Spines Increase a Cell's Surface Area,so the Spiniest Diatoms Should

Spines increase a cell's surface area,so the spiniest diatoms should be the most buoyant.Which selective force below might explain the observed shift in spine number?

A) More predators were present during the ice age, favoring diatoms with more spines
B) Endothermic animals in colder climates tend to have smaller surface area to volume ratios to conserve heat
C) Diatoms with more spines could swim better allowing them to stay afloat in colder water
D) As Yellowstone Lake warmed up the water density decreased, favoring less buoyant diatoms
E) During the ice age Yellowstone Lake would have received more light from reflection off of the snow, allowing diatoms to live at greater depths