Browsing by Author "Ndhlovu, Aldwin"
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- Biogeographical patterns of endolithic infestation in an invasive and an indigenous intertidal marine ecosystem engineerPublication . Ndhlovu, Aldwin; McQuaid, Christopher D.; Nicastro, Katy; Marquet, Nathalie; Gektidis, Marcos; Monaco, Cristián J.; Zardi, GerardoBy altering the phenotypic properties of their hosts, endolithic parasites can modulate the engineering processes of marine ecosystem engineers. Here, we assessed the biogeographical patterns of species assemblages, prevalence and impact of endolithic parasitism in two mussel species that act as important ecosystem engineers in the southern African intertidal habitat, Perna perna and Mytilus galloprovincialis. We conducted large-scale surveys across three biogeographic regions along the South African coast: the subtropical east coast, dominated by the indigenous mussel, P. perna, the warm temperate south coast, where this species coexists with the invasive Mediterranean mussel, M. galloprovincialis, and the cool temperate west coast dominated by M. galloprovincialis. Infestation increased with mussel size, and in the case of M. galloprovincialis we found a significantly higher infestation in the cool temperate bioregion than the warm temperate region. For P. perna, the prevalence of infestation was higher on the warm temperate than the subtropical region, though the difference was marginally non-significant. On the south coast, there was no significant difference in infestation prevalence between species. Endolith-induced mortality rates through shell collapse mirrored the patterns for prevalence. For P. perna, endolith species assemblages revealed clear grouping by bioregions. Our findings indicate that biogeography affects cyanobacteria species composition, but differences between biogeographic regions in their effects are driven by environmental conditions.
- Parasitism by endolithic cyanobacteria reduces reproductive output and attachment strength of intertidal ecosystem engineersPublication . Ndhlovu, Aldwin; McQuaid, Christopher D.; Nicastro, Katy; Zardi, Gerardo I.Mussels are ecological engineers in intertidal communities; they afect coastal species richness by increasing habitat spatial complexity, bufering against environmental extremes, and providing protection from predators. Parasitic activities of endolithic cyanobacteria on mussels weaken their shells, requiring the expenditure of energy on shell repair, with potential indirect efects on organisms that rely on mussels as habitat providers. Given the seasonality of reproduction and the need for strong attachment during winter storms, we examined the consequences of redirecting energy for shell repair to two other energetically expensive processes: reproduction and byssal attachment. We examined seasonality in the efects of cyanobacterial infestation on reproduction and attachment strength in two intertidal mussels, the indigenous Perna perna and the invasive Mytilus galloprovincialis from the south coast of South Africa, using both qualitative and quantitative analyses. Reproductive efects were examined by measuring the weight of mussel gonads and the density of eggs within each gonad for co-occurring infested and non-infested mussels, while attachment strength was measured for mussels exhibiting diferent levels of infestation. Endolithic infestation was found to afect reproduction by reducing the mass of gonads, but not the density of eggs within them. Attachment strength was closely correlated with the degree of endolithic infestation, with very infested mussels requiring much less force to detach them from the substratum than mussels with low or no infestation. Thus, endolithic infestation afected mussel ftness directly, by increasing the probably of mortality through wave dislodgement and by reducing reproductive output.