A comparative study of behavioural responses of larval decapod crustaceans to light and pressure

Responses of 9 species of decapod crustacean Stage I zoeae to light and hydrostatic pressure were analyzed with a video system. Phototactic responses were measured in a light field that simulates the underwater angular light distribution. These responses probably function during diel vertical migration and were compared to past studies of responses in a narrow light field. Ascent and descent responses were measured upon a pressure decrease. The descent response is used for depth regulation and it is suggested that the ascent response may facilitate avoidance of the feeding and respiratory currents of benthic animals. Responses to light and pressure were variable and the different species were grouped by responses into 4 categories: (1) no phototaxis/ascend upon a rapid pressure decrease, (2) negative photoaxis/ascend upon a rapid pressure decrease, (3) negative phototaxis/ descend upon a rapid pressure decrease, and (4) positive phototaxis/descend upon a rapid pressure decrease. The groupings are not taxonomically consistent as related species occur in the different categories. There is a variable relationship between category and adult habitat. Finally, for cases where the larval vertical distributions are well known, there is reasonable agreement between behaviour and larval distribution in the water column.