The putative impact of exploitation on rocky infratidal macrofaunal assemblages: a multiple-area comparison

Abstract

The putative impact of subsistence foragers along the Transkei coast of South Africa was determined by comparing the community-level attributes of infratidal macrofaunal assemblages in three ‘no-take’ reserves with those at adjacent exploited localities. The objective of this study was to ascertain whether the differences in the assemblages found at exploited and non-exploited localities were consistent along this coast. Two-way ANOVAs indicated that the presence/absence of exploitation had no effect on univariate community measures. Macrofaunal biomass was the only measure which showed significant differences amongst locations and interaction effects. Abundance/biomass comparison curves revealed that all the exploited sites except one showed the configuration typical of moderately disturbed sites and that all the non-exploited sites except one showed the trend typical of undisturbed sites. Two-way crossed ANOSIM tests indicated that treatment and location both had significant effects on these assemblages and that there were also significant differences between each pair of locations. The latter probably reflects regional differences in species composition due to the fact that this coast lies at the junction of two zoogeographic marine provinces. The multidimensional scaling (MDS) ordinations derived from abundance and biomass estimates revealed two major clusters of sites, one representing sites in the southern region and the other sites within the central and northern regions. The non-exploited sites within each region were situated above and to the right of the corresponding exploited sites. Similarity percentage analyses (SIMPER) indicated that the major species contributing to the average dissimilarity between the exploited and non-exploited localities varied regionally. There was, however, a fair amount of consistency in terms of the functional groups highlighted by these analyses. Some of the species adversely affected by exploitation are dependent on primary substrata either for their food supplies or for attachment. Likewise many of the species which appeared to benefit from exploitation were phytal-associated forms.