Ciclo annuale del fitoplancton nelle acque costiere del Parco Naturale della Maremma II. Flora e variazioni delle comunità

Abstract

Annual cycle of phytoplankton in the coastal waters of the « Parco Naturale della Maremma ». II. Flora and communities variations.—The hydrology of the marine coastal area of the Parco Naturale della Maremma and the annual cycle of phytoplankton standing crop have been examined in a preceding paper (Lenzi Grillini e Lazzara, 1978). In the present paper the species list and the main features of marine phytoplankton communities of the same area are reported as a result of an annual cycle of monthly collections effected in seven stations. The most conspicuous seasonal bloomings are due to Skeletonema costatum (Grev.) Cleve in February and to some species of the Chaetoceros gen. in November; the dinoflagellates play a minor role throughout the year, except for Gonyaulax minima Matz. with a light blooming episode in summer. The annual cycle of bottom living diatoms found in the samples appears to be very similar in its shape to the cycle of the pelagic species, as for the standing crop and for the species number. The community structure variations have been analyzed by means of diversity and dominance indexes and of species frequency diagrams. As it concerns the differences in species composition among the seven stations, the area in front of the rocky shore, with deeper and more saline waters, appears to be very homogeneous, whereas some differences have been observed in the shallow waters, in front of the sandy shore and under the influence of the Ombrone River mouth.