Clearance rate (CR) measurements in Mytilus galloprovincialis were determined over 16 experiments in which the mussels were exposed to diets characterized by variable chlorophyll content (0.28–104.88 µg Chla L–1) in order to: (1) establish the lower trigger level and the saturation reduction, (2) elucidate whether these thresholds were controlled by an on/off switch or by a progressive response, and (3) determine whether the experimental time exerted an effect on the CR measurement under extreme conditions, quantified in terms of chlorophyll content. The results demonstrated that time exerted a significant effect on CR, which varied throughout the experiment in different diets. The CR response differed fundamentally in the significant reduction of CR after prolonged exposure to low and high chlorophyll-content diets compared with the medium ones. Taking into account the data from the sixth hour onwards, a sharp lower trigger level threshold was established at 2.08 µg Chla L–1, showing an on/off CR response. The threshold for saturation reduction was about 26.91 µg Chla L–1 and showed a progressive response to chlorophyll concentration.