Brackish Water Coastal Lagoon Research Articles

Artificial Neural Networks for Mapping Coastal Lagoon of Chilika Lake, India, Using Earth Observation Data

This study presents the environmental mapping of the Chilika Lake coastal lagoon, India, using satellite images Landsat 8-9 OLI/TIRS processed using machine learning (ML) methods. The largest brackish water coastal lagoon in Asia, Chilika Lake, is a wetland of international importance included in the Ramsar site due to its rich biodiversity, productivity, and precious habitat for migrating birds and rare species. The vulnerable ecosystems of the Chilika Lagoon are subject to climate effects (monsoon effects) and anthropogenic activities (overexploitation through fishing and pollution by microplastics). Such environmental pressure results in the eutrophication of the lake, coastal erosion, fluctuations in size, and changes in land cover types in the surrounding landscapes. The habitat monitoring of the coastal lagoons is complex and difficult to implement with conventional Geographic Information System (GIS) methods. In particular, landscape variability, patch fragmentation, and landscape dynamics play a crucial role in environmental dynamics along the eastern coasts of the Bay of Bengal, which is strongly affected by the Indian monsoon system, which controls the precipitation pattern and ecosystem structure. To improve methods of environmental monitoring of coastal areas, this study employs the methods of ML and Artificial Neural Networks (ANNs), which present a powerful tool for computer vision, image classification, and analysis of Earth Observation (EO) data. Multispectral satellite data were processed by several ML image classification methods, including Random Forest (RF), Support Vector Machine (SVM), and the ANN-based MultiLayer Perceptron (MLP) Classifier. The results are compared and discussed. The ANN-based approach outperformed the other methods in terms of accuracy and precision of mapping. Ten land cover classes around the Chilika coastal lagoon were identified via spatio-temporal variations in land cover types from 2019 until 2024. This study provides ML-based maps implemented using Geographic Resources Analysis Support System (GRASS) GIS image analysis software and aims to support ML-based mapping approach of environmental processes over the Chilika Lake coastal lagoon, India.

Distinct community assembly processes and habitat specialization driving the biogeographic patterns of abundant and rare bacterioplankton in a brackish coastal lagoon

The ecological diversity patterns and community assembly processes along spatio-temporal scales are least studied in the bacterioplankton sub-communities of brackish coastal lagoons. We examined the biogeographic patterns and relative influences of different assembly processes in structuring the abundant and rare bacterioplankton sub-communities of Chilika, the largest brackish water coastal lagoon of India. Rare taxa demonstrated significantly higher α- and β-diversity and biogeochemical functions than abundant taxa in the high-throughput 16S rRNA gene sequence dataset. The majority of the abundant taxa (91.4 %) were habitat generalists with a wider niche breadth (niche breadth index, B = 11.5), whereas most of the rare taxa (95.2 %) were habitat specialists with a narrow niche breadth (B = 8.9). Abundant taxa exhibited a stronger distance-decay relationship and higher spatial turnover rate than rare taxa. β-diversity partitioning revealed that the contribution of species turnover (72.2–97.8 %) was greater than nestedness (2.2–27.8 %) in causing the spatial variation in both abundant and rare taxa. Null model analyses revealed that the distribution of abundant taxa was mostly structured by stochastic processes (62.8 %), whereas deterministic processes (54.1 %) played a greater role in the rare taxa. However, the balance of these two processes varied across spatio-temporal scales in the lagoon. Salinity was the key deterministic factor controlling the variation of both abundant and rare taxa. Potential interaction networks showed a higher influence of negative interactions, indicating that species exclusion and top-down processes played a greater role in the community assembly. Notably, abundant taxa emerged as keystone taxa across spatio-temporal scales, suggesting their greater influences on other bacterial co-occurrences and network stability. Overall, this study provided detailed mechanistic insights into biogeographic patterns and underlying community assembly processes of the abundant and rare bacterioplankton over spatio-temporal scales in a brackish lagoon.

