Coscinodiscus Centralis Research Articles

The effect of the tidal cycle on the phytoplankton community assemblage in a mangrove-dominated tropical tidal creek.

A comparative assessment of phytoplankton dynamics during low tide (LT) and high tide (HT) was conducted from February 2022 to January 2023 in a tropical mesotidal creek, Manori, Mumbai, India. In total, 124 phytoplankton species were recorded. The HT resulted in greater species richness (124 species) and diversity indices (Shannon-Wiener's index) than the LT (102 species). The Pielou's evenness (J') and Simpson's dominance index (1-D) did not show significant fluctuations with the tides due to the marine phytoplankton species moving rhythmically in and out of the creek with the tides. Overall, the seasonal abundance was maximum during pre-monsoon at HT (5.79 × 103 u/L) and lowest in monsoon at LT (0.45 × 103 u/L), whereas spatial abundance was maximum at S1 (HT- 4.04 × 103 u/L) at HT and lowest at S3 (LT- 0.75 × 103 u/L) at LT. The diatoms dominated in their abundance (1.83 × 103 u/L and 3.82 × 103 u/L in HT) and diversity (77 in LT and 92 in HT). The species such as Coscinodiscus centralis, Coscinodiscus granii, Coscinodiscus radiatus, Triops furca, Melosira varians, Nitzchsia palea, Chaetoceros affinis, Skeletonema marinoi, Stephanocyclus meneghinianus, Planktoniella sol and Skeletonema costatumwere the dominant native residents in the creek. SIMPER analysis revealed that the maximum similarity was during the monsoon (47.65%), and the minimum was during the pre-monsoon (38.10%) at LT. However, in HT, the maximum similarity of phytoplankton shifted to post-monsoon (63.85%) and the minimum during the pre-monsoon (46.71%). The mean value of richness (d') and Shannon's diversity (H') showed a moderate phytoplankton diversity in the system. The environmental parameters (water temperature > pH > nitrate > salinity > DO > Alk > silicate) have a greater influence on the distribution of the phytoplankton community with tides as revealed by the Canonical correspondence analysis. Therefore, it has been found that tides play a significant role in the distribution and abundance of the phytoplankton community in a mesotidal creek environment.

Ion fluxes Involved in the Adaptation of the Estuarine Diatom Coscinodiscus centralis Ehrenberg to Salinity Stress.

Although estuarine diatoms have a wide range of salt tolerance, they are often severely stressed by elevated salt concentrations. It remains poorly understood how estuarine diatoms maintain ionic homeostasis under high-salinity conditions. Using a scanning ion-selective electrode technique, this study determined the fluxes of H+, Na+, and K+ involved in the acclimatization of the estuarine diatom Coscinodiscus centralis Ehrenberg after an elevation in salinity from 15 psu to 35 psu. The C. centralis cells exhibited marked H+ effluxes after a transient treatment (TT, 30 min) and short-term treatment (ST, 24 h). However, a drastic shift of H+ efflux toward an influx was induced in the long-term treatment (LT, 10 days). The Na+ flux under TT, ST, and LT salinity conditions was found to accelerate the Na+ efflux. More pronounced effects were observed under the ST and LT salinity conditions compared to the TT salinity condition. The K+ influx showed a significant increase under the LT salinity condition. However, the salinity-induced Na+/H+ exchange in the estuarine diatom was inhibited by amiloride and sodium orthovanadate. These results indicate that the Na+ extrusion in salt-stressed cells is mainly the result of an active Na+/H+ antiport across the plasma membrane. The pattern of ion fluxes under the TT and ST salinity conditions were different from those under the LT salinity conditions, suggesting an incomplete regulation of the acclimation process in the estuarine diatom under short-term salinity stress.

