Ecological Modelling 356 (2017) 25–37 Contents lists available at ScienceDirect Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel Comparative study of food webs from two different time periods of Hooghly Matla estuarine system, India through network analysis Nabyendu Rakshit a , Arnab Banerjee a , Joyita Mukherjee a , Moitreyee Chakrabarty b , Stuart R. Borrett c,d , Santanu Ray a,∗ a Ecological Modelling Laboratory, Department of Zoology, Visva-Bharati University, Santiniketan 731235, West Bengal, India b PG Department of Conservation Biology, DGP Govt. College, Durgapur 713214, West Bengal, India c Department of Biology and Marine Biology and Center for Marine Science, University of North Carolina Wilmington, Wilmington, NC 28403, United States d Duke Network Analysis Center, Social Science Research Institute, Duke University, Durham, NC 27708, United States a r t i c l e i n f o Article history: Received 31 December 2016 Received in revised form 10 April 2017 Accepted 10 April 2017 Keywords: Trophic structure Ecological network analysis Food web Ecopath Niche overlap Mixed trophic impact Ecological indicators Overfishing a b s t r a c t Two mass-balanced network models of Hooghly Matla estuarine system, from two different time peri- ods (less exploited phase → 1985–1990 and highly exploited phase → 1998–2003) have been constructed for quantitative comparison. The models are used to estimate the important biological interactions and relationships among different ecologically important groups. 20 functional groups based on species of dif- ferent habitats from coastal areas in this ecosystem have been identified, including shrimps, squids, crabs, mackerel, small pelagics, demersal fishes, benthic feeders, predator fishes and trash fish. The biomass val- ues for these components are estimated from catch production and bottom trawling surveys. The values of Ecotrophic Efficiency in the models are high (>0.5) for most groups of higher trophic levels. Interac- tions among different components are clearly understood from the outputs of models with a focus on energy flow. Most fish population are observed to approach high degree of exploitation with change in the overall trophic structure mainly due to top down effects. Several system statistics and network flow indices from the model outputs indicate that this estuary is facing degradation and stress resulting in some degrees of instability. © 2017 Elsevier B.V. All rights reserved. 1. Introduction The Hooghly Matla estuarine ecosystem with adjacent man- groves is one of the largest detritus based ecosystems of the world (Pillay, 1958) and has great importance in costal landscape of India. Estuarine system are of interest because the most sensitive land- water-atmosphere interactions are pronounced at these region. It provides diverse habitat for wide variety of aquatic resources of ecological and economic significance including finfish, prawn, bivalve, gastropod, fiddler crab and plankton etc. (Mitra et al., 2000, 1997; Nath et al., 2004). Beside this, like other estuaries, the Hooghly Matla system also has great significance as it supports many essential fisheries of high economic value. ∗ Corresponding author. E-mail addresses: nabyendu.rakshit@visva-bharati.ac.in (N. Rakshit), arnab.banerjee@visva-bharati.ac.in (A. Banerjee), joyitamukherjee07@gmail.com (J. Mukherjee), miotreyeebanerjee@gmail.com (M. Chakrabarty), borretts@uncw.edu (S.R. Borrett), sray@visva-bharati.ac.in (S. Ray). But recent years have seen this ecosystem to have degraded gradually owing to the different anthropogenic factors such as overfishing, development of agriculture and sewage from aqua- culture farms, expansion of human settlements (900 km −2 ; 2001 census), establishment of Farakka barrage in the upper stream of river, construction of Kolkata-Haldia ports and climatic factors like rise in temperature, sea level, salinity and increasing frequency of severe cyclones such as Nargis, Bijli and Aila in recent years (Hazra et al., 2010, 2002). These hamper the ecological balance affecting the food web of the concerned system (Islam, 2013) .The increas- ing trend of fish yield over years (from 27014.5 t in 1984–93 to 64204.3 t in 1999–2003) has resulted into a drastic decline in the fish catch per unit effort (CPUE) from 189.7 kg in 1990–91 to 44 kg in 2002–03 (Mitra et al., 1997; Nath et al., 2004; Sinha, 2004). Tech- nically this is termed as overfishing; a form of overexploitation where the amount of fish caught reduces the population below the level at which fish population can naturally sustain itself. This may happen in water bodies of any sizes from small ponds and rivers to oceans and can result in resource depletion, reduced biological growth rates, low biomass level in fish population. Futhermore, it can lead to critical situations where fish population are no longer http://dx.doi.org/10.1016/j.ecolmodel.2017.04.003 0304-3800/© 2017 Elsevier B.V. All rights reserved.