Co-occurrence patterns and environmental factors associated with rapid onset of Microcystis aeruginosa bloom in a tropical coastal lagoon

The environmental factors contributing to the Microcystis aeruginosa bloom (hereafter referred to as Microcystis bloom) are still debatable as they vary with season and geographic settings. We examined the environmental factors that triggered Microcystis bloom outbreak in India's largest brackish water coastal lagoon, Chilika. The warmer water temperature (25.31–32.48 °C), higher dissolved inorganic nitrogen (DIN) loading (10.15–13.53 μmol L−1), strong P−limitation (N:P ratio 138.47–246.86), higher water transparency (46.62–73.38 cm), and low-salinity (5.45–9.15) exerted a strong positive influence on blooming process. During the bloom outbreak, M. aeruginosa proliferated, replaced diatoms, and constituted 70–88% of the total phytoplankton population. The abundances of M. aeruginosa increased from 0.89 × 104 cells L−1 in September to 1.85 × 104 cells L−1 in November and reduced drastically during bloom collapse (6.22 × 103 cells L−1) by the late November of year 2017. The decrease in M. aeruginosa during bloom collapse was associated with a decline in DIN loading (2.97 μmol L−1) and N:P ratio (73.95). Sentinel-3 OLCI-based satellite monitoring corroborated the field observations showing Cyanophyta Index (CI) > 0.01 in September, indicative of intense bloom and CI < 0.0001 during late November, suggesting bloom collapse. The presence of M. aeruginosa altered the phytoplankton community composition. Furthermore, co-occurrence network indicated that bloom resulted in a less stable community with low diversity, inter-connectedness, and prominence of a negative association between phytoplankton taxa. Variance partitioning analysis revealed that TSM (16.63%), salinity (6.99%), DIN (5.21%), and transparency (5.15%) were the most influential environmental factors controlling the phytoplankton composition. This study provides new insight into the phytoplankton co-occurrences and combination of environmental factors triggering the rapid onset of Microcystis bloom and influencing the phytoplankton composition dynamics of a large coastal lagoon. These findings would be valuable for future bloom forecast modeling and aid in the management of the lagoon.

Seagrasses and local environment control the bacterial community structure and carbon substrate utilization in brackish sediments

Seagrasses are complex benthic coastal ecosystems that play a crucial role in organic matter cycling and carbon sequestration. However, little is known about how seagrasses influence the structure and carbon utilization potential of benthic bacterial communities. This study examined the bacterial communities in monospecific and mixed meadows of seagrasses and compared with bulk (unvegetated) sediments from Chilika, a brackish water coastal lagoon of India. High-throughput sequencing of 16S rRNA genes revealed a vegetation effect in terms of differences in benthic bacterial community diversity, composition, and abundances in comparison with bulk sediments. Desulfobacterales, Chromatiales, Enterobacteriales, Clostridiales, Vibrionales, and Acidimicrobiales were major taxa that contributed to differences between seagrass and bulk sediments. Seagrasses supported ∼5.94 fold higher bacterial abundances than the bulk due to rich organic carbon stock in their sediments. Co-occurrence network demonstrated much stronger potential interactions and connectedness in seagrass bacterial communities compared to bulk. Chromatiales and Acidimicrobiales were identified as the top two keystone taxa in seagrass bacterial communities, whereas, Dehalococcoidales and Rhizobiales were in bulk communities. Seagrasses and local environmental factors, namely, water depth, water pH, sediment salinity, redox potential, total organic carbon, available nitrogen, sediment texture, sediment pH, and sediment core depth were the major drivers of benthic bacterial community composition. Carbon metabolic profiling revealed that heterotrophic bacteria in seagrass sediments were much more metabolically diverse and active than bulk. The utilization of carbon substrate guilds, namely, amino acids, amines, carboxylic acids, carbohydrates, polymers, and phenolic compounds was enhanced in seagrass sediments. Metabolic mapping predicted higher prevalence of sulfate-reducer and N2 fixation metabolic functions in seagrass sediments. Overall, this study showed that seagrasses control benthic bacterial community composition and diversity, enhance heterotrophic carbon substrate utilization, and play crucial roles in organic matter cycling including degradation of hydrocarbon and xenobiotics in coastal sediments.

