The occurrence of Potamon species (Decapoda, Brachyura) relative to lotic stream factors in Greece

This paper shows the current distributions of species of Potamon in Greece, and evaluates the effects of stream order and distance from the mouth of the river on the distributions of the species in river drainages. We present new records of Potamon fluviatile (Herbst, 1785) in the Kalamas, Aheron, and Arachthos river drainages in southwestern mainland Greece; and in the Pinios, Piros-Tethreas, Pamisos, and Evrotas drainages in Peloponnesos, Greece. Our collections of Potamon ibericum (Bieberstein, 1808) in the Strymon-Aggitis drainage indicates the presence of its populations in these river systems since previous studies. The average crab occurrence (average = 0.26) at lower river km (range = 0-150 km) was significantly greater than that (0) at higher river km (range = 151-450 km). Likewise, average crab occurrence (average = 0.26) in lower stream orders (1st and 2nd) was significantly greater than that (0) at lower stream orders (4th and 5 th). Water temperature may be involved in limiting crab distributions in rivers as lower temperatures were correlated with greater distances from the river mouth where fewer crabs were encountered.