Processes of calcification and sedimentation of the tropical marine green macro-alga genus Halimeda and effects of ocean acidification on its calcareous microstructure

Calcifying green macro-algae of the genus Halimeda are common organisms in tropical shallow marine environments. These ramified benthic algae grow by forming successional segments that exhibit an internal skeletal microstructure of the calcium carbonate polymorph aragonite. The calcareous segments become part of the sediment after death. As macro-algae of the genus Halimeda often occur in large quantities and are able to build extensive bioherms, dropped segments from these algae are considered as an important source for carbonate sediments in many shallow water and coral reef environments. Thus detailed knowledge on the calcification of the alga is crucial for estimations on the carbonate budget and sediment dynamics of tropical settings, as this process directly determines the sediment contribution of Halimeda. Furthermore, it is a prerequisite when effects on the formation of its calcium carbonate microstructure under ocean acidification have to be assessed. In this study, internal microstructural features of segments from the species Halimeda opuntia, a cosmopolitan species of the genus Halimeda, are investigated using scanning electron microscopy. The first aim is to study the alga´s calcified microstructure in detail in order to be able to explain the formation of skeletal features in relation to known physiological processes of the alga. Thereby, lifetime primary cementation is identified to be an important process for calcium carbonate deposition in the algal segment. The second aim is to determine potential alterations in the formation of these microstructural features due to elevated seawater pCO2 and the corresponding shift in seawater carbon chemistry. Laboratory experiments show that especially the process of lifetime primary cementation is affected by elevated seawater pCO2. Based on the microstructural investigations, a theoretical model is developed on how physiological daytime and nighttime processes influence the formation of skeletal features in the genus Halimeda. The model also illustrates the basic relationships between changes in the seawater carbon chemistry and changes observed in the skeletal microstructure of the segment under elevated seawater pCO2. As a third objective, segments from living Halimeda and segments recovered from surface sediments are studied and compared using scanning electron microscopy to investigate the occurrence of post-sedimentary processes that alter the original skeletal microstructure. By the investigation of thin-sections of numerous sedimentary segments, species-specificity of Halimeda sediments is observed. Segments found in sediments predominantly originate from heavily calcified lithophytic species of the genus Halimeda, such as from the lineage Opuntia. Microstructural investigations also reveal that the process of lifetime primary cementation strongly determines the preservation potential of Halimeda segments in the sediment. Thus ocean acidification is assumed to impair both the alga´s environmental competitiveness (e.g., grazing protection, pathogen defense, structural integrity) and its carbonate sediment contribution to tropical coastlines and reef islands

Rapid bioerosion in a tropical upwelling coral reef

Coral reefs persist in an accretion-erosion balance, which is critical for understanding the natural variability of sediment production, reef accretion, and their effects on the carbonate budget. Bioerosion (i.e. biodegradation of substrate) and encrustation (i.e. calcified overgrowth on substrate) influence the carbonate budget and the ecological functions of coral reefs, by substrate formation/consolidation/erosion, food availability and nutrient cycling. This study investigates settlement succession and carbonate budget change by bioeroding and encrusting calcifying organisms on experimentally deployed coral substrates (skeletal fragments of Stylophora pistillata branches). The substrates were deployed in a marginal coral reef located in the Gulf of Papagayo (Costa Rica, Eastern Tropical Pacific) for four months during the northern winter upwelling period (December 2013 to March 2014), and consecutively sampled after each month. Due to the upwelling environmental conditions within the Eastern Tropical Pacific, this region serves as a natural laboratory to study ecological processes such as bioerosion, which may reflect climate change scenarios. Time-series analyses showed a rapid settlement of bioeroders, particularly of lithophagine bivalves of the genus Lithophaga/ Leiosolenus (Dillwyn, 1817), within the first two months of exposure. The observed enhanced calcium carbonate loss of coral substrate (>30%) may influence seawater carbon chemistry. This is evident by measurements of an elevated seawater pH (>8.2) and aragonite saturation state (Ωarag >3) at Matapalo Reef during the upwelling period, when compared to a previous upwelling event observed at a nearby site in distance to a coral reef (Marina Papagayo). Due to the resulting local carbonate buffer effect of the seawater, an influx of atmospheric CO2 into reef waters was observed. Substrates showed no secondary cements in thin-section analyses, despite constant seawater carbonate oversaturation (Ωarag >2.8) during the field experiment. Micro Computerized Tomography (μCT) scans and microcast-embeddings of the substrates revealed that the carbonate loss was primarily due to internal macrobioerosion and an increase in microbioerosion. This study emphasizes the interconnected effects of upwelling and carbonate bioerosion on the reef carbonate budget and the ecological turnovers of carbonate producers in tropical coral reefs under environmental change.Sistema Nacional de Áreas de Conservación/[028-2013-SINAC]/SINAC/Costa RicaSistema Nacional de Áreas de Conservación/[72-2013-SINAC]/SINAC/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Kalzifizierungs- und Sedimentationsprozesse der tropischen marinen Grünalge der Gattung Halimeda und Auswirkungen der Ozeanversauerung auf ihre kalkige Mikrostruktur

