Is the Wild Coast in eastern South Africa a distinct marine bioregion?

Abstract

The South African coastline can be divided into at least four temperature-defined marine bioregions, including the tropical northeast coast, the subtropical east coast, the warm-temperate south coast, and the cool-temperate west coast. There are also two biogeographical transition zones, the southwest coast and the southeast coast (or Wild Coast). The former is sometimes considered a distinct marine bioregion, but no such status has yet been suggested for the Wild Coast. Previous data on the distribution of a recently described but very common coastal crab, Hymenosoma longicrure, indicated that this species could be a Wild Coast endemic. If confirmed, this would be a first indication that this region harbours unique fauna, and that additional research is required to determine whether the Wild Coast constitutes a distinct bioregion that needs to be managed separately from other coastal regions. In the present study, we generated novel genetic data for H. longicrure and compared the species' range with that of its southern African congeners. We found that H. longicrure occurs north of the Wild Coast, where its range overlaps with that of H. projectum. This finding rejects the idea that the Wild Coast harbours endemic fauna and suggests that the ranges of the two species may be linked to the subtropical and tropical bioregions, respectively, with some southward dispersal facilitated by the southward-flowing Agulhas Current. We conclude that there is as yet no compelling evidence that the Wild Coast is a distinct marine bioregion, and concur with previous biogeographical studies which have suggested that the Wild Coast is an area in which species from the subtropical and warm-temperate bioregions have overlapping ranges. Nonetheless, that fact that no biological information is available for the majority of the region's estuaries highlights the necessity of comprehensively documenting the biodiversity of this understudied region to fully resolve this issue.

Rejection of the genetic implications of the “Abundant Centre Hypothesis” in marine mussels

“…A similar result was found for the microsatellite data, although the location of the boundary differed (it was located between sites P1 and P2) and may reflect marker-specific differences in lineage sorting 66 or selection 67 . Similarly, the distinctness of the COI haplotypes from the northernmost site (P9), which was not found with microsatellites, matches the location of previously reported phylogeographic breaks that separate subtropical from tropical fauna 61,[68][69][70] , and may thus also reflect differential adaptation across a temperature gradient.…”

Discovery of populations endemic to a marine biogeographical transition zone

“…Despite its importance as a biogeographical transition zone that limits the southward dispersal of Western Indian Ocean fauna into the temperate regions at the southern tip of Africa, the Wild Coast has received comparatively little scientific attention. The present study represents a significant advancement in that regard, and rejects the finding of a previous study that tentatively rejected the idea that the Wild Coast has endemic biodiversity (Jooste et al, 2018). Given the very small range of the northern Wild Coast lineage, a fine-scale sampling approach is clearly required to properly document the biodiversity of this poorly-studied region, and determine whether the spatial genetic patterns found here are unique to C. kraussi or represent a more general phenomenon.…”

“…The transition zone is extensive and stretches over several hundred kilometres, although there is disagreement concerning the exact boundaries between the marine biogeographical provinces in this area (Lombard, 2004;Spalding et al, 2007;Teske et al, 2011;von der Heyden, 2009). Based on species turnover, the distinctness of this region's fauna is only weakly supported (Emanuel et al, 1992;Turpie & Clark, 2007), and there are no prior records of endemic species (Jooste et al, 2018). This study reports the first evidence for genetically distinct populations whose ranges are limited to the Wild Coast transition zone.…”

“…Similarly, most genetic studies have found extensive range overlap between sister lineages of temperate and subtropical species in this region (Teske et al, 2008;Zardi et al, 2007). Evidence for endemicity was so far limited to distinct genetic clusters rather than taxonomically-described morphospecies (Jooste et al, 2018), but, even for these, the evidence was not strong. The rocky shore limpets Scutellastra barbara and S. longicosta had south-east coast lineages whose ranges approximately matched those of the C. kraussi lineage from the central and southern Wild Coast (Mmonwa et al, 2015).…”

Discovery of populations endemic to a marine biogeographical transition zone

“…The transition zone is extensive and stretches over several hundred kilometres, although there is disagreement concerning the exact boundaries between the marine biogeographical provinces in this area (Lombard, 2004; Spalding et al., 2007; Teske et al., 2011; von der Heyden, 2009). Based on species turnover, the distinctiveness of this region's fauna is only weakly supported (Emanuel, Bustamante, Branch, Eekhout, & Odendaal, 1992; Turpie & Clark, 2007), and there are no prior records of endemic species (Jooste, Oliver, Emami‐Khoyi, & Teske, 2018). This study reports the first evidence for genetically distinct populations whose ranges are limited to the Wild Coast transition zone.…”