Presented are hourly logged data retrieved from the GHL sensors system (means over 4 benthocosm units with respective 95% confidence intervals).The experiment consisted of three treatments: 0HW = no heat wave; 1HW = one single summer heat wave; and 3HW = three subsequent heat waves. In all three treatments, working with continuous flow-through of fjord water maintained the natural small-scale variability of most environmental parameters except temperature, which was adjusted to the logged thermal regime of the year 2009.