Multivariate comparisons of rocky infratidal macrofaunal assemblages from replicate exploited and non-exploited localities on the Transkei coast of South Africa

Abstract

Multivariate analyses, in the form of dendrograms, MDS (multidimensional scaling) ordinations, 2-way crossed ANOSIMs (analyses of similarities) and SIMPER (similarity percentage) analyses, were used to examine the influence of human predators on rocky infratidal assemblages. Comparisons are based on mean macrofaunal abundance and biomass estimates obtained from samples collected at multiple sites within 3 'no-take' marine reserves and at 3 adjacent exploited localities on the Transkei coast of South Africa. The dendrogram and MDS derived from the abundance estimates revealed 2 major subdivisions, one representing the sites in the 2 southern localities, and the other the sites within the central and northern localities of Transkei. Similar trends were evident in analyses based on biomass estimates, the major exception being the presence of an outlying site. Temperate species which were either restricted to or attained higher abundances and biomasses in the southern region appeared to be primarily responsible for this sub-division of sites. Two-way crossed ANOSIMs indicated that there were significant differences in the assemblages found under the exploited and non-exploited treatments and between the 3 pairs of locations. Two-way SIMPER analyses suggested that the major differences in the assemblages under the 2 treatment regimes were the lower abundance and biomass of sessile filter feeders and microalgal grazers that are dependent on the primary substratum and the greater abundance of phytal-associated species under exploited conditions. These differences are in accordance with expectations based on our knowledge of the organisms targeted by shellfish-gatherers.