Phosphorus,Nitrogen and Chlorophyll-a Are Significant Factors Controlling Ciliate Communities in Summer in the Northern Beibu Gulf,South China Sea

Ciliates (protozoa) are ubiquitous components of plankton community and play important roles in aquatic ecosystems in regards of their abundance, biomass, diversity and energy turnover. Based on the stratified samples collected from the northern Beibu Gulf in August 2011, species composition, abundance, biomass, diversity and spatial pattern of planktonic ciliates were studied. Furthermore the main environmental factors controlling ciliate communities were determined. A total of 101 species belonging to 44 genera and 7 orders (i.e., Oligotrichida, Haptorida, Euplotida, Sessilida, Pleurostomatida, Scuticociliatida and Tintinnida) were identified. The variation of ciliate communities was significant at horizontal level, but that was not at vertical level. Based on cluster analysis, ciliate communities were divided into three main groups. Redundancy analysis (RDA) revealed that Group A, existing in the waters with higher concentration of phosphorus and nitrogen, was dominated by Tintinnidium primitivum. Group B in the waters with lower temperature and chlorophyll-a concentration, was dominated by Leegaardiella ovalis. Group C, existing in the waters with higher temperature and chlorophyll-a concentration, was dominated by large Strombidium spp. and Mesodinium rubrum. Combining multiple analytic methods, our results strongly supported that phosphorus, nitrogen and chlorophyll-a were the most significant factors affecting the ciliate communities in the northern Beibu Gulf in summer. Concentration of phosphorus and nitrogen primarily influenced ciliate biomass, implying a potential impact of eutrophication on ciliate growth. The correlation with chlorophyll-a concentration, on one hand indicate the response of ciliates to the food availability, and on the other hand, the ciliates containing chloroplasts or endosymbionts may contribute greatly to the chlorophyll-a.     

Impacts of environmental scenarios on chlorophyll-a in the management of shallow, eutrophic lakes following biomanipulation: An application of a numerical model

Accurate prediction of species changes in lake ecosystems following biomanipulation measures is of paramount importance in view of water quality management. The temporal variation of phytoplankton biomass as chlorophyll-a and transparency as Secchi depth measurements are studied in the Lake Bleiswijkse Zoom, The Netherlands, with a comprehensive structural dynamic model. In the formulation of the biological model, phytoplankton as several species, zooplankton, detritus, planktivores and benthivores, and piscivores are considered to be major contributing state variables for the model. The primary goal of this paper is to describe the possible impacts of several environmental scenarios on chlorophyll-a biomass qualitatively as it would help lake and environmental managers and relevant authorities elucidate the processes of eutrophication and biomanipulation in a broad way. Some of the scenarios that have been studied by this model are: (1) The effect of fixed stoichiometry in terms of internal nitrogen and phosphorus that are tied up within algal cells; (2) the effects of external phosphorus limitation; (3) light limitation and external nitrogen limitation on algal growth; (4) probable consequences that have taken place within the chlorophyll-a biomass due to change in biomasses of various aquatic organisms; and (5) possible changes of chlorophyll-a biomass due to higher temperatures caused by global warming.     

Effects of planktivore abundance on chlorophyll-a and Secchi depth

We used two analyses to test the hypothesis that planktivore abundances contribute to the residual variations of Secchi depth or chlorophyll-a plotted with respect to mean summer epilimnetic total phosphorus. The first analysis involved 15 lake years of data from six lakes. The data set comprised mark-recapture assessments of piscivore and planktivore numbers and estimates of mean summer chlorophyll-a, total phosphorus and Secchi depth. We found that residual chlorophyll-a variation was not significantly (p>0.05) correlated with planktivore densities, but that planktivore densities did contribute (p<0.02) to the residual variation of Secchi depth on mean total phosphorus. The second analysis included all of the data used in the first plus an additional 13 lake years of data from the literature. These data showed that the percentage of the total fish community comprising planktivores did not significantly (p>0.05) contribute to the residual variation in chlorophyll-a with respect to mean summer total phosphorus. Together, our results suggest that planktivore abundance has a significant cascading impact on water clarity, but no long term statistically significant impact on mean summer chlorophyll-a concentration.     

