The present work deals with the temporal and bathymetrical variations of the epifaunal community associated with two species of pearl oysters (Pinctada mazatlanica and Pteria sterna) during a seed collecting season from June to November 1989 . A total of 63 items (species, genera and/or families) were recorded ; their variations in presence and abundance were followed during three periods (June-July, August-September and October-November) . The collectors were examined for different immersion times (2, 4, 6 and 8 weeks) for each period . Community structure was compared through the Brillouin Index, the Morisita Index and the Importance Value .We define the chronology of spatfall for both species of pearl oysters and their bathymetrical distribution . Relationships between these species and the epifaunal community present into the collectors were analysed, searching for possible noxious effects on the survival of juvenile pearl oysters, and identifying index species related with their spatfall . A strategy for starting massive seed collection of both species is established, particularly for P. mazatlanica .
The relationship between the shell dimensions of pearl oysters. Pinctada nmzallaiiica (Hanley 1856) and Pteria sterna (Gould lHSl), was studied to determine the possible change of form of Ihc shell during growth. The intention was to delermine the number, size and location of nuclei that could be implanted in oysters used for Mabe pearl production. Using the database of our Pearl Culture Research Programme developed in Bahia de La Paz. Mexico, we obtained measurements of 500 shells of P. mazatlaniai and 500 shells of P. sterna, representing i years of continuous growth under extensive culture conditions. The heightlength, height-thickness and the height-weight relationships of both species were analysed, as was the height-wing length relationship for /'. sterna. There was isometric growth up to tOOmm shell height, and negative-allometric growth after 120-12 5 mm for P. mazatlanica. The heightthickness relationship followed a linear model. whereas the height-weight relationship was exponential. No clear allometric pattern was found in P. sterna and all relationships litted the power equation.
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