Fig 1.
Location of Barrow Island in NW of Western Australia off the Pilbara coast, and the 15 water quality and coral health monitoring sites relative to the primary excavation areas (a materials offloading facility (MOF) sites and turning basin, and tanker access channel (LNG sites)).
Fig 2.
Sediment smothering in different coral morphologies during a large-scale capital dredging project–see text for explanation.
Legends on the images indicate the site name (see Fig 1), distance from dredging activities (km), and days since the start of dredging (19 May 2010). The images show the differing susceptibility of a range of morphologies to sediment deposition with colonies with concave areas and depressions on the surface more commonly accumulating sediment compared to more hemispherical, rounded morphologies. For the arrows, S = sediment accumulation.
Fig 3.
Sediment smothering during a dredging project, showing different susceptibility of different morphologies–see text for explanation.
Legends on the images indicate the site name (see Fig 1), distance from dredging activities (km), and days since the start of dredging (19 May 2010). (A) A mix of morphologies including massive (hemispherical) colonies, encrusting and branching (tabulate) morphologies showing smothering of the flat, low lying encrusting form at Day 433. (B–D) Images showing the sediment clearing abilities of branching morphology compared to underlying massive, hemispherical morphology of the Porites spp. For the arrows, M = mucus or mucous sheet, B = bleaching, S = sediment accumulation, R = reparation/repair.
Fig 4.
Time series of images showing sediment smothering during a dredging project, showing the different susceptibility of two different morphologies–see text for explanation.
Legends on the images indicate the site name (see Fig 1), distance from dredging activities (km), and days from the start of dredging (19 May 2010). The images show the superior sediment clearing abilities of branching (tabulate) morphology of the Acropora spp. compared to underlying massive, hemispherical morphology of the Porites spp. which becomes smothered with fine sediments. White arrows indicate mucous sheet formation (see text).
Fig 5.
Time series of images showing sediment smothering during a dredging project, showing the different susceptibility of different morphologies in Porites spp.–see text for explanation.
Colonies in (A) and (B) were from site LNG2, 1.0 km away from the dredging. Legends on the images indicate days since the start of dredging on 19 May 2010 (see text). The images show the contrasting the sediment clearing capacity of the Porites spp. colonies with subtly differing morphologies (bumpy versus smooth, see text). For the arrows, M = mucus or mucous sheet, B = bleaching, S = sediment accumulation, R = reparation/repair contrasting.
Fig 6.
Effects of long-term sediment smothering on corals during a dredging project–see text for explanation.
Legends on the images indicate the site name (see Fig 1), distance from dredging activities (km), and days since the start of dredging on 19 May 2010). The time series for colonies (from three different sites) over 380 days of the dredging show tissue bleaching in surface hollows of massive Porites spp. that were at some stage covered with sediment and eventual recovery of pigmentation. (D-F) Show similar sediment smothering and/or bleaching in hollows of the massive Porites spp. (background) whilst the overlying branching Acropora, Pocillopora and Porites species in the foreground show no smothering. For the arrows, M = mucus or mucous sheet, B = bleaching, S = sediment accumulation, R = reparation/repair.
Fig 7.
Time series of images of sediment smothering in a foliose Turbinaria spp. during a dredging project–see text for explanation.
Shown is a coral colony located at site MOFB (see Fig 1) 1.0 km away from the nearest dredging over the 533 d Barrow Island capital dredging program, showing various degrees of smothering, bleaching and recovery/repair (see text). For the arrows, M = mucus or mucous sheet, B = bleaching, S = sediment accumulation, R = reparation/repair.
Fig 8.
Mucous sheet formation and mucus production in massive, foliose and branching coral colonies during a dredging project–see text for explanation.
Legends on the images indicate the site name (see Fig 1), distance from dredging (km), and days since the start of dredging (19 May 2010). For the arrows, M = mucus or mucous sheet, B = bleaching.
Fig 9.
A, B, C. Time sequence of branching, massive and encrusting coral colonies during a dredging project–see text for explanation. Legends on the images indicate the site name (see Fig 1), distance from dredging activities (km), and days since the start of dredging on 19 May 2010). Images show the growth of some colonies over the dredging program. For the arrows, M = mucus or mucous sheet.
Fig 10.
A-D. Distance decay relationship for physical parameters (turbidity sedimentation, light availability) and biological parameters (mucus sheet production, smothering and mortality) during a large-scale dredging project. Shown are (A) the average daily nephelometry-derived suspended sediment concentration (SSC) and (B) Sediment deposition index (range 0–1), against distance (km) from dredging (see Fig 1) during the pre-dredging, baseline phase, and from the start of dredging (Day 0, 19 May 2010) until completion (4 Nov 2011). The 2D plots show (C) fortnightly maximum 14 d running mean NTU, (D) 60 d running mean sediment deposition index, (E) 14 day running mean daily light integral over the dredging phase, the proportional increase in clay and silt in benthic sediments (F), the proportion of coral colonies having a mucous score of >3 (6–33% coverage) (G), the proportion of coral colonies having a sediment cover score of >3 (6–33% coverage) and estimated probability of non-zero Porites spp. mortality (H). Red and orange lines indicate the estimated distance of 10% (ED10) and 50% (ED50) effect as determined by fitted regression.
Table 1.
Effect distances (ED) in km for a 90% decline (ED10) and 50% decline (ED50) in physical pressure parameter: SSCs (NTU), benthic light (DLI), sediment deposition and changes in silt and clay content and (B) biological response parameters including: sediment smothering and mucous sheet covering in massive Porites spp.
The physical and biological parameters were measured at 17 locations at different distances from the dredging activities (Fig 1). Effect distances were calculated from the predicted value at the farther site distance (34.8 km) to that of the predicted value at the closest site distance (190 m), with confidence bounds estimated from a posterior sample from Bayesian model fits.
Fig 11.
Changes in the particle size distribution of surficial seabed sediments collected from multiple locations from 200 m to 34 km away from the dredging before and after dredging.
Shown are A) ternary plot of the percentage composition of the sediments collected (see Fig 1) expressed as percentage gravel, sand and silt and clay (62.5–0.02 μm). (B) Site level summaries of the clay and silt content immediately after dredging compared to before dredging, against distance (km) from the dredging.