Abstract
The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ15N) and carbon (δ13C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.
Highlights
With the global increase in sea surface temperature (Bopp et al, 2013; Pisano et al, 2020; Séférian et al, 2020), species that prefer warmer waters will increase its northward expansion, as it has been seen for round sardinella (Sardinella aurita), in the Mediterranean Sea (Sabatés et al, 2006) and in the eastern Atlantic waters (Zeeberg et al, 2008)
How these shifts in their distribution might affect inter-specific interactions will depend on many factors, but among them, the trophic niche overlap of sympatric species and its trophic interactions are important in many marine ecosystems (e.g., Checkley et al, 2009; Kadin et al, 2019), including the Mediterranean Sea (e.g., Albo-Puigserver et al, 2016, 2019; Bachiller et al, 2020; Coll et al, 2019)
We investigate the feeding ecology of sardinella, and how it relates to two sympatric species, sardine and anchovy, that were described in Bachiller et al (2020), in the Gulf of Alicante (Geographical Sub-Area 06—hereafter GSA; FAO, 2018)
Summary
With the global increase in sea surface temperature (Bopp et al, 2013; Pisano et al, 2020; Séférian et al, 2020), species that prefer warmer waters will increase its northward expansion, as it has been seen for round sardinella (Sardinella aurita), in the Mediterranean Sea (Sabatés et al, 2006) and in the eastern Atlantic waters (Zeeberg et al, 2008). We combine stomach content analysis under the microscope with DNA metabarcoding, applying a novel diet characterization procedure which deals with the prey quantification limitation of genetic approaches (Amundsen & Sánchez-Hernández, 2019), and we include stable isotope analyses of carbon and nitrogen (δ13C and δ15N) that integrate trophic information in a longer timeframe (Nielsen et al, 2018) This way, we determine whether sardinella is mainly a filter feeder, or an effective particulate feeder, which uses the whole prey size spectrum available. Since we previously documented large proportions of microplastics and parasites in the diet of anchovy and sardine (Pennino, Bachiller, et al, 2020), we analyzed them in stomach contents of sardinella, which could provide an indirect indicator about its health
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