Diatoms In Waters Research Articles

Linking Seasonal Reduction of Microbial Diversity to Increase in Winter Temperature of Waters of a Chilean Patagonia Fjord

Since microorganisms play a major role in the biogeochemistry of the ocean, understanding structure and dynamics of natural microbial communities is crucial in assessing the impact of environmental changes on marine ecosystems. In order to identify key environmental drivers of microbial community structure in Chilean Patagonian fjords, we analyzed composition of the prokaryotic community over an annual cycle at a single sampling site in Puyuhuapi Fjord. Distinctive communities represented mainly by Actinomycetales, Rhodobacteraceae, Cryomorphaceae and Flavobacteriaceae were associated with Estuarine Fresh Waters, whereas Cenarchaeaceae and Oceanospirillales were representative of Modified Sub Antarctic Waters present in the fjord. Salinity and oxygen were first-order factors explaining segregation of microbial communities in these contrasting water masses. Positive correlations of members of Flavobacteriaceae, Alteromonadales and Verrucomicrobiales with diatoms in subsurface waters and of Flavobacteriales (Cryomorphaceae and Flavobacteriaceae), Rhodobacteraceae and Pelagibacteraceae with dinoflagellates in surface waters suggest that phytoplankton composition could define specific niches for microorganisms in Puyuhuapi fjord waters. A dramatic reduction of richness and individual abundances within Flavobacteriaceae, Rhodobacteraceae and Cenarchaeaceae families was principally explained by seasonal increase of surface water temperature, with major reduction associated with changes in temperature during winter conditions. Taxa that are sensitive to increased temperature are key components of organic matter and element cycling, and we therefore suggest that potential decrease in diversity associated with rising of surface water temperature could impact current biogeochemical status of Patagonian fjord ecosystems.

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

Abstract. The Southern Ocean provides a vital service by absorbing about one-sixth of humankind's annual emissions of CO2. This comes with a cost – an increase in ocean acidity that is expected to have negative impacts on ocean ecosystems. The reduced ability of phytoplankton and zooplankton to precipitate carbonate shells is a clearly identified risk. The impact depends on the significance of these organisms in Southern Ocean ecosystems, but there is very little information on their abundance or distribution. To quantify their presence, we used coulometric measurement of particulate inorganic carbonate (PIC) on particles filtered from surface seawater into two size fractions: 50–1000 µm to capture foraminifera (the most important biogenic carbonate-forming zooplankton) and 1–50 µm to capture coccolithophores (the most important biogenic carbonate-forming phytoplankton). Ancillary measurements of biogenic silica (BSi) and particulate organic carbon (POC) provided context, as estimates of the biomass of diatoms (the highest biomass phytoplankton in polar waters) and total microbial biomass, respectively. Results for nine transects from Australia to Antarctica in 2008–2015 showed low levels of PIC compared to Northern Hemisphere polar waters. Coccolithophores slightly exceeded the biomass of diatoms in subantarctic waters, but their abundance decreased more than 30-fold poleward, while diatom abundances increased, so that on a molar basis PIC was only 1 % of BSi in Antarctic waters. This limited importance of coccolithophores in the Southern Ocean is further emphasized in terms of their associated POC, representing less than 1 % of total POC in Antarctic waters and less than 10 % in subantarctic waters. NASA satellite ocean-colour-based PIC estimates were in reasonable agreement with the shipboard results in subantarctic waters but greatly overestimated PIC in Antarctic waters. Contrastingly, the NASA Ocean Biogeochemical Model (NOBM) shows coccolithophores as overly restricted to subtropical and northern subantarctic waters. The cause of the strong southward decrease in PIC abundance in the Southern Ocean is not yet clear. The poleward decrease in pH is small, and while calcite saturation decreases strongly southward, it remains well above saturation ( > 2). Nitrate and phosphate variations would predict a poleward increase. Temperature and competition with diatoms for limiting iron appear likely to be important. While the future trajectory of coccolithophore distributions remains uncertain, their current low abundances suggest small impacts on overall Southern Ocean pelagic ecology.

