What: Nutrient data (NH4, NO2, NOx, PO4, SiO4) of the water column and pore water during a nutrient enrichment and macrofauna exclusion experiment. A total of 24 plots were set up parallel to the shore, with presence of the three seagrass species (Syringodium isoetifolium, Thalassodendron ciliatum and Thalassia hemprichii) in each plot. The experiment was the factorial combination of two treatments: macrofauna exclusion using cages (three levels: open, closed and uncaged) and nutrient enrichment using garden NPK fertilizer (two levels: ambient and enriched). Each treatment combination was replicated four times. The macrofauna exclusion cages were made of wooden pegs (0.5 x 0.5m wide and 0.5 m high) and were covered with a plastic net (14 mm diagonal mesh size). This mesh-size excludes macrofauna, but not small fish and mesofauna. This macrofauna exclusion technique (Casini et al., 2008) simulates the consequences for the food web of losing a top predators and macrograzers. Open cages had all the side meshes halved to allow partial access from all four sides, and uncaged plots were marked with four wooden pegs. The cages were anchored by metal T bars and cleaned every 2 weeks to remove organisms and filamentous algae that would otherwise affect light penetration and water flow. Nutrient enrichment was simulated by issuing nitrogen-phosphorus-potassium (NPK) [15:9:20] fertilizer pellets. NPK fertilizer fast release pellets were packed into cotton tubes and then into a perforated plastic tubes to simulate slow release of nutrients. The tubes were filled with 75g of pellets and five tubes were placed in each of the enriched plots (375g in total per plot) following the protocol by Heck et al. (2000). The tubes were buried half-way into the sediment to ensure enrichment of both the water column and the sediment. Fertilizer was replaced every 3 weeks, making a total of 1125 grams of fertilizer released per enriched plot at the end of the experiment. All plots were separated by at least 3 metres, proven as a no-overspill area in previous nutrient enrichment experiments (Lotze & Worm, 2000). When: Data was collected between July 19th and September 20th of 2017 in four sampling times. Day 0 (19.07.2017), Day 20 (09.08.2017), Day 38 (31.08.2017) and Day 63 (19.09.2017). Porewater data was only collected in the last sampling time (day 63). Where: Data collection and experiment took place in Changuu Island (Zanzibar Archipelago, Tanzania; 06˚11'S, 39˚16'E). Changu Island is located 3 km from Stone Town, Zanzibar's busiest town. Changuu remains relatively unaffected by nutrient runoff pollution, although it has a small tourist resort and a large tortoise centre with daily boat traffic bringing tourists from Stone town. The study area is characterised by a fringing reef around a multi-specific seagrass ecosystem. The substrate is primarily carbonate sediment. Average water depth is approximately 30 cm at Spring Low and 5 m at Spring high tide with an average depth of 2 m. Why: Nutrient data was collected to study the ambient nutrient levels in the waters and the enriched nutrient levels in the fertilized plots during the experiment. How: To determine ambient and enriched nutrient concentrations in the water, water column samples were collected for nutrient analysis from each of the 24 plots at each sampling time (for day 0 this was the only variable taken after setting up the treatments to detect nutrient enrichment). Porewater samples were only collected at the end of the experiment. For the samples in the water column, 20-ml Leur syringes were used. One sample was taken within each treatment plot. Porewater sampling was performed by pushing a 30cm cylindrical PVC core into the sediment of each of the treatment plots. After extraction of the core, a rhizon soil moisture sampler (Eijkelkamp Soil & Water, Netherlands) connected to a Leur syringe was placed in a hole corresponding to a depth of 5 cm below the sediment surface. Making a vacuum with the syringe, the water was pulled out of the sediment cores. After the sampling, the samples were immediately filtered (0.45-μm pore size, Whatman GF/F filters) in pre-rinsed 50 ml polyethylene bottles, frozen (−20 ̊ C), and transported to ZMT for analysis. Analysis was performed using a continuous flow injection analyzing system (Skalar SAN++-System) to obtain Nitrate + Nitrite (NOx), ammonia (NH4), dissolved inorganic nitrogen (DIN = NOx + NH4), silicate and phosphate (PO4−3) following Grasshoff et al. (1983). The measuring procedure had a relative standard deviation < 3.5% with reference to the linear regression of an equidistant 10-point calibration line from NIST standards.