Application of a new multi-metric phytoplankton index to the assessment of ecological status in marine and transitional waters

Patterns of phytoplankton size spectra variation with gradients of environmental stress have been observed in freshwater, transitional waters and marine ecosystems, driving the development of size spectra based assessment tools.In this study, we have tested on transitional and coastal waters a new Index of Size spectra Sensitivity of Phytoplankton (ISS-Phyto), which integrates simple size spectra metrics, size class sensitivity to anthropogenic disturbance, phytoplankton biomass (chlorophyll a) and taxonomic richness thresholds. ISS-Phyto has been tested both among and within ecosystems along pressure gradients based on expert view assessment; the adequacy of symmetric and both left and right asymmetric models of phytoplankton size class sensitivity have been compared.The results showed that ISS-Phyto consistently discriminated between anthropogenic and natural disturbance conditions. Left asymmetric models of size spectra sensitivity, assuming greater disturbance tolerance with respect to eutrophication and organic enrichment of increasingly large size classes, showed the best fit comparing all ecosystems; in three of the four considered ecosystems (Varna, Helsinki, Mompás-Pasaia), they seemed to discriminate best between different levels of disturbance also within ecosystems. Moreover, they demonstrated significant and inverse patterns of variation along the overall pressure gradient as well as along the inorganic phosphorus (DIP), chlorophyll a and trophic index (TRIX) gradients.Therefore, ISS-Phyto, originally developed for transitional waters, seems to be an adequate assessment tool of ecological status also in coastal marine waters; moreover, it seems adequate to describe within ecosystem disturbance gradients. Hence, ISS-Phyto helps to understand the relationships between anthropogenic impact and ecosystem response from the individual point of view, with reference to the simple parameter of body size.     

Decoding Size Distribution Patterns in Marine and Transitional Water Phytoplankton: From Community to Species Level

Understanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism’s behavior which exploring patch resources in transitional and marine phytoplankton communities.     

Alteration of the food web along the Antarctic Peninsula in response to a regional warming trend

In the nearshore coastal waters along the Antarctic Peninsula, a recurrent shift in phytoplankton community structure, from diatoms to cryptophytes, has been documented. The shift was observed in consecutive years (1991–1996) during the austral summer and was correlated in time and space with glacial melt‐water runoff and reduced surface water salinities. Elevated temperatures along the Peninsula will increase the extent of coastal melt‐water zones and the seasonal prevalence of cryptophytes. This is significant because a change from diatoms to cryptophytes represents a marked shift in the size distribution of the phytoplankton community, which will, in turn, impact the zooplankton assemblage. Cryptophytes, because of their small size, are not grazed efficiently by Antarctic krill, a keystone species in the food web. An increase in the abundance and relative proportion of cryptophytes in coastal waters along the Peninsula will likely cause a shift in the spatial distribution of krill and may allow also for the rapid asexual proliferation of carbon poor gelatinous zooplankton, salps in particular. This scenario may account for the reported increase in the frequency of occurrence and abundance of large swarms of salps within the region. Salps are not a preferred food source for organisms that occupy higher trophic levels in the food web, specifically penguins and seals, and thus negative feedbacks to the ecology of these consumers can be anticipated as a consequence of shifts in phytoplankton community composition.     

Spatial Diversity of Bacterioplankton Communities in Surface Water of Northern South China Sea

The South China Sea is one of the largest marginal seas, with relatively frequent passage of eddies and featuring distinct spatial variation in the western tropical Pacific Ocean. Here, we report a phylogenetic study of bacterial community structures in surface seawater of the northern South China Sea (nSCS). Samples collected from 31 sites across large environmental gradients were used to construct clone libraries and yielded 2,443 sequences grouped into 170 OTUs. Phylogenetic analysis revealed 23 bacterial classes with major components α-, β- and γ-Proteobacteria, as well as Cyanobacteria. At class and genus taxon levels, community structure of coastal waters was distinctively different from that of deep-sea waters and displayed a higher diversity index. Redundancy analyses revealed that bacterial community structures displayed a significant correlation with the water depth of individual sampling sites. Members of α-Proteobacteria were the principal component contributing to the differences of the clone libraries. Furthermore, the bacterial communities exhibited heterogeneity within zones of upwelling and anticyclonic eddies. Our results suggested that surface bacterial communities in nSCS had two-level patterns of spatial distribution structured by ecological types (coastal VS. oceanic zones) and mesoscale physical processes, and also provided evidence for bacterial phylogenetic phyla shaped by ecological preferences.     

