Abstract
Anthoptilum grandiflorum and Halipteris finmarchica are two deep-sea corals (Octocorallia: Pennatulacea) common on soft bottoms in the North Atlantic where they are believed to act as biogenic habitat. The former also has a worldwide distribution. To assist conservation efforts, this study examines spatial and temporal patterns in the abundance, diversity, and nature of their faunal associates. A total of 14 species were found on A. grandiflorum and 6 species on H. finmarchica during a multi-year and multi-site sampling campaign in eastern Canada. Among those, 7 and 5 species, respectively, were attached to the sea pens and categorized as close associates or symbionts. Rarefaction analyses suggest that the most common associates of both sea pens have been sampled. Biodiversity associated with each sea pen is analyzed according to season, depth and region using either close associates or the broader collection of species. Associated biodiversity generally increases from northern to southern locations and does not vary with depth (∼100–1400 m). Seasonal patterns in A. grandiflorum show higher biodiversity during spring/summer due to the transient presence of early life stages of fishes and shrimps whereas it peaks in fall for H. finmarchica. Two distinct endoparasitic species of highly modified copepods (families Lamippidae and Corallovexiidae) commonly occur in the polyps of A. grandiflorum and H. finmarchica, and a commensal sea anemone frequently associates with H. finmarchica. Stable isotope analyses (δ13C and δ15N) reveal potential trophic interactions between the parasites and their hosts. Overall, the diversity of obligate/permanent associates of sea pens is moderate; however the presence of mobile/transient associates highlights an ecological role that has yet to be fully elucidated and supports their key contribution to the enhancement of biodiversity in the Northwest Atlantic.
Highlights
Corals form one of the most complex biological habitats of the deep sea, offering a variety of microhabitats that serve as feeding, shelter, foraging and spawning sites to other species [1,2,3,4]
The present study focuses on two of the most common ones: Anthoptilum grandiflorum (Anthoptilidae) and Halipteris finmarchica (Halipteridae) which were recently found to act as essential larval fish habitat [3]
Species Identification and Diversity A total of 1647 individuals belonging to 14 species (7 scored as close associates or symbionts) were found on the 175 colonies of A. grandiflorum examined and a total of 189 individuals belonging to 6 species (5 close associates) occurred on the 43 colonies of H. finmarchica (Table 2, Fig. 2, 3, 4 and 5)
Summary
Corals form one of the most complex biological habitats of the deep sea, offering a variety of microhabitats that serve as feeding, shelter, foraging and spawning sites to other species [1,2,3,4]. A review catalogued 983 invertebrate species associated with 74 species of deep-sea corals; 114 of the associates were characterized as symbionts (living in a close relationship with the coral host) of which 53% were parasites (detrimental to the host) and 47% were commensals (having no impact on the host) [7]. To our knowledge, trophic relationships between deep-sea corals and their associated species have not been explicitly studied. Additional information exists for soft corals (excluding Pennatulacea and Helioporacea) from other regions, with a total of 59 symbionts (83% listed as commensals and 17% as parasites) catalogued on 42 octocorals [13]. Sea pens can be collected whole, allowing precise determination/quantification of faunal species living in, on or around them, which is not always the case with larger or more fragile branching corals (e.g. gorgonians) for which analyses of colony fragments is often the rule
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