| Summary: | The reproductive ecology of colonies of Lophelia pertusa (Linné 1758) and Madrepora oculata Linné (1758) from the Porcupine Seabight (Thérèse Mound and South Porcupine Seabight site) and the Darwin Mounds (NE Rockall Trough—L. pertusa only) was investigated using histological techniques. Samples of L. pertusa exhibited seasonal reproduction, whereas the evidence for M. oculata is equivocal but suggests multiple cohorts of gamete production. L. pertusa produces a single cohort of around 3,000 oocytes, whereas M. oculata produces two cohorts, with a total fecundity of around 60 oocytes. The maximum observed oocyte size in L. pertusa was 140 ?m and in M. oculata was 405 ?m. From these oocyte sizes and the timing of reproduction, a lecithotrophic larva is expected, though not observed. This seasonality of reproduction fits with the phytodetrital food fall occurring around July in the Seabight area. L. pertusa was found to be non-reproductive at the Darwin Mound site. Though unable to be specifically tested, this may suggest that the increased trawling activity in this area might be keeping colonies below sexually viable sizes, as seen in numerous shallow water situations. All areas in the NE Atlantic are coming under threat from increased fishing and commercial exploration practices. This study shows that these highly seasonal reproducers could be sensitive to these fishing operations and care must be taken so as not to repeat the destruction that has occurred on shallower reefs.
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