Oligotrophic waters of the Northwest Atlantic support taxonomically diverse diatom communities that are distinct from coastal waters

Diatoms are important components of the marine food web and one of the most species-rich groups of phytoplankton. The diversity and composition of diatoms in eutrophic nearshore habitats have been well documented due to the outsized influence of diatoms on coastal ecosystem functioning. In contrast, patterns of both diatom diversity and community composition in offshore oligotrophic regions where diatom biomass is low have been poorly resolved. To compare the diatom diversity and community composition in oligotrophic and eutrophic waters, diatom communities were sampled along a 1,250 km transect from the oligotrophic Sargasso Sea to the coastal waters of the northeast US shelf. Diatom community composition was determined by amplifying and sequencing the 18S rDNA V4 region. Of the 301 amplicon sequence variants (ASVs) identified along the transect, the majority (70%) were sampled exclusively from oligotrophic waters of the Gulf Stream and Sargasso Sea and included the genera Bacteriastrum, Haslea, Hemiaulus, Pseudo-nitzschia, and Nitzschia. Diatom ASV richness did not vary along the transect, indicating that the oligotrophic Sargasso Sea and Gulf Stream are occupied by a diverse diatom community. Although ASV richness was similar between oligotrophic and coastal waters, diatom community composition in these regions differed significantly and was correlated with temperature and phosphate, two environmental variables known to influence diatom metabolism and geographic distribution. In sum, oligotrophic waters of the western North Atlantic harbor diverse diatom assemblages that are distinct from coastal regions, and these open ocean diatoms warrant additional study, as they may play critical roles in oligotrophic ecosystems.     

Multiple simultaneous detection of Harmful Algal Blooms (HABs) through a high throughput bead array technology,with potential use in phytoplankton community analysis

As an alternative to traditional, morphology-based methods, molecular techniques can provide detection of multiple species within the HAB community and, more widely, the phytoplankton community in a rapid, accurate and simultaneous qualitative analysis. These methods require detailed knowledge of the molecular diversity within taxa in order to design efficient specific primers and specific probes able to avoid cross-reaction with non-target sequences. Isolates from Florida coastal communities were sequence-analyzed and compared with the GenBank database. Almost 44% of the genotypes obtained did not match any sequence in GenBank, showing the existence of a large and still unexplored biodiversity among taxa. Based on these results and on the GenBank database, we designed 14 species-specific probes and 4 sets of specific primers. Multiple simultaneous detection was achieved with a bead array method based on the use of a flow cytometer and color-coded microspheres, which are conjugated to the developed probes. Following a parallel double PCR amplification, which employed universal primers in a singleplex reaction and a set of species-specific primers in multiplex, detection was performed in a cost effective and highly specific analysis. This multi-format assay, which required less than 4 h to complete from sample collection, can be expanded according to need. Up to 100 different species can be identified simultaneously in a single sample, which allows for additional use of this method in community analyses extended to all phytoplankton species. Our initial field trials, which were based on the 14 species-specific probes, showed the co-existence and dominance of two or more species of Karenia during toxic blooms in Florida waters.     

