Fauna associated with cold water gorgonians and sea pens

This paper describes the fauna associated with the gorgonians Paragorgia arborea (530 colonies), Primnoa resedaeformis (370 colonies) and Paramuricea placomus (68 colonies) and the sea pens Kophobelemnon stelliferum (584 colonies), Virgularia mirabilis (114 colonies), Funiculina quadrangularis (278 colonies) and Pennatula phosphorea (36 colonies) recorded by video from 18 locations on the Norwegian continental margin. The fauna associated with gorgonians was more diverse than that of the sea pens, with 21 and 12 taxa recorded. P. arborea had the highest number of associates; in total ~38% of the colonies had associates on them. Amphipods dominated numerically contributing with 72% to the total number of taxa observed. Shrimps and the basket star Gorgonocephalus sp. were frequently observed on all gorgonian species. Rarefaction analysis indicated that the number of associated taxa was richest for P. resedaeformis. The fauna associated with the sea pens consisted mainly of shrimps and ophiuroids, for which the sea pens play a key role as a shelter and/or as a feeding platform. The ophiuroid Asteronyx loveni was only observed on F. quadrangularis, which is used as a platform to reach better feeding conditions. The squat lobster Munida sp. was often observed close to the sea pen K. stelliferum which presumably offer shelter against predators. We argue that both sea pens and gorgonians play an important role as a habitat, and that a better understanding of their ecological importance is essential to develop sound scientific advice on sustainable habitats and fisheries management of deep-water ecosystems. •HD videos allowed us to study the behaviour and biodiversity of the mobile megafauna of sea pens and gorgonians.•The diversity of the associated fauna on sea pens is lower compared to gorgonians.•The morphology of the coral species and its local environment determine the biodiversity patterns.•Sea pens play a key role as a shelter and/or as a feeding platform for crustaceans and ophiuroids