A considerable metabolic activation and low ingestion rates were observed when copepods were exposed at a high light intensity, these phenomena being proportional to the amount of light above a certain threshold. This threshold was different in different species, depending on illumination at the depth of capture. This suggests that different light intensities could act in the sea as upper barriers for dispersion of different species, by causing a phototactic negative response, reinforced photokinetically in such a manner that the copepods tend to go away from the light source swimming at a speed proportional to the amount of light, and resulting in a corresponding increase of the metabolic processes and inhibition of the feeding activity. In some cases, with direct sunlight, the respiratory rates accounted for 20-30% or even more of the body C consumed daily, and ingestion was completely repressed, so the death of animals after some hours of exposure can be produced not only for the reported harmful effect of the UV component, but also by this unbalanced metabolism. In some cases (Temora, young Calanus helgolandicus) a 2nd threshold at low light intensity was also detected, and light below this threshold produced an increase in respiration with reduction of feeding, this change then being attributed to a phototactic positive response. Anomalocera patersoni showed metabolic activation only with low light intensities. When food was present, respiration and excretion rates were higher at all light intensities, although the largest increase occurred at light intensities below the corresponding threshold of activation. The different response obtained with some species (Temora, Anomalocera), according to different light conditions prior to experiments, indicated an endogenous rhythm that could produce an inversion or variation in the phototactic or photokinetic response after the animals had spent a period of time in light or darkness. High ingestion rates on Artemia nauplii and strong inhibition in algae consumption of the omnivorous species Calanus and Pleuromamma gracilis when exposed to high intensity of light suggest that light can induce a more active carnivorous feeding in these species, when present near the surface in the daytime.