MEPS 607:113-127 (2018)  -  DOI: https://doi.org/10.3354/meps12794

ABSTRACT: The invasive mytilid mussel Semimytilus algosus was first recorded on South African shores in 2009 and rapidly spread to occupy 500 km of the West Coast, where it dominates lower portions of the rocky shore. To identify mechanisms underlying the invasive success of S. algosus, the life-history parameters survivorship, reproductive output, recruitment, growth rate and shell and byssus strength were compared among S. algosus and another alien, Mytilus galloprovincialis, and the indigenous mussels Aulacomya atra and Choromytilus meridionalis. To standardise the effects of wave exposure and shore height on life history patterns, all observations and sampling were limited to the low shore at the research site, Bloubergstrand. The 4 mussel species employed very different means of maximising survival and/or space occupancy. S. algosus proved to be a typical r-selected species, with low survival due to its weak shell and byssal strength. Unexpectedly, it grew relatively slowly but had a high reproductive output and exceptionally high recruitment rate that largely account for its invasive success. This study therefore demonstrates how life-history traits influence the invasive success of alien species and allows predictions about their relative impacts on intertidal rocky shores.

KEY WORDS: Invasive species · Competition · Rocky shores · Recruitment · Growth · Reproduction