Changes of the plankton community in a shallow, subtropical lagoonal system and its relation to environmental conditions were investigated during an annual cycle to provide information on its spatial and seasonal variation pattern. The study carried out at four sites (three in the Peixe lagoon and one in the Ruivo lagoon), which are located in the Lagoa do Peixe National Park, southern Brazil. The system has a temporary connection to the Atlantic Ocean by a narrow channel. The phytoplankton density was higher in the Peixe lagoon whereas the specifi c richness was higher in the Ruivo lagoon which is also a site with the lower salinity. The phytoplankton biomass near the channel showed seasonal variation with the highest value in fall and lowest in winter. Zooplankton richness was inversely correlated with salinity, and had the highest values in the Ruivo lagoon. Ordination analysis indicated seasonal and spatial patterns in plankton community in this lagoonal system, related to variation in salinity. In addition, the wind action and precipitation were important factors on the spatial and seasonal salinity changes in the lagoon with direct infl uence on the plankton community dynamics.

Falcula hyalina Takano (1983: 24) is an epizoic diatom commonly associated with coastal copepods in many parts of the world (Takano 1983, Mahoney & Gibson 1983, Hiromi et al. 1985, Prasad et al. 1989, Souza-Mosimann et al. 1989, Fernandes & Calixto-Feres 2012, Li et al. 2014). The species was described and illustrated using the transmission electron microscope by Takano (1983) who differentiated it from other taxa of the genus—F. rogallii Voigt (1960: 86), F. media Voigt (1960: 87), F. semiundulata Voigt (1960: 87), F. paracelsiana Voigt (1961: 54) and F. media var. subsalina Proshkina-Lavrenko (1963: 36)—by the morphometric features of the valve (length, width, and stria and areolae density). Some years later, Prasad et al. (1989) improved the morphological features of F. hyalina using the scanning electron microscope and discussed the relation of the species with similar taxa. Round et al. (1990), in the diacritic description of the genus, raised the question that F. hyalina had some features that could not match with Falcula, such as the wider sternum and poroidal apical pore field (ocellulimbus), as opposed to a series of slits at the apices. Therefore, the taxonomic position of F. hyalina still remains uncertain.

Cocconeis sawensis Al-Handal & Riaux-Gobin (2014: 217), first described from a saline lake in Southern Iraq (Middle East), is observed for the first time in South America attached on Cladophora sp. from Peixe lagoon in Southern Brazil. Specimens were examined with light and electron microscopy and some morphometric variations were observed in relation to the type material. Valves from Peixe lagoon exhibit rhombo-elliptic outline with broadly cuneate to rounded apices with slightly smaller dimensions. The number of striae shows a broader range of variation on both valves and areolae density in the raphe valve is lesser. The fimbria of the raphe valva valvocopula are elongated with unequal length and shape. Different arrangement of the hymenes were also observed in the sternum valve. More information on the environment where the species was found and its relation to the populations of the species from Florida and Napuka Atoll are provided.

The chapter is about the study of environmental conditions and the structure of the benthic diatoms community in Peixe Lagoon, which is inserted in a National Park in southern Brazil. The study was carried out covering four seasons from 2011 to 2012. The system is shallow (<60 cm) located parallel to the coastline, and it is connected to the ocean through a single channel, which occurs naturally or through human action. In this lagoon, during the study, the water temperature ranged between 15.3 and 32.1°C, and the dissolved oxygen presented higher value in the winter (12.5 mg.L −1 ) and lower value in the summer (7.5 mg.L −1 ). The lagoon ranged from mesotrophic to hypereutrophic conditions. The salinity varied between 1.3 and 36.2%, and these variations were mainly related to meteorological conditions. The community of diatoms in Peixe Lagoon is composed by 62 taxa distributed in 30 genera composed largely of marine, brackish, and few freshwater species. Among the attributes of the community, composition better reflects the environmental variations. The opening and closing of the channel, salinity, temperature, and the action and direction of the wind are variables influencing the dynamics of the microphytobenthic community.