The red algal family Halymeniaceae has been recently the subject of taxonomic revisions based strictly on molecular data. As a result, the number of genera ascribed to it has been decreasing and many generic definitions changed profoundly owing to inconsistencies in diacritical vegetative and particularly reproductive characters in standard literature. Reproductive uniformity within this family has been claimed since the late 19^th century and is generally supported by recent authors. In this study we report on consistent significant differences in the architecture of carpogonial and auxiliary cell ampullae, as well as in early postfertilization events, among Mediterranean species currently assigned to the genus Grateloupia C. Agardh and provide new interpretations of these features. We recognize several distinct types of ampullae and postfertilization events that distinguish groups of species, these groups proving to be strongly supported by rbcL phylogenies. As a result we conclude that the genus Grateloupia as presently circumscribed should be segregated into multiple genera. In addition to Grateloupia sensu stricto, we resurrect Dermocorynus P.L. Crouan et H.M. Crouan, Pachymeniopsis Y. Yamada ex S. Kawabata, Phyllymenia J. Agardh and Prionitis J. Agardh, all of which have been subsumed in Grateloupia by previous authors. New genera based on our anatomical and rbcL results for G. doryphora (Montagne) M. Howe, G. subpectinata Holmes and G. proteus Kützing will be described in subsequent papers.

The analysis of a sample taken in a lava tube cave on Île Amsterdam (southern Indian Ocean) revealed the presence of three interesting small-celled naviculoid diatom taxa. Based on light and detailed scanning electron microscopy, two of these taxa are described as new: Mayamaea cavernicola sp. nov. and Sellaphora barae sp. nov. A third taxon, Chamaepinnularia aerophila Van de Vijver et Beyens, was previously only found in the type locality on the nearby Crozet Archipelago. The three taxa are compared to other morphologically similar species from Europe, South America and the (sub-)Antarctic Region.

Corallina L. is the type genus of the subfamily Corallinoideae (Aresch.) Foslie and Corallina officinalis L. is the type species of the genus. This name has been applied worldwide, particularly in temperate waters. An attempt to obtain sequence data from the lectotype specimen was not successful. In order to establish a species concept for C. officinalis based on molecular sequence data as well as morphology, an epitype was selected from Devon, England within the vague type locality ‘in O [Oceano] Europaeo’, and from which mitochondrial (cox1) and plastid (rbcL) data were obtained. A second species, Corallina elongata Ellis et Solander (type locality Cornwall, England), was shown previously to include at least two species based on DNA sequences. The lectotype of C. elongata is an illustration and therefore an epitype was selected to provide molecular sequence data, using the same markers as for C. officinalis. These molecular sequences for C. officinalis and C. elongata are compared with those of a third, recently described species from Great Britain, Corallina caespitosa R.H. Walker, J. Brodie et L.M. Irvine: these data provide an example for studying Corallina species taxonomy and diversity in other parts of the world. The implications of this work are discussed in relation to concepts of species distribution.

The dinoflagellate Ostreopsis siamensis was studied as part of a broad national monitoring program along the Lebanese coastal waters. The monthly and spatial variations of its density in water samples were carried out at 4 different rocky stations from September 2000 to December 2001 and for a longer period (April 1997-December 2001 and January 2010 to December 2010) in one of the stations.

Results showed that O. siamensis is present almost in all rocky shores along the Lebanese coastline from south to north between May and November when the surface seawater temperature ranges from 23 to 30.5 °C, with a maximum in abundance between July and September. In 2001, the population densities reached 10 500 cells/L in July and 5 700 cells/L in September at two stations both located in the southern coast. In 2010, the analysis of larger water volumes revealed the presence of this species in February, March and April; however densities were lower than 1–3 cells/L. Significant positive correlation was observed (P<0.01) between the occurrence of the species and nitrate concentrations, whereas the correlation was negative with orthophosphates. Our results suggest that O. siamensis is a thermophilic species. It constitutes a permanent component of the microalgal flora of Lebanese waters and its abundance depends on water enrichment.