Seasonal variations in PCR-DGGE fingerprinted viruses infecting phytoplankton in large and deep peri-alpine lakes

Double-stranded DNA viruses infecting eukaryotic algae (e.g., phycodnaviruses) and cyanobacteria (e.g., cyanophages) are now recognized as widespread and ubiquitous in aquatic environments. However, both the diversity and functional roles of these viruses in fresh waters are still poorly understood. We conducted a year-long study in 2011 of the community structure of planktonic virus groups in the upper lit layer of two important freshwater natural ecosystems in France, Lake Annecy (oligotrophic) and Lake Bourget (oligo-mesotrophic). Using PCR-DGGE to target a number of different structural and functional signature genes, i.e.,g20, g23, psbA, polB, and mcp, the phytoplankton viruses were shown to display temporal and spatial variability. There were marked seasonal changes in community structure for all viral groups in Lake Bourget, but only for T4-like myoviruses and psbA-containing cyanophages in Lake Annecy. The multivariate statistical analyses revealed that (1) various environmental factors can directly or indirectly explain the community structure observed for each phytoplankton viral group, and (2) temporal patterns of T4-like myovirus community structure were similar between the two lakes. In general, our results (1) suggest that the observed algal virus patterns were associated with significant shifts in phytoplankton biomass and/or structure, which in turn were shaped by the abiotic environment, and (2) support the Bank model proposed by Breitbart and Rohwer (Trends Microbiol 13:278–284, 2005). This study provides new evidence that freshwater lakes contain a significant diversity of algal viruses, and that the distribution of these viruses strongly mirrors that of their hosts.     

Temporal and Spatial Diversity of Bacterial Communities in Coastal Waters of the South China Sea

Bacteria are recognized as important drivers of biogeochemical processes in all aquatic ecosystems. Temporal and geographical patterns in ocean bacterial communities have been observed in many studies, but the temporal and spatial patterns in the bacterial communities from the South China Sea remained unexplored. To determine the spatiotemporal patterns, we generated 16S rRNA datasets for 15 samples collected from the five regularly distributed sites of the South China Sea in three seasons (spring, summer, winter). A total of 491 representative sequences were analyzed by MOTHUR, yielding 282 operational taxonomic units (OTUs) grouped at 97% stringency. Significant temporal variations of bacterial diversity were observed. Richness and diversity indices indicated that summer samples were the most diverse. The main bacterial group in spring and summer samples was Alphaproteobacteria, followed by Cyanobacteria and Gammaproteobacteria, whereas Cyanobacteria dominated the winter samples. Spatial patterns in the samples were observed that samples collected from the coastal (D151, D221) waters and offshore (D157, D1512, D224) waters clustered separately, the coastal samples harbored more diverse bacterial communities. However, the temporal pattern of the coastal site D151 was contrary to that of the coastal site D221. The LIBSHUFF statistics revealed noticeable differences among the spring, summer and winter libraries collected at five sites. The UPGMA tree showed there were temporal and spatial heterogeneity of bacterial community composition in coastal waters of the South China Sea. The water salinity (P=0.001) contributed significantly to the bacteria-environment relationship. Our results revealed that bacterial community structures were influenced by environmental factors and community-level changes in 16S-based diversity were better explained by spatial patterns than by temporal patterns.     

A seasonal study of the distribution of surface state variables in Liverpool Bay. IV. The spring bloom

Physical, chemical, and phytoplankton distributions observed in Liverpool Bay during early and terminal stages in development of the spring bloom in May, 1977, are described. Qualitative and quantitative changes in phytoplankton distributions are interpreted with respect to the contemporaneous chemical and physical hydrography and quantified changes in the hydrography between the periods of observation. In early May, a physical discontinuity demarcated the biological, physical, and most of the chemical characteristics of the offshore and coastal waters. Phytoplankton numbers were greatest in the inshore waters and decreased seaward. The diatom bloom was concentrated in coastal areas where the nutrient status of the waters was least favourable to sustain it. The waters bounded by the front and the coast were composed of a number of physically and chemically distinct water types and each had associated with it a qualitatively distinct phytoplankton population. During the early stage of the spring bloom no abnormal concentrations or accumulations of phytoplankton were associated with the front. By late May areas of diverse phytoplankton density had developed in the inshore waters, major differences in qualitative composition were associated with various density fields and the physical discontinuity, separating offshore and coastal waters, had developed into the site of greatest phytoplankton density. The spatial and temporal changes in the phytoplankton populations are shown to be related to the nutrient status of the waters both within and at the boundaries of the various density fields.     

