ABSTRACT
The predator-prey interaction between the round goby (Neogobius melanostomus) and dreissenid mussels (zebra mussel Dreissena polymorpha and quagga mussel Dreissena rostriformis bugensis) is an important factor determining distributions and abundances of each species in the Laurentian Great Lakes. Round gobies are found throughout the lower Great Lakes, and their spread has probably been facilitated by the fact that this species co-evolved with and readily preys on dreissenids. Reviewed research has shown that round gobies have decreased dreissenid densities at some locations, but there are exceptions, and round goby impacts on dreissenids may not be universal. We propose that a complete understanding of round goby impacts requires knowledge of dreissenid defenses and how dreissenids interact with bio-mechanical adaptations of round gobies. Round goby adaptations include a feeding style in which the sh breaks dreissenid byssal threads through torsion and possession of molariform pharyngeal teeth in larger gobies that aid in crushing mussel shells. Dreissenid defenses include seeking shelter (i.e., rock crevices), aggregating with conspecics, increasing byssal thread attachment strength, and increasing shell thickness. However, these defenses have mainly been identied relative to other molluscivorous shes and not the round goby. To illustrate how complex round
goby-dreissenid interactions can be, we present results of two eld studies. In the rst study, we show that where round gobies and quagga mussels have co-existed for about 6 years, densities of dreissenids correlate with rock rugosity as measured by the area of vugs (cavities left by eroded fossils, primarily brachiopods) (F1,27 = 17.8, P < 0.001). In the second study, we present data on the movement of dreissenids from established populations to initially dreissenid-free substrates in the presence of round gobies. Based on study outcomes, we propose that in the presence of high round goby densities, dreissenids strike a balance between lowered risk of predation by occupying sheltered habitats (under rocks and in crevices), and enhanced feeding opportunities (and likely spawning) by occupying more exposed habitats. Because both predator and prey have strategies with costs and benets that can vary regionally, or even at the level of the microhabitat, we propose that interactions between round gobies and dreissenid mussels will vary at multiple spatial scales.
