Distribution of saltmarsh plant communities associated with environmental factors along a latitudinal gradient on the south-west Atlantic coast

ISACCH J. P., C.S.B. COSTA, L. RODRÍGUEZ-GALLEGO, D. CONDE, M. ESCAPA, D.A. GAGLIARDINI Y O.O. IRIBARNE

JOURNAL OF BIOGEOGRAPHY

Blackwell Publishing

Año: 2006 vol. 33 p. 888 - 900

0305-0270

Aim: To produce an inventory of SW Atlantic saltmarshes (from latitude 31º 48´ S to 43º 20’ S) using remotely sensed images and field sampling; to quantify their total area; to describe the biogeographic variation of main habitats characterized by dominant vascular plants, in relation to major environmental factors; to test the hypothesis of predominance of reversal pattern in plant distribution (sedges and grasses dominate the lower, regularly inundated zones, and the upper zones are occupied by more halophytic species)  previously described (West, 1977); and to compare these SW Atlantic saltmarshes with others worldwide. Methods: GPS-positioned field samples of dominant emergent plant species were obtained from most coastal saltmarshes (14) between southern Brazil and Northern Patagonia, Argentina. Landsat satellite images were obtained and coastal saltmarsh habitats were quantified by supervised classification, utilizing points gathered in the field. Results: Three main plant species dominated the low and middle intertidal saltmarsh, Spartina alterniflora Loesel., S. densiflora Brong. and Sarcocornia perennis (P. Mill.) A.J. Scott. The total area of the studied coastal saltmarshes was 2133 km2, comprising 380 km2 of Spartina alterniflora marsh, 366 km2 of Spartina densiflora marsh, 746 km2 of Sarcocornia perennis marsh and 641 km2 of brackish marsh (dominated by Juncus acutus L., J. kraussii Hochst., Scirpus maritimus L., S. americanus Pers. and Phragmites australis (Cav.) Trin.). Cluster analysis showed three habitat types: saltmarshes dominated by (1) S. densiflora and brackish species,(2) S. alterniflora and S. perennis, and (3) S. densiflora only. The analysis of abiotic variables showed significant differences between groups of habitats and coordinated gradients of the abiotic variables. The SW Atlantic coast showed decreasing mean annual rainfall (1200 to 196 mm) and increasing mean tidal amplitude (<0.5 to >2.5 m) from 31º to 43º of latitude. Main conclusions: SW Atlantic saltmarshes are globally important by virtue of  their total extent. Remote sensing showed that the reversal pattern in plant distribution is not widespread. Indeed, SW Atlantic saltmarshes are better characterized by the presence of halophytic genera Spartina and Sarcocornia. Our results support the interpretation that SW Atlantic saltmarshes constitute a class of Temperate type (sensu Adam, 1990) with transitional characteristics between Australasia-South Africa saltmarshes and West Atlantic saltmarshes.