Net ecosystem dissolution and respiration dominate metabolic rates at two western Atlantic reef sites

Abstract

Ocean acidification is changing surface water chemistry, but natural variability due to nearshore processes can mask its effects on ecosystem responses. We present an approach of quantitatively resolving net ecosystem metabolism from an array of long-term time series stations, offering perhaps the longest record of such processes over a reef to date. We used 8 and 6 yr of in situ, high-quality frequency observations to characterize the changes in dissolved inorganic carbon and oxygen in La Parguera, Puerto Rico and Cheeca Rocks, Florida, respectively. Net respiration and net dissolution are the dominant metabolic processes at both systems, with a narrow window of ~4 months under net calcification. The annual mean net ecosystem calcification (NEC) rates for La Parguera (À0.68 AE 0.91 kg CaCO 3 m À2 yr À1 ) and Cheeca Rocks (À0.48 AE 0.89 kg CaCO 3 m À2 yr À1 ) were on the lower end of typical NEC ranges determined for other reef areas using chemistry-and census-based approaches. At Cheeca Rocks, 53% of the variance in NEC can be explained by net ecosystem production (NEP) and 30% by aragonite saturation state (Ω arag ). At La Parguera, NEC is primarily driven by changes in NEP. The linear relationship between NEC and NEP showed a significant slope (AE standard error) of 1.00 AE 0.005 and 0.88 AE 0.04 for La Parguera and Cheeca Rocks, respectively. These results suggest that NEP appears to play a prominent role on NEC, and Ω arag probably is not the most informative measure to monitor when attempting to resolve the long-term impacts of ocean acidification.

Coral Reef Carbonate Chemistry Reveals Interannual, Seasonal, and Spatial Impacts on Ocean Acidification Off Florida

“…However, increasing DIC during the early autumn reduced pH and Ω Ar at inshore reefs, despite rising TA during this season. Similar seasonal patterns in pH and Ω Ar have been identified in previous studies in South Florida (Enochs et al, 2019;Manzello et al, 2012;Meléndez et al, 2020Meléndez et al, , 2022Muehllehner et al, 2016) and other coral reefs of the world (Kleypas et al, 2011;Takeshita et al, 2018) emphasizing the key role of the metabolism of the benthic communities controlling local carbonate chemistry in shallow ecosystems.…”

“…From 2014 to 2015, Enochs et al (2019) observed localized acidification around navigational inlets. Longer time series (∼8 years) from a moored autonomous pCO 2 (MapCO2) buoy have also been used to describe the seasonal variability and metabolic rates in the FCR, but these data are limited to a single inshore site in the Upper Keys (Meléndez et al, 2020(Meléndez et al, , 2022. Together, these studies highlight the spatiotemporal complexity of the carbonate chemistry system in the FCR, though their relatively short duration or limited spatial scope has hampered their ability to examine these trends in the context of OA.…”