The vertical distribution and abundance of Chthamalus stellatus Poli and Chthamalus montagui Southward (Crustacea, Cirripedia) at two localities of the Istrian peninsula coast (North Adriatic)

Two species of chthamalid barnacles are well established from the upper to the lower limit of the midlittoral zone on the rocky shores of the North Adriatic Sea: Chthamalus stellatus, Poli and Chthamalus montagui, Southward. The present study deals with the vertical distribution and abundance for each species at two localities of the Istrian peninsula coast (North Adriatic Sea). For this purpose chthamalid populations were monitored in 2015 along the Slovenian marine coast (Bay of Koper, Gulf of Trieste) and along the Croatian marine coast, near Rovinj (west Istrian coast), both on limestone. The main aim of the study was to establish if there was a relationship between the vertical distribution and abundance of these two species at different spatial scales: small (between sites, about 1 kilometer) and large (between localities, 10s of kilometers). The selected localities are slightly different in tidal range, in orientation and wave exposure. Three sites were randomly selected at each locality and two transects per tidal level (upper, middle and lower) were chosen on each site. The abundance of each chthamalids species in 1 dm2 plots was determined at three different tidal levels along each transect. The results indicated that the vertical distribution of C. montagui and C. stellatus was very similar between localities and even among sites, but their abundance varied. At both localities, C. montagui was more abundant in the upper and middle tidal levels, while C. stellatus was more abundant at the lower tidal level. It was also found that C. montagui was more abundant in sheltered conditions (Bay of Koper), while C. stellatus on the coast more exposed to the wave action (near Rovinj), at all tidal levels.