Coastal ecosystems are subject to a wide variety of abiotic conditions. Water motion within coastal ecosystems is a key abiotic factor controlling species abundances and biological processes yet is often not measured. Coastal ecosystems are also susceptible to invasive species due to increased anthropogenic activity. Invasive species can have severe ecological impacts on recipient ecosystems causing changes in biodiversity, habitat complexity and species interactions. After being introduced for aquaculture purposes worldwide, the Pacific oyster, Crassostrea gigas, has become one of the most globalised marine invertebrates. Ecological impacts associated with C. gigas invasions have been both positive and negative depending upon the context. However, invasions onto beds of the native blue mussel, Mytilus edulis, have seen shifts in dominance from mussels to oysters. Although invasions of C. gigas have been investigated, the influence of water motion on its invasion success and interactions with native M. edulis is almost unknown. Thus here, a combination of laboratory and field experiments were conducted to identify (i) predation patterns by native predators on M. edulis and C. gigas to quantify biotic resistance towards invasions; (ii) how these predation patterns change with hydrodynamic disturbance; (iii) how oscillatory flow velocity affects the clearance rates and relative impacts on resources of M. edulis compared to C. gigas; and (iv) how competitive interactions between M. edulis and C. gigas can affect their growth rates, health and mortality.