Map of Argentina and study region indicating the positions of survey sites and the distribution of species range limits.

<p>Numeric codes for sites as used in other figures with corresponding location details listed. Province and transition zone borders are indicated by dashed lines. Shaded region indicates transition zone. The distribution of species range limits along the study region: Data for shallow water mollusks are from a database of biogeographical distributions of more than 932 species along the southwest Atlantic from 10 to 55°S (P. Pappalardo, unpublished data). Distribution data compiled from intensive literature search. The figure plots the percentage of species with southern and northern range endpoints for each latitudinal band (1 degree bins) between 36 and 46°S, the limits of our study region. Data for intertidal invertebrates and algae come from the one-time field surveys described in this study. The peak of range boundaries occurs in the transition zone.</p

Mean percentage cover (± SE) of dominant sessile functional groups of the low, mid-low, and mid intertidal zones.

<p>Note the different y-axis scales used. The shaded background indicates those sites within the biogeographical transition zone. ND = no data.</p

Mean number of species per 0.25 m² (± SE) of dominant sessile functional groups of the low, mid-low, and mid intertidal zones.

<p>Note the different y-axis scales used. The shaded background indicates those sites within the biogeographical transition zone. ND = no data.</p

Summary of documented changes in abundance of functional groups and their coincidence (yes/no) with biogeographic limits.

*<p>Multivariate characterization of community structure based on biomass of functional groups.</p><p>NA = not evaluated.</p><p>? = unknown.</p

Nested ANOVA tests of overall species richness in relation to region (Argentinean Province, Magellanic Province and Transition Zone) and among-site differences for a) low, b) mid-low, and c) mid intertidal zones.

<p>Bold values are significant at α = 0.05.</p

Dendogram depicting sites numbered 1–20 from north to south for low, mid-low, and mid intertidal zones.

<p>Biogeographical regions are coded by coloured symbols.</p

Nested ANOVA tests of functional group abundances in relation to Region (Argentinean Province, Magellanic Province and Transition Zone) and among-site differences for a) low, b) mid-low, and c) mid intertidal zones.

<p>Bold values are significant at α = 0.05.</p

List of identified genera assigned to the different functional groups.

<p>List of identified genera assigned to the different functional groups.</p

Mean number of species per 0.25 m² (± SE) of dominant mobile functional groups of the low, mid-low, and mid intertidal zones.

<p>Note the different y-axis scales used. The shaded background indicates those sites within the biogeographical transition zone. ND = no data.</p

Relationship between mean species number across sites and the coefficient of variation of biomass among sites across the region for individual functional groups across the different intertidal zones.

<p>Relationship between mean species number across sites and the coefficient of variation of biomass among sites across the region for individual functional groups across the different intertidal zones.</p