Reproduction of a bathyal pennatulacean coral in the Canadian Arctic

Abstract

While reproduction in deep-sea corals remains incompletely understood, there is a particularly crucial shortage of information related to corals living in deep waters of the Arctic Ocean. In the present study, colonies of the deep-sea pennatulacean coral Umbellula encrinus were collected in Baffin Bay (High Canadian Arctic) at bathyal depths between 2006 and 2010. From examination of gamete sizes, maturity levels and densities at several time points, U. encrinus was determined to be a gonochoric species with an equal sex ratio and a broadcast-spawning strategy. Fully mature oocytes measured between 800 and 950 μm in diameter, consistent with lecithotrophic larval development. Potential fecundity was ~4200 mature oocytes colony−1 and ~5300 mature spermatocysts colony−1. Gametogenesis was synchronous between sexes; a single main cohort of oocytes and spermatocysts was seen to increase in size throughout the year. Gametogenetically mature colonies were detected in late June during the earliest possible spring samplings. Spent colonies were detected in July and August. Early stages of gametogenesis appeared in early September shortly after the spawning months and more advanced growth stages occurred in late September and early November, after which time sampling was prevented by ice cover. The spawning season in U. encrinus appears to occur once a year, closely following the disappearance of the ice cover, when chlorophyll-a in Baffin Bay increases. The initiation of gametogenesis coincides with a period of sustained phytoplankton production and continues until the entire bay freezes over in fall. Since mature gametes were found in both male and female colonies just after the spring melt, gamete maturation likely continues under the ice. Both depth and latitude were shown to impact gamete development and fecundity in U. encrinus, with more advanced and fertile colonies occurring in deeper water and at higher latitudes.