In polar and tropical regions, the rates of primary production of microalgal communities associated with macroalgae, seagrasses and marine invertebrates are comparable or sometimes higher to those of the phytoplankton component. These benthic microalgal communities, which are mainly represented by diatoms, appear to be composed by a limited number of genera, belonging to different growth forms that can be considered fully adapted to the epibenthic lifestyle. In spite of the key role played in the food chain, the biodiversity of epibenthic diatom communities worldwide is poorly studied and ecological studies based on a rigorous taxonomic and quantitative approach are still rare due to the small size of such organisms. Indeed, most of the species have average size less than 20 microns with taxonomic characters not resolvable in light microscopy, so the scanning electron microscopy results the only possible approach for a correct quantitative analysis of such floristic communities. International collaborations, intended to last in the next years, have been institutionalized in a multi-annual project aimed to describe the biodiversity and the community structure of epibenthic diatom communities on different host organisms (macroalgae, seagrasses, invertebrates, vertebrates) from Polar, Mediterranean and Tropical regions. So far, investigations have been carried out on diatom communities living on macroalgae from coastal areas of five Antarctic and two Arctic stations whereas, in Mediterranean and tropical regions, diatom assemblages were analysed from seagrasses, hydrozoans, gastropods, crustaceans and recently marine turtles. For all diatom communities investigated, our results confirm that their biodiversity, both in terms of specie richness and relative abundances, has been so far strongly underestimated and that their community structure appear mainly influenced by the nature of the host organism rather than by other ecological parameters. Many of the diatoms collected during the previous studies were also characterized by valves with peculiar morphologies and regular pore patterns that induced us to hypothesize their connection with specific biological meanings and hidden functional properties. Multidisciplinary researches, some still in progress, have allow us to demonstrate that the valves of many of the investigated species present linking or mechanical microstructures and photonic crystal-like pore arrangements responsible for surprising optical properties, being capable of filtering and focalizing light at different waveleghs. Our ongoing research aims to unreveal the biological significance of such structures and properties as well as to promote diatoms as innovative materials and biomimetical model for micromechanical, optical and biosensoring applications.
Mario De Stefano is Associate Professor of Botany and Marine Biology at the Environmental, Biological and Pharmaceutical Science and Technology Department of University of Campania, Naples, Italy. His researches focuses on taxonomy, ecology and phylogeny of benthic diatom communities worldwide with a consolidate experience in several diatom/host community models including seagrasses, mangroves, macrophytes, soft, hard and biogenic substrata, sponges, bryozoans and, more recently, sea urchins, corals, marine turtles, whales. During his career he has been also particularly interested in studying diatom communities from extreme environments (Antarctica and Arctic regions, deserts, volcanic habitats) for which he participated in six Antarctic and two Arctic expeditions. Prof. De Stefano is a recognized international expert of Scanning Electron Microscopy. During his researches he has developed innovative procedures aimed at preserving the in-situ integrity of microcommunities during SEM observation, thus allowing their taxonomic identifications at species level and first quantitative ecological surveys through direct SEM counting. The astonishing beauty of diatoms and their important ecological value have also led Prof. De Stefano to win twice the “International Science and Engineering Visualization Challenge”, the famous international competition for the best scientific photography sponsored by National Science Foundation and Science.
From 2010 Prof. De Stefano is promoting and coordinating an international research program called “MicroBioinspiration” where the functional morphologies of marine protists, invertebrates, vertebrates and plants are studied by Scanning Electron Microscope and used as models for biomimetic researches. Within that program he is conducting studies on the functional properties of diatom frustules and on their potential use for micro and nanotechnological applications in the fields of optics, mechanics and biosensing.
Prof. De Stefano, to date, is author of 76 peer reviewed papers, a monograph, 7 reviews and more than 100 proceedings of national and international conferences. So far, he has described and formally established 4 genera, 11 species and 7 new varieties of diatoms.