Temperature dependent change in the complexity of form of Chondrus crispus fronds.

Chondrus crispus, a perennial red seaweed, experiences extreme temperature variation living in the intertidal zone of the western North Atlantic. We examined morphological plasticity of this species in response to temperature by growing fronds at 5 and 20 °C, temperatures representative of winter and summer surface seawater in the Gulf of Maine. As expected, C. crispus had higher growth rates at the higher temperature when growth rate was measured in terms of length, biomass, surface area, dichotomy and branch production. The higher growth rate of fronds at 20 °C was associated with a distribution of accumulated biomass into more surface area/unit biomass and more branches/unit length or biomass. These differences resulted in the growth of morphologically more complex thalli at the higher temperature, as measured by significantly higher fractal dimension and ratio of perimeter to square root of the surface area of thalli grown at 20 °C compared to those grown at 5 °C. The morphological distribution of new tissue has implications for the uptake and exchange of nutrients and light harvesting such that plants grown at 20 °C would have more efficient exchanges due to (1) a larger ratio of interface with the bulk media (surface area)/metabolically active biomass and (2) more turbulent mixing and increased convective heat transfer at the thallus surface due to the increased thallus complexity.