Influence of environmental heterogeneity on the distribution of micro-zooplankton community along the tropical coastal waters.

This study mainly focused on the water quality variability and distribution of micro-zooplankton (MZP) along the coastal waters of Tamil Nadu. Dendrogram analysis using water quality data categorized the study area into three regions: North (Chennai), Central (Puducherry), and South (Karaikal). The MZP consists of 40 ciliates and 8 dinoflagellates, with spirotrichea (52.4 %) significantly dominant, followed by dinophyceae (21.1 %), phyllopharyngea (14.7 %), and others (11.8 %). Paracyrtophoron tropicum, a new report in the coastal waters of India, was identified by comparing its molecular phylogeny (18S rRNA accession no: MT500569) to previously reported species. Statistical analysis revealed a positive correlation between P. tropicum abundance and water temperature, PO4, SiO4, TP, Chl-a, and Trichodesmium erythraeum, suggesting that they might not directly control the growth of P. tropicum but indirectly influence it via food availability, i.e., T. erythraeum. However, to understand these species interactions and ecological pathways, further long-term monitoring studies are required.

Factors regulating phytoplankton biomass along the Indian coast: elucidation with long-term data.

Long-term variations in phytoplankton biomass from nine coastal states along the Indian coast were studied and co-related with biotic and abiotic factors. Surface water temperature, dissolved inorganic nutrients (nitrogen and phosphorous), and plankton (phytoplankton and zooplankton) biomass data were collected between 1992 and 2015. Linear regression analysis showed a considerable increase in dissolved inorganic nutrients. A substantial increase in the frequency and intensity of phytoplankton blooms (> 3 mg/m3) was observed along the Indian coast. The considerable increase in dissolved inorganic nutrient concentrations could be the major reason for an increase in phytoplankton bloom occurrences. Availability of light and periodicity in zooplankton population were also regulating phytoplankton biomass. Our results revealed that multiple factors are influencing phytoplankton biomass along the Indian coast; particularly, the increase in nutrient concentrations is promoting plankton biomass. Moreover, significant increase in zooplankton biomass can have substantial impact on the biogeochemical cycling and energy transfer to higher trophic levels.

Distribution patterns and seasonal variations in phytoplankton communities of the hypersaline Pulicat lagoon, India.

Phytoplankton structure and patterns are key components to forecast the net result of the gain and loss process that outline the resilience of the lagoon ecosystem. In order to understand the phytoplankton community structure and its relationship with the environmental variables in the shallow hypersaline Pulicat lagoon, east coast of India, observations were carried out during August 2018-January 2019 covering the three seasons: premonsoon (PrM), monsoon (M), and postmonsoon (PoM). The salinity of the lagoon varied with a minimum of 12.1 for the M and a maximum of 81.65 during the PoM. The clustering analysis performed on the phytoplankton abundance data separated the lagoon into three sectors: north sector (NS), central sector (CS), and south sector (SS). A total of 59 taxa/morphotypes from four taxonomic classes (Bacillariophyceae, Chlorophyceae, Cyanophyceae, and Dinophyceae) were recorded during the study period. The class Bacillariophyceae was dominant in the lagoon both spatially and temporally by 44.06% with Chaetoceros borealis as dominant species. Presence of characteristic species like Dunaliella sp. was observed in the higher salinity, whereas Pediastrum duplex and Scenedesmus sp. were dominant in the freshwater influx areas. The individual-based functional approach allowed grouping these taxa into 11 functional entities based on the derived 4 functional trait values (cell size, trophic regime, mobility, and coloniality). Formation of algal blooms of Protoperidinium sp. (3.3×105ind L-1) and Odentella sp. (2.8×105ind L-1) was observed in the SS during PoM as a result of reduced water exchange in the lagoon. During the same period, toxin-producing strains like Anabaena sp. and Nostoc sp. of Cyanophyceae were also recorded. Correlating the three sectors of the lake (NS, CS, and SS), it is observed that the physical, chemical, and biological properties of the lake varied continuously depending on the season and freshwater availability. Seasonal nutrient stoichiometry played a significant role in regulating the community structure and distribution pattern of phytoplankton communities of the lagoon.

Composition and distribution of planktonic ciliates with indications to water quality in a shallow hypersaline lagoon (Pulicat Lake, India).

Planktonic ciliate composition and distribution together with physicochemical variables were investigated in a shallow hypersaline lagoon, Pulicat, India, during three seasons, i.e., pre-monsoon (PRM), monsoon (MON), and post-monsoon (POM). The low freshwater inflow, evaporation, and closure of the lake mouth were the main factors for the hypersaline conditions in Pulicat Lake. The average depth and salinity were 1.8 ± 0.12 m (0.8 to 2.8 m) and 35.3 ± 1.68 (12.5 to 61), respectively. A total of 29 ciliate taxa belonging to 18 genera and five classes were identified. Strombidium conicum (24%) was the dominant species followed by Euplotes sp. (10.7%) and Stenosomella sp. (7.02%). Spirotrichea (84%) was the dominant class followed by Oligohymenophorea (9.6%) and Heterotrichea (5.8%). Fabrea salina, a typical species in hypersaline systems, was abundant at locations where the salinity was more than 35. Multivariate analysis using the Bray-Curtis similarity, followed by SIMPROF (Similarity Percentage Analysis), on ciliate abundance data revealed three ciliate assemblages characterizing south, central, and north of the lake at 40% similarity (SIMPROF, cophenetic correlation = 0.622, P = 5%). Both ciliate abundance and chlorophyll-a were positively correlated with salinity. Species richness and evenness were higher in the south sector when compared with those in the other two sectors. Biotic-environmental interaction through canonical correspondence analysis (CCA) inferred that the combined effects of salinity, chlorophyll-a, and nutrient levels are the key factors responsible for the distribution of the ciliate species, suggesting that ciliates can be considered to be potential bioindicators of water quality.

Scales and drivers of seasonal pCO2 dynamics and net ecosystem exchange along the coastal waters of southeastern Arabian Sea.

The impact of seasonal coastal upwelling on the dynamics of dissolved inorganic carbon (DIC) and sea-air fluxes of CO2 along the coastal waters of Kochi was investigated during 2015, as a part of Ecosystem Modelling Project. The surface water pCO2 varied from 396 to 630µatm during the study period. Significant inter-seasonal variations were found in the distribution of physico-chemical variables and surface pCO2. An increase of 102.1µatm of pCO2 was noticed over a two-decade period with a rate of 5.3µatmy-1. There was an agreement between the fluxes of CO2 and net ecosystem production (NEP) with respect to the trophic status while NEP was higher than CO2 fluxes by a factor of 3.9. The annual net ecosystem exchange (NEE) was estimated to be 15.02mmolCm-2d-1 indicating that the coastal waters of Kochi are highly heterotrophic in nature.