MCR LTER: Coral Reef: Landscape-scale patterns of nutrient enrichment in a coral reef ecosystem: implications for coral to algae phase shifts, Adam et al., Ecol. Appl.

These data and analyses code were generated in support of the manuscript: Adam TC,
Burkepile DE, Holbrook SJ, Carpenter RC, Claudet J, Loiseau C, Thiault L, Brooks, AJ,
Washburn L, and RJ Schmitt, Ecological Applications We investigated the potential role of anthropogenic nutrient loading in driving recent
coral-to-macroalgae phase shifts on reefs in the lagoons surrounding Moorea, French
Polynesia. We used nitrogen (N) tissue content and stable isotopes (δ15N) in an abundant
macroalga ( Turbinaria ornata ) together with empirical models of nutrient discharge to
describe spatial and temporal patterns of nutrient enrichment in the lagoons. Turbinaria ornata were collected at 190 sites around Moorea in January, May, and August 2016. These
sampling periods corresponded with distinct seasonal shifts in rainfall and wave forcing.
Our results revealed that patterns of N enrichment were linked to rainfall, wave-driven
circulation, and distance from anthropogenic nutrient sources, especially human sewage. In
addition to describing high resolution patterns of N enrichment from 2016, we also analyzed
core MCR time series on N tissue content in Turbinaria ornata from three habitats (fringing
reef, back reef, and reef crest) at the six core MCR LTER sites between 2007 and 2013. These
data showed that fringing reefs have been consistently enriched in N relative to back reefs,
which are enriched relative to the reef crest. Further, these patterns mirror long-term
patterns of nitrate and nitrite concentrations in the water column. We also analyzed core
MCR time series on benthic communities and fishes and found that back reef sites that were
consistently enriched in N between 2007 and 2013 experienced large increases in macroalgae
while macroalgae remained much less abundant at back reef sites with lower N. These phase
shifts to macroalgae occurred despite island-wide increases in the density and biomass of
herbivorous fishes over the time period. Together, these results indicate that nutrient
loading may be an important driver of coral-to-macroalgae phase shifts in the lagoons of
Moorea even though the reefs harbor an abundant and diverse herbivore assemblage,
emphasizing the important role that bottom-up factors can play in driving
coral-to-macroalgae phase shifts.