A morphometric approach to the development of Paracentrotus lividus larvae fed with different microalgae diets

This study integrates the project “Ouriceira Aqua: Aquaculture and Enhancement of Gonad Production in the Sea Urchin (Paracentrotus lividus)” (16-02-01-FMP-0004). This study had the additional support of Fundação para a Ciência e Tecnologia (FCT), through the strategic project UID/MAR/04292/2019 granted to MARE - Marine and Environmental Sciences Centre.

Paracentrotus lividus is the most valuable sea urchin species in the European roe markets. Its economic value has been driving an intense exploration of wild populations leading to their over-exploitation in several areas of the Mediterranean and eastern Atlantic coast. The full production of P. lividus in aquaculture can potentially supply the European market for sea urchin roe reducing the impact over the wild populations. However, the low survival rates of sea urchin planktonic stages represent a critical bottleneck for the full cycle production for commercial purposes. Together with the zootechnical challenges, the selection of a suitable microalgal diet is fundamental to overcome this challenge. In the present study, we conducted two larvae rearing experiments testing the effect of five microalgae diets in the larvae development, age at competence and survival. The experimental diets tested were: Rhodomonas baltica (rho); Phaedactylum tricornutum (phae); Chaetoceros calcitrans (chae); a mix diet of rho and phae (1:1); and a mixed diet of rho and chae (1:1). The larvae were reared in closed system in triplicate tanks (50 L) at a density of 4 larvae/mL with seawater temperature ranging between 18.5 and 20°C. The daily feed concentration was adapted to the larval stage of development and standardized to the ratio between microalgae biovolume. Larvae samples were regularly collected to measure larvae body length, body width, post-oral arm length and the rudiment length. Linear models were fitted to the larval measurements and the model residuals were analyzed as an indication of larvae body condition. The larval survival was assessed volumetrically every two days. The results showed that the larvae fed with rho attained age at competence (at 18 days post fecundation, DPF, in experiment I and at 16 DPF at experiment II) earlier than larvae fed with phae, chae or with the mixed diets. On the other hand, the larvae fed with the rho and chae mixed diet presented higher survival rate (32 %). Moreover, the preliminary analysis of the linear model residuals showed that the mixed diet promoted the development of larvae with better condition. These results indicated that the rho diet promoted a reduction of the planktonic phase albeit with costs in terms of larval condition and survival rate.

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