Effects of dredging on critical ecological processes for marine invertebrates, seagrasses and macroalgae, and the potential for management with environmental windows using Western Australia as a case study

Abstract

Dredging can have significant impacts on benthic marine organisms through mechanisms such as sedimentation and reduction in light availability as a result of increased suspension of sediments. Phototrophic marine organisms and those with limited mobility are particularly at risk from the effects of dredging. The potential impacts of dredging on benthic species depend on biological processes including feeding mechanism, mobility, life history characteristics (LHCs), stage of development and environmental conditions. Environmental windows (EWs) are a management technique in which dredging activities are permitted during specific periods throughout the year; avoiding periods of increased vulnerability for particular organisms in specific locations. In this review we identify these critical ecological processes for temperate and tropical marine benthic organisms; and examine if EWs could be used to mitigate dredging impacts using Western Australia (WA) as a case study. We examined LHCs for a range of marine taxa and identified, where possible, their vulnerability to dredging. Large gaps in knowledge exist for the timing of LHCs for major species of marine invertebrates, seagrasses and macroalgae, increasing uncertainty around their vulnerability to an increase in suspended sediments or light attenuation. We conclude that there is currently insufficient scientific basis to justify the adoption of generic EWs for dredging operations in WA for any group of organisms other than corals and possibly for temperate seagrasses. This is due to; 1) the temporal and spatial variation in the timing of known critical life history stages of different species; and 2) our current level of knowledge and understanding of the critical life history stages and characteristics for most taxa and for most areas being largely inadequate to justify any meaningful EW selection. As such, we suggest that EWs are only considered on a case-by-case basis to protect ecologically or economically important species for which sufficient location-specific information is available, with consideration of probable exposures associated with a given mode of dredging

A meta‐analysis reveals global patterns of sediment effects on marine biodiversity

“…The main variations in biological responses are hypothesized to be explained by the following: (a) phototrophic corals will be more sensitive to light attenuation than heterotrophic corals (e.g., Erftemeijer, Riegl, et al, ); (b) early life‐history stages will be more sensitive to elevated suspended sediment levels than later life‐history stages in fish (e.g., Wenger et al, ); and (c) highly mobile species will be more capable of avoiding increased sedimentation than sessile species in soft‐sediment communities (e.g., Fraser et al, ; Gomes, Correa, Sá, Neto, & Bernardino, ), making sessile species particularly susceptible to increased rates of sedimentation. However, the current evidence base for marine ecosystem‐scale impacts of sediments is scattered and incomplete (Brodie et al, ; Fraser et al, ; Wenger et al, ), requiring synthesis and a better understanding of the variability or generality of biological responses to support more rigorous assessment of the environmental impact of sediment disturbances.…”

“…Anthropogenic activities along the coastal fringe (e.g., urbanization) have also led to an increase in coastal erosion (Mentaschi, Vousdoukas, Pekel, Voukouvalas, & Feyen, 2018), hastening the flow of sediments to coastal waters. Additionally, the expansion of shipping and port activities requires an increase in dredging services (e.g., Barletta, Cysneiros, & Lima, 2016;Fraser et al, 2017;Jones, Bessell-Browne, Fisher, Klonowski, & Slivkoff, 2016), which also cause episodic events of elevated turbidity associated with the dumping of dredged sediments over coastal waters. Given the extended degradation of marine ecosystems as a consequence of increased inputs of sediments (Bessell-Browne, Negri, et al, 2017;De'ath & Fabricius, 2010;Eyre & Ferguson, 2006;Humanes, Fink, et al, 2017;Wilber & Clarke, 2001), the number of studies exploring the impacts of sediment pollution has proliferated considerably in recent years (Figure 1).…”

“…Several qualitative reviews of ecological impacts of light attenuation, suspended sediment and sedimentation on specific biological communities have been published (Airoldi, 2003;Bell et al, 2015;Erftemeijer, Riegl, et al, 2012;Erftemeijer & Robin Lewis, 2006;Fabricius, 2005;Jones et al, 2015Jones et al, , 2016Rogers, 1990). The main variations in biological responses are hypothesized to be explained by the following: (a) phototrophic corals will be more sensitive to K E Y W O R D S algae, benthic communities, corals, fish, marine biota, seagrass, sedimentation, stress factors, suspended sediments light attenuation than heterotrophic corals (e.g., Erftemeijer, Riegl, et al, 2012); (b) early life-history stages will be more sensitive to elevated suspended sediment levels than later life-history stages in fish (e.g., Wenger et al, 2017); and (c) highly mobile species will be more capable of avoiding increased sedimentation than sessile species in soft-sediment communities (e.g., Fraser et al, 2017;Gomes, Correa, Sá, Neto, & Bernardino, 2017), making sessile species particularly susceptible to increased rates of sedimentation. However, the current evidence base for marine ecosystem-scale impacts of sediments is scattered and incomplete (Brodie et al, 2012;Fraser et al, 2017;Wenger et al, 2017), requiring synthesis and a better understanding of the variability or generality of biological responses to support more rigorous assessment of the environmental impact of sediment disturbances.…”

Data set of submerged sand deposits organised in an interoperable spatial data infrastructure (Western Sardinia, Mediterranean Sea)

“…In Italy, in the Emilia-Romagna region, a geodatabase named IN_SAND was developed which helps the managers to plan the SSD exploitation (Correggiari et al, 2012(Correggiari et al, , 2016. It is also known that the dredging operation can negatively affect the marine ecosystems and in particular the sessile benthic communities (Rogers, 1990;Desprez, 2000;Erftemeijeret al, 2012;Fraser et al, 2017). For this reason, accurate procedures that aimed to minimise the impact of nourishment operations (including dredging) are adopted by several countries and must be required when a nourishment project is developed (Finkl and Khalil, 2005;Radermacher et al, 2017).…”

“…In Italy, for this reason, ISPRA and CNR developed the ENV_SAND database (Grande et al, 2015), which aimed to collect the data acquired during the monitoring programme of a nourishment project, including the dredging of the SSDs (Nicoletti et al, 2018;MATTM-Regioni, 2018). The introduction of these geodatabases provides instruments that could be very helpful in the management of SSDs, not only in terms of sand volume but to (i) support the environmental impact assessments, (ii) monitor the marine environmental conditions during the activities and (iii) manage the impact of dredging and nourishment activities on marine ecosystems (Erftemeijeret al, 2012;Fraser et al, 2017;Nicoletti et al, 2018;MATTM-Regioni, 2018).…”