Diel temperature and pH variability scale with depth across diverse coral reef habitats

Tyler Cyronak,Travis A Courtney,Todd Martz,Bradley D Eyre,David I Kline,Andreas J Andersson,Laura Stoltenberg,Jennifer Smith,Heather Page,Yuichiro Takeshita,Martin Tresguerres,Nichole N Price,Eric H Decarlo

doi:10.1002/lol2.10129

Abstract

AbstractCoral reefs are facing intensifying stressors, largely due to global increases in seawater temperature and decreases in pH. However, there is extensive environmental variability within coral reef ecosystems, which can impact how organisms respond to global trends. We deployed spatial arrays of autonomous sensors across distinct shallow coral reef habitats to determine patterns of spatiotemporal variability in seawater physicochemical parameters. Temperature and pH were positively correlated over the course of a day due to solar heating and light‐driven metabolism. The mean temporal and spatial ranges of temperature and pH were positively correlated across all sites, with different regimes of variability observed in different reef types. Ultimately, depth was a reliable predictor of the average diel ranges in both seawater temperature and pH. These results demonstrate that there is widespread environmental variability on diel timescales within coral reefs related to water column depth, which needs to be included in assessments of how global change will locally affect reef ecosystems.

Highlights

The mean spatial range across each sensor array was generally lower than the diel range of any given sensor, with the mean spatial range in temperature varying from 0.2C to 1.2C and pH from 0.02 to 0.11
Irrespective of the underlying physiological mechanisms, the widespread variability observed across coral reef ecosystems in this study indicates that there are extensive shallow sections of coral reefs inhabited by organisms that are potentially better able to cope with global changes in temperature and pH
Diel oscillations in temperature and pH were both driven by solar irradiance, and as a result, the diel range of both parameters were positively correlated across all sites

Summary

Methods

Study sites Sensor arrays consisting of 3–4 pH and temperature sensors were deployed at five locations representing six distinct coral reef habitats (Fig. 1; Table 1). The SeapHOx is an autonomous sensing package outfitted with a Honeywell Durafet III combination pH electrode and Seabird MicroCAT (SBE37) to measure temperature and salinity (Bresnahan et al 2014). The SeaFET uses the same pH sensing technology as the SeapHOx; there is no integrated salinity sensor and seawater temperature is measured by the Durafet thermistor. Seawater pH was calibrated to the total scale by taking bottle samples next to the sensors either predeployment in a holding tank or during the deployment, following best practices (Bresnahan et al 2014). Bottle sample pH was calculated using CO2SYS with inputs of dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements made in the laboratory and salinity and temperature measurements from the SeapHOx (Pierrot et al.2006; Takeshita et al 2018).

Results

Discussion

Conclusion