Another clear, hot day on the far northern GBR, we made an early start diving to the study site at 40m and then returned for a quick breakfast before getting down to some serious ROV work. Diving gives you an incredible appetite – we all have four meals a day and still feel hungry! The ROV work this morning involved retrieving the temperature/light loggers from various depths down to 100m depth. The loggers are small electronic devices which record the water temperature and the light level every five minutes – we put them down two days ago with the ROV but finding them again is quite a task! The ROV has a position finding device but unfortunately it is “line of sight” (underwater sight that is) and the ROV was down over a wall- basically “out of sight”. So, we try and use landmarks (seamarks?) and compass headings (yes the ROV has one of those too!) which works surprisingly well. Some of the loggers are being left down for a year so finding these again after all that time might be quite challenging. Needless to say the task does involve a fair bit of searching around which is a good chance to find unusual corals and sure enough we found some at around 90 metres depth - quite a find having reef corals this deep. The loggers will tell us how the temperature and light varies through the year on the deep reef. Light is one of the most important factors in determining where reef corals live - they need high levels of light to survive. Just how much light gets down to the seafloor where the corals are depends upon how clear the water above is - if there is too much plankton growth in the water then not enough light can penetrate to depth. We know that shallow reefs need clear waters to thrive and we suspect that because they are so much deeper the deep reefs will need super-clear waters.