Does method of kelp (Saccharina latissima) storage affect its food value for promoting somatic growth of juvenile green sea urchins (strongylocentrotus droebachiensis)?

摘要

Harvested for their gonads, sea urchin populations are declining worldwide primarily as a result of overfishing. Consequently, research is now focusing on full life cycle aquaculture of these organisms. If juvenile or adult sea urchins are to be fed macroalgae (a preferred food of echinoids) in commercial-scale operations, suitable methods for storing large amounts of algae will be required. In this study, the effect of various storage methods for the kelp Saccharina latissima on somatic growth of juvenile green sea urchins, Strongylocentrotus droebachiensis, was evaluated. Juvenile S. droebachiensis (initial test diameter, 4.5-10.7 mm) were held in laboratory tanks, supplied with flow-through seawater, and fed ad libitum one of the following S. latissima treatments: (1) frozen long term (>2 mo), (2) frozen short term (1 wk), (3) air-dried, or (4) fresh. Measurements of test diameter and whole wet weight of the sea urchins were taken monthly for 16 mo. Mean (+or-SE) final sizes in the treatments ranged between 17.7+or-0.4 mm and 21.7+or-0.4 mm for test diameter and between 2.9+or-0.2 g and 4.9+or-0.2 g for wet weight (sea urchins fed long-term frozen kelp and air-dried kelp, respectively). There were no significant differences in growth rate - for either test diameter or wet weight - among sea urchins fed short-term frozen, air-dried, or fresh kelp, but those individuals fed long-term frozen kelp grew significantly slower than those on any of the other 3 diets. It is unclear, however, whether this difference is the result of the long-term freezing process per se or the result of differences in the biochemical nature of the kelp plants when they were collected for freezing. Because air drying should be relatively cheaper than freezing (in terms of energy cost), and air-dried kelp may be more easily stored and transported than frozen or fresh kelp, air drying is an obvious choice for long-term storage of kelp if it is to be used as a food for juvenile green sea urchins.