Population ecology of the barnacle Chthamalus stellatus in the northwest Mediterranean

Abstract

This study examined patterns in the distnbution and demography of the barnacle Chthamalus steiiatus (Poli) at different spatial scales in the northwest Mediterranem. Prelirninary data indicated that the abundance and size of barnacles decreased from high-shore to low-shore habitats. The generality of these patterns was investigated at several locations (10s to 100s of km apart), at several sites within locations (100s to 1000s of m apart) and at different times. Patterns were consistent with the prelirninary observations, despite considerable spatial and temporal variabiiity at smaii and large spatial scales. The foliowing models were proposed to explain the observed patterns: (1) recruitment was intnnsicaiiy greater high on the shore, (2) limitation of recruitment due to pre-emption of the substratum was greater low than high on the shore, (3) environmental conditions reduce growth low on the shore, and (4) mortality was greater low on the shore. The predictions of these models were tested by examining patterns of recruitment, growth and mortality of barnacles and avaiiability of free space in relation to height on the shore, at several spatial scales and through time. Successful recruitment of barnacles was observed at different heights on the shore where resident organisms were removed, despite a trend toward a larger number of recruits high on the shore at 1 location (Livorno). Availabiiity of bare rock for recruitment was greater high on the shore, implying that pre-emption of the substratum was more intense low on the shore. There was no evidence to suggest that barnacles grew faster on the high shore than on the low shore. The opposite pattern was observed for young barnacles in several cases. Mortality rates were generally greater in low-shore than high-shore habitats for young and for adult barnacles. Patterns emerged over a background of considerable spatial and temporal vanation. These results emphasized the importance of pre-emption of space and mortality of juveniles in generating patterns in the distnbution and structure of populations of barnacles on rocky shores in the northwest Mediterranean.

Variability in abundance of algae and invertebrates at different spatial scales on rocky sea shores

“…Regional patterns were largely due to the low abundance of cyanobacteria and barnacles at Punta Bianca, the northernmost shore in the study, which also supported more mussels than the other shores. In a previous study, Benedetti-Cecchi et al (2000b) found considerably more variation in patterns of growth of barnacles among shores 10s to 100s of km apart than among quadrats 10s of cm apart. There was also considerable variability in recruitment of barnacles at the regional scale, although recruitment was much more variable among quadrats.…”

“…Variation among tidal heights was significantly larger than horizontal variability at the scale of the patch for these organisms. Previous studies have shown that pre-emption of the substratum and postrecruitment mortality due to unknown processes can account for the decline in cover of barnacles from the top to the bottom of the shore , 2000b. Variation in recruitment might also contribute to these differences, as observed elsewhere (Grosberg 1982).…”

Changes in temporal variance of rocky shore organism abundances in response to manipulation of mean intensity and temporal variability of aerial exposure

“…This result was in agreement with theoretical modelling and empirical laboratory studies indicating that when fluctuations in environmental forcing variables are strongly autocorrelated in time or space, long-lasting negative conditions for species persistence become more likely and this can increase the risk of extinction of organisms (Heino 1998, Pike et al 2004). Alternatively, the large fluctuations in abundance of Chthamalus stellatus observed under reduced variability of aerial exposure might be determined by chance effects, like the coincidence of aerial exposure with the timing of recruitment of barnacles (between May and August on our shores, Benedetti-Cecchi et al 2000). In this scenario, effects of the sequence of events rather than temporal variability per se would have driven temporal variance in the abundance of barnacles.…”

Patterns of distribution of marine assemblages from rocky shores: evidence of relevant scales of variation

“…Only a few papers quantified the relative contribution of newly settled, juvenile, or adult organisms to the distributional patterns of the same species, also distinguishing brooders from free-spawners (Åberg & Pavia 1997, Hyder et al 1998, Hughes et al 1999, Benedetti-Cecchi et al 2000, Jenkins et al 2000. There are 3 papers (Fowler-Walker & Connell 2002, Irving et al 2004, Kelaher et al 2004) that have examined spatial patterns over very broad spatial scales (1000s of kilometers), at the expense of detailed middle and/or small-scale analyses.…”