Abstract
Unsustainable land uses may result in poor watershed management, increased soil erosion, poorly-planned urban development, increased runoff, and sewage pollution, creating an environmental stress gradient across coastal coral reefs. This study was aimed at: 1) Evaluating water quality within and outside the Canal Luis Peña Natural Reserve (CLPNR), Culebra Island, Puerto Rico; 2) Determining if there was any significant environmental stress gradient associated to land-based non-point source pollution; and 3) Characterizing shallow-water coral reef communities across the gradient. Strong gradient impacts associated to sediment-laden and nutrient-loaded runoff pulses, in combination with non-point raw sewage pulses, and sediment bedload, impacted coastal coral reefs. Water quality showed significant spatio-temporal fluctuations (p<0.0001), largely responding to heavy rainfall and subsequent runoff pulses. Benthic community structure showed significant spatial variation along the environmental stress gradient (p=0.0002). Macroalgae, dead coral surfaces, algal turf, and low coral species richness, species diversity index (H’c), and evenness (J’c) dominated benthic assemblages across reefs frequently impacted by runoff pulses and sediment bedload. The combination of fecal coliform and enterococci concentrations were correlated with variation in benthic community structure (Rho=0.668; p=0.0020). The combined variation in salinity, dissolved oxygen and enterococci concentrations explained 75% of the observed spatial variation in benthic assemblages (R2=0.7461; p=0.0400). Local human stressors affected coral reefs within no-take CLPNR and risk analyses suggest it may offset its ecological benefits. There is a need to design and implement integrated coastal-watershed management strategies to address multiple land use activities, including erosion-control best management practices, watershed reforestation, and sewage pollution control.
Highlights
Long-term degradation of coral reef ecosystems has largely resulted from a combination of human factors, including those with local scale impacts, such as poor land use (Sladek-Nowlis, Roberts, Smith & Siriila, 1997; Ramos-Scharrón, Amador & Hernández-Delgado, 2012; Ramos-Scharrón, Torres-Pulliza & Hernández-Delgado, 2015), sedimentation (Pastorok & Bilyard, 1985; Rogers, 1990), eutrophication (Cloern, 2001; Díaz-Ortega & Hernández-Delgado, 2014; Ennis, Brandt, Grimes & Smith, 2016), sewage pollution (Bonkosky, Hernández-Delgado, Sandoz, Robledo et al, 2009; Hernández-Delgado, Sandoz, Bonkosky, Mattei et al, 2010), and fishing (Hawkins & Roberts, 2004)
This study was aimed at: 1) Evaluating the physical and microbiological water quality conditions within and outside the Canal Luis Peña No-Take Natural Reserve (CLPNR); 2) Determining if there was any significant environmental stress gradient associated to land-based non-point source pollution; and 3) Characterizing shallow-water coral reef communities across the gradient
These sites were shallow grounds located in the inner part of Ensenada Honda Bay
Summary
1.1 Synergistic Impacts of Local and Global-Scale Factors in Coral Reef DeclineLong-term degradation of coral reef ecosystems has largely resulted from a combination of human factors, including those with local scale impacts, such as poor land use (Sladek-Nowlis, Roberts, Smith & Siriila, 1997; Ramos-Scharrón, Amador & Hernández-Delgado, 2012; Ramos-Scharrón, Torres-Pulliza & Hernández-Delgado, 2015), sedimentation (Pastorok & Bilyard, 1985; Rogers, 1990), eutrophication (Cloern, 2001; Díaz-Ortega & Hernández-Delgado, 2014; Ennis, Brandt, Grimes & Smith, 2016), sewage pollution (Bonkosky, Hernández-Delgado, Sandoz, Robledo et al, 2009; Hernández-Delgado, Sandoz, Bonkosky, Mattei et al, 2010), and fishing (Hawkins & Roberts, 2004). Modeling efforts suggest further coral reef decline in the near future under current trends of environmental and climate-related change (Buddemeier, Jokiel, Zimmerman, Lane et al, 2008; Buddemeier, Lane & Martinich, 2011; Hernández-Pacheco, Hernández-Delgado & Sabat, 2011; Hoeke, Jokiel, Buddemeier & Brainard, 2011; Freeman, Kleypas & Miller, 2013). This can further compromise ecosystem resilience, functions and services (Veron, Hoegh-Guldberg, Lenton, Lough et al, 2009). Coral reef conservation efforts need to extend beyond the coral reef boundaries and the shoreline up into adjacent watersheds to enhance the ability to recover coral reef ecosystem resilience (Shelton & Richmond, 2016)
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