A zoogeographic and functional approach to the selection of marine reserves on the west coast of South Africa

TLDR

The study develops and applies three objective criteria to assess marine reserve sites on South Africa’s west coast, concluding that a representative reserve must include both small‑scale physical and biotic variation and large‑scale geographic representativeness. The authors use macro‑scale zoogeographic analysis of 2,000 invertebrate species and meso‑ to local‑scale intertidal community surveys linked to habitat diversity to develop objective criteria for marine reserve selection. The analysis identifies five major zoogeographic regions, including a distinct Namaqua province, and shows that the Groen‑Spoeg area—kept near‑pristine by limited mining—exemplifies both its province and sub‑province, features a globally unique dense limpet assemblage, and exhibits species composition that varies more with wave exposure than with large‑scale zoogeography, thereby ranking the area as a high‑priority conservation site while demonstrating the method’s broader applicability.

Abstract

Three objective criteria for assessing sites being considered as marine nature reserves are developed and applied to a region of the west coast of South Africa, between the Groen and the Spoeg rivers, that has been mooted as a possible nature reserve. On a national and regional macroscale, zoogeographic analyses of 2 000 species of invertebrates were used to reappraise accepted marine biogeographic provinces. On a mesoscale and local scale, the intertidal community composition of rocky shores was examined and related to the physiographic habitat diversity. Five major zoogeographic regions are identified around the southern African coast, including a distinct Namaqua province. The Groen-Spoeg area, which receives no adequate conservation, is representative of both the major zoogeographic province that it falls in and the Northern Namaqua sub-province. A long period of limited human access as a result of diamond-mining has kept the shore near-pristine. On a global scale, the region is unique in the extent to which the system is dominated by dense assemblages of limpets. The species-composition of intertidal rocky-shore communities varies greatly according to the degree of wave exposure, and this small-scale variation, reflecting physiographic heterogeneity of the shore, can exceed large-scale zoogeographic variations. Therefore, in order to be representative, a reserve will need to incorporate small-scale variations in physical conditions and biotic composition, as well as large-scale geographic representativeness. The approaches used demonstrate that the Groen-Spoeg has a high priority for conservation; they are also generally applicable to the objective assessment of potential reserves, although they need to be coupled with other criteria, including socio-economic issues.