RELATING PHYTOPLANKTON BIOMASS AND PRODUCTION TO EPISODIC PHYSICAL FORCING IN SOUTHEASTERN LAKE MICHIGAN

Spatial and temporal dynamics in phytoplankton reflect of the combined effects of the physical and chemical environments and associated biological responses. Although alterations in phytoplankton are well-documented for a variety of lentic waters, the exact linkages between environmental forcing and phytoplankton assemblages remain poorly understood (particularly for coastal systems). A recurrent sediment resuspension event occurs every late winter/early spring in southeastern Lake Michigan, often extending greater than ten km in width and 300 km in length. Inherently, such a large-scale and dramatic physical process would be thought to dramatically influence phytoplankton assemblages; however, linkages between the turbidity plume and phytoplankton assemblages have been postulated, but never verified. As such, the episodic nature of the plume provided an opportunity to examine the effects of a short-term physical forcing event on coastal phytoplankton in relation to more persistent, seasonal meteorological forcing. Lake phytoplankton assemblages within and outside of the RCP were examined during the spring isothermal period from 1998 to 2000. Here, we describe results from the 1998 and 1999 field seasons characterizing the distribution of phytoplankton biomass and composition within and adjacent to the RCP and their relationship to particulate and dissolved constituents. In addition, the spatial and temporal patterns in production and photosynthetic characteristics of the phytoplankton community are examined.     

九龙江河口浮游植物的时空变动及主要影响因素

于2009年春（5月）、夏（8月）、秋（11月）在九龙江河口水域进行了水文、化学和生物的生态完全示范区综合外业调查,研究了九龙江河口浮游植物的种类组成、密度分布、季节变化、空间差异及主要影响因素,并结合前期资料分析了年际变动。结果表明,九龙江河口的浮游植物共记录7个门类75属134种。主体是硅藻,绿藻次之,甲藻和蓝藻较少,黄藻检出率高,裸藻和金藻零星检出。种类组成的空间差异大,绿藻在河口内区淡水水域比硅藻更占优势, 中肋骨条藻（Skeletonema costatum）、短角弯角藻（Eucampia zodiacus）、圆筛藻（Coscinodiscus spp.）、颗粒直链藻（Melosira granulata）、微小小环藻（Cyclotella. caspia）是河口区咸淡水水域及近海区的主要种类。浮球藻（Planktosphneria gelotinosa）、栅藻（Scenedesmus spp.）、盘星藻（Pediastrim spp.）、小席藻（Phormidium tenus）是河口内区淡水水域的主要种类。根据浮游植物的生态类型及其生境特征大致可分为三大类群。浮游植物密度夏季最高,平均为358.68103cells/L,密集中心的季节变化明显,密度分布由优势类群的密度分布决定。中肋骨条藻和短角弯角藻的数量庞大,导致优势种突出,多样性降低,种间分布不均匀,群落结构简单化。与史料比对,种类组成因淡水藻类的列入而更丰富,密度年际降低,中肋骨条藻仍是第一优势种,但优势度有较大降幅,优势类群有重大年际变化,细胞个体较小的种类占优。盐度和营养盐对浮游植物的分布及密度变化造成极大的时空差异,存在线性、复合线性、多项回归等复杂的相关关系。     

An approach to analyzing environmental drivers to shape spatial variations in body-size structure of biofilm-dwelling protozoa during an annual cycle in marine ecosystems

As an inherent trait, body-size structure has been used to summarize functional features of a community instead of taxonomic resolutions due to the high redundancy for bioassessment. In this study, the multivariate approaches were used to determine the environmental drivers to the spatial variation in body-size structure based on an annual dataset of biofilm-dwelling protozoa. Samples were monthly collected at four stations within a gradient of pollution in coastal waters of the Yellow Sea, northern China during a 1-year cycle. The second-stage (2STAGE) clustering and ordination analyses demonstrated that the annual patterns were significantly different among four sampling stations. Mantel analysis showed the spatial variations in body-size structures of the protozoa were significantly correlated with the water quality status along the pollution gradient. Best matching analysis revealed that the potential environmental drivers to shape the spatial difference in body-size structure may be pH, chemical oxygen demand (COD) and nutrients (e.g., soluble phosphates, ammonia and nitrates). It is suggested that the multivariate approaches used may determine the environmental drivers to shape the spatial variations in body-size structure of biofilm-dwelling protozoa in marine ecosystems.     

