Artificial marine structures facilitate the spread of a non‐indigenous green alga, Codium fragile ssp. tomentosoides, in the north Adriatic Sea

Abstract

Summary 1.Artificial structures have become ubiquitous features of coastal landscapes. Although they provide novel habitats for the colonization of marine organisms, their role in facilitating biological invasions has been largely unexplored. 2. We investigated the distribution and dynamics of the introduced green alga, Codium fragile ssp. tomentosoides , at a variety of spatial scales on breakwaters in the north Adriatic Sea, and analysed experimentally the mechanisms underlying its establishment. We assessed the provision of sheltered habitats by breakwaters, the role of disturbance (e.g. from recreational harvesting and storms) acting at different times of the year, and the interactions between Codium and the dominant native space-occupier, the mussel Mytilus galloprovincialis . 3. Codium fragile ssp. tomentosoides has established viable populations on artificial structures along the shores investigated. The density, cover and size (length, branching and weight) of annual erect thalli of Codium was enhanced in sheltered conditions, resulting in the monopolization of landward low-shore habitats of breakwaters. 4. On the landward sides of breakwaters, disturbance enhanced recruitment of Codium . The time when bare space was provided within mussels beds was crucial. Removal of mussels in April or January did not affect the recruitment of Codium , whereas harvest in August, shortly before Codium gamete release, doubled its success. On the seaward sides of breakwaters, the effects of disturbance were more complex because mussels both inhibited recruitment of Codium and provided shelter from wave action to adult thalli. 5. Synthesis and applications . Artificial structures can provide suitable habitats for non-indigenous marine species and function as corridors for their expansion. Physical (wave exposure) and biotic (resident assemblages) features of artificial habitats can be important determinants of their susceptibility to biological invasions. Alternative options in the design of artificial structures and effective management of native assemblages could minimize their role in biological invasions. In particular, increased water motion and retention of space by mussels in spring-summer would be effective in reducing the ability of C. fragile ssp. tomentosoides to persist on the breakwaters investigated in this study.

Predation contributes to invasion resistance of benthic communities against the non-indigenous tunicate Ciona intestinalis

“…Our findings in Chile illustrate how suspended structures may facilitate the supply of propagules of introduced species (Bulleri and Airoldi 2005;Herborg et al 2009), and how native predators can suppress the spread of invasive species into natural benthic communities. The invasive ascidian, Ciona intestinalis, despite the well-established populations on artificial structures, appears unable to colonize surrounding, natural communities due to predation pressure from native benthic species.…”

“…The increasing abundance of anthropogenic structures deployed in the sea (e.g., harbor piers, seawalls, and suspended culture systems) offer novel niches for opportunistic colonizers, including non-indigenous species, which often settle and establish into the fouling communities developing on these structures (Glasby and Connell 1999;Bulleri and Airoldi 2005;Herborg et al 2009). Although these artificial structures are now recognized as invasion hotspots (Bulleri and Chapman 2010), subsequent invasions to natural habitats are limited (Glasby et al 2007).…”

Assessment of goods and services, vulnerability, and conservation status of European seabed biotopes: a stepping stone towards ecosystem-based marine spatial management

“…Sensitivity to human activities: In the last decades, various alien species have become prominent constituents of fouling communities (Bulleri & Airoldi, 2005;ICES, 2007;Tyrell & Byers, 2007;Shenkar & Loya, 2009). This fact, which may be partially attributed to the considerably low biological competition characterizing the bare or scarcely colonized immersed artificial structures (Bulleri & Airoldi, 2005;Shenkar & Loya, 2009), could render artificial habitats along with their associated fouling communities as suitable early warning indicators for a wide range of biological invasions (Hulme, 2006).…”

“…This fact, which may be partially attributed to the considerably low biological competition characterizing the bare or scarcely colonized immersed artificial structures (Bulleri & Airoldi, 2005;Shenkar & Loya, 2009), could render artificial habitats along with their associated fouling communities as suitable early warning indicators for a wide range of biological invasions (Hulme, 2006). Several researchers have emphasized the need to consider limiting coastal artificial structures and destruction of natural hard-substratum as a means to hinder further spread and proliferation of alien species (Bulleri & Airoldi, 2005;Tyrell & Byers, 2007).…”

Facilitation of the introduced green alga Caulerpa racemosa by resident algal turfs: experimental evaluation of underlying mechanisms

“…To date, positive effects of native species on the establishment of invaders have been largely overlooked in marine environments (but see Ceccherelli et al 2002, Levin et al 2002, Bulleri & Airoldi 2005, Stachowicz & Byrnes 2006, Bulleri et al 2008. The introduced green alga Caulerpa racemosa (Forsskål) J. Agardh has been indicated as a driver of change in patterns of abundance and distribution of resident assemblages on rocky ) and sandy (Argyrou et al 1999) bottoms of the western Mediterranean Sea.…”