Phytoplankton biomass and chlorophyll-a in some shallow lakes in central Europe

Based on 388 parallel data of phytoplankton biomass and chlorophyll-a of two shallow lakes and two ponds, the following results were obtained:

1. Relative chlorophyll-a content of phytoplankton biomass varied between 0.08–1.88%; chlorophyll-a concentration showed great differences among lakes.
2. Significant correlations (r = 0.68–0.92) were established between phytoplankton biomass and chlorophyll-a concentration. The regression in the artificial ponds was non-linear.
3. In parallel with the increase of average cell volume, a decrease in relative chlorophyll-a content was observed. A significant correlation (r = + 0.83) between the two variables was found. Relative chlorophyll-a content of phytoplankton is a log-function of average cell volume.

     

Comparison of water level and eutrophication indicators during the wet and dry period in a eutrophic urban lake

Eutrophication modifies lakes' ecological balances and threatens its viability. To date, eutrophication management strategies have been related to nutrient reduction in the lakes' water column. However, nutrient reduction strategies are complicated by the variations of the lake's water level, nutrient concentration, and eutrophication symptom, which are primarily known to be influenced by the local rainfall patterns. Therefore, this study aimed to compare the variability of water level, total phosphorus, and total chlorophyll-a concentrations in Slim River Lake during wet and dry seasons. In this study, water sampling and depth measurements were carried out from six sampling points for 1 year. Water samples were used to quantify total phosphorus and total chlorophyll-a. Our results showed that mean water levels in the studied lake ranged from 1.36 m to 5.46 m in the wet season and from 1.31 m to 5.41 m in the dry season, which implicated no significant difference (p > .05) between seasons in most sampling points. Total phosphorus present at concentrations exceeding 10 mg/L and showed small variations between wet and dry seasons. Mean total phosphorus concentrations varied from 10.55 mg/L to 26.66 mg/L in the wet season and 10.77 mg/L to 21.76 mg/L in the dry season and showed no significant difference between seasons. In addition, mean chlorophyll-a concentrations ranged from 14.35 mg/m³ to 180.13 mg/m³ and from 14.15 mg/m³ to 39.27 mg/m³ in wet and dry seasons, respectively. Chlorophyll-a concentrations showed significant differences (p < .05) between seasons in the deepest sampling points in the lake. The observed seasonal variations in total chlorophyll-a suggest the importance of algae monitoring during the wet season even when no apparent surge of phosphorus concentration is detected.     

Zooplankton biomass in tropical reservoirs in southern Brazil

In order to test the hypothesis that zooplankton biomass distribution (total and taxonomic groups) was influenced by the nutrient concentration and primary productivity distribution in three tropical reservoirs, subsurface samples were taken in the fluvial, transitional and lacustrine regions of three reservoirs (oligotrophic, mesotrophic and eutrophic) in southern Brazil (Paraná State) in March and September 2002. Zooplankton biomass ranged from 0.04 to 264.47 mg DW m⁻³. Higher biomass values were observed for cladocerans (73.60%; 0.01–259.86 mg DW m⁻³), followed by copepods (22.05%; 0.01–69.69 mg DW m⁻³) and rotifers (4.35%; 0.01–11.52 mg DW m⁻³). In general, the total zooplankton, rotifer, cladoceran and copepod biomass, and chlorophyll-a and total nutrient concentrations showed a similar longitudinal distribution within the reservoirs. Total zooplankton, rotifer and cladoceran biomass were related to the chlorophyll-a concentration, and zooplankton biomass was related to the total phosphorus distribution. This may have been due to the significant multicolinearity between the chlorophyll-a and total phosphorus concentrations. Cyanobacteria influenced the taxonomic group biomass results by interfering with the filter feeding in larger zooplankton species, which favoured the dominance of smaller species. As regards the longitudinal distribution of copepod biomass, cyanobacteria biomass determined the displacement of the microcrustaceans to the fluvial region of Iraí Reservoir. Our results supported the hypothesis formulated and the primary productivity was the major predictor of the zooplankton biomass distribution in the reservoirs. Handling editor: S. Dodson     

