Talitrid (Crustacea, Amphipoda) orientation as across scale bioindicator of sandy beaches environmental conditions: A meta-analytic approach

Sand-hoppers and beach-hoppers (Amphipoda, Talitridae) are well known as key species of sandy beach ecosystems. Behavioural traits (e.g., orientation) and their variation have been extensively studied in different contexts and proposed as bioindicator of impacts on coastlines. To assess the common sun orientation strategy and its potential use as across-scale bioindicator, a meta-analysis was conducted on a large dataset of observations on talitrid orientation, including beaches in the Mediterranean and Eastern Atlantic coasts. The metaanalysis was conducted through a machine learning application by creating ''virtual talitrid orientation” trained with data from beaches of the considered geographical areas and various environmental conditions. Then, the orientation of virtual talitrids was tested on different test sets. In each of the test conditions, the results showed the presence of a dominant direction towards the sea, while the distribution of deviations from the dominant direction corresponded to a random distribution. Meteorological variation or changes in beach morphological features influenced the orientation, causing changes in the orientation angle distributions. The main difference was the variability of orientation around the dominant direction, which was greater in Mediterranean beaches with respect to Atlantic ones. A possible explanation is the lower tide excursion and wind power and the greater variation in exposure of the Mediterranean beaches with respect to the Eastern Atlantic ones, where talitrid orientation showed a more rigid adaptation to beach physical features. The consistency of talitrid orientation can be used as a reference standard for management, revealing natural and/or anthropogenic disturbances at different scales, from local/regional to geographical.