Morphometric traits of lschyromene lacazei Racovitza, 1908 (Isopoda: Sphaeromatidae) differ between artificia and natural littoral hard surfaces in a Western Mediterranean location

The effect of artificial structures on littoral communities is well characterized regarding abundance and species composition, but the alterations of the fitness or the reproductive performance of individual species remains less well known. We compared 276 specimens from two populations (one living on an artificial seawall and another on a natural rocky shore) of the locally dominant isopod lschyromene lacazei based on their morphometric characteristics and growth pattern. The population dwelling on the artificial surface showed lower values for all the body dimensions. In both populations, growth pattern was negatively allometric concerning body length related to cephalic size and pleotelson width, and positively allometric for pereon and pleon lengths. Pereon of individuals from natural surface became proportionally larger with length and the difference was most remarkable with respect to width, since growth was negatively allometric in the population from the man-made surface and positively allometric on that from the natural one. Previous research related smaller body size with lower reproductive output and metabolic fitness in isopods, so it can be concluded that the population on the seawall was negatively affected by environmental condition. The cause of the difference in size was not identified, but might be related to a stronger water flow on the artificial surface.