Aim: Seasonal patterns diatom community on Acrostichum danaeifolium were examined in a wetland in southern Brazil. Methods The adhered diatoms were removed from the plant, species identification and growth forms were performed, and determined physical-chemical parameters of water. Results In total, 96 taxa belonging to 46 genera were identified. Nitzschia frustulum, Pseudostaurosira brevistriata and Plagiogramma tenuissimum were abundant species. Distinct growth forms that formed low-and high-profile ecological guilds and a mobile guild were observed. Navicula and Nitzschia were the genera with the greatest number of species, and these diatoms formed mucilage tubes. The water temperature varied from 10-26 °C, the depth from 0.35-0.80 m, the transparency from 0.20-0.23 m, the flow from 9.4-42.12 m3 s–1, the pH from 7.08-8.89, the electrical conductivity from 0.65-15.83 mS cm–1, the total organic phosphorus from 0.03-0.11 mg L–1, and the total organic nitrogen from 0.29-0.49 mg L–1. In summer, marine species such as Thalassiosira eccentrica and Rhaphoneis castracanii were also present. Conclusions The high-profile guild prevailed in all seasons of the year, with higher number of growth forms in the guild in winter. The richness found on A. danaeifolium shows that this plant provide a favorable habitat for epiphytic diatoms in wetlands such as Lagoa Pequena.

Considering the insufficient scientific knowledge of diatoms attached to plants in wetlands, this study aims to present their floristic composition in Arroio Pseudônimo and also images of species that represent first records for the State of Rio Grande do Sul, Brazil. Twelve samples from the fern Acrostichum danaeifolium fronds were collected, over four seasons (from May 2011 to January 2012). Acrostichum danaeifolium has a limited distribution in Arroio Pseudônimo (Lagoa Pequena), Pelotas. Epiphytic material was removed and permanent slides were prepared for observation and identification. Physical (temperature, depth, water transparency and flow) and chemical (pH, electrical conductivity, phosphorus and nitrogen) variables of water were measured. The diatom flora showed high species richness (157); Nitzschia displayed the highest number of taxa (22). The community was composed of taxa characteristic of fresh water (26%), estuarine (50%) and marine (14%), from classes Bacillariophyceae (75%), Coscinodiscophyceae (17%) and Fragillariophyceae (8%). The greatest richness occurred in summer (99 species) and autumn (90), compared to spring (46) and winter (29). Twenty-three species are recorded for the first time to Rio Grande do Sul.

No abstract

Knowledge about the diversity and spatiotemporal variability of epiphytic diatom communities in estuarine meadows has great relevance for coastal ecology and, thus, contributes to understanding the impact of natural and anthropogenic changes on seagrass meadows. The community of epiphytic diatoms in Ruppia maritima L. meadows was investigated in two environments with different levels of anthropogenic impact and nutrient loads. Both impacted and non-impacted meadows had similar conditions in terms of water depth, temperature and transparency but distinct nutrient loads and salinity ranges. A total of 159 diatom taxa were found on Ruppia maritima leaves during the monitoring period, including freshwater (30.8%), marine (25.1%), brackish (9.4%) and cosmopolitan (8.8%) taxa. The most abundant species were C. placentula, T. tabulata, M. pumila and T. fasciculata, in addition to A. tenuissimus, C. adhaerens and M. moniliformis. Although present in both sites, C. placentula and T. tabulata were the dominant species in the impacted site. We found that 32% of the taxa were exclusive to the non-impacted site, 23% to the impacted site and 45% were common to both sites. The study sites showed marked differences in community attributes; i.e., higher richness, diversity and equitability and lower dominance were found in the non-impacted site, which is distant from anthropogenic sources of domestic and industrial sewage and has low concentrations of dissolved N and P in water and low values of sediment organic matter. Nutrient concentration and salinity were the main factors behind the spatial and temporal variability in the structure of the epiphytic community when all other environmental variables were similar (water depth, temperature, transparency and host plant). The influence of temperature and salinity on community structure was site-dependent. This study revealed the high richness and diversity of epiphytic diatoms in the meadows of the Patos Lagoon estuary (PLE) and the high spatial and temporal heterogeneity of the communities, and it shows the potential of epiphytic community studies for the assessment of environmental quality in seagrass meadow habitats.

No abstract