A trophic latitudinal gradient revealed in anchovy and sardine from the Western Mediterranean Sea using a multi-proxy approach

Eneko Bachiller,Angelique Jadaud,Marta Albo-Puigserver,Joan Giménez,Neus Marí-Mena,José María Bellido,Maria Grazia Pennino,Marta Coll,Antonio Esteban,Elena Lloret-Lloret,Belén Carro

doi:10.1038/s41598-020-74602-y

Abstract

This work combines state-of-the-art methods (DNA metabarcoding) with classic approaches (visual stomach content characterization and stable isotope analyses of nitrogen (δ15N) and carbon (δ13C)) to investigate the trophic ecology of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) at high taxonomic and spatial resolution in the Western Mediterranean Sea. Gut contents observed are in accordance with the dietary plasticity generally described for anchovy and sardine, suggesting a diet related to the opportunistic ingestion of available prey in a certain area and/or time. Genetic tools also showed modest inter-specific differences regarding ingested species. However, inter-specific and intra-specific differences in ingested prey frequencies and prey biomass reflected a latitudinal signal that could indicate a more effective predation on large prey like krill by anchovy versus sardine, as well as a generalized higher large prey ingestion by both species southwards. In fact, both species presented lower δ15N in the northernmost area. This latitudinal gradient indicates changes in the trophic ecology of anchovy and sardine that coincide with previously described better biological conditions for fish in the southern part of the study area as well as higher landings of both species in recent years.

Highlights

European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) are two of the most exploited small pelagic fish in the Mediterranean Sea, representing ca. 50% of the total Mediterranean fish landings[1]
Most studies have been focused on the northwesternmost Mediterranean area, the Gulf of L ion[20], whereas the ecological status and trophic ecology of small pelagic fish in the whole Western Mediterranean Sea remains uncertain[21]
Gut content analysis by visual inspection and DNA metabarcoding only provides a snapshot of what the fish has ingested in the last few h ours[29,33], which can lead to some bias if we are interested in the long term trophic ecology of the species

Summary

Introduction

European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) are two of the most exploited small pelagic fish in the Mediterranean Sea, representing ca. 50% of the total Mediterranean fish landings[1]. Changes in body condition, growth, size at first maturity and disappearance of older ages have been observed for both species, shows a latitudinal trend with higher incidence of change in the northern versus the southern part of the Western Mediterranean S ea[7,8,9,11]. In this sense, understanding ecological processes affecting fluctuations of such fisheries stocks has been a key issue in recent s tudies[2,12]. The gut content characterization technique presents some limitations, as for example some gelatinous species and certain fish eggs that are difficult to detect due to their high vulnerability to the digestion p rocesses[34]

Methods

Results

Conclusion