Herbivory by reef fishes and the production of dimethyl sulfide and acrylic acid

The content of dimethylsulfoniopropionate (DMSP) in selected marine reef macrophytes was examined and related to levels of DMSP and one of its decomposition products, dimethylsulfide (DMS), in guts of herbivorous fish. Concentrations of short-chain fatty acids and acrylic acid (ACR), another decomposition product of DMSP, were also measured in gut contents. The fatty acid data provide evidence for bacterial fermentation within fish intestines. Unlike previous observations of gut microflora, the concentrations of ACR in these guts did not support a role for ACR as an inhibitor of the gut microflora. DMSP also appears to concentrate in the tissues of certain fish, but not in others. These results illustrate the complex trophic interactions which determine the dynamics of DMSP in the marine food web.