The Impact of Temperature on the Nutritional Composition of Dulse (Devaleraea mollis) and its Influence on Juvenile Red Abalone (Haliotis rufescens)

The world is experiencing changes in weather patterns that are affecting not only ecosystems but agricultural systems and bringing uncertainty to food production. The research continues to grow on the impacts of climate change and developing solutions to mitigate its harmful effects on our industrial food systems is imperative for food security. Humans rely on a global food system spanning vegetation and terrestrial animals, with increasing growth in aquaculture. Understanding how changes in temperature and increases in carbon dioxide change our foods allows for mitigation and regulations to be implemented. It is well documented in agriculture how plants adapt to climate change and its effect on the nutrition of produce. With the growth of the seaweed farm sector, it is essential to understand how increasing temperatures change seaweeds and how these changes impact natural ecosystems. Changes in primary producers such as seaweed can reverberate throughout the food chain, impacting higher trophic levels, inducing stress, and degrading ecosystem health. To determine how the changes in nutritional composition that could result from climate change affect the growth of herbivorous animals, the direct effects of temperature on seaweeds needs to be understood. This project aimed to determine the changes in protein and carbohydrate concentration in a primary producer in varying temperature ranges and its influence on the growth of an herbivorous animal. The seaweed dulse, Devaleraea mollis, was cultured at three different temperatures (13°C, 15°C and 17°C) which was fed to juvenile red abalone (Haliotis rufescens) of two different size classes (small 15.6±1.76mm, and medium 42.86±4.65mm), and maintained in ambient seawater separate from the culture system. For the small size class, a total of 288 abalone were divided into 24 rearing troughs, (trough = experimental unit) with twelve abalone per trough, and randomly assigned to a diet treatment group. The medium size class totaled 63 abalone divided into 21 rearing troughs, with three abalone per trough, and randomly assigned a diet treatment group. Initial and final length and weight measurements were taken on the abalone and used to evaluate the condition factor (CF) and change in body weight ratio (BWR) as an indication of overall health. Seaweed samples were also collected and sent to the UC Davis Analytical Laboratory for nutritional analysis. Significant pairwise tests on linear mixed effects regressions on CF, BWR of the small class abalone, and protein and total nitrogen percentage in the dulse were found. The results showed condition factor significantly differed between the small size class of abalone fed the 13°C to the 15°C and 17°C cultured dulse, and change in body weight ratio showed significant differences between the small class fed 13°C and 17°C cultured dulse. These results indicate that juvenile red abalone in the small size class fed the 17°C cultured dulse had a significantly better physiological status evaluated by their condition factor and change in body weight ratio than other diets. The 17°C cultured dulse also had significantly higher protein percentages than the 13°C and 15°C cultures. Linear mixed models for the carbohydrate analysis (total glucose, starch and total non-structural carbohydrates) showed no differences between the treatment groups. In conclusion, our study indicates that temperature may affect protein synthesis in dulse, which could influence the growth of abalone. Further research to extrapolate the acclimation period of dulse grown with excess nutrients in different temperatures is needed to fully understand its influence on abalone