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Nalley EM, Tuttle LJ, Conklin EE, Barkman AL, Wulstein DM, Schmidbauer MC, Donahue MJ. A systematic review and meta-analysis of the direct effects of nutrients on corals. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 856:159093. [PMID: 36183766 DOI: 10.1016/j.scitotenv.2022.159093] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 09/14/2022] [Accepted: 09/24/2022] [Indexed: 06/16/2023]
Abstract
Chronic exposure of coral reefs to elevated nutrient conditions can modify the performance of the coral holobiont and shift the competitive interactions of reef organisms. Many studies have now quantified the links between nutrients and coral performance, but few have translated these studies to directly address coastal water quality standards. To address this management need, we conducted a systematic review of peer-reviewed studies, public reports, and gray literature that examined the impacts of dissolved inorganic nitrogen (DIN: nitrate, nitrite, and ammonium) and dissolved inorganic phosphorus (DIP: phosphate) on scleractinian corals. The systematic review resulted in 47 studies with comparable data on coral holobiont responses to nutrients: symbiont density, chlorophyll a (chl-a) concentration, photosynthesis, photosynthetic efficiency, growth, calcification, adult survival, juvenile survival, and fertilization. Mixed-effects meta-regression meta-analyses were used to determine the magnitude of the positive or negative effects of DIN and DIP on coral responses. Zooxanthellae density (DIN & DIP), chl-a concentration (DIN), photosynthetic rate (DIN), and growth (DIP) all exhibited positive responses to nutrient addition; maximum quantum yield (DIP), growth (DIN), larval survival (DIN), and fertilization (DIN) exhibited negative responses. In lieu of developing specific thresholds for the management of nutrients as a stressor on coral reefs, we highlight important inflection points in the magnitude and direction of the effects of inorganic nutrients and identify trends among coral responses. The responses of corals to nutrients are complex, warranting conservative guidelines for elevated nutrient concentrations on coral reefs.
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Affiliation(s)
- Eileen M Nalley
- Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, 46-007 Lilipuna Road, Kāne'ohe, HI 96744, USA.
| | - Lillian J Tuttle
- Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, 46-007 Lilipuna Road, Kāne'ohe, HI 96744, USA; U.S. Geological Survey, Hawai'i Cooperative Fishery Unit, University of Hawai'i at Hilo, Hilo, HI 96720, USA
| | - Emily E Conklin
- Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, 46-007 Lilipuna Road, Kāne'ohe, HI 96744, USA
| | - Alexandria L Barkman
- Kewalo Marine Laboratory, Pacific Biosciences Research Center, University of Hawai'i at Mānoa, 41 Ahui Street, Honolulu, HI 96813, USA
| | - Devynn M Wulstein
- Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, 46-007 Lilipuna Road, Kāne'ohe, HI 96744, USA
| | - Madeline C Schmidbauer
- Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, 46-007 Lilipuna Road, Kāne'ohe, HI 96744, USA
| | - Megan J Donahue
- Hawai'i Institute of Marine Biology, University of Hawai'i at Mānoa, 46-007 Lilipuna Road, Kāne'ohe, HI 96744, USA
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Kikuchi T, Anzai T, Ouchi T, Okamoto K, Terajima Y. Assessing the impact of watershed characteristics and management on nutrient concentrations in tropical rivers using a machine learning method. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 316:120599. [PMID: 36343855 DOI: 10.1016/j.envpol.2022.120599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/28/2022] [Accepted: 11/02/2022] [Indexed: 06/16/2023]
Abstract
Excessive loadings of terrestrial nitrogen and phosphorus, as well as their imbalances with silicon, have been recognized as one of the major causes of water quality and ecosystem deterioration in receiving waters. In this study, a periodic water quality monitoring was conducted in the rivers and streams of a tropical island (Ishigaki Island, Japan) to identify the factors controlling the concentrations of dissolved inorganic nitrogen (DIN), total phosphorus (TP) and dissolved silicon (DSi) with a special focus on the catchment characteristics (e.g., land use, surface geology, topography). Random Forest (RF) machine learning algorithm was employed to develop predictive models for nutrient concentrations from the catchment properties. The developed models could predict nutrient concentrations with sufficient accuracy, demonstrating that the studied nutrients are strongly affected by catchment properties. Agricultural land uses (e.g., livestock barn, sugarcane field) were ranked as the most important parameters for DIN and TP, while broadleaf forest was the most influential factor for DSi. Using the RF models, the contributions of DIN originating from sugarcane fields (i.e., fertilizers) and barns (i.e., manure) to riverine DIN were estimated, which were up to 60% in total in the studied river basins. Furthermore, the yield of DIN from sugarcane fields, calculated as the concentration of DIN derived from sugarcane fields divided by the percent area of sugarcane fields, strongly positively correlated with the areal coverage of limestone, suggesting that fertilizer-derived DIN is more prone to leaching out from cropland soil to groundwater and rivers in catchments with a higher dominance of calcareous geology. These results, including the methodology employed, have implications for water quality assessment and management in inland and coastal waters not only at the study site but also other regions.
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Affiliation(s)
- Tetsuro Kikuchi
- Crop, Livestock and Environment Division, Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1 Ohwashi, Tsukuba, Ibaraki, 305-8686, Japan.
| | - Toshihiko Anzai
- Tropical Agriculture Research Front, JIRCAS, 1091-1 Maezato-Kawarabaru, Ishigaki, Okinawa, 907-0002, Japan.
| | - Takao Ouchi
- Ibaraki Kasumigaura Environmental Science Center, 1853, Okijuku-machi, Tsuchiura, Ibaraki, 300-0023, Japan.
| | - Ken Okamoto
- Tropical Agriculture Research Front, JIRCAS, 1091-1 Maezato-Kawarabaru, Ishigaki, Okinawa, 907-0002, Japan.
| | - Yoshifumi Terajima
- Tropical Agriculture Research Front, JIRCAS, 1091-1 Maezato-Kawarabaru, Ishigaki, Okinawa, 907-0002, Japan.
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Lesser MP. Eutrophication on Coral Reefs: What Is the Evidence for Phase Shifts, Nutrient Limitation and Coral Bleaching. Bioscience 2021. [DOI: 10.1093/biosci/biab101] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Coral reefs continue to experience extreme environmental pressure from climate change stressors, but many coral reefs are also exposed to eutrophication. It has been proposed that changes in the stoichiometry of ambient nutrients increase the mortality of corals, whereas eutrophication may facilitate phase shifts to macroalgae-dominated coral reefs when herbivory is low or absent. But are corals ever nutrient limited, and can eutrophication destabilize the coral symbiosis making it more sensitive to environmental stress because of climate change? The effects of eutrophication are confounded not just by the effects of climate change but by the presence of chemical pollutants in industrial, urban, and agricultural wastes. Because of these confounding effects, the increases in nutrients or changes in their stoichiometry in coastal environments, although they are important at the organismal and community level, cannot currently be disentangled from each other or from the more significant effects of climate change stressors on coral reefs.
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Affiliation(s)
- Michael P Lesser
- University of New Hampshire, Durham, New Hampshire, United States
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