Introduction
Seawater temperature is a critical environmental factor that significantly affects the fitness and aquaculture industry of commercially important marine invertebrates, including sea urchins. Early life stages are particularly vulnerable to ocean warming (OW), which can reduce survival and growth by up to 80% under 2-4°C increases. Increasing broodstock food resources and availability may reduce the negative impacts of OW by increasing larval tolerance. Emerging studies assess offspring success after pre-exposing parents to warming conditions, which suggests the existence of beneficial carryover effects known as transgenerational effects. However, whether transgenerational acclimation to OW and nutrition is possible in sea urchins remains largely unknown (Zhao et al., 2018). Because sea urchins cannot synthesize carotenoids de novo, dietary provision of these pigments is essential as they play a critical role in egg production and offspring quality (Shpigel et al., 2006). This study evaluated whether maternal conditioning to high and low carotenoid diets influences the resilience of Paracentrotus lividus (Lamarck, 1816) larvae to increased temperatures, aiming to optimize hatchery production strategies against OW.
Materials and Methods
Paracentrotus lividus broodstock (N=120) was acclimated in recirculating aquaculture systems (RAS) and reared for four months on two temperature scenarios: local environmental temperature (18°C) and predicted warming temperature 21.5°C (+3.5°C), following IPCC predictions for 2100. During conditioning, the individuals were fed with two isoproteic and isolipidic formulated diets: a high carotenoid diet (HC) enriched with Nannochloropsis sp., and a low carotenoid diet (LC). At the end of the conditioning trial, proximate composition of female gonads ((e.g., carotenoids; eicosapentaenoic acid - EPA; total polyunsaturated fatty acids-PUFA; omega-3 (n-3) PUFA)) was assessed. Sea urchins were induced to spawn through injection with 0.5 M KCl in the peristomal membrane. To isolate maternal investment and minimize paternal genotypic variance, all eggs were fertilized using a sperm pool from males conditioned at 18 °C x HC. Following spawning, oocytes (n = 50 eggs per female) and fecundity were quantified in four females per broodstock treatment. The larval experiments followed a 2×2×2 factorial approach. Larvae from each maternal conditioning treatment were exposed to both 18 °C and +3.5 °C. Within these temperature treatments, two distinct larval nutritional treatments were established to assess larval survival: 1) an exogenous nutrition treatment, where larvae were reared under a standard mixed microalgal diet (Chaetoceros calcitrans and Rhodomonas lens), and 2) an endogenous nutrition treatment, where larvae were left unfed to isolate and quantify the direct impact of maternal egg reserves. Larval rearing was conducted in 600 mL beakers stocked at 2.5 larvae/mL. To evaluate survival, larvae from each treatment were sampled at the 4, 6, 8-arm and competence stages, with the corresponding age in days post-fertilization (DPF) recorded.
Results
Conditioning temperature and diet significantly influenced the proximate composition of female gonads. Females fed HC diet and exposed to +3.5°C showed enhanced accumulation of carotenoids (67.46 µg.g-1 DW), EPA (10.68%), n-3 PUFA (16.45 %), and total PUFA (36.60 %). Egg diameter (90-97 µm) was not affected by temperature or diet treatments. Fecundity was affected by diet, with the highest yields observed in females fed the HC diet and exposed to 18 °C (8.4 × 104 eggs.g-1). Maternal conditioning had a significant influence on larval survival across both fed and unfed treatments. When females were conditioned at 18 °C, fed larvae from both HC and LC diets reached the competence stage at 20 DPF when reared at 18 °C. However, survival was higher in larvae from the HC diet, with 13 %. Conversely, when exposed to +3.5°C, larvae from the LC diet stopped development at the 4-arm stage, while those from the HC diet developed to the 6-arm stage and reached 16 DPF with a survival of 9%. A similar pattern was observed when females were conditioned at +3.5 °C. When larvae were reared at 18 °C, fed larvae from both maternal diets achieved competence at 20 DPF, with higher survival observed on those from the HC diet (13%). However, when kept at +3.5°C, larvae from LC diet stopped at the 4-arm stage and died by 8 DPF, while larvae from HC reached the 6-arm stage and reached 20 DPF with 3.39% survival. Among the unfed larval treatments, maternal HC diet consistently extended larval longevity. When females were conditioned at 18 °C and fed an HC diet, their unfed larvae survived until 12 DPF in both temperature conditions (18 °C and +3.5 °C). Similarly, when females were conditioned at +3.5°C and HC diet, unfed larvae survived until 12 DPF at 18°C and until 10 DPF at +3.5°C.
Discussion
This study demonstrates that the synergistic effects of temperature and diet quality strongly influence maternal provisioning and offspring resilience. Specifically, a combination of an HC diet and + 3.5°C was found to significantly enhance the accumulation of carotenoids and critical fatty acids (EPA, n-3 PUFA, and PUFA) in female gonads. This represents a maternal investment strategy to help offspring cope with thermal stress. This was further evidenced by larval survival rates under different temperature conditions. Fed larvae from females conditioned to the HC diet and +3.5°C achieved the competence stage with significantly higher survival rates when reared at 18°C compared to larvae from the LC diet. These maternal carry-over effects were evident when the larvae were exposed to +3.5°C, with higher survival capacities observed in both fed and unfed larvae. These findings highlight that optimizing broodstock nutrition is a vital strategy to trigger beneficial carry-over effects that enhance larval survival. Incorporating high-quality diets into hatchery protocols offers the aquaculture industry a promising solution to support production and build resilience against increasingly challenging environmental conditions.
References
Shpigel, M., Schlosser, S. C., Ben-Amotz, A., Lawrence, A. L., & Lawrence, J. M. (2006). Effects of dietary carotenoid on the gut and the gonad of the sea urchin Paracentrotus lividus. Aquaculture, 261(4), 1269-1280. https://doi.org/10.1016/j.aquaculture.2006.08.029
Zhao, C., Zhang, L., Shi, D., Ding, J., Yin, D., Sun, J., ... & Chang, Y. (2018). Transgenerational effects of ocean warming on the sea urchin Strongylocentrotus intermedius. Ecotoxicology and environmental safety, 151, 212-219.https://doi.org/10.1016/j.ecoenv.2018.01.014