TEMPERATURE-DEPENDENT CHANGE IN THE COMPLEXITY OF FORM OF CHONDRUS-CRISPUS FRONDS

Chondrus crispus, a perennial red seaweed, experiences extreme tempera ture variation living in the intertidal zone of the western North Atla ntic. We examined morphological plasticity of this species in response to temperature by growing fronds at 5 and 20 degrees C, temperatures representative of winter and summer surface seawater in the Gulf of Ma ine. As expected, C. crispus had higher growth rates at ihs higher tem perature when growth rare was measured in terms oi length, biomass, su rface area, dichotomy and branch production. The higher growth rate of fronds at 20 degrees C was associated with a distribution of accumula ted biomass into more surface area/unit biomass and more branches/unit length or biomass. These differences resulted in the growth of morpho logically more complex thalli at the higher temperature, as measured b y significantly higher fractal dimension and ratio of perimeter to squ are root of the surface area of thalli grown at 20 degrees C compared to those grown at 5 degrees C. The morphological distribution of new t issue has implications for the uptake and exchange of nutrients and li ght harvesting such that plants grown at 20 degrees C would have more efficient exchanges due to (1) a larger ratio of interface with the bu lk media (surface area)/metabolically active biomass and (2) more turb ulent mixing and increased convective heat transfer at the thallus sur face due to the increased thallus complexity.