Complex seasonal patterns of primary producers at the land-sea interface

Seasonal fluctuations of plant biomass and photosynthesis are key features of the Earth system because they drive variability of atmospheric CO₂, water and nutrient cycling, and food supply to consumers. There is no inventory of phytoplankton seasonal cycles in nearshore coastal ecosystems where forcings from ocean, land and atmosphere intersect. We compiled time series of phytoplankton biomass (chlorophyll a) from 114 estuaries, lagoons, inland seas, bays and shallow coastal waters around the world, and searched for seasonal patterns as common timing and amplitude of monthly variability. The data revealed a broad continuum of seasonal patterns, with large variability across and within ecosystems. This contrasts with annual cycles of terrestrial and oceanic primary producers for which seasonal fluctuations are recurrent and synchronous over large geographic regions. This finding bears on two fundamental ecological questions: (1) how do estuarine and coastal consumers adapt to an irregular and unpredictable food supply, and (2) how can we extract signals of climate change from phytoplankton observations in coastal ecosystems where local‐scale processes can mask responses to changing climate?     

Invertebrate communities in dry-season pools of a large subtropical river: patterns and processes

In order to develop an optical model to map the extent of coastal waters, the authors analyzed variations in bio-optical constituents and submarine optical properties along a transect from the nutrient-enriched coastal bay, Himmerfjärden, out into the open Baltic Sea. The model is a simple implementation of the “ecosystem approach,” because the optical constituents are proxies for important components of ecosystem state. Yellow substance or colored dissolved organic matter (CDOM) is often a marker for terrestrial freshwater or decay processes in the littoral zone. Phytoplankton pigments, especially chlorophyll a, are used as a proxy for phytoplankton biomass that may be stimulated by fluvial or coastal inputs of anthropogenic nutrients. Suspended particulate matter (SPM) is placed in suspension by tidal or wind-wave stirring of shallow seabeds, and is therefore an indicator for physical forcing. It is the thesis of this article that such constituents, and the optical properties that they control, can be used to provide an ecological definition of the extent of the coastal zone. The spatial distribution of the observations was analyzed using a steady-state model that assumes diffusional transport of bio-optical variables along an axis perpendicular to the coast. According to the model, the resulting distribution along this axis can be described as a low-order polynomial (of order 1–3) when moving from a “source” associated with land to the open-sea “sink.” Order 1 implies conservative mixing, and the higher orders imply significant biological or chemical processes within the gradient. The analysis of the transect data confirmed that the trend of each optical component could be described well using a low-order polynomial. Multiple regression analysis was then used to weigh the contribution of each optical component to the spectral attenuation coefficient K _d(490) along the transect. The results showed that in this Swedish Baltic case study, the inorganic fraction of the SPM may be used to distinguish between coastal and open-sea waters, as it showed a clear break between coastal and open-sea waters. Alternative models may be needed for coastal waters in which fronts interrupt the continuity of mixing.     

广东省典型水库浮游植物群落特征与富营养化研究

研究了广东省19座主要水库2000年丰水期和枯水期浮游植物状况,并根据浮游植物群落结构和多样性指数对水库进行营养状况评价。结果表明,东江流域的新丰江和白盘珠水库水质良好,属于贫营养型水库;大部分水库为中营养型,而鹤地、契爷石和石岩这3座位于沿海经济发达地区水库属于富营养型。流域上游水库水质明显优于下游水库,山区水库水质优于沿海水库,东江流域水库水质普遍较好。北江流域次之,而粤西沿海和珠江三角洲地区各水库均受到不同程度的污染。     

Distribution and genetic diversity of the parasitic dinoflagellate Amoebophrya in coastal waters of China

