Contrasting reproductive strategies in three deep-sea octocorals from eastern Canada: Primnoa resedaeformis, Keratoisis ornata, and Anthomastus grandiflorus

Abstract

Various aspects of reproduction were studied in three deep-sea octocorals belonging to the order Alcyonacea that co-occur at bathyal depths on the continental edge and the slope of eastern Canada. The main goals were to expand knowledge of deep-water heterotrophic corals and ascertain whether reproductive strategies could explain the known patterns of occurrence. Anthomastus grandiflorus is a gonochoric species with a female-biased sex ratio that exhibits internal fertilization and brooding of planula larvae. Conversely, Primnoa resedaeformis and Keratoisis ornata rely on broadcast spawning and external fertilization; their sexuality remains undetermined as spermatocysts were not found. In P. resedaeformis, the presence of mixed size classes of oocytes in samples from all months, depths, and locations studied suggests continuous oogenesis or overlapping development of oocyte cohorts, indicative of a gametogenic cycle spanning more than a year. No evidence of periodicity was found in this species, although it could have been masked by the striking bathymetric variation in potential relative fecundity (oocytes polyp−1). The two other octocorals displayed a clear annual breeding pattern. Spawning in K. ornata and larval release in A. grandiflorus occurred in late summer and fall, respectively, possibly in response to environmental factors, as supported by shifts in the reproductive peak of A. grandiflorus across latitudes. The three species are presumed to share a nonfeeding larval mode, and data on their reproductive potential do not present any striking disparities. Published data on bycatches and video surveys in Atlantic Canada indicate that the gonochoric brooder A. grandiflorus is more widely distributed than the two free spawners, P. resedaeformis and K. ornata, which is contrary to common dispersal potential paradigms.