations were studied during an annual cycle (November 2007–October 2008) in a Near-shore (NS) and a Harbour (H) station located in an upwelling area (Sagres, SW Iberian Peninsula). The higher water residence time, water stability and shallowness of harbours in comparison with open waters likely contributed to the differences found between stations regarding chemical variables, statistical correlations and harmful algal proliferations. Also, several differences were noticed from a previous assessment ( Loureiro et al., 2005) including higher SST, lower nitrate and chlorophyll a concentrations, along with a shift in the microplankton community structure from diatom to nanoflagellate predominance. These variations feasibly reflect the response of this dynamic system to regional environmental modifications contributing to the understanding of common patterns in environmental change trends. The division of the sampling period into (1) non-upwelling (Non-Uw), (2) “spin-up” of upwelling (SU-Uw), and (3) “spin-down” and relaxation-downwelling (SD-Rel) stages allowed the identification of natural groupings of microplankton samples by Multi Dimensional Scaling (MDS) analysis. Dissolved organic nitrogen (DON) and viruses were the most significant abiotic and biotic variables, respectively, contributing to the dissimilarities between these stages (SIMPER analysis) and, therefore, potentially affecting the microplankton community structure. Harmful algal species and a stable viral community appeared to be favoured by SD-Rel conditions. Data seem to indicate that both Gymnodinium catenatum and Heterosigma akashiwo, the most abundant potentially harmful species, have been imported into the sampling area. Also, the H location, together with potential retention sites developing around the Cabo de São Vicente upwelling centre, may contribute to the local accumulation of harmful species. The associations found between harmful algal species and bacterioplankton and virioplankton call for detailed studies in order to evaluate species-specific interactions.

KELIMPAHAN PLANKTON DI EKOSISTEM PERAIRAN TELUK GILIMANUK, TAMAN NASIONAL, BALI BARAT

Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 Plankton abundance in Gilimanuk Bay of National Park Ecosystem, West Bali . An observation of plankton condition in Gilimanuk Bay of National Park, West Bali was conducted during March 2006. This study aimed to observ the environmental quality of Gilimanuk Bay water. The parameters observed were focused on the phytoplankton and zooplankton communities. Ten points of observation was done. Plankton abundance varied with location group from 4428 to 1716224 sel/m3 and 23938 individu/m3 (67.73 %) for microplankton and macroplankton, respectively. Microplankton community structure was dominated by the group of diatoms, such as Coscinodiscus , Chaetoceros , Guinardia , Navicula. Pseudonitzshia. The genus Ceratium (the group of dinoflagellates) was found in relatively abundant, but still normal condition. The structure of macroplankton was dominated by copepods 23938 individu/m3 (67.73 %). The other hand, information about mangrove, sea grass and coral reef and asssosiation with fauna in these ecosystem of Gilimanuk Bay very rarely. We need observed this subject for base line data to improving management of marine resources development. Keywords: plankton, environment condition, Gilimanuk Bay

Summer microplankton community structure across the Scotia Sea: implications for biological carbon export

Abstract. During the austral summer of 2008, we carried out a high resolution survey of the microplankton communities along a south to north transect covering a range of environments across the Scotia Sea, Southern Ocean; high and low productivity, sea-ice to open water conditions, and over a number of oceanographic fronts and bathymetric features. Cluster analysis revealed five distinct communities that were geographically constrained by physical features of bathymetry and fronts. From south to north the communities were: (1) the South Orkney group, a mixed community of naked dinoflagellates and heavily silicified diatoms, (2) southern Scotia Sea, a mixed community of cyptophytes and naked dinoflagellates, (3) central Scotia Sea, dominated by naked dinoflagellates, (4) southwest of the island of South Georgia, lightly silicified diatoms and naked dinoflagellates (5) northwest of South Georgia, dominated by diatoms. Data from a previous summer cruise (2003) to the Scotia Sea followed a similar pattern of community distribution. MODIS images, Chlorophyll a and macronutrient deficits revealed dense phytoplankton blooms occurred around the island of South Georgia, were absent near the ice edge and in the central Scotia Sea and were moderate in the southern Scotia Sea. Using these environmental factors, together with community composition, we propose that south of the Southern Antarctic Circumpolar Current Front, biogenic silica is preferentially exported and north of the front, in the vicinity of South Georgia, carbon is exported to depth.

