Bull Kelp Resistance to Increased Temperatures

Bull kelp (Nereocystis luetkeana) is a canopy forming foundation species found along the Central and Northern California coast. It provides food and shelter for many organisms, contributes to carbon sequestration, and also supports local economies. However, recently there has been a massive kelp die off along the Northern California coast due to warming events and sea star wasting disease, shifting healthy kelp forests to urchin barrens. Although greater than 90% of bull kelp along Northern California has disappeared, a handful of persistent remnant patches remain. Previous studies have shown that warmer water temperatures negatively impact the different life history stages of kelp. However, there is a lack of information about the temperature effects on the different life stages of bull kelp on these apparently more resistant remnant patches, which is what our study aims to investigate. Mesocosm experiments were conducted to culture bull kelp collected from Central California and Northern California under two temperature treatments (12℃ and 17℃) and determine growth in two life history stages: microscopic gametophyte stage and macroscopic sporophyte stage. Bull kelp from both regions showed some resistance to warming temperatures in both life history stages. However, the bull kelp from Central California showed more growth in both life history stages in the warm treatment. These results indicate that the remnant patches may have some resistance toward warming waters; bull kelp from Central California has the highest amount of resistance, presumably because they could be adapted to warmer temperatures. As sea surface temperatures increase due to climate change our bull kelp cultures will inform management efforts toward kelp forest restoration.