Scotia Arc bryozoans from the LAMPOS expedition : a narrow bridge between two different faunas

The known Magellan bryozoans total more than 220 species. Those of the Antarctic Peninsula also reach a similar total. Endemism of the former is about 55%, whereas that of the latter is higher, varying from 65% to more than 90% (Moyano, 1991; Hayward, 1995). The physical links between the two bryozoan faunas are the Scotia Arc archipelagos, which might constitute stepping stones between South America and the Antarctic for dispersal and interchange of SCI. MAR., 69 (Suppl. 2): 103-112 SCIENTIA MARINA 2005


INTRODUCTION
about 55%, whereas that of the latter is higher, varying from 65% to more than 90% (Moyano, 1991; The known Magellan bryozoans total more than Hayward, 1995).220 species.Those of the Antarctic Peninsula also The physical links between the two bryozoan reach a similar total.Endemism of the former is faunas are the Scotia Arc archipelagos, which might constitute stepping stones between South America *Received April 14,2004. Accepted March io, 2005.and the Antarctic for dispersal and interchange of faunal elements (Crame, 1999;Gorny, 1999;Moyano, 1996Moyano, , 1999Moyano, , 2000;;Barnes and De Grave, 2000).
This, and other issues concerning the role of the Scotia Arc archipelagos in interactions between the Antarctic and Subantarctic ecosystems, led to the German LAMPOS cruise on board RV "Polarstern" in April-May 2002 (ANT XIX/5; Arntz and Brey, 2003).The bryozoan collection gathered included some 80 species.
The species collected were dominated in mass by large flexible colonies of flustriform and cellariiform bryozoans, whereas the encrusting species were less abundant, forming calcareous sheets on small pebbles.A new genus and species were discovered among the former and a new species in the latter.
Preliminary results of the German LAMPOS expedition plus previously published data from several authors are employed in this work to assess the role of bryozoans in linking the Magellan and Antarctic ecosystems.

MATERIALS AND METHODS
Table 1 gives station data for the LAMPOS expedition of RV "Polarstern", which yielded bryozoans.Samples were collected by means of an Agassiz trawl and stored in an aqueous ethanol solution of at least 90%.In the Universidad de Concepcion Bryozoology Laboratory they were transferred to 70% ethanol to be sorted and identified.
Colony pieces to be photographed by SEM were boiled in a NaCIO solution, rinsed with tap water, dried from 70% ethanol and finally coated with gold.
Analysis of the zoogeographical affinity between Antarctic and Subantarctic bryozoan faunas from the Magellan area to the Antarctic Peninsula through the Scotia Arc archipelagos was performed primarily using the bryozoan faunal list obtained from the LAMPOS expedition and subsequently in combina-tion with other faunal lists by Hastings (1943), Hayward (1995) and Lopez de la Cuadra and Garcia Gomez (2000).

