During the past century dramatic changes in the composition and structure of species assemblages have been observed worldwide. These changes took a sharp increase in recent years. Global changes such as climatic changes and species introductions are superimposed on more or less local habitat degradation, pollution and overexploitation. A detailed knowledge of the taxonomic composition of the flora and fauna at a local scale is important because it represents the only mean to assess subtle changes in the distribution and abundance of species, in particular of rare species. The present study discusses 15 interesting macroalgal species from the French Mediterranean coast. Among them, Antithamnion amphigeneum, A. piliferum, Cordylecladia guiryi, Goniotrichiopsis sublittoralis, Jania adhaerens, Laurencia chondrioides and Phyllophora sicula are reported and described for the first time from the region and 7 species are considered as introduced. For each species, the geographical distribution and the ecology are discussed.

Morphological studies of selected taxa in the Cymbellaceae from French Pyrenees including the description of a new species : Delicata couseranensis sp. nov. Lakes and wet rocks in the French Pyrenees are inhabited by diversified diatom communities. Taxa of Cymbellaceae are particularly numerous. Morphological studies using light- and scanning electron microscopy of selected species are presented herein. One of them belongs to the genus Delicata and is described as a new species, Delicata couseranensis sp. Nov. The new species is close to Delicata judaica (Lange-Bertalot et Krammer) Krammer et Lange-Bertalot in morphology but differs in the dimensions, the length/breadth ratio and the number of puncta in 10 µm. The detailed morphology of seven recently described species is also examined: Cymbella perparva Krammer, Cymbella maggiana Krammer, Cymbella simonsenii Krammer, Cymbella neoleptoceros Krammer var. tenuistriata Krammer, Cymbella subhelvetica Krammer, Cymbella lange-bertalotii Krammer and Cymbopleura laeviformis Krammer. The taxonomic affinities of all these taxa are discussed and data on their ecology and biogeography are given.

A renewed interest in investigating the relationships existing between body size and environmental variables is pervading ecological studies. Phytoplankton has a long tradition as model system in studies of community ecology and several research concepts were developed using these organisms. In this paper we try to review the relevance of analyzing the morphological features of phytoplankton in ecology. Starting with a brief account of allometric relationships existing in phytoplankton, we i) examine the physical context in which phytoplankton grow, and ii) highlight the role of their size in nutrient uptake, and that of their shape in light harvesting. Moreover, the way in which the morphology of phytoplankton organisms cope with the hydrodynamical conditions of a given water-body are considered. In addition, we also included a paragraph on the role of grazing in moulding the size and the shape structure of phytoplankton assemblages. An account on the main research currents about the role of morphology in the definition of morpho-functional traits of phytoplankton is offered. All these approaches, which can be viewed as complementary of taxonomy, both molecular and “traditional”, are promising tools to better understand the functioning of aquatic ecosystems and may offer a vast array of new perspectives in the field of aquatic ecology and phytoplankton research as well as a simplified tool to perform water quality monitoring.

The DNA-localizing fluorochrome DAPI (4′, 6-diamidino-2-phenylindole) and chicken erythrocytes standard (RBC) were used with image analysis and static microspectrophotometry to estimate nuclear DNA contents in 14 species and varieties of Dictyotales from the Atlantic Ocean (Spain and USA) and the Mediterranean Sea (Spain). Negligible differences were found between specimens fixed in Carnoy's solution (EtOH) and methanol-Carnoy's (methacarn). Present and previously published nuclear DNA content estimates expand our database to include 17 species and varieties representing seven genera with a 2C range of 0.7 – 1.7 pg. Intraplant variation (endopolyploidy) was observed in most isolates and 8C nuclei were quantified in five species. In four species, fluorescence intensity (If) levels in 2C gametophyte nuclei were found to closely approximate 50% of 4C values in vegetative cells of mature sporophytes, consistent with meiosis and a sexual life history in diplobiontic algae. Availability of consensus higher-level phylogenetic trees for Dictyotales has opened the way for determining evolutionary trends in DNA amounts. Both estimated genome sizes and published chromosome numbers for Dictyotales suggest that evolution in the order was accompanied by multiple, discrete polyploidy events which are largely obscured by subsequent small scale loss or gain of chromosomes (aneuploidy). Members of the genus Dictyota are characterized by a narrow range of 2C genome sizes (0.7–0.9 pg) relative to other Dictyotales investigated (1.0–1.7 pg).