Combined use of carbon, nitrogen and sulfur stable isotopes reveal trophic structure and connections in deep-sea mesopelagic and demersal fish communities from the Southeastern Pacific Ocean

The trophic structure of deep-sea fish communities has been poorly studied in the Southeastern Pacific Ocean. Here, using the analysis of multiple (CNS) stable isotopes, we provide a first approach to characterize the structure of a marine food web including mesopelagic (9 species) and demersal (13 species) fishes. At a species level, Dissostichus eleginoides were the most 13C-depleted and the grenadier Coryphaenoides ariommus the most 13C-enriched species. The most 15N-depleted species was the lanternfish Diogenichthys laternatus and macrourid fishes Trachyrincus villagai and C. ariommus the most 15N-enriched. 834S values showed less variation, but ranged considerably, varying between 10.5 and 17.7 & PTSTHOUSND;: C. ariommus was the most 34S-depleted species and D. eleginoides the most 34S-enriched. At a whole study level, individual 813C and 815N values were positively correlated. Re-lationships between 813C and 834S, and 815N and 834S were both negative. When analyses were conducted separately for demersal and mesopelagic fishes, 813C showed a positive correlation with 815N. There was a negative relationship between 813C and 834S in demersal fish but no apparent relationship between 815N and 834S. In mesopelagic fishes, there was no statistical support for relationships between 813C and 834S or 815N and 834S. Mean log-transformed total length (TL) and mean 815N were related in mesopelagic fishes, but there was no apparent relationship between TL and 813C or 834S values. In the case of demersal fishes there was no rela-tionship between TL and either 815N, 813C or 834S. Using cluster analysis, species were classified into 4 distinct trophic groups (G1 -G4) that display different trophic strategies according to the literature. Groups G1 and G2 included zooplanktivorous, micronektonivorous and gelatinovorous fishes associated with pelagic habitats. Groups G3 and G4 include micronektonivorous, piscivorous and generalist fishes foraging in benthic habitats. The demersal fish Dissostichus eleginoides was classified as a member of G1, suggesting that its diet in northern Chile is likely dominated by pelagic prey. In addition, Macrourus holotrachys (G3) showed very marked individual variability in 815N values indicating considerable intraspecific variation in diet and foraging behavior. Given that this species had isotope values that extended across values typical of benthic and pelagic habitats, it suggests that some individuals may perform vertical migrations. Our results also highlighted that some demersal species (M. holotrachys and Coryphaenoides ariommus) had & delta;34S values that indicate the assimilation of some chemosynthetic-derived sulfur.Our results provide isotopic information on deep-water species in this region and show likely coupling be-tween the demersal and mesopelagic assemblages. This information improves our understanding of deep-sea ecosystem functioning and provides key information for fisheries management and conservation initiatives.

Automated summary

Using stable isotope analysis, this study provides the first characterization of the trophic structure of deep-sea fish communities in the Southeastern Pacific Ocean. The results indicate a correlation between carbon assimilation and nitrogen assimilation, as well as a relationship between body length and nitrogen assimilation in demersal fishes. This information enhances our understanding of deep-sea ecosystem functioning and has implications for fisheries management and conservation initiatives.