Effects of water temperatures, UV radiation and low vs high PAR on phlorotannin content and germination in zoospores of Saccorhiza dermatodea (Tilopteridales, Phaeophyceae)

Abstract

Steinhoff F.S., Wiencke C., Wuttke S. and Bischof K. 2011. Effects of water temperatures, UV radiation and low vs high PAR on phlorotannin content and germination in zoospores of Saccorhiza dermatodea (Tilopteridales, Phaeophyceae). Phycologia 50: 256–263. DOI: 10.2216/09-107.1Global climate change will have multiple effects on our environment and might especially change marine coastal ecosystems and their communities due to rising water temperatures and changing light regimes in the water column. Due to the key role of zoospores in the life-history cycle of kelps, we investigated how zoospores of the shallow water species Saccorhiza dermatodea (B. de la Pylaie) J.E. Areschoug respond to interactive effects of changing water temperatures, low/high photosynthetically active radiation (PAR) and UV radiation (UVR). Zoospores were examined with respect to germination pattern (germination rates, light micrographs) and phlorotannin content (Folin–Ciocalteu method). In summer 2007, we exposed S. dermatodea zoospores, obtained from fertile thalli in Kongsfjorden (Svalbard, Norway), to low PAR laboratory [UV-B∶UV-A∶PAR (W m−2) 8∶114∶100; 2–17°C] and high PAR outdoor experimental conditions [UV-B∶UV-A∶PAR (W m−2) 0.1∶5∶100; 7°C] for 8 h. Under low PAR+UVR conditions and at 2–12°C, almost 98% of zoospores germinated in all light treatments. The germination rate was reduced under PAR+UV-A+UV-B only in the 17°C and 7°C outdoor treatment, to 21.4% and 9.6%, respectively. Light microscopic investigations showed differences in germling appearance, growth and pigmentation in the outdoor treatment and at 17°C low PAR conditions, compared with all other treatments, after an exposure time of 8 h. However, phlorotannin content within zoospores remained unaffected by changing UV and low/high PAR conditions. These results suggest that combined effects of present water temperatures, high PAR and UVR can exhibit similar effects on germination as the combined effects of unnatural high temperatures (17°C), low PAR and UVR. With respect to global climate change, the ecological implications of the present study illustrate that zoospores of S. dermatodea are able to survive enhanced water temperatures up to 12°C. Moreover, high PAR in combination with UVR might potentially affect zoospores of S. dermatodea stronger than expected in clear waters.