High zinc exposure leads to reduced dimethylsulfoniopropionate (DMSP) levels in both the host and endosymbionts of the reef-building coral Acropora aspera

Zinc speciation promotes distinct effects on dinoflagellate growth and coral trypsin-like enzyme activity

Zinc is an essential metal to living organisms, including corals and their symbiotic microalgae (Symbiodiniaceae). Both Zn(II) deprivation and overload are capable of leading to dysfunctional metabolism, coral bleaching, and even organism death. The present work investigated the effects of chemically defined Zn species (free Zn, ZnO nanoparticles, and the complexes Zn-histidinate and Zn-EDTA) over the growth of the dinoflagellates Symbiodinium microadriaticum, Breviolum minutum, and Effrenium voratum, and on the trypsin-like proteolytic activity of the hydrocoral Millepora alcicornis. B. minutum was the most sensitive strain to any form of added Zn. For the other strains, the complex [Zn(His)2] better translated metal load into growth. This complex was the only tested compound that did not interfere with the trypsin-like activity of Millepora alcicornis extracts. Also, histidine was able to recover the activity of the enzyme inhibited by zinc. [Zn(His)2] is a potential biocarrier of zinc for microalgae or coral cultivation. These findings suggest that the control of chemical speciation of an essential metal could lead to useful compounds that assist autotrophy, while not affecting heterotrophy, in the coral holobiont.

Influence of global warming and industrialization on coral reefs: A 600-year record of elemental changes in the Eastern Red Sea

The Red Sea has been recognized as a coral reef refugia, but it is vulnerable to warming and pollution. Here we investigated the spatial and temporal trends of 15 element concentrations in 9 coral reef sediment cores (aged from the 1460s to the 1980s AD) to study the influence of global warming and industrialization on the Eastern Red Sea coral reefs. We found Na, Ca, Cr, Fe, Co, Ni, and Sr concentrations were higher in the northern Red Sea (i.e., Yanbu), whereas Mg, P, S, Mn, and Cd concentrations were higher in the southern Red Sea (i.e., Thuwal & Al Lith) reef sediments. In the central (i.e., Thuwal) to southern (i.e., Al Lith) Red Sea, the study revealed diverse temporal trends in element concentrations. However, both reef sedimentation rates (-36.4 % and -80.5 %, respectively) and elemental accumulation rates (-49.4 % for Cd to -12.2 % for Zn in Thuwal, and -86.2 % for Co to -61.4 % for Cu in Al Lith) exhibited a declining pattern over time, possibly attributed to warming-induced thermal bleaching. In the central to northern Red Sea (i.e., Yanbu), the severity of thermal bleaching is low, while the reef sedimentation rates (187 %), element concentrations (6.7 % for S to 764 % for Co; except Na, Mg, Ca, Sr, and Cd), and all elemental accumulation rates (190 % for Mg to 2697 % for Co) exponentially increased from the 1970s, probably due the rapid industrialization in Yanbu. Our study also observed increased trace metal concentrations (e.g., Cu, Zn, and Ni) in the Thuwal and Al Lith coral reefs with severe bleaching histories, consistent with previous reports that trace metals might result in decreased resistance of corals to thermal stress under warming scenarios. Our study points to the urgent need to reduce the local discharge of trace metal pollutants to protect this biodiversity hotspot.

Atmospheric Trace Metal Deposition near the Great Barrier Reef, Australia

Aerosols deposited into the Great Barrier Reef (GBR) contain iron (Fe) and other trace metals, which may act as micronutrients or as toxins to this sensitive marine ecosystem. In this paper, we quantified the atmospheric deposition of Fe and investigated aerosol sources in Mission Beach (Queensland) next to the GBR. Leaching experiments were applied to distinguish pools of Fe with regard to its solubility. The labile Fe concentration in aerosols was 2.3–10.6 ng m−3, which is equivalent to 4.9%–11.4% of total Fe and was linked to combustion and biomass burning processes, while total Fe was dominated by crustal sources. A one-day precipitation event provided more soluble iron than the average dry deposition flux, 0.165 and 0.143 μmol m−2 day−1, respectively. Scanning Electron Microscopy indicated that alumina-silicates were the main carriers of total Fe and samples affected by combustion emissions were accompanied by regular round-shaped carbonaceous particulates. Collected aerosols contained significant amounts of Cd, Co, Cu, Mo, Mn, Pb, V, and Zn, which were mostly (47.5%–96.7%) in the labile form. In this study, we provide the first field data on the atmospheric delivery of Fe and other trace metals to the GBR and propose that this is an important delivery mechanism to this region.