Structural variation of potentially toxic epiphytic dinoflagellates on Thalassia testudinum from two coastal systems of Colombian Caribbean

Some benthic dinoflagellates produce toxins that can affect other organisms including humans, and their proliferation seems to be related to the environmental variability. For this reason, the present study aims to compare the structural variation of potentially toxic dinoflagellates associated with the seagrass Thalassia testudinum from two nearby systems, with different environmental characteristics in Colombian Caribbean, corresponding to a brackish water coastal lagoon and an adjacent bay. Between January 2014 and December 2015, leaves of T. testudinum were collected monthly to obtain the dinoflagellates. Salinity, temperature, dissolved oxygen, pH, nutrients and total suspended solids (TSS) were measured, and precipitation data and the Oceanic Niño Index (ONI) were obtained. Dinoflagellates were detached from the leaves, morphologically identified by analyzing their thecal plates arrangements, and quantified using a Sedgewick-Rafter chamber. The information was analyzed using standard statistics and regression models. Fourteen species of potentially toxic epiphytic dinoflagellate belonging to four genera were recorded, being Prorocentrum the most representative in number of species. The maximum density, dominated by P. lima, were found in Bahía Chengue during the rainy season of 2014 (18452 and 20109 cells g−1 w.w.), with salinity of 35.50, high temperatures (>29.60 °C), dissolved oxygen >6 mg L−1, pH close to 8 and TSS >85 mg L−1. Densities at the Lagoon were lower than 80 cells g−1 w.w. with the highest values of Prorocentrum sp.1 under different environmental conditions. With the statistical relationships between the most abundant species and the main environmental variables, fundamental niche models were proposed in which cells could proliferate. The degree of risk to human health due to the presence of these potentially toxic epiphytic dinoflagellates will not be resolved until their toxicity discarded.

Seasonal and spatial dynamics of bacterioplankton communities in a brackish water coastal lagoon

Coastal ecosystems, one of the most productive ecosystems, are subjected to natural and anthropogenic stresses. Coastal bacterioplankton communities are highly dynamic due to spatiotemporal heterogeneity in the environmental parameters. We investigated the seasonal and spatial variation in bacterioplankton communities, their abundances and environmental drivers during one year period in Chilika, a brackish water coastal lagoon of India. High-throughput sequencing of 16S rRNA genes of bacterioplankton communities showed that they were dominated by heterotrophs namely α-Proteobacteria SAR11 and their sub-clades (SAR11_Ib, Chesapeake-Delaware_Bay, Candidatus_Pelagibacter, and SAR11_Surface_1), actinobacterial lineages (hgcI, CL500-29, and Candidatus_Aquiluna), β-Proteobacteria MWH-UniP1, β-Proteobacteria OM43, and verrucomicrobial clade Spartobacteria ‘LD29’. Synechococcus was the dominant member within autotrophic cyanobacterial community. Response ratio derived from comparisons of taxon-specific absolute abundances and indicator analyses showed that SAR11_Surface_1 sub-clade occupied high-salinity environment especially during summer and winter and emerged as a strong indicator for mesohaline-polyhaline salinity regime. In contrast, Spartobacteria ‘LD29’, Actinobacteria hgcI, and CL500-29 preferred low-salinity freshwater environment and were strong indicators for oligohaline-mesohaline regimes. Spatiotemporal patterns were governed by ‘distance-decay’ and ‘similarity-time’ relationships. Bacterioplankton communities were mostly determined by salinity, dissolved oxygen, phosphate, and pH which resulted 'species sorting' leading to biogeographical patterns in the bacterioplankton communities. Modeling analysis revealed the characteristic shift in the indicator bacterioplankton taxa along with estuarine salinity gradient. This study has provided baseline information on the bacterioplankton communities and their environmental drivers within an anthropogenically impacted cyclone prone coastal lagoon which would be useful in assessing the impact of multiple stressors on this vulnerable ecosystem.

