Distribution of neuromass in a Michigan stream ecosystem.

Neuromass, the mass of central nervous tissue per unit area, is suggested as a new parameter for studying ecosystems. Its use is demonstrated with a comparison of biomass and neuromass distributions for a stream riffle ecosystem in the Huron River, southeastern Michigan. Biomass and neuromass were estimated for three animal groups: small invertebrates, crayfish, and fish. For small invertebrates the mass of the longitudinal nerve cord was estimated with histological sectioning and volumetric calculation. For crayfish and fish the central nervous system was dissected out and weighed. Total biomass was about 12 g dry wt/m2 and was dominated by small invertebrates that made up 76% of the total. Total neuromass was about 0.2 g wet wt/m2. Fish neuromass made up 93% of the total neuromass even though their biomass contribution was only 18% of the total. These results are discussed in relation to the potential of this approach for developing a view of information processing at the ecosystem level of organization.