River–reservoir transition zones are nitrogen fixation hot spots regardless of ecosystem trophic state

Reservoir hydrodynamics may create heterogeneity in nitrogen (N) fixation along the riverine–transition–lacustrine gradient. In particular, N fixation may be highest in reservoir transition zones where phytoplankton biomass is also expected to be relatively high. We investigated spatial patterns of N fixation in three Texas (USA) reservoirs of varying trophic state. We sampled 6–9 stations along the longitudinal axes of the major inflows and measured N fixation using the acetylene reduction method. Total N, total phosphorus (P), and algal biomass (as chlorophyll-a) were also measured at each sample location. Measurable N fixation was observed in all reservoirs and was light-dependent. Nitrogen fixation was consistently low in the riverine zone, highest in the transition zone, and low in lacustrine zone of all reservoirs. The absolute magnitude of N fixation was similar in two relatively unproductive reservoirs and an order of magnitude higher in the eutrophic reservoir. A similar pattern was observed in mean nutrient and chlorophyll-a concentrations among reservoirs. However, chlorophyll-a concentrations were highest in the riverine zone of each reservoir and exhibited a monotonic decrease in the downstream direction. Maximum chlorophyll-a concentrations did not coincide with maximum N fixation rates. Results of our study indicate that reservoir transition zones can be biogeochemical hot spots for planktonic N fixation, regardless of trophic state. Therefore, transition zones may be the most at risk locations for water quality degradation associated with increased reservoir productivity. Water quality managers and aquatic scientists should consider the spatial heterogeneity imposed by unique hydrodynamic controls in reservoir ecosystems. Handling editor: Luigi Naselli-Flores     

Trophic state of a lowland reservoir during 10 years after restoration

The restored Maltañski Reservoir was studied from its filling with water in 1990 till 2000. Total phosphorus, chlorophyll-a, and Secchi depth, as well as the Carlson's trophic state index (TSI) values based on those three parameters showed characteristic patterns of changes among seasons and years. Within each year, the lowest trophic state was usually observed in winter and the highest in summer. Because of the high loads of phosphorus received by the reservoir, this element did not limit primary production. TSI values calculated on the basis of total phosphorus were always markedly higher than calculated on chlorophyll-a and Secchi depth (similar to each other). The trophic upsurge phase lasted only a few months after the filling of the reservoir in 1990. Similar symptoms were observed after its refilling in the spring of 1993. The trophic depression phase lasted until the end of 1995. After that time a significant correlation between phosphorus concentration in the reservoir and in river waters flowing into the reservoir was observed. The successive phases of reservoir ageing, determined on the basis of phosphorus concentration, were not accompanied by changes in chlorophyll-a content. The influence of the top-down mechanism (biomanipulation effect) resulted in relatively low values of chlorophyll-a after the filling of the reservoir with water in 1990 and in 1993. As early as 1992 chlorophyll-a values reached a very high level and stayed at that level until the end of the study in 2000 (except for the short decline in 1993).

     

Interactions between landcover pattern and geospatial processing methods: Effects on landscape metrics and classification accuracy

Remote sensing data is routinely used in ecology to investigate the relationship between landscape pattern as characterised by land use and land cover maps, and ecological processes. Multiple factors related to the representation of geographic phenomenon have been shown to affect characterisation of landscape pattern resulting in spatial uncertainty. This study investigated the effect of the interaction between landscape spatial pattern and geospatial processing methods statistically; unlike most papers which consider the effect of each factor in isolation only. This is important since data used to calculate landscape metrics typically undergo a series of data abstraction processing tasks and are rarely performed in isolation. The geospatial processing methods tested were the aggregation method and the choice of pixel size used to aggregate data. These were compared to two components of landscape pattern, spatial heterogeneity and the proportion of landcover class area. The interactions and their effect on the final landcover map were described using landscape metrics to measure landscape pattern and classification accuracy (response variables). All landscape metrics and classification accuracy were shown to be affected by both landscape pattern and by processing methods. Large variability in the response of those variables and interactions between the explanatory variables were observed. However, even though interactions occurred, this only affected the magnitude of the difference in landscape metric values. Thus, provided that the same processing methods are used, landscapes should retain their ranking when their landscape metrics are compared. For example, highly fragmented landscapes will always have larger values for the landscape metric “number of patches” than less fragmented landscapes. But the magnitude of difference between the landscapes may change and therefore absolute values of landscape metrics may need to be interpreted with caution. The explanatory variables which had the largest effects were spatial heterogeneity and pixel size. These explanatory variables tended to result in large main effects and large interactions. The high variability in the response variables and the interaction of the explanatory variables indicate it would be difficult to make generalisations about the impact of processing on landscape pattern as only two processing methods were tested and it is likely that untested processing methods will potentially result in even greater spatial uncertainty.     

