The Cave Pearls have grown into a robust Arduino based underwater logging platform, that is easy to assemble from preexisting components, which can be adapted to many other environmental monitoring applications. The datalogger itself is open-source, with parts, code, build instructions, etc. available at: https://thecavepearlproject.org/how-to-build-an-arduino-data-logger/
We've developed a "minimum build" of the research logger for classroom instruction, using Dupont jumper cables to reduce the assembly time to about 1 hour. The starter code provided on Github includes support for using the multi-color indicator LED as a light sensor, so the logger can be integrated into educational curriculum even if adopters don't add any extra sensors.
We have been using this simple data logger in an environmental monitoring course to help students learn how to program the Arduino to support sensors & communication. When connected to a USB cable, this logger can also act as a simple data acquisition system, displaying sensor data from real time experiments using the new graphing function built into the free Arduino software.