Effects of shell morphology on mechanics of zebra and quagga mussel locomotion

Abstract

SUMMARYAlthough zebra mussels (Dreissena polymorpha) initially colonized shallow habitats within the North American Great Lakes, quagga mussels (Dreissena bugensis) are becoming dominant in both shallow-and deep-water habitats. Shell morphology differs among zebra, shallow quagga and deep quagga mussels but functional consequences of such differences are unknown. We examined effects of shell morphology on locomotion for the three morphotypes on hard (typical of shallow habitats) and soft (characteristic of deep habitats) sedimentary substrates. We quantified morphology using the polar moment of inertia, a parameter used in calculating kinetic energy that describes shell area distribution and resistance to rotation. We quantified mussel locomotion by determining the ratio of rotational (K rot ) to translational kinetic energy (K trans ). On hard substrate, K rot :K trans of deep quagga mussels was fourfold greater than for the other morphotypes, indicating greater energy expenditure in rotation relative to translation. On soft substrate, K rot :K trans of deep quagga mussels was approximately one-third of that on hard substrate, indicating lower energy expenditure in rotation on soft substrate. Overall, our study demonstrates that shell morphology correlates with differences in locomotion (i.e. K rot :K trans ) among morphotypes. Although deep quagga mussels were similar to zebra and shallow quagga mussels in terms of energy expenditure on sedimentary substrate, their morphology was energetically maladaptive for linear movement on hard substrate. As quagga mussels can possess two distinct morphotypes (i.e. shallow and deep morphs), they might more effectively utilize a broader range of substrates than zebra mussels, potentially enhancing their ability to colonize a wider range of habitats.Key words: biological invasions, bivalve, functional morphology, Great Lakes, kinetic energy, locomotion, mollusc, moment of inertia, sediment. THE JOURNAL OF EXPERIMENTAL BIOLOGY Mussel morphology and movementA shell morphology that facilitates locomotion across particular substrate types might affect fitness and survival of zebra and quagga mussels on those substrates. Zebra mussels are known to move in response to various environmental factors (e.g. light, nitrogenous waste, oxygen and substrate type) that influence habitat selection and survival (see Burks et al., 2002;Kilgour and Mackie, 1993;Kobak, 2001;Kobak and Nowacki, 2007;Marsden and Lansky, 2000;Toomey et al., 2002).The objective of this study was to directly examine the effects of shell morphology on locomotion of different mussel morphotypes (i.e. zebra, shallow quagga and deep quagga mussels) on hard versus soft sedimentary substrates. We determined the effects of shell shape on locomotory function by calculating translational and rotational kinetic energy (K trans and K rot , respectively) for zebra and quagga mussels moving across hard and soft substrate types. K trans and K rot directly account for effects of shell size and shape on locomotory function, as K tr...

Will the Displacement of Zebra Mussels by Quagga Mussels Increase Water Clarity in Shallow Lakes during Summer? Results from a Mesocosm Experiment

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