Calcifying green macro-algae of the genus Halimeda are common organisms in tropical shallow marine environments. These ramified benthic algae grow by forming successional segments that exhibit an internal skeletal microstructure of the calcium carbonate polymorph aragonite. The calcareous segments become part of the sediment after death. As macro-algae of the genus Halimeda often occur in large quantities and are able to build extensive bioherms, dropped segments from these algae are considered as an important source for carbonate sediments in many shallow water and coral reef environments. Thus detailed knowledge on the calcification of the alga is crucial for estimations on the carbonate budget and sediment dynamics of tropical settings, as this process directly determines the sediment contribution of Halimeda. Furthermore, it is a prerequisite when effects on the formation of its calcium carbonate microstructure under ocean acidification have to be assessed. In this study, internal microstructural features of segments from the species Halimeda opuntia, a cosmopolitan species of the genus Halimeda, are investigated using scanning electron microscopy. The first aim is to study the alga´s calcified microstructure in detail in order to be able to explain the formation of skeletal features in relation to known physiological processes of the alga. Thereby, lifetime primary cementation is identified to be an important process for calcium carbonate deposition in the algal segment. The second aim is to determine potential alterations in the formation of these microstructural features due to elevated seawater pCO2 and the corresponding shift in seawater carbon chemistry. Laboratory experiments show that especially the process of lifetime primary cementation is affected by elevated seawater pCO2. Based on the microstructural investigations, a theoretical model is developed on how physiological daytime and nighttime processes influence the formation of skeletal features in the genus Halimeda. The model also illustrates the basic relationships between changes in the seawater carbon chemistry and changes observed in the skeletal microstructure of the segment under elevated seawater pCO2. As a third objective, segments from living Halimeda and segments recovered from surface sediments are studied and compared using scanning electron microscopy to investigate the occurrence of post-sedimentary processes that alter the original skeletal microstructure. By the investigation of thin-sections of numerous sedimentary segments, species-specificity of Halimeda sediments is observed. Segments found in sediments predominantly originate from heavily calcified lithophytic species of the genus Halimeda, such as from the lineage Opuntia. Microstructural investigations also reveal that the process of lifetime primary cementation strongly determines the preservation potential of Halimeda segments in the sediment. Thus ocean acidification is assumed to impair both the alga´s environmental competitiveness (e.g., grazing protection, pathogen defense, structural integrity) and its carbonate sediment contribution to tropical coastlines and reef islands

Sediment Composition and Facies of Coral Reef Islands in the Spermonde Archipelago, Indonesia

Sedimentological and geomorphological characteristics of coral reef islands are strongly related to past and recent boundary conditions such as the hydrodynamic regime, wind directions, sea-level fluctuations, and the ecological footprint of the surrounding reef complexes. Alterations in the physical, chemical, and biological boundary controls may affect the stability of reef islands. Additionally, these factors are of importance in the context of future climate change. Such alterations through time may well be documented within the sedimentary record of reef islands and a better knowledge on its effects could help to improve our understanding of island responses to future changes of the status quo. However, detailed studies on the sedimentology and geomorphology of reef islands from southwest Sulawesi, Indonesia, are still rare. Here we report on the sedimentary composition and related facies zonation of four uninhabited coral reef islands in the Spermonde Archipelago. Sediment samples from onshore- and reef-flat environments were analyzed in regard to their grain size, component assemblages and facies distribution. Our results show that the analyzed island sediments are characterized by medium- to coarse-grained sand fractions and are well to poorly sorted. Across all islands examined, the surface sediment is predominately composed of materials identified as scleractinian coral and coralline red algae fragments, with minor additions from bivalves, gastropods and foraminifers. Importantly, statistical analyses of the variations in the percentage of these components allow for a clear sedimentary distinction of the four study sites into three outer shelf islands, situated closer to the open marine Makassar Strait, and one inner shelf island. On the inner shelf island, additional subsurface sedimentological analyses indicate a potential shift in major sediment contributors through time, preserved as coral-dominated accumulations within the subsurface samples, and coralline red algae-dominated deposits on top. These findings highlight the practical use of detailed sedimentological studies for the reconstruction of environmental changes in the Spermonde Archipelago

Shallow‐marine carbonate cementation in Holocene segments of the calcifying green alga Halimeda

