BIODIVERSITAS ISSN: 1412-033X Volume 20, Number 7, July 2019 E-ISSN: 2085-4722 Pages: 1787-1793 DOI: 10.13057/biodiv/d200701 Community structure of Echinoderms in seagrass beds of Pacitan beaches, East Java, Indonesia FARID KAMAL MUZAKI 1, , EDWIN SETIAWAN 1, , GHULAM FATHIR AUTHAR INSANY 1 , NURUL KUSUMA DEWI 2 , IWENDA BELLA SUBAGIO 3 1 Department of Biology, Faculty of Science, Institut Teknologi Sepuluh Nopember. Jl. Arief Rahman Hakim - Surabaya 60111, East Java, Indonesia. Tel./fax.: +62-31-5963857,  email: rm_faridkm@bio.its.ac.id;  edwin@bio.its.ac.id. 2 Department of Biology Education, Faculty of Teacher Training and Education, Universitas PGRI Madiun. Jl. Setiabudi 85 Kartoharjo, Madiun 63118, East Java, Indonesia 3 Department of Biology Education, Faculty of Mathematics and Natural Science, IKIP PGRI Jember. Jl. Jawa 10, Sumbersari, Jember 68121, East Java, Indonesia Manuscript received: 19 March 2019. Revision accepted: 1 June 2019. Abstract. Muzaki FK, Setiawan E, Insany GFA, Dewi NK, Subagio IB. 2019. Community structure of Echinoderms in seagrass beds of Pacitan beaches, East Java, Indonesia. Biodiversitas 20: 1787-1793. In this study, we attempt to access diversity and community structure of Echinoderms on seagrass beds in each three belt transect (width 2 m, length 100 m) in Tawang and Pidakan beaches, Pacitan, East Java, Java. Observed parameters were species richness, composition, and abundance, as well as diversity indices: Shannon- Wiener's diversity index (H'), Simpson's dominance index (D) and Pielou's evenness index (J). At the end of the study, we identified one species of sea star (Asteroidea), seven species of brittle stars (Ophiuroidea), ten species of sea cucumbers (Holothuroidea) andnine species of sea urchins (Echinoidea). The most dominant species were Ophiocoma dentata (F. Ophiocomidae), Diadema setosum (F. Diadematiidae), Ophiomastix annulosa (F. Ophiocomidae) and Echinometra mathaei (F. Echinometridae). Value of H’ ranged from 0.538 to 1.252 in Tawang and 1.041 to 1.704 in Pidakan; which showing higher species richness and diversity in Pidakan. Echinoderm in the study area was not evenly distributed; D. setosum was very dominant in Tawang beach, while those three other species were more common in Pidakan. Furthermore, most of Holothuroid and Ophiuroid were found only in Pidakan which have relatively more complex habitat. Keywords: Diversity, Echinoderms, Pidakan beach, seagrass bed, Tawang beach INTRODUCTION Biodiversity assessment of marine ecosystem is very useful to understand the ecological patterns, ecosystem function and conservation management (Setyastuti et al. 2018) as well as to detects, monitor, measures and estimates the fluctuation of diversity and the implications of its changes to the ecosystem function (Iken et al. 2010; Wheeler et al. 2012); for examples are the study of seagrass ecosystem by Daby (2003), Bishop (2008), Herrera- Silveira et al. (2010), Norldund and Gulstrom (2013), Siddiq et al. (2016) and Furqan and Muzaki (2018). Seagrass beds are providing habitat function, food source and shelter for the marine organism (Azkab 2001) and stable seagrass ecosystems are controlled by animal- plant interactions (Heck and Valentine 2007). The complexity of multispecies interactions in seagrass beds between fauna associations with seagrasses will support the sustainability of ecosystems (Lundberg and Moberg 2003). One group of animal living in seagrass beds are echinoderms, which utilize the seagrass beds as the food source, shelter, nursery, and spawning (Vaitilingon 2003; Dissanayake and Gunnar 2012; Vonk et al. 2009; Bos et al. 2011). In the seagrass system, echinoderms such as Holothuroids are positive as a major bioturbator because they can increase the productivity and through their excretory physiology, they also can increase local nutrients (Uthicke 2001; Wolkenhauer et al. 2010; Jamieson et al. 2011; Costa et al. 2014; Wolfe and Byrne 2017) and potential to help buffer the effects of ocean acidification (Schneider et al. 2011; Schneider et al. 2013; Wolfe and Byrne 2017). Echinoids has an important role in controlling the algal cover on hard substrates, they directly impact the seagrass and algae for releasing and recycling nutrients obtained from food in the form of microalgae, bacteria, and organic detritus in sediments (Moriarty et al. 1985; Wiedemeyer 1992), while asteroids also play an important role in maintaining community structures as predators (Gaymer et al. 2004; Verling et al. 2003). In the southern coast of Pacitan, East Java, seagrass beds occurred in almost all of the coastline; particularly in Tawang which is a traditional port for coastal fisheries, and Pidakan which is a location for tourism. In these areas, the data on marine biodiversity is still lacking; and this study is aimed to access diversity and community structure of echinoderms in the area. Thus, data obtained from this study can be used as a baseline for local coastal management. MATERIALS AND METHODS Study area The research takes place in the area of Tawang and Pidakan beaches in the coastal area of Pacitan, East Java,