Evaluation of Gonad Taste and Color Using Defined Commercial Diets for the Aquaculture of the Green Sea Urchin, Strongylocentrotus droebachiensis
For the past two decades, U.S. green sea urchin fisheries have become valuable and important commercial resources. Processed gonads (uni) are sold primarily to Japan but also to French, Belgian and North American markets with worldwide sales exceeding $500 million in 1995 and U.S. export of fresh and processed sea urchins exceeding $150 million that same year. However, sea urchin populations along the coasts of the U.S. have been overexploited, resulting in up to a 75% reduction in landings and numbers of licensed urchin fishermen. Successful aquaculture of sea urchins in land- and near shore-based facilities can help restore commercial populations and preserve the role of this ecologically important herbivore in the sub-tidal marine community.
Uniquely, sea urchin gonads grow in size not only because gametogenesis increases the size and/or numbers of germinal cells present, but also because somatic cells within the germinal epithelium, the nutritive phagocytes (NP), store extensive nutrient reserves before gametogenesis begins. Changing fall photoperiod causes intragonadal nutrient reserves to be transferred from nutritive phagocytes to dividing and differentiating gametes, thus the commercial quality of green sea urchin gonads decreases.
Using our understanding of mechanisms involved, earlier efforts developing gonads containing primarily nutritive phagocytes and a preliminary dietary study using seven diets of varying amounts of protein and carotenes (to be completed in December 2005), we will produce gonads of superior taste, texture and firmness (= shelf life). Successful manipulation of gametogenesis in sea urchins coupled with the application of superior diets will be vitally important for the future of land- and near shore-based aquaculture efforts.
Objective 1. To feed a panel of three commercial feeds that maintain all dietary nutrients constant and vary protein and carotene content (determined through preliminary feeding study using eight different diets) to green sea urchins maintained under invariant photoperiod in a commercial tray system. We will also collect field animals for comparative purposes.
Objective 2. To produce urchin gonads whose color is similar (yellow to orange) to high quality urchins harvested during the urchin fishing season.
Photoperiod manipulation of gametogenesis coupled with superior diets in land-based aquaculture facilities will allow additional crops to be produced outside of the normal urchin reproductive season coinciding with periods of greater demand than supply.
Development of aquaculture techniques for sea urchins that enhance wild-harvested animals may be the only way to create a sustainable resource. In Maine, the urchin fishery currently supports 1000 jobs, including fishermen, tenders, buyers and processors. Loss of these remaining jobs would cause a significant hardship. Additionally, cultured urchins may provide economical opportunities in the Northwest, Northeast, Gulf and Hawaii, thus reducing the threat of overfishing. The methods we will use suggest reasonably simple means for suppressing gametogenesis that can be carried out in land-based facilities. These methods should be accessible to anyone in the industry with the appropriate facilities and will yield large gonads (>20% GI).