RESUMEN
The Gulf of Mannar (GoM), located between India and Sri Lanka, has astonishing faunal richness and diversity. Two oceanographic data sets supplemented with satellite remote sensing observations are discussed here to show the unique ecological setting in the GoM sustaining a rich and diverse fauna. We tested the hypothesis that a specific stretch of a large marine environment behaves differently from the rest of the region due to its peculiar geographical position. Primarily, unlike the adjacent Indian southwestern shelf in the Southeastern Arabian Sea, oxygen deficiency associated with coastal upwelling imparting physiological stress to marine fauna does not occur in the GoM. Secondly, the GoM along the Indian coastline receives an adequate amount of primary (plankton) food from the Arabian Sea and the Bay of Bengal through the advected water associated with the seasonally reversing surface currents. Thirdly, the GoM water has high transparency, aerated sandy seafloor conducive for the growth of diverse corals and much sensitive fauna. All these indicate that an astonishingly rich and diverse aquatic fauna in the GoM is a biological manifestation of a conducive geographical setting and propose that similar other environments worldwide, protected from oxygen deficiency, might also be functioning as a refuge for marine life.
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Antozoos , Animales , India , Plancton , Sri LankaRESUMEN
A baseline investigation of the chromatographic characterization of phytoplankton pigments with complementing microscopy was conducted in Mahanadi estuary, Chilika lagoon, and coastal waters off Gopalpur along the east coast of India. Marker pigments specific to different phytoplankton groups have been discerned in these contrasting coastal ecosystems. A total of 16 phytoplankton pigments were identified. Irrespective of seasons, Chilika lagoon was characterized by a high concentration of zeaxanthin, indicating the predominance of picocyanobacteria. Zeaxanthin and fucoxanthin were the major diagnostic pigments in Mahanadi estuary during monsoon and other seasons, respectively. In coastal waters off Gopalpur, algal blooms resulted in a higher concentration of fucoxanthin during pre-monsoon and monsoon season. The pigment ratios were comparatively higher for Chilika lagoon than for Mahanadi estuary and off Gopalpur, irrespective of seasons. The present study highlights the advantages of the chromatography technique in identifying small-sized phytoplankton in coastal ecosystems in comparison to conventional microscopy.
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Ecosistema , Fitoplancton , Bahías , Monitoreo del Ambiente , India , Estaciones del Año , Agua de MarRESUMEN
The long-term distribution of in situ optically active substances (OAS), accuracy assessment of satellite retrieved chlorophyll-a (chl-a) and its long-term trend has been carried out at a coastal site of the north-western Bay of Bengal. The temporal distribution of chl-a, total suspended matter (TSM) and absorption due to coloured dissolved organic matter at 440 nm (aCDOM440) discerned a common peak during southwest monsoon season (August-October). Chl-a also showed a prominent peak during pre-southwest monsoon period (March-April). The spatial variability of TSM and aCDOM440 was maximum during southwest monsoon, whereas in the case of chl-a, it was during pre-southwest monsoon. The accuracy assessment of chl-a retrieved from Moderate Resolution Imaging Spectroradiometer-Aqua (MODISA), Ocean Colour Monitor-2 (OCM-2) and Visible Infrared Imager Radiometer Suite (VIIRS) showed overestimation in nearshore waters. The error in satellite measurement of chl-a was within the range of 33 to 51%. The chl-a retrieved from MODISA was most accurate as indicated by statistical analysis. The long-term trend in satellite chl-a clearly indicated bi-modal distribution with a primary peak during pre-southwest monsoon attributed to recurrent phytoplankton bloom that was mostly confined to nearshore waters. Whereas, the secondary peak in chl-a, during the end of southwest monsoon, spreads far offshore.
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Bahías , Clorofila A/análisis , Monitoreo del Ambiente , Clorofila , Fitoplancton , Estaciones del AñoRESUMEN
The present study is focused on understanding long-term trend in distribution of chlorophyll-a and its association with water quality parameters in coastal waters of northwestern Bay of Bengal. In situ observations were carried out in monthly frequency during January 2009 to March 2017 at two ecologically important study sites, off Gopalpur and off Visakhapatnam. A bimodal distribution of chlorophyll-a was observed off Gopalpur with primary and secondary peak during pre- and post-monsoon, respectively. In contrast, maximum chlorophyll-a concentration was noticed in monsoon irrespective of sporadic higher magnitudes during pre-monsoon in coastal waters off Visakhapatnam. The pivotal role of river influx and coastal upwelling was discerned in enriching coastal waters off Gopalpur with macronutrients and in turn on chlorophyll-a distribution. Adequate availability of silicate signified favorable condition for diatom growth in coastal waters off Gopalpur leading to preponderance. Influence of coastal upwelling and nutrient-controlled growth of phytoplankton was observed in coastal waters off Visakhapatnam.
