Higher Nighttime Rates of CaCO3 Dissolution in the Nature Reserve Reef, Eilat, Israel in 2015–2016 Compared to 2000–2002. Issue 1 (28th December 2022)

• Record Type: Journal Article
• Authors: Moav‐Barzel, O.; Erez, J.; Lazar, B.; Silverman, J.
• Is Part Of: Journal of geophysical research. Volume 128:Issue 1(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-28
• Subjects: ocean acidification -- eutrophication -- coral reef -- calcification -- CaCO3 dissolution -- community metabolism; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2021JG006763
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: The current study (2015–2016) evaluated changes in the net community calcification (NCC) and maximum nighttime CaCO3 dissolution ( D max ) in the Nature Reserve Reef (NRR), northern Gulf of Eilat (GOE), and northern Red Sea, compared to measurements made at the same site during 2000–2002. The NCC and D max were calculated as a function of the reef‐water residence time, the difference between the open‐sea total alkalinity (TA) and its reef‐water daily average (for NCC), and its nighttime maximum (for D max ). The average NCC was 50 ± 13 and 68 ± 22 mmol C m −2 day −1 in 2000–2002 and 2015–2016, respectively. This change is consistent with the live coral cover increase in the NRR during this period, following the final removal of fish cages from the northern GOE in 2008. In contrast, wintertime D max values in 2015–2016 were five times higher on average compared to 2000–2002. We hypothesize that these higher rates could be the result of increased boring organism activity and sedimentary organic content, which developed throughout the fish farming period and are maintained by the naturally occurring seasonal eutrophication in the northern GOE. Where, in general, D max was higher during the winters, when nighttime reef water aragonite saturation ( Ω arag ) was lower, while open water chlorophyll a and nitrate were higher, compared to summertime. Thus, it is possible that the combination of seasonal eutrophication and ocean acidification (OA) in the GOE and possibly other coral reef sites around the world, may shift coral reefs to net dissolution even sooner than previously predicted from OA alone. Plain Language Summary: Biogenic deposition and dissolution of CaCO3 in coral reefs are affected by ocean acidification (OA) and eutrophication due to discharge of nutrients and organic waste. OA is expected to shift coral reefs from net calcification to net dissolution by mid‐21st century. In this study, we compared daily deposition and nighttime dissolution of CaCO3 measured during 2000–2002 and 2015–2016 in the Nature Reserve Reef (NRR), Gulf of Eilat (GOE), and northern Red Sea. The average net community calcification was higher by ∼20%, but the nighttime CaCO3 dissolution was more frequent and 3‐fold to 5‐fold higher in 2015–2016 compared to 2000–2002. We propose that the higher dissolution in 2015–2016 was caused by eutrophication during the late 1990s and 2000s primarily due to fish farming in cages in the northern GOE. We hypothesize that excess nutrients and organic matter loading supported the development, activity, and abundance of organisms that dissolve CaCO3 in the carbonate framework of the NRR as well as increase the organic content and abiotic dissolution in reef sediments. Thus, the combination of eutrophication and OA in the GOE and possibly other coral reefs around the world, could shift coral reefs to net dissolution sooner than previously predicted from OA alone. Key Points: Maximum nighttime CaCO3 dissolution was dramatically higher in the Eilat Reef in 2015–2016 compared to 2000–2002 There was a small increase in ocean acidification (OA) and coral live cover between the two periods Eutrophication and acidification may shift reefs to net dissolution of sooner than previously predicted from OA alone