Higher Nighttime Rates of CaCO3 Dissolution in the Nature Reserve Reef, Eilat, Israel in 2015–2016 Compared to 2000–2002

Abstract

AbstractThe current study (2015–2016) evaluated changes in the net community calcification (NCC) and maximum nighttime CaCO3 dissolution (Dmax) 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 Dmax 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 Dmax). 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 Dmax 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, Dmax was higher during the winters, when nighttime reef water aragonite saturation (Ωarag) 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.