Physiological responses of coastal and oceanic diatoms to diurnal fluctuations in seawater carbonate chemistry under two CO<sub>2</sub> concentrations

Abstract. Diel and seasonal fluctuations in seawater carbonate chemistry are common in coastal waters, while in the open-ocean carbonate chemistry is much less variable. In both of these environments, ongoing ocean acidification is being superimposed on the natural dynamics of the carbonate buffer system to influence the physiology of phytoplankton. Here, we show that a coastal Thalassiosira weissflogii isolate and an oceanic diatom, Thalassiosira oceanica, respond differentially to diurnal fluctuating carbonate chemistry in current and ocean acidification (OA) scenarios. A fluctuating carbonate chemistry regime showed positive or negligible effects on physiological performance of the coastal species. In contrast, the oceanic species was significantly negatively affected. The fluctuating regime reduced photosynthetic oxygen evolution rates and enhanced dark respiration rates of T. oceanica under ambient CO2 concentration, while in the OA scenario the fluctuating regime depressed its growth rate, chlorophyll a content, and elemental production rates. These contrasting physiological performances of coastal and oceanic diatoms indicate that they differ in the ability to cope with dynamic pCO2. We propose that, in addition to the ability to cope with light, nutrient, and predation pressure, the ability to acclimate to dynamic carbonate chemistry may act as one determinant of the spatial distribution of diatom species. Habitat-relevant diurnal changes in seawater carbonate chemistry can interact with OA to differentially affect diatoms in coastal and pelagic waters.

A role for diatom-like silicon transporters in calcifying coccolithophores.

Biomineralization by marine phytoplankton, such as the silicifying diatoms and calcifying coccolithophores, plays an important role in carbon and nutrient cycling in the oceans. Silicification and calcification are distinct cellular processes with no known common mechanisms. It is thought that coccolithophores are able to outcompete diatoms in Si-depleted waters, which can contribute to the formation of coccolithophore blooms. Here we show that an expanded family of diatom-like silicon transporters (SITs) are present in both silicifying and calcifying haptophyte phytoplankton, including some globally important coccolithophores. Si is required for calcification in these coccolithophores, indicating that Si uptake contributes to the very different forms of biomineralization in diatoms and coccolithophores. Significantly, SITs and the requirement for Si are absent from highly abundant bloom-forming coccolithophores, such as Emiliania huxleyi. These very different requirements for Si in coccolithophores are likely to have major influence on their competitive interactions with diatoms and other siliceous phytoplankton.

Physiological Responses of a Model Marine Diatom to Fast pH Changes: Special Implications of Coastal Water Acidification.

Diatoms and other phytoplankton in coastal waters experience rapid pH changes in milieu due to high biological activities and/or upwelled CO2-rich waters. While CO2 concentrating mechanisms (CCMs) are employed by all diatoms tested to counter low CO2 availability in seawater, little is known how this mechanism responds to fast pH changes. In the present study, the model diatom Thalassiosira pseudonana was acclimated for 20 generations to low pH (7.81) at an elevated CO2 of 1000 μatm (HC) or to high pH (8.18) at ambient CO2 levels of 390 μatm (LC), then its physiological characteristics were investigated as cells were shifted from HC to LC or vice versa. The maximal electron transport rate (ETRmax) in the HC-acclimated cells was immediately reduced by decreased CO2 availability, showing much lower values compared to that of the LC-acclimated cells. However, the cells showed a high capacity to regain their photochemical performance regardless of the growth CO2 levels, with their ETRmax values recovering to initial levels in about 100 min. This result indicates that this diatom might modulate its CCMs quickly to maintain a steady state supply of CO2, which is required for sustaining photosynthesis. In addition, active uptake of CO2 could play a fundamental role during the induction of CCMs under CO2 limitation, since the cells maintained high ETR even when both intracellular and periplasmic carbonic anhydrases were inhibited. It is concluded that efficient regulation of the CCM is one of the key strategies for diatoms to survive in fast changing pH environment, e.g. for the tested species, which is a dominant species in coastal waters where highly fluctuating pH is observed.

