An investigation of the impacts on biodiversity and ecosystem functioning of soft sediments by the non-native polychaete Sternaspis scutata (Polychaeta: Sternaspidae) Rachel Shelley a, ⁎, Stephen Widdicombe b , Malcolm Woodward b , Tim Stevens a , C. Louise McNeill b , Michael A. Kendall b a SEOES, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK b Plymouth Marine Laboratory, Prospect Place, Plymouth, PL1 3DH, UK abstract article info Keywords: Benthos Infaunal Invasive Non-native In recent years the non-native polychaete Sternaspis scutata has rapidly expanded its range in inshore muddy sediments along the coast of SW England (UK). To determine the impact the arrival of this moderately large infaunal deposit feeding polychaete could have on benthic biodiversity and ecosystem function, a mesocosm experiment has been conducted. Sternapsis scutata were added to undisturbed sediment cores containing natural fauna. Individuals of S. scutata were added at densities 2x and 10x the current abundance of this species at the collection site in Plymouth Sound. Nutrient fluxes and macrobenthic diversity were assessed after a period of fifty days. Despite the very large increase in biomass caused by the addition of S. scutata to the sediment cores there was no significant difference in the diversity of the resident benthic biota in treated cores. It is concluded that despite its size, the relative immobility of S. scutata dictates that its presence has little impact on the species around it. The addition of this species did significantly reduce the release of nitrite (NO 2 - ) and increase the release of ammonium (NH 4 + ) from the sediment. These findings support the assertion that the relationship between biodiversity and ecosystem functioning is idiosyncratic. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The arrival of non-native species and their impact on biodiversity is an issue that has been of concern to ecologists and environmental managers for many years. Such species may alter habitats physically, change established patterns of predation or drive increased competi- tion for space or trophic resources. The over-riding concern of coastal managers is that these pressures will result in the loss of biodiversity and consequentially ecosystem function (Kohler and Courtenay, 1986; Naeem, 2002; Covich et al., 2004). Ruiz et al. (1997) suggested that in America, most of the estuaries were affected by invading species but emphasised that the size and nature of the impacts were poorly understood and were difficult to predict. Subsequently, much of the research on the impacts of non-native species on the structure and function of shallow water marine assemblages has come from studies of species living on hard substrata particularly ascidians (e.g. Blum et al., 2007; Altman and Whitlatch, 2007), molluscs (e.g. Kushner and Hovel, 2006) or algae (e.g. Britton-Simmons, 2004). On hard substrata, competition for space on the rock surface can be of primary significance in determining the composition of the biota; however when new species move into a sand or mud dwelling assemblage, the three dimensional nature of the sediment could potentially reduce the severity of species interactions. The best documented example of a non-native species invading soft sediment relates to addition of the polychaete worm Marenzellaria spp. to the biota of the Baltic Sea (Essink and Dekker 2000; Kotta et al., 2001). This complex of species appears to have had an impact on the populations of the resident species, in particular the amphipod Monoporeia affinis (Kotta and Olafsson, 2003) and on the polychaete Nereis diversicolor (Kotta et al., 2001). The invasion of Marenzellaria also changed the function of benthic sediments, increasing fluxes of ammonium and phosphorus to the water column (Hietanen et al., 2007). Other studies of invasions in soft sediments are less comprehensive and have often focussed on the impacts of predators (e.g. McDonald et al., 2001; Mistri, 2004; Ross et al., 2004; Hollebone and Hay 2007), and are of lesser relevance to a discussion that follows of the impact of the deposit feeding polychaete Sternaspis scutata (Ranzani, 1817) on the benthic biota. Townsend et al. (2006) reported that the infaunal deposit-feeding polychaete Sternaspis scutata, a species regarded as non-native, had greatly expanded its range in U.K. waters in recent years. Prior to 1986 the species was only known from a single site at Portland Harbour (Hiscock and Hannam, 1986), by 2005 the species was recorded in muddy sediments along ∼ 125 km of the coastline of SW England. Sternapsis scutata is a moderately sized polychaete (reaching 30 mm in length with a body diameter of 15 mm) (Rouse and Pleijel, 2001). It is Journal of Experimental Marine Biology and Ecology 366 (2008) 146–150 ⁎ Corresponding author. Tel.: +441752 584567. E-mail address: rachel.shelley@plymouth.ac.uk (R. Shelley). 0022-0981/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2008.07.018 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe