Non-native habitat as home for non-native species: comparison of communities associated with invasive tubeworm and native oyster reefs

Introduction vectors for marine non-native species, such as oyster culture and boat foul- ing, often select for organisms dependent on hard substrates during some or all life stages. In soft- sediment estuaries, hard substrate is a limited resource, which can increase with the introduction of hard habitat-creating non-native species. Positive interactions between non-native, habitat-creating species and non-native species utilizing such habitats could be a mechanism for enhanced invasion success. Most previous studies on aquatic invasive habitat-creating species have demonstrated posi- tive responses in associated communities, but few have directly addressed responses of other non- native species. We explored the association of native and non-native species with invasive habitat- creating species by comparing communities associated with non-native, reef-building tubeworms Ficopomatus enigmaticus and native oysters Ostrea conchaphila in Elkhorn Slough, a central Califor- nia estuary. Non-native habitat supported greater densities of associated organisms—primarily highly abundant non-native amphipods (e.g. Monocorophium insidiosum, Melita nitida), tanaid (Sinelebus sp.), and tube-dwelling polychaetes (Polydora spp.). Detritivores were the most common trophic group, making up disproportionately more of the community associated with F. enigmaticus than was the case in the O. conchaphila community. Analysis of similarity (ANOSIM) showed that native species' community structure varied significantly among sites, but not between biogenic habi- tats. In contrast, non-natives varied with biogenic habitat type, but not with site. Thus, reefs of the invasive tubeworm F. enigmaticus interact positively with other non-native species.