File:American malacological bulletin (1987) (18157728751).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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GOSLINER: SOUTH AFRICAN OPISTHOBRANCHS 245
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35° S Fig. 1. Geographical regions examined in this study (CT - Cape Town, FB - False Bay, KN - Knysna, PE - Port Elizabeth, UM - Umgazana, DU - Durban, SO - Sodwana Bay). data for the entire region as a single fauna. Rather, it is appropriate to define different geographical areas in order that their biogeographical affinities may be contrasted. Seven areas (Fig. 1) were selected in order that comparisons can be made. They represent most of the previously described variation in oceanographic conditions and include the geographic extent of the region. In addition, these areas were selected because they have been reasonably well studied and are likely to reflect an accurate sample of the total opisthobranch fauna of the region. The areas chosen are centered at Cape Town (Lamberts Bay to Cape Point), False Bay (Buffel's Bay to Rooi Els), Knysna (Still Bay to Storm's River Mouth), Port Elizabeth (Jeffreys Bay to Port Alfred), Umgazana (Gonubie to Port St. Johns), Durban (Park Rynie to Salt Rock) and Sodwana Bay (Adlam's Reef to Kosi Bay). The localities in parentheses represent the geographical limits of each area considered. Not all areas are of equal size nor have they been sampled with equal intensity. For example, virtually no sublittoral samples have been collected from Umgazana. Despite these potential biases, several distinct patterns emerge. RESULTS Distributional data within southern Africa and outside the region are presented for 237 species of opisthobranchs (Appendix 1). The percentages of endemic, circumtropical, Indo-Pacific, Atlantic and cosmopolitan species present in each of the seven regions are compared (Fig. 2). Several obvious trends emerge when these data are compared. There is a high incidence of endemism in the southwestern portion of southern Africa, which abruptly diminishes in the localities to the east of Port Elizabeth. There is also a small percentage of Indo-Pacific and circumtropical species present in the southwestern portion of southern Africa, which increases markedly in an eastward direction. A significant number of Atlantic species is found in the southwestern and south-eastern portions of the Cape Province but these are notably absent from Transkei and Natal localities. Even more significant is the abrupt faunal shift in the geographical affinities between Port Elizabeth and Umgazana. In Cape Town, False Bay, Knysna and Port Elizabeth the majority of species are endemic or Atlantic. In Umgazana, Durban and Sodwana Bay most species are circumtropical or Indo-Pacific. DISCUSSION FACTORS THAT AFFECT BIOGEOGRAPHICAL CONCLUSIONS Biogeographical studies are limited by the level of knowledge of the geographical area of immediate concern, and by the available data from adjacent or associated regions. This is certainly true of the opisthobranch fauna of southern Africa. Relatively few studies have been conducted on the opisthobranch faunas of the west coast of Africa. Ev. Marcus and Er. Marcus (1966, 1968) recorded 19 species of

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