24 February 2017

First record of a potentially invasive mussel Mytella charruana in Manila Bay

Human activities have, in many unprecedented ways, accelerated biological shifts and nuances in our planet. Such is the case for Manila Bay and its inhabitants. A slew of anthropogenic activities such as land and sea-based transportation, sedimentation, fisheries, and reclamation and land conversion has put the ecosystem at high risk for biological invasions.

Meet the Charru mussel Mytella charruana, a newly reported species in Manila Bay, which has been previously documented to be invasive in Florida. A team of researchers led by Dr. Benjamin Vallejo (University of the Philippines Diliman) and SeaLifeBase staff, Jeniffer Conejar-Espedido (University of the Philippines Los Banos) confirms its first recorded presence in the area. Previously identified as Mytilus spp., the bivalve was later identified via DNA barcoding to be Mytella charruana, suggesting its phylogenetic position within the Perna clade. Increasing trend in its abundance from 2014 to 2015 indicates likelihood of establishment and probable competition with the native mussel Perna viridis.  

What makes the species different from Perna and Modiolus is its dark bluish to brown hue and a bluish to purplish nacreous interior. It is also bigger (average of 2.8 cm shell length) compared to another non-indigenous mussel in the area, Mytilopsis, which only grows to 1 cm SL.

Mytella charruana from the Manila Bay PICES
collectors. Photographs by J. Conejar-Espedido.
How did M. charruana reach Manila Bay?

Researchers suggest it is likely to have been introduced via ballast water or through fouled ship hulls. Since mytilids in general adapt and highly reproduce in estuarine and coastal conditions, the persistence of M. charruana is likely.

The spat was first observed at the start of southwest monsoon rainy season. Assuming it has a similar life history profile as that of P. viridis, its introduction must have occurred between late April and early May 2014. This suggests possible competition between the two species. The increasing abundance of M. charruana also indicates its establishment in Manila Bay, but this is yet to be verified in succeeding years. How it could affect the populations of the native P. viridus is, however, is unknown. Further studies on the reproduction, ecology, community dynamics and population genetics are recommended.

Dr. Vallejo’s team also includes, Leanna Manubag, Kevin Carlo Artiaga, Amor Damatac II, Ivan Christian Imperial, Tyrll Adolf Itong, Ian Kendrich Fontanilla and Ernelea Cao.