Experiment on performance of two invertebrate predators on warming and temperature variability: Energy uptake of Hemigrapsus takanoi and Asterias rubens

Energy uptake of H. takanoi and A. rubens during the experimental period (72 and 64 days, respectively) measured under 4 temperature conditions: ambient ('constant'), warm ('constant'), ambient sinusoidal and warm sinusoidal. The experiments were conducted from July to September 2017 in the Kiel Indoor Benthocosms (KIBs), at GEOMAR Kiel, Germany. The energy uptake was evaluated at different scales summing the energy uptake for the particular scale of interest: (i) large-scale as the overall sum of the energy uptake, (ii) small-scale (Phase) of 8-day wavelength, for 2-day feeding periods were energy was summed at minimum (Min), maximum (Max) and mean temperatures after minimum (Descending) or maximum (Ascending) during each sinusoidal temperature cycle, and (iii) medium-scale (Period) of 16 days, where energy uptake was summed for 'Pre-heat' (July 19th to August 4th), 'Heat' (August 4th to August 20th) and 'Post-heat' (August 20th to September 5th). To estimate energy uptake, A. rubens and H. takanoi were fed M. edulis mussels every second day. Each individual of A. rubens received five mussels of 25 to 35 mm size (total length). For H. takanoi, 20 mussels of 9 to 12mm were offered. For A. rubens, the shell of every consumed mussel was measured. In the case of H. takanoi, the average size (10.5 mm) of the mussels offered was taken for further estimated on energy uptake. A predictive relationship between soft tissue dry weight of mussels (g) and mussel length (mm) was used to calculate dry mass and energy uptake according to Brey et al., as 18.85 Joules per mg dry mass of mussels.