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Sea Urchins in integrated systems; their nutrition and roe enhancement

Final Report Summary - SPIINES 2 (Sea urchins in integrated systems; their nutrition and roe enhancement)

The SPIINES2 project focused on the two most commonly fished, farmed and consumed sea urchin species in Europe, Paracentrotus lividus and Strongylocentrotus droebachiensis. Part of work was engaged in incorporating pigments into the diets of urchins. The gut wall and gonad material were analysed to produce a carotenoid pigment profile for cultivated P. lividus urchins fed on (a) an artificial feed pellet and (b) Ulva and Gracilaria. There was a modified chlorophyll compound present in both gut wall and gonad material which remained unidentified. This compound was not present though in the gut wall and gonad material of urchins fed on a diet of Ulva and Gracilaria.

The gut wall of urchin samples fed on Ulva and Gracilaria contained a high proportion of lutein which was not present in gut wall samples from urchins fed on the pellet diet. A lower proportion of lutein was found in the gonads of urchins fed on Ulva and Gracilaria whereas no lutein was found in the gonads of urchins fed on the pellet diet. The main pigments in the gut wall of Strongylocentrotus droebachiensis were the fucoxanthin breakdown products fucoxanthinol and amaroucixanthin A. These are not unexpected and the prevalence of this carotenoid in the diet of wild urchins (similar results also seen in P. lividus). The carotenoid pigment profile of the gonads of this species were similar to others examined in this study, with echinenone (predominantly the 9’cis form) dominating along with various isomers forms of v-carotene.

High-performance liquid chromatography (HPLC) analysis was carried out on two commercial diets obtained from the United States (US) to profile their carotenoid pigment composition. The diet pellets were extracted using a standard acetone extraction technique. HPLC trace (a) showed a US diet pellet that was extracted using acetone extraction. Both diets contained the same pigments but diet 1 had twice the pigment concentration of diet 2. The results appear to show a pigment composition of v-cryptoxanthin and v-carotene. However, the samples were then subjected to a further procedure known as saponification. This removes any unwanted lipids from the sample. HPLC trace showed the US diet profile after saponification.
It shows that the putative v-cryptoxanthin was in fact an esterified form of zeaxanthin and smaller amounts of lutein. In conclusion the US diets contain a mixture of the carotenoids zeaxanthin and v-carotene with small amounts of lutein. Wild urchins would not be exposed to esterified carotenoids in their natural diet and use of such carotenoids in artificial diets would require a dependence on the ability to de-esterify such carotenoids, which may in turn reduce the efficiency of uptake and subsequent deposition in the desired target organ, namely the gonad.

Deliverable 11: An experiment to compare the effects of three different diets on sea urchin growth was performed over 91 days during the summer period. The diet treatments consisted of pellets fed daily at a ratio of 0.5 % of urchin biomass ('pellet diet'); 'seaweed diet' consisting of the algae Ulva and Gracilaria fed 3 times a week; and a mixed diet wherein the urchins were fed either pellets or seaweed rotated weekly.

Deliverable 12 concerned integrated open-water culture of juvenile sea urchin (Paracentrotus lividus) and Atlantic salmon (Salmo salar) on the north-west coast of Scotland. The survivorship, growth and lipid data shows that hatchery reared juvenile Paracentrotus lividus can assimilate fish farm derived material and thrive in the salmon cage environment. This suggests that the integration of P. lividus with Atlantic salmon provides viable means to culture this species, even at this latitude, which is the northernmost limit of its range.

Deliverable 13: Sea urchin gonad biomass is a reliable indicator of nutritional state; urchins with extra nutrient available would store reserves in the nutritive phagocytes of the gonad and display an increased gonad biomass. While pre-mature, and therefore not containing gonad or marketable quantities, the urchins fed seaweed had a much higher gonad index than those in the other treatments suggesting that the urchins fed mussels were either not able or not inclined to ingest sufficient mussel tissue to promote gonad growth. As the mussels in the pearl nets did show evidence of having been predated upon by the urchins (gnawed and empty mussel shells remaining) it may be the case that the mussel is not the preferred food of this species. However, the growth rates observed on the seaweed (kelp) fed treatment was over the anticipated rate.

Deliverable 16: To determine whether a pre-harvest starve might influence the shelf life of sea urchins, urchins were fed for approximately 2.5 months on locally grown and collected Laminaria saccharina followed by continued feeding or a pre-harvest starvation period of 8 days. No significant differences in spoilage rate between treatments were found for up to 24 hours. From 48 hours onwards urchins that were fed algae demonstrated a significantly higher rate of spoilage than starved urchins. Clearly a pre-harvest starvation period would assist in prolonging shelf life. The build-up of bacteria was also investigated for urchins reared under different conditions. For 3 months in the research aquaria of the Scottish Association for Marine Science sea urchins were reared on Laminaria saccharina. Furthermore, assessment of potential differences in rate of spoilage was investigated for different species, using Psammechinus miliaris and Paracentrotus lividus. There were no significant differences between the two species for the first 24 hours.

Deliverable 17: Urchins were tested for the presence of harmful types such as extraneous pathogens of E. coli throughout the experiments to determine whether poor hygiene standards were existing while handling the products. There was no presence of E. coli which supports hygienic handling and sterile laboratory experiment conditions.

Deliverable 18:
- starving the urchins prior to transport reduces the spoilage rate significantly after 24 hours of storage. It also creates a product more aesthetically pleasing to the eye once open. A 48-hour starvation period (time for the gut to evacuate) is recommended.
- salmon-farm reared urchins have a higher rate of spoilage from 24 hours of storage- the solution would be to keep them cooler or starve prior to harvest.
- salmon-pellet fed urchins (pellets having been freezer stored) showed significantly lower spoilage rates than algal fed urchins. Algae has a natural bacterial film - perhaps not best to use in packaging - the brown water leaching from the algae is also not appealing to the buyer.
- ideally the best way to transport urchins to the market would under refrigerated conditions, however this is expensive. Experiments replicating transport conditions were carried out successfully at approximately 12-13 degrees Celsius - it is best to pack ice in with the urchins;
- slightly damp environment allows urchins to live for longer.
- most transportation should not take longer than 24 hours (Europe) - all depends on what the buyer will do with the product upon arrival - sell fresh or freeze until required.
- urchin 'look' disintegrates drastically 72 hours storage onwards (spine loss/dry).

Deliverables 19 and 21 cover minutes and action points from meetings.