An investigation of habitat connectivity of ‘Potamon fluviatile lanfrancoi’ over time

Abstract

The purpose of this study is to investigate the habitat connectivity of the endemic Maltese freshwater crab, Potamon fluviatile lanfrancoi, over time. This was achieved by investigating both its (i) spatial and (ii) temporal distribution and by (iii) conducting semi-structured interviews with local farmers and elderly locals from Baħrija, San Martin, and Wied il-Lunzjata in Gozo. For investigating the (i) spatial distribution of the species, burrow dimensions, burrow orientation and sediment type were recorded along transects in three sites, namely Baħrija, San Martin, and Wied il-Lunzjata. The burrow dimensions ranged between 2cm to 14.5cm in height and 2cm and 14cm in width; the most common burrow orientation curved eastwards, while the most common burrow sediment types were friable rock and dry soil. Furthermore, the valley width of Baħrija and Wied il-Lunzjata was observed to decrease downstream due to the steeper valley embankments, which also exhibited a lower number of burrows than found upstream. For the (ii) temporal distribution of the species, orthophotos of the three sites from the years 1950s, 1998 and 2012 were compared so as to identify the overall habitat change over time which revealed an increase in houses and roads in their surrounding areas. Moreover, a hydrology and habitat connectivity map identified the connectedness between Ġnejna and Binġemma, and l-Imtarfa and Marsa which are recorded habitats of the species. The (iii) semistructured interviews which were conducted revealed how freshwater quantity has decreased over time, and how the interviewees regarded the species in a positive or a neutral way. The results obtained suggest that the connectivity which exists between habitats of P. fluviatile lanfrancoi might have facilitated its natural expansion over time, especially due to the wetter climate and abundant springs which were present 200 years ago, however nowadays the connectivity is much lower due to human-induced barriers and activities, and the changes in hydrology and climate.