VARIACIÓN ESPACIO-TEMPORAL DEL RECLUTAMIENTO EN MOLLUSCA Y ECHINODERMATA EN LA BAHÍA DE LA PAZ, BAJA CALIFORNIA SUR, MÉXICO.

Abstract

ABSTRACT Rocky shores are considered environments with high species diversity, where organisms of almost all marine phyla are represented. Defined by the dominance of their invertebrate fauna, mollusks and echinoderms are part of the most common and important organisms distributed in these environments. Recruitment plays an important role in shaping the structure of their communities by regulating the stability and fluctuations observed in their populations; however, most of the investigations in this matter have focused in the study of species of ecological or economical importance. For that reason, we considered relevant the evaluation of this process in mollusks and echinoderms in the rocky litoral of Bahía de La Paz. We evaluated the spatial and temporal changes in the recruitment of mollusks and echinoderms bimonthly during an annual period from May 2009 to April 2010. Using artificial collectors ex profeso designed (N= 330) deployed at three sites in Bahía de La Paz: El Portugués, El Corralito y El Pulguero, we evaluated the variations of abundance and species composition globally and between sites through ecological indexes of dominance (I.V.I), species richness (S), diversity (H´log 2) and eveness (J’). Additionally, environmental variables such as temperature, salinity, pH, oxygen, chlorophyll a, and seston (with its organic and inorganic fractions) were measured. We used multivariate analysis such as Cluster analysis to visualize seasonality patterns of recruitment between sites and Canonical Correspondance Analysis to visualize the relationship between biological and environmental variables. A total of 3,800 organisms of both Phyla were collected. Mollusks were present through the entire period of evaluation with a total of 3292 organisms belonging to 60 species, 52 genuses, 38 families, 11 orders, and three classes. Echinoderms recruited seasonally from September 2009 to February 2010 with a total of 507 organisms belonging to 10 species, eight genuses, seven families, six orders, and four classes. Seven species were dominant (six mollusks and one echinoderm): Ostrea conchaphila, Holothuria (Thymiosycia) impatiens, Laevicardium elenense, Crucibulum spinosum, Anadara multicostata, Atrina maura y Alaba supralirata, and represented an accumulated percentage of 75% of total abundance. There were no statistical differences (p>0.05) VIII in temporal and spatial abundance of organisms recruited bimonthly. There were statistical differences (p<0.05) in species richness between sites, but not in diversity and eveness (p>0.05). The cluster analysis using the Morisita index indicated a clear seasonal pattern in El Pulguero (0.48) in comparison with El Corralito (0.64) and El Portugués (0.91). The Canonical Correspondance Analysis indicated a correlation between environmental and biological variables (r2=0.85). The environmental variables showed a seasonal pattern mainly in temperature (maximum in June- August and minimum in November-December) and chlorophyll a (maximum in November-December and minimum in May-Jun 2009).