Spatial and seasonal reef calcification in corals and calcareous crusts in the central Red Sea

Abstract

The existence of coral reef ecosystems critically relies on the reef carbonate framework produced by scleractinian corals and calcareous crusts (i.e., crustose coralline algae). While the Red Sea harbors one of the longest connected reef systems in the world, detailed calcification data are only available from the northernmost part. To fill this knowledge gap, we measured in situ calcification rates of primary and secondary reef builders in the central Red Sea. We collected data on the major habitat-forming coral genera Porites, Acropora, and Pocillopora and also on calcareous crusts (CC) in a spatioseasonal framework. The scope of the study comprised sheltered and exposed sites of three reefs along a crossshelf gradient and over four seasons of the year. Calcification of all coral genera was consistent across the shelf and highest in spring. In addition, Pocillopora showed increased calcification at exposed reef sites. In contrast, CC calcification increased from nearshore, sheltered to offshore, exposed reef sites, but also varied over seasons. Comparing our data to other reef locations, calcification in the Red Sea was in the range of data collected from reefs in the Caribbean and Indo-Pacific; however, Acropora calcification estimates were at the lower end of worldwide rates. Our study shows that the increasing coral cover from nearshore to offshore environments aligned with CC calcification but not coral calcification, highlighting the potentially important role of CC in structuring reef cover and habitats. While coral calcification maxima have been typically observed during summer in many reef locations worldwide, calcification maxima during spring in the central Red Sea indicate that summer temperatures exceed the optima of reef calcifiers in this region. This study provides a foundation for comparative efforts and sets a baseline to quantify impact of future environmental change in the central Red Sea.

Iron Deficiency in Seagrasses and Macroalgae in the Red Sea Is Unrelated to Latitude and Physiological Performance

“…With a few exceptions (Almahasheer et al, 2016a,b,c), corals and phytoplankton are the main focus of research on primary producers in the Red Sea (Cantin et al, 2010;Ziegler et al, 2014;Kürten et al, 2015;Sawall et al, 2015;Roik et al, 2016;Qurban et al, 2017, among others). However, other important and uncharismatic habitat-forming macrophytes, such as seagrasses and macroalgae within coral reefs , are common but poorly studied in the Red Sea.…”

Year-Long Monitoring of Physico-Chemical and Biological Variables Provide a Comparative Baseline of Coral Reef Functioning in the Central Red Sea

“…Reefs in the central Red Sea are exposed to physico-chemical changes driven by a seasonal cycle [49], as exemplified by the prominent variability of sea water temperatures [51]. These coral reefs commonly stretch over coastal platforms and form offshore reef structures and lagoonal inshore areas that give rise to spatial environmental gradients [52–54]. This setting offers the opportunity to explore spatio-temporal coral reef dynamics under unique conditions.…”

Coral reef carbonate budgets and ecological drivers in the naturally high temperature and high total alkalinity environment of the Red Sea

“…So far, reef growth in 334 the Red Sea has mostly been investigated regarding the effect of high temperature on calcification rates of reef-335 building corals (Cantin et al, 2010;Roik et al, 2015;. In this study we present the first 336 comprehensive estimate of reef carbonate budgets for the central Red Sea.…”

“…A detailed account of benthic community structure of the 282 study sites is provided in Roik et al (2015) and the mean values used for the calculation of benthic accretion rates 283 (Gnetbenthos kg m -2 y -1 ) for the Gbudget estimation are presented in Tables S2-3. 284 285…”

“…We surveyed benthic calcifiers and non-calcifiers and categorized them as follows: % cover total hard 164 coral, % hard coral morphs (branching, encrusting, massive, and platy/foliose), % major reef-building coral families 165 (Poritidae, Acroporidae, and Pocilloporidae), % cover calcareous crusts, % cover algae & sponges). For a detailed 166 description of the benthic surveys please refer to Roik et al (2015). In addition, benthic rugosity was assessed using 167 the Tape and Chain Method (Perry et al, 2012 …”