PROLONGED DARKNESS AND DIATOM MORTALITY .1. MARINE ANTARCTIC SPECIES

The effect of prolonged periods of darkness (up to 10 months) was inve stigated in the diatom species Thalassiosira antarctica Comber, T. tum ida (Janisch) Hasle, Porosira pseudodenticulata (Hustedt) Joust, Probo scia inermis (Castracane) Jordan and Ligowski and Fragilariopsis kergu elensis (O'Maera) Hustedt isolated from the Southern Ocean. Sudden dar kness did not induce resting spore formation. All species survived in their vegetative stage. High levels of photosynthesis were resumed in T. antarctica, T. tumida and P. inermis upon re-exposure to light at a ll times tested during a 3 month dark period. Cellular chlorophyll a, carbon and nitrogen decreased at the beginning of the dark period and remained more or less stable suggestive of a low maintenance respirati on. Species specific survival times varied from less than 4 months up to 9 months. After returning to the former light regime during the spe cies specific survival times T. antarctica, T. tumida, P. pseudodentic ulata and P. inermis began growing at rates similar to those in the pr e-dark phase.