A comparative analysis of the relationship between phytoplankton standing crops and environmental parameters in four eutrophic prairie reservoirs

An analysis was performed with multivariate statistical methods of the relationship between chlorophyll a concentrations and eighteen physico-chemical parameters measured over a six year period in four eutrophic Nebraska reservoirs. In the reservoirs with relatively clear water early in the growing season, physical factors (Secchi depth, turbidity, temperature) and non-nutrient chemical factors (alkalinity, hardness, C. O. D.) were significantly related to chlorophyll a concentrations, but macronutrients (nitrogen and phosphorus) were not. In the reservoir with persistent abiogenic turbidity, chemical factors including nitrogen and phosphorus were significant but physical factors were not. Six models based upon intercorrelations between measured parameters and chlorophyll a are evaluated for their usefulness in accounting for chlorophyll a variance. The best model accounts for 67–70 percent of the total variation in chlorophyll a in the four reservoirs.     

Discovery of predictive rule sets for chlorophyll-a dynamics in the Nakdong River (Korea) by means of the hybrid evolutionary algorithm HEA

This paper presents a hybrid evolutionary algorithm (HEA) to discover complex rule sets predicting the concentration of chlorophyll-a (Chl.a) based on the measured meteorological, hydrological and limnological variables in the hypertrophic Nakdong River. The HEA is designed: (1) to evolve the structure of rule sets by using genetic programming and (2) to optimise the random parameters in the rule sets by means of a genetic algorithm. Time-series of input–output data from 1995 to 1998 without and with time lags up to 7 days were used for training HEA. Independent input–output data for 1994 were used for testing HEA. HEA successfully discovered rule sets for multiple nonlinear relationships between physical, chemical variables and Chl.a, which proved to be predictive for unseen data as well as explanatory. The comparison of results by HEA and previously applied recurrent artificial neural networks to the same data with input–output time lags of 3 days revealed similar good performances of both methods. The sensitivity analysis for the best performing predictive rule set unraveled relationships between seasons, specific input variables and Chl.a which to some degree correspond with known properties of the Nakdong River. The statistics of numerous random runs of the HEA also allowed determining most relevant input variables without a priori knowledge.     

Effects of phytoplankton species composition on absorption spectra and modeled hyperspectral reflectance

Understanding the spectral characteristics of remotely-sensed reflectance by different phytoplankton species can assist in the development of algorithms to identify various algal groups using satellite ocean color remote sensing. One of the main challenges is to separate the effect of species composition on the reflectance spectrum from other factors such as pigment concentration and particle size structure. Measuring the absorption spectra of nine different cultured algae, and estimating the reflectance of the different species, provides a useful approach to study the effects of species composition on the bio-optical properties. The results show that the absorption spectra of different species exhibit different spectral characteristics and that species composition can significantly change the absorption characteristics at four main peaks (438, 536, 600 and 650 nm). A ‘distance angle index’ was used to compare different phytoplankton species. Results indicate that this index can be used to identify species from the absorption spectra, using a database of standard absorption spectra of known species as reference. By taking into account the role of species composition in the phytoplankton absorption model, the performance of the model can be improved by up to 5%. A reflectance-species model is developed to estimate the remotely-sensed reflectance from the absorption spectra, and the reflectance of different phytoplankton species at the same chlorophyll-a concentration is compared, to understand effects of species composition on the reflectance spectra. Different phytoplankton species can cause up to 33% difference in the modeled reflectance at short wavelengths under the condition of the same chlorophyll-a concentration, and variations in the reflectance spectrum correspond to the colors of the algae. The standard deviation of the reflectance among different species shows that the variations from 400 to 450 nm are sensitive to species composition at low chlorophyll-a concentrations, whereas variations in the 510 to 550 nm range are more sensitive under high chlorophyll-a concentrations. For this reason, the green bands may be more suitable for estimating species composition from hyperspectral satellite data during bloom conditions, whereas the blue bands may be more helpful in detection of species under low chlorophyll-a concentrations. In this theoretical approach, variations in reflectance at the same chlorophyll-a concentration can be used to identify phytoplankton species. Another approach to identify phytoplankton species from remotely-sensed hyperspectral reflectance measurements would be to derive the absorption spectra of phytoplankton from the reflectance measurements, and compare these with a standard database of absorption spectra.     

