Exploring the effects of salinity and temperature gradients on Nereocystis luetkeana sorus incubation and subsequent spore release in the San Juan Islands

Abstract

Climate change continues to subject kelps of the Salish Sea to unpredictable and unforeseen conditions. Circumstances such as increased freshwater input from riverine outflow and rising temperatures in the estuarine waters of Washington State and British Columbia have been attributed as leading causes for widespread kelp decline. To assess the potential for compounding deleterious effects induced by large temperature and salinity swings, bull kelp (Nereocystis luetkeana) sorus samples were collected from two nearshore habitats along the Friday Harbor coastline. The sori were then incubated in a range of conditions from 8ppt - 32 ppt salinity and 10°C - 22°C in an attempt to mimic recently observed conditions in local waters. The results highlight a small window of viable incubation for the most extreme end (low salinity, high temperature) of the exposure gradient while requiring longer durations for those in control treatments, depending on specific incubation parameters. An exploration into the effects of a range of salinity and temperature exposures during the sorus development of the brown algae, Nereocystis luetkeana, returned mixed spore density results, with varying incubation success. The state of the sori also varied during incubation, with boils appearing on all of the 8ppt treatments except for in phase 3 with the 8ppt 10°C treatment sori. For spore density, the highest density observed was in the 32 ppt 16°C treatment, and the most evident relationship visible was shown by lower spore count at lower salinities.