Characterization and role of major deep-sea pennatulacean corals in the bathyal zone of Eastern Canada

Pennatulaceans (Octocorallia: Pennatulacea), commonly called sea pens, are colonial corals that typically anchor themselves into soft sediment (mud, sand), allowing them to colonize large areas of the sea floor from the intertidal zone down to the abyssal plain. Sea pens can occur sparsely or form large aggregations, suggesting that they may provide an important structural habitat to other organisms by increasing the complexity of the muddy seabed. The investigation of the three most common sea pens (Anthoptilum grandiflorum, Halipteris finmarchica and Pennatula aculeata) of the continental slope of Newfoundland and Labrador (Northwest Atlantic) showed different morphologies and adaptations to environmental parameters. Variations in their morphology were visible along bathymetric and latitudinal gradients, following food availability. This study identified different feeding strategies according to stable isotope signatures and macromorphologies (polyp diameter, colony length, shape). Different defense strategies were also identified based on the presence and localisation of sclerites in the tissues. Reproductive strategies were determined for A. grandiflorum and H. finmarchica, with both species presenting a seasonal spawning between April (Southern Newfoundland) and July/August (Labrador). The latitudinal shift in spawning followed the development of the surface phytoplankton bloom (i.e. sinking of phytodetritus). Low fecundity at the polyp level (13 and 6 oocytes polyp-1, respectively) yielded similar whole-colony fecundity in the two species (500-6000 oocytes colony-1). The measure of fecundity is discussed to highlight the importance of standardizing metrics (mature oocyte just before spawning) to avoid an overestimation of the fecundity and to allow comparison among species. Only ~20% of the oocyte matured in both species. The remaining oocytes in A. grandiflorum disappeared, indicating that oogenesis develops and culminates over 12 months. In H. finmarchica the persistence of the small oocytes indicates protracted oogenesis (>12 months). Finally, an analysis of the associated biodiversity showed that sea pens have relatively few associates but that they play an important role in their life history. Some associates are obligate (e.g. parasitic copepods) and others facultative symbionts (the sea anemone Stephanauge nexilis). The seasonal (April-May) presence of fish larvae (Sebastes spp.) and shrimp larvae (Pandalus borealis, Pasiphae multidentata and Acanthephyra pelagica) emphasize the role of sea pens as nursery habitat, and provides an argument to recognize them as an essential fish habitat

Diversity, Distribution and Nature of Faunal Associations with Deep-Sea Pennatulacean Corals in the Northwest Atlantic

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

Map showing the five geographic regions where colonies of the sea pens <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> were collected along the continental slope.

<p>LC: Laurentian Channel, GB: Grand Banks, FC: Flemish Cap, NNL: North Newfoundland, LB: Labrador.</p

Rarefaction curves for <i>Anthoptilum grandiflorum</i> (left panels) and <i>Halipteris finmarchica</i> (right panels), based on close associates only (top two panels) or all associates in spring and fall (bottom four panels).

<p>(A) Close associates of <i>A. grandiflorum</i>; (B) all the associated fauna of <i>A. grandiflorum</i> in the fall and (C) in spring/summer. (D) Close associates of <i>H. finmarchica</i>; (E) all the associated fauna of <i>H. finmarchica</i> in the fall and (F) in spring/summer. LC: Laurentian Channel, GB: Grand Banks, FC: Flemish Cap, NNL: North Newfoundland, LB: Labrador.</p

Species found on the sea pens <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> during the present study (2006–2007).

<p>* 6 more larvae were found in April 2009 with a third species identified as <i>Pasiphaea multidentata</i>.</p><p>Species found on the sea pens <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> during the present study (2006–2007).</p

Number of colonies sampled in the different geographic regions.

<p>LC: Laurentian Channel, GB: Grand Banks, FC: Flemish Cape, NNL: North Newfoundland, LB: Labrador.</p><p>Number of colonies sampled in the different geographic regions.</p

Carbon and nitrogen stable isotope signatures (δ¹³C and δ¹⁵N), and trophic level (TL) of <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> and their dominant associates.

<p>n: number of samples analysed (mean ± SE).</p><p>Carbon and nitrogen stable isotope signatures (δ¹³C and δ¹⁵N), and trophic level (TL) of <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> and their dominant associates.</p

Principal component analyses and biplots based on the associated species of <i>Anthoptilum grandiflorum</i> (A, B) and <i>Halipteris finmarchica</i> (C, D).

<p>Green up triangle: spring; yellow circle: summer; blue down triangle: fall; black square: winter.</p

Influence of increasing depth on total mean yield (MEYtot) of all associates on colonies of <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> in the different geographic regions (only sites with more than 10 colonies harbouring associated species were used).

<p>LC: Laurentian Channel, GB: Grand Banks, FC: Flemish Cape, LB: Labrador, n: number of sea pen colonies analysed. Empty cells correspond to regions without enough data available for analyses.</p><p>Influence of increasing depth on total mean yield (MEYtot) of all associates on colonies of <i>Anthoptilum grandiflorum</i> and <i>Halipteris finmarchica</i> in the different geographic regions (only sites with more than 10 colonies harbouring associated species were used).</p

<i>Lamippe bouligandi</i>, a parasitic copepod living inside the polyps of <i>Anthoptilum grandiflorum</i>: (A) in situ view of the copepod (arrow) through the transparent polyp wall, (B) a female, (C) a male.

<p>Scale bar in A = 1 mm, in B = 500 µm and in D = 100 µm.</p