IDENTIFICATION, DISTRIBUTION AND AQUACULTURE OF THE WESTERN HEMISPHERE MUSSEL Mytella charruana IN THE PHILIPPINES  

Beginning early 2014, mussels were found by shellfishers different from native Philippine mytilids, Perna viridis, Modiolus philippinarum and M. modulaides (=M. metcalfei) in Manila Bay (14.46^oN, 120.89 ^oE) and in Western Tambac Bay (16.28^oN, 119.92^oE) in July 2014.  These mussels with a black periostracum were later reported (Feb 2015) in the Calmay River Estuary 16.0272^oN, 120.3147^oE  near the village of Tucok (Dagupan City) with subsequent reports in Longos, San Fabian, Pangasinan (16.12^oN, 120.39^oE) in February 2016.

About 50 mussels from Tucok were preserved in 95% ethanol and sent to the University of Maine for genetic evaluation using amplified mtDNA sequences coding for cytochrome oxidase 1 (mtCO1) using universal LCO and HCO primers, and sequenced with LCO primers.  P. viridis and Modiolus brasiliensis are the closest outgroups to the Mytella phylogeny, with the latter having closest sequences.  Comparison of the Philippine mussels (P4.1 LCO) was made to sequences from deSouza et al. (2015)¹ of two divergent sequences of female mtCO1 lineages in Mytella that are distinct from another divergent male lineage using M. brasiliensis as the outgroup.  Using Basic Local Alignment Search Tool (BLAST), there is a 100% identity match over ~600 bases to Haplotype B of Mytella charruana, the Charru mussel, that has a range on the Pacific coast of the Americas from Guaymas, Mexico to Ecuador, and also introduced to the Atlantic coast of the USA at Jacksonvile, Florida in 1989.

All sites with Charru have considerable seasonal salinity fluctuations (2-30ppt) and stratification during the dry season, but are primarily within mesohaline and polyhaline salinity regimes.  Salinity tolerance studies showed that they die at salinities above 30ppt. Charru mussels set on traditional Philippine spat collectors designed for culture of P. viridis.  Prices fetched in local markets is comparable P. viridis, suggesting good commercial viability for aquaculture.

¹deSouza et al. 2015. Estuarine, Coastal & Shelf Science 156:165-174.