Rocky shores of a major southern African Marine Protected Area are almost free from intertidal invertebrate alien species

Abstract

A major threat to marine ecosystems is the establishment and proliferation of invasive alien species. This study addresses gaps in our knowledge regarding marine alien invertebrate species in the Kogelberg Biosphere Reserve (KBR) and adjacent Betty’s Bay Marine Protected Area (MPA) in the Western Cape of South Africa, together a potentially important area for south-coast marine conservation. Understanding the distribution and geographical expansion of these species is critical for conservation planning. A quantitative systematic survey of the intertidal rocky shore region was undertaken. The mytilid Mediterranean mussel, Mytilus galloprovincialis, and the bryozoan Watersipora subtorquata were the only alien species recorded along the coastline, which included the MPA. The abundance of M. galloprovincialis was significantly higher outside the MPA, and the abundance of W. subtorquata was significantly higher inside the MPA. With only two alien species recorded, the Betty’s Bay MPA and its surroundings support relatively few marine alien species with regards to rocky shore invertebrate biodiversity. Conservation implications: It is important that the Betty’s Bay MPA and its adjacent coastline maintain its current status as an area with relatively few marine alien species. The conservation implications on management require routine surveys of this region to detect early introductions of any additional species.