2.4. Absorption Efficiency

Food absorption efficiency was measured by comparing the proportions of organic matter in the algal cells and mussels feces according to the equation of Conover [34]: AE = (F − E)/[(1 − E)F], where F is a relationship between dry weight and ash-free dry weight of algal food while E is a relationship between dry weight and ash-free dry weight of fecal pellets. Fecal pellets from each treatment were collected daily and placed in separate vials. Collected feces were filtered on preweighted glass fiber filters (Whatman GF/C, 0.45 μm) and washed with 0.5 M ammonium formate to remove salts [35]. Then, samples were dried at 100°C for 48 h and dry weights were recorded immediately after cooling in a desiccator. Eventually, samples were ashed in a furnace at 450°C for 2 h and then reweighted to obtain the ash-free dry weight. The results are the average of six different measurements per condition.