The secondary productivity means

Gross primary productivity (GPP) of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers). Secondary productivity is defined as the rate of formation of new organic matter by consumers.