The Hatillo Limestone, Pueblo Viejo district, Dominican Republic: Marginal reef or impermeable cap?

The Hatillo Limestone and the underlying Los Ranchos Formation are exposed over an east-west distance of 100 km in the eastern Dominican Republic. The lowermost portion of the Hatillo Limestone in the Pueblo Viejo district contains a Late Lower Albian fossil assemblage including corals and rudist bivalves indicative of a near-shore reef environment. Diamond drilling in the Pueblo Viejo district and exposures in the open pits show that the Hatillo Limestone conformably overlies the Early Cretaceous Los Ranchos Formation. Volcanogenic massive sulfide beds, exposed in the Moore pit, provide evidence for an Early Cretaceous, syn-mineralization paleosurface. Altered and mineralized clasts in the epiclastic, sedimentary host-rock section at the Pueblo Viejo mine indicate that the ore deposits were open to erosion during hydrothermal alteration and mineralization. The Hatillo Limestone did not overlie the ore deposits during the mineralizing event and, consequently, could not have acted as an impermeable cap to ascending hydrothermal fluids. Intra-oceanic island arc volcanism (Los Ranchos Formation) overlapped at the Aptian–Albian boundary (112 Ma) with a marginal fringing reef (basal Hatillo Limestone). The marginal reef gradually gave way to deeper-water facies as Hatillo Limestone deposition progressed through the middle Albian. Low-angle reverse faulting, penetrative deformation, and metamorphic recrystallization affected the Hatillo Limestone as well as the Los Ranchos and Maimón formations during the Late Cretaceous. Deformation intensity and metamorphic grade progressed from incipient metamorphism in the Pueblo Viejo district to schists in the Maimón Formation to amphibolite near a faulted contact with the Loma Caribe peridotite.

Depositional Architecture and Facies of a Complete Reef Complex Succession: A Case Study of the Permian Jiantianba Reefs, Western Hubei, South China

The Upper Permian Changhsingian Jiantissanba reef complex is a well-known platform marginal reef, located in the western Hubei Province, China. Based on field observations and lithological analysis of the entire exposed reef complex, 12 reef facies have been distinguished according to their sedimentary components and growth fabrics. Each of the lithofacies is associated with a specific marine environment. Vertically traceable stratal patterns reveal 4 types of the lithologic associations of the Jiantianba reef: (1) heterozoan reef core association: developed in the deep marginal platform with muddy composition; (2) photozoan reef core association developed within the photic zone; (3) tide-controlled reef crest association with tidal-dominated characteristic of lithofacies in the shallow water; and (4) reef-bank association dominated by bioclastic components. The entire reef complex shows a complete reef succession revealing a function of the wave-resistant and morphological units. This study displays a complete sedimentary succession of Jiantianba reef, which provides a more accurate and comprehensive description of the reef lithofacies and a better understanding of the structure and composition of organic reefs.

Health assessment of a marginal reef site in Southeastern Brazil: integrating ecological indicators and anthropogenic pressures to guide management decisions

Coastal marine ecosystems provide important services yet have been under increased local and global anthropogenic pressures worldwide. Hence, health assessment studies are necessary to guide management actions ensuring biodiversity conservation and the maintenance of ecosystem services. We applied a protocol previously developed by our group for the Food and Agriculture Organization (FAO) to assess the health of a marginal reef ecosystem at Armação dos Búzios, Southeastern Brazil - a touristic destination that has experienced a rapid urbanization since the last decades. The protocol evaluates temporal trends in Ecological Indicators (diversity, singularity and species substitution) and an Environmental Pressure Index. Quantitative benthic and pressure data obtained for 11 sites in 2000/2001 were used as the baseline and compared to data generated in 2016/2017. Most sites showed a decreased singularity and increased diversity over time. This suggests sites are becoming more homogenous in terms of species composition. Despite some variability among sites, the Environmental Pressure Index exhibited almost the same pattern as ten years ago with the same sites ranked as the least and the most subjected to anthropogenic pressures. Differences among sites were mainly driven by urban development. This study represents an important tool for the ecosystem management of the area.

Health assessment of a marginal reef site in Southeastern Brazil: integrating ecological indicators and anthropogenic pressures to guide management decisions

Coastal marine ecosystems provide important services yet have been under increased local and global anthropogenic pressures worldwide. Hence, health assessment studies are necessary to guide management actions ensuring biodiversity conservation and the maintenance of ecosystem services. We applied a protocol previously developed by our group for the Food and Agriculture Organization (FAO) to assess the health of a marginal reef ecosystem at Armação dos Búzios, Southeastern Brazil - a touristic destination that has experienced a rapid urbanization since the last decades. The protocol evaluates temporal trends in Ecological Indicators (diversity, singularity and species substitution) and an Environmental Pressure Index. Quantitative benthic and pressure data obtained for 11 sites in 2000/2001 were used as the baseline and compared to data generated in 2016/2017. Most sites showed a decreased singularity and increased diversity over time. This suggests sites are becoming more homogenous in terms of species composition. Despite some variability among sites, the Environmental Pressure Index exhibited almost the same pattern as ten years ago with the same sites ranked as the least and the most subjected to anthropogenic pressures. Differences among sites were mainly driven by urban development. This study represents an important tool for the ecosystem management of the area.

Assessing health status of corals at a tropical marginal reef site through bleaching and decadal change in population parameters

Scleractinian corals are key organisms in structuring reef habitats and coral cover is being lost due to local and global stressors caused and/or exacerbated by anthropogenic activities. Despite being hardly touched upon, studies of size-frequency distributions serve as snapshots of coral populations’ status and provide information on population decline or growth over time. In our study we have intermittently monitored two Brazilian scleractinians species, the endemic Mussismilia hispida and Siderastrea stellata, since 2000 in an important coral marginal reef site at Armação dos Búzios, Rio de Janeiro, Brazil. We measured length, width and arc of all colonies from both species found across transects at eleven sites. In total, over 5,000 colonies have been measured over the past 17 years. Although the frequency of small and medium colonies remained relatively constant, we observed a clear decline in the frequency of larger colonies (> 30 cm) for both species, particularly the most common S. stellata. Additionally, we have been monitoring colonies for bleaching in five of these sites throughout 2017 to assess health status. The relationship between observed bleaching prevalence/intensity and environmental variables (temperature, light availability and sedimentation) may elucidate how changes in local conditions influence coral health.

Assessing health status of corals at a tropical marginal reef site through bleaching and decadal change in population parameters

Scleractinian corals are key organisms in structuring reef habitats and coral cover is being lost due to local and global stressors caused and/or exacerbated by anthropogenic activities. Despite being hardly touched upon, studies of size-frequency distributions serve as snapshots of coral populations’ status and provide information on population decline or growth over time. In our study we have intermittently monitored two Brazilian scleractinians species, the endemic Mussismilia hispida and Siderastrea stellata, since 2000 in an important coral marginal reef site at Armação dos Búzios, Rio de Janeiro, Brazil. We measured length, width and arc of all colonies from both species found across transects at eleven sites. In total, over 5,000 colonies have been measured over the past 17 years. Although the frequency of small and medium colonies remained relatively constant, we observed a clear decline in the frequency of larger colonies (> 30 cm) for both species, particularly the most common S. stellata. Additionally, we have been monitoring colonies for bleaching in five of these sites throughout 2017 to assess health status. The relationship between observed bleaching prevalence/intensity and environmental variables (temperature, light availability and sedimentation) may elucidate how changes in local conditions influence coral health.