Abstract
Deep-water gorgonian corals are long-lived organisms found worldwide off continental margins and seamounts, usually occurring at depths of ∼200–1,000 m. Most corals undergo sexual reproduction by releasing a planktonic larval stage that disperses; however, recruitment rates and the environmental and biological factors influencing recruitment in deep-sea species are poorly known. Here, we present results from a 4-year field experiment conducted in the Gulf of Maine (northwest Atlantic) at depths >650 m that document recruitment for 2 species of deep-water gorgonian corals, Primnoa resedaeformis and Paragorgia arborea. The abundance of P. resedaeformis recruits was high, and influenced by the structural complexity of the recipient habitat, but very few recruits of P. arborea were found. We suggest that divergent reproductive modes (P. resedaeformis as a broadcast spawner and P. arborea as a brooder) may explain this pattern. Despite the high recruitment of P. resedaeformis, severe mortality early on in the benthic stage of this species may limit the abundance of adult colonies. Most recruits of this species (∼80%) were at the primary polyp stage, and less than 1% of recruits were at stage of 4 polyps or more. We propose that biological disturbance, possibly by the presence of suspension-feeding brittle stars, and limited food supply in the deep sea may cause this mortality. Our findings reinforce the vulnerability of these corals to anthropogenic disturbances, such as trawling with mobile gear, and the importance of incorporating knowledge on processes during the early life history stages in conservation decisions.
Highlights
Deep-water gorgonian corals (Octocorallia: Alcyonacea; ‘‘sea fans’’) are increasingly being recognized as important foundation species of deep-sea benthic ecosystems, on seamounts and continental margins [1]
We retrieved 2 P. arborea recruits at the deepest location, one of which was composed of more than 20 polyps, the largest recruit retrieved in our study (Fig. 3B – inset)
Recruitment on the collectors was high for P. resedaeformis, but limited for P. arborea
Summary
Deep-water gorgonian corals (Octocorallia: Alcyonacea; ‘‘sea fans’’) are increasingly being recognized as important foundation species of deep-sea benthic ecosystems, on seamounts and continental margins [1]. With their typical arborescent shape, these organisms form structures, which foster biodiversity, either as substrate for epifaunal communities [2,3,4], or by creating shelter for bottom-dwelling fish from strong currents and predators [5,6]. Physical factors influencing recruitment (or post-settlement mortality) have not been assessed for deep-water gorgonian corals For sessile organisms, these factors include predation, disturbance (physical or biological) and space and/or resource competition [20]. Corals undergo asexual reproduction when additional polyps bud from the primary polyp to form a juvenile colony
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