The role of elevated sea temperatures in coral bleaching has been well documented.  Many of the sea temperature records utilized for purposes of widespread, multi-species bleaching predictions in recent publications, have been acquired through satellite remote sensing. Satellites estimate sea temperatures at only a narrow range of depths near the surface of the ocean and may therefore not adequately represent the true temperatures endured by the world’s coral ecosystems.

To better characterize sea temperature regimes that coral reef ecosystems experience, as well as better define the individual thresholds for each species that bleaches, in-situ sea temperature sensors are required. Commercial sensors are expensive in large quantities, however, thus reducing the capacity to conduct large-scale research programs to elucidate the range of significant scales of temperature variability.

This new temperature logger autonomously records temperatures onto a memory chip, and provides better accuracy (+0.05 oC) than comparable commercial sensors (+0.2 oC).

At the Atlantic Oceanographic and Meteorological Laboratory (AOML), Natchanon Amornthammarong, an instrumentation scientist, developed a low-cost (roughly US $9 in parts) and high-precision sea temperature logger that uses an Arduino microprocessor board and a high accuracy thermistor.

This new temperature logger autonomously records temperatures onto a memory chip, and provides better accuracy (+0.05 oC) than comparable commercial sensors (+0.2 oC). It can remain submerged for over a year without a change of its two AA-sized batteries. Moreover, it is not difficult to build—anyone who knows how to solder can build the temperature logger.

In March 2019, students at middle and high schools in Broward County, Florida built close to 60 temperature loggers.  During 2019-2020, these sensors will be deployed by Reef Check Foundation, a global-scale coral reef monitoring organization, as well as by other programs, to determine worldwide sea temperature regimes through a dedicated project, the Opuhala Project (https://www.coral.noaa.gov/opuhala).

The low-cost of materials for the developed temperature logger, coupled with its measurement accuracy, will enable new science to be conducted which would not be possible otherwise. The expanded number of global observations from the new sensors will help fine-tune satellite algorithms to better predict sea temperatures under the conditions and locations of where the sensors are deployed. Data from the sensors will also be combined with other in-situ coral observations to derive more accurate temperature thresholds for coral bleaching, enabling scientists to better understand the physiological dynamics of this phenomenon and other biological events.