Epiphytic diatoms in lotic and lentic waters - diversity and representation of species complexes

Small streams and shallow ponds represent sensitive ecosystems and attached diatoms can serve as integrative indicator with fast response to environmental changes. Development of methods for ecological monitoring throughout Europe and their calibration for particular ecoregions are not finished yet and databases need to be filled by data from undersampled regions and overlooked substrates. The present study aims to explore the diversity of epiphytic diatoms in unexplored catchment areas with special attention to substrate specificity and distribution of unresolved diatom species complexes. Significant differences were found in diversity of both regions and water types (lotic/lentic). No significant differences were found in the case of substrates. CCA analysis showed significant influence of pH, water streaming (streaming/stagnant) and Lemna substrate to species composition. Surprisingly species complexes represent the majority of epiphytic assemblages with no significant differences between lotic and lentic waters or substrates except of Lemna. The high representation of complexes does not lead automatically to reduction of overall diversity of the sample.

Latitudinal diversity patterns of diatoms in the Southwestern Atlantic and Antarctic waters

Latitudinal changes in the species richness of planktonic diatoms in Southwestern Atlantic and Antarctic waters (29 degrees-76 degrees S) were analyzed from local to regional scale in three spring and one summer seasons. A total of 220 diatom species (16-87 per station) were recorded. Despite the noticeable interannual variability, species richness showed a maximum in the northern sector of the Brazil-Malvinas Confluence Zone and a highly significant decrease with latitude.

Hyperspectral optical discrimination of phytoplankton community structure in Funka Bay and its implications for ocean color remote sensing of diatoms

Identification of phytoplankton functional groups is key to understanding marine biogeochemical cycles. For more accurate understanding of phytoplankton community structure and its implications for ocean color remote sensing applications, we investigated seasonal changes in phytoplankton pigments with high-performance liquid chromatography (HPLC), hyperspectral absorption coefficients of detritus (ad(λ)), phytoplankton (aph(λ)), and colored dissolved organic matter (aCDOM(λ)), and hyperspectral aph(λ) derived from remote sensing reflectance (aph_Rrs-derived(λ)) in the coastal waters of Funka Bay from 2010 to 2012. Chlorophyll a (Chl a) concentrations measured by HPLC ranged from 0.29 to 8.6mgm−3. Phytoplankton community compositions, as estimated by chemotaxonomic analysis (CHEMTAX) based on HPLC phytoplankton pigments, showed a seasonal succession of diatoms, chlorophyll b-containing phytoplankton (chlorophytes and prasinophytes), and cyanobacteria. Additionally, to identify the dominant type of phytoplankton with an alternative technique to CHEMTAX analysis, we employed a derivative spectroscopy/similarity index (SI) approach for aph(λ) as an optical detection technique for discriminating between different types of phytoplankton. In particular for diatom-dominated stations, SI values relative to the second derivative spectra of aph(λ) of diatom cultures, isolated from our study region, were significantly higher than those for chlorophyll b-containing phytoplankton- and cyanobacteria-dominated stations. Furthermore, we found a strong relationship between the SI values calculated from the second derivative spectra and the composition of diatoms as estimated by CHEMTAX. These results suggest that the two different methods validated each other's performance and precision in estimating relative diatom abundance from bulk samples and that it is possible to optically discriminate the dominance of diatoms using derivative spectra of aph(λ). We extended this combination approach to hyperspectral aph_Rrs-derived(λ), using a quasi-analytical algorithm within 400–546nm range. We found a significant correlation between SI values obtained from the second derivative spectra of aph_Rrs-derived(λ)/aph_Rrs-derived(443) and the composition of diatoms derived by CHEMTAX, but it was not as high as for aph(λ) measured by filter-pad analysis. These results indicate that using hyperspectral optical data of aph(λ) and Rrs(λ) with derivative spectroscopy is potentially a promising approach to identify seasonal variability in the composition of diatoms in coastal waters. Furthermore, a hyperspectral approach in combination with CHEMTAX analysis as a reference for phytoplankton community structure has proven useful in improving our understanding of phytoplankton community structure in the coastal waters of Funka Bay.