Dimethylsulphide, DMSP-lyase activity and microplankton community structure inside and outside of the Mauritanian upwelling

We investigated the relationship between microplankton composition and dimethylsulphide (DMS) concentration in the Mauritanian upwelling in July/August 2006. As well as DMS and DMSP-lyase activity (DLA), we made some accompanying measurements of the precursor of DMS, DMSP (dimethylsulphoniopropionate) in the particulate and dissolved fraction, and photosynthetic pigments. At well-stratified offshore stations, chlorophyll- a concentrations were low (<0.5 mg m −3) with microplankton biomass dominated by coccolithophores and dinoflagellates. Water-column stratification became less pronounced closer inshore and the increased CO 2 fugacity and lowered sea surface temperature indicated significant upwelling at around 20°N. The highest chlorophyll- a levels were found in this region and in general, much higher chlorophyll- a and microplankton biomass was encountered inshore, and the microplankton assemblage was composed of a greater abundance and diversity of diatoms with planktonic ciliates, dinoflagellates, flagellates, and coccolithophores a smaller proportion of the total biomass. DMS was generally <2 nM at the most offshore stations whilst more variable (up to 14 nM) closer inshore, reflecting the influence of upwelling and higher microplankton biomass. DLA was highest in the surface mixed layer, and the highest recorded value of DLA (45 nM DMS h −1) was recorded at the surface alongside elevated DMS at the 20°N upwelling region. These data are the first coupled measurements of DMS, DLA, DMSP and microplankton species composition in an upwelling system and emphasise the patchy nature of DMS production and its complex relationship with microplankton species composition. This study provides a characterisation of DMS and community composition in a productive upwelling system, a system which is predicted to undergo an intensification of upwelling due to climate change.

The microplankton succession in the Ría de Vigo revisited: species assemblages and the role of weather-induced, hydrodynamic variability

We have analysed meteorological, hydrographic, and microplankton species abundance data, collected every 3–4 days during 1987 in the Ría de Vigo (NW Iberian Peninsula), to investigate the effect of environmental variability on the structure of the microplankton community. Three microplankton assemblages were distinguished, composed chiefly of: small- to medium-sized centric and pennate diatoms (i.e., C- and/or R-species, r-strategists), small-sized organisms from different taxonomic groups (i.e., C- or S-species, r-strategists), and medium- to large-sized dinoflagellates (i.e., S-species, K-strategists). Community changes were related to different scales of meteorological and hydrographic variability. At the seasonal scale, the succession from r-strategists towards K-strategists, or from C- and/or R-species towards S-species, was related with the annual cycle of mixing/stratification and high/low flushing. Within this seasonal pattern, a series of short-term ‘successions’ were identified, the onset of which co-occurred with hydrodynamic changes induced by meteorological disturbances. These results support the conclusions articulated in a previous paper on microplankton community structure during 1991 concerning: (1) the relative persistence of characteristic microplankton assemblages and their ecological interpretation in terms of adaptive strategies, and (2) the key role of weather-induced, hydrodynamic variability, especially at short-term scales, in shaping the structure of the community. The contrasting meteorology in 1987 and 1991 would explain interannual differences of community structure, such as the larger proportion of diatoms in 1991 than in 1987 due to increased intensity and duration of the upwelling seasonal cycle that year. At the species level, the early phase of the seasonal succession was characterised by the coexistence (i.e., single-species biomass, B i ≤40% of total biomass) or alternating dominance ( B i >40% B T) among (C–R) species, while the late part was characterised by the alternating dominance among species with different adaptive strategies. For instance, in September–October, the short-term succession started with the dominance of the (C–R) species Leptocylindrus danicus (∼80% of B T, during 3 weeks), followed by the (S–R) species Ceratium fusus+ Ceratium furca (∼70% of B T, 1 week), and finished with the dominance of small microheterotrophs (∼70% of B T, 2 weeks).

Microplankton community structure and the impact of microzooplankton grazing during an Emiliania huxleyi bloom, off the Devon coast

Phytoplankton and microzooplankton community structure and the impact of microzooplankton grazing were investigated during a one-day study of an Emiliania huxleyi bloom off the coast of Devon during July 1999. Vertical profiles were undertaken at four stations, along a transect which crossed from a low reflectance to a high reflectance area as seen by satellite imagery. Microzooplankton dilution grazing experiments, coupled with pigment analysis to determine class specific grazing rates, were performed at two of these stations.Highest concentrations of chlorophyll-a (5·3 mg m−3) and accessory pigments were measured inside the area of high reflectance. Phytoplankton standing stocks ranged between 1588 and 5460 mg C m−2 and were also highest in the area of high reflectance. The phytoplankton community was dominated by coccolithophores and diatoms in low reflectance waters and by photosynthetic dinoflagellates in high reflectance areas. Microzooplankton standing stocks ranged between 905 and 2498 mg C m−2. Protozoa dominated the microzooplankton community. The protozoan community comprised a relatively even mixture of heterotrophic dinoflagellates, non-choreotrich and choreotrich ciliates in low reflectance waters. However, non-choreotrich ciliates dominated the communities inside the high reflectance area. Of the heterotrophic ciliates, a predatory ciliate Askenasia sp. dominated both non-choreotrich abundance and biomass.Results from grazing experiments showed that 60–64% of the chlorophyll-a biomass was consumed daily by the microzooplankton. Highest grazing mortality was associated with peridinin (dinoflagellates) and alloxanthin (cryptophytes). Lower grazing rates were found on fucoxanthin (diatoms and prymnesiophytes). Our results indicate that grazing on E. huxleyi in the area of remotely sensed high reflectance was low and highest grazing was on photosynthetic dinoflagellates and cryptophytes.

