Qualitative assessment of the diet of European eel larvae in the Sargasso Sea resolved by DNA barcoding

Abstract

European eels ( Anguilla anguilla ) undertake spawning migrations of more than 5000 km from continental Europe and North Africa to frontal zones in the Sargasso Sea. Subsequently, the larval offspring are advected by large-scale eastward ocean currents towards continental waters. However, the Sargasso Sea is oligotrophic, with generally low plankton biomass, and the feeding biology of eel larvae has so far remained a mystery, hampering understanding of this peculiar life history. DNA barcoding of gut contents of 61 genetically identified A. anguilla larvae caught in the Sargasso Sea showed that even the smallest larvae feed on a striking variety of plankton organisms, and that gelatinous zooplankton is of fundamental dietary importance. Hence, the specific plankton composition seems essential for eel larval feeding and growth, suggesting a linkage between eel survival and regional plankton productivity. These novel insights into the prey of Atlantic eels may furthermore facilitate eel larval rearing in aquaculture, which ultimately may replace the unsustainable use of wild-caught glass eels.

A low trophic position of Japanese eel larvae indicates feeding on marine snow

“…A feeding ecology based on consuming marine snow can explain the observations of the DNA barcoding study of leptocephalus food contents [8] and of ciliates being consumed [7] because marine snow comprises detritus-like materials from all types of marine organisms that aggregate together, and thus these species or their tissue fragments could be present in the material ingested by leptocephali. Direct observations of the food contents of various species of leptocephali have consistently shown material that appears to be amorphous marine snow or discarded appendicularian houses and zooplankton faecal pellets [3][4][5] (see the electronic supplementary material, figure S3).…”

“…Therefore, marine snow and appendicularian houses contain micro-organisms such as bacteria and protozoans and colonizing animals such as ciliates, copepodid stages, and anthozoan, mollusc and polychaete larvae [6,22]. The aggregation of organismal materials in POM probably explains the presence of the DNA sequences detected in small European eel larvae [8], although leptocephali may also sometimes directly consume small organisms.…”

“…These observations suggested that marine snow or discarded appendicularian (filter feeding tunicates) houses were the main food of leptocephali, and these types of POM are consistently present in the surface layer of the world's oceans [6]. However, ciliates have been observed in their intestines [7] and DNA barcoding analyses detected sequences of a wide range of marine animals in the gut contents of small European eel leptocephali [8].…”

Feeding selectivity of bivalve larvae on natural plankton assemblages in the Western English Channel

“…As part of this study, we performed molecular analysis of gut content of bivalve larvae following the bottle incubations, and where there were sufficient larvae, on the gut content of larvae taken directly from the field. Recent studies have used DNA-based techniques for dietary analysis including PCR amplification of 18S genes from the gut content of zooplankton (Nejstgaard et al 2003;Troedsson et al 2007;Nejstgaard et al 2008;Troedsson et al 2009;Durbin et al 2012), including meroplanktonic larvae (Maloy et al 2009;Riemann et al 2010;Fileman et al 2014). If the gut content of the predator can first be removed to reduce coamplification of host DNA, then general or universal primers designed to conserved regions (Holland et al 1991) targeting the 18S gene can be used.…”

Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. II. Protozooplankton and copepods

“…Consequently, there is motivation for improved understanding of ecological processes that supports the early life of the Atlantic eels in this region (Munk et al 2010). Early studies suggested that the prey of eel larvae includes larvacean houses and zooplankton faecal pellets (Mochioka & Iwamizu 1996), but recent data suggest that the diet encompasses a wide range of plankton organisms, including gelatineous zooplankton and copepods (Riemann et al 2010).…”