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Rio Tinto AlcanEnvironmental Impact StatementSouth of <strong>Embley</strong> ProjectTable 6-2 Benthic Habitat SurveysLocationNumber ofTowed Transects orDrop Video Drift SitesMethodSurvey dateProposed disposal ground 18 Towed sled Oct 07Mounds areas (10km WNW from the port) 9 Towed sled Oct 07Proposed port area 9 Towed sled Oct 07Sub-tidal soft reef area (150m south of theport)9 Drop video Oct 07Hey River Terminal Preliminary inspection Drop video Oct 07Hey River Terminal 10 Drop video Nov 08Hey River Terminal 12 Drop video June 09Hornibrook Terminal Preliminary inspection Drop video June 08Hornibrook Terminal 11 Drop video June 09Humbug Terminal Preliminary inspection Drop video June 08Humbug Terminal 7 Drop video June 08Pera Head** Preliminary inspection Drop video Oct 07Pera Head 299 (points on grid) Drop video June 08Boyd Point** Preliminary inspection Drop video Oct 07Boyd Point 114 (points on grid) Drop video June 08Pera Head to Thud Point 19 Drop video June 10Port area departure channel 20 Drop video June 10Nine Mile Reef 4 Drop video June 10** Preliminary inspection following identification of hard coral reefs6.3.1.2 Dominant Reef Habitat SurveysThe distribution of dominant reef habitat types (hard coral or soft -coral sponge) betweenBoyd Point and Thud Point were determined through site inspection following inference fromavailable bathymetric charts, bathymetric survey commissioned by RTA and interpreted aerialphotography. Slope analysis overlain with detailed contour information was also applied toassist in the delineation of reef patches. Drop camera video inspection was undertaken at PeraHead and Thud Point to assist in confirming the inferred presence of these reef areas. Detaileddrop camera video surveys (described below) in 2007 and 2008 had already confirmed theextent of reef habitats at Pera Head and Boyd Point.Drop camera video inspection was also undertaken from Nine Mile Reef approximately 6kmsouth-south-west of the proposed disposal ground. This is the nearest substantial seabedfeature to the proposed spoil ground.Inspection of potential reef habitat south of Thud point was not undertaken due to the very lowlikelihood of turbid plumes extending inshore beyond Thud Point. This was confirmed throughturbid plume modelling (refer to Section 6.9.2.2).6.3.2 Inshore and Offshore Reef HabitatsWhile the vast majority of the Gulf of Carpentaria consists of open sandy and muddy habitats,some reef habitat occurs. Fringing and nearshore reefs occur on many parts of western CapeYork and are recorded in parts of Albatross Bay, including much of the southern foreshore andJantz /Duyfken Point (Baker and Sheppard 2006), but are generally poorly mapped.The iron stone formations present along the western Cape York shoreline support thedevelopment of shallow fringing hard coral and soft benthos reef communities. Reef habitatsimilar to what is present within the Project area is located approximately 75km to the north ofAlbatross Bay, in the vicinity of the mouth of Port Musgrave (refer Figure 1-1 for regionalmap). Dog Reef extends approximately 7km to the south of the mouth of Port Musgrave andSection 6 Marine Page 6-18
Rio Tinto AlcanEnvironmental Impact StatementSouth of <strong>Embley</strong> Projectaverages about 800m in width. It is a rocky algal reef system with patchy live hard and softcoral cover along its deepest fringe. Kerr Reef is situated approximately 16 km north-north westof the mouth of Port Musgrave, and supports a high live hard coral cover compared withinshore reef areas (Pers. obs. T. Koskela 2009).There are also recently discovered deeper sub-tidal reefs in the Gulf of Carpentaria that are wellbelow the surface and consist of a thin and patchy veneer of live corals (Harris et al. 2004).None of these deeper reefs are known to occur in the vicinity of the study area.6.3.2.1 Proposed Port AreaNear shore fringing reef communities in the vicinity of the proposed port area occur at BoydPoint, Pera Head and between Pera Head and Thud Point. These comprise both reefs containinghard corals and low profile reefs containing soft coral sponge assemblages. The reef habitatshave established primarily over ironstone formations. Overall, reef systems between Boyd Pointand Thud Point covered approximately 418ha (refer Figure 6-18), comprising 144ha ofvalidated reef extent and 274ha of inferred reef. A breakdown of reef habitats is included inTable 6-3.Three abiotic habitats silty sand, coarse sand and rock were identified around Boyd Pointand Pera Head. Video results confirm the presence of fringing and submerged reefs located atBoyd Point, approximately 2.0km north of the proposed port, and Pera Head approximately2.8km south of the proposed port. These reefs cover an area of approximately 49ha and 72ha,respectively. Results of percentage cover for sponges, soft corals and hard corals are presentedin Figure 6-19. Percentage cover of reefs between Pera Head and Thud Point was inferredfrom the detailed Boyd Point and Pera Head survey on the basis that the reefs occupied similarinshore environments and appeared similar during drop camera video inspections.Hard corals over the reef areas include species from the following genera: Porites, branchingAcropora, Turbinaria, Monitipora, Lobophyllia, Platygyra, Pavona and Favia. Identification ofcorals to species level was not possible as this would have required scientific divers enteringwaters where saltwater crocodiles pose a safety threat. While hard corals are present, there isalso abundant sponge and soft-coral fauna and marine algae.Two small patches of submerged sponge and soft coral reef occur 150m south of the proposedport, and another two approximately 1km north-east of the proposed access channel. Together,these habitats total approximately 23ha. Sponge and soft coral assemblages adjacent to PeraHead are estimated at 48ha (refer Figure 6-19). Inferred extent of sponge soft coral habitatbetween Pera Head and Thud Point is estimated to be approximately 117ha.A summary of reef areas and extent of their dominant benthic assemblage (hard coral orsponge soft coral) is provided in Table 6-3.Table 6-3Inshore Reef Areas and Extent of Dominant Benthic AssemblagesLocationTotal area(ha)Hard Coral(ha)Sponge Soft Coral(ha)Boyd Point 49 49 0Port area (between Boyd Point to Pera Head) 23 0 23Pera Head 72 24 48South from Pera Head to Thud Point (inferred) 274 157 117Images of benthic habitats from Boyd Point reef, Pera Head reef, the port area, Thud Point reefand open benthic habitat within the departure channel area are provided within Plate 6-2.Section 6 Marine Page 6-19
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