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.
