Parallels and Contrasts Between Limnoperna fortunei and Species of Dreissena

Abstract

Limnoperna fortunei (the golden mussel), Dreissena polymorpha (the zebra mussel), and Dreissena rostriformis bugensis (the quagga mussel) are considered among the most aggressive freshwater invaders. All three species share several biological traits, such as their sessile mode of life attached to hard substrata by a byssus (although quagga mussels can also dwell on muddy bottoms), similar sizes, similar longevity, and similar time to sexual maturity. The spawning period, however, is usually longer for L. fortunei. Ecologically, they also share similarities (e.g., suspension feeding mode), but the dreissenids thrive and reproduce in colder waters (especially D. r. bugensis), and are significantly less tolerant to low pH and calcium concentrations, hypoxic conditions, and pollution. Rates of intrabasin spread of L. fortunei in South America are roughly similar to those of D. polymorpha in North America, but interbasin spread is generally faster for the zebra mussel, probably partly due to cultural and economic differences between their respective invasive ranges. Geographic spread of quagga mussels has been much slower than that of zebra mussels, but once the former colonize waterbodies already populated by zebra mussels, they usually become dominant, both spatially and numerically. Judging from their respective environmental tolerance limits, in particular calcium concentrations, it is expected that both species of Dreissena may eventually colonize much of Europe, Asia, and North America, but colonization of South America, Africa, and Australia is less likely. In contrast, L. fortunei, which tolerates much lower calcium concentrations, could spread to areas presently occupied by the dreissenids as well as Africa and Australia. Should the three species overlap, it seems likely that L. fortunei will outcompete the dreissenids in warmer, more polluted, less oxygenated, and more acidic waters as well as in waters with lower calcium concentrations. However, the outcome of their competitive interactions when conditions are suitable for all three species is unclear. L. fortunei and both species of Dreissena are functionally similar, and as a consequence, many of their impacts on the systems they invade are also similar, yet the magnitude of these effects, and in some cases even their sign, can differ widely depending on the invasive species and environmental constraints. Future research on the golden mussel should focus on shedding light on the many unknown aspects of its biology and ecology, which are particularly critical for a comprehensive assessment of its interactions with local biota.