This study simulated a 9-months warming scenario on the common seagrass Zostera marina from winter into summer (December 2015 - August 2016) in the Western Baltic Sea (Kiel Fijord), using outdoor mesocosms. Two treatments were applied: Ambient temperature regime (Ambient) and Ambient + 3.6C (Heat) over the entire course of the experiment. Temperature regimes were compared to the 22-year temperature average in the area. A number of seagrass response parameters were measured throughout the experiment including parameters related to shoot mortality and reproduction (shoot abundance, growth of new shoots, abundance of flowering shoots), (ii) shoot growth (growth rate, leaf production, lengths of the 3rd leaf, number of green leaves per shoot), (ii) biomass (above and below ground biomass per shoot) and (iv) pigmentation (chlorophyll-a, beta-carotene).