DNA metabarcoding reveals the diet of the invasive fish Oreochromis mossambicus in mangroves of Sao Tome Island (Gulf of Guinea)

Invasive species can trigger profound effects on recipient ecosystems, namely through the food web. Despite being recognized as one of the worst invasive species, little is known about the feeding ecology of the Mozambique tilapia Oreochromis mossambicus. To understand how this invasive species might impact food webs, we applied metabarcoding to analyze its diet's composition in two African mangroves, in the Obo Natural Park in the oceanic island of Sao Tome. Given the particular importance of mangroves as fish nurseries, we specifically aimed to determine if this invader might predate on other fish species. However, we found that tilapia were mostly phytoplanktivorous and indication on predation of other fish was very limited. Instead, due to their local high densities, tilapia may impact basal trophic levels and nutrient availability with the potential to cascade through the food web by means of bottom-up disruption. In addition, we recorded important changes in the taxonomic composition of the diet, linked to locations and life stages, suggesting that its opportunistic feeding associated with its aggressive territorial behavior may result in resource competition with native species with which it has overlapping dietary niches.