METABOLIC RESPONSES OF LOW-TEMPERATURE-ACCLIMATED CAULERPA-TAXIFOLIA (CHLOROPHYTA) TO RAPIDLY ELEVATED-TEMPERATURE

Caulerpa taxifolia (Vahl) C. Agardh, collected from the Mediterranean at a depth of 10 m in February 1993 at a sea temperature of 13.7 degre es C and maintained in ambient seawater under weak natural sunlight, e xhibited a net photosynthetic maximum (P-max(n)) of 193 mu mol O-2 g d w(-1) h(-1) at 25.4 degrees C, a minimum of 90 mu mol O-2 gdw(-1) h(-1 ) at 13.8 degrees C and intermediate production capacities at 17.7, 21 and 29.1 degrees C. Dark respiration (-R) varied directly, consuming 7.1% of gross photosynthetic product (P-max(g)) at 13.8 degrees C and 7.4% of P-max(g) at 25.4 ''C. The initial rate of photosynthesis (a), the light compensation irradiance (I,) and the ratio of gross photosyn thetic capacity to absolute dark respiration (P-max(g)/.R) did not var y significantly as a function of seawater temperature. The light inten sity at which the initial slope intercepted the horizontal asymptote ( I-k) varied linearly with temperature. Neither photoinhibition nor diu rnal variation in rates of photosynthesis or respiration were observed . Although the production capacity of C. taxifolia must be limited dur ing the winter months by low seawater temperature, calculations show t hat gross primary production will exceed total respiratory consumption on cloudless days when incident noon peak irradiance is greater than 32 mu mol photons m(-2) s(-1) Based on cloud-free conditions and a the oretical incident noon peak irradiance of 138 mu mol photons m(-2) s(- 1) at 10 m depth on the Cote d'Azur in late February, net production b y C. taxifolia should approximate 378 mu mol O-2 g dW(-1) d(-1).