Geographic variation in stable isotopic and fatty acid composition of anguilliform leptocephali and particulate organic matter in the South Pacific

Abstract

The feeding ecology of leptocephali has remained poorly understood because they apparently feed on particulate organic matter (POM), which varies in composition, and it is unclear which components of the POM they assimilate. The δ13C and δ15N stable isotope (SI) and fatty acid (FA) compositions of 3 families of leptocephali and POM were compared in 3 latitudinal current zones of the western South Pacific. The δ15N signatures of leptocephali and POM overlapped, with both having their lowest values in the southern current zone. POM in general (across all zones) contained 38 FAs and was rich in saturated FAs (SFA) (16:0, 18:0, 14:0), while leptocephali contained 50 FAs, with high proportions of 16:0, and higher contributions of 22:6ω3, 20:5ω3, 18:1ω9, 16:1ω7 and other FAs than found in the POM. Serrivomeridae leptocephali in the north had higher δ15N signatures and were also distinguished from Nemichthyidae and Muraenidae larvae by their FA compositions (higher SFAs, lower 22:6ω3 and 20:5ω3). Although SI signatures of the Serrivomeridae larvae did not clearly vary with size, 16:0 and 18:0 FA proportions decreased with increasing larval size, and 22:6ω3 and 16:1ω7 increased in larger larvae. Correspondences between the latitudinal variations in nitrogen SI signatures and FA compositions of POM with those of leptocephali and the presence of FA markers of both autotrophic and heterotrophic organisms were consistent with leptocephali feeding on POM. POM can contain various materials from primary producers and heterotrophic microorganisms, but differences in the SI signatures and FA compositions in leptocephali remain to be explained through further research. (Résumé d'auteur

The ecology of oceanic dispersal and survival of anguillid leptocephali

“…In addition, a DNA barcoding study on small European eel larvae found that sequences were present from a wide range of organisms ), which appears to be consistent with what would be expected to be found in marine snow that contains many types of organismal and other materials (Alldredge and Silver 1988;Holloway and Cowen 1997;Shanks and Walters 1997;Kiørboe 2000). Stable isotope studies indicate that leptocephali probably do not consume all types of POM or do not assimilate everything they consume (such as fecal pellets), and their isotopic signatures and trophic position are not consistent with feeding on other food sources such as zooplankton (Miller et al 2013a;Feunteun et al 2015;Liénart et al 2016).…”

Assemblage structure, vertical distributions and stable‐isotope compositions of anguilliform leptocephali in the Gulf of Mexico

“…Isotopic variation was evident among leptocephali collected in the GOM and off NC. This variation could be driven by differences in the baseline POM, as well as regional variability in the nutritional quality of POM assimilated by leptocephali (Lienart et al ). The δ 13 C values (−26 to −18‰) of leptocephali collected in the GOM were comparable to coastal GOM larval fish species that derive their carbon from phytoplankton (Thayer et al , ), thus supporting a diet consisting of material at or near the base of the food chain.…”

“…Feunteun et al () noted that leptocephali in the western Indian Ocean might feed on different POM components depending on region, depth and season. In the South Pacific Ocean, Lienart et al () reported geographic differences in both POM and leptocephali. An alternative explanation for differences in δ 13 C values may be due to different assimilation times of food or leptocephali assimilating POM differently (Lienart et al , ).…”

“…In the South Pacific Ocean, Lienart et al () reported geographic differences in both POM and leptocephali. An alternative explanation for differences in δ 13 C values may be due to different assimilation times of food or leptocephali assimilating POM differently (Lienart et al , ). The guts were empty for the majority of GOM leptocephali and perhaps these larvae fed on POM at some time prior to our collections.…”

“…As food items had not been identified from leptocephalus guts, an early hypothesis was that leptocephali did not actively feed, but instead absorbed organic carbon (Hulet, 1978;Pfeiler, 1986). Subsequent studies, however, found that leptocephali do feed on various types of particulate organic matter (POM; Feunteun et al, 2015;Liénart et al, 2016;Miller et al, 2011Miller et al, , 2013, which can include marine snow-related items such as faecal pellets, larvacean houses (Feunteun et al, 2015;Govoni 2010;Miller et al, 2011;Mochioka & Iwamizu, 1996;Otake et al, 1993) and protozoa (Govoni, 2010). This diet suggests that leptocephali could be important routes for the recycling POM in the open ocean (Miller et al, 2013).…”