Madrepora oculata forms large frameworks in hypoxic waters off Angola (SE Atlantic).

This study aims to map the occurrence and distribution of Madrepora oculata and to quantify density and colony sizes across recently discovered coral mounds off Angola. Despite the fact that the Angolan populations of M. oculata thrive under extreme hypoxic conditions within the local oxygen minimum zone, they reveal colonies with remarkable heights of up to 1250 mm-which are the tallest colonies ever recorded for this species-and average densities of 0.53 ± 0.37 (SD) colonies m-2. This is particularly noteworthy as these values are comparable to those documented in areas without any oxygen constraints. The results of this study show that the distribution pattern documented for M. oculata appear to be linked to the specific regional environmental conditions off Angola, which have been recorded in the direct vicinity of the thriving coral community. Additionally, an estimated average colony age of 95 ± 76 (SD) years (total estimated age range: 16-369 years) indicates relatively old M. oculata populations colonizing the Angolan coral mounds. Finally, the characteristics of the Angolan populations are benchmarked and discussed in the light of the existing knowledge on M. oculata gained from the North Atlantic and Mediterranean Sea.

Biomimetic mineral self-organization from silica-rich spring waters.

Purely inorganic reactions of silica, metal carbonates, and metal hydroxides can produce self-organized complex structures that mimic the texture of biominerals, the morphology of primitive organisms, and that catalyze prebiotic reactions. To date, these fascinating structures have only been synthesized using model solutions. We report that mineral self-assembly can be also obtained from natural alkaline silica-rich water deriving from serpentinization. Specifically, we demonstrate three main types of mineral self-assembly: (i) nanocrystalline biomorphs of barium carbonate and silica, (ii) mesocrystals and crystal aggregates of calcium carbonate with complex biomimetic textures, and (iii) osmosis-driven metal silicate hydrate membranes that form compartmentalized, hollow structures. Our results suggest that silica-induced mineral self-assembly could have been a common phenomenon in alkaline environments of early Earth and Earth-like planets.