Moderate stoichiometric homeostasis in the sea urchin Lytechinus variegatus: effects of diet and growth on C:N:P ratios

in sea urchin C:N (R = −0.74 and R = 0.93, for diet and growth effects, respectively) and N:P ratios (R = 0.60 and R = −0.63, also, respectively, for diet and growth effects). Among potential compensatory mechanisms helping to preserve certain levels of homeostasis, ingestion rates (g WW diet per g WW of urchin) were higher for seagrass and macroalgae diets than for the nutrient-rich formulated diet. In contrast, absorption and growth efficiencies displayed significant negative associations with nutrient contents in diets and did not exhibit nutritional compensation. Overall, our results suggest that resource stoichiometry strongly determines the growth rate of individuals (R = 0.88, P < 0.01), and moderate variability in C:N:P ratios of sea urchins possibly arise from differences in the allocation of proteins and RNA to body components, similarly to what has been proposed by the growth rate hypothesis.