Janet E. Kübler1,2, Simona Augyte3, Steven R. Dudgeon1, and Charles Yarish2
1Department of Biology, California State University, Northridge, CA, USA
2Ecology and Evolutionary Biology, University of Connecticut, Stamford, CT, USA
3Ocean Era Inc., Kailua-Kona, HI, USA
Laminaria farlowii is of interest as a novel species for aquaculture in Southern California. Its thermal biology and climate change resilience are not well known. Wild populations of L. farlowii live primarily below the seasonal thermocline but individuals have been successfully cultivated in near surface conditions of light intensity and temperature. We examined the thermal biology of gametophytes and sporophytes of L. farlowii. We grew gametophytes and juvenile sporophytes across gradients of temperatures (9-20°C) and light intensity (20-80 µmol photons m-2.s-1), finding growth rates were saturated by all light intensities tested and sensitive to temperature. Optimal growth temperatures were 13°C for gametophytes and 15°C for sporophytes. In a separate experiment, sporophytes were exposed to thermal regimes differing in mean temperature (10-20°C) and thermal variability, under a photoperiod chosen to induce sorus formation. Growth rates were not significantly different from 14-18°C but sori were formed only at mean temperature of 15°C. We evaluated the ability of L. farlowii sporophytes to survive brief simulated marine heat waves (upshock of 3°C for 3 or 5 days), finding no detectable effect on growth rate after 4 days of recovery despite decreased photosynthetic electron transport rates after both 3 and 5-day simulated marine heatwave treatments. Comparing that thermal tolerance to the annual sea surface temperature in Santa Barbara, California from 2007 to 2021, we predict that L. farlowii could be actively growing near the surface 75% of the time and survive brief marine heat waves.