Spatial and temporal variability of phytoplankton dynamics in-relation to essential oceanographic variables in the south east coast of Bangladesh

Phytoplankton form the base of food chain and play a key role in maintaining the global climate system. However, very limited knowledge is available about the phytoplankton ecology of Bangladesh coast which is a representation of sub-tropical coastal ecosystem. Thus, this study aimed to understand the spatial and temporal variability of phytoplankton community in-relation to environmental variables in the South East coast of Bangladesh. Monthly data on essential oceanographic variables (i.e. temperature, salinity, dissolved oxygen, turbidity, silicate, nitrate and phosphate) and phytoplankton species abundance were collected from January 2022 to December 2022. We found a strong spatial and temporal variability in essential oceanographic variables and phytoplankton community compositions in Naf – Saint Martin Peninsula of Bangladesh. Estuarine ecosystem is characterized by high nutrients and low salinity while offshore ecosystem was found with comparatively low nutrients and high salinity. About 154 phytoplankton species were identified from the study area through year round sampling events. In the estuarine ecosystem Skeletonema marino, Coscinodiscus centralis, Coscinodiscus argus and Coscinodiscus traducens were found as the major contributing species at the estuarine ecosystem while Chaetoceros radican, Tripos trichoceros, Cylindrotheca Closterium, Chaetoceros convulutus, Tripos muelleri, and Cyclotella striata were found as the major contributing species at the offshore ecosystem. Our study found that 6 explanatory variables (i.e. temperature, salinity, turbidity, silicate, nitrate and phosphate) jointly explained about 78% variability in phytoplankton community dynamics. Nitrate concentration explained maximum variability (19%) followed by phosphate (17%), salinity (15%), silicate (12%), turbidity (10%) and surface temperature (5%). This study will play a key role in understanding the spatial and temporal variability of phytoplankton dynamics in the sub-tropical coastal ecosystem.

Spatio-temporal variations of phytoplankton assemblage in coastal waters of Maharashtra, north-eastern Arabian Sea

Seasonal variations in phytoplankton species and abundance along the coast of Maharashtra from two different locations (Mumbai and Ratnagiri) and depths were investigated during August 2014-May 2017. A total of 84 species of phytoplankton were recorded from the region out of which 67 were diatoms, 16 dinoflagellates and one blue green alga. Seventy-five and 60 species of phytoplankton were recorded from Ratnagiri and Mumbai respectively. Diatoms dominated the phytoplankton community (81.7-93.3%) followed by dinoflagellates (4.7-7.2%) and blue green algae in both locations. Maximum phytoplankton density was recorded during post-monsoon season followed by pre-monsoon and monsoon seasons at Mumbai and Ratnagiri. Highest average phytoplankton cell density recorded was 9.09 x 104 cells l-1 and 4.06 x 104 cells l-1 during post-monsoon season at Ratnagiri and Mumbai respectively. Maximum cell density was observed at 20 m depth from Mumbai and Ratnagiri. Thalassiosira subtilis, Trieres mobiliensis, Skeletonema costatum, Coscinodiscus centralis and Ditylum brightwelli were the most abundant phytoplankton species recorded at Mumbai, whereas Chaetoceros curvisetus, S. costatum, Trichodesmium erythraeum, Chaetoceros lorenzianus and Ditylum brightwelli were abundant in Ratnagiri waters. The blue green alga, T. erythraeum was abundantly recorded during pre-monsoon season. Species diversity index (H’) ranged from 4.72 to 5.52 and was higher during post-monsoon season compared to pre-monsoon and monsoon. Highest phytoplankton diversity was observed at 20 m depth compared to 40 m depth.Keywords: Arabian Sea, Diversity, Mumbai, Phytoplankton, Ratnagiri

Effects of micro-features of fossil diatom on the macroscopic behaviour of soils

Diatomaceous soils frequently occur in lacustrine and marine deposits. They are usually thought of as one type of material with unusual geotechnical properties characterised by high Atterberg limits, natural water content, compressibility as well as high shear strength. The combination of high liquid limits and high friction angles appears to be a contradiction in the framework of classical soil mechanics, but studies showing relations between their unusual geotechnical properties and micromechanical features of fossil diatoms may provide the key to solving this puzzle. This study considers two diatom species, Aulacoseira granulata and Coscinodiscus centralis. The study identifies the effects of their microscopic features on the macroscopic behaviour of soils. The study involves first, tests of Atterberg limits, and then oedometric and triaxial tests on samples with different proportions of the two species. Results show that the microscopic shapes of the diatoms have observable effects on the macroscopic responses of soils.

