Abstract
Aggregations of the Ponto-Caspian invasive zebra mussel (Dreissena polymorpha) constitute a suitable habitat for macroinvertebrates, considerably increasing their abundance and providing effective antipredator protection. Thus, the overall effect of a mussel bed on particular predator species may vary from positive to negative, depending on both prey density increase and predator ability to prey in a structurally complex habitat. Alien Ponto-Caspian goby fish are likely to be facilitated when introduced into new areas by zebra mussels, provided that they are capable of utilizing mussel beds as habitat and feeding grounds. We ran laboratory experiments to find which prey (chironomid larvae) densities (from ca. 500 to 2,000 individuals m−2) in a mussel bed make it a more beneficial feeding ground for the racer goby Babka gymnotrachelus (RG) and western tubenose goby Proterorhinus semilunaris (WTG) compared to sandy and stone substrata (containing the basic prey density of 500 ind. m−2). Moreover, we checked how food availability affects habitat selection by fish. Mussel beds became more suitable for fish than alternative mineral substrata when food abundance was at least two times higher (1,000 vs. 500 ind. m−2), regardless of fish size and species. WTG was associated with mussel beds regardless of its size and prey density, whereas RG switched to this habitat when it became a better feeding ground than alternative substrata. Larger RG exhibited a stronger affinity for mussels than small individuals. WTG fed more efficiently from a mussel bed at high food abundances than RG. A literature review has shown that increasing chironomid density, which in our study was sufficient to make a mussel habitat an attractive feeding ground for the gobies, is commonly observed in mussel beds in the field. Therefore, we conclude that zebra mussels may positively affect the alien goby species and are likely to facilitate their establishment in novel areas, contributing to an invasional meltdown in the Ponto-Caspian invasive community.
Highlights
The zebra mussel, Dreissena polymorpha, is a habitat-forming ecosystem engineer of Ponto-Caspian origin, invasive in Europe and North America (Karatayev, Burlakova & Padilla, 2002)
Experiment 1 The number of prey individuals consumed by fish (Fig. 2) and their feeding efficiency (Fig. 3) were affected by fish species and substratum type/food abundance, as shown by significant interactions between these factors in the General Linear Model (GLM) analyses, but independent of fish size (Table 2)
western tubenose goby Proterorhinus semilunaris (WTG) tended to utilize zebra mussel feeding grounds more efficiently than racer goby Babka gymnotrachelus (RG): it started to consume the same amount of food from mussels as from sand and more than from stones at a lower difference in food abundance between these substrata (12 larvae in a mussel bed, compared to 16 needed for RG) (Fig. 2)
Summary
The zebra mussel, Dreissena polymorpha, is a habitat-forming ecosystem engineer of Ponto-Caspian origin, invasive in Europe and North America (Karatayev, Burlakova & Padilla, 2002). At high densities (up to 24,000 or more individuals m-2) it exerts strong, multi-level impact on aquatic communities by filtering suspended matter and forming habitats for benthic organisms (Karatayev, Burlakova & Padilla, 2002) This bivalve can be beneficial for many invasive (Ricciardi & MacIsaac, 2000) and native (Karatayev, Burlakova & Padilla, 2002; Gergs & Rothhaupt, 2008) macroinvertebrates (Table 1) by providing them with suitable food (e.g. mussel pseudofaeces) and efficient antipredator shelters in a 3D structure of shells and byssally attached mussels (Gonzalez & Burkart, 2004; Kobak, Jermacz & Płachocki, 2014). The yellow perch Perca flavescens, which does not feed on mussels, was experimentally shown to grow better in the presence of zebra mussel colonies due to the increased abundance of their macroinvertebrate prey (Thayer et al, 1997)
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