Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
First Advisor
Coleen Suckling
Abstract
The green sea urchin (Strongylocentrotus droebachiensis) fishery was once prosperous in the Gulf of Maine, peaking in the 1980s and early 1990s. However, since the early 1990s, the fishery has dramatically declined despite having harvesting restrictions. To sustain the industry, production through aquaculture is necessary, but hatchery production methods are not yet optimized, with settlement success and post-settlement survival as low as 1-5%, and the spatial scale for field grow-out may be limited in some regions due to climate change. Additionally, there are knowledge gaps in fishery management regarding whether oversized S. droebachiensis help sustain natural stocks. This dissertation presents three manuscripts addressing production bottlenecks and filling in fishery knowledge gaps required for sustaining this industry. Chapter 1 aimed to improve hatchery larval settlement success and post-settlement survival using a range of abiotic cues (temperature, salinity) and biotic cues as potential food resources (benthic diatom sp. or conspecific biofilms with or without macroalgae and conspecific conditioned seawater). Abiotic cues such as increasing temperature by 2°C above the hatchery temperature of 12°C did not enhance settlement, and the optimal salinity for settlement was between 30-33. The use of conspecific biofilms increased settlement success by 80%, and the combination of using the benthic diatom Cylindrotheca closterium with then macroalgae Ulva lactuca conditioned seawater provided adequate settlement success of 50%. Post-settlement survival was not significantly improved, but juvenile growth rates were enhanced by 30-40% utilizing C. closterium and U. lactuca food sources. Chapter 2 determined whether hatchery-produced juveniles could be thermally primed which utilizes controlled exposures to heat to enhance their resilience to thermal heterogeneity in the field, such as marine heatwaves. Juveniles were exposed to industry and environmentally temperature regimes encompassing five phases: initial condition (12°C for 7 days), thermal priming (19°C for 6 days), a first recovery period (12°C for 4 weeks), a triggering temperature to test if priming was successful (22°C for 10 days), and a final recovery period (12°C for 4 weeks). Responses such as oxygen uptake, survival, and growth were measured to determine whether juvenile tolerance was enhanced. The combination of priming and triggering did not successfully increase the resilience of juveniles to elevated temperatures of 22°C but did show tolerance to single exposures of 19°C and 22°C, providing important insights into farm location suitability. Although the thermal priming design did not work, there is a large scope to utilize other temperatures, durations, and ages of S. droebachiensis towards enhancing resilience. Chapter 3 examined whether the upper size limit (>76 mm test diameter) placed on the S. droebachiensis fishery in the Gulf of Maine is inhibiting population growth by conducting a series of behavioral and reproductive trials on small (< 60 mm) and large (> 65 mm) size classes. Reproductive output for the smaller S. droebachiensis size class appeared to be more successful, producing eggs which were 4% larger, with 2% and 10% higher fertilization and hatching success respectively compared to their larger counterparts. While behavioral trials resulted in inconclusive results regarding whether large S. droebachiensis were inhibiting smaller size classes from reaching food sources in a competitive environment, there is an indication that upper size limits in fishery management for S. droebachiensis may need further sampling efforts but are likely not a suitable strategy for sustaining the population. Collectively, the results from this dissertation identify solutions to production bottlenecks as well as recognizing the next steps towards a sustainable industry.
Recommended Citation
Plee, Tara, "ENHANCING GREEN SEA URCHIN (STRONGYLOCENTROTUS DROBACHIENSIS) PRODUCTION TOWARD SUSTAINABILITY" (2024). Open Access Dissertations. Paper 1649.
https://digitalcommons.uri.edu/oa_diss/1649