Community composition and diversity of phytoplankton in relation to environmental variables and seasonality in a tropical mangrove estuary

This paper presents the aspects of phytoplankton communities along a tropical mangrove estuary in Sarawak, Malaysia. Data were collected monthly from the study area from January 2013 to December 2013 and was pooled into seasons to examine the influence of seasonality. The estuary revealed relatively species-rich, and a total of 102 species under 43 genera were recorded comprising 6 species of Cyanophyceae; 4 species of Chlorophyceae; 62 species of Bacillariophyceae and 30 species of Dinophyceae. The species composition, as well as the mean abundance (cellsL-1) of phytoplankton, were found in order of Bacillariophyceae>Dinophyceae> Cyanophyceae> Chlorophyceae. Mean abundance of phytoplankton ranged from 5694 to 88890 cellsL−1 over the study period with its higher value in the dry season. Species recorded from the estuary were dominated by Pleurosigma normanii, Coscinodiscus sp, Coscinodiscus centralis, Coscinodiscus granii, Dinophysis caudata, Ceratium carriense, Ceratium fusus, and Ceratium lineatum. Abundance of phytoplankton demonstrated positive correlation with chlorophyll a (r=0.69), ammonium (r=0.64) and silica (r=0.64). Significant differences (ANOSIM and nMDS) were observed in the species community structure between intermediate and the wet season. Canonical correspondence analysis (CCA) showed that most of the species assemblages were positively correlated with surface water temperature, salinity, pH, ammonium and nitrate in the intermediate and dry season towards larger species composition in the respective seasons whereas silica showed influence on the species assemblage in the wet season. The findings suggest that the Sibuti mangrove estuary is productive in terms of diversified phytoplanktons and their variability in assemblage, those are influenced by the hydrological and biological factors.

Struktur Komunitas Plankton sebagai Indikator Kualitas Perairan Budidaya di Tambak Lorok Semarang

Plankton is organisms that had an important role in water as natural feed of fishes and as an indicator. This study aimed to identify water quality which was suitable for fish cultivation reviewed from physics-chemicals parameters of water and its saprobic status in Tambak Lorok Tanjung Mas Kota Semarang. Sampling were take based on 5 stations that could represented from plankton variety of condition water stability . Plankton samples were by using net plankton number 25, then preserved with alcohol 70% and formalin 4%. Variables of ponds water quality measured were temperature, salinity, dissolved oxygen, pH, turbidity, N concentration, and Pb content. Identification of planktons used SRC method under microscop. The result of plankton analysis in Tambak Lorok water showed 42 phytoplankton species, the commonly species found are Coscinodiscus centralis, Coscinodiscus granii, Gyrosigma sp., Navicula radiosa, Pandorina sp., and Melosira sp. Meanwhile, zooplankton found was 22 species with common species are Cyclops, Harpaticoida, Tricodesmium evythraeum, Brachinus plicatilis, and Lensia subtilis. Phytoplankton diversity index are 0.057-0.367 and equity index are 0.025-0.176. Zooplankton diversity index are 0.247-0.360 and equity index are 0.157-0.201. This indices showed that there were low level of species diversity and community stability, dominance since the species occurred. Measurement of water quality variables indicated that Tambak Lorok had been contaminated and needed a preliminary management before d be used as fish cultivation ponds, because the analysis result was not appropriate with Government water quality regulation. Based on the measurement, soprobic index categories on α/β-Mesosaprobic to Oligosaprobic phase and the degree of pollution is very mild to moderate. Keywords : Community Structure, plankton, Tambak Lorok, Tanjung Mas, Semarang