Lutein-chlorophyll-a energy transfer in detergent micelles

Absorption, fluorescence and fluorescence excitation spectra were determined for equimolar mixed micellar detergent solutions of lutein and chlorophyll-a in the concentration range from 9·10^?6 to 1.8·10^?4 M, with detergent (triton-X100) concentrations from 3·-10^?4 to 7·10^?3 M. In the range of detergent concentrations studied the pigments incorporated into the detergent micelles attained a high local concentration (0.1 to 0.01 M), reminiscent of pigment concentration within the chloroplast. A lutein → chlorophyll-a energy transfer with an efficiency of about 15% was found in these systems. In dilute (9·10^?6 M) pigment solution with concentrated (7·10^?3 M) detergent practically no transfer is observed. The extent of aggregation and the efficiency of transfer depend on the composition of the system. The aggregation of chlorophyll-a is partly inhibited by lutein molecules. It is shown that the energy transfer efficiency as function of distance follows anr ^?3 relationship,R ₀ being 22 å.     

Limnological and ecological characteristics of tropical highland reservoirs in Tigray, Northern Ethiopia

The semi-arid highlands of Northern Ethiopia (Tigray) have numerous small reservoirs that have been created by microdams in an attempt to provide water supply for irrigation and livestock drinking. Although the reservoirs have substantial added value to residents, their use as water resource is jeopardized by eutrophication and a high occurrence of blooms of toxic cyanobacteria. So far, there is no systematic information available on the limnological and aquatic ecological characteristics of these dams. We carried out a standardized survey of 32 reservoirs and assessed a wide set of morphometric, abiotic and biotic variables. The sampling was performed during two seasons, September–October 2004 (end of the wet season/start of the dry season) and April–May 2005 (towards the end of the dry season). Using multivariate analysis, we revealed dominating patterns of variable associations and compared the variability in these patterns among seasons. According to standardized PCA and RDA analyses, the most important axis of variation was mainly represented by a gradient in nutrients and altitude that was also positively associated with phytoplankton biomass, suspended matter and oxygen concentration, and negatively with water transparency. For most variables, correlations between the wet and dry season were weak, which suggests that individual reservoirs behaved rather differently in their response to seasonal changes. Nevertheless, a Mantel correlation (r = 0.32; P = 0.035) showed a weak but significant overall concordance in the variable association patterns among seasons. A number of reservoirs became very shallow or fell dry in the dry season, a process that was associated with an increase in suspended matter and conductivity and a decrease in transparency. These reservoirs contained lower amounts of fish and tended to be less eutrophic than the deeper, permanent systems, as they had lower levels of phosphorus and chlorophyll-a. With multiple regression analysis, we constructed most parsimonious models in an attempt to explain the variation in key biotic variables: phytoplankton and cyanobacteria biomass, cladoceran biomass, fish biomass and the abundance of submerged vegetation. Phytoplankton and fish biomass tended to be positively related with the concentration of total phosphorus, whereas cladoceran biomass was not associated with nutrient concentrations. The positive association of fish and phytoplankton with nutrient concentrations suggests a bottom-up control, whereas the absence of an association between zooplankton and nutrient concentrations may be indicative for top-down control. The biomass of cyanobacteria was negatively related to the biomass of cladocerans (Daphnia), which likely reflects a top-down effect. Most reservoirs were turbid. The occurrence and abundance of macrophytes tended to be positively related to water transparency and was negatively associated to TP and the amount of livestock frequenting the reservoirs. However, macrophytes were not limited to clear-water reservoirs. Handling editor: L. M. Bini     

