First Report of the Non-Indigenous Irus Sp. (Bivalvia: Veneridae) from the South Harbor of Manila Bay, Philippines

Abstract

The presence of Irus sp. has been recorded in various locations in the Indo-Pacific, Western Asia, and various countries in Europe. This study reports the first identification of the non-indigenous Irus sp. (Bivalvia: Veneridae) in Manila Bay, Philippines. This identification is crucial in assessing and understanding their interaction with the port’s ecosystem. The abundance of the bivalve was determined based on a research project’s surveillance and morphological features of the bivalve shells were described. Molecular identification was done using DNA barcoding of the COI gene and phylogenetic analysis. Results showed that Irus sp. was present in all sampling collections during the 2-year duration of the project. It has a relatively low to moderate abundance (6.21% - 34.04%) in 2021 and an increase in relative abundance (11.81% - 54.19%) was observed in 2022. It is unclear how Irus thrive well in the port of Manila since there is a lack of in depth-studies regarding their ecology. However, it is possible that they can tolerate anthropogenically-disturbed environments like that of Manila Bay ports. Meanwhile, DNA barcoding revealed >99% match between the study specimens and two species of Irus sp. (Irus irus and Irus macrophylla). Its shell characteristics fit the description of Irus sp. but there were no observed morphological distinctions between the two species. Further, phylogenetic analysis showed polyphyly of the Irus clade. A large barcoding overlap was observed and this may confound the finding that the collected Irus sp. indeed belongs to two different species. Both the occurrence of polyphyly and absence of barcoding gap call for further taxonomic evaluation of the genus. The findings of the study warrant the need for constant monitoring of its abundance, research on its physiology and behavior, and risk assessment of its invasive potential.