Indirect effects of invasive species affecting the population structure of an ecosystem engineer

Abstract

Citation: Waser, A. M., W. Splinter, and J. van der Meer. 2015. Indirect effects of invasive species affecting the population structure of an ecosystem engineer. Ecosphere 6(7):109. http://dx.doi.org/10.1890/ES14-00437.1Abstract. Species invasion is of increasing concern as non-native species often have negative impacts on ecosystems that they were introduced to. Invaders negatively affect the abundance of native species due to direct interactions like predation and competition. Additionally, invaders may benefit native biota by imposing indirect effects on resident species interactions. Invaders indirectly affect resident species via both density-mediated indirect interactions (DMIIs) and trait-mediated indirect interactions (TMIIs). Previous studies on these different indirect interactions have largely examined the effects on structuring ecological systems, with paying little attention to the role of body size. Here, we experimentally demonstrate that an invasive habitat modifier of European coastal waters, the Pacific oyster (Crassostrea gigas), alters the population structure of native mussels (Mytilus edulis) by modifying the size specific predator-prey interaction between the mussels and the shore crab (Carcinus maenas). In laboratory split-plot experiments, the presence of Pacific oysters reduced the mortality of unconditioned mussels as well as mussels that were acclimatized in presence of predatory cues, while being exposed to predation by crabs of two different size classes. The reduction in mortality was size-dependent both in terms of the predators and the prey. The presence of oysters notably reduced mussel mortality in presence of small crabs, while the mortality rate in presence of big crabs was less affected. Mussels that benefited the most by the presence of oysters were those of recruitment stages, smaller than 20 mm in shell length. Our results suggest that oysters cause a strong shift in the population structure of M. edulis, reducing particularly the mortality of smaller sized mussels.

Invading oysters and native mussels: from hostile takeover to compatible bedfellows

“…The higher survival at the base of the large oysters was, however, traded off for retarded growth (see also Waser et al. , ). Furthermore, below the canopy of oysters, detrimental overgrowth by barnacles on mussels was low relative to exposed positions (Buschbaum et al.…”

Exploring the decline of oyster beds in Atlantic Canada shorelines: potential effects of crab predation on American oysters (Crassostrea virginica)

“…Crab-bivalve interactions have been shown to be complex [56,57] particularly those involving habitat-forming species like oysters [20,27,58]. As this study illustrates, to better understand the role of newly arrived predators on a coastal system, it is important to gather information from multiple sites and conduct experimental manipulations [42].…”

“…However, predation on shellfish has been recently exacerbated by the arrival and establishment of invasive species, some of which have proven to be eager predators of commercial bivalves [26,27]. The European green crab (Carcinus maenas) has well documented impacts on shellfish and other invertebrates throughout its native and invaded ranges [28][29][30][31].…”

Quantifying Tidal Movements of the Shore Crab Carcinus maenas on to Complex Epibenthic Bivalve Habitats

“…Consequently, the complex structures formed by these two bivalve species are likely to provide different resources in terms of nesting sites, shelter from predators, and feeding opportunities, thus potentially leading to differences in the species community (Markert et al 2009). Moreover, the conversion of mussel beds into oyster-dominated beds may ultimately lead to a change of feeding opportunities for predators (Eschweiler and Christensen 2011;Waser et al 2015Waser et al , 2016a.…”

“…The classification into size classes was based on (1) the migration behavior: small shore crabs (< 35-mm CW) are mostly juveniles and burrow on the tidal flats during low tide (Hunter and Naylor 1993) and (2) size preference of mussels: crabs smaller than 50-mm CW hardly prey on mussels bigger than 1 cm in shell length (Elner and Hughes 1978;Smallegange and Van der Meer 2003;Waser et al 2015). Moreover, it has to be noted that in the Wadden Sea, C. maenas typically reaches a maximum size of about 75-mm CW, but specimens larger than 65 mm are scarce (Klein Waser et al 2016b).…”