Seasonal Variation in the Spatial Distribution of Basking Sharks (Cetorhinus maximus) in the Lower Bay of Fundy,Canada

The local distribution of basking sharks in the Bay of Fundy (BoF) is unknown despite frequent occurrences in the area from May to November. Defining this species’ spatial habitat use is critical for accurately assessing its Special Concern conservation status in Atlantic Canada. We developed maximum entropy distribution models for the lower BoF and the northeast Gulf of Maine (GoM) to describe spatiotemporal variation in habitat use of basking sharks. Under the Maxent framework, we assessed model responses and distribution shifts in relation to known migratory behavior and local prey dynamics. We used 10 years (2002-2011) of basking shark surface sightings from July-October acquired during boat-based surveys in relation to chlorophyll-a concentration, sea surface temperature, bathymetric features, and distance to seafloor contours to assess habitat suitability. Maximum entropy estimations were selected based on AICc criterion and used to predict habitat utilizing three model-fitting routines as well as converted to binary suitable/non-suitable habitat using the maximum sensitivity and specificity threshold. All models predicted habitat better than random (AUC values >0.796). From July-September, a majority of habitat was in the BoF, in waters >100 m deep, and in the Grand Manan Basin. In October, a majority of the habitat shifted southward into the GoM and to areas >200 m deep. Model responses suggest that suitable habitat from July - October is dependent on a mix of distance to the 0, 100, 150, and 200 m contours but in some models on sea surface temperature (July) and chlorophyll-a (August and September). Our results reveal temporally dynamic habitat use of basking sharks within the BoF and GoM. The relative importance of predictor variables suggests that prey dynamics constrained the species distribution in the BoF. Also, suitable habitat shifted minimally from July-September providing opportunities to conserve the species during peak abundance in the region.     

Productivity gradient affects the temporal dynamics of testate amoebae in a neotropical floodplain

Testate amoeba communities are influenced by temporal variation in the productivity levels in the environment, and may be used as an indicator group for these changing conditions. Here, we analysed the effect of temporal variation in the levels of productivity variables on testate amoeba community of the upper Paraná River floodplain. We evaluated the hypothesis that the frequency and abundance of the testate amoeba community change along an environmental gradient, with different taxa establishing at different points along the gradient in response to changes in the levels of productivity variables. We predicted that the number of species would increase and decrease at points associated with higher and lower levels of productivity variables, respectively. Testate amoeba species were sampled quarterly between 2000 and 2012 from six lakes in the upper Paraná River floodplain, Brazil. We recorded 110 species belonging to 11 families. Threshold Indicator Taxa Analysis identified positive and negative significant shift points in response to the concentration of chlorophyll-a, total nitrogen, and total phosphorus on the frequency and abundance of the testate amoeba community. Our results indicated that change intervals in the levels of productivity variables were associated with the establishment of different taxa. The main bioindicator species of productivity were Difflugia acuminata, D. amphoralis, D. helvetica multilobata, D. kempny, D. lobostoma multilobata, D. parva, D. schurmanni, D. ventricosa, and Lesquereusia ovalis. These species were linked to the increase and decrease in the levels of productivity, confirming the ecological importance of the role of these organisms as bioindicators in aquatic ecosystems.     

Zooplankton response to climate warming: a mesocosm experiment at contrasting temperatures and nutrient levels

Zooplankton community response to the combined effects of nutrients and fish (hereafter N + F) at contrasting temperatures was studied in a long-term experiment conducted in 24 shallow lake mesocosms with low and high nutrient levels. We found a positive effect of N + F on zooplankton biomass, chlorophyll-a and turbidity. In contrast, zooplankton species and size diversity decreased with added N + F, as did submerged macrophyte plant volume inhabited (PVI). The community composition of zooplankton in high N + F mesocosms was related to chlorophyll-a and turbidity and to macrophyte PVI in the low N + F mesocosms. Macrophytes can protect zooplankton from fish predation. Compared to N + F effects, temperature appeared to have little effect on the zooplankton community. Yet analysis of community heterogeneity among treatments indicated a significant temperature effect at high N + F levels. The results indicate an indirect temperature effect at high N + F levels that can be attributed to temperature-dependent variation in fish density and/or chlorophyll-a concentration.     

