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Keywords:

  • Antarctic biogeography;
  • cline;
  • boulder fauna;
  • bryozoans;
  • sponges;
  • cnidarians

Aim

To investigate the affinities and similarities between coastal (marine) encrusting faunas along the Andes–Scotia Arc–Antarctic Peninsula mountain chain with a uniform sampling strategy.

Location

Twelve different samples sites were selected on the (southern) South American and (western) Antarctic continents. The sites spanned 25° of latitude along the Andes–Scotia Arc–Antarctic Peninsula mountain chain from Tierra del Fuego to the Ross Sea (Antarctica).

Methods

Encrusting faunal colonists were identified on rocky (boulder/cobble) surfaces constituting a total surface area of 2 m2 from each of twelve localities at depths from the intertidal zone to 12 m. Faunal suites of sites were subjected to differing but common modern analyses, Detrended Correspondance Analysis (DCA) and TWINSPAN.

Results

Typically the number of encrusting species increased with depth and decreased with isolation (remote islands, such as South Georgia and Bird Island had depauperate faunas). The proportion of the total fauna constituted by bryozoans, sponges and other taxa changed with site latitude and isolation. Ordination (DCA) of the site species data matrix revealed distinct Patagonian, Falkland and Antarctic groupings. Ordination of just the Antarctic grouping revealed a cline from the northerly and shallower sites to those more southerly and deep. TWINSPAN analysis of the same data set largely supported the ordination. Ordination at generic level showed a high degree of similarity with the species ordination pattern.

Main conclusions

The north/south, deep/shallow, cline found shows distinct faunistic patterning within biogeographic zones. The separation of sites within and outside the Polar Frontal Zone (PFZ) support more classically based historic biogeographic studies. The major difference between the findings of this study was the organization of sites into a cline vs. distinct zones. The simplest explanation for why studies yeild such different findings must lie with the considerable differences in the types of data sets used; historical records or (as here) short-term, uniform, sampling strategies.