Using DNA Metabarcoding to Uncover the Diet of the Invasive Mozambique Tilapia (Oreochromis mossambicus) in Mangroves from the Island of São Tomé ^†

Abstract

Biological invasions are considered one of the main extinction drivers of native species worldwide. Invasive species have detrimental effects on local ecosystems by means of competition, predation, habitat modification and nutrient cycling, as well as disease spreading. Along with ecological impacts, there are socio-economic consequences to human populations dependent on the services provided by these ecosystems. One of the most fundamental steps towards understanding the influence of invasive species is to determine their role on the local food web. The Mozambique tilapia (Oreochromis mossambicus) is an extremely aggressive opportunistic feeder that has a high biological and ecological plasticity, including flexible reproductive strategies (including mouthbrooding) and tolerance to a wide range of temperature, salinity and dissolved oxygen conditions. Its biological traits coupled with being used in aquaculture have made it a successful invader, widely distributed outside its native range. Yet, its populations have rarely been studied in the wild; hence, its potential impacts remain largely unknown. In this study, we investigate the diet of the invasive Mozambique tilapia in two mangroves of the oceanic island of São Tomé. We applied metabarcoding to simultaneously identify multiple taxa in tilapia gut content samples, using high-throughput sequencing. To achieve a greater taxonomic coverage, we combined the use of two barcodes, the 18S ribosomal RNA and the cytochrome C oxidase subunit I genes, to target phytoplankton and animal species, respectively. We found a total of 251 amplicon sequence variants belonging to 96 taxa. The results revealed diet differences between specimens from the two mangrove locations, not only regarding the level of biodiversity, but also in the frequencies of the occurrence of certain functional groups. Some taxa, such as diatoms, green algae and rotifers were found in the gut contents at both mangroves, whereas others, such as arthropods and mollusks, were almost exclusive to one of them. These findings provide useful insights into the ecological implications of the biological invasion of vulnerable island ecosystems, offering some specific guidance on how to minimize the impact of tilapia on the mangroves of the São Tomé Island.