Reproductive ecology of a polar deep-sea scleractinian, Fungiacyathus marenzelleri (Vaughan, 1906)

The deep-sea solitary scleractinian, Fungiacyathus marenzelleri (Vaughan, 1906) is found at depths of 300–6328 m, and is cosmopolitan in distribution. Previously this species had been examined from 2200 m depth in the Northeast Atlantic and 4100 m in the Northeast Pacific. This study examines gametogenesis and fecundity of this species from its shallowest occurrences worldwide, from ∼600 m depth in the Southern Ocean. Samples were collected during three cruises to the Western Antarctic Peninsula during 2008 and processed for histological analysis. Similar to studies of other populations, F. marenzelleri in the Southern Ocean is gonochoric with gametes forming in clusters within the mesenteries. Samples numbers were low, but oocyte size-frequency patterns suggest irregular spawning (no larvae were detected) with no differences between the three months analyzed. Though fecundity (2837±121 per polyp) was similar to that seen in the NE Atlantic (2892±44.4 per polyp), oocyte sizes were much larger in this southern population. Maximum oocyte size was 1400 μm (750 μm NE Atlantic and NE Pacific), with previtellogenic oocytes reaching a size of around 300 μm before undergoing vitellogenesis. This study demonstrates phylogenetically constrained reproductive mode across three oceans, with local environmental adaptations such as increased lipid loading during vitellogenesis, potentially enhancing cold-water survivorship by increased food availability in juvenile stages.