Changing Isotopic Food Webs of Two Economically Important Fish in Mediterranean Coastal Lakes with Different Trophic Status

Abstract

Transitional waters are highly productive ecosystems, providing essential goods and services to the biosphere and human population. Human influence in coastal areas exposes these ecosystems to continuous internal and external disturbance. Nitrogen-loads can affect the composition of the resident community and the trophic relationships between and within species, including fish. Based on carbon (δ13C) and nitrogen (δ15N) stable isotope analyses of individuals, we explored the feeding behaviour of two ecologically and economically important omnivorous fish, the eel Anguilla anguilla and the seabream Diplodus annularis, in three neighbouring lakes characterised by different trophic conditions. We found that A. anguilla showed greater generalism in the eutrophic lake due to the increased contribution of basal resources and invertebrates to its diet. By contrast, the diet of D. annularis, which was mainly based on invertebrate species, became more specialised, focusing especially on polychaetes. Our results suggest that changes in macroinvertebrate and fish community composition, coupled with anthropogenic pressure, affect the trophic strategies of high trophic level consumers such as A. anguilla and D. annularis. Detailed food web descriptions based on the feeding choices of isotopic trophospecies (here Isotopic Trophic Units, ITUs) enable identification of the prey taxa crucial for the persistence of omnivorous fish stocks, thus providing useful information for their management and habitat conservation.

Impact of environmental micropollutants and diet composition on the gut microbiota of wild european eels (Anguilla anguilla)

“…A. anguilla is a generalist predator. Though it feeds mainly on invertebrates and fish, some individuals exhibit scavenger behaviour feeding on dead animals (Sporta Caputi et al, 2020). Our results meet this assumption since eels from Pas-du-Bouc, which have a microbiome composition influenced by the proportion of fish, mammals and bird preys in their diet, also showed a lower microbial alphadiversity (Observed and Chao1).…”

Seasonal Food Web Dynamics in the Antarctic Benthos of Tethys Bay (Ross Sea): Implications for Biodiversity Persistence Under Different Seasonal Sea-Ice Coverage

“…Before the sea-ice break-up, consumers showed 13 C-depleted values typical of benthic resources (Norkko et al, 2007;Calizza et al, 2018;Michel et al, 2019;Rossi et al, 2019). Their wide isotopic niches and Carbon Ranges suggested high trophic generalism within the community in this period (Layman et al, 2007;Jackson et al, 2011;Careddu et al, 2017;Sporta Caputi et al, 2020). After the sea-ice break-up, the increased availability of sympagic algae allowed consumers to specialize on this carbon source, making the coupling of distinct energy channels less marked (Kaehler et al, 2000;Dunton, 2001;Knox, 2006).…”

“…The isotopic niche metrics of populations at both sampling times were calculated in accordance with Layman et al (2007) and Jackson et al (2011). These metrics, originally proposed for application at community level, can also be used at population level to obtain information on trophic diversity within a single population (Layman et al, 2007;Jackson et al, 2011;Careddu et al, 2017;Sporta Caputi et al, 2020). Carbon Range (CR) and Nitrogen Range (NR) were measured as the difference between the lowest and highest δ 13 C and δ 15 N values, respectively.…”

“…The proportional similarity of diet among taxa was measured by the Bray-Curtis similarity index. The index is based on the contribution of each resource to the diet of each consumer and it ranges from 0, when no common resources are found for the compared groups, to 1, when the compared groups have the same resources in the same proportions (Calizza et al, 2018;Costantini et al, 2018;Sporta Caputi et al, 2020).…”

Food Chains and Food Webs in Aquatic Ecosystems

“…To test a hypothesis that differences in invertebrate and fish assemblages in lakes characterized by different trophic conditions determine patterns of variation in the trophic niche width of the fish species depending on their specific feeding habits, Caputi et al [20] studied the feeding behavior of two omnivorous species (Anguilla anguilla and the seabream Diplodus annularis), which are ecologically and economically important, using the stable isotope analysis of carbon (δ 13 C) and nitrogen (δ 15 N). They found that A. anguilla was a generalist in the eutrophic lake, whereas D. annularis became more specialist, suggesting that changes in macroinvertebrate and fish community composition affect the trophic strategies of high-trophic level consumers.…”