Assessment of the benthic biota of a deep coastal ecosystem by remote and in situ sampling techniques Kris I. Waddington A,C , Jessica J. Meeuwig A , Scott N. Evans B and Lynda M. Bellchambers B A M470 Centre for Marine Futures, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. B Department of Fisheries Western Australia, PO Box 20, North Beach, WA 6920, Australia. C Corresponding author. Email: Kris.Waddington@uwa.edu.au Abstract. Deep coastal ecosystems ( 4 35 m) occur on the continental shelf of many regions and are poorly understood relative to shallow-water ecosystems. These ecosystems frequently support commercially important benthic-associated species, such as the western rock lobster – the most valuable single-species fishery in Australia. We used remote (towed video) and in situ (diver collection) sampling techniques to investigate the benthic biota of deep coastal ecosystems along the temperate west coast of Australia. We tested the hypotheses that (1) there is no difference in benthic assemblage structure between shallow and deep coastal ecosystems, (2) there is no difference in benthic assemblage structure between locations, and (3) both sampling techniques provide comparable descriptions of benthic assemblages. Deep coastal ecosystems were found to have significant algal and sponge assemblages, suggesting that a reduction in irradiance with depth is not constraining algal distribution. Differences in sponge, algal and macroinvertebrate community composition were detected at a regional scale between study locations. Both sampling techniques identified differences in the composition of benthic assemblages according to location, and yielded similar outcomes with respect to sponge and algal assemblages, suggesting that a single method of habitat classification can be used in future studies to determine broad scale patterns in benthic assemblage composition. Additional keywords: algae, diver sampling, habitat classification, macroalgae, sponges, temperate, towed video. Introduction Benthic communities occupying areas of the continental shelf deeper than 35 m – here termed ‘deep coastal ecosystems’ – occur in many regions, yet are poorly understood compared with shallow-water areas (Littler et al. 1986; Spalding et al. 2003). Limited knowledge of benthic communities in deep coastal ecosystems relates to logistical difficulties and expense asso- ciated with sampling them compared with shallow coastal ecosystems. For instance, for hard-bottom communities, tax- onomically specific abundance data and voucher specimens typically must be collected using specialised divers as such communities are not amenable to collection using trawl or sled. This makes collection of relatively few ecological samples expensive. Remote sampling using towed video systems or autonomous underwater vehicles (AUVs) provides an alter- native but these systems have limitations in that voucher spe- cimens are not provided and the level of taxonomic resolution is reduced. An understanding of benthic communities in deep coastal ecosystems is important as these ecosystems support commercially important fish and invertebrate species (Rogers et al. 1999; Waddington et al. 2008). Given the recognised role of benthic communities in providing habitat and food for eco- nomically important species (Dayton et al. 1995; Turner et al. 1999; Waddington et al. 2008), data on benthic community composition is a key component of understanding processes occurring in deep coastal ecosystems. Deep coastal ecosystems are likely to differ from shallow ecosystems. For instance, an increase in depth may result in a decrease in wave action (Brey 1991), potentially leading to differences in benthic algal assemblages (Phillips et al. 1997; Wernberg and Connell 2008) and the composition of associated invertebrate fauna (Tuya et al. 2008). Irradiance is also reduced as water depth increases, which may affect macroalgal community composition (Kirkman 1989; Staehr and Wernberg 2009). We investigated the benthic community composition of deep coastal ecosystems along the temperate west coast of Australia. This region has clear waters, is oligotrophic and strongly influenced by the Leeuwin Current – a poleward- flowing low-nutrient current (Hanson et al. 2005). The Leeuwin Current coupled with low terrestrial runoff (Li et al. 1999) means that pelagic production is low and benthic production is important for supporting fisheries in the region (Lenanton et al. 1991). Like many coastal systems, substantially more effort has been expended in understanding shallow coastal regions com- pared with deep coastal ecosystems in this region. Shallow coastal reefs are dominated by the kelp Ecklonia radiata (Phillips et al. 1997; Wernberg et al. 2003a; Kendrick et al. 2004), which reaches 1–2 m in length (Wernberg et al. 2003b) CSIRO PUBLISHING Marine and Freshwater Research, 2010, 61, 1164–1170 www.publish.csiro.au/journals/mfr Ó CSIRO 2010 10.1071/MF09273 1323-1650/10/101164