High incidence of exotic ostracods in the rice fields of a protected Mediterranean wetland

Mediterranean rice fields are human-impacted temporary waterbodies filled during summer, a hot period with scarce rains, that are susceptible to biological invasions. These anthropogenic ecosystems have been previously identified as potential gateways for exotic ostracods to colonize nearby wetlands. In this work, we compared the rice field ostracod composition with a shallow lake in a protected Mediterranean wetland (Albufera N2000 site, Eastern Iberian Peninsula). We found 37 ostracod species, 13 of which were considered exotic. Rice fields harbored the highest number of both native and exotic ostracod taxa (16 and 12 species, respectively). Our hypothesis that exotic species were more abundant during summer while native species dominated the community in winter was confirmed by the analysis of temporal changes along the rice field cycle. Comparing the ostracod composition of rice fields with that of the littoral and central parts of the hypertrophic Lake Albufera showed a clear differentiation according to a spatially constrained cluster analysis, with the richest ostracod community corresponding to the rice fields and the lowest species richness to the center of the lake, where vegetation was scarce. Finally, we suggest some criteria for considering an ostracod species as native or exotic when its origin is unknown and discuss the potential origin of the exotic species found, the pathways they might have used to arrive and establish in new areas, and the biological traits that may facilitate the spread of ostracods over new areas after their arrival.