Effect of meteorological and hydrographic disturbances on the microplankton community structure in the Ría de Vigo (NW Spain)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 203:23-45 (2000) - doi:10.3354/meps203023 Effect of meteorological and hydrographic disturbances on the microplankton community structure in the Ría de Vigo (NW Spain) E. Nogueira1,*, F. Ibanez2, F. G. Figueiras1 1Instituto de Investigacións Mariñas, CSIC, Eduardo Cabello, 6, 36208 Vigo, Spain 2 Observatoire Océanologique, Laboratoire d¹Océanographie Biologique et Ecologie du Plancton Marin, CNRS ESA 7076, BP 28, 06230 Villefranche-sur-Mer, France *Present address: Imperial College of Science, Technology and Medicine, RSM, Prince Consort Road, London SW7 2BP, United Kingdom. E-mail: e.nogueira@ic.ac.uk ABSTRACT: The relationships between meteorological and hydrographic disturbances and microplankton community structure and organisation were investigated in the Ría de Vigo, an estuarine ecosystem affected by coastal upwelling. The frequency and duration of sampling (ca twice per week from September 1990 to May 1992) are appropriate to reveal the impact of disturbances in the context of the seasonal cycle. Perturbations were identified statistically and related to recognisable meteorological and hydrographic processes that are expected to influence microplankton dynamics. According to the frequency of disturbances (between 8 and 14 yr-1) the ecosystem could be classified as intermediate-frequency disturbed in relation to the microplankton community organisation time-scales. Meteorological and thermohaline disturbances promoted changes in microplankton community structure (disjunctions). The time-series of thermohaline properties, a proxy for allogenic processes related with mixing regimes and estuarine circulation, was the best indicator of changes in community structure: 15 out of the 21 disjunctions (ca 70%) coincided with thermohaline disturbances. Disturbances of the nutrient fields were related to allogenic forcing but also, markedly during the productive season, to re-structuring of the microplankton community. They pointed out autogenic community-driven processes. Microplankton assemblages revealed by the species-oriented ordination technique were interpreted in terms of the replication strategies: well-defined groups of competitor (C), disturbance-tolerant ruderal (R) and stress-tolerant (S) species were discerned. At a seasonal time-scale, succession progressed according to the sequence from r- to K-selection strategies. C-species dominated spring assemblages, during the period of transient thermoclines, while S-species contributed more to summer assemblages, when the thermocline was fully developed and the ecosystem was under nutrient stress. R-species showed an intermittent pattern and their relative abundance increased when environmental variability was more acute, during the winter and spring to summer (clear-water phase) transition. The regime of allogenic disturbances operating at intermediate frequency during the productive season allowed the maintenance of relatively high microplankton diversity at the functional (assemblage) level: all types of replication strategies were present during summer and early autumn. The results support the applicability of the intermediate disturbance hypothesis (IDH) to microplankton community structure in the Ría de Vigo. KEY WORDS: Disturbances · Microplankton community structure · Replication strategies · Intermediate disturbance hypothesis (IDH) · Ría de Vigo Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 203. Online publication date: September 18, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

Change of microplankton community structure in response to fertilization of an arctic lake

Microplankton in an oligotrophic arctic lake were assessed by direct counts for one summer prior to nutrient additions and three summers during which inorganic nitrogen and phosphorus were added to the lake at approximately ten times ambient loading rates. Protozoa increased significantly in both number and biomass following fertilization, and community structure changed from dominance by oligotrichs prior to fertilization to dominance by the bacterivorous peritrich Epistylis rotans in the second and third years of fertilization. Rotifer abundance and biomass was not significantly different among summers, although one species, Conochilus natans that had not been seen previously, was present during the second and third year of fertilization. By the third year of fertilization both protozoan and rotifer biomass had declined from peak levels, while crustacean zooplankton nauplius abundance had increased suggesting the emergence of top-down regulatory controls as the lake became eutrophic.