Behavioural adaptation of Talitrus saltator populations to beaches with different dynamics and degree of human disturbance along Tunisian coasts

The sun orientation of five populations of Talitrus saltator (Montagu 1808) was investigated on sand beaches along the northern and eastern Tunisian coasts, which had different dynamics and impacts and had not yet been studied in this respect. The tests were performed on the beaches immediately after sampling at different times of the day, and environmental factors were recorded at the same time, which may influence orientation. The populations from Cap Bon and eastern Tunisian coasts, where the beaches are relatively protected and still in a pristine state, had the best performances both considering the deviations of the samples from the expected seawards directions and their concentration around the means. On the other hand, the populations from the more exposed and impacted beaches of the north-western coast had both higher dispersion and deviated significantly from the seaward direction. The latter populations, which were collected in two locations on the same coast submitted to different degrees of human impact and occupations by tourism activities, were compared using a multivariate analysis adapted to angular data (Spherical Projected Linear Models). Air humidity, the time of the day and sampling location were shown to influence significantly the orientation of the samples, temperature differences having a minor effect. These results permit to infer on the effect of human impact on amphipod orientation, also by taking into account the variation due to changing environmental factors.