Amoebophrya is an obligate endoparasite infecting wide ranges of marine organisms in coastal and oceanic waters. The parasitoid has received growing attention, due to its enormous genetic diversity in seawaters and suppressive effects on the growth of host dinoflagellates. Harmful algal blooms (HABs) caused by planktonic dinoflagellates have significantly impacted the coastal environment and mariculture in China. Series of studies have been conducted to reveal the occurrence mechanism and negative impacts of HABs in past decades, while the factors contributing to the recession of HABs have rarely been studied. Thus, the host range, prevalence and diversity of Amoebophrya along the coastline of China were systemically investigated to facilitate future studies on the ecological roles of the parasitoid. Overall, 10 dinoflagellate taxa were found to be infected by Amoebophrya spp., and the prevalence ranged from 0.03% to 2.50%. Sequencing of environmental genomic DNA revealed substantial diversity and significant regional heterogeneity of Amoebophryidae sequences derived from 12 coastal bays, while no significant correlation was observed among geographical locations. Phylogenetic analyses of 18S rDNA sequences derived from individual Amoebophrya-infected cells indicated the host divergence of the parasitoid and lend credence to the multiple species assumption. The results further revealed the broad host range, wide distribution and substantial diversity of Amoebophrya in the coastal waters of China, that should not be neglected in future studies on the succession of HABs, as well as the ecological significance of this parasitoid in marine microbial food webs.     

The response of phytoplankton community to anthropogenic pressure gradient in the coastal waters of the eastern Adriatic Sea

In order to test the response of phytoplankton to anthropogenic pressure, data of chlorophyll a concentration, phytoplankton abundance, and composition are analyzed in relation to anthropogenic pressure gradient and environmental variables such as temperature, salinity and nutrients. Investigated sites encompassed wide tropic range according to a preliminary determination of anthropogenic pressure, quantified through the LUSI index. Statistical analyses indicated nitrates and silicates as proxies of freshwater influence, and phytoplankton single metrics such as concentrations of chlorophyll a and abundances as indicators of anthropogenic pressure. Boundary values for different water quality classes for coastal waters under indirect freshwater influence (Type II) are obtained according to gradient between concentration of chlorophyll a and pressure index (LUSI), which empirically fit to exponential equation. The response of phytoplankton diversity was not linear, as the highest diversity was observed in the area with intermediate disturbance level. CCA analysis identified Skeletonema marinoii, Scrippsiella trochoidea, Guinardia flaccida, Leptocylindrus spp., Prorocentrum spp., Proboscia alata, Eutreptiella spp., and Pseudonitzschia spp. as local eutrophication indicators, whose abundances increased with nutrients loads.     

Geochemical factors impacting nitrifying communities in sandy sediments

Sandy sediment beaches covering 70% of non-ice-covered coastlines are important ecosystems for nutrient cycling along the land-ocean continuum. Subterranean estuaries (STEs), where groundwater and seawater meet, are hotspots for biogeochemical cycling within sandy beaches. The STE microbial community facilitates biogeochemical reactions, determining the fate of nutrients, including nitrogen (N), supplied by groundwater. Nitrification influences the fate of N, oxidising reduced dissolved inorganic nitrogen (DIN), making it available for N removal. We used metabarcoding of 16S rRNA genes and quantitative PCR (qPCR) of ammonia monooxygenase (amoA) genes to characterise spatial and temporal variation in STE microbial community structure and nitrifying organisms. We examined nitrifier diversity, distribution and abundance to determine how geochemical measurements influenced their distribution in STEs. Sediment microbial communities varied with depth (p-value = 0.001) and followed geochemical gradients in dissolved oxygen (DO), salinity, pH, dissolved inorganic carbon and DIN. Genetic potential for nitrification in the STE was evidenced by qPCR quantification of amoA genes. Ammonia oxidiser abundance was best explained by DIN, DO and pH. Our results suggest that geochemical gradients are tightly linked to STE community composition and nitrifier abundance, which are important to determine the fate and transport of groundwater-derived nutrients to coastal waters.