MEPS 334:155-163 (2007)  -  doi:10.3354/meps334155

Balancing survival and reproduction: seasonality of wave action, attachment strength and reproductive output in indigenous Perna perna and invasive Mytilus galloprovincialis mussels

G. I. Zardi*, C. D. McQuaid, K. R. Nicastro

Department of Zoology & Entomology, Rhodes University, Grahamstown 6140, South Africa

ABSTRACT: The indigenous mussel Perna perna and the invasive mussel Mytilus galloprovincialis coexist on the low shore of the South African south coast, with partial habitat partitioning. P. perna dominates the lower mussel zone, where hydrodynamic stress is higher than in the high mussel zone, where M. galloprovincialis dominates. Attachment strength and gonad maturation are highly demanding processes in terms of energy, the former allowing mussels to withstand wave forces, while the latter contributes to recruitment rates. During an 18 mo study, both biological parameters fluctuated seasonally. The invasive and the indigenous species spawned in different periods; gamete maturation was positively correlated with sea surface temperature only for P. perna. For both species, attachment strength was negatively correlated with sea surface temperature, but increased in response to wave action through the production of more and thicker threads. Peaks in attachment strength coincided with periods of relatively low gamete production for both species, suggesting that mussels cannot afford to invest simultaneously in both processes. P. perna attachment strength was always significantly higher than that of M. galloprovincialis , while the latter had a greater reproductive output. We suggest that, although high gamete production improves the ability of M. galloprovincialis to colonise free space, it may energetically limit its capacity to invade wave exposed shores.

KEY WORDS: Attachment strength · Reproductive output · Invasive · Mytilus galloprovincialis · Perna perna

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