The data set contains area and polyp growth data of juvenile Hydractinia echinata in two experiments. The colonies were exposed to two different food conditions HF = high food, LF = low food and two diffent temperature conditions 18 °C and 21 °C.

To evaluate the effect of ambient and future environmental conditions on the marine hydroid H. echinata, the influence of variable temperature and food availability on the growth of juvenile hydroid colonies was tested in two different experiments (= scenarios), mimicking two different environments (subtidal = scenario 1, intertidal = scenario 2). In both scenarios, colonies were exposed to two different temperatures (control and high) cross-factored with two different food conditions (LF=low food, HF=high food), while scenario 2 contained an additional temperature step to simulate temperature fluctuations in the intertidal. Each colony was analyzed morphometrically on a weekly basis in terms of colony area and number of polyps, as indicators for individual growth performance. These parameters were determined during both experiments by analyzing weekly photographs of colonies at 5-46 days post-settlement (scenario 1) and 8-36 days post-settlement (scenario 2) taken with a binocular microscope (Leica M205 C, Leica Microsystems, Germany). In scenario 1, the photographs of animals in the HF and LF treatments were taken three days apart for logistical reasons. The area of each colony was determined graphically by an automated script developed in Matlab (Version R2015b, The MathWorks, Inc., USA). The script identifies the shape of the largest patch on each glass tile and excludes the spaces between the stolonal channels. For the determination of polyp number, only completely developed polyps equipped with tentacles were counted, whereas buddies were ignored. In the treatments HF/18 °C and LF/18°C of the second scenario, daily pictures of eight colonies (four colonies of each treatment) were taken between day 8 and 27 post-settlement to develop and validate a numerical growth model.