We analyse the cycling of mass in over 200 real-world aquatic weighted food webs, that quantify feeding relationships between groups of species. The majority of matter cycling described through Finn Cycling Index (FCI) can be traced back to microorganisms that assimilate dead organic matter. This microbial loop recycles a significant fraction of primary production. We show how the very skew distribution of FCI at the network level originates from approximately lognormal distributions of distinct groups of nodes.
We use multiple regression to explain the node values of FCI. The indirect effects of detrital nodes, trophic level and bilateral reciprocity of flows around the node in question play significant roles. Imports and respirations relative to the total system throughflow complement reciprocity in predicting the value of FCI of whole food webs.
Mass cycling in food webs with 5% geometric mean is larger than 1.7\% cycling achieved in 2011 by the world (EXIOBASE). We study the cycling at country level in a number of mass and embodied emissions networks.