Toxicity assessment of cobalt and selenium on marine diatoms and copepods

Abstract Cobalt and selenium are emerging concerns for marine organisms due to their raising levels in ambient environment and toxicity. Bioassay tests were conducted on marine plankton for evaluation and assessment of cobalt and selenium toxicity. Considering the ecological importance, diatoms such as Odontella mobiliensis, Coscinodiscus centralis, Skeletonema costatum and copepod Longipedia weberi, mysid shrimp were selected for the toxicity evaluation. The 96-h IC50 of 1.08 ± 0.04 mg/l for the diatom O. mobiliensis and 3.52 ± 0.02 mg/l for C. centralis, 4.0 ± 0.42 mg/l, and 3.56 ± 0.22 mg/l were derived as 96-h LC50 for the copepod L. weberi and mysid shrimp respectively, for Cobalt. The selenium concentrations of 9.30 ± 1.01 mg/l and 20.34 ± 1.05 mg/l were derived as a 96-h IC50 value on the diatoms O.mobiliensis and Skeletonema costatum respectively while 96-h LC50 values were derived as 0.97 ± 0.08 mg/l for copepod L.weberi and 1.13 ± 0.15 mg/l for mysid shrimp. The chronic toxicity values of Co were found in the range of 0.22–0.57 mg/l for Co and 0.12–1.72 mg/l for Se on plankton. The cobalt was found to be more toxic to the diatoms than selenium whereas copepods were more sensitive to selenium than the cobalt. The level of toxicity is varied due to the difference in the mode of toxicity and sensitivity among the species. The safe limits were derived by species sensitivity distribution (SSD) based on the chronic values of Co and Se. The ambient concentration of 22 μg/l for Se and 18 μg/l for Co are the safe level for the protection of plankton in the coastal waters.

Environmental variables, algal pigments and phytoplankton in the Atlantic Ocean off the coast of Badagry, Lagos

The phytoplankton diversity, environmental variables and algal pigments of the Atlantic Ocean off the coast of Badagry, Lagos were investigated for twelve months between May 2015 and April 2016. The water chemistry characteristics reflected sea water conditions. At the two stations, the range of values recorded for some physico-chemical variables were rainfall (4.1 - 449.3mm), air temperature (23 - 30°C), water temperature (25-31°C), salinity (26.6 - 31.81‰), pH (7.9 - 8.12) and total dissolved solids (26980.1–32900.1mg/L), The phytoplankton diversity consisted of 44 species belonging to three main algal groups namely: 30 species of diatoms (Bacillariophyta) making up 80.49%, five species of blue-green algae (Cyanophyta) making up 13.57% and nine species of dinoflagellate (Dinophyta) accounting for the remaining 5.94%.. Notable species were Coscinodiscus centralis, Coscinodiscus radiatus, Thalassionema nitzschioides and Thalassionema longissima (Diatoms) and a blue-green algae Trichodesmium thiebautii. Nitrate was the key limiting nutrient with regards to algal pigment concentration. The values for the correlation of chlorophyll a (r=0.590, p <0.05), chlorophyll b (r=0.496, p<0.01) and phaeophytin a (r=0.286) with nitrate were significantly positively correlated. Hence, Nitrate is the trigger nutrient for increased algal pigments concentration in the study area.Keywords: Sea, Lagoon, neritic, diatoms, physico-chemical, phytochemicals

Toxicity of Nickel on the Selected Species of Marine Diatoms and Copepods.

Toxicity values for nickel on marine diatoms and copepods were derived based on bioassay tests. The 96h IC50 of nickel on diatoms, Odontella mobiliensis and Coscinodiscus centralis were 0.31 ± 0.01 and 0.62 ± 0.02mg/L and LC50 valueson copepods, Oithona similis and Acartia danae were 2.78 ± 0.14 and 2.34 ± 0.32mg/L, respectively. The species mean chronic values of nickel were 0.016, 0.17, 0.57 and 0.42mg/L for O. mobiliensis, C. centralis, O. similis and A. danae, respectively. A hazardous concentration was derived and evaluated using the species sensitivity distribution (SSD) method. SSD indicated that 13µg Ni/L is the maximum allowable concentration for protection of 95% plankton species in coastal and marine ecosystem of India. Diatoms are more sensitive to nickel than copepods by almost an order of magnitude. The toxicity values derived in the present study may be useful to calculate ambient water quality criteria/standard for nickel.

