An investigation of benthic sediments and macrofauna within pearl farms of Western Australia J.E. Jelbart ⁎, M. Schreider, G.R. MacFarlane University of Newcastle, School of Environmental and Life Sciences, University Drive, Callaghan, NSW 2308, Australia abstract article info Article history: Received 30 November 2010 Received in revised form 6 July 2011 Accepted 8 July 2011 Available online 20 July 2011 Keywords: Aquaculture Pearl farming Benthic macrofauna Benthic sediments Pinctada maxima The Kimberley The pearl oyster (Pinctada maxima) aquaculture industry in the Kimberley region of Western Australia has been established for decades. However, investigation of benthic sediments and macrobenthic communities within pearl farms for this region has not taken place until now. Pearl oysters may have the potential to foul the benthic layer under the farms through the deposition of feces and pseudo-feces from the cultured oysters and fouling organisms, and the fallout of debris from the longlines that suspend the pearl oysters. This organic waste and debris can accumulate in the sediments below the oyster longlines and potentially lead to organic enrichment and even eutrophication. Other aquacultures (such as some finfish and other shellfish) have caused eutrophication of marine sediments and a concurrent change in benthic macrofauna. For two years we sampled the sediments below three P. maxima pearl oyster farms in remote regions of the Kimberley coast. Sediment core samples were taken to measure physico-chemical variables (redox potential, nutrients loads and total organic matter) while grab samples collected the benthic macrofauna (N 1 mm in size). Each farm was compared to four control locations (total = 12 control locations) within the same region. At all three pearl farms there was no indication of eutrophication (nutrient enrichment). We concluded that the variability in benthic physico-chemistry beneath pearl farms was within the bounds of natural variability at reference locations. There were also no consistent differences in the benthic macrofauna assemblages below the pearl oyster farms when compared to control locations. There was considerable natural variability of the benthic macrofauna among all locations, but especially among the reference locations. The reference locations were as different from one another as they were from the farm locations, indicating that the diversity of benthic macrofauna taxa, and their relative abundances within sediments underlying the farms fell within the range of natural variability found at these spatial scales. The importance of robust assessment of potential environmental impact of aquaculture facilities is stressed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The gold or silver lipped pearl oyster, Pinctada maxima, forms the basis of Australia's pearl oyster culture industry located on the Kimberley coast of northern Western Australia (Fletcher et al., 2006; Prince, 1999). No artificial feed or chemicals are required in the culture of pearl oysters. The primary potential impact is thought to be the deposition of feces and pseudofeces from the cultured oysters and the fallout of debris from the longlines that suspend the pearl oysters (Gifford et al., 2004; O'Connor et al., 2003; Yokoyama, 2002). Pearl oysters (like other bivalves) are filter feeders of suspended particles in the water column. They produce biodeposits in the form of feces and pseudofecal pellets as a waste product. It is thought that these biodeposits are similar in composition to the natural sediments because they are derived from phytoplankton and suspended particles (Grant et al., 1995). However these biodeposits and shell debris can accumulate in the sediments below the oyster longlines and potentially lead to localised organic enrichment and even eutrophication (a detrimental increase of nutrients such as carbon and nitrogen). Further, the cleaning of biofouling organisms from oyster shells during deployment may accumulate beneath the lease. This may reduce oxygen content (Hatcher et al., 1994), increase nutrient load and alter dependent benthic macrofaunal communities (Chamberlain et al., 2001; Kaspar et al., 1985; Pearson and Rosenberg, 1978). Few studies to date have directly considered the potential impacts of pearl oyster farming on the marine benthos (but see Enzer Marine, 1998; Fletcher et al., 2006; O'Connor et al., 2003; Prince, 1999; Wells and Jernakoff, 2006; Yokoyama, 2002). Although a number of studies have established impacts on benthic systems from other bivalve aquacultures, namely mussel aquaculture (e.g. Crawford et al., 2003; Grant et al., 1995; Hatcher et al., 1994; Lasiak et al., 2006; Miron et al., 2005), it cannot be assumed that pearl oyster aquaculture may exhibit the same impacts. This is due to inherent differences in stocking Aquaculture 319 (2011) 466–478 ⁎ Corresponding author. Tel.: + 61 249505322; fax: + 61 249505737. E-mail address: jane.jelbart@newcastle.edu.au (J.E. Jelbart). 0044-8486/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2011.07.011 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online