Determination of fish trophic levels in an estuarine system

Abstract

The concept of trophic level is particularly relevant in order to improve knowledge of the structure and the functioning of an ecosystem. A precise estimation of fish trophic levels based on nitrogen isotopic signatures in environments as complex and fluctuant as estuaries requires a good description of the pelagic and benthic trophic chains and a knowledge of organic matter sources at the bottom. In this study these points are considered in the case of the Gironde estuary (south west France, Europe). To obtain a good picture of the food web, fish stomach content analyses and a bibliographic synthesis of the prey feeding ecology were carried out. Fish trophic levels were calculated from these results and δ 15 N data. The feeding link investigation enabled us to identify qualitatively and quantitatively the different preys consumed by each fish group studied, to distinguish the prey feeding on benthos from those feeding on pelagos and to characterize the different nutritive pools at the base of the system. Among the species studied, only Liza ramada and the flatfish (Platichthys flesus and Solea solea) depend mainly on benthic trophic compartments. All the other fish groups depend on several trophic (benthic and/or pelagic) sources. These results enabled us to correct the calculation of fish trophic levels which are coherent with their feeding ecology data obtained from the nitrogen isotopic integrative period. The present work shows that trophic positions are linked with the feeding ecology of fish species and vary according to individual size. Ecological data also allow the correction of the isotopic data by eliminating absurd results and showing the complementarity of the two methods. This work is the first to consider source variability in the fish food web. This is an indispensable step for trophic studies in a dynamic environment. The investigation of matter fluxes and recycling processes at the food web base would provide an useful improvement in future estuarine food web research.

Diet and trophic status of fish landed by tropical artisanal bait fishers, Mida creek Kenya

“…This may indicate fishing down the food web as a result of overfishing pressure. Pasquaud et al (2010) reported similar range of trophic levels (2.8-3.9) from an estuarine fishery as reported here. However, McClanahan and Mangi (2004) reported hook fishermen as landing higher trophic level fishes (3.6) compared to basket trap (2.5) and other gears (> 2.5).…”

Ekologi Trofik Komunitas Ikan di Perairan Segara Menyan, Subang, Jawa Barat (Trophic Ecology of the Fish Community in Segara Menyan Coastal Lagoon, Subang, West Java)

“…Berbagai pendekatan yang telah berkembang dalam memahami jejaring trofik, berawal dari pengamatan langsung terhadap isi lambung dari setiap individu hingga pada akhirnya dapat menentukan jenis makanan pada tingkat populasi (Pasquaud et al, 2009). Pasquaud et al (2009) juga menyatakan bahwa pendekatan yang lebih baru dengan menggunakan teknik isotop stabil untuk menentukan aspek-aspek kualitatif dan kuantitatif dari dinamika dan struktur jejaring trofik. Studi lain dengan menggunakan berbagai teknik untuk mengevaluasi interaksi mangsa-pemangsa (prey-predator) dan dinamika dalam transfer dan aliran energi (Zetina-Rejón et al, 2003;Sá et al, 2006;Haputhantri et al,2008).…”

Role of Demersal Zooplankton as a Food Source for Higher Trophic Levels at Fukido Estuary, Ishigaki Island, Okinawa, Japan

“…This method is convenient because it can be carried out rapidly and economically, providing a direct estimation of prey contents (Hyslop, 1980;Pasquaud et al, 2010;Winemiller et al, 2011). However, stomach content analysis has some limitations, because living organisms digest food more rapidly than non-living organic matter (Fry and Ewel, 2003).…”

“…As a result, there has been an increasing number of studies using dual stable carbon and nitrogen isotopes to determine the relationship between predators and their food sources (Fry, 2007;Nakamura et al, 2008;Pasquaud et al, 2010;Vinagre et al, 2012;Tue et al, 2013). The δ 15 N in the tissues of a consumer is typically 2.6‰ to 3.4‰ richer than that in their prey; thus, δ 15 N studies are often conducted to estimate the trophic position of species in the food web (Deniro and Epstein, 1981;Post, 2002;Fry, 2007).…”