Identification of Odontella aurita by rbcL gene sequence – a high antibacterial potential centric marine diatom

The antibacterial potential of centric marine diatoms has been compared against the clinical pathogens and identified the potential diatom by rbcL gene sequencing. Totally, five diatoms namely Odontella aurita, Thalassiosira subtilis, Chaetoceros curvisetus, Skeletonema costatum and Coscinodiscus centralis were isolated from Cuddalore coastal waters. The diatoms were morphologically identified and isolated using micro capillary-pipette and serial dilution method. The isolated diatoms were cultured in Guillard’s f/2 medium to get biomass for the antibacterial study. The dried biomass of the cultured diatoms was individually extracted with methanol, ethanol and hexane. All the obtained extracts were tested against Staphylococcus haemolyticus, Proteus vulgarius and Vibrio alginolyticus. The crude ethanol extract of O. aurita was exhibited highest zone of inhibition against all the test pathogens. The MIC of O. aurita was recorded as 50 μg/ml against both Staphylococcus haemolyticus and Proteus vulgarius whilst 75 μg/ml against Vibrio alginolyticus. This study indicates that O. aurita possesses antibacterial activities but the release of antibiotics depends on physical or chemical rupture of algal cells and extractive solvents. Based on the maximum antibacterial activity, O. aurita was further identified by rbcL gene sequencing. The rbcL gene could be an identical region for the species level identification of diatoms.

Wavelength and orientation dependent capture of light by diatom frustule nanostructures.

The ecological success of diatoms is emphasized by regular blooms of many different species in all aquatic systems, but the reason behind their success is not fully understood. A special feature of the diatom cell is the frustule, a nano-patterned cell encasement made of amorphous biosilica. The optical properties of a cleaned single valve (one half of a frustule) from the diatom Coscinodiscus centralis were studied using confocal micro-spectroscopy. A photonic crystal function in the frustule was observed, and analysis of the hyperspectral mapping revealed an enhancement of transmitted light around 636 and 663 nm. These wavelengths match the absorption maxima of chlorophyll a and c, respectively. Additionally, we demonstrate that a highly efficient light trapping mechanism occurred, resulting from strong asymmetry between the cribrum and foramen pseudo-periodic structures. This effect may prevent transmitted light from being backscattered and in turn enhance the light absorption. Based on our results, we hypothesize that the multi-scaled layered structure of the frustule improves photosynthetic efficiency by these three mechanisms. The optical properties of the frustule described here may contribute to the ecological success of diatoms in both lentic and marine ecosystems, and should be studies further in vivo.

Large, omega-3 rich, pelagic diatoms under Arctic sea ice: sources and implications for food webs.

Pelagic primary production in Arctic seas has traditionally been viewed as biologically insignificant until after the ice breakup. There is growing evidence however, that under-ice blooms of pelagic phytoplankton may be a recurrent occurrence. During the springs of 2011 and 2012, we found substantial numbers (201–5713 cells m−3) of the large centric diatom (diameter >250 µm) Coscinodiscus centralis under the sea ice in the Canadian Arctic Archipelago near Resolute Bay, Nunavut. The highest numbers of these pelagic diatoms were observed in Barrow Strait. Spatial patterns of fatty acid profiles and stable isotopes indicated two source populations for C. centralis: a western origin with low light conditions and high nutrients, and a northern origin with lower nutrient levels and higher irradiances. Fatty acid analysis revealed that pelagic diatoms had significantly higher levels of polyunsaturated fatty acids (mean ± SD: 50.3±8.9%) compared to ice-associated producers (30.6±10.3%) in our study area. In particular, C. centralis had significantly greater proportions of the long chain omega-3 fatty acid, eicosapentaenoic acid (EPA), than ice algae (24.4±5.1% versus 13.7±5.1%, respectively). Thus, C. centralis represented a significantly higher quality food source for local herbivores than ice algae, although feeding experiments did not show clear evidence of copepod grazing on C. centralis. Our results suggest that C. centralis are able to initiate growth under pack ice in this area and provide further evidence that biological productivity in ice-covered seas may be substantially higher than previously recognized.

