Developing a Second High Quality Crop for the Northeastern Green Sea Urchin Using Land-Based Aquaculture
The fishery for the green sea urchin (Strongylocentrotus droebachiensis) has rapidly grown to become the second largest in the Northeastern United States behind lobsters. Overfishing has drastically depleted once abundant natural populations. Two other problems naturally affect the industry. One of these is poor roe quality in a large percentage of the urchins harvested, leading to a lower than maximum price. Another is the short period when roe quality is high.
There is a window of time from September until February when urchins have firm, ripe gonads. If urchins in a land-based aquaculture facility could be fed a prepared food and be induced to ripen again after February, then the period of availability of highest quality roe could be expanded, greatly increasing the market potential for Gulf of Maine urchin roe.
We have coupled enhancement of gonadal growth of poorly fed urchins utilizing prepared food with photoperiodic manipulation of the gametogenic cycle to produce an out-of-season crop. This crop could be used to exploit a lucrative end of summer market now supplied by Chile. Recently spawned urchins (March 1995; < 6% gonad index) were held under artificial illumination, using astronomic clocks set to simulate June photoperiod and were fed 3g prepared food/animal/week. This resulted in a significant increase in gonad size compared with field populations (> 25% gonad index) without a corresponding increase in test size.
Histological examination of monthly samples of gonads indicates that this growth is a result of an increase in size of nutritive phagocytes (which tire intragonadal nutrient storage cells) yielding significantly higher gonadal indices than those simultaneously observed in field populations. After three months on this feeding regime, urchins were then exposed to September photoperiod which is known to naturally stimulate gametogenesis for urchins in the field. Stereological analysis of histological sections indicates that spermatogonia in such animals undergo rapid proliferation and normal spermatogenesis three months early. Oogonia also proliferate early, but resulting oocytes undergo minimal vitellogenesis. Testes and ovaries both increase in size to gonad indices of 28-30% which is based on accumulation of normal spermatozoa in males and continued growth of nutritive phagocytes in females; color of resulting roe needs to be adjusted to yield more orange.
We will address questions about large scale, commercial feasibility of this technology and about color of the resulting roe by:
1) Building and testing a modular tank unit (7500 urchins) that could be duplicated for commercial, land-based sea urchin aquaculture
2) Using the resulting modular unit to generate an out-of-season, second crop of sea urchins using a modified artificial food (containing a carotenoid that will be assimilated into gonads at a high rate) and photoperiod manipulation.
We will address questions about vitellogenesis and about the nature of the photoperiod que by:
1) Comparing gene expression during natural (= ambient photoperiod) and laboratory (= out-of season photoperiod) induction of gametocyte mitosis in male and female sea urchins and vitellogenesis in oocytes
2) Investigating the effects of total irradiance and spectral composition of ultraviolet and visible radiation on photoperiod initiation of gametogenesis in sea urchins
1) Build and test a modular tank unit that could be duplicated for commercial, land-based, sea urchin aquaculture
2) Use the resulting modular unit to generate an out-of-season, second crop of sea urchins using artificial food and photoperiod manipulation
3) Compare gene expression during natural (= ambient photoperiod) and laboratory (= out-of-season photoperiod) induction of gametocyte mitosis in male and female sea urchins and vitellogenesis in oocytes
4) Investigate the effects of total irradiance and spectral composition of ultraviolet and visible radiation on photoperiod initiation of gametogenesis in sea urchins
1) Monitor dissolved oxygen, ammonium concentration, nitrogenous waste, feeding and cleaning regimes and quality of resulting roe for 7500 urchins in our modular test tank
2) Manipulate photoperiod over a five-month period using astronomic clocks and information from item 1 to generate an out-of-season crop of ripe sea urchins
3) Assess gene expression during natural and laboratory photoperiodic induction of gonocyte mitosis and vitellogenesis using differential display polymerase chain reaction (ddPCR)
4) Assess the effects of irradiance and spectral composition on the photoperiod induction of gametocyte mitosis using gonad indices, histology, stereology and ddPCR
On the eastern coast of the United States, adult green sea urchins (Strongylocentrotus droebachiensis) are the subject of a fishery for their ripe gonads. The Japanese and others eat the ripe ovaries and testes as "uni," a popular kind of sushi. In the Gulf of Maine, unregulated harvesting has resulted in near complete loss of productive beds and a projected collapse of this fishery. Also, as stocks dwindle in numbers and as demand increases, urchins with lower quality roe (smaller gonads with poor color, taste and texture) are taken and the average dollar value of the harvest continually drops. A suite of technologies exists for developing modular, land-based aquaculture ventures to help alleviate loss of quality and profit. We intend to test and continue to improve this technology at pilot commercial scale.
Objectives 1, 2 and 4 of this grant were completed in full; objective 3 was partially completed.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Walker, C., N. McGinn, L. Harris and M. Lesser (1998). New perspectives on sea urchin gametogenesis and their relevance to aquaculture. Journal of Shellfish Research 17(5):1507-1514.
- Harrington, L., C. Walker and M. Lesser (2007). Stereological analysis of nutritive phagocytes and gametogenic cells during the annual reproductive cycle of the green sea urchin, "Strongylocentrotus droebachiensis." Invertebrate Biology 126(2):202-209, Spring 2007.
- Walker, C., T. Unuma, N. McGinn, L. Harrington and M. Lesser (2001). Reproduction of sea urchins. Edible Sea Urchins: Biology and Ecology, John M. Lawrence, ed., pp. 5-26.
- Walker, C., L. Harrington, M. Lesser and W. Fagerberg (2005). Nutritive phagocyte incubation chambers provide a structural and nutritive microenvironment for germ cells of "Strongylocentrotus droebachiensis," the Green Sea Urchin. Biological Bulletin 209:31-48.
- Walker, C. and M. Lesser (1997). Prepared food coupled with manipulation of photoperiod yield an out-of-season crop for the green sea urchin. Bulletin of the Aquaculture Association of Canada 97-1:31-34.
- Lesser, M. and C. Walker (1998). Introduction to the special section on sea urchin aquaculture. Journal of Shellfish Research 17(5):1505-1506.
- Walker, C. and M. Lesser (1998). Manipulation of food and photoperiod promotes out-of-season gametogenesis in the green sea urchin, "Strongylocentrotus droebachiensis": implications for aquaculture. Marine Biology 132:663-676.
- Harrington, L. (1999). Annual changes in the nutritive phagocytes of the green sea urchin, "Strongylocentrotus droebachiensis": relevance to gametogensis and aquaculture. Master's Thesis, University of New Hampshire.
- Bottger, S., C. Walker and T. Unuma (2004). Care and maintenance of adult echinoderms. Chapter 2 in: Experimental analysis of the development of sea urchins and other non-vertebrate deuterostomes.