Proceedings of the Second Mediterranean Symposium on Marine

PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)
170
Statistical procedures
Fig. 1: Studied
area and
sampling
localities. Dots
are impacted
localities (1-6)
and arrows are
controls (7-12).
Effects <strong>of</strong> human disturbance and depth were tested on species richness and total
coverage by using 4-way analysis <strong>of</strong> variance (ANOVA): anthropogenic disturbance
(impacted and control) and depth (5 and 10 m) were considered as fixed and orthogonal
factors, locality (6 levels), nested in condition, and site (3 levels), nested in locality, as
random. Cochran’s test was used to examine a priori <strong>the</strong> homogeneity <strong>of</strong> variances.
Multivariate patterns <strong>of</strong> macroalgal assemblages were displayed by non-metric
multidimensional scaling (nMDS); data were 4 th root transformed and <strong>the</strong> similarity
matrices were built with Bray-Curtis index, considering locality centroids (<strong>the</strong> mean
coverage values <strong>of</strong> each taxon in <strong>the</strong> 3 sites <strong>of</strong> each locality).
Taxa contributions to dissimilarity between impacted localities and controls at both
depths were assessed by PRIMER SIMPER routine (Clarke and Warwick, 2001). Pattern
distribution <strong>of</strong> <strong>the</strong> invasive species C. racemosa was analysed by using 4-way ANOVA. A
posteriori comparison <strong>of</strong> levels <strong>of</strong> significant factors was performed by SNK test.
RESULTS
Two-hundred and sixteen quadrats were observed and a total <strong>of</strong> 61 conspicuous taxa
were identified. The number <strong>of</strong> taxa per quadrat ranged from a minimum <strong>of</strong> 3 to a
maximum <strong>of</strong> 15 and <strong>the</strong> total algal coverage per quadrat varied between 40 and 100%;
mean values per locality varied between 5.6 ± 2.1 and 10.8 ± 1.8 for species richness
and between 71.4 ± 14.5 % and 100 ± 0.0 % for algal coverage (Fig. 2); no significant
differences were found in relation to disturbance and depth, while both variables varied
among localities and sites within localities (Table 1).