Quantifying Climatological Ranges and Anomalies for Pacific Coral Reef Ecosystems

Coral reef ecosystems are exposed to a range of environmental forcings that vary on daily to decadal time scales and across spatial scales spanning from reefs to archipelagos. Environmental variability is a major determinant of reef ecosystem structure and function, including coral reef extent and growth rates, and the abundance, diversity, and morphology of reef organisms. Proper characterization of environmental forcings on coral reef ecosystems is critical if we are to understand the dynamics and implications of abiotic–biotic interactions on reef ecosystems. This study combines high-resolution bathymetric information with remotely sensed sea surface temperature, chlorophyll-a and irradiance data, and modeled wave data to quantify environmental forcings on coral reefs. We present a methodological approach to develop spatially constrained, island- and atoll-scale metrics that quantify climatological range limits and anomalous environmental forcings across U.S. Pacific coral reef ecosystems. Our results indicate considerable spatial heterogeneity in climatological ranges and anomalies across 41 islands and atolls, with emergent spatial patterns specific to each environmental forcing. For example, wave energy was greatest at northern latitudes and generally decreased with latitude. In contrast, chlorophyll-a was greatest at reef ecosystems proximate to the equator and northern-most locations, showing little synchrony with latitude. In addition, we find that the reef ecosystems with the highest chlorophyll-a concentrations; Jarvis, Howland, Baker, Palmyra and Kingman are each uninhabited and are characterized by high hard coral cover and large numbers of predatory fishes. Finally, we find that scaling environmental data to the spatial footprint of individual islands and atolls is more likely to capture local environmental forcings, as chlorophyll-a concentrations decreased at relatively short distances (>7 km) from 85% of our study locations. These metrics will help identify reef ecosystems most exposed to environmental stress as well as systems that may be more resistant or resilient to future climate change.     

Studies on the primary production of the river Shatt Al-Arab at Basrah,Iraq

The study was conducted on the Shatt Al-Arab River at Basrah, Iraq from September 1976 to August 1977 at three stations located at the upstream, middle and lowest parts of Basrah city. There was a bimodal seasonal variation of chlorophyll-a, the concentration of which ranged between 0.52–3.25 mg/m³. The gross primary production ranged between 6.03–37.02 mgC/m³/hr and showed a unimodal seasonal variation with a maximum in August. From the concentration of chlorophyll-a and from measurement of primary productivity it was clear that the section of the river at the upstream end of Basrah city was poorest and that at the middle of the Basrah city below Ashar Channel was the richest. A positive corelation between primary productivity and chlorophyll-a.     

Development of a Multicolor Line-Focus Microscope for Rapid Acquisitions of Excitation Spectra

To conduct rapid microscope observations with the excitation spectral measurement for photosynthetic organisms, a wavelength-dispersive line-focus microscope was developed. In the developed system, fluorescence signals at multiple positions on a sample excited with different wavelengths can be detected as a two-dimensional image on the EMCCD camera at the same time. Using the developed system, one can obtain excitation spectra at every pixel over the excitation wavelength range from 635 to 695 nm, which covers the full range of the Q_y bands of both chlorophyll-a and chlorophyll-b. Recording the reference laser spectra at the same time ensures robust measurement against the moderate spectral fluctuation in the excitation laser. Using an objective lens with a numerical aperture of 0.9, the lateral and axial resolutions of 0.56 and 1.08 μm, respectively, were achieved. The theoretically limited and experimentally estimated spectral resolutions of the excitation spectral measurement were 0.86 and 1.3 nm, respectively. The validity of the system was demonstrated by measuring fluorescent beads and single cells of a model alga, Chlamydomonas reinhardtii. Intrachloroplast inhomogeneity in the relative intensity of the chlorophyll-b band could be visualized in Chlamydomonas cells. The inhomogeneity reflects the intrachloroplast variation in the local peripheral antenna size.