Silicate as the Probable Causative Agent for the Periodic Blooms in the Coastal Waters of South Andaman Sea

Periodic algal blooms of three diatom species such as Coscinodiscus centralis, Rhizosolenia alata andRhizosolenia imbricata were observedduringSeptember 2011, December 2011 and March 2012 in the coastal waters of South Andaman Sea at Junglighat bay area (11° 39 N and 92° 43 E). The blooms were intense, with Coscinodiscus at aconcentration of 89,000 cells mL-1(contributing 85 to 98% to the total phytoplanktonpopulation), Rhizosolenia alataat a concentration of 13,000 cellsmL-1(86-93%) and Rhizosolenia imbricata at aconcentration of 19,000 cells. mL-1(91-99%). Nutrients, most importantly nitrate and silicate have emerged as the key factors controlling phytoplankton growth in this area.

In vitro Antioxidant Activity of Marine Diatoms

The in vitro total antioxidant assay, total phenolic content, DPPH assay, FRAP assay of the acetone extracts from four centric diatoms (Chaetoceros simplex, Skeletonema costatum, Odontella mobiliensis, Coscinodiscus centralis) and three pennate diatoms (Nitzschia closterium, Pleurosigma angulatum and Navicula sp.) were performed. The centric diatom, O. mobiliensis was found higher amount of phenolic content (0.75 ± 0.06) followed by C. simplex. The maximum total antioxidant activity of 45.03 ± 2.1 ascorbic acid equivalent/g was observed in P. angulatum followed by the centric diatom C. simplex. The O. mobiliensis was showed significantly higher DPPH radical scavenging activity of 70.04 ± 4.17 % followed by C. simplex (55.69 ± 2.52 %) and P. angulatum (49.57 ± 2.74 %). The phenolic compounds of acetone extracts were not major contributor to the antioxidant capacities of these diatoms. The pigments such as, chlorophylls and carotenoids may be the main contributor of antioxidant activity in this study. The total antioxidant activity may be increased when extracted other solvent. Thus, these species can be act as natural antioxidant source for food preservation and protection of organisms from the degenerative diseases.

Diversity of Phytoplankton in Different Stations from Muthupettai, South East Coast of India

The distributions of phytoplankton and its community structure in relation to physico-chemical parameters in aquaculture discharge waters and adjacent waters of Muthupettai lagoon were studied. Physico-chemical parameters and nutrients concentration were fluctuated depends on the seasonal chances, whereas the total of 101 phytoplankton species were recorded, Among them, 76 species of diatoms (Bacillariophyceae), 17 species of dinoflagellates (Dinophyceae), 5 species of blue greens (Cyanophyceae), 2 species of green algae (Chlorophyceae) and 1 species of silicoflagellates (Chrysophyceae) were recorded, where, Nitzschia seriata, Coscinodiscus centralis, Thalassiothrix frauenfeldii, and Ceratium furca were the most abundant in phytoplankton community. The percentage composition were recorded as Diatom>Dinoflagellates>Blue greens>Greens>Silicoflagellate respectively. The study revealed that there are no effects due to the aquaculture discharge waters for the mangrove ecosystem. This study also revealed seasonal environmental variables and phytoplankton distributions in Muthupettai lagoon.

Influence of environmental variables on phytoplankton floristic pattern along the shallow coasts of southwest Bay of Bengal

Multivariate statistical methods are used to study the spatial and temporal variations of physico-chemical parameters and phytoplankton floristics of the southwest coast of Bay of Bengal. Over 94 species of phytoplankton represented by 77 species of diatoms, 11 species of dinoflagellates and 6 species of blue-green algae were recorded. Higher phytoplankon species diversity was found in premonsoon when salinity and nitrate concentrations were low and reactive silicate and inorganic phosphates were moderate, while species diversity was low during summer with when increased sea surface temperature, salinity and low nutrients availability. During summer season Coscinodiscus centralis, Diatoma vulgare and Rhizosolenia alata were dominant, especially Coscinodiscus sp. distributed in all stations whereas Skeletonema costatum, Biddulphia sinensis and Ditylum brightwelli were abundant in the premonsoon season. From principal component analysis and multiple regression analysis, it is evident that variables like sea surface temperature and light extinction coefficient are the most important factors influencing the seasonal pattern of phytoplankton population, although nutrients like nitrate, inorganic phosphate and silicate have also important contributors in deriving phytoplankton population density of this part of the Bay of Bengal.

