Evaluation of red snapper Lutjanus campechanus trophic dynamics with simultaneous stomach content and stable isotope analysis

Abstract

The importance of multiple prey taxa to red snapper Lutjanus campechanus diet was investigated using simultaneous stomach content analysis (SCA) and stable isotope analysis (SIA) over a 2 yr period in the north-central Gulf of Mexico (GOM) across 3 depth strata and 3 artificial structure types. Stable nitrogen isotope values were also used to estimate the trophic positions (TPs) of red snapper and prey items. SCA results showed that a variety of taxonomic prey groups were consumed, but the most frequent prey were stomatopods, portunid crabs and several families of fish. Some isotopic differences were found between red snapper size and age classes and across habitat types and depth strata for each sampling year; however, no consistent differences were found across the entire study period. Stable isotope mixing model results showed that diet varied annually, with sciaenid fishes being the greatest contributor in 2016 and portunid crabs in 2017, with the remaining proportions split across other taxa. Red snapper TP ranged from 3.4 to 4.8, while that of most prey groups was highly variable. The consistency in red snapper isotope values and the isotopic inconsistency of prey groups suggests that individual red snapper feed evenly across a taxonomically and isotopically diverse prey field. These results help develop a better understanding of reef ecology and food web structure in the northern GOM. Future investigations of red snapper diet that characterize reef habitats in terms of the available prey field and environmental conditions would improve our understanding of its trophic role in reef food webs.