Early‐diagenetic cementation of tropical carbonates results from the combination of numerous physico‐chemical and biological processes. In the marine phreatic environment it represents an essential mechanism for the development and stabilization of carbonate platforms. However, diagenetic cements that developed early in the marine phreatic environment are likely to become obliterated during later stages of meteoric or burial diagenesis. When lithified sediment samples are studied, this complicates the recognition of processes involved in early cementation, and their geological implications. In this contribution, a petrographic microfacies analysis of Holocene Halimeda segments collected on a coral island in the Spermonde Archipelago, Indonesia, is presented. Through electron microscopical analyses of polished samples, this study shows that segments are characterized by intragranular cementation of fibrous aragonite, equant High‐Mg calcite (3.9 to 7.2 Mol% Mg), bladed Low‐Mg calcite (0.4 to 1.0 Mol% Mg) and mini‐micritic Low‐Mg calcite (3.2 to 3.3 Mol% Mg). The co‐existence and consecutive development of fibrous aragonite and equant High‐Mg calcite results initially from the flow of oversaturated seawater along the aragonite template of the Halimeda skeleton, followed by an adjustment of cement mineralogy towards High‐Mg calcite as a result of reduced permeability and fluid flow rates in the pores. Growth of bladed Low‐Mg calcite cements on top of etched substrates of equant High‐Mg calcite is explained by shifts in pore water pH and alkalinity through microbial sulphate reduction. Microbial activity appears to be the main trigger for the precipitation of mini‐micritic Low‐Mg calcite as well, based on the presumable detection of an extracellular polymeric matrix during an early stage of mini‐micrite Low‐Mg calcite cement precipitation. Radiocarbon analyses of five Halimeda segments furthermore indicate that virtually complete intragranular cementation in the marine phreatic environment with thermodynamically/kinetically controlled aragonite and High‐Mg calcite takes place in about 100 years. Collectively, this study shows that early‐diagenetic cements are highly diverse and provides new quantitative constraints on the rate of diagenetic cementation in tropical carbonate factories.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659https://doi.pangaea.de/10.1594/PANGAEA.92398

Fluctuating sea-level and reversing Monsoon winds drive Holocene lagoon infill in Southeast Asia

Abstract Many lagoons surrounded by reefs are partially or completely infilled with reef-derived detrital carbonate sediment. Sediment deposits in such restricted environments are archives of prevailing environmental conditions during lagoon infill. For Indonesia, no paleoenvironmental reconstructions based on Holocene lagoon sediments exist. Here we analyze the sedimentary record obtained from five percussion cores penetrating 10 m into the unconsolidated subsurface of a reef island in the Spermonde Archipelago, Indonesia. The combined compositional, textural and chronostratigraphic analyses reveal that the sedimentary infill of the lagoon underlying the island, starting 6900 years cal BP, was interrupted between 5800 and 4400 years cal BP, when sea level was ~ 0.5 m higher than at present, and monsoon intensity was lower. After the intensity of the monsoons increased to modern levels, and sea level dropped to its present position, lagoonal sedimentation was re-initiated and created the foundation for an island that built up since 3000 years cal BP. Our study provides the first geological evidence for the strong sensitivity of detrital carbonate systems in Indonesia to fluctuations in sea level and dominant wind direction. It thus sheds light on how changing environmental conditions in the context of global warming could affect the morphological development of reef systems, and thereby also habitable coastal areas

Some Oceanographic Features of Pelabuhanratu Bay, West Java, Indonesia

Pelabuhanratu Bay plays a big role for the flow of nutrients from the land to the sea of Sothern-Java. This study was conducted in Pelabuhanratu Bay, Sukabumi, West Java, in March 2012. The aim of this study is to measure the oceanographic parameters (physical and chemical) of Pelabuhanratu Bay i.e. tides, waves, current, temperature, salinity, depth, density, dissolved oxygen (DO), total suspended solids (TSS), turbidity, pH and nutrients. The bay directly faces the Indian Ocean, during the surveyed we found mean angle of wave refraction was about ~4.3° ± 1.5°, with left side wind direction. Overall the current direction has an irregular trend. The tidal cycle of the bay is diurnal, with the temperature decrease into the deep layer. Only the surface exhibits a slightly lower salinity compared to the rest of the water column. Some parameters (i.e. TSS, DO) found in high concentration but declining following the depth. Other chemical concentrations (e.g. ortho-phosphate, silicate) also showed diminished after 10-15 depth measurement

Genetic and morphological divergence in the warm-water planktonic foraminifera genus <i>Globigerinoides</i>

The planktonic foraminifera genus Globigerinoides provides a prime example of a species-rich genus in which genetic and morphological divergence are uncorrelated. To shed light on the evolutionary processes that lead to the present-day diversity of Globigerinoides, we investigated the genetic, ecological and morphological divergence of its constituent species. We assembled a global collection of single-cell barcode sequences and show that the genus consists of eight distinct genetic types organized in five extant morphospecies. Based on morphological evidence, we reassign the species Globoturborotalita tenella to Globigerinoides and amend Globigerinoides ruber by formally proposing two new subspecies, G. ruber albus n.subsp. and G. ruber ruber in order to express their subspecies level distinction and to replace the informal G. ruber “white” and G. ruber “pink”, respectively. The genetic types within G. ruber and Globigerinoides elongatus show a combination of endemism and coexistence, with little evidence for ecological differentiation. CT-scanning and ontogeny analysis reveal that the diagnostic differences in adult morphologies could be explained by alterations of the ontogenetic trajectories towards final (reproductive) size. This indicates that heterochrony may have caused the observed decoupling between genetic and morphological diversification within the genus. We find little evidence for environmental forcing of either the genetic or the morphological diversification, which allude to biotic interactions such as symbiosis, as the driver of speciation in Globigerinoides