Jakop Schwoerbel1, Wouter Visch1, Jeffrey Wright1, Alecia Bellgove2, J. Craig Sanderson3, Catriona Macleod1, Catriona L. Hurd1
1Institute for Marine and Antarctic Studies (IMAS), 20 Castray Esplanade, Battery Point, Tasmania, 7004, Australia
2Deakin University, Warrnambool Campus, Princes Highway, Warrnambool, Victoria 3280, Australia
3TASSAL GROUP LIMITED., G.P.O. Box 1645, Hobart, Tasmania, 7001, Australia
The brown seaweed Ecklonia radiata (Order Laminariales) is a candidate for aquacultural cultivation in southern Australia, but we know little about the microscopic life stages compared to macroscopic sporophytes. This study uses thermal response curves (4 °C to 30 °C) to examine the effect of season on temperature optima for gametophyte growth and subsequent sporophyte development, for E. radiata from two sites that have different seasonal temperature profiles and hydrography: north-eastern Tasmania (12.4 °C to 17.4 °C) and south-eastern Tasmania (11.6 °C to 16.7 °C) the former experiencing higher temperatures and for longer periods. Gametophytes were cultured for 6 weeks in each of 4 seasons, in a temperature gradient table. Gametophyte size was recorded after 4 weeks, and sporophytes production after 6 weeks. The thermal response curves showed temperature optima for gametophytes around 20 °C for spring, summer, and autumn (winter experiment ongoing). We observed clear differences in gametophyte size between the two sites in spring, with the northern site growing substantially larger, but this was not observed in summer or autumn. Sporophyte density was generally low (< 0.4 mm-2) with no site consistently producing more sporophytes. Temperature optima for sporophyte production lay between 15 and 17 °C at both sites. The results inform the best times to collect reproductive material to set up stock cultures for aquaculture as well as optimal temperatures for culture growth.