Ultrastructural and microspectrophotometric characterization of multiple species of cyanobacterial photosymbionts coexisting in the colonial ascidian Trididemnum clinides (Tunicata, Ascidiacea, Didemnidae)
Trididemnum clinides is a multi-photosymbiotic ascidian that inhabits shallow coral reef lagoons. Three types of cyanobacteria are harboured in the tunic of the ascidian colony; of these, two are unicellular coccoid cyanobacteria and the other is a multicellular filamentous type. They
also differ in ultrastructure and distribution patterns within the host tunic. Microspectrophotometric analysis revealed the composition of photosynthetic pigments in each photosymbiont. One of the coccoid types is yellowish-green and is distributed under the colony surface. This photosymbiont
cell preferentially absorbs red and blue light, and therefore the dominant colour in the inner tunic is green. The other two types of coexisting photosymbionts contain the green-light-absorbing R-phycoerythrin as the major photosynthetic pigment; they exploit the wavelengths of light not used
by the first type of photosymbiont. In T. clinides, the outer and inner photosymbionts in the tunic have different photosynthetic pigments, which adapt to each microhabitat, thereby sharing the incident light resources effectively.
Keywords: R-phycoerythrin; ascidian tunic; colour-niche; cyanobacteria; microhabitat; microspectrophotometry; ultrastructure
Document Type: Research Article
Affiliations: 1: Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-2213, Japan 2: Kobe University Research Center for Inland Seas, Iwaya, Awaji, Hyogo 656-2401, Japan
Publication date: 01 August 2009
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