Mytella charruana a native mussel species found in South America, Atlantic and Pacific coastlines. Recently, this species was observed to co-occur with a native mussel Perna viridis, in Bolinao, Pangasinan, Philippines. Nonnative mussels in novel environments may pose a threat to native mussels since they can compete for food and space. One way of assessing which species may dominate and persist over time is by comparing the reproductive parameters of both natural populations exposed to the same local environmental conditions. This was conducted through monthly sampling per mussel species in experimental mussel lines in traditional culture area of P. viridis. The size frequency distribution of both populations was compared over time to determine timing of recruitment. Samples per size frequency was dissected to determine size at sexual maturity and sex ratios. Initial results showed that spats of M. charruana was highest during the month of June while spats of P. viridis were highest in July. Dissected samples showed that M. charruana matures earlier (9mm) compared to P. viridis (11mm). Since M. charruana recruit first, it could limit the space available for of P. viridis to settle and grow. If growth, survival rates and reproductive period of M. charruana is higher over time, this could give it a competitive advantage over P. viridis. Further studies determining physiological resilience to the seasonal variability as well as changing environmental conditions associated with climate change will be essential to evaluate the ecological and economic impacts of M. charruana in Bolinao, Pangasinan and other recently reported areas i.e. SE Asia.