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Zoological Studies 51(2): 150-159 (2012) Diverse Interactions between Corals and the Coral-Killing Sponge, Terpios hoshinota (Suberitidae: Hadromerida) Jih-Terng Wang 1, *, Yi-Yun Chen 1 , Pei-Jie Meng 2,3 , Yu-Hsuan Sune 3 , Chia-Min Hsu 4 , Kuo-Yen Wei 1 , and Chaolun Allen Chen 4,5,6 1 Graduate Institute of Biotechnology, Tajen Univ., Pingtung 907, Taiwan 2 National Museum of Marine Biology and Aquarium, Pingtung 944, Taiwan 3 Institute of Marine Biodiversity and Evolution, National Dong Hwa Univ., Checheng, Pingtung 944, Taiwan 4 Institute of Oceanography, National Taiwan Univ., Taipei 108, Taiwan 5 Biodiversity Research Center, Academia Sinica, Nangang, Taipei 115, Taiwan 6 Taiwan International Graduate Program (TIGP)- Biodiversity, Academia Sinica, Nangang, Taipei 115, Tawian (Accepted September 15, 2011) Jih-Terng Wang, Yi-Yun Chen, Pei-Jie Meng, Yu-Hsuan Sune, Chia-Min Hsu, Kuo-Yen Wei, and Chaolun Allen Chen (2012) Diverse interactions between corals and the coral-killing sponge, Terpios hoshinota (Suberitidae: Hadromerida). Zoological Studies 51(2): 150-159. Terpios hoshinota is an encrusting sponge which can kill corals by overgrowing them. However, little is known about interactions between sponges and corals. Using visual observations and scanning electron microscopy (SEM), 4 features, including hairy tips, thick tissue threads, compact edges, and disintegrated tissues, displayed at the coral-facing front of Terpios were summarized from examining 20 species of corals. Hairy tips, found on 13 species of coral victims, were occupied by cyanobacteria, sponge tissues, and spicules. Thick tissue threads, found on only 7 coral species, were obviously an extension of Terpios tissues. Twelve coral species displayed a compact edge at the Terpioscoral border, in which some Terpios fronts had extruding spicules. Disintegrated tissue was only found on the coral side in 5 species of coral, but that on the sponge side was only found on 1 coral species. Only a few disintegrated tissues being found at the Terpios-coral border suggests that allelochemicals are not the major player in Terpios-coral interactions. The interactions also did not display species specificity, except in the case of Terpios having been retrogressively grown over by a coral, which was only found in Millepora exaesa. Under SEM examination, coral nematocysts were usually found on the surface of the invading Terpios, but they did not seem to retard the growth of the sponge. In summary, exploitation of the substratum by T. hoshinota on coral does not move forward in a consistent manner. The performance of Terpios, such as when overgrowing a coral, building a clear border, or being retrogressively overgrown by a coral, may rely on the viability status of both organisms. http://zoolstud.sinica.edu.tw/Journals/51.2/150.pdf Key words: Terpios, Cyanobacteria, Coral-killing sponge, Substrata competition. In coral reefs, sponges are a well-known space competitor (Suchanek et al. 1983, Rützler 2002), but few are recognized as real threats to the survival of corals. Terpios hoshinota Rützler and Muzik, 1993, a cyanobacteriosponge, is an exception, as its high growth rate can encrust almost every type of hermatypic coral encountered. Its widespread infection was first reported in Guam (Bryan 1973), and subsequently in the Ryukyus, Japan (Rützler and Muzik 1993, Reimer et al. 2011) and Green I. (Lyudao), Taiwan (Liao et al. 2007). Terpios hoshinota was also found in Truk Lagoon in American Samoa, Cebu I. in the Philippines, Thailand (Plucer-Rosario 1987), and even on the *To whom correspondence and reprint requests should be addressed. Tel: 886-8-7624002. Fax: 886-8-7621645. E-mail:jtw@mail.tajen.edu.tw 150