The Southern Ocean silica cycle

The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.

Colonization dynamics of periphytic diatoms in coastal waters of the Yellow Sea, northern China

The colonization features of periphytic diatoms were studied in coastal waters of the Yellow Sea, northern China from May to June 2010, using glass slides as an artificial substratum. Samples were collected at a time interval of 1, 3, 7, 10, 14, 21 and 28 d from two depths of 1 and 3 m. The dynamics of diatom colonization process had a similar pattern in community structure and fitted the logistic model in growth curve at both depths. The maximum abundance and the time for reaching 50% maximum abundance (10 d) showed no significant differences (P>0.05) between two depths 1 and 3 m. Although the diatom communities represented similar taxonomic composition, they differed in the temporal pattern of structural parameters and in succession dynamics of dominant species between the two layers. The species richness showed significantly higher values during the colonization period more than 14 d, while the species diversity and evenness represented a higher variability with significantly different values (P<0.05) at a depth of 1 m than at a deeper layer. The results suggest that the diatom colonization follows the logistic model growth curve and differs in colonization features between different depths in the coastal waters, and that the sampling strategy at 1 m is more effective to detect the ecological features for bioassessment in marine ecosystems.

Diatom distribution in surface sediments from Chinese inshore waters and the relationship to modern environmental variables

Diatoms are widely used to study past and present changes in the marine environment. Unimodal models are appropriate for exploring the relationship between environmental properties in Chinese inshore waters and fossil diatom species derived from modern surface sediments. The best-fit relationships between two multivariate datasets (diatom species and environmental variables) were identified using canonical correspondence analysis (CCA), which is a constrained ordination technique. The absolute abundance of diatoms in the Chinese inshore waters ranged from 500 to 48 000 valves/g, and the average absolute abundance of all the 29 sites was 11 300 valves/g. 153 species and varieties of diatoms belonging to 42 genera in all were identified in the Chinese inshore waters. There were 28 dominant diatom species in all. According to the absolute abundance of the dominant species and the spatial distribution of the currents from the Chinese inshore waters, 12 diatom assemblages were distinguished from north to south, which reflected the different oceanographic conditions at the regional scale. Of the eight environmental variables considered, the most important environmental variable is winter sea surface salinity (WSS), which was also the only environmental variable with statistical significance. Therefore, it may be used to establish a transfer functions for the Chinese inshore waters in future paleoclimate studies.

Mink (Neovison vison) as a natural vector in the dispersal of the diatom Didymosphenia geminata

