Delineating the food web structure in an Indian estuary during tropical winter employing stable isotope signatures and mixing model.

The food and feeding links and sources in an impacted tropical estuary situated along India's western coast, the Ulhas River Estuary (URE) was analyzed employing the stable carbon and nitrogen isotopic signatures (δ13C and δ15N). Three basal carbon sources, such as mangrove leaves, particulate organic matter (phytoplankton), and detritus, were analyzed together with eight consumer groups from various trophic guilds. The δ13C varied from - 19.67 to - 24.61‰, whereas δ15N ranged from 6.31 to 15.39‰ from the primary consumer to the top predator species. The stable isotope mixing model developed for URE revealed a phytoplankton based pelagic food chain and detritus based benthic food chain in URE. The fairly larger value of SEA (Standard Ellipse Area) in the URE suggest a much broader food web structure and high trophic diversity in the ecosystem. Higher influence of detritus on the assimilated diet of majority of consumers and evidences of nitrogen enrichment in the basal sources such as detritus and particulate organic matter by anthropogenic activities in URE point towards nitrogen pollution and subsequent trophic disturbance in this tropical estuarine ecosystem.

Ecosystem health status and trophic modeling of an anthropogenically impacted small tropical estuary along India's west coast.

The tropical estuaries are characterized with high biological production and also impacted by anthropogenic activities. Describing these estuaries in terms of ecological data and trophic dynamics to reveal the ecological impacts is gaining attention recently. In this study, the ecological structure is analyzed for a heavily impacted small macrotidal tropical estuary, Ulhas river estuary (URE), situated near Mumbai megacity in the western coast of India, to delineate the impact of anthropogenic stressors on the ecosystem functioning. The URE is being exploited for sand and fisheries resources, and also faces risks from anthropogenic activities. The ecological data of URE were compiled for 2017-18 together with the most relevant literature estimates to construct an ecosystem model. A trophic organization in 20 functional groups was identified for URE using Ecopath modeling approach. The functional groups identified in the food web ranged from detritus and primary producers (trophic level (TL) = 1) to large pelagics (TL = 4.14). Detritivory: herbivory ratio (1.35) indicated that the detritus chain is dominant over the primary producer's chain. The total system throughput (TST) was estimated as 16 736.2 t km-2year-1. The indices such as net system production (NSP = 1 398.781 t km-2 year-1), total primary production/total biomass (TPP/TB = 25.17), biomass/total system throughput (TB/TST = 0.01), recycling index (Finn's Cycling Index = 13.94%), system omnivory index (0.3), relative ascendency (25.6%), and system overhead (74.4%) classified URE as an immature system. The eco-exergy index (30748.54 gm detritus equivalent m-2) showed that the ecosystem is a moderately stable and relatively less organized network. The estuarine fish community index (EFCI) yielded a value of 38 indicating the poor health status of the fish community in URE. The study delivers a comprehensive understanding of the ecosystem setting in URE and characterizes the prevailing condition. The ecological indicators analyzed here point towards a medium to a high level of impact in URE due to anthropogenic activities.

Lack of genetic differentiation in milkfish, Chanos chanos (Forsskål, 1775), revealed by mitochondrial ATPase 6/8 genes.

The milkfish, Chanos chanos, is a commercially important cultured species which is distributed throughout south and southeast Asian countries. Captive breeding and seed production techniques have been standardized recently in India and there is a need for analyzing its population structure along the Indian coast. A total of 80 samples from four different locations across the Indian coast were analyzed by using ATPase 6/8 genes. Analysis revealed the existence of 25 haplotypes across populations with the haplotype diversity in the range of 0.5684-0.8053 and the nucleotide diversity varied from 0.001838 to 0.002519. The variation within and among populations accounted for 97.43% and 2.75%, respectively. The observed FST values were found to be non-significant (p > 0.05). Results from this study indicated that there is lack of genetic divergence between the populations of milkfish along the Indian coast.