Meiobenthic diversity in space and time: The case of harpacticoid copepods in two Mediterranean microtidal sandy beaches Katerina Sevastou a, ⁎, Nikolaos Lampadariou b , Anastasios Eleftheriou a, c a Department of Biology, University of Crete, P.O. Box 2208, 71409 Heraklion, Crete, Greece b Hellenic Centre for Marine Research, Institute of Oceanography, P.O. Box 2214, 71003 Heraklion, Crete, Greece c Hellenic Centre for Marine Research, Institute of Marine Biology and Genetics, P.O. Box 2214, 71003 Heraklion, Crete, Greece abstract article info Article history: Received 20 January 2011 Received in revised form 24 June 2011 Accepted 28 June 2011 Available online 12 July 2011 Keywords: Meiobenthic Copepods Alpha Diversity Beta Diversity Turnover Diversity Sandy Beaches Eastern Mediterranean Meiobenthic data from two microtidal sandy beaches of the eastern Mediterranean (Crete, Greece) were used to investigate patterns of both alpha and beta diversity in space and time. Copepod assemblages and environmental variables related to sediment characteristics, morphodynamics and food were studied over a year at four distinct habitats at each beach; the retention, resurgence and saturation zones of Salvat's intertidal scheme (midlittoral zone), and the surf zone of the sublittoral. Αlpha diversity analysis indicated similar species richness at both beaches when the whole 13-month data set was considered but was higher at the sheltered site when each sampling period was examined separately. Both beaches supported higher diversity in the sublittoral zone. Species richness increased seawards at the midlittoral zone of the sheltered site whereas, no pattern was evident at the exposed site, where the intense hydrodynamic conditions homogenized the sediments. Beta diversity increased markedly towards the sublittoral, indicating greater differences in alpha diversity between the sublittoral and the midlittoral zone. Species turnover was more variable at the exposed beach and at the most landward stations, where environmental conditions change often between extremes. A proportion of the variation in alpha diversity was explained by food availability at both beaches and additionally by grain size at the sheltered site. However, no environmental variable explained beta diversity patterns. Although the results of our study support the hypothesis of Multicausal Environmental Severity proposed for sandy beach macrofauna, we believe the classic Intermediate Disturbance Hypothesis is a more appropriate framework for the meiofauna communities of the studied sites. © 2011 Elsevier B.V. All rights reserved. 1. Introduction During the last decades, widespread concern has emerged on biodiversity loss and its effects on ecosystem processes and functioning due to the accelerating influence human activities have on community structure and diversity. As a result, many scientific articles dealing with biological diversity have been published. However, in spite of all this effort, most of the published scientific work has focused on the terrestrial environment (relevant literature cited in Hooper et al., 2005), while relatively little has been done in the marine systems. In this context, it is necessary that priorities should be directed towards inventories of marine species and how they affect ecosystem services (Snelgrove et al., 1997), the investiga- tion of biodiversity patterns at large spatial and temporal scales, and the identification of key mechanisms (Raffaelli, 2006). In 2000, Clarke and Lidgard (2000) and Gray (2000) pointed out that until that time there had been almost no studies of beta diversity in the sea and emphasized the extreme importance such studies would have for the description of marine biodiversity. Not surprisingly, many subsequent articles on a variety of marine habitats and organisms have addressed the issue, or at least incorporated measures of beta diversity (e.g., Ellingsen, 2002; Gaertner et al., 2007; Giberto et al., 2007; Koulouri et al., 2006; Perez-Mendoza et al., 2003; Price, 2002), including a few focused on meiofauna (De Troch et al., 2001; Veit-Köhler et al., 2010). While alpha diversity commonly refers to the diversity of a defined assemblage or habitat (within habitat diversity), beta diversity is primarily applied as a measure of the change in diversity between samples along transects, or across environmental gradients, or even at different spatial configurations or sampling units (Magurran, 2004). Since beta diversity is not a scale of diversity, Gray (2000) suggested instead using the term ‘turnover diversity’ as used by Clarke and Lidgard (2000). However, the term ‘turnover’ usually refers to temporal changes of diversity and lies at the heart of MacArthur and Wilson's (1967) theory of island biogeography (Magurran, 2004). Magurran (2004) stresses that the interplay of alpha and beta diversity over ecologically and evolutionary time is a topic that warrants much more consideration. Nevertheless, since the excep- tional work of Sepkoski (1988) no marine study has examined species Journal of Sea Research 66 (2011) 205–214 ⁎ Corresponding author at: Present address: Hellenic Centre for Marine Research, Institute of Oceanography, P.O. Box 2214, 71003 Heraklion, Crete, Greece. Tel.: +30 2810 337849. E-mail address: sevastou@hcmr.gr (K. Sevastou). 1385-1101/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.seares.2011.06.004 Contents lists available at ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares