Effects of temperature and light availability on juvenile bull kelp sporophytes Nereocystis luetkeana: Informing better restoration practices on understory bull kelp

Abstract

Kelp forests are globally important ecosystems that provide critical ecological services, including coastal protection, habitat engineering, carbon sequestration, and nutrient cycling. In this study, I examined the effects of two abiotic factors, temperature and light, on the growth and photosynthetic efficiency of juvenile bull kelps Nereocystis luetkeana. Samples were placed in four treatments under ambient temperatures of 11 °C and elevated temperatures of 15 °C (± 2.5 °C), and two different ambient light intensities (average 2 μmol photons m⁻² s⁻¹ and 40 μmol photons m⁻² s⁻¹) for 7 days. These two physiological parameters operated on two distinct time frames and revealed different effects of temperature and light on the bull kelps. Chlorophyll fluorescence, the measurement of photosynthetic efficiency, declined after the acclimation period and was able to recover without significant differences between all treatments. Within the growth metric, overall growth rate and stipe elongation rate were governed by temperature and light in varying degrees. Temperature had a larger effect on the overall growth rate, whereas light had a bigger effect on the stipe elongation rate. This experiment showed the intricate nature of kelp tissues, allocating energy toward different tissue types under two separate abiotic drivers.