Considerable resources have been invested worldwide in response to the spread of the diatom Didymosphenia geminata in rivers and streams. Considering the very low possibility of elimination of an invasive microbe, management has focused on biosecurity protocols, addressed exclusively toward the human role in dispersal (e.g. ‘check, clean dry’ campaigns and gear-washing stations for recreational users). Natural dispersal by wildlife vectors may also play an important role in the spread of D. geminata and other algal species, potentially limiting or negating the efficacy of biosecurity measures. We investigated the possibility that introduced mink (Neovison vison) may be a potential dispersal agent for D. geminata and other stream diatoms in Chilean Patagonia. Neovison were trapped near a zone of strong and persistent D. geminata blooms in the fifth order Río Simpson, and also in a fourth order upstream tributary, Río Huemules, the latter with smaller, more incipient blooms. Epibiotic D. geminata cells were identified from Neovison at Río Simpson (44% positive, average 791 cells per animal, n=18 animals), and Río Huemules (20% positive, average 40 cells per animal, n=5 animals). Many other species were also observed: 20 genera, 5683 cells per mink in Río Simpson, and 18 genera, 3605 cells per mink in Río Huemules. Navicula, Epithemia, Fragilaria and Placoneis were among the genera most frequently encountered. Neovison are known to prefer the riparian ecotone of streams of all sizes, have the capacity to travel several kilometers upstream and downstream, and possibly as far as 10 km overland to colonize new catchments. Together with an estimated survival time of 60 or more days for D. geminata in a humid environment (e.g. mink fur), Neovison represent a potentially significant factor in the colonization of upstream reaches and adjacent catchments. We comment on the potential for other wildlife vectors in Patagonia, and respective alternative patterns of short- to long-distance dispersal of diatoms in continental waters. Our results suggest that wildlife vectors should be considered in the management of D. geminata, and in the case of Neovison, integrative management of multiple invasive species, and a reassessment of conservation priorities may be necessary.

Phytoplankton composition under contrasting oceanographic conditions: Upwelling and downwelling (Eastern Australia)

Phytoplankton abundance and distribution along the east coast of Australia are driven primarily by the southward flowing East Australian Current (EAC), which transports tropical water masses to temperate latitudes. The Solitary Islands Marine Park (SIMP, ~30°S) is located north of the EAC separation point (~32°S) in this tropical–temperate transition zone. In this study, we describe the oceanographic context (wind, current and nutrient load) during a wind-driven downwelling and a current-driven upwelling event, both sampled in austral winter only ten days apart. We investigate the effect of these contrasting oceanographic conditions on phytoplankton abundance, composition and distribution along a cross-shelf transect. During downwelling we find a cross-shelf transition in microphytoplankton composition from an offshore- to an inshore-community associated with nutrient gradients (nitrate and silicate). Strong vertical mixing leads to increased occurrences of benthic diatoms in near-shore surface waters. During upwelling conditions, elevated nutrient availability results in maximum microphytoplankton abundances (mainly oceanic diatoms) and increased species richness on the mid-shelf. An increase in dinoflagellates and silicoflagellates (mid-shelf) and the appearance of tropical phytoplankton (especially picoplankton and dinoflagellates, offshore) signals a strong impact of the EAC across all shelf communities. Nanoplankton are a major part of the winter phytoplankton community during both oceanographic regimes (~40–50% of TChl a). Our findings provide evidence of EAC-driven, nutrient-rich, slope water intrusion in the SIMP as expressed by cross-shelf phytoplankton variability. We suggest that rapid (~weekly) changes in phytoplankton composition along the east Australian coast are likely to be enhanced by the climate change-induced warming/strengthening of the EAC.

Influence of Sample Sizes on Analyzing Community Parameters of Periphytic Diatoms for Bioassessment Using an Artificial Substrate in Coastal Waters

ABSTRACT: Influence of sample sizes on analyzing community parameters of periphytic diatoms was studied in coastal waters of the Yellow Sea from May 2010 to June 2010. Samples were collected from two depths of 1 m and 3 m using an artificial substrate. Based on a 95% probability, 15, 8, and 5 replicate slides (∼260, 140, and ∼90 cm2) were sufficient for recovering the diatom communities with specified cumulative contributions of 99%, 95%, and 90% at two depths, respectively. To achieve less than 10% standard errors (coefficients of variation), six (105 cm2) replicate slides were required for biodiversity analysis of the microperiphyton communities with various colonization times at two depths. More replicate sides were required for the young diatom communities (less than 14 days) than the mature samples (greater than 14 days). These results suggest that six replicate slides at two depths may be sufficient to analyze community parameters of periphytic diatoms in costal waters.

