Hydrobiologia (2016) 764:103–113 DOI 10.1007/s10750-015-2283-4 PHYTOPLANKTON & SPATIAL GRADIENTS Phytoplankton colonization patterns. Is species richness depending on distance among freshwaters and on their connectivity? Luigi Naselli-Flores . Rosa Termine . Rossella Barone Received: 10 December 2014 / Revised: 30 March 2015 / Accepted: 11 April 2015 / Published online: 21 April 2015 Ó Springer International Publishing Switzerland 2015 Abstract Phytoplankton assemblages in two Sicil- during time. The composition of samples collected in ian water bodies were compared to test the hypothesis nearby located temporary ponds suggests that phyto- that colonization events and the successful establish- plankton in this area belongs to a species-rich meta- ment of a new species in an aquatic ecosystem may community which favored its re-establishment in the depend on the number of water bodies in a given area lake. Aquatic ecosystems conservation plans cannot and on their relative distance. The two ecosystems are thus neglect the role of small waters located in the both natural, shallow lakes and they are protected sites catchments. hosting a rich avifauna. Lake Biviere di Gela is located in an area with a high density of ponds, whereas Lake Keywords Passive dispersal Á Mediterranean ponds Á Pergusa is an isolated waterbody without other aquatic Conductivity fluctuations Á Water-level fluctuations ecosystems in its surroundings. Both lakes had almost disappeared about 10 years ago because of the over- exploitation of their main inflows. They were therefore re-filled using water from other catchments and their Introduction phytoplankton has been sampled since their re-filling. The results show that Lake Pergusa has maintained a Almost all freshwater aquatic ecosystems with an open species-poor phytoplankton assemblage since its re- water habitat host phytoplankton. Phytoplankton filling, whereas Lake Biviere di Gela has been showing assemblages may quickly develop in newly created progressively richer phytoplankton assemblages lakes and ponds immediately after their impoundment. Even ‘‘old’’ ecosystems with a well established com- munity may experience immigration of new species at Guest editors: Luigi Naselli-Flores & Judit Padisa´k/ a quite constant rate (Padisa´k et al., 2010). Although Biogeography and Spatial Patterns of Biodiversity of these evidences are widely acknowledged among Freshwater Phytoplankton freshwater ecologists, there is a lack of studies in scientific literature about phytoplankton colonization L. Naselli-Flores (&) Á R. Barone Section of Botany and Plant Ecology, Department of processes and most of the information is reported in an Biological, Chemical and Pharmaceutical Sciences and anecdotal way. This is partly due to the relatively small Technologies, University of Palermo, Palermo, Italy dimensions of these organisms, to their cryptic method e-mail: [email protected] of dispersal and to the inherent difficulties in recog- R. Termine nizing colonization events: little attention is paid to a L.I.S.A. – ‘‘Kore’’ University of Enna, Enna, Italy few new species appearing annually in a list of 123 104 Hydrobiologia (2016) 764:103–113 phytoplankton species, especially when their contri- Few attempts were made to evaluate the dispersal bution to total biomass is low and when studies are of phytoplankton by wind using air sampler and/or carried out over a period of time of a few years. More in buckets containing water (Genitsaris et al., 2011b and general, for a long time studying biogeography of literature therein). These investigations, while con- microorganisms has been considered worthless due to firming the high dispersal potential of phytoplankton a supposed cosmopolitanism in their distribution, and (Sharma & Rai, 2011a), do not offer useful insights on only recently microbial ecologists put in discussion the phytoplankton distribution and colonization rates (i.e., real extent of this pattern (see Fontaneto & Brodie, the arrival and successful establishment of new 2011; Incagnone et al., 2015; Padisa´k et al., 2015). species per time interval). Actually, a sharp decou- To better understand phytoplankton dispersal and pling exists between dispersal potential and actual colonization patterns, freshwater ecosystems should establishment rates, and a high dispersal potential per be considered as biological islands scattered across the se does not guarantee that colonization is effectively land masses in a dry ocean (Ripley & Simovich, 2009). realized (Bohonak & Jenkins, 2003). Successful Actually, according to island biogeography theory, colonization depends on the chances that phytoplank- valleys, promontories, mountaintops, and other iso- ton organisms and propagules have i) to reach a lated spaces (such as