Studies of a benthic time series: reproductive biology of benthic invertebrates in the Rockall Trough

SynopsisThe reproductive biology of a wide variety of deep-sea echinoderms from the northeast Atlantic has been examined. Time series samples of asteroids, ophiuroids, echinoids and holothurians are available from Station “M” and the Scottish Marine Biological Association's Permanent Station in the Rockall Trough and from opportunistic sampling in other areas of the northern Rockall Trough. Examination of these time series samples has established three main reproductive patterns in these taxa and one example of protandric hermaphroditism. The dominant reproductive pattern is the aperiodic production of relatively few large eggs usually in excess of 600μm diameter. Although the oogenic pattern is similar in most of these species, the follicle cell distribution and breakdown of relict oocytes vary considerably, particularly at family level. A second reproductive pattern is the production of numerous small eggs c. 100μm diameter, indicative of planktotrophic development. The five species exhibiting this pattern show intra- and interspecific synchrony of egg production with a proliferation of young oocytes in February to April of each year, vitellogenesis during summer and autumn and a synchronous spawnout in January–April of each year. In the apparent constant conditions of the deep sea, this synchrony of reproduction is related to the rapid descent of surface primary production. Two rarer reproductive patterns observed are the production of intermediate sized eggs (c. 300–400μm diameter) suggesting the formation of a lecithotrophic larva, and lastly a single case of protandric hermaphroditism, and the subsequent production of a large egg. In none of the species examined have we found any evidence of brooding. The variation in the reproductive pattern of individual species is discussed in relation to the constancy of the physico-chemical environment of the deep-sea.