Colonization dynamics of periphytic diatoms in coastal waters of the Yellow Sea, northern China

The colonization features of periphytic diatoms were studied in coastal waters of the Yellow Sea, northern China from May to June 2010, using glass slides as an artificial substratum. Samples were collected at a time interval of 1, 3, 7, 10, 14, 21 and 28 d from two depths of 1 and 3 m. The dynamics of diatom colonization process had a similar pattern in community structure and fitted the logistic model in growth curve at both depths. The maximum abundance and the time for reaching 50% maximum abundance （10 d） showed no significant differences （P〉0.05） between two depths 1 and 3 m. Although the diatom communities repre- sented similar taxonomic composition, they differed in the temporal pattern of structural parameters and in succession dynamics of dominant species between the two layers. The species richness showed significantly higher values during the colonization period more than 14 d, while the species diversity and evenness rep- resented a higher variability with significantly different values （P〈0.05） at a depth of 1 m than at a deeper layer. The results suggest that the diatom colonization follows the logistic model growth curve and differs in colonization features between different depths in the coastal waters, and that the sampling strategy at i m is more effective to detect the ecological features for bioassessment in marine ecosystems.

Changing assembly processes during a primary succession of plant communities on Mediterranean roadcuts

Aims Studying plant ecological succession provides insights into the spatiotemporal processes underlying community assembly and is of primary importance for restoration ecology.We investigate here colonization events and local community assembly over an original primary succession occurring on roadcuts after roadwork.For this,we addressed both the changes in species presence–absence(incidence data)to highlight pre-establishment filters and in species relative abundances to further assess the influence of local biotic processes.Methods We studied 43 limestone roadcuts in Mediterranean France,covering five age classes up to an age of 80 years,along with 13 natural cliffs as a reference,and we counted 14322 plant individuals on these sites.We applied a constrained nonsymmetric correspondence analysis of both the incidence(presence–absence)and abundance data to assess the variation of these data along the chronosequence.Important Findings Along the first 30 years,the initially abundant short-lived species declined both in terms of incidence and abundance and were replaced by longer lived herbaceous and woody species.This first phase was characterized by species that are widespread in the surrounding scrublands and was comparable to an early secondary succession there.After 30 years,there were continuing changes in incidence data with age,but no more significant change in species’abundances.This second phase was marked by the late colonization of specialists that did not become dominant.Although colonization and establishment limitation was thereby apparent for specialist species,a slow convergence of community composition toward the situation of natural cliffs could be detected in the older stages of the chronosequence.These findings convey insights into the natural dynamics of man-made outcrop plant communities and may be useful for the ecological management and restoration of such contexts.It also illustrates the interest of comparing incidence and abundance data to investigate the relative influence of ecological determinants on the assembly of plant communities.