Abstract
AbstractAimBiological invasions and changes in land and sea use are among the five major causes of global biodiversity decline. Shipping and ocean sprawl (multiplication of artificial structures at the expense of natural habitats) are considered as the major forces responsible for marine invasions and biotic homogenization. And yet, there is little evidence of their interplay at multiple spatial scales. Here, we aimed to examine this interaction and the extent to which the type of artificial habitat alters the distribution of native and non‐indigenous biodiversity.LocationSoutheast Pacific—Central Chilean coastline.MethodsSettlement plates were deployed upon two types of artificial habitats (floating and non‐floating hard substrates) at a total of ten study sites, exposed to either international or local traffic. After colonization periods of 3 and 13 months, plates were retrieved to determine their associated fouling sessile assemblages at an early and late stage of development, respectively. Putative confounding factors (temperature, metal concentrations) were taken into account.ResultsWhile traffic type had no detectable effect, there were strong differences in community structure between habitats, consistent across the study region. These differences were driven by non‐indigenous species which contributed to 58% and 40% of the community structure in floating habitats after 3 and 13 months, respectively—roughly 10 times greater than in their non‐floating counterparts. Assemblages on floating structures also displayed a lower decline in similarity with increasing distance between sampling units, being thus more homogenous than non‐floating habitats at the regional scale.Main conclusionsWith the absence of international traffic effect, the colonization success by non‐indigenous species appears to be mainly habitat‐dependent and driven by local propagules. Floating structures not only provide specific niches but characteristics shared with major introduction and dispersal vectors (notably hulls), and in turn constitute important corridors to invasions and drivers of biotic homogenization at multiple scales.
Highlights
Biodiversity is declining at an unprecedented rate, over multiple spatial scales, in response notably to climate change, pollution, direct exploitation of biota, changes in land and sea use, and bioinvasions (Catford, Bode, & Tilman, 2018; IPBES, 2019; Nowakowski, Frishkoff, Thompson, Smith, & Todd, 2018; Pecl et al, 2017)
Theory predicts that habitats are not prone to invasion for a given immigration rate (Davis et al, 2000; Lockwood et al, 2013). This prediction is empirically supported in terrestrial ecosystems by work at broad scales which used proxies of combined colonization and propagule pressures, such as human population or distance to the nearest conurbation (Aikio et al, 2012; Chytrý et al, 2008; Pyšek et al, 2015)
This non‐indigenous tunicate is a common hitchhiker of ship hulls, and the abundance of its recruits is likely to give a proxy of its associated propagule pressure (Lockwood et al, 2009; Zhan, Briski, Bock, Ghabooli, & MacIsaac, 2016)
Summary
Biodiversity is declining at an unprecedented rate, over multiple spatial scales, in response notably to climate change, pollution, direct exploitation of biota, changes in land and sea use, and bioinvasions (Catford, Bode, & Tilman, 2018; IPBES, 2019; Nowakowski, Frishkoff, Thompson, Smith, & Todd, 2018; Pecl et al, 2017). Human‐mediated species introductions redefine biogeographic boundaries (e.g. Wallace realms, Elton, 1958) and contribute substantially to biotic homogenization at multiple spatial scales (Capinha, Essl, Seebens, Moser, & Pereira, 2015; McKinney & Lockwood, 2005) In this context, there are urgent needs to determine the ecological and evolutionary mechanisms promoting the establishment and spread of NIS in order to help building up appropriate management and conservation strategies from local habitats to landscapes (Caselle, Davis, & Marks, 2018; Fitzgerald, Tobler, & Winemiller, 2016; Fridley & Sax, 2014; Kalusová et al, 2017). We further predicted an interaction between traffic and habitat categories, revealing whether the resistance mechanisms conferred by each habitat are vulnerable to colonization and propagule pressures
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