Y. Yoneshigue-Valentin and J.L. Valentin,     Instituto de Estudos do Mar Almirante Paulo Moreira, 28910 Arraial do Cabo, Rio de Janeiro, Brazil

Publisher Summary

The central–southern Brazilian littoral is characterized by coastal upwelling in the Cabo Frio region. The region of Cabo Frio is an area of considerable phytogeographical importance, representing a biogeographic break point in the distribution of several algal taxa along the Brazilian coast. At Cabo Frio, the seasonal composition of the summer and winter flora is generally linked to seasonal variations of upwelling, and seasonal differences are not so clear at warmer sites. In this chapter, the local distribution of species and communities is hypothesized, which depends on variable environmental gradients such as temperature, hydrodynamic conditions, and light. This dependence varies according to climatic, hydrologic, and seasonal changes. The chapter describes the structure of algal communities of the Cabo Frio region and the correspondence between algal distribution and environmental gradients. The qualitative ecological study using factorial analysis of correspondence elucidated the ordination of macroalgal species along different environmental gradients typical of the Cabo Frio region at the SE coast of Brazil. Different species associations were defined in the functions of different factors like upwelling, hydrodynamism, and shore topography.

I Introduction

The central-southern Brazilian littoral is characterized by coastal upwelling in the Cabo Frio region (latitude 23°S). Probably related to the upwelling, the region of Cabo Frio is an area of considerable phytogeographical importance, representing a biogeographic break point in the distribution of several algal taxa along the Brazilian coast (Oliveira Filho, 1977). In this region, species of tropical and subtropical affinities (Taylor, 1931) can be encountered, together with species of temperate affinities (Yoneshigue-Braga, 1977; Yoneshigue and Figueiredo, 1983; Yoneshigue and Oliveira Filho, 1984; Yoneshigue and Villaça, 1986, 1989). In this chapter, we hypothesize that the local distribution of species and communities depends on variable environmental gradients such as temperature, hydrodynamic conditions (intensity of upwelling), and light (which depend on exposure and rocky topography). This dependence should vary according to climatic, hydrologic, and seasonal changes.

This chapter aims to describe the structure of algal communities of the Cabo Frio region, and to examine the correspondence between algal distribution and environmental gradients.

II General Characteristics of the Study Area

The study region ranges from Cabo Frio island (23°01′S) to Búzios (22°44′S), some 100 km to the north (Fig. 2.1). Marine waters at Cabo Frio have three different origins:

Under the influence of prevailing E–NE winds, the surface water at Cabo Frio flows to the open sea and is replaced by CSAW from a depth of approximatively 300 m. This pattern inverts during the passage of cold fronts of southern origin. Two main austral seasons can be defined: (1) a spring–summer season, with tropical maritime anticyclone becoming established under prevailing E–NE winds favorable to upwelling; and (2) an autumn–winter season with frequent cold polar front passages and a rapid succession of changing wind cycles unfavorable to upwelling. The hydrology of the water column near Cabo Frio shows both cold and warm homogeneous conditions, but is normally characterized by a ther-mocline that fluctuates according to the intensity and direction of the winds.

III Materials and Methods