Practice question

Question

A food chain involving Spartina (a plant), the marsh periwinkle snail, the blue crab and an unknown fungus was identified in a Spartina-dominated salt marsh in North America. A study involving control and crab-exclusion experiments revealed: A. Radulations (scrape marks) on the leaf surface made by the snails indicate the presence of snail faeces, fungi and dead plant tissue. B. The fungi were present only at the radulations. C. The density of the radulations increased with higher snail densities. D. Spartina density decreased with increase in the snail density till it reached zero. E. In control experiments, all four species were present till the end. Select the option that correctly depicts the positive ( +) and negative (-) interaction-type between fungi-snail and Spartina-crab, respectively: