Periphyton accumulation rates were measured bimonthly at FCE LTER sites in Florida Bay and Shark Slough. Glass slides were used as artificial substrates for periphyton growth. Twenty slides were incubated for 2 months in triplicate periphytometers (flow-through plastic boxes) at the surface (SRS sites) and bottom (FB) at each site. Twelve artificial blades (made from transparency film) were incubated for 2 months in triplicate in specially constructed wire frames at the bottom at sites TS/PH 9, TS/PH 10 and TS/PH 11. Data are presented in terms of grams dry and ash-free dry mass per area per time. This is part of continuous data collection to test the hypothesis that phosphorus and nitrogen limit productivity at the upstream and downstream ends, respectively, of the FCE transects. Conclusions await longer-term data collection.