Date of Award

Spring 1980

Project Type

Dissertation

Program or Major

Botany

Degree Name

Doctor of Philosophy

Abstract

A detailed study of the marine flora of Tunisia was conducted by assessing the seasonal variation of seaweed populations along a 35 m transect at one site (La Marsa), as well as by qualitatively describing the species composition throughout the country, and comparing the floristic affinities of the Tunisian flora with other Mediterranean and northeastern Atlantic areas. The occurrence and distribution of the Tunisian flora were correlated with a variety of parameters, including water temperature, salinity, substrata and currents. The seasonal studies at La Marsa, which is within the Gulf of Tunis, were undertaken monthly between October, 1974 and August, 1975. Sixty five taxa of seaweeds were recorded at the transect site. The Phaeophyta showed the most dramatic seasonal variation and sensitivity to temperature variations, with a 41% decrease in percent occurrence from fall to summer. In contrast, the Rhodophyta and Chlorophyta only decreased by 7% and 5%, respectively, during the same period.

A total of 170 species of seaweeds was collected from 29 sites throughout Tunisia. Of these, 55 species are newly reported for the country. An additional 116 species have been reported by other investigators from Tunisia, primarily from deep water habitats. Thus, a total of 286 taxa of seaweeds are known from the country. Two distinct floristic regions are evident with Tunisia, namely, the northern and southeastern areas that are separated by a sill between Tunisia and Sicily. Using Cheney's floristic affinity ratio, (Chlorophyta + Rhodophyta)/Phaeophyta, it was shown that northern Tunisia had a cold water flora, while the southeastern Tunisia had a mixed vegetation with reduced numbers of cold water species. Northern Tunisia lies within the western cooler basin, while the southeast coast is in the eastern, warm basin. The pronounced temperature demarcation between the two regions probably accounts for their differential floristic composition. A comparison of the Tunisian flora with the Red Sea, as well as several northeastern Atlantic (Portugal, Spain, Morocco, Canary Islands) and Mediterranean sites were made using Jaccard's Similarity Coefficient. The highest percent similarity was between Tunisia and Sicily, while the lowest was between Tunisia and the Red Sea. The close geographical proximity of Tunisia and Sicily, as well as the similarity of their temperature, salinity, and current regimes probably accounts for their high floristic affinities.

The phytogeographic distribution of the two major marine vegetational units within Tunisia, i.e., the Red Sea-Indian Ocean and the northeastern Atlantic algal components, was compared throughout the Mediterranean. The northeastern Atlantic species were predominant in the western basin and the more northern portions of the Mediterranean, while the Red Sea-Indian Ocean component was evenly distributed throughout the Mediterranean but of reduced species diversity. More than 90% of the water in the Mediterranean comes from the Atlantic Ocean through the Gibraltar sill and upon its entrance major counterclockwise currents are established within the western and eastern basins. The above described currents carry the cold surface waters from the Atlantic and establish low water temperatures in the western basin; in turn they are primarily responsible for the dispersal of Atlantic taxa in the Mediterranean. The opening of the Suez Canal in 1869 was an important factor determining the migration of Red Sea biota into the Mediterranean. The Red Sea-Indian Ocean component occurs in low numbers probably because of a limited inflow of sea water from the Red Sea into the Mediterranean.

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