Salinity and macrophyte drive the biogeography of the sedimentary bacterial communities in a brackish water coastal lagoon

Salinity and macrophyte drive the biogeography of the sedimentary bacterial communities in a brackish water coastal lagoon

Salinity and macrophyte drive the biogeography of the sedimentary bacterial communities in a brackish water tropical coastal lagoon

Brackish water coastal lagoons are least understood with respect to the seasonal and temporal variability in their sedimentary bacterial communities. These coastal lagoons are characterized by the steep environmental gradient and provide an excellent model system to decipher the biotic and abiotic factors that determine the bacterial community structure over time and space. Using Illumina sequencing of the 16S rRNA genes from a total of 100 bulk surface sediments, we investigated the sedimentary bacterial communities, their spatiotemporal distribution, and compared them with the rhizosphere sediment communities of a common reed; Phragmites karka and a native seagrass species; Halodule uninervis in Chilika Lagoon. Spatiotemporal patterns in bacterial communities were linked to specific biotic factors (e.g., presence and type of macrophyte) and abiotic factors (e.g., salinity) that drove the community composition. Comparative assessment of communities highlighted bacterial lineages that were responsible for segregating the sediment communities over distinct salinity regimes, seasons, locations, and presence and type of macrophytes. Several bacterial taxa were specific to one of these ecological factors suggesting that species-sorting processes drive specific biogeographical patterns in the bacterial populations. Modeling of proteobacterial lineages against salinity gradient revealed that α- and γ-Proteobacteria increased with salinity, whereas β-Proteobacteria displayed the opposite trend. The wide variety of biogeochemical functions performed by the rhizosphere microbiota of P. karka must be taken into consideration while formulating the management and conservation plan for this reed. Overall, this study provides a comprehensive understanding of the spatiotemporal dynamics and functionality of sedimentary bacterial communities and highlighted the role of biotic and abiotic factors in generating the biogeographical patterns in the bacterial communities of a tropical brackish water coastal lagoon.

Hydrodynamics, temperature/salinity variability and residence time in the Chilika lagoon during dry and wet period: Measurement and modeling

This paper investigated the hydrodynamics, spatio-temporal variability of temperature/salinity and the residence time of tracer concentrations in a largest brackish water coastal lagoon in Asia, namely the Chilika lagoon, India. An integrated approach combined the measurement and 2D hydrodynamic-advection/dispersion model is used to simulate circulation and temperature/salinity, and estimated the water residence time in lagoon under different forcing mechanisms, such as tide, wind and freshwater discharge during the dry and wet periods. Water circulation inside the lagoon is simulated when wind is included with the tide only forcing during dry period, and freshwater influx is included with the tide and wind forcing during wet period. Under the realistic forcing conditions, the computed temporal variability of water temperature and salinity are well correlated with the measurements in both the periods. The spatial variations of water temperature within the lagoon is influenced by the meteorological conditions, tide and freshwater influx as well as the shallowness of the lagoon, whereas the salinity is spatially controlled by the freshwater influx from the riverine system and seawater intrusion through the tidal inlets. The numerical model results show that in the Chilika lagoon tidal and river influx affect significantly the residence time spatially, and is site specific. The residence time varies from values of 4–5 days in the outer channel (OC) and 132 days at the northern sector (NS) in the main body of lagoon. The current study represents a first attempt to use a combined model approach, which is therefore, a useful tool to support the ecological implication of the lagoon ecosystem.

Diatoms from isolated islands II: Pseudostaurosira diablarum, a new species from a mangrove ecosystem in the Galápagos Islands.

Identifying and describing biodiversity remains fundamental to developing a proper understanding of ecological and biogeographic processes. In this paper, we describe Pseudostaurosira diablarum Seddon & Witkowski sp. nov., a new diatom (Bacillariophyceae) species discovered from Las Diablas wetlands, a brackish water coastal lagoon on the Galápagos Islands. The taxon was observed in both the surface (i.e., extant) and core (i.e., sub-fossil) material from the lagoon, found on shaded mangrove substrata with salinities between 5.2 and 8 g L−1. These observations were confirmed by estimating the salinity tolerances of core samples from the palaeoecological record using a diatom salinity transfer function. We provide light and electron microscope images of P. diablarum sp. nov. Under the light microscope, the best diagnostic features are its lanceolate–elliptical shape, and the striae which are composed of a single row of areolae and do not occur all the way to the apices. Under the scanning/transmission electron microscope, the most distinctive features are the delicate closing plates which are less articulated and branched than in many of the other members of this genus, in addition to the simple, stunted spines which interrupt the striae on the valve margin. The taxon described here constitutes further evidence that the Diablas wetlands are an important site for diatom research, with the potential to provide insights into the processes resulting in the dispersal and evolution of its diatom species.

