Effective detection methods for Pectinatella magnifica Leidy 1851 colony distribution using statoblasts

A rapidly expanding range of Pectinatella magnifica has been reported globally. Although many studies have been conducted to manage this invasive species, surveying methods have mainly been limited to visual observation of bryozoan colonies. For efficient monitoring and early detection of bryozoan species, we compared three different monitoring methods: visually detecting bryozoan colonies (visual observation of colonies, VOC), floating statoblasts (statoblasts in filtered water, SFW), and attached statoblasts (statoblasts attached to artificial substrate, SAS). Using these sampling methods, we compared the occurrences of P. magnifica in the littoral zones of lotic ecosystems from 117 sites in South Korea from 2015 to 2019. Occurrence frequency of P. magnifica was higher using both SFW (37.3%) and SAS (72.5%) than the traditional VOC (28.0%) method. The agreement of occurrence detection of P. magnifica between VOC, SFW and SAS was more consistent in tributaries than in main channels. Density estimations using colony (VOC) and statoblast detection methods (SFW, SAS) also showed a higher positive correlation in tributaries. To identify early P. magnifica invasion in an unidentified area, collecting statoblasts is a more efficient alternative to determine the occurrence of bryozoan species in field conditions.