Drivers and predictions of coral reef carbonate budget trajectories

The largest threat to the long-term existent of coral reefs is climate change, and this topic has received much attention over the past 20 years as coral bleaching and mortality events have become more frequent and more intense. As a result of these events, changes in different aspects of coral reef ecosystems have potentially changed the balance of carbonate accretion and erosion. These geomorphic consequences of coral bleaching have yet to received significant attention, with most studies being conducted on reef ecology, and here we begin to rectify this omission. Using data collected on inner Seychelles reefs from 1994 to 2014 we track the carbonate budget of these reefs across the 1998 coral bleaching event when 90% of coral cover was lost, and subsequent recovery. We found that while all reefs were estimated have positive budgets, and thus were accreting in 1994, in 2005 almost all reefs were in an erosional (negative budget) state. By 2014, 7 reefs had recovered to positive carbonate budgets. However, where macroalgae was previously found, and was now dominant, carbonate budgets remained negative. Boosted regression tree models indicated that reefs with higher massive coral, low macroalgae cover and low biomass of excavating parrotfishes in 1994 were more likely to recover by 2014. However, in 2016 a second bleaching-induced mass-mortality of corals occurred. If this mortality is similar to 1998, we predict that six of eight reefs that had positive budgets in 2014 would recover to positive budgets again by 2030. However, no currently negative budget reef would recover. Our results highlighted that coral reef framework maintenance potential should not be assumed from ecological state, and that management has a role to play in promoting resilient carbonate accretion on coral reefs

Caribbean-wide decline in carbonate production threatens coral reef growth

This a post-print, author-produced version of an article accepted for publication in Nature Communications. Copyright © 2013 Nature Publishing Group . The definitive version is available at http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2409.htmlGlobal-scale deteriorations in coral reef health have caused major shifts in species composition. One projected consequence is a lowering of reef carbonate production rates, potentially impairing reef growth, compromising ecosystem functionality and ultimately leading to net reef erosion. Here, using measures of gross and net carbonate production and erosion from 19 Caribbean reefs, we show that contemporary carbonate production rates are now substantially below historical (mid- to late-Holocene) values. On average, current production rates are reduced by at least 50%, and 37% of surveyed sites were net erosional. Calculated accretion rates (mm year(-1)) for shallow fore-reef habitats are also close to an order of magnitude lower than Holocene averages. A live coral cover threshold of ~10% appears critical to maintaining positive production states. Below this ecological threshold carbonate budgets typically become net negative and threaten reef accretion. Collectively, these data suggest that recent ecological declines are now suppressing Caribbean reef growth potential

Rhodolith Beds Are Major CaCO3 Bio-Factories in the Tropical South West Atlantic

Rhodoliths are nodules of non-geniculate coralline algae that occur in shallow waters (<150 m depth) subjected to episodic disturbance. Rhodolith beds stand with kelp beds, seagrass meadows, and coralline algal reefs as one of the world's four largest macrophyte-dominated benthic communities. Geographic distribution of rhodolith beds is discontinuous, with large concentrations off Japan, Australia and the Gulf of California, as well as in the Mediterranean, North Atlantic, eastern Caribbean and Brazil. Although there are major gaps in terms of seabed habitat mapping, the largest rhodolith beds are purported to occur off Brazil, where these communities are recorded across a wide latitudinal range (2°N - 27°S). To quantify their extent, we carried out an inter-reefal seabed habitat survey on the Abrolhos Shelf (16°50′ - 19°45′S) off eastern Brazil, and confirmed the most expansive and contiguous rhodolith bed in the world, covering about 20,900 km2. Distribution, extent, composition and structure of this bed were assessed with side scan sonar, remotely operated vehicles, and SCUBA. The mean rate of CaCO3 production was estimated from in situ growth assays at 1.07 kg m−2 yr−1, with a total production rate of 0.025 Gt yr−1, comparable to those of the world's largest biogenic CaCO3 deposits. These gigantic rhodolith beds, of areal extent equivalent to the Great Barrier Reef, Australia, are a critical, yet poorly understood component of the tropical South Atlantic Ocean. Based on the relatively high vulnerability of coralline algae to ocean acidification, these beds are likely to experience a profound restructuring in the coming decades

Palaeozoic stromatoporoid diagenesis: a synthesis

Supplementary Information: the online version contains supplementary material available at https://doi.org/10.1007/s10347-021-00628-x.Nuffield Foundation; Deutsche Forschungsgemeinschaft (grant no JA 2718/3-1);Nuffield Foundation; Deutsche Forschungsgemeinschaft (grant no JA 2718/3-1)

Growth forms and palaeoenvironmental interpretation of stromatoporoids in a Middle Devonian reef, southern Morocco (west Sahara)

The article can be obtained from the link below.Growth forms of well-preserved stromatoporoids, including genera Actinostroma, Stachyodes, and Stromatopora, are described for the first time from the Devonian Sabkhat Lafayrina reef complex of southern Morocco (west Sahara), one of the best exposed Middle-Devonian stromatoporoid-dominated fossil reefs. Three facies types representing the well illuminated fore-reef, reef-core and transition to back-reef facies display the distribution and growth of stromatoporoids in a high latitude setting at 40–50° south of the palaeoequator. Stromatoporoids are largely in growth position and reflect the well-preserved reef architecture. Although outcrops are low topography, the reef's prominent profile is indicated by presence of spur and groove form and a clearly defined reef margin. Stromatoporoids are mostly laminar and domical forms, with little evidence of ragged margins, and indicate normal turbulence shallow waters, with low sediment deposition.This work was partly funded by the Paul Ungerer Stiftung