Trophic pathways supporting a marine-estuarine-dependent species of fishery importance in the eastern Pacific

Abstract

Ecological modeling using stable isotopes combined with network analysis provides a holistic view of how different trophic pathways support the productivity of fishery species. The yellow snapper Lutjanus argentiventris is a species with high abundance and frequency in mangrove creeks of the central Pacific, Colombia, where it remains in its juvenile stages and has a high fisheries importance. Stable isotopes (δ13C and δ15N) and network analysis were used to analyze the food web of this species in a mangrove estuarine system. We collected 75 specimens of three size classes, small (4 to < 10 cm), medium (10–20 cm), subadults (> 20 cm). The snappers δ13C values were between –25.8 to –21.4%0 and between 9.3 to 11.2%0 for δ15N. We also analyzed 226 isotopic data from prey specimens (> 20): omnivorous-shrimps, detritivore-shrimps, herbivore-crabs, omnivore-carnivore-crabs, porcelain-crabs, benthic and subtidal fish. Prey values for δ13C were between –27.5 to –19.1‰ and for δ15N between 2.1 to 10.0‰. Smaller-size juveniles were different in δ13C compared with medium-size juveniles and subadults; which didn’t show differences between them. Trophic position (TP) of all specimens was between 3.6 and 4.1, with few variations between size classes, indicating that L. argentiventris is a predator moving between the third and fourth TP. Simmr analysis for all specimens indicated that the highest probability contribution were from benthic fish (x̅ = 28% BCI:12–42%), detritivore shrimps (x̅ = 25% BCI:13–35%) and subtidal fish (x̅ = 12% BCI:2–24%). The network analysis showed that the food web involving L. argentriventris consists of 16 trophogroups and a total of 72 connections tending to be homogeneous. A modularity analysis showed that there are four trophic communities along this food web. This work provides evidence that the mangrove food web is highly complex despite only modeling a single top predator species.

Keywords

• Stable isotopes
• Lutjanus argentiventris
• Isotopic composition
• Trophic dynamics
• Colombia