Symbiotic Relationships between Microalgal Zooxanthellae and Reef-Building Coral Polyps in the Process of Autotrophic an
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Symbiotic Relationships between Microalgal Zooxanthellae and Reef-Building Coral Polyps in the Process of Autotrophic and Heterotrophic Nutrition1 E. A. Titlyanova, * and T. V. Titlyanovaa a
Zhirmunsky National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, 690041 Russia *e-mail: [email protected] Received December 7, 2019; revised January 31, 2020; accepted February 2, 2020
Abstract—The present review briefly summarizes the results of the studies on coral reefs of the Indo-Pacific conducted by the authors and their colleagues who participated in joint publications and research since the late 1970s until recently. Experimental field and laboratory-based works were carried out during expeditions aboard the R/V Kallisto and R/V Akademik Aleksandr Nesmeyanov, as well as at marine biological stations in Japan, China, Vietnam, and Israel. The main goal of these studies was to obtain data on the variety and mechanisms of symbiotic relationships that are established between a host animal and its intracellular symbionts when the host carries out its most important life functions. Keywords: reef-building corals, zooxanthellae, symbiotic relationships DOI: 10.1134/S1063074020050107
INTRODUCTION Coral reefs are the most widely distributed and productive coastal ecosystem in the tropical biogeographic region [5, 26, 29, 37, 45]. Reef-building corals are system-forming organisms of coral reefs. Modern reef-building, or hermatypic, corals consist of invertebrates of the phylum Coelenterata, mainly the class Anthozoa, subclass Hexacorallia (hexacorals), order Scleractinia. Among hermatypic corals, there are also members of other orders and even classes of coelenterates [63]; however, most of them belong to scleractinians, which are the subject of our study (Fig. 1). Scleractinian corals are mainly colonial animals. One of their life forms is a polyp (Figs. 2a, 2b), which has a vase-shaped body with an oral disc in the upper part and a pedal disc at the opposite end. The oral disc has a mouth located at the center and is surrounded by tentacles on the periphery. The mouth leads into the gastrovascular cavity with numerous folds of mesenteries inside. The polyp’s external surface, from the tentacles to the pedal disc, is covered by a tissue consisting of two rows of cells, that is, the ectoderm and endoderm. Each endodermal cell of the polyp tissue contains from one to three or four cells of symbiotic algae referred to as zooxanthellae (Fig. 2c). Live tissue 1 Invited paper published in connection with the 50th anniversary
of the foundation of Zhirmunsky Institute of Marine Biology (now Zhirmunsky NSCMB).
covers the outer carbonate skeleton of a colony of coral polyps [63]. In scleractinian corals, zooxanthellae are largely different, genetically determined forms of the unicellular alga Symbiodinium microadriaticum LaJeunesse belonging to the family Symbiodiniaceae, order Suessiales, class Dinophyceae [45]. A zooxanthella has a single complex-shaped chloroplast with one
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