AUTHOR=Branch George M. , Steffani Nina , Pfaff Maya C. , Baliwe Ndiviwe G. , Zeeman Zannè 

TITLE=Complex interplays between limpets and alien species in South Africa: multispecies interactions, zonation and size effects

JOURNAL=Frontiers in Marine Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1190456

DOI=10.3389/fmars.2023.1190456

ISSN=2296-7745

ABSTRACT=<p>Integrating observations and experiments, we address the progressive effects of three alien species, the mussels <italic>Mytilus galloprovincialis</italic> and <italic>Semimytilus patagonicus</italic>, and the barnacle <italic>Balanus glandula</italic>, on limpet species in South Africa. We describe four aspects: (1) Interactions among algae, the limpet <italic>Scutellastra granularis</italic> and <italic>M. galloprovincialis</italic>. (2) The influences of <italic>B. glandula</italic> on <italic>S</italic>. <italic>granularis</italic> and on the periwinkle <italic>Afrolittorina knysnaensis</italic>. (3) Transformation of the zonation of <italic>S. granularis</italic> by the successive arrival of these three aliens. (4) Assessment of how effective the published predictors of the effects of <italic>M. galloprovincialis</italic> have been when applied to <italic>S. patagonicus</italic>. We conclude: (a) <italic>Scutellastra granularis</italic> improves mussel survival and condition by regulating algae that would otherwise overgrow and smother the mussels. (b) <italic>Balanus glandula</italic> has largely occupied the upper half of rocky shores, and at high densities depletes or eliminates suitable bare-rock habitat for <italic>S. granularis</italic>. However, it has positive effects on another gastropod, <italic>A. knysnaensis.</italic> (c) <italic>Mytilus galloprovincialis</italic> dominates the midshore and has positive effects on the recruitment of <italic>S. granularis</italic>, but negatively influences adults of this limpet, so that its size composition, density, reproductive output and zonation are all altered by this mussel. (d) <italic>Semimytilus patagonicus</italic> presents different challenges to those created by <italic>M. galloprovincialis</italic>, settling at much greater densities, lower down the shore, and reaching smaller maximum sizes. Rather than generating a favourable habitat for epizootic <italic>S. granularis</italic> recruits and juveniles, it almost completely excludes that limpet. We conclude that the influences of alien species are not readily predictable, depending on the nature of the invader and recipient species, environmental conditions and complex interactions among species. Collectively, the three alien species now cover almost all zones on wave-exposed rocky shores, completing the ‘zonation squeeze’ on limpets, but are less influential on wave-sheltered shores and in years when recruitment is low.</p>