Sabella spallanzanii and seafloor biodiversity enhancement in a marine soft-sediment system

Abstract

Predicting and managing the potential economic, social, and ecological impacts of bioinvasions is a key goal of non-indigenous species (NIS) research worldwide. The marine fan worm, Sabella spallanzanii, is an ecosystem engineering NIS that forms dense filter-feeding canopies on hard substrata and large clumps of individuals in soft sediment habitats. In this study, we investigated the epifaunal assemblages associated with Sabella clumps of increasing size and complexity from soft-sediment benthic ecosystems in Auckland Harbour, New Zealand. The diversity and abundance of epifaunal taxa increased with clump size. Species accumulation curves suggest that with further increases in Sabella clump size, diversity will continue to increase. There were no differential effects on taxa related to feeding mode or motility despite the potential for Sabella to reduce food to suspension feeders (through competition) and increase food supply to deposit feeders (through biodeposition). Our results provide an example of local biodiversity enhancement by an NIS, though some of the species benefitting from Sabella were themselves non-indigenous or of uncertain origin (cryptogenic/indeterminate). Longer term studies of the impacts of Sabella on native biodiversity and ecosystem functioning, including on food webs, are important next steps.