lakes and ponds) that show suitable (aquatic) environment for their establishment different biogeographic and biodiversity levels than and, once arrived, ii) to pass through a series of the areas immediately surrounding them can be treated chemical, physical, and biological filters that may as true islands (Cox & Moore, 2010). Accordingly, prevent their successful establishment. Apart biologi- immigration and successful colonization by phyto- cal features of the colonizing species and its tolerance plankton species firstly depend on their ability to to a determined range of physical and chemical disperse over the physical barrier represented by the conditions (Bennett et al., 2010; Soininen et al., surrounding dry land. According to Ronce (2007), 2013; Florencio et al., 2014), both regional and local dispersal can be defined as ‘‘any movement by factors contribute to determine the strength of this organisms or propagules with potential consequences filters (Sharma & Rai, 2011b). In the first group of for gene flow across space.’’ However, regarding factors, the altitude distribution of water bodies phytoplankton, dispersal cannot occur as a movement (Vyverman, 1992; Catala´n et al., 2009; Wang et al., performed by the organisms themselves and it needs a 2012), as well as the spatial distance among them, and transporting vector (passive dispersal) to be achieved. thus their isolation and density in a given territory Even if the exact passive dispersal methods are elusive (Soininen et al., 2007; Ripley & Simovich, 2009 and (Kristiansen, 2008), both physical and biological literature therein), was found to influence colonization vectors are considered suitable carriers to spread success. Among local factors, the morphological phytoplankton across space (Boo et al., 2010). Gen- features of the water body (e.g., surface area, depth) itsaris et al. (2011a) showed that several phytoplank- to be colonized (Frisch et al., 2012; Borics et al., 2015) ton species, both as living cells and as resting stages, play an important role in allowing/contrasting the have a high potential for wind-mediated passive establishment of immigrant species. In addition, the dispersal. As recently reviewed by Incagnone et al. biotic interactions existing in a well-structured com- (2015), several animals (including humans) contribute munity, which historically determined its composition to successfully disperse propagules of freshwater by strengthening the relationships existing among its organisms in the same size range of living phyto- members during time, generally determine a series of plankton cells/colonies (or their resting stages) among inhibitory effects (priority effects), against the suc- freshwaters. Although biological vectors as aquatic cessful establishment of recent immigrants (e.g., birds may represent more effective dispersal vectors Louette & De Meester, 2007; Symons & Arnott, than wind (Rogers, 2014), only a few investigations 2014). were found in the literature addressed at considering The comparison of the phytoplankton assemblages the role of these animals as dispersal agents for in two Sicilian shallow lakes (Lake Pergusa and Lake phytoplankton (Kristiansen, 1996, 2008; Cellamare Biviere di Gela) suggested, in accordance to the island et al., 2010; Padisa´k et al., 2015). biogeography theory, that the frequency of coloniza- 123 Hydrobiologia (2016) 764:103–113 105 tion events and the successful establishment of new characterized by a single aquifer system which during phytoplankton species in an aquatic ecosystem may the rainy season also feeds a high number ([100) of depend on the geographical distribution of water temporary ponds located within the same catchment of bodies (i.e., their number and relative distance in a the lake; these authors also studied in details the given area: structural connectivity) and by the effec- quality of sediments and calculated the hydrological tive movements of individuals (or vectors) among the balance of the area. The catchment of the lake is water bodies (functional connectivity). intensively cultivated and horticulture and olive grove Both the lakes had disappeared in the past years prevail. Both the lakes have no surface outflow and no because of the over-exploitation of their main inflows important inflow, being mainly fed by underground to fulfill agriculture water demand. However, since waters and, during the rainy season, by ephemeral these are protected areas, both were re-filled with surface streams. Both the lakes are subjected to a water from other catchments in order to preserve the typical Mediterranean climate alternating mild rich biota they host. This offered the opportunity to relatively rainy winters with warm, dry summers. follow the pattern of changes which occurred in their