The ultimate objective of the project is to control every life stage of the most valuable species of European edible sea urchins (Paracentrotus lividus and Strongylocentrotus droebachiensis) under intensive cultivation (closed cycle echini culture) to produce high quality gonads (roe, i.e.: the edible part of the animal) at a pilot scale.
The obstacles that prevent the intensification of echini culture have been clearly identified:
(1) post-settlement survival and growth rate need to be improved, and
(2) the carrying capacity of the rearing structures needs to be increased by bypassing main limiting factors, i.e. depletion in dissolved carbonates and accumulation of carbonic acid.
Moreover, the quality control of gonads and optimisation of gonad growth are key factors that have to be addressed. The proposed work aims to investigate aspects of the biology of cultivated sea-urchin related to these obstacles, to finalize technical enhancements of the cultivation procedure in either eliminating or bypassing these obstacles, and to adapt the rearing method presently used for Paracentrotus lividus to Strongylocentrotus droebachiensis.
The sea-urchin cultivation procedure use special devices constituted by several superposed shallow tanks. The shallow tanks, viz. the so-called toboggans, hang over a reserve tank where water is treated before being reused. This treatment includes aeration, decantation and thermoregulation. A centrifugal pump transfers water from the reserve tank to the top level, and the water then re-circulates thanks to gravity from one level to the other. Water renewal is regulated between 250 and 600 % of the total volume per day following the population density. In this semi-intensive cultivation procedure, the biomass is maintained below 5-6 kg of sea urchins larger than 10 mm diameter per m2 of toboggan (growth structure) or between 0.2 and 1 kg of sea urchins smaller than 10 mm per m2 of tobbogan (pre-growth structure). The control of the whole life cycle of sea urchins in closed cycle cultivation aiming to obtain adult individuals with high gonadal productivity was demonstrated to be possible in such installations. A method for production of large individuals - viz. the standard rearing method or SRM - was already perfected through some basic aspects clearly need to be improved. These aspects have been previously identified and will be the subject of the investigations detailed below.
Task 1: To improve early postmetamorphics survival and growth rate by investigating improving feeding of precompetent and competent larvae and start-feeding routines of early postmetamorphics, and determining the optimal biochemical composition of the proposed food.
Methodology: The food given to the larvae (microalgae) and the early juveniles (biofilm and macroalgal plantlets) will be controlled by biochemical analysis and standardized. The use of microalgae previously enriched in different lipids, sterols, amino acids will be investigated. These enriched foods will be tested and their impact on the development and survival rate of larvae and post-metamorphics will be measured.
Task 2: To increase the optimal biomass of adult sea-urchins in the cultivation structures by controlling factors which limits the biological carrying capacity of the physical cultivation environment. These limiting factors have been already identified: the depletion in dissolved carbonates that is incorporated in the skeleton of the sea-urchins during somatic growth, and the accumulation of carbonic acid produced both by respiration and skeletogenesis.
Methodology: The somatic growth of post-metamorphics under various alkalinity conditions will be measured to precisely determine the variations of alkalinity tolerated by cultivated post-metamorphic. The dissolved inorganic carbon (DIC) cycle in a cultivation structure for different biomasses will also be studied. The data collected will be integrated in the mathematical model to take the carbonate factor into account in the calculations (see task
V) and to evaluate the potential impact of a particular filter used to stabilize alkalinity in intensive cultivation.
Task 3: To develop an objective quantitative method for quality control, and to investigate the effect of enrichment of artificial foods (i.e.: pellets) on gonad quality.
Methodology: Near infrared spectroscopy (NIR) is a fast method to measure the quality of seafood, but a precise calibration is required with traditional methods: biochemical and histological standards and colorimetric methods.
Task 4: To study the bioecological differences between Paracentrotus lividus and Strongylocentrotus droebachiensis reared in similar cultivation system and adapt consequently the cultivation method.
Methodology: The production of Strongylocentrotus droebachiensis will be upscaled from laboratory scale to pilot scale adapting the methodology already successfully used for Paracentrotus lividus. Passive integrated transponder (PIT) tags will be used for the individual identification of broodstock animals. This is a new methodology for tagging sea urchins, which has been recently developed. It is the only practical alternative to physical isolation of individual broodstock animals.
Task 5: To update an existing mathematical model of cultivated sea urchins' productivity with information gathered during this project. To perform a forecast microeconomic analysis of an echini culture activity.
Methodology: Computer modelling of the production cycle involves calibration, modification and expansion of an existing model developed by partner 1. The model will be expanded to include the survival of early post-metamorphics, the gonads' quality and the effect of alkalinity on somatic growth and will also be calibrated for Strongylocentrotus droebachiensis.
Funding SchemeCSC - Cost-sharing contracts