Wang et al. – Coral-Terpios Interactions 151 Great Barrier Reef (Fujii et al. 2011). Damage caused by an invasion of Terpios caused nearly 30% loss of coral coverage on some reefs in Guam (Plucer-Rosario 1987). At Green I., Taiwan, an unprecedented overgrowth by Terpios on corals was found in 2006, which also caused almost 30% coral coverage loss along a 100-m transect belt (Liao et al. 2007). The complete recovery from a Terpios encrustation, e.g., at Anae I. in Guam, took more than 10 yr, when the disturbance level decreased (Plucer-Rosario 1987). Therefore, once a Terpios outbreak occurs, there will be long-term impacts on a coral reef ecosystem and on activities that rely on a healthy condition of the reefs. Ecologically, T. hoshinota is distributed above the limit of the euphotic zone, probably due to the presence of endosymbiotic photosynthetic cyanobacteria (Bryan 1973, Plucer-Rosario 1987, Rützler and Muzik 1993). A histological examination of T. hoshinota indicated that the sponge contained a high percentage (> 50%) of intercellular cyanobacteria and 5%-18% of cells were in the dividing stage (Rützler and Muzik 1993, Hirose and Murakami 2011). High abundances and activities of cyanobacteria contained in T. hoshinota suggest that a potential source of the sponge’s nutrients is derived from photosynthetic bacteria (Rützler and Muzik 1993). It was hypothesized by Bryan (1973) that Terpios probably kills coral for nutrients with toxic chemicals, but comparisons between tissue-depleted and healthy coral suggested that the sponge might just overgrow the coral surface to occupy more space (Plucer-Rosario 1987). During growth, Terpios moves forward by lateral propagation, extending short, fine tendrils across crevices to new substrate (Rützler and Muzik 1993). Terpios hoshinota can also develop tissue threads, instead of whole sheets of tissue, to move over a shaded area and establish new territory (Soong et al. 2009). However, Terpios occasionally exhibits retrogression (i.e., negative growth) and can even be overgrown by some corals (e.g., Montipora and Porites) or red calcareous algae (Plucer-Rosario 1987). Thus, Terpios does not always win during its advance. Interactions between Terpios and corals were examined from the viewpoint of changes in the bacterial community. Tang et al. (2011) indicated that invasion by Terpios onto corals initiates a shift in the coral bacterial community from one on healthy corals to that found on corals with blackband disease. Their results suggested that harmful bacteria weakening the coral might favor Terpios outcompeting the coral for substratum (Tang et al. 2011). As yet, only limited information briefly describing how Terpios invades victimized corals is available (Bryan 1973, Plucer-Rosario 1987, Rützler and Muzik 1993, Soong et al. 2009, Tang et al. 2011), and it is not clear how different coral species respond to an invasion by Terpios at the coral-sponge border under a fine scale. Therefore, the aim of this study was to examine the border between these 2 antagonists with scanning electron microscopy (SEM). Our findings provide insights into interactions between an aggressively invading sponge and its coral victims. MATERIALS AND METHODS Sample collection and maintenance Field observations of coral-Terpios interactions were conducted at Gon-Guam and Chai- Ko, Green I., Taiwan (22°39'N, 121°29'E) from Aug. 2008 to July 2010. Due to the strong northeasterly monsoon in winter, observations were made more intensively during summer (May-Sept.). During the investigation, interactions between coral and Terpios were recorded with an underwater camera. To further examine the interaction border between corals and Terpios, 19 species of scleractinian coral and 1 hydrozoan coral with T. hoshinota invasion were collected by scuba diving from 3-5 m in depth at Gon-Guam and Chai-Ko on 28 July 2010 and examined by SEM. The 19 scleractinian corals included Isopora palifera, Montipora aequituberculata, Mon. peltiformis, Hydnophora rigida, Favia stelligera, Psammocora digitata, Echinopora lamellose, Echinophyllia aspera, Goniastrea edwardsi, G. aspera, Pocilliopora verrucosa, Acropora digitifera, Stylophora pistillata, Platygyra ryukyuensis, Leptoria phrygia, Favites chinensis, Cyphastrea microphthalma, Porites lutea, and Por. cylindrical. The hydrozoan coral examined was Millepora exaesa. Every species was duplicated by collecting a sample from 2 different colonies, and the interactions were photographed before collection. Terpios-coral specimens were sealed in a plastic bag underwater when collected and preserved in fixative once the diver had left the water. Terpios hoshinota on I. palifera was also collected and maintained in an aquarium (60 × 45 × 45 cm) equipped with illumination (12-h:12-h light dark regime and 70-90 μE/m 2 /s photosynthetically
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