Dispersal beyond the local patch in clonal plants was typically thought to result from sexual reproduction via seed dispersal. However, evidence for the separation, transport by water, and re-establishment of asexual propagules (asexual hydrochory) is mounting suggesting other important means of dispersal in aquatic plants. Using an unprecedented sampling size and microsatellite genetic identification, we describe the distribution of seagrass clones along tens of km within a coastal lagoon in Southern Portugal. Our spatially explicit individual-based sampling design covered 84 km 2 and collected 3 185 Zostera noltei ramets from 803 sites. We estimated clone age, assuming rhizome elongation as the only mechanism of clone spread, and contrasted it with paleo-oceanographic sea level change. We also studied the association between a source of disturbance and the location of large clones. A total of 16 clones were sampled more than 10 times and the most abundant one was sampled 59 times. The largest distance between two samples from the same clone was 26.4 km and a total of 58 and 10 clones were sampled across more than 2 and 10 km, respectively. The number of extremely large clone sizes, and their old ages when assuming the rhizome elongation as the single causal mechanism, suggests other processes are behind the span of these clones. We discuss how the dispersal of vegetative fragments in a stepping-stone manner might have produced this pattern. We found higher probabilities to sample large clones away from the lagoon inlet, considered a source of disturbance. This study corroborates previous experiments on the success of transport and re-establishment of asexual fragments and supports the hypothesis that asexual hydrochory is responsible for the extent of these clones.

Phytobenthos, one of biological quality elements according to the Water Framework Directive (WFD), is a key component in the evaluation of the ecological status of lake ecosystems. Nevertheless, studies on phytobenthic and periphytic communities in lakes are vastly outnumbered when compared with the corresponding phytoplanktic communities (Cantonati & Lowe 2014). Diatoms, as the most important representatives of phytobenthos, are characterized by having a short life cycle, widespread distribution and a distinct sensitivity to the slightest environmental changes. These features enable a relatively easy monitoring of an ecosystem and detection of changes in the ecological status. Distribution and composition of diatom communities are mainly conditioned by the lake depth and substrate type, the amount of available light and shading effect. The shallow littoral strip of the lake is inhabited by species adapted to high irradiance, large temperature oscillations and constant fluctuations in the water level. In the lake's deep zone, where conditions are often dominated by low light availability, strong effect of shading by phytoplankton and attenuated oxygen concentration with bacterial degradation processes, a distinct diatom community is present. Plitvice Lakes, a specific hydrogeological phenomenon composed of 16 cascading lakes, constitutes a referent lake ecosystem for the water quality evaluation and monitoring of the phytobenthic community. The purpose of this study was to compare differences in the composition and abundance of diatom communities and to determine the ecological status of lakes Kozjak and Prosce. Benthic samples, along with the samples for chemical analysis of water, were collected during 2015 and 2016, from the deepest point and from the shallow littoral point on both lakes. After cleaning of samples and preparation of permanent slides diatoms were identified, measured and counted to 400 frustules on each slide. Water quality of the investigated lakes was determined using several multimetric diatom indices: Croatian saprobic index - SIHRIS, Croatian trophic diatom index - TIDRH, Pollution Sensitivity Index - IPS. The relationship between samples and nutrient concentrations was tested using multivariate analysis of canonical correspondence (CCA) to investigate the influence of chemical and physical factors on the composition of the community.

The dispersal potential of sexual and asexual propagules of Zostera noltii was experimentally quantified in still water and under different currents in microcosm and mesocosm facilities. We estimated sinking rates of seeds and changes over time in shoot buoyancy, shoot viability, fragment breakage, shoot growth rate and spathe release rate of floating fragments. The fast sinking rates of detached Z. noltii seeds suggest a small spatial scale of dispersal insufficient to connect fragmented populations, whereas the traits of floating fragments, particularly shoot buoyancy and shoot survival (>55 d), suggest a potential for long distance dispersal (>2300 km) that could connect distant patches and allow colonization of new areas. We showed that the Z. noltii vegetative and reproductive fragments have the potential to extend the dispersal achieved by detached seeds alone. (C) 2013 Elsevier B.V. All rights reserved.