SEASONALITY OF RED AND GREEN MACROALGAE FROM ANTARCTICA - A LONG-TERM CULTURE STUDY UNDER FLUCTUATING ANTARCTIC DAYLENGTHS

The seasonal development of the endemic Antarctic alga Palmaria decipiens (Palmariales, Rhodophyta) and of the Antarctic-cold temperate algae Iridaea cordata, Gigartina skottsbergii (Gigartinales, Rhodophyta), Enteromorpha bulbosa (Ulvales, Chlorophyta) and Acrosiphonia arcta (Acrosiphoniales, Chlorophyta) was monitored during two years in a culture study under fluctuating daylengths mimicking the conditions on King George Island (Antarctica). Temperature was kept constant at 0°C and nutrient levels were maintained at 0.6 moles m-3 nitrate and 0.025 moles m-3 phosphate. In P. decipiens, blades on germlings and on thalli from the previous season are initiated under Antarctic winter conditions and show maximum growth in October. Formation of blades on old thalli of I. cordata and G. skottsbergii started between June and August, maximum growth occurred in December. Sporangia started to form in G. skottsbergii in September and March and spore release was observed 9 months later at ≥27 μmol photons m-2s-1. E. bulbosa and A. arcta grew optimally in November and December conditions. Spore or gamete release was observed in December and January in plants kept at 46 μmol m -2 s-1 and in January to March in plants kept at lower photon fluence rates, respectively. The minimum light requirements for completion of the life cycle were 31.4 mol m-2 year-1 in A. arcta, 47.1 mol m-2 year-1 in E. bulbosa and P. decipiens and 141.3 molm-2 year-1 in I. cordata and G. skottsbergii. These values suggest lower distribution limits of either 53±23 m, 49 ±22 m and 38±17 m in clear offshore waters or of 28 ±5 m, 26±5 m and 20±4 m in small inshore fjords of the Antarctic Peninsula region. © 1990 Springer-Verlag.