Parasitism by endolithic cyanobacteria reduces reproductive output and attachment strength of intertidal ecosystem engineers

Ndhlovu, Aldwin; McQuaid, Christopher D.; Nicastro, Katy; Zardi, Gerardo I.

http://hdl.handle.net/10400.1/17772

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Authors

Ndhlovu, Aldwin

McQuaid, Christopher D.

Nicastro, Katy

Zardi, Gerardo I.

Abstract(s)

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.