Abstract
The Mediterranean fanworm, Sabella spallanzanii, is an introduced and established “unwanted species” in New Zealand, subject to nationwide targeted surveillance in port, marina, urban and natural environments. S. spallanzanii has the potential to change soft-sediment benthic habitats due to the physical presence of the fanworm’s tube and associated biological activities, particularly suspension feeding and bio-deposition. A 6-month field experiment was conducted to investigate the impacts of S. spallanzanii on existing communities within invaded soft-sediment habitats. Macrofaunal communities were assessed using traditional sampling and taxonomy while microbial and eukaryotic communities were characterised using metabarcoding of 16S and 18S ribosomal genes, respectively. Live and mimic S. spallanzanii were transplanted at different densities (10 - 50 individuals per m2) into experimental plots with existing assemblages, to test for potential biological and/or physical effects on benthic communities. Analyses revealed consistent, significant differences in macrofaunal, eukaryote and bacterial assemblages in the presence of live S. spallanzanii and mimics, indicating that these effects are brought about by biological and physical functions associated with the worms. The presence of S. spallanzanii did not alter total abundance and taxa richness of benthic assemblages but resulted in compositional differences. Changes in the structure of native benthic communities, as indicate by this study, can potentially impact functioning of soft-sediment habitats, through alterations to nutrient cycling, bioturbation and benthic-pelagic coupling. Quantitative measurements of impacts are crucial to understand the trajectory of marine invasions, their roles in re-structuring communities, and to guide management efforts.
Highlights
Non-indigenous species (NIS) can have profound impacts on marine coastal ecosystem functioning, by altering community structure, native species richness and ecological processes (Ruiz et al, 1999; Molnar et al, 2008)
This effect was consistent across benthic macrofaunal, eukaryote and bacterial assemblages, and indicates that S. spallanzanii may affect benthic community structure through both biological and physical processes and mechanisms
Small mobile taxa and larger bioturbator taxa such as ophiuroids, a burrowing crab (Pilumnus novaezealandiae), and a burrowing holothurian (Taeniogyrus dendyi) were less abundant, or absent, in treatment plots compared to controls
Summary
Non-indigenous species (NIS) can have profound impacts on marine coastal ecosystem functioning, by altering community structure, native species richness and ecological processes (Ruiz et al, 1999; Molnar et al, 2008). Some NIS can regulate the availability of resources to other species by changing the physical state of the ecosystems they invade. Such species are termed “ecosystem engineers” (Jones et al, 1994) or “transformier species” (Richardson et al, 2000), which have the potential to disproportionately affect the functioning of coastal habitats (Cuddington and Hastings, 2004). Ecosystem engineers modulate invaded environments through physical and biological mechanisms. The proliferation of an invasive filter-feeding clam in San Francisco Bay (USA) caused persistent changes in planktonic food webs and benthic macrofaunal community structure through alteration of benthic-pelagic coupling (Peterson, 2002; Cloern and Jassby, 2012)
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