Deep-sea corals inhabit seamounts and act as ecosystem engineers, creating habitats that provide refuge and feeding grounds for fish and invertebrate species. These slow‑growing organisms are susceptible to anthropogenic stressors, leading many coral assemblages to be classified as vulnerable marine ecosystems (VMEs) in need of protection. This study addresses a key gap in knowledge of deep‑sea coral reproduction, a life‑history trait central to VME classification, by (i) quantifying the reproductive mode and strategy of two deep‑sea chrysogorgiid species, Metallogorgia melanotrichos and Iridogorgia magnispiralis, and (ii) determining how fecundity and gamete characteristics differ among M. melanotrichos colonies. Branch fragments were analyzed histologically (sectioning, staining, and imaging tissue slices), after which gametes were identified, counted, stage‑classed, and sized. Results suggest both species are gonochoric broadcast spawners that produce lecithotrophic larvae, with quasi‑continuous and asynchronous reproduction inferred from the simultaneous presence of multiple gamete cohorts. Fecundity in M. melanotrichos was correlated with deep‑water currents and seamount summit depth, whereas surface productivity showed no consistent relationship with fecundity but did identify some outlier colonies, underscoring the role of seamount topography and hydrodynamics in shaping reproductive capacity. This first documentation of chrysogorgiid reproduction provides essential baseline data to guide future research and management of VMEs.
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