No geographical variation but strong microhabitat partitioning: integrative taxonomy and infestation ecology of Octolasmis barnacles on Scylla serrata across three Indonesian ecoregions

Abstract

Species identification of Octolasmis barnacles on mud crabs based solely on morphology can be challenging, and whether infestation parameters vary geographically across the vast Indonesian archipelago remains unknown. This study integrated morphological taxonomy and DNA barcoding using the cytochrome c oxidase subunit I (COI) gene to identify species and compare the infestation ecology of Octolasmis on Scylla serrata across four locations representing three Indonesian ecoregions: Singkawang and Tanah Laut (Sunda Shelf), Donggala (Wallacea), and Teminabuan (Papua). A total of 240 crabs (60 per location) were examined. Phylogenetic analysis confirmed the presence of two morphospecies, Octolasmis cor and O. angulata. However, Bayesian Poisson Tree Processes (bPTP) species delimitation analysis revealed potential cryptic diversity, partitioning O. cor into four distinct lineages and O. angulata into three lineages (support values 0.951–1.000). Generalized linear models with Bonferroni correction showed no significant differences among locations for prevalence, intensity, or abundance (P>0.05). O. cor exhibited higher prevalence (85%) and intensity (40.2±8.7) than O. angulata (72%; 15.1±4.3). Co-infestation recorded the highest intensity (62.0±12.1). Paired t-tests demonstrated that both species had a significant preference for the hyperbranchia over the hypobranchia (P<0.001). These findings confirm that Octolasmis infestation parameters on S. serrata are homogeneous across the ecoregions studied, suggesting that control strategies could potentially be implemented nationally. However, the cryptic lineages detected by bPTP warrant further investigation with additional genetic markers and broader geographic sampling.