Diversity and germination patterns of diatom resting stages at a coastal Mediterranean site

Many planktonic diatoms produce resting stages that survive in the sediment and allow species persistence over periods in which vegetative growth does not occur. With the aim of depicting the annual variability of diatom benthic stage production and understanding the rela- tionships between planktonic and benthic dynamics, we quantified diatoms in surface waters and their viable resting stages in surface sediments at the long-term ecological research station MareChiara (LTER-MC) in the Gulf of Naples (Mediterranean Sea) over 15 mo. A considerable fraction of the diatom species recorded in the water column was also obtained from germination in surface sediments, showing that the formation of resting stages is a widespread life strategy in coastal areas. The most abundant taxa recorded in the plankton were several species of the genera Chaetoceros, Skeletonema, Thalassiosira, Cyclotella, Pseudo-nitzschia and Bacteriastrum. Species of the latter 2 genera were never retrieved from the sediment. Peaks of viable resting stages were generally recorded in the same period as blooms of the individual species in the plankton. Repeated germination experiments with the same sediments demonstrated that some species are more resistant than others to prolonged darkness, while different daylength conditions did not produce a clear effect on germination patterns. This first time-series analysis of a coastal seed bank demonstrates that the assemblage of viable diatoms in the sediment varies over the year, reflecting the diatom dyna mics in the water column, but also species-specific characteristics in survival capability and likely the disturbance due to biotic and abiotic factors.

Remarks on the morphology and distribution of some rare centric diatoms in southern Brazilian continental shelf and slope waters

This paper provides information on the morphology and occurrence of extant diatoms of the family Asterolampraceae and Azpeitia species of the southernmost Brazilian continental shelf and slope waters in the Southwestern Atlantic Ocean (28 -34ºS), under the influence of Tropical, Subtropical, Subantarctic Waters, terrestrial discharges from La Plata River and Lagoa dos Patos lagoon. Plankton was sampled (20 µm net; vertical hauls) at the same 27 stations in winter 2005 and summer 2007. Among Asterolampraceae, Asteromphalus flabellatus was the most frequent species (57% of samples) observed mainly in winter samples (92%) in Subtropical Shelf Water but also under the influence of La Plata River plume (salinity &lt;35). Lower frequencies were observed for Asterolampra marylandica, Asteromphalus elegans, Asteromphalus heptactis and Spatangidium arachne. Four species of Azpeitia were observed: A. barronii and A. neocrenulata for the first time in the South Atlantic Ocean while A. africana and A. nodulifer had already been registered in equatorial and southern areas of Brazil. All Azpeitia species were rare (19%) in offshore samples (100-200 m depth. Remarks on the morphology based on light and scanning electron microcopy observations are provided along with their distribution in the study area.

Fouling diatoms of Andaman waters and their inhibition by spinal extracts of the sea urchin Diadema setosum (Leske, 1778)

Diatoms play a central role in biofouling by attracting microscopic reproductive propagules of macroorganisms. This study reports on the seasonal variation of fouling diatoms in waters of the South Andaman Sea and evaluation of their inhibition by spinal extracts of the sea urchin Diadema setosum on glass slides. Pennate diatoms were more abundant than centric diatoms in the fouling film. The genera Navicula and Amphora were dominant throughout the study. Apart from that, an abundance of the genera Cocconeis and Thalassiosira was observed during the pre-monsoon period; Nitzschia was abundant during the monsoon period and Achnanthes and Thalassiosira during the post-monsoon period. Two separate fractions were extracted from the spines using ethanol and distilled water as solvents. The ethanol extract fraction showed inhibition against eight major fouling diatoms. The ethanol extract exhibited a higher inhibitory effect than the aqueous extract against biofilm formation, confirming that the organic fraction has microfouling inhibitory compounds.

