Sediment and Turbidity Associated with Offshore Dredging Increase Coral Disease Prevalence on Nearby Reefs

Abstract

In recent decades, coral reef ecosystems have declined to the extent that reefs are now threatened globally. While many water quality parameters have been proposed to contribute to reef declines, little evidence exists conclusively linking specific water quality parameters with increased disease prevalence in situ. Here we report evidence from in situ coral health surveys confirming that chronic exposure to dredging-associated sediment plumes significantly increase the prevalence of white syndromes, a devastating group of globally important coral diseases. Coral health surveys were conducted along a dredging-associated sediment plume gradient to assess the relationship between sedimentation, turbidity and coral health. Reefs exposed to the highest number of days under the sediment plume (296 to 347 days) had two-fold higher levels of disease, largely driven by a 2.5-fold increase in white syndromes, and a six-fold increase in other signs of compromised coral health relative to reefs with little or no plume exposure (0 to 9 days). Multivariate modeling and ordination incorporating sediment exposure level, coral community composition and cover, predation and multiple thermal stress indices provided further confirmation that sediment plume exposure level was the main driver of elevated disease and other compromised coral health indicators. This study provides the first evidence linking dredging-associated sedimentation and turbidity with elevated coral disease prevalence in situ. Our results may help to explain observed increases in global coral disease prevalence in recent decades and suggest that minimizing sedimentation and turbidity associated with coastal development will provide an important management tool for controlling coral disease epizootics.

Reserves as tools for alleviating impacts of marine disease

“…Elevated exposure to secondary plume water is an important driver of coral disease assemblages and appears to undermine the potential of protected areas to alleviate tissue loss from white syndromes, a devastating group of diseases [45]. Secondary waters are characterized by finer sediment fractions and higher chlorophyll-a concentrations that reflect enhanced phytoplankton biomass from nutrient enrichment [54].…”

“…For example, the passage of intense tropical storms is associated with subsequent disease in organisms as diverse as plants [40], urchins [41] and reef corals [42]. Furthermore, other marine disease outbreaks are linked to chronic exposure to pollutants, such as sewage [43], terrestrial sediment or agricultural herbicides [44,45], nutrients and fertilizers [46,47], and aquaculture [48]. Given that pressures on marine biodiversity are projected to escalate adjacent to polluting population centres and coastlines [9] and with predicted increases in the number of intense tropical storms [49], it is imperative to further assess the potential role protected areas could play in managing marine diseases subject to environmental disturbances.…”

Communities and change in the anthropocene: understanding social-ecological vulnerability and planning adaptations to multiple interacting exposures

“…Close to one quarter of the world's population lives within 100 km of the coast, meaning that coastal systems have experienced disproportionately rapid expansion of economic activity and infrastructure development (Small and Nicholls 2003). Coastal dredging for land reclamation and port construction increases sedimentation and turbidity and has been linked with significantly higher incidence of coral disease in Western Australia (Pollock et al 2014). Extractive industries, including mining and fossil fuel exploitation, can create exposure to new stressors in coastal communities.…”

Settlement Patterns of Corals and other Benthos on Reefs with Divergent Environments and Disturbances Histories around the Northeastern Arabian Peninsula

“…Over the past several decades, reefs have been increasingly degraded by overfishing, pollution, sedimentation, disease and coral predator outbreaks (Maina et al, 2013;Riegl et al, 2013;Pollock et al, 2014;Wear and Thurber, 2015;Mumby, 2016). These stressors have resulted in an estimated loss of up to 50% of coral cover from many reefs in the past several decades (De'ath et al, 2012;Hughes et al, 2017), with a third of reef-building coral species now considered at risk of extinction (Carpenter et al, 2008).…”