Orientation of crustacean burrows in the Bay of Panzano (Gulf of Trieste, Northern Adriatic Sea)

Three burrow systems produced by Jaxea nocturna and one cluster of burrows produced by Upogebia pusilla where investigated in the Bay of Panzano, Northern Adriatic Sea, to determine preferred orientations. The distributions of dip directions differ between both producers. Steep shafts into the consolidated mud followed by large, shallowly inclined tunnels oriented in a manner similar to a spiral are characteristic for Jaxea nocturna burrows. In contrast, the Y-shaped burrows of Upogebia pusilla have entrance shafts that are less steep which are connected by a near-horizontal section, where a blind ending tunnel branches. Orientations of the dominating, shallowly inclined burrow parts are not randomly distributed in either Jaxea or in Upogebia burrows. Three preferred axial orientations with almost equal proportions in each direction are characteristic for the Jaxea burrow from the centre of the bay. This system transforms to a squared structure near the coast, where one direction parallels the shoreline and the other is oriented at right angles to the coast. The latter orientation demonstrates significant constancy in all investigated burrows. Upogebia burrow clusters coincide with the three preferred orientations of the Jaxea burrow from the bay centre, but the proportions of the directions are unequal. Burrow segments connecting the steep entrance shafts in Upogebia are oriented almost parallel to the shoreline, whereas at right angles to the coast the flat blind-ending tunnels incline towards the open sea. The study shows a strong coincidence between empirical and theoretical distributions of the dominating orientations in both species.