Effects of temperature on the darkness survival of marine microplanktonic algae

Thirty-seven species of marine microplanktonic algae from 10 taxonomic classes were tested for their viability in axenic culture after prolonged exposure to darkness at 2°, 10°, and 20°C. The darkness test periods were prolonged in weekly installments up to a maximum of 1 year, and viability retention (survival) was judged from the capability for resuming growth after replacement in light. The 2°C-tests showed 32% of the species reaching the limits of survival with 5-6 months of darkness exposure, but another similar percentage continued to tolerate darkness for double this period. These darkness toleration limits were considerably shorter at 20°C for the strains known to be isolated from cold marine regions, whereas the warm-water strains showed the reverse temperature effect in surviving significantly longer at 10°-20°C than at 2°C. Irrespective of temperature or algal class, the bulk of the more resistant survivors was formed by the strains qualifying as benthic types, about 70% of which tolerated 11-12 months and the rest at least 5-6 months of darkness. A few randomly chosen benthic strains extended this toleration to 3 years of darkness. It was concluded that phytoplankters retain darkness-endurance capacity determined by their ecological origin and with no obvious taxonomic correspondence. The concept of ecological races, characterized by temperature control of darkness survival, is discussed.