On the use of the FluoroProbe®, a phytoplankton quantification method based on fluorescence excitation spectra for large-scale surveys of lakes and reservoirs

Although microscope analysis is very useful for studying phytoplankton community composition, it does not allow for high frequency (spatial and/or temporal) data acquisition. In an attempt to overcome this issue, fluorescence-based approaches that use selective excitation of pigment antennae have spread rapidly. However, the ability of spectral fluorescence to provide accurate estimates of phytoplankton biomass and composition is still debated, and only a few datasets have been tested to date.In this study, we sampled of a wide range of water bodies (n = 50) in the Ile-de-France region (North Central France). We used the resulting extensive dataset to assess the ability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton community composition in lakes and reservoirs.We demonstrated that FP data yields better estimates of total phytoplankton biovolume than do spectrophotometric chlorophyll a measures and that FP data can be further corrected using the average chlorophyll a to biovolume ratio among phytoplankton groups. Overall, group-specific relationships between FP and biovolume data were consistent. However, we identified a number of cases where caution is required. We found that Euglenophytes are expected to depart from the global FP vs. biovolume relationship of the ‘green’ group due to varying Fv/Fm and pigment content in response to environmental conditions (photoautotrophic vs. photoheterotrophic growth). Then, it appears necessary to consider the composition of the Chromophytes community in order to obtain a good agreement between both biomass estimation methods. Finally, we confirmed the misattribution toward the ‘red’ group of phycoerythrin-containing cyanobacteria and the occurrence of a strong scattering in the relationship between the FP vs. biovolume of the ‘blue’ group that can be partly attributed to the occurrence of large colony-forming cyanobacteria (e.g., Microcystis spp, Aphanizomenon flos-aquae).We propose correcting procedures to improve the quality of data obtained from spectral fluorescence tools in the context of large-scale sampling of lakes and reservoirs.     

Seasonal and spatial distribution of chlorophyll-a concentrations and water conditions in the Gulf of Tonkin, South China Sea

The Gulf of Tonkin is a semi-closed gulf northwest of the South China Sea, experiencing reversal seasonal monsoon. Previous studies of water conditions have been conducted in the western waters of the gulf, but very few studies of the Chlorophyll-a (Chl-a) distribution have been carried out for the entire gulf. The present study investigates seasonal and spatial distributions of Chl-a and water conditions in the Gulf of Tonkin by analyzing Sea-viewing Wide Field-of-View Scanner (SeaWiFS) derived Chlorophyll-a (Chl-a), in situ measurements, sea surface temperatures (SST), and other oceanographic data obtained in 1999 and 2000. The results show seasonality of Chl-a and SST variations in the Gulf of Tonkin, and reveal phytoplankton blooming events in the center part of the gulf during the northeast monsoon season. In summer, Chl-a concentrations were relatively low (<0.3 mg m⁻³) and distributed uniformly throughout most of the area, with a belt of higher Chl-a concentrations along the coast, particularly the coast of Qiongzhou Peninsula; in winter, Chl-a concentration increased (0.5 mg m⁻³) in the entire gulf, and phytoplankton blooms offshore-ward from the northeast coast to the center of the gulf, while Chl-a concentrations reached high levels (0.8-1 mg m⁻³) in the center of the blooms. One peak of Chl-a concentrations was observed during the northeast monsoon season in the year. SST were high (27-29 °C) and distributed uniformly in summer, but lower with a large gradient from northeast (17 °C) to southwest (25 °C) in winter, while strong northeast winds (8-10 m/s) were parallel to the east coast of the gulf. Comparison of Chl-a values shows that SeaWiFS derived Chl-a concentrations match well with in situ measurements in most parts of the gulf in May 1999, but SeaWiFS derived Chl-a are higher than in situ data in river mouth waters. The seasonal variation of Chl-a concentrations and SST distribution were associated with the seasonally reversing monsoon; the winter phytoplankton blooms were related to vertical mixing and upwelling nutrients drawn by the northeast wind.     

