The ecological role of Pholas dactylus (Mollusca, Bivalvia) empty burrows

The study of biological rhythms has been widely explored in terrestrial and marine systems. Time-lapse photography can document species behaviour, avoiding observer disturbance, and record abundance and interactions. The present work aims to assess the role of the rock-boring bivalve Pholas dactylus Linnaeus, 1758 as a habitat former in the Conero Riviera, documenting the behaviour of the species associated with the common piddock and its burrows. The scan method approach was used to record two behaviours along 6 days of recording: Burrow Interaction (BI) and No Interaction (NI). A total of 34 taxa belonging to 5 phyla were identified, each one represented by one class: Gastropoda, Polychaeta, Malacostraca, Echinoidea and Teleostei. BI data were mainly related to standing on top of burrows, entering or leaving the burrows, or digging to keep it clean, with Gastropoda, Malacostraca and Teleostei displaying distinct activity patterns. The use of video monitoring enabled the analysis of species activity across diel cycles, highlighting the ecological value of the burrows created by P. dactylus and its role as an ecosystem engineer. This also provided new insights into the behavioural dynamics of benthic organisms associated with cryptic habitats.