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Dredging in the marine environment to create and maintain navigable shipping channels and allow safe ship access is a necessary component of most ports and coastal infrastructure developments (Foster et al. 2010). Dredging involves the removal of sediment and/or rock from the seabed (McCook et al. 2015) and the excavation, and often the subsequent disposal at sea in dredge material placements sites, can generate suspended sediment that can impact upon nearby epibenthic marine communities ie it is a potential hazard (Rogers 1990, Foster et al. 2010, Erftemeijer et al. 2012, Jones et al. 2016). Well recognised cause-effect pathways include suspended sediment interfering with filtering and feeding mechanisms, increased turbidity (water cloudiness) changing light quantity and quality (for benthic primary producers), and increased sediment deposition causing smothering (Jones et al. 2016).

Predicting the environmental consequences before a dredging program is an important part of the environmental impact assessment (EIA) stage and predicated upon establishing a relationship between these dredging pressures (light reduction, suspended sediment, sediment deposition etc) and biological responses in underlying communities ie developing thresholds. In Australia, this information is used in zonation schemes to predict where effects may occur, translating the hazard of dredging to a risk, and typically on a spatial basis (GBRMPA 2012b, EPA 2016). If dredging is permitted then the thresholds are also used in monitoring programs, where they can inform proponents of conditions that are approaching or exceeding levels where …