Experimental validation of the growth rings of Loxechinus albus (Molina, 1782) in southern Chile (Echinodermata: Echinoidea)

Abstract

To validate the periodic formation of growth rings in the genital plates of the Chilean edible sea urchin Loxechinus albus (Molina, 1782), an experimental sea urchin population grouped in five size classes (less than 15.0 mm, 20.0–29.9 mm, 50.0–59.9 mm, 70.0–79.9 mm and more than 100.0 mm) was confined to intertidal pools of the Marine Reserve of Mehuin. Size and weight were controlled monthly, from March 1991 to March 1992. At the same time, 50 sea urchins were collected each month from the non-manipulated population, involving the entire range of size distribution present in the study area. From these specimens, the genital plates were taken for ring reading, edge analysis and marginal increase analysis. The data were fitted to the individual growth model of Von Bertalanffy by means of a non-linear method (Marquardt's Algorithm). Asymptotic test diameter ( TD ∞) ranged between 141.2 and 131.7 mm, K (intercept on the TD)-axis) between 0.164 and 0.104 and t 0 (time at age 0; settlement on botttom) between −0.23 and −0.77. In the case of the growth equation for weight, asymptotic weight ( W ∞) ranged between 1207.3 and 740.1 g, and the relationship between test diameter and wet weight was W = 0.00054( TD) 2.94. The regression analysis used for estimating the growth parameters showed no statistically significant differences (95%) between the manipulated and the non-manipulated populations (rings at present and past ages). Moreover, all the growth parameters overlap at the 95% confidence interval obtained from the non-linear fit, showing no statistical differences. On the other hand, a significant relationship was found between the number of plates of a single column of the coronal system and age, which could be useful for the identification of this important demographic parameter in non-destructive field studies.