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D.G. REID AND C. OSORIO 



dense Macrocystis beds made sampling difficult). The large mussel 

 Choromytilus chorus was not found alive, but probably occurred in 

 the shallow sublittoral. 



The giant kelp Macrocystis provides a habitat for a characteristic 

 association of molluscs in the Magellanic region. During our survey 

 we found Leptochiton medinae, Plaxiphora aurata, Fissurella oriens, 

 Aulacomya atra and Hiatella solida in the holdfasts, and a similar 

 fauna has been recorded from holdfasts further south, in the Beagle 

 Channel (Ojeda & Santelices, 1984; but also including Pareuthria, 

 Xymenopsis and a cerithiopsid). However, on the kelp lamina we 

 found molluscs to be very scarce, and only occasional specimens of 

 Nacella mytilina, Fissurella oriens and Flabellina falklandica were 

 encountered. In the Beagle Channel the kelp lamina supports a larger 

 community of molluscs, of which the most characteristic are Nacella 

 mytilina, Margarella violacea, Chlamys vitrea (King & Broderip, 

 1 832) and Gaimardia trapesina (Lamarck, 1819) (King & Broderip, 

 1832; Castilla, 1985; Waloszek, 1984; D.G. Reid, pers. obs.). 



During our survey we did not neglect to examine trawled sedi- 

 ment and washings from intertidal algae for the presence of small 

 molluscs. Nevertheless, no small rissoiform gastropods were found. 

 This is surprising in view of the 23 species, many of them intertidal, 

 belonging to the families Eatoniellidae, Cingulopsidae and Rissoidae 

 that were recorded from southern Chile and Tierra del Fuego by 

 Ponder & Worsfold (1994). Possibly the low and fluctuating salinity 

 of large parts of the Estero Elefantes fjord system might be con- 

 nected with the apparent scarcity of small gastropod species in the 

 shallow-water habitats that we examined. 



Biogeographical affinities of the molluscs 



Many different authors have discussed the marine biogeographical 

 'provinces' of the west coast of South America, basing their classi- 

 fications on various taxonomic groups, ecological systems and 

 depth ranges. Those who have referred specifically to molluscs 

 include Dall ( 1 909), Carcelles & Williamson ( 1 95 1 ), Stuardo ( 1 964), 

 Dell (1971), Marincovich (1973) and Viviani (1979), and their 

 conclusions have been summarized, and their data enlarged, by 

 Brattstrom & Johanssen (1983). In general there is agreement that 

 two provinces can be recognized to the south of the tropical zone; a 

 northern warm-temperate Peruvian Province south of about 2-6°S, 

 and a southern cold-temperate Magellanic Province from the south- 

 ern tip of the continent northwards. The boundary between these two 

 provinces has most often been placed at the northern end of Isla 

 Chiloe (about 42°S), where numerous marine invertebrates show 

 their distributional end points. Nevertheless, most authors have 

 recognized that the division is not a sharp one, and that there is a 

 broad area of overlap between species that are typical of each 

 province, so that a transitional zone can be defined, lying between 30 

 and 46°S (Brattstrom & Johanssen, 1983). Regional classifications 

 of this kind are susceptible to incomplete data and to problems of 

 sampling. They are also necessarily somewhat artificial, since the 

 geographical ranges of different taxa can be determined by various 

 environmental and biological factors, and influenced by their differ- 

 ent histories and dispersal capabilities. Nevertheless, they can provide 

 a useful summary of distributional data. 



In this context, our study area is of interest since it lies at the 

 southern end of the transitional zone (46°S), and in a region of the 

 Chilean coastline for which distributional data for molluscs is poor. 

