Coexisting native and non-indigenous gammarideans in Lake Constance - Comparative morphology of mouthparts (Crustacea, Amphipoda, Gammaridea)

Mayer, G., Maas, A. & Waloszek, D. 2012. Coexisting native and non-indigenous gammarideans in Lake Constance - Comparative morphology of mouthparts (Crustacea, Amphipoda, Gammaridea). Spixiana 35(2): 269-285. Over the past two decades the amphipod communities of German inland waters have changed dramatically. The Ponto-Caspian gammaridean Dikerogammarus villosus has severely impacted the biocoenosis of the concerned waters in a wide area of western and central Europe, by decreasing or even eliminating populations of native or earlier established gammarideans. In 2002 this invasive species was also recorded in Lake Constance, a prealpine lake in Germany, Austria and Switzerland. Within five years it has spread almost throughout the littoral zone of the entire lake, where it is now the dominant gammaridean species on hard substrates. However, in Lake Constance the coexistence between this so-called "killer-shrimp" and the native Gammarus lacustris, and the earlier established G. roeselii seems to be possible. Furthermore, a local population of another amphipod, Crangonyx pseudogracilis, has existed in Lake Constance since 2007 despite the presence of D. villosus. In our SEM study of the structures involved in food acquisition of the gammarideans inhabiting Lake Constance we discovered morphological differences that seem to enable these animals to feed on different kinds of food. D. villosus, despite its ecological impact, is not a specialized predator, but an opportunistic omnivore. The mouthparts of G. lacustris possess specializations for retaining very small food particles and those of G. roeselii for scraping periphyton off the substrates. By contrast, C. pseudogracilis seems to be specialized to feed on detritus and carrion. These different abilities to utilize food resources, as determined by morphology, may be a reason for the coexistence of the four gammaridean species in Lake Constance.