Resting stage cells of diatoms in deep waters in Kumano-Nada, central part of Japan

The abundance and species composition of viable resting stage cells of diatoms were investigated in deep waters (200, 500 and 1,000 m depths) collected at neighboring stations in Kumano-Nada, central part of Japan, in April, August and October 2006. Viable resting stage cells were enumerated by the modified extinction dilution method (most probable number (MPN) method) based on incubation. Resting stage cells were detected from all samples, except at 500 m depth in August, in a range of abundances between 200-4,415 cells L � 1 . The resting stage cells of diatoms observed belonged to four genera of the Centrales, Chaetoceros spp. (C. curvisetus, C. socialis and Chaetoceros sp.), Leptocylindrus danicus, Skeletonema spp. and Thalassiosira spp., and two of the Pen- nales, Cylidrotheca closterium and Navicula sp., along with one centric and three pennate unidentified diatoms, in total. It is indicated, in this study, that the abundances enumerated by the MPN method could represent those of disassembled resting stage cells originally aggregated in marine snow, of which the sinking rate is reportedly great (e.g. 68 m day � 1 ). This, eventually, suggests that the abun- dance and species composition of resting stage cells in the deep waters reflected the states of blooms occurring just before our sam- plings in the surface water of the Kumano-Nada region. In this region, coastal upwelling occasionally occurs, implying that such rest- ing stage cells sinking from the euphotic layer to deeper depths might have some chance to return to the surface and be able to act as a seeding population for further blooms.

A study on the fine structure of marine diatoms in Korean coastal waters: Genus Thalassiosira 5

Thalassiosira species were collected from October 2007 to January 2009 in an attempt to better understand species diversity of the genus Thalassiosira in Korean coastal waters. A total of 5 Thalassiosira species (T. concaviuscula, T. oceanica, T. partheneia, T. simonsenii and T. nanolineata) were identified here. Most species in this study were of small size, and 5 species were recorded for the first time in Korean coastal waters. Using a scanning electron microscope (SEM), we described distinctive characteristics of fine structure that proved to be important diagnostic characteristics for the identification of each species. The most important diagnostic characteristics for Thalassiosira species identification were the marginal strutted processes, the position of labiate processes, and the areolation. The differential characteristics of the species studied were: T. concaviuscula has a double layered external tubes on the marginal strutted processes; T. oceanica shows marginal ridges that are interlinked between the marginal strutted processes; the valve face of T. partheneia is fairly convex and its labiate process is positioned midway between two strutted processes; T. simonsenii is characterized by two labiate processes and somewhat coarse areolae; and, T. nanolineata has several central strutted processes and linear areolation.

Influence of grazing formulations on the emergent properties of a complex ecosystem model in a global ocean general circulation model

Sensitivity to nonlinear equations may be a characteristic feature of biological models, particularly those that are complex. A complex marine ecosystem model (PlankTOM5.2) that incorporates multiple plankton functional types (PFTs) was embedded in a global ocean general circulation model (OGCM) and its performance assessed for four different formulations of multiple-prey zooplankton functional response: Michaelis–Menten (MM: Holling Type II), Sigmoidal (S: Holling Type III), Blackman (B) and Ivlev (Iv). Predictions of the four simulations were compared for the North Atlantic and North Pacific oceans. Remarkable differences were seen in both spatial extent and magnitude of predicted distributions of PFTs, as well as bulk properties, highlighting how the choice of functional response has a major impact on the resulting ecosystem structure. The range of average concentration of diatoms in surface waters was particularly marked, varying between 0.04 mg m −3 (B and MM) and 0.13 mg m −3 (S) in spring and between 0.01 mg m −3 (B) and 0.07 mg m −3 (S) in autumn. Differences in ecosystem structure affected predicted export flux, which varied by more than 25% among the simulations. Overall, our work highlights that accuracy is required in ecosystem formulation if reliable predictions are to be made when using complex marine ecosystem models embedded in OGCMs and therefore the need for further studies, with appropriate validation, that address structural sensitivity.