SPONGE LARVAL PHOTOTAXIS: A COMPARATIVE STUDY

Resumen

Recent work has shown that larvae of the tropical demosponge Reniera sp. are capable of instantaneous responses to abrupt changes in light intensity, a behaviour that allows them to settle in dark areas under coral rubble on the reef flat at Heron Is. GBR. To determine how widespread this kind of phototactic behaviour is among sponge larvae, ontogenetic changes in the photoresponse of larvae from two temperate demosponges and a calcareous sponge were studied. Most larvae from Scypha sp. swam away from a white light source for 3 days until settlement and metamorphosis; Haliclona cf. permollis larvae swam away from light for 48 hours; and larvae from Halichondria panicea were benthic until settlement and metamorphosis, and showed no responsiveness to gradients of light intensity. These results demonstrate that sponge larvae are capable of responding to environmental stimuli like other metazoan larvae and show that a coordinated behavioural response to stimuli is possible even in the absence of neurons or junctions that would allow electrical signalling between cells