Phytoplankton biomass distribution and identification of productive habitats within the Galapagos Marine Reserve by MODIS, a surface acquisition system, and in-situ measurements

The Galapagos Marine Reserve (GMR) is one of the most diverse ecosystems in the world. Phytoplankton are the base of the ecosystem food chain for many higher trophic organisms, so identifying phytoplankton biomass distribution is the first step in understanding the dynamic environment for effective management of the GMR. Moderate Resolution Imaging Spectroradiometer (MODIS) and hyperspectral surface acquisition system derived chlorophyll, in-situ chlorophyll fluorescence, nitrate, salinity, and temperature were collected from March 2005 to the onset of a mild El Niño in November 2006. Islands in the eastern GMR, such as San Cristobal and Espanola, are the first to experience impacts of El Niño and southern migration of the Equatorial Front. Productive habitats were defined as surface waters with salinities > 34, temperatures < 24 °C, and chlorophyll a > 0.4 mg m^− 3. Six temporally variable productive habitats identified were: west of Isabela Island, southwest of Floreana Island, south of Santa Cruz, between Santiago and Santa Cruz Islands, and on the eastern side near San Cristobal Island. Model results coupled with surface acquisition system derived chlorophyll indicated productive habitats may also occur for short periods and at a distance from islands such as when the Equatorial Undercurrent (EUC) and South Equatorial Current (SEC) collide over the seamounts north of Isabela Island. All productive habitats were related to topographic upwelling from the EUC into surface waters.     

Influence of nitrogen/phosphorus ratios on the productivity of Nile river phytoplankton

Mixtures of different concentrations of both nitrogen and phosphorus were used at various N/P ratios to investigate the maximum growth of Nile River Phytoplankton using bioassay studies. A ratio 4:1 N/P gave a high algal mass production and high content of chl(a) of phytoplankton. A high diversity value 1.48 was obtained during the experimental run. Bacillanophyta was the dominant group followed by chlorophyta and cyanophyta in all treatments. The growth rate reached its maximum value (1.69) after 16 days of incubation. Positive correlation was established between phytoplankton and orthophosphate, nitrate, organic nitrogen and dissolved oxygen of the Nile River water.     

Phytoplankton community succession shaping bacterioplankton community composition in Lake Taihu, China

PCR-denaturing gradient gel electrophoresis (DGGE) and canonical correspondence analysis (CCA) were used to explore the relationship between succession of phytoplankton community and temporal variation of bacterioplankton community composition (BCC) in the eutrophic Lake Taihu. Serious Microcystis bloom was observed in July-December 2008 and Bacillariophyta and Cryptophyta dominated in January-June 2009. BCC was characterized by DGGE of 16S rRNA gene with subsequent sequencing. The DGGE banding patterns revealed a remarkable seasonality which was closely related to phytoplankton community succession. Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. CCA revealed that temperature and phytoplankton played key roles in structuring BCC. Sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in freshwater: Alphaproteobacteria, Betaproteobacteria, Bacteroidetes and Actinobacteria. The cluster STA2-30 (affiliated with Actinobacteria) was found almost across the sampling time at the two study sites. We observed that the family Flavobacteriaceae (affiliated with Bacteroidetes) tightly coupled to diatom bloom and the cluster ML-5-51.2 (affiliated with Actinobacteria) dominated the bacterioplankton communities during Microcystis bloom. These results were quite similar at the two sampling sites, indicating that BCC changes were not random but with fixed pattern. Our study showed insights into relationships between phytoplankton and bacterioplankton communities at species level, facilitating a better understanding of microbial loop and ecosystem functioning in the lake.     

三峡小江回水区藻类集群与主要环境要素的典范对应分析研究

三峡成库后支流回水区水华频繁发生,备受关切。基于2年的野外跟踪观测结果,利用典范对应（CCA）分析方法,建立了藻类生境要素同藻类集群演替的多元统计模型。研究发现,所建立的CCA模型有效且具有较高的显著性;水库季节性调蓄所形成的不同藻类生境条件是诱导集群出现演替的关键。在低水位运行下,藻类生境近似于天然河道,总悬浮颗粒物和流量变化对集群影响明显,水体扰动剧烈迫使耐受于不稳定水动力条件的藻种易于形成优势;而在高水位运行状态下,藻类生境接近深水湖泊,适宜于低温和具有运动功能的藻类将耐受于该生境状态并在集群中占优。     

Cluster analysis of hyperspectral optical data for discriminating phytoplankton pigment assemblages in the open ocean

