For every 100 cyprids of B. amphitrite which attached during night time, between 230 and 530 cyprids attached during the day. They avoided attachment under direct sunlight, however, suggesting that they preferred diffuse light. Cyprids of B. tintinnabulum showed a more marked preference for diffuse light and settled in greater numbers during dusk and daybreak, rather than about noon. In contrast, larvae of C. stellatus settled most abundantly in direct sunlight.

Artificial illumination at night encouraged the settlement of all three species. B. amphitrite settled most at an intensity of five foot candles. B. tintinnabulum settled more at 0.5 than at one or more foot candles. C. stellatus settled more at 35 foot candles than at lesser illuminations. These preferences probably play an important part in leading the larvae to the different habitats favoured by each species.