Attività Fotosintetica di Alghe Marine Nella Grotta Delle Viole (Isola S. Domino - Tremiti)

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Abstract
Photosynthetic rates of some algae in the marine cave « Grotta delle Viole » (Is. S. Domino - Tremiti). — The « Grotta delle Viole » is one of the several marine caves located along the calcareous rocky southern littoral of the Island S. Domino (Tremiti) in the Adriatic Sea. Morphologically this cave is a tunnel, which connects the open littoral sea with a little bay. Availing of these environmental factors, we have chosen three stations to measure the photosyn-thetic yield, under completely natural conditions, of algae particularly important for some marine communities, described in an other paper (see, Pignatti S. et al. 1967). In station 1 (fig. 1) we have a biotope with strongly reduced light and in the neighbouring stations 2 and 3, two biotopes exposed to sun-light. We have studied three species living in dark places (« Peyssonelia » cfr. « harveyana », « Palmophyllum crassum » and « Pseudolithophyllum expansum » two of well lighted habitas (« Padina pavonia » and « Dictyota dichotoma » and one of intermediate place (« Codium difforme ») Some information on the optical conditions of the seawater have been obtained with a photoelectric cell, filters were used to measure the red and blue light penetration (Tab. 1, 2). This part of the Adriatic Sea is characterized by high penetration of blue light. In the cave this light is highly predominant. The photosynthetic rates were measured in natural conditions by determining the output in time O2 using the Winkler method (Tab. 3) and the CO2 changes by measuring pH-changes in short time intervals with an original method using a submarine incubation cell, of our design, equipped with the electrodes of a pH-meter and a spot-light galvanometer as measure instrument. The data obtained with the latter method have been statistically analized, their significance discussed and reported in Tab. 4. On the basis of the results, the species, which are confined in places with reduced light intensity, show a low but measurable photosynthetic surplus only in their natural habitats, transferred in high-light intensity they show a deficit. This fact can suggest the hypotheses: deactivation of the chlorophyll in green and blue light or competitive inhibition due to the presence of accessory pigments. The species of sunny habitats transferred in low-light intensity show an assimilatory deficit, that in this case, with great probability, is due to the progressive reduction of the photosynthetic process. These considerations explaine also the observed distributions of the species and of the algal communities (fig. 1), since each of them is connected with a light optimum. It seems important moreover to note that here, for the first time, data are given also on photosynthetic activity of Lithothamnia.

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