Phytoplankton dynamics in a highly eutrophic estuary in tropical Brazil

The port of Recife in northeastern Brazil is an important ecological and social area but little is known about its environmental quality. Observations, sampling and measurements of phytoplankton were performed during spring and neap tides in the dry (January-February, 2005) and rainy (June, 2005) seasons to assess the environmental quality of the port of Recife. The area had chlorophyll-a concentrations ranging from 3.30 to 54.40 mg m-3, the highest values occurring at low tide during the dry season. A total of 129 species were identified: 53 of them in the dry season and 97 in the rainy season. Diatoms were the most diverse group and comprised 75.47% of the phytoplankton collected in the dry season and 60.82% of those collected in the rainy season. The dry season was characterized by Coscinodiscus sp. and Helicotheca tamesis; the rainy season by Oscillatoria sp. and Coscinodiscus centralis. Species diversity indices varied from 1.06 to 3.74 bits cel-1. Low indices were related to the dominance of Helicotheca tamesis, Coscinodiscus centralis, Coscinodiscus sp. and Aulacoseira granulata. Seasonal forcing, rather than the estuarine flux, determined the phytoplankton community structure. The area is exposed to seasonally varying negative impacts due to metropolitan degradation and the high level of eutrophication.

Seasonal effects of wastewater to the water quality of the Caeté river estuary, Brazilian Amazon

Bragança's socioeconomic situation is highly dependent on estuarine and marine biological resources that are influenced by tidal cycles and climatology. Field measurements (hydrological, hydrodynamic and microbiological variables) were taken in the most urbanized zone from Caeté estuary to characterise the quality of the local environment. During the dry period, the estuary was more eutrophic and presented the highest temperature (30.5 degrees C in Oct./06), salinity (17 psu in Feb./07), pH (8.24 in Feb./07) and fecal coliform (> 1000 MPN/100 ml in Dec./06 and Feb./07) values. The phytoplankton Cyclotella meneghiniana, Coscinodiscus centralis and other r-strategist species were observed. The lack of basic hydric canalization was responsible for the local contamination, especially during the dry period when more concentrated wastewater from the city was emitted into the estuary, showing the human influence on the reduction of local estuarine water quality. In Bragança, the fishery is considered one of the main economic activities so, this contamination is worrisome because a large part of the local economy depends on biological resources and, thus, the contamination could negatively affect the environmental health of this Amazon ecosystem.

Estrutura sazonal e espacial do microfitoplâncton no estuário tropical do rio Formoso, PE, Brasil

Este trabalho teve como objetivo determinar as variações espaço-temporal do microfitoplâncton e variáveis ambientais no estuário do rio Formoso, litoral sul do estado de Pernambuco. As coletas ocorreram em três pontos, no período chuvoso (maio a julho/2002) e estiagem (outubro a dezembro/2002). As amostras do plâncton foram obtidas através de arrastos horizontais superficiais, com rede de abertura de malha de 64¼m. Foram registrados in situ dados sobre temperatura e transparência e, concomitantemente, coletadas amostras de água utilizando a garrafa tipo Kitahara para a análise de salinidade, pH, oxigênio dissolvido, sais nutrientes e biomassa. Foram identificados 204 táxons predominando o grupo das diatomáceas (75%), destacando-se como dominantes Chaetoceros costatus Pavillard, Chaetoceros curvisetus Cleve, Chaetoceros sp., Coscinodiscus centralis Ehrenberg, seguidas dos dinoflagelados (10,79%), cianofíceas (6,37%), clorofíceas (3,92%), euglenofíceas (3,43%) e silicoflagelados (0,49%). As concentrações de oxigênio demonstraram uma alta capacidade de renovação do ambiente devido ao aporte de águas marinhas; maiores concentrações de nutrientes e biomassa algácea ocorreram durante o período chuvoso e nas baixa-mares. A pluviometria e o aporte marinho foram os parâmetros que mais influenciaram na hidrologia e na distribuição da comunidade fitoplanctônica com reflexo na riqueza taxonômica.