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Bahías/química , Clorofila A/análisis , Diatomeas/crecimiento & desarrollo , Monitoreo del Ambiente/métodos , Fitoplancton/crecimiento & desarrollo , Agua de Mar/química , Biomasa , Océano Índico , Ríos/química , Estaciones del Año , Calidad del AguaRESUMEN
Seasonal distribution of phytoplankton community and size structure was assessed in three different tropical ecosystems of the western Bay of Bengal viz. estuary (Mahanadi), lagoon (Chilika), and coastal waters (off Gopalpur) in response to ambient hydrobiology. Salinity regimes differentiated the study regions as contrasting ecosystems irrespective of seasons (pre-monsoon, monsoon, post-monsoon). Taxonomic account revealed a total no of 175, 65, and 101 phytoplankton species in the estuary, lagoon, and coastal waters, respectively. Prevalence of marine, brackish, and fresh water types in the coastal waters, lagoon, and estuary, respectively, characterized the contrasting nature of the study regions in hosting the phytoplankton community. In general, phytoplankton abundance was observed in increasing order of coastal waters > estuary > lagoon during post-monsoon and pre-monsoon, while lagoon > coastal waters > estuary during monsoon. Bacillariophyta dominated the phytoplankton community in the estuary and coastal waters during all the seasons. In contrast, the lagoon exhibited a diverse array of phytoplankton group such as cyanophyta, dinophyta, and bacillariophyta during monsoon, post-monsoon, and pre-monsoon, respectively. Over the seasons, microphytoplankton emerged as the dominant phytoplankton size class in the coastal waters. Diversely, nanophytoplankton contributed to major fraction of chlorophyll-a concentration in the estuary and lagoon. Interestingly, pre-monsoon dinophyta bloom (causative species: Noctiluca scintillans with cell density 9 × 104 cells·l-1) and monsoon bacillariophyta bloom (causative species: Asterionellopsis glacialis 5.02 × 104 cells·l-1) resulted decline in species diversity. Multivariate statistical analysis deciphered salinity as a major environmental player in determining the distribution, diversity, and composition of phytoplankton communities in the three contrasting environments. Trophic state indices signified the lagoon and estuary as hypereutrophic during all season. The coastal water was marked as highly eutrophic through trophic state index during monsoon and pre-monsoon.
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Ecosistema , Monitoreo del Ambiente , Fitoplancton/fisiología , Cianobacterias , Tormentas Ciclónicas , Diatomeas , Dinoflagelados , Estuarios , Agua Dulce/química , Salinidad , Estaciones del Año , Agua de Mar/químicaRESUMEN
In order to establish the natural processes and geochemical factors responsible for enrichment of trace metal ions (Cu, Co, Ni, Zn and Cr) with respect to textural parameters (sand, silt and clay weight percentages) along with depth, multivariate statistical approach has been carried out for sediments in different water zones of Chilika lake, the largest brackish water lagoon in Asia. The rotated varimax factor results reveal that Cobalt enrichment is controlled by both textural parameters as well as adsorption mechanism. In fresh and saline water region, textural parameters and in mixed water, adsorption phenomenon predominates. Zn in fresh water is related to clay, whereas it is in adsorbed state in mixed water. Cu in fresh water sediments is in absorbed state and in mixed water it is related to depth and Co concentration. Cr does not show any specific association in fresh water, but in both mixed and saline water it is associated with clay minerals. Although both textural parameters and adsorption mechanism play an important role for the enrichment of trace metal ions in these lagoonal sediments, their relative importance varies with specific metal ions as well as the water quality. Sequential extraction technique was used to characterize the various forms of metals in the < 63 micro size sediments of Chilika lake. The concentrations determined indicated selective accumulation of the various metals in the different phases with spatial variability in different water zones. Slightly higher availability of Co and Zn near Balugaon township in exchangeable phase may be related to anthropogenic activities. Among the non-lithogenous (NL) phases, reducible phase associated with higher concentration of Ni, Cu and Cr. Organic bound Zn and Co contributed highest percentages among NL fractions. Residual fraction contributed more than 50% in most of the cases, reflected the predominance of physical weathering, high erosion rate along the drainage basin.