UNIVERSITÀ POLITECNICA DELLE MARCHE
FACOLTÀ DI SCIENZE
DOTTORATO DI RICERCA IN BIOLOGIA ED ECOLOGIA MARINA
VI CICLO-NUOVA SERIE
The epiphytic diatom genus Mastogloia G.H.K. Thwaites in W.
Smith from different biogeographic areas
Tesi di dottorato di:
Chiara Pennesi
Tutore:
Dott. Cecilia Totti
Cotutore
Prof. Michel Poulin
Anno Accademico 2009-2010
Benthic diatoms represent an important component of aquatic ecosystems, both for
their contribution to primary production (they account for more than 25% of the
primary productivity of the earth) and for their role in the food chain. Benthic
diatoms along with cyanobacteria are the first algae to colonize the submerged
substrates, both in freshwater and in marine environments, enhancing the further
colonization by other organisms. Approximately 60% of the known diatoms genera
are represented by benthic forms. The systematics of benthic diatoms is still partly
unexplored and most of the species are described only by means of observations at
light microscope. Therefore, in most cases, a revision of their classification and
taxonomical identity is highly recommended.
The genus Mastogloia Thwaites ex Smith includes a number of species living as
epilithic or epiphytic on seaweeds and seagrasses, and, together with other biraphid
(i.e. Diploneis, Amphora) and monoraphid (i.e. Cocconeis, Achnanthes) genera, is
highly biodiversified and quantitatively significant in benthic communities. Until
1974, the systematics of the Mastogloia was based on observations through light
microscopy. The coming of the scanning electron microscopy (SEM) in 1935 by
Michael Knoll gave a large increase in diatomologica research. Indeed, Ricard in
1975 described the valve ultrastructure of several species of Mastogloia, using for the
first time the SEM. In 1933, Hustedt proposed the dichotomous key for the
Mastogloia genus, and listed 140 species included into ten sections: Paradoxae,
Inaequales, Ellipticae, Decussatae, Constrictae, Sulcatae, Apiculatae, Undulatae,
Rostellatae and Lanceolatae. However, at now the knowledge of the systematics of
this genus appears still incomplete.
The aim of this work is a revision of the Mastogloia genus, with a special focus
in reviewing the Hustedt’s key determination, updating some morphological
terminology. Both species instituted after Hustedt and new species were included into
the sections, considering also their geographic distribution. Furthermore, this study
contributes in improving the knowledge of benthic diatom biodiversity.
Mastogloia species living as epiphytes on marine macrophytes (both seagrasses
and seaweeds) were studied in several temperate and tropical coastal areas. Samples
were collected from 1999 to 2006 from Slovenia (Izola, Adriatic Sea), Italy (western
Calabria, and Tyrrhenian Sea), Republic of Malta (Mediterranean Sea), Greece
(Patmos island, Aegean Sea), Turkey (Gulf of Kusadasi, Aegean Sea), Egypt (Sharm
El-Sheikh, Red Sea), Vietnam (South China Sea, three different areas in Phù Bay),
Singapore (Saint John's island, South China Sea), Indonesia (Siladen island, Celebes
Sea) and Iceland (Hvalfjordur and Halakot, Atlantic Ocean). Macrophyte samples
were treated with the acid cleaning procedure of von Stosch, to obtain the cleaned
frustules of epiphytic diatoms. Cleaned diatoms were observed at light microscope
(ZEISS Axioscop) and at Philips SEM 515.
Sixty-one species of Mastogloia, among these, thirteen are new species and two
are new varieties, were described. Moreover, species were divided into Hustedt’s
sections, as follows: M. erythraea Grunow 1860 and M. paradoxa Grunow in Cleve
1895 belonging to the section Paradoxae; M. pusilla Grunow 1878, M.
manokwariensis Cholnoky 1963, M. cuneate (Meister 1937) Simonsen 1990, M.
corallum Paddock & Kemp 1988, M. amoyensis Voigt 1942 and M. tenuis Hustedt
1933 belonging to the section Inaequales; M. crucicula (Grunow 1877) Cleve 1895
var. crucicula, M. crucicula var. alternans Zanon 1948, M. cribrosa Grunow 1860,
M. ovata Grunow 1860, M. fimbriata (Brightwell) Grunow 1863, M. ovalis A.
Schmidt 1893 in Schmidt et al. 1874–1959, M. ovulum Hustedt 1933, M. gilberti A.
Schmidt 1893 in Schmidt et al. 1874–1959, M. pseudolatecostata Yohn & Gibson
1982, M. binotata (Grunow 1863) Cleve 1895 and M. cocconeiformis Grunow 1860
belonging to the section Ellipticae; M. varians Hustedt 1933 belonging to the section
Decussatae; M. borneensis Hustedt 1927 in Schmidt et al. 1874–1959, M. depressa
Hustedt 1933, M. baldjikiana Grunow 1893 in Schmidt et al. 1874–1959, M.
submarginata Cleve & Grunow in Cleve 1881, M. cannii Kemp & Paddock 1990 and
M. pumila (Grunow in Van Heurck) Cleve 1895 belonging to the section Sulcatae.
Considering the biogeographic distribution of the genus, the species of
Mastogloia are mainly distributed in tropical and subtropical regions, although they
also occur in temperate zones. In the only one subpolar area samples in this study
(Iceland), no Mastogloia species were found. No correlation occurs between the
biogerographic distribution and the belonging to Hustedt’s sections.