Comparing Contributions of Mussels and Fish As Biogeochemical Hotspots

Mussels and fish are known to generate nutrient hotspots, but whether aggregations of these two disparate consumer groups overlap and interact to influence nutrient dynamics remains unexplored. We asked where and when fish and mussel biomass coincides, and what are the relative contributions of each to nutrient cycling? We estimated fish biomass at replicate stream reaches containing mussels and reaches without mussels in three rivers in southeastern Oklahoma during summer and fall of 2015. We also measured nitrogen and phosphorous excretion rates of dominant fish species to compare with previously measured mussel excretion rates. Biomass estimates and excretion rates were combined to estimate areal excretion rates of fish and mussels. In general, mussel biomass (15.14-56.99 g dry tissue m^-2) was greater when compared to fish biomass in mussel reaches (1.40 - 9.50 g dry tissue m^-2) and in control reaches (1.34 -7.79 g dry tissue m^-2). Mussel areal excretion rates (175.19 µg N m^-2 h^-1, 15.87 µg P m^-2 h^-1) were also higher than those of fish (54.78 µg N m^-2 h^-1, 15.21 µg P m^-2 h^-1). Future efforts will evaluate the more diffuse occurrences of fishes compared to the aggregated occurrences of mussels towards nutrient hotspots and ecosystem function.