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

Baillon, Sandrine (2014) Characterization and role of major deep-sea pennatulacean corals in the bathyal zone of Eastern Canada. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

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.

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