Eloise J. Bennett1, Ellie R. Paine1, Damon Britton1, Catriona L. Hurd1
1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
Dissolved organic carbon (DOC) that is released by macroalgae is an intrinsic component of the carbon cycle in the coastal ocean yet knowledge on environmental regulation of DOC release by macroalgae is lacking. Temperature is a critical abiotic factor regulating macroalgal physiology. This study examines the effect of temperature on rates of DOC release and key temperature-dependent physiological traits of Ecklonia radiata. Blades were incubated at a range of temperatures (4-28°C) for 14 days and a range of physiological traits were then assessed. There was no effect of temperature on rates of DOC release. Thermal performance curve (TPC) of growth revealed a thermal optimum (Topt) of 15.6°C, a critical thermal minimum (CTmin) of 4.3°C, a critical thermal maximum (CTmin) of 26.9°C and a maximum rate (rmax) of 0.05 g WW-1 • d-1. TPC of photosynthesis revealed a Topt of 21.8°C, a CTmin of <4°C, a CTmax of 28.8°C and a rmax of 6.7 µmol O2 • g WW-1 • h-1. Chlorophyll a and fucoxanthin content and FV/FM were significantly affected by temperature but did not fit any linear or non-linear temperature response models. The C:N ratio of blades increased with temperature whilst %N decreased and %C was unaffected. This study reveals that whilst temperature was a key factor regulating physiological pathways in E. radiata, thermal stress did not affect DOC release.