Stable isotope analyses provide new insights into ecological plasticity in a mixohaline population of European eel

Abstract

Recent studies have shown that anguillid eel populations in habitats spanning the marine-freshwater ecotone can display extreme plasticity in the range of catadromy expressed by individual fishes. Carbon and nitrogen stable isotope analysis was used to differentiate between European eels (Anguilla anguilla) collected along a short (2 km) salinity gradient ranging from <1 per thousand to approximately 30 per thousand in Lough Ahalia, a tidal Atlantic lake system. Significant differences were recorded in mean delta13C, delta15N and C:N values from eels collected from fresh, brackish and marine-dominated basins. A discriminant analysis using these predictor variables correctly classified ca. 85% of eels to salinity zone, allowing eels to be classified as freshwater (FW), brackish (BW) or marine (MW) residents. The results of the discriminant analysis also suggested that a significant proportion of eels moved between habitats (especially between FW and BW). Comparisons of several key population parameters showed significant variation between eels resident in different salinity zones. Mean condition and estimated age was significantly lower in MW eels, whilst observed length at age (a correlate of growth) was significantly higher in MW eels, intermediate in BW and lowest in FW eels. This study has demonstrated that the ecology of eels found along a short salinity gradient can be extremely plastic and that stable isotope analysis has considerable utility in demonstrating intra-population variation in diadromous fishes.

Preservation methods alter stable isotope values in gelatinous zooplankton: implications for interpreting trophic ecology

“…Ontogenetic trophic shifts have been observed in a wide range of marine mammals and Wsh (e.g. Olson 1996;Harrod et al 2005;KnoV et al 2008), but the existence of such dietary changes within gelatinous species is not well documented.…”

“…SIA provides a useful tool for examining ontogenetic dietary shifts in a range of consumers (e.g. Olson 1996;Harrod et al 2005;KnoV et al 2008); however, such patterns have not been examined in jellyWsh. If preservation eVects exist, and are not constant across a gradient of consumer body size, this may aVect our capacity to correctly interpret information regarding trophic ecology from isotope data based on preserved samples.…”

Japanese eel Anguilla japonica do not assimilate nutrition during the oceanic spawning migration: evidence from stable isotope analysis

“…15 N values varied largely (5.2-12.6 ‰) among the mesopelagic species, and positive enrichment with body length was observed within species such as longneck eel (KUB: r = 0.976, p > 0.1), 236 Harrod et al (2005) found much more depleted δ 13 C values (-23.6 ‰ average) in European eels (> 30cm in body length) collected in the freshwater habitat than those in the marine habitat (-16.3 ‰ average). Likewise, Bardonnet & Riera (2005) observed a significant shift of isotopic signatures from marine glass eels to river pigmented eels, where the pigmented eels, after starting to assimilate terrigenous organic matter sources, were observed to have lower δ 13 C (-26.7 to -22.7 ‰) than the marine glass eels (-21.4 ± 0.3 ‰).…”

Técnicas Y Aplicaciones Multidisciplinares De Los Isótopos Ambientales

“…Las especies catádromas son aquellas que inician su ciclo de vida en el mar, desde donde luego migran a cursos de agua dulce para crecer y desarrollarse, y cuando alcanzan su madurez sexual, regresan a las aguas marinas de origen, para completar su proceso reproductivo, como la anguila. Harrod, et al (2005) estudiaron la plasticidad ecológica de la anguila europea (Anguilla anguilla) en una gradiente de salinidades de 1-30 g/l en el lago Ahalia (oeste de Irlanda). Encontraron tres grupos de anguilas en función de las señales isotópi-cas medidas (δ 15 N y δ 13 C), las de agua dulce, las de agua salobre y las marinas.…”