Inter-annual variations of macrobenthic communities over three decades in a land-locked coastal lagoon (Santo André, SW Portugal)

Santo André is an enclosed brackish water coastal lagoon with temporary connections to the sea by a man-made channel. The exchange and mixture of saltwater and freshwater is irregular and the lagoon may show daily and seasonal fluctuations, but also long-term variation. Different benthic communities may be present along the annual cycle according to the magnitude of episodic freshwater and sea water inputs.In the last 30 years the communication with the sea has followed different regimes from year to year and, as a consequence, macrobenthic communities, assessed several times during the period before the opening to the sea, shifted from freshwater to marine affinities. Major differences were found between 1979 and 2010, with a preponderance of species with marine affinity, and the 1980s in which the organisms with freshwater affinity prevailed. Benthic communities are frequently used to assess aquatic environmental condition. Metrics used in the indices currently under discussion to assess ecological status of aquatic ecosystems within the scope of European Water Framework Directive were applied to Santo André data and the applicability of these metrics to assess quality in this coastal land-locked lagoon was discussed.

Monitoring and Management of Environmental Changes along the Orissa Coast

Orissa, the maritime state along the east coast of India, has a coastline of 480 km. The southern part of the coast has a narrow shelf, but the north Orissa coast has an extended continental shelf. The coastline is bestowed with six major estuaries, India's second largest mangrove forest (Bhitarkanika Sanctuary), Asia's largest brackish water coastal lagoon (Chilika), extensive sandy beaches rich in heavy minerals, the world's largest rookery for the Olive Ridley sea turtle (Gahirmatha sandy beach within Bhitarkanika sanctuary), and two species of horseshoe crabs. In the last few decades there has been tremendous pressure on the coastal zone for the development of fisheries, aquaculture, ports, harbours, and urban settlements. These developments have led to environmental changes, some of which are irreversible, and thus have become issues of concern for the public as well as the state government. Some of the important environmental changes taking place, and which seriously affect the economy of the region, are tropical cyclones and associated storm surges, floods, decline in mangrove forests, accelerated shoreline changes, and transformation of the coastal lagoon ecosystem. This paper documents different coastal environmental features and their changes, observed during the last few decades through secondary data, field surveys, and remote sensing observations, and suggests a framework for a coastal zone management programme in the state.

Parasites of carp bream, Abramis brama, from Lake Jamno, Poland

Abstract A total of 40 carp bream, Abramis brama (L.) from Lake Jamno were examined for their parasites in May 2002. Lake Jamno is a brackish-water coastal lagoon, strongly eutrophied and polluted by communal and industrial sewage from the city of Koszalin. The survey yielded 15 parasite species, representing different systematic groups, including 7 monogeneans Dactylogyrus auriculatus, D. falcatus, D. wunderi, D. zandti, Gyrodactylus elegans, Gyrodactylus sp., Diplozoon paradoxum; 4 digeneans (at the stage of metacercaria) Diplostomum sp., Tylodelphys clavata, Ichthyocotylurus platycephalus, I. variegatus; 1 cestode Caryophyllaeus laticeps; 2 crustaceans Ergasilus sieboldi, Argulus foliaceus; and 1 hirudinean Caspiobdella fadejewi. Monogeneans constituted the most abundant parasite group, accounting for 61.5 % of all parasite individuals collected. They were followed by the cestodes (20.7 %), digenean flukes (16 %), crustaceans (0.7 %), and leeches (0.2 %).

New information on the biogeographical and ecological distribution of Pionosyllis anophthalma Capaccioni & San Martín, 1989 (Polychaeta, Syllidae)

1 - Two individuals of the Mediterranean endemic species Pionosyllis anophthalma Capaccioni & San Martin, 1989 were found in a brackish water coastal lagoon in Northern Greece (Agiasma, Nestos river). 2 - The species is reported for the first time in Greece and in a non-tidal brackish water coastal lagoon. 3 - The record adds some new information concerning the geographical and habitat distributional ranges of the species. 4 - Pionosyllis anophthalma is associated with vegetated bottoms and shows a wide tolerance to salinity variations. 5 - An intraspecific morphological variation was observed in the material examined compared to the species’ holotype.