Meeting Abstract
Conditions in the intertidal zone differ at high and low tide. Exposure to stressful low tide conditions (high light and temperature, wind and low humidity) may have immediate and persistent negative effects on the photosynthetic ability of seaweeds. We utilized laboratory manipulations to investigate the effects of stressful low tide conditions on the photosynthetic health of the low intertidal canopy-forming seaweed Egregia menziesii. We compared responses of individuals in five treatments: one no-emersion treatment (low light, low temperature, no desiccation) and 4 realistic emersion treatments: low stress (low light, moderate temperature, low desiccation), low light + desiccation (low light, moderate temperature, constant wind), high stress (high light, high temperature, ambient desiccation), and high light + hydration (high light, high temperature, seawater spray every 5 minutes). We assessed the seaweed’s photosynthetic potential by measuring dark–adapted Maximum Quantum Yield (MQY) via pulse amplitude-modulated fluorometry, evaluated tissue damage by quantifying tissue colour (as % of total area with visible discolouration), and measured biomass loss. After a 2 hour simulated low tide, we assessed performance each day for 3 consecutive days. We found that both high light and desiccation reduced photosynthetic performance and resulted in tissue damage and biomass loss although the individual effects of these factors were not equal in magnitude. Our study suggests that even a single stressful low tide can have permanent consequences for the seaweed. Understanding how individual seaweeds respond to combinations of environmental factors will aid in predicting how seaweed populations will be affected by the changing climate.