 Most previous studies of Chilean molluscs have concentrated upon 

 the far south, the Magellan Strait and Tierra del Fuego, and on areas 

 further to the north, including Isla Chiloe (see Introduction). There- 

 fore, it is not surprising that of the 62 species we have recorded from 

 the Laguna San Rafael and Estero Elefantes, 17 (27%) are extensions 



to the known ranges. In the Systematic Descriptions we have 

 reviewed the published information on the geographical ranges of 

 these 62 species, and these are tabulated in Figure 8, with the 

 provincial boundaries of Brattstrom & Johanssen (1983) superim- 

 posed. Clearly, these data cannot be used in isolation to judge the 

 validity of biogeographic boundaries, since the sampling of species 

 is restricted to those occurring in one locality, and is not representa- 

 tive of the entire Chilean coastline. They do, however, add new 

 information to the previous compilation and demonstrate the 

 biogeographic affinities of the fauna we have studied. 



In Figure 8 we have divided the species into four categories: 

 Antarctic (extending south of the Antarctic convergence), Magellanic 

 (from Cape Horn up to and including the transitional zone, 30- 

 56°S), widespread (occurring both south and north of the transitional 

 zone, including two species extending north of the equator) and 

 Peruvian (occurring in the Peruvian Province up to and including the 

 transitional zone, 1^-6°S). The predominantly southern (Magellanic) 

 character of the fauna is apparent, since 30 species (48%) are strictly 

 Antarctic or Magellanic, and a further 26 of the widespread species 

 (42%) extend also to the south of our study area. Only five of the 

 species (8%) are strictly Peruvian. Furthermore, our records are the 

 northernmost for 11 species, and the southernmost for only 6 

 species. In their compilation of the distributions of marine inverte- 

 brates along the western coast of South America, Brattstrom & 

 Johanssen (1983) included 99 molluscan species; their list was 

 biased towards the better known Peruvian species, supporting their 

 assertion that the invertebrate fauna of Chile as a whole was pre- 

 dominantly northern in character and origin. These authors included 

 only seven Magellanic molluscs with northern limits at or to the 

 south of Isla Chiloe (42°S). To these our records add a further 15 

 species with northern limits between 42-46°S, thus emphasizing the 

 importance of the southern component of the Chilean fauna, and of 

 this region as a distributional boundary for many molluscs. 



As pointed out by Brattstrom & Johanssen (1983) the biogeo- 

 graphical composition of the Chilean invertebrate fauna varies with 

 depth, the southern (Magellanic) component becoming more pro- 

 nounced in deeper water. Since the water is colder at depth, sublittoral 

 Magellanicspecies penetrate further north into the transitional zone 

 than strictly intertidal species. This trend is also evident in our data 

 (Fig. 8). Of the 26 species found only in our samples dredged from 

 5-15 m, 65% were Magellanic and Antarctic, 35% widespread and 

 none Peruvian. Of the remaining 36 species occurring in the eulittoral 

 zone and sublittoral fringe, 39% were Magellanic, 47% widespread 

 and 14% Peruvian. 



Human exploitation of molluscs 



Throughout much of the Chilean coastline the larger molluscs of 

 intertidal and shallow subtidal habitats are heavily exploited for 

 food by the local inhabitants (Osorio et ai, 1979; Moreno et al., 

 1984; Duran et al, 1987; SERNAP, 1998). Edible species found in 

 the present survey were Chiton granosus, Nacella magellanica, 

 Fissurella nigra, F oriens, F picta, Tegula atra, Trochita trochi- 

 formis, Argobuccinumpustulosumranelliforme, Concholepas conch- 

 olepas, Mytilus edulis chilensis, Choromytilus chorus, Aulacomya 

 atra, Zygochlamys patagonica, Mulinia edulis, Ensis macha, Tagelus 

 dombeii, Venus antiqua and Retrotapes exalbidus. Of these, only the 

 bivalves and Concholepas concholepas are collected in commercial 

 quantities elsewhere in Chile, and only the three large mytilids are 

 cultivated. The exploitation of marine molluscs has a long history, 

 for in precolonial times the indigenous people relied heavily upon 

 them for food. Evidence of this was found on Isla Traiguen, where 

 three extensive middens were examined (stations 4, 9, 10), the 



