This study tests the general hypothesis that habitat disruption caused by the release of copper mine wastes in coastal waters has a negative impact on gene flow among populations of the kelp Lessonia nigrescens Bory. Hierarchical sampling was performed within continuous, undisturbed stands and at the northern and southern edges of a 40 km gap caused by mine wastes. Our results, based on RAPD markers, showed a strong genetic structure even in the absence of the disrupting effect of the mine wastes. No pattern of isolation by distance is apparent, however, which indicates that populations are at migration-drift disequilibrium, and suggests that most events of spore recruitment and/or gametophyte fertilization occur within a few metres. On the other hand, some long distance dispersal is likely to occur, which prevents isolation by distance within the spatial scale of 40 km. When comparing continuous stands across the disrupted habitat, an increased genetic differentiation associated with the interruption of the species distribution was observed. A Multiple Correspondence Analysis (MCA) clearly separated the sampling units into 2 groups, each representing a separate stand. Other lines of evidence supporting the idea of genetic disruption came from the mean pairwise differentiation estimates (F ST ) and from the Analyses of Molecular Variance (AMOVA). Finally, the southern edge of the interruption in the distribution of L. nigrescens showed clear signals of a recent founding event, suggesting that northward recolonisation is currently occurring.
KEY WORDS: Kelp · Habitat disruption · Heavy metal · Gene flow · RAPD
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 288: [129][130][131][132][133][134][135][136][137][138][139][140] 2005 2001). Furthermore, there is increasing evidence that these habitat discontinuities represent a key factor in reducing gene flow among marine populations and, thus, favours genetic differentiation. Examples include rock-reef fishes, where sandy beaches or deeper waters among islands can inhibit gene flow even in the presence of tidal currents (Bernardi 2000, Riginos & Nachman 2001, intertidal snails (Johnson & Black 1995) and other animal populations (reviewed by Palumbi 1994, Bohonak 1999. In seaweeds, accumulating evidence shows that, in most cases, gene flow occurs mainly between populations separated by short distances as a result of their short dispersal capacity . As a consequence, any interruption in their distribution is expected to accelerate genetic differentiation. For example, it was shown that natural discontinuities of the coast, such as estuaries and sandy beaches, strongly increases population differentiation at spatial scales of 5 km in the rocky intertidal red alga Mazzaella laminarioides (Faugeron et al. 2001, Faugeron 2002. Similar responses were reported for the brown alga Laminaria digitata, where relatively short interruptions (15 to 20 km) in its usually continuous distribution increases genetic differentia...