Reefs of tomorrow: eutrophication reduces coral biodiversity in an urbanized seascape

Abstract

Although the impacts of nutrient pollution on coral reefs are well known, surprisingly, no statistical relationships have ever been established between water quality parameters, coral biodiversity and coral cover. Hong Kong provides a unique opportunity to assess this relationship. Here, coastal waters have been monitored monthly since 1986, at 76 stations, providing a highly spatially resolved water quality dataset including 68 903 data points. Moreover, a robust coral species richness (S) dataset is available from more than 100 surveyed locations, composed of 3453 individual colonies' observations, as well as a coral cover (CC) dataset including 85 sites. This wealth of data provides a unique opportunity to test the hypothesis that water quality, and in particular nutrients, drives coral biodiversity. The influence of water quality on S and CC was analyzed using GIS and multiple regression modeling. Eutrophication (as chlorophyll‐a concentration; CHLA) was negatively correlated with S and CC, whereas physicochemical parameters (DO and salinity) had no significant effect. The modeling further illustrated that particulate suspended matter, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) had a negative effect on S and on CC; however, the effect of nutrients was 1.5‐fold to twofold greater. The highest S and CC occurred where CHLA <2 μg L−1, DIN < 2 μm and DIP < 0.1 μm. Where these values were exceeded, S and CC were significantly lower and no live corals were observed where CHLA > 15 μg L−1, DIN > 9 μm and DIP > 0.33 μm. This study demonstrates the importance of nutrients over other water quality parameters in coral biodiversity loss and highlights the key role of eutrophication in shaping coastal coral reef ecosystems. This work also provides ecological thresholds that may be useful for water quality guidelines and nutrient mitigation policies.

Temperature shapes coral-algal symbiosis in the South China Sea

“…have also caused a rapid decline in the coral cover4445. In the present study, nutrients had only a marginal impact on coral-algal symbiosis, considering nutrients contribute the most to coral cover and species richness loss compared with other water quality parameters46, suggesting a lack of symbiotic flexibility in response to seawater pollution such as eutrophication. Increases in coastal nutrients are frequently linked to human activities4748, which suggests that human activities can also affect coral-algal symbiosis.…”

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ15N records in the Pearl River estuary

“…This suggests that the coral decline in the Pearl River estuary was primarily driven by eutrophication caused by the development of the PRD megacity. The greater severity of mortality toward the Pearl River estuary (Figure S3), where DIN concentrations are higher (Duprey et al, ), also supports this interpretation. Duprey et al () have suggested an annual average concentration of 2 µM DIN as a threshold for the coral communities of the Pearl River estuary: beyond this threshold, coral communities experience a severe decrease in coral cover and coral‐specific richness.…”

“…The greater severity of mortality toward the Pearl River estuary (Figure S3), where DIN concentrations are higher (Duprey et al, ), also supports this interpretation. Duprey et al () have suggested an annual average concentration of 2 µM DIN as a threshold for the coral communities of the Pearl River estuary: beyond this threshold, coral communities experience a severe decrease in coral cover and coral‐specific richness. During the period 1990–1995, the DIN concentration in eastern HK was consistently above this threshold (Figure a), suggesting that the coral communities' decline was caused by an increase in the DIN concentration.…”

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).…”

“…Also, it may result in a chronic increase in water turbidity, declining sunlight penetration, and in a chronic deterioration of sediment quality (Livingston, 2001). 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).…”