The Sandy-Beach Fauna of Mexico

Abstract

The macroscopic infauna of 11 sandy beaches along the Gulf of Mexico coast and the Pacific coast of Mexico were examined during the summer of 1972. Mexican sandy-beach fauna is impoverished in terms of numbers of species along both coasts in comparison with American tropical beaches. The Gulf of Mexico sand fauna is numerically more abundant and the Pacific sand fauna is significantly less abundant than the respective faunas of American tropical sand beaches. The isopod Excirolana braziliensis and the polychaete Scolelepis agilis are the most frequently occurring species in the sand fauna of Mexico. The purpose of this study was to make a preliminary description of the sandy-beach fauna along the Mexican coastline. The objective was to establish species composition, abundance, and zonation patterns for each beach, and to compare similarities and differences among the faunas. Studies on American sub-tropical and tropical sandy beaches are limited. Dahl (1952) described worldwide zonation patterns of boreal, temperate, and tropical beaches, characterizing each by three or four species of larger invertebrates, predominantly Crustacea. Previous studies of American tropical sand beaches are those of Rodriguez (1959) in Venezuela, Dexter (1972) in Panama, and Dexter (1974) in Costa Rica and Colombia. METHODS. Beaches were selected as study sites on the basis of their accessibility and distribution along the coastline. Eleven beaches were sampled, three in the Gulf of Mexico, and eight along the Pacific coast. Sampling was done during the summer of 1972. In order that direct comparisons could be made between the sandy-beach fauna of Mexico and that of tropical America (Dexter 1972; 1974), identical sampling techniques were used. A systematic sampling design was chosen. The beaches were divided into strata, the width of which depended on the area exposed at low tide. Strata varied from 1 to 8 m within the Gulf of Mexico and from 3 to 25 m within the Pacific beaches. Four repetitive samples, 1 m apart, were taken from the upper level of each stratum. Sampling procedure consisted of placing a 0.1 m2 quadrat over the sand at low tide, removing sand to a depth of 5 cm, and sieving it through a 500 i-mesh net. Organisms were separated from the sand residue by careful sorting and by flotation in a saturated sugar solution.