Chronic nutrient enrichment increases prevalence and severity of coral disease and bleaching

Abstract

Nutrient loading is one of the strongest drivers of marine habitat degradation. Yet, the link between nutrients and disease epizootics in marine organisms is often tenuous and supported only by correlative data. Here, we present experimental evidence that chronic nutrient exposure leads to increases in both disease prevalence and severity and coral bleaching in scleractinian corals, the major habitat-forming organisms in tropical reefs. Over 3 years, from June 2009 to June 2012, we continuously exposed areas of a coral reef to elevated levels of nitrogen and phosphorus. At the termination of the enrichment, we surveyed over 1200 scleractinian corals for signs of disease or bleaching. Siderastrea siderea corals within enrichment plots had a twofold increase in both the prevalence and severity of disease compared with corals in unenriched control plots. In addition, elevated nutrient loading increased coral bleaching; Agaricia spp. of corals exposed to nutrients suffered a 3.5-fold increase in bleaching frequency relative to control corals, providing empirical support for a hypothesized link between nutrient loading and bleaching-induced coral declines. However, 1 year later, after nutrient enrichment had been terminated for 10 months, there were no differences in coral disease or coral bleaching prevalence between the previously enriched and control treatments. Given that our experimental enrichments were well within the ranges of ambient nutrient concentrations found on many degraded reefs worldwide, these data provide strong empirical support to the idea that coastal nutrient loading is one of the major factors contributing to the increasing levels of both coral disease and coral bleaching. Yet, these data also suggest that simple improvements to water quality may be an effective way to mitigate some coral disease epizootics and the corresponding loss of coral cover in the future.

Combined effects of warming and ocean acidification on coral reef Foraminifera Marginopora vertebralis and Heterostegina depressa

“…The stress caused by overgrowing population of photosymbionts has been described by Wooldridge (2009) to physiologically affect corals and lower their bleaching thresholds. Furthermore, a 3-yr field experiment demonstrated the same effect, where corals bleached more in artificial nutrient enrichment treatments (Vega Thurber et al 2013).…”

Bacterial predation in a marine host-associated microbiome

“…We then examined the prevalence of Halobacteriovorax across coral microbiomes using a 3-year time series of 16S rRNA libraries generated from the surface mucus layer of corals (Supplementary Methods) that were exposed to increased nitrogen and phosphorus to simulate nutrient pollution, environmental factors that indirectly contribute to coral disease (Vega Thurber et al, 2014). Halobacteriovorax was prevalent in 479% of all samples (n = 198) and not detected in the other samples.…”

Unsustainable Land Use, Sediment-Laden Runoff, and Chronic Raw Sewage Offset the Benefits of Coral Reef Ecosystems in a No-Take Marine Protected Area

“…Also, large scale, climate change-related sea surface warming (Hoegh-Guldberg, 1999;Li & Reidenbach, 2014), massive coral bleaching (Miller, Muller, Rogers, Waara et al, 2009), mass coral mortalities (Miller, Waara, Muller & Rogers, 2006), and ocean acidification (Pandolfi, Connolly, Marshall & Cohen, 2011) have resulted in significant biodiversity loss (Jones, McCormick, Srinivasan & Eagle, 2004) and in the alteration of ecosystem functions (Bellwood, Hughes, Folke & Nyström, 2004), benefits (Veron, Hoegh-Guldberg, Lenton, Lough et al, 2009), and resilience (Carilli, Norris, Black, Walsh et al, 2009;Elmhirst, Connolly & Hughes, 2009;Anthony, Maynard, Dí az-Pulido, Mumby et al, 2011). Large-scale, climate change-related phenomena often operate atop of multiple local scale factors, which in combination, can often magnify local impacts on coral reef ecosystem resilience (Hughes, Rodrigues, Bellwood, Ceccarelli et al, 2007;Ledlie, Graham, Bythell, Wilson et al, 2007;Vega-Thurber, Burkepile, Fuchs, Shantz et al, 2013;Duprey, Yasuhara & Baker, 2016) and on overall biodiversity (Foden, Maze, Vié , Angulo et al, 2008;Bellard, Environmental Management and Sustainable Development ISSN 2164-7682 2017 Bertelsmeier, Leadley, Thuiller et al, 2012;Rogers, 2013).…”

“…Increasing sedimentation is often linked to increasing turbidity and eutrophication (Meesters, Bak, Westmacott, Ridgley et al, 1998). The combination of increasing eutrophication and sea surface temperature (SST) has been implicated in magnifying coral bleaching severity (Vega-Thurber, Burkepile, Fuchs, Shantz et al, 2013) and coral reef decline (Carilli, Norris, Black, Walsh et al, 2009;Anthony, Maynard, Dí az-Pulido, & Mumby, 2011). Improving the conservation of watersheds and the implementation of sustainable land use strategies have become paramount for the conservation and rehabilitation of coral reef ecosystems in the context of climate change.…”

“…Eutrophication may also foster phytoplankton blooms (Bell, 1992;McComb, 1995;Arhonditsis, Karydis, & Tsirtsis, 2003), harmful algal blooms (Anderson, Glibert, & Burkholder, 2002), rapid macroalgal growth (Naim, 1993), a long-term decline in fisheries productivity (Hodgkiss & Yim, 1995), and a net decline in seagrass (Duarte, 1995;Tomasko, Dawes & Hall, 1996) and coral reef communities (Lapointe & Clark, 1992;Cloern, 2001;Dí az-Ortega & Herná ndez-Delgado, 2014;Duprey, Yasuhara, & Baker, 2016). Corals are particularly susceptible to eutrophication as a result of declining growth rates (Tomascik & Sander, 1985;Tomascik, 1990), reproductive output (Tomascik & Sander, 1987b), larval settlement rates (Tomascik, 1991), increased incidence of diseases (Kaczmarsky, Draud, & Williams, 2005), altered Environmental Management and Sustainable Development ISSN 2164-7682 2017 microbiology (Kline, Kuntz, Breitbart, Knowlton et al, 2006), and increased susceptibility to bleaching (Vega-Thurber, Burkepile, Fuchs, Shantz et al, 2013;Wiedenmann et al, 2013), and mortality (Pastorok & Byliard, 1985), often impacting benthic community structure (Tomascik & Sander, 1987a). These impacts are often confounded with sedimentation effects (Rogers, 1990;Meesters, Bak, Westmacott, Ridgley et al, 1998;Risk, 2014), and can be readily magnified by climate change-related factors (Ateweberhan, Feary, Keshavmurthy, Chen et al, 2013).…”