POPULATION-STRUCTURE AND GROWTH OF PINCTA DA-MAZATLANICA (PTERIOIDA, PTERIIDAE), GOLFO-DE-NICOYA, COSTA-RICA

Population size structure and growth were studied in Pinctada mazatlan ica between September 1993 to September 1994, in Isla Pan de Azucar, G olfo de Nicoya, Costa Rica. The population of specie are established m ainly in those sites where the substrate offers protected shelters. Po pulation density was estimated a 2.42 +/- 0.8 individuals per m(2), re lated to the total explored area 2250 m(2), between 0.4 m to 7.5 m dep th). The most relevant morphometric variables for characterizing this species are shell height and shell width. The maximum height and weigh t found were 141.50 mm y 496.30 g respectively. The maximum class freq uencies is 60-95 mm for the heigth (75% of the population). The equati on of von Bertalanffy was A= 139.5[1 - e(-0.083(t-0,32)0,55 x 0.083/2 pi (t-0,65)-stn2 pi(0,32-0,65)]) for height and Pt= 445.46 [1 - e(-0.0 83(t-0.32))](3) for weight. Approximately 73.6% of the population is r eached within twelve months of age. The average growth rate calculate for P, mazatlanica was 7.93 mm/mo during the first eigth months. in th e next twelve months increments are en the order of 3.88 mm/mo, decrea sing to 1.68 mm/mo in the last months. The relationship between shell height-weight was P= 5.31 x 10(-5) A(3.22848), indicate isometric grow th.