SEM analysis of the epibenthic diatoms on Eudendrium racemosum (Hydrozoa) from the Mediterranean Sea

Turkish Journal of Botany Turk J Bot (2014) 38: 566-594 © TÜBİTAK doi:10.3906/bot-1305-52 http://journals.tubitak.gov.tr/botany/ Research Article SEM analysis of the epibenthic diatoms on Eudendrium racemosum (Hydrozoa) from the Mediterranean Sea 1 1 1 2 1, Tiziana ROMAGNOLI , Cecilia TOTTI , Stefano ACCORONI , Mario DE STEFANO , Chiara PENNESI * Department of Life and Environmental Sciences, Faculty of Science, Polytechnic University of the Marche, Ancona, Italy 2 Department of Environmental, Biological and Pharmaceutical Science, and Technology, 2nd University of Naples, Caserta, Italy 1 Received: 23.05.2013 Accepted: 25.02.2014 Published Online: 31.03.2014 Printed: 30.04.2014 Abstract: In this work, the valve fine structure, morphology, and dimensions of the epibenthic diatoms living on the marine hydroid Eudendrium racemosum Cavolini were investigated through SEM analysis. Hydroid samples were collected from the Ligurian Sea (Mediterranean Sea), from October 2002 to October 2003, with monthly frequency, allowing definition of the annual cycle of diatom communities. Following several taxonomic/systematic papers, this floristics paper documents 32 new records of diatoms (13 araphid, 17 biraphid, 2 monoraphid), which have been classified into different growth forms (adnate, erect, motile, tube-dwelling). Moreover, new information on morphologic data and biodiversity in the Mediterranean Sea are offered, indicating their ecological preferences. Key words: Biodiversity, epizoic diatoms, Eudendrium racemosum, microphytobenthos, morphology, scanning electron microscopy 1. Introduction Benthic diatoms of shallow coastal marine areas give a reliable contribution to the dynamics of aquatic ecosystems in terms of primary production, nutrient fluxes, and roles in the trophic web (MacIntyre et al., 1996; Totti, 2003). Communities of benthic diatoms can develop associated to different substrata, from the soft bottom (epipelon, epipsammon, and endopelon) (Totti, 2003) to rocks (epilithon) (Totti et al., 2007; Çolak Sabancı and Koray, 2010), macroalgae and seagrasses (epiphyton) (Totti et al., 2009; Pennesi et al., 2011, 2012, 2013; Çolak Sabancı, 2012; Majewska et al., 2013; Lobban and Pennesi, 2014), and animals (epizoon) (Round, 1971; Romagnoli et al., 2007). The peculiar microenvironments provided by marine animals, i.e. metabolite-rich and potentially grazer-free, are successfully exploited by several pennate diatom genera belonging to araphids, biraphids, and monoraphids (Round, 1981). Pennate diatoms are reported to colonize sponges (Cerrano et al., 2004a, 2004b; Totti et al., 2005), hydrozoans (Di Camillo et al., 2005; Romagnoli et al., 2007; Bavestrello et al., 2008), bryozoans (Wuchter et al., 2003), arthropods (Ikeda, 1977; Hiromi and Takano, 1983; Patil and Anil, 2000), mollusks (Gillan and Cadée, 2000; D’Alelio et al., 2011), and vertebrates (Bennett, 1920; Hart, 1935; Holmes, 1985), sometimes with a high degree of host specificity. The main strategy accounts for the development of well-differentiated growth forms, * Correspondence: 566 which allow establishing different modes of contact with the substratum: adnate species (both biraphids and monoraphids) strongly adhering horizontally to the substratum by means of the raphidic valve and having limited motility; erect species (araphids, biraphids, and monoraphids) adhering vertically through mucous pads or stalks/peduncles; and motile diatoms (biraphids) having movement capability enabling them to glide above the substratum (Round, 1971; Round et al., 1981). Moreover, it has been pointed out that some species may exhibit more than one growth form, reflecting different strategies of spatial utilization (Hudon and Bourget, 1981; Round et al., 1981; Hudon and Legendre, 1987; Tuji, 1999, 2000; Chen et al., 2010), which are adopted in terms of the competitive advantage obtained. Among animals, hydroids represent a very suitable habitat for diatom growth. Round et al. (1961) documented different kinds of diatom assemblages, including erect (Grammatophora Ehrenberg, Licmophora C.Agardh, Striatella C.Agardh, Synedra Ehrenberg), adnate (Cocconeis Ehrenberg), and motile (Navicula Bory de Saint-Vincent) genera lying on the hydroid Amphisbetia operculata Linnaeus (basionym: Sertularia operculata Linnaeus). Dense assemblages of Cocconeis pseudonotata De Stefano & Marino have been reported at the border of the theca of the hydroid Clytia linearis Thorneley (Di Camillo et al., 2005). Romagnoli et al. (2007) defined ROMAGNOLI et al. / Turk J Bot the epizoic communities associated with marine hydroid Eudendrium racemosum Cavolini in terms of abundance, biomass, and community structure during its annual cycle in the Ligurian Sea. The present paper provides new detailed morphological information on diatom taxa associated with the marine hydroid Eudendrium racemosum from the Ligurian Sea through scanning electron microscopy (SEM) analysis; moreover, some notes about their ecological behavior are given. 2. Materials and methods Eudendrium racemosum specimens were collected on a concrete quay of the Santa Margherita Ligure harbor (Ligurian Sea; 44°19′52.36″N, 9°12′58.29″E), near a freshwater drain (personal communication) at 0.5 m of depth from October 2002 to October 2003, with a monthly frequency. Samples were fixed in filtered seawater with 4% neutralized formaldehyde. In the laboratory, hydroid colonies were cut into 3 parts (basal, central, and apical) and then put into a glass tube filled with filtered seawater and treated in a sonic bath (BRANSON 2200) to allow the detachment of diatoms from the hydroid stem. Details of this procedure were reported by Romagnoli et al. (2007). Taxonomical determinations have been based mainly on SEM observations. For this purpose, fixed samples were washed with distilled water and cleaned with sulfuric and nitric acids following the von Stosch method (Hasle and Syvertsen, 1996). One or more drops of cleaned material were then poured on a Nucleopore polycarbonate filter fixed on a stub and left to air dry completely. The stub was then sputter-coated with a thin layer of gold-palladium in a Balzer Union evaporator and analyzed by SEM (Philips EM 515 scanning electron microscope). Samples and slides used in this work are stored at the Herbarium of the Polytechnic University of the Marche (Italy), Department of Life and Environmental Sciences (DISVA). 3. Results Araphid, biraphid, and monoraphid diatom taxa discussed in this paper have been alphabetically listed within each araphid, biraphid, and monoraphid group, starting from orders. Electron microscopy micrographs of analyzed species are illustrated in Figures 1–14. The taxonomical analysis of Cocconeis species found, such as C. convexa Giffen, C. dirupta var. flexella (Janisch & Rabenhorst) Grunow in Van Heurck, C. distans Gregory, C. molesta var. crucifera Grunow in Van Heurck, C. neothumensis var. marina De Stefano et al., C. (...truncated)