NOTE DIVERSITY AND MORPHOLOGY OF SKELETONEMA SPECIES IN SOUTHERN BRAZIL, SOUTHWESTERN ATLANTIC OCEAN 1 Marli Bergesch 2 Institute of Oceanography, Federal University of Rio Grande -FURG, 96201-900 Rio Grande RS, Brazil Marines Garcia Botany Department, Federal University of Pelotas -UFPEL, 96001-610, Pelotas, RS, Brazil and Clarisse Odebrecht Institute of Oceanography, Federal University of Rio Grande -FURG, 96201-900 Rio Grande RS, Brazil We examined the morphology of Skeletonema spe- cies occurring in coastal waters of southern Brazil, on the basis of LM, SEM, and TEM analyses of six isolated strains and of 13 field samples from the Patos Lagoon estuary and the adjacent Cassino Beach. We concluded that the genus Skeletonema is highly diverse in coastal waters of southern Brazil, with the occurrence of four confirmed species: S. costatum, S. pseudocostatum, S. potamos, and S. trop- icum. In addition, EM details must still be provided for S. menzelii, and genetic studies should be con- ducted to confirm the identity of S. cf. grethae and S. subsalsum. The high diversity in this geographic area can be attributed to the proximity of the Sub- tropical Convergence and to the freshwater ecosys- tems of Patos Lagoon and La Plata River that favor the presence of warm-, cold-, and brackish-water species. Key index words: diatom; estuary; South America; surf zone; taxonomy Abbreviations: FPP, fultoportulae process; IFPP, intercalary fultoportulae process; IRPP, inter- calary rimoportulae process; s.s., sensu stricto; TFPP, terminal fultoportulae process; TRPP, terminal rimoportulae process The cosmopolitan diatom Skeletonema, originally named Melosira costata Grev. (Grev.), includes several geographically widespread species, with morphologi- cal and genetic variations, although gaps in their world distribution were recently suggested (Kooistra et al. 2008). Reexamination of the type material of the main species of Skeletonema, S. costatum (Grev.) Cleve, under EM revealed that besides the most abundant morphotype S. costatum, S. grevillei Sarno et Zingone was also identified (Zingone et al. 2005). At present, 11 Skeletonema species were recognized based on genetic and morphological data (Medlin et al. 1991, Sarno et al. 2005, 2007, Zingone et al. 2005), though ambiguities were revealed between both identification tools, which could indicate the existence of cryptic diversity (Kooistra et al. 2008). The main objective of this study was to identify the species of Skeletonema present in the Patos Lagoon estuary and in the adjacent Cassino Beach, southern Brazil, based on LM and EM observations of their frustule morphology. The analyzed samples were obtained in the framework of a long-term study (Abreu et al. 2009, Odebrecht et al. 2009) conducted in a shallow embayment (32°01¢ S; 52°06¢ W), in the main chan- nel of Patos Lagoon (32°09¢ S; 52°06¢ W), and in the surf zone of the adjacent oceanic Cassino Beach (32°12¢ S; 52°10¢ W). A total of 13 plankton samples containing Skeletonema species and six isolated strains were selected from the monthly monitoring program for our taxonomic study (Table 1). Plank- ton net (20 lm) surface haul samples were pre- served with formaldehyde buffered with borax (4% final concentration) and were selected based on a minimum Skeletonema spp. density (>10 3 cells Æ L )1 ). In addition, water temperature (mercury thermo- meter) and salinity (Model 33 SCT; Yellow-Springs Instrument Co. Inc., Yellow Springs, OH, USA) were measured. In October 2003 and 2004, and February 2005, six clonal cultures of Skeletonema were isolated from natural samples (Table 1) and maintained as described in another study (L. I. Meinerz, M. Berg- esch, C. Odebrecht, and P. Abreu, unpublished data). The frustules were cleaned following Simon- sen (1974) and mounted with Hyrax medium. LM images were obtained using a Diagnostic digital camera and Spot Basic software on a Zeiss Axiovert 135 microscope (Diagnostic Instruments, Sterling Heights, MI, USA) with phase and interference 1 Received 2 April 2008. Accepted 12 June 2009. 2 Author for correspondence: e-mail docmarli@furg.br. J. Phycol. 45, 1348–1352 (2009) Ó 2009 Phycological Society of America DOI: 10.1111/j.1529-8817.2009.00743.x 1348