Percent of Sea Slug Respiratory Carbon Demand Provided by Indwelling

Multiple Choice

Percent of sea slug respiratory carbon demand provided by indwelling dinoflagellates.
-If we assume that carbon is the sole nutrient needed by sea slugs to drive their cellular respiration, then based on the graph, during which season(s) is it least necessary for P. ianthina to act as a chemoheterotroph?

A) winter
B) spring
C) summer
D) fall
E) spring and fall