Geographic patterns of abundance and length distribution of the limpet Siphonaria lessoni in the Southwest Atlantic

SORIA SABRINA; VALERIA TESO; PALOMO MARIA GABRIELA

Congreso; CERF 2012. The Changing Coastal and Estuarine Environment: A Comparative Approach; 2012

The abundance center hypothesis assumes that the species have abundant populations in the center of their distribution, where individual success is greater due to the optimal physical and biotic conditions. In turn, individuals from more abundant populations have smaller lengths due to intraspecific competition. The main objectives of this study were to test the abundance center hypothesis of Siphonaria lessoni and the hypothesis of the relationship between abundance and length. Siphonaria lessoni (Gastopoda: Siphonariidae) is distributed-spreaded from southern Brazil (27°35´S, 48°32´W) to Tierra del Fuego (54º48´S, 68°19´W). Eight samples were carried out in the middle intertidal collecting all individuals of S. lessoni into quadrants of 25 x 25 cm. The sites were: La Pedrera (Uruguay), Mar del Plata, Quequén, Espigón, Lobería, Playas Doradas, Pirámides, Puerto Madryn, and Playa Larga (Argentina). The individuals collected were counted and measured in the laboratory. The relationship between abundance and distribution of populations of S. lessoni showed an irregular pattern. The organism length decreases significantly in relation to the increasing density (y=-2.68x+41.62, R²=0,864). The distribution and abundance of a species can be determined by a single factor, as postulated by the abundance center hypothesis, or by multiple factors interacting in complex ways in space and time. The abundance of S. lessoni along the coast could be affected by small environmental changes such as proximity to outfall, degree of exposure in the harbor, association with mussel community and residence on cliff area. In places with abundant populations of S. lesson note that the average length of individuals is lower, showing other example of intraspecific competition. The abundance center hypothesis was tested in the intertidal limpet Lottia gigantea in North America, even though our proposal is to consider a model with multiple factors in a future study.