Differential morphological features of two Dendronephthya soft coral species suggest differences in feeding niches
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ORIGINAL PAPER
Differential morphological features of two Dendronephthya soft coral species suggest differences in feeding niches Michal Grossowicz & Yehuda Benayahu
Received: 23 February 2011 / Revised: 31 March 2011 / Accepted: 1 April 2011 / Published online: 3 May 2011 # Senckenberg, Gesellschaft für Naturforschung and Springer 2011
Abstract Octocorals are characterized by pinnate tentacles and internal sclerites. Their feeding ability is determined by the morphological features of the polyps. Capture of their food by these corals is also affected by the flexibility of the colony, which in turn is determined by the features of the sclerites. We studied the morphological features of two azooxanthellate octocorals, Dendronephthya hemprichi and D. sinaiensis, whose depth distribution partially overlaps at Eilat (northern Red Sea). Following Gause’s Law, such coexistence is considered to be possible if each species is adapted to utilize different food items. In order to examine this Law, the features of the polyps of the two species and their sclerites were studied. Each side of their tentacles displays 11–13 pinnules, which are longer at the tentacles’ distal end compared to its median section and proximal end, with the distal pinnules of D. sinaiensis being longer than those of D. hemprichi. At the proximal end of the tentacles of D. sinaiensis, the pinnules emerge perpendicularly, unlike in D. hemprichi, where they emerge from the lateral sides; the distance between the rows of pinnules is, therefore, shorter for the former. These findings imply that the filtered phytoplankton by the two species may differ in size. Their sclerites also differ in size and shape, and therefore the expansion and contraction abilities of their polyps also differ, and may thus affect their respective feeding abilities. The findings indicate that D. hemprichi and D. sinaiensis are adapted to utilize different food items, and therefore support Gause’s Law and explain the coexistence of the two species. M. Grossowicz : Y. Benayahu (*) Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel e-mail: [email protected]
Keywords Octocorallia . Polyp morphology . Gause’s Law . Sclerites . Niche overlap . Feeding . Red Sea
Introduction The sub-class Octocorallia (Cnidaria: Anthozoa) comprises more than 2,000 species, with a worldwide distribution and found in a variety of habitats (Bayer 1973; Fabricius and Alderslade 2001). Octocorals are characterized by polyps with eight pinnate tentacles and internal calcareous skeletal elements, termed sclerites. The octocoral order Alcyonacea is the largest and the member species may or may not contain symbiotic algae in their tissue (they are zooxanthellate vs. azooxanthellate species, respectively). Alcyonacean species constitute the second most important benthic component on many coral reefs, including those of the Gulf of Aqaba (northern Red Sea) (Benayahu and Loya 1977, 1981). Goldberg (1973) and Kinzie (1973) reported that var
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