Crepuscular

Crepuscular animals are most active during the low-light periods of dawn and dusk. On coral reefs, the crepuscular period is the most dangerous — visual predators still have enough light to hunt, but the switch between diurnal and nocturnal communities creates confusion and exposure opportunities for large hunters. Many predatory fish (jacks, barracuda, sharks) are highly crepuscular, timing their attacks on the transition period when prey are moving to or from shelter. The "crepuscular rush" is a well-known phenomenon in reef ecology.