Seasonal reproduction of the brachiopod Frieleia halli and the scaphopod Cadulus californicus at bathyal depths in the deep sea

Two benthic species of invertebrates from the physically seasonless bathyal depths of the San Diego Trough off southern california USA showed highly synchronous reproductive cycles. Although the common pattern in the deep-sea benthos seems to be year-round reproduction, these two species are exceptions. The brachiopod Frieleia halli Dall spawned between January and April (1971) and the scaphopod mollusc Cadulus californicus Pilsbry and Sharp in late summer between July and October. Furthermore, F. halli. has maintained a predictable annual gametogenic cycle for three years (1970–1972). Several factors are suggested as possibly important in synchronizing their reproductive cycles, but no single environmental cue can be conclusively demonstrated as a definite influence.