Data from: Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment

The structural framework provided by corals is crucial for reef ecosystem
function and services, but high seawater temperatures can be detrimental
to the calcification capacity of reef-building organisms. The Red Sea is
very warm, but total alkalinity (TA) is naturally high and beneficial for
reef accretion. To date, we know little about how such detrimental and
beneficial abiotic factors affect each other and the balance between
calcification and erosion on Red Sea coral reefs, i.e., overall reef
growth, in this unique ocean basin. To provide estimates of present-day
reef growth dynamics in the central Red Sea, we measured two metrics of
reef growth, i.e., in situ net-accretion/-erosion rates (Gnet) determined
by deployment of limestone blocks and ecosystem-scale carbonate budgets
(Gbudget), along a cross-shelf gradient (25km, encompassing nearshore,
midshore, and offshore reefs). Along this gradient, we assessed multiple
abiotic (i.e., temperature, salinity, diurnal pH fluctuation, inorganic
nutrients, and TA) and biotic (i.e., calcifier and epilithic bioeroder
communities) variables. Both reef growth metrics revealed similar patterns
from nearshore to offshore: net-erosive, neutral, and net-accretion
states. The average cross-shelf Gbudget was 0.66kg CaCO3m−2yr−1, with the
highest budget of 2.44kg CaCO3m−2yr−1 measured in the offshore reef. These
data are comparable to the contemporary Gbudgets from the western Atlantic
and Indian oceans, but lie well below optimal reef production (5–10kg
CaCO3m−2yr−1) and below maxima recently recorded in remote high coral
cover reef sites. However, the erosive forces observed in the Red Sea
nearshore reef contributed less than observed elsewhere. A higher TA
accompanied reef growth across the shelf gradient, whereas stronger
diurnal pH fluctuations were associated with negative carbonate budgets.
Noteworthy for this oligotrophic region was the positive effect of
phosphate, which is a central micronutrient for reef building corals.
While parrotfish contributed substantially to bioerosion, our dataset also
highlights coralline algae as important local reef builders. Altogether,
our study establishes a baseline for reef growth in the central Red Sea
that should be useful in assessing trajectories of reef growth capacity
under current and future ocean scenarios.