Understanding how species of kelp perform under different environmental factors is critical for the management of kelp farming and its effects on carbon sequestration. In this study we evaluated how low salinity and water temperature affect two kelp species: bull kelp (Nereocystis luetkeana) and ribbon kelp (Alaria marginata). Pulse-amplitude modulated (PAM) fluorometry was used as a proxy for health, while wet weight and the hole-punch measurement method determined growth. At Friday Harbor Laboratories (San Juan Island, WA), we collected and exposed ribbon and bull kelp to different treatments under grow lights for a standard photoperiod (12 hours/day) in closed-circulatory sea tables for 72 hours. Our treatments were high temperature (20ºC/ 30PSU), low salinity (12ºC/ 25PSU), high temperature with low salinity (20ºC/ 25PSU), and control (12ºC/ 30PSU). The results of the stress test via PAM fluorometry demonstrated 0% survivability of bull kelp for both heat and the combination of heat and salinity at 24 and 48 hours (Fv/Fm = 0) while ribbon kelp survived. When comparing percent change of wet weights, ribbon kelp gave a p-value of <0.05, with significant differences between combined treatment with control and salinity treatments, whereas bull kelp gave a p-value >0.05, however temperature treatments of bull kelp did not survive (Kruskal-Wallis test and Dunn post-hoc). These results indicate that heat has a more significant effect on kelp than salinity. This data is increasingly relevant as the environmental effects of climate change increase global temperatures and could identify which kelp species are most vulnerable.

Purple sea urchins (Strongylocentrotus purpuratus) pose a serious threat to the environment by consuming entire kelp forests that serve ecological functions like carbon sequestration. We compared the preference of purple sea urchins on various kelp species to understand how feeding habits changed across different environments: temperature (ambient 13 °C, high 20 °C) and salinity (ambient 30 PSU, low 22 PSU). Urchins were collected from the subtidal zone in Friday Harbor, San Juan Island, WA. At the University of Washington Friday Harbor Labs, urchins were exposed to either ambient (6.8L), high temperature and ambient salinity (6.8L), low salinity and ambient temperature (6.8L), or high temperature and low salinity water (3.1L). Within these treatments urchins were given Bull Kelp (Nereocystis luetkeana), Ribbon Kelp (Alaria marginata), and Fringed Sieve Kelp (Neoagarum fimbrata) for 24 hours. To track kelp consumed, we weighed the kelp before and after each trial. Results showed that Bull Kelp was consumed the most in every environment except high temperature, low salinity. In low salinity and high temperature urchin feeding was significantly different and lower from the ambient environment, as most urchins ate nothing over 24 hours (Kruskal Wallis and Dunn’s test, p-value > 0.05). Our findings suggest that in areas with lower salinity and higher temperatures, urchins may be a smaller threat to kelp. In many environments, bull kelp is most vulnerable to urchin feeding, making it an important species for conservation efforts.