Distribution and diversity of species associated with deep-sea gorgonian corals off Atlantic Canada

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Abstract

This paper describes the associated fauna of the deep-sea gorgonian corals Paragorgia arborea and Primnoa resedaeformis. Composition and distribution of this fauna is described based on material from the continental shelf and slope off Atlantic Canada (300–600 m depth). Samples were collected from five areas with Remotely Operated Vehicle, video grab, and bottom trawl. The collected material consists of 25 samples, 13 from P. arborea and 12 from P. resedaeformis.

A total of 114 species and 3915 individuals were recorded. The P. resedaeformis fauna was more abundant and diverse than the fauna of P. arborea, with 2651 specimens and 97 species found on the former and 1264 specimens and 47 species on the latter. Rarefaction analysis indicated that many more associated species are still to be found. Species richness and abundance was significantly correlated with coral morphology (e.g., number of branches, wet weight, and % exposed skeleton). Crustaceans dominated the fauna, contributing 46 % to the total number of individuals and 26 % to the total number of species. Two coral microhabitats were identified: 1) young and live parts of colonies and, 2) old parts with deposits and exposed skeleton. Most of the associated fauna was found in the latter habitat. There was a clear difference in fauna composition of the two coral species. Sessile hydroids, anemones, and molluscs were more abundant on P. resedaeformis. These organisms occurred attached to the hard substratum provided by the exposed skeleton. Parasitic copepods and polychaetes were more common on P. arborea. Two copepods, a lichomolgid ecto-parasite and a lamippid gall-forming endoparasite, were associated with P. arborea. The echinoderm Gorgonocephalus lamarckii was found in the high current environment on the outer branches of P. arborea. The shrimp Pandalus propinquus was hiding and resting on colonies of both coral species.

Many of the associated taxa are also found on tropical gorgonians but the deepsea gorgonians lack the diverse decapod and gastropod-fauna of their tropical counterparts. The species richness of the deep-sea gorgonian coral fauna was higher than what has been observed for tropical gorgonians. In contrast to the tropical associates very few are obligate symbionts. Nevertheless, several of the species are rare in other habitats and have been recorded on the same and other gorgonian species in early studies from the eastern North Atlantic. The sampling gear collected the fauna differently. Corals from bottom trawls had a poorer associated fauna that differed in composition with material collected by ROV or video assisted grab.