Reproductive traits of a nonindigenous amphipod associated with alternative habitat structures in presence of an invasive ecosystem-engineering polychaete

Understanding reproductive traits of invasive species and their modulation by different invaded habitats is crucial for monitoring invasive processes. The invasive ecosystem engineers (IEE) affect their habitat structure, generating cascading effects that may modulate their own or other species’ reproductive traits. In this study, we aim to evaluate the reproductive activity of a nonindigenous species (NIS), the amphipod Melita palmata , in a SW Atlantic coastal lagoon whose habitat structure has been modified by the IEE (reef builder) Ficopomatus enigmaticus . Experiments showed that: (1) the frequency of M. palmata mate pairings (reproductive rate) is higher in reefs built by the IEE than in the facies formed by sediment and valves in reef-free areas (namely sediment); (2) the ratio of mate pairings relative to receptive available females (mate access ratio) is higher in sediment; (3) higher density of M. palmata increases its reproductive rate in both habitats, and (4) lower M. palmata density and reduced habitat structure enhance the mate access ratio. Results suggest that M. palmata reproduction is either density- or habitat-dependent at higher or lower population densities, respectively. This reproductive plasticity might contribute to the permanence of NIS in new systems, the recognition of new habitats, and counteract potential reproductive isolation.