Data from: Year-long monitoring of physico-chemical and biological variables provide a comparative baseline of coral reef functioning in the central Red Sea

Coral reefs in the central Red Sea are sparsely studied and in situ data on physico-chemical and key biotic variables are missing to provide an important comparative baseline. To fill this gap, we monitored three reefs along a cross-shelf gradient during a full year, simultaneously collecting data on currents, temperature, salinity, dissolved oxygen (DO), chlorophyll-a, turbidity, inorganic nutrients, sedimentation, bacterial communities of reef water, and bacterial and algal composition of epilithic biofilms. Some of these environmental parameters resemble projected ‘future ocean’ conditions. Summer temperatures (29 - 33 °C) and salinity levels (39 PSU) exceeded average maxima for coral reefs globally, while DO levels were comparably low (2 - 4 mg L-1). Reef environments were highly variable over time and between reefs. Temperature and salinity differences were most pronounced between seasons. Conversely, DO, chlorophyll-a, turbidity, and sedimentation varied strongest between reefs. Similarly, biotic communities were highly dynamic between reefs and seasons. Differences in bacterial biofilms were driven by differentially abundant bacterial taxa that belonged to the families Rhodobacteraceae, Flavobacteriaceae, Flammeovirgaceae, and Pseudanabaenaceae. In algal biofilms, green crusts, brown crusts, and crustose coralline algae were most abundant and accounted for most of the variability of the communities. Higher bacterial diversity of biofilms coincided with increased algal cover during spring and summer. We identified temperature, salinity, DO, and chlorophyll-a as the physico-chemical drivers of biotic community structures by multivariate matching. These parameters are forecasted to change most with the progression of global warming and increased nutrient input, which also suggests an immediate bottom-up effect on Red Sea benthic communities as a result of climate change and anthropogenic influence. In conclusion, our study presents foundation data to provide a comparative baseline to support coral reef studies in the region and to gain insight into coral reef functioning in the Red Sea.