RESULTS
The species collected during the LAMPOS cruise are shown in Table 2 and the dendrogram comparing different Subantarctic and Antarctic stations on the basis of their bryozoans is shown in Fig- ure 1.The number of species per station varied between 5 and 21, with an average of 12.The richest station was that at Burdwood Bank (south of Falkland Islands -Mas Malvinas) with 21 spp.and the poorest stations were stns.207 and 217 off South Sandwich with only 5 spp.each.The last three stations, near Elephant island are very close, so the real number of species should be some 29.
The 78 species of Table 2 belong to ten different zoarial forms.Most frequent were the encrusting species (32%), followed by the flustriform ones (15.4%).The erect (50 spp.), rigid (18 spp.) and flexible (32 spp.) forms constitute the largest number in comparison with the encrusting (32 spp.) and the irregular plurilaminar celleporiform forms (3 spp.).The flustriform species predominate within the flexible forms and also in the number of zoaria and mass considering the whole set of species and samples.
The dendrogram (Fig. 1) shows two clear-cut sets of stations on the basis of their bryozoan species.The largest group includes 6 stations subdivided in turn into two clusters: Subantarctic stns.145 and 153 and Antarctic stns 238, 251, 252 and 253.The two sets exhibit an affinity of only 5%.The  station group 164, 207 and 217, which does not unite with the larger one, joins the most isolated places of the Scotia Arc in relation to South America and Antarctica.As these primary results do not indicate a clear pattern of bryozoan distribution along the Scotia Arc archipelagos or the relationships between South America and the Antarctic, a larger set of data, compiled from the works of several authors published over the past 60 years, was analysed (Table 3, Figs. 2 and 3  In order to further test the zoogeographical pattern shown in the dendrogram in Figure 2, an analysis of the bryozoan genera present in the Scotia Arc archipelagos was carried out in comparison with the Subantarctic Magellan region and "Australasia" sensu Mawson (i.e.Australia and New Zealand (Table 5 and Fig. 3, Appendix 2).The list of bryozoan genera in Appendix 2 does not contain all the genera known to exist south of the Antarctic Convergence, but certainly more than 85% of them.
There are also some Subantarctic genera not listed here like Sclerodomus.
The dendrogram in Figure 3 exhibits the same pattern as Figure 2, this time on the basis of bryozoan genera, showing the Scotia Arc closely united with the Antarctic Peninsula and joining the Magellan region with New Zealand and Australia.TABLE 5. -Geographical distribution of 72 cheilostomatid bryozoan genera from the Scotia Arc archipelagos in Antarctic and Subantarctic areas after the data by Lopez de la Cuadra and Garcia Gomez (2000) and Moyano (this study).MAG = Magellan area including Patagonian shelf; ANZ = Australian and New Zealand areas; ARS = Scotia Arc archipelagos; PAN = Antarctic Peninsula.Information on bryozoan genera from New Zealand and Australia after Gordon (1984Gordon ( , 1986Gordon ( , 1989) )

DISCUSSION
The role of the Scotia Arc archipelagos in the interactions between Antarctic and Subantarctic ecosystems stimulated the LAMPOS cruise on board the German research vessel "Polarstern" in April-May 2002.The bryozoan collection gathered included some 80 species that belong to two completely different groups: a Subantarctic group to the west and north of Shag Rocks and an Antarctic group originating from east and south of that archipelago.
Both groups are dominated by large flexible bryozoan colonies, namely flustriform, buguliform and cellariiform, plus some rigid forms such as eschariform and reteporiform.The encrusting species are less abundant, forming calcareous sheets on small pebbles.Most species were previously known except for two new ones.One of them belongs to a new flustrine genus and the other to the cribriline genus Parafigularia.
Systematically the links of Antarctic and Subantarctic Bryozoa are more at the generic than at the specific level although, as demonstrated above, the highest generic affinity appears between the Scotia Arc and the Antarctic Peninsula.There are some species, mostly from shallow waters, like Celleporella bougainvillei, Inversiula nutrix and Beania inermis, living in Magellan South America and at the Antarctic Peninsula (See Moyano, 1999, Moyano andCancino, 2002).More abundant are vicariant species such as Parafigularia magellanica and P. discors, Aulopocella petiolata and A. brachyrhyncha, Adelascopora stellifera and A. secunda, Austroflustra australis and A. vulgaris.However, more abundant are species endemic to each fauna.These statements result from a comprehensive analysis of all known bryozoan species, both Magellan and Antarctic.
In the bryozoans collected during the LAMPOS cruise, connections between the two faunas are almost non-existent, probably due to the collecting depths of more than 200 m.In this context, all archipelagos showed a typical Antarctic bryozoan fauna.The limit between the two faunas seems to be situated not too far off Shag Rocks, probably coinciding with the Antarctic Convergence boundary.

TABLE 3 .
FIG. 3. -Dendrogram showing the relationships among the Scotia Arc with Subantarctic and Antarctic areas on the basis of the shared bryozoan genera (Table 5, Appendix 2); MAG: Magellan area; ANZ: Australia -New Zealand realm; ARS: Scotia Arc archipelagos; PAN: Antarctic Peninsula.

TABLE 2 .
-Bryozoa collected during the LAMPOS expedition between Punta Arenas and the northernmost tip of the Antarctic Peninsula.
BRYOZOAN ZOOGEOGRAPHY IN THE SCOTIA ARC 105

TABLE 2 (
Cont.).-Bryozoa collected during the LAMPOS expedition between Punta Arenas and the northernmost tip of the Antarctic Peninsula.
H BRYOZOAN ZOOGEOGRAPHY IN THE SCOTIA ARC 109