Optical measurements including remote sensing provide a potential tool for the identification of dominant phytoplankton groups and for monitoring spatial and temporal changes in biodiversity in the upper ocean. We examine the application of an unsupervised hierarchical cluster analysis to phytoplankton pigment data and spectra of the absorption coefficient and remote-sensing reflectance with the aim of discriminating different phytoplankton assemblages in open ocean environments under non-bloom conditions. This technique is applied to an optical and phytoplankton pigment data set collected at several stations within the eastern Atlantic Ocean, where the surface total chlorophyll-a concentration (TChla) ranged from 0.11 to 0.62 mg m^− 3. Stations were selected on the basis of significant differences in the ratios of the two most dominant accessory pigments relative to TChla, as derived from High Performance Liquid Chromatography (HPLC) analysis. The performance of cluster analysis applied to absorption and remote-sensing spectra is evaluated by comparisons with the cluster partitioning of the corresponding HPLC pigment data, in which the pigment-based clusters serve as a reference for identifying different phytoplankton assemblages. Two indices, cophenetic and Rand, are utilized in these comparisons to quantify the degree of similarity between pigment-based and optical-based clusters. The use of spectral derivative analysis for the optical data was also evaluated, and sensitivity tests were conducted to determine the influence of parameters used in these calculations (spectral range, smoothing filter size, and band separation). The results of our analyses indicate that the second derivative calculated from hyperspectral (1 nm resolution) data of the phytoplankton absorption coefficient, a_ph(λ), and remote-sensing reflectance, R_rs(λ), provide better discrimination of phytoplankton pigment assemblages than traditional multispectral band-ratios or ordinary (non-differentiated) hyperspectral data of absorption and remote-sensing reflectance. The most useful spectral region for this discrimination extends generally from wavelengths of about 425-435 nm to wavelengths within the 495-540 nm range, although in the case of phytoplankton absorption data a broader spectral region can also provide satisfactory results.     

Biomarkers of algal populations in phytoplankton,filamentous algae,and sediments from the eastern basin of Lake Erie 2003–2005

Algal carotenoids (n:16) and chlorophylls (n:7) were determined in phytoplankton (n:60), filamentous algae (n:14) and sediments (n:44), collected from two nearshore sites in eastern Lake Erie (Van Buren Point (VBP), 6.5 m; Point Gratiot (PG), 17 m), during summer and fall of 2003, 2004 and 2005. The most prominent biomarkers for diatoms (fucoxanthin), cryptophytes (alloxanthin), chlorophytes (chlorophyll-b) and cyanobacteria (zeaxanthin) revealed temporal variations in phytoplankton community composition, which were correlated to water temperatures: i) seasonal succession, from diatoms with some cryptophytes in June (cool), to an increased percentage of chlorophytes and cyanobacteria in August and September (warm); ii) differences between 2004 (cool; cryptophytes more abundant) and 2005 (warm; chlorophytes more abundant). Filamentous algae (chlorophytes, epiphytic diatoms; some cyanobacteria) varied in condition, according to levels of chl-a, pheopigments, and class biomarkers: high, at VBP (growing; decaying; bont/E suspect); low, at PG (mostly dead). Relative to phytoplankton, sediments were depleted in several biomarkers (chl-a; diadino-, neo- and violaxanthin) but enriched with others, particularly at PG (pheopigments; diatoxanthin; canthaxanthin, echinenone; alloxanthin). Sediment composition was characterized by strong differences between sites (chl-a, chl-b and fucoxanthin nearly 10-fold greater at VBP than PG) and increasing accumulation of biomarkers from year-to-year. A linear log–log function, relating total carotenoids to total chlorophylls (intercept −0.516, slope 1.054, r² 0.96), implied increased biodegradation among specimen types: levels of pigments (pmol/g ww) decreased three orders of magnitude, from phytoplankton, through filamentous algae, to sediments. Deviation from a 1:1 relationship indicated 1.7-fold depletion of carotenoids relative to chlorophylls at mid-range.     

Application of a 3D hydrodynamic-biological model for seasonal and spatial dynamics of water quality and phytoplankton in Lake Erie

In large lakes, temporal variability is compounded by strong spatial variability associated with mesoscale physical processes such as upwelling and basin-scale circulation. Here we explore the ability of a three dimensional model (ELCOM-CAEDYM) to capture temporal and spatial variability of phytoplankton and nutrients in Lake Erie. We emphasized the east basin of the lake, where an invasion by dreissenid mussels has given special importance to the question of spatial (particularly nearshore-offshore) variability and many comparative observations were available. We found that the model, which did not include any simulation of the mussels or of smaller diffuse nutrient sources, could capture the major features of the temperature, nutrient and phytoplankton variations. Within basin variability was large compared to among-basin variability, especially but not exclusively in the western regions. Consistent with observations in years prior to, but not after, the mussel invasion the model predicted generally higher phytoplankton concentrations in the nearshore than the offshore zones. The results suggest that the elevated phytoplankton abundance commonly observed in the nearshore of large lakes in the absence of dreissenid mussels does not have to depend on localized nutrient inputs but can be explained by the favourable light, temperature and nutrient environment in the shallower and energetic nearshore zone. The model is currently being extended to allow simulation of the effects of dreissenid mussels.