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Rising sea surface temperatures and extreme heat waves are affecting symbiont-bearing tropical calcifiers such as corals and Large Benthic Foraminifera (LBF). In many ecosystems, parallel to warming, global change unleashes a host of additional changes to the marine environment, and the combined effect of such multiple stressors may be far greater than those of temperature alone. One such additional stressor, positively correlated to temperature in evaporation-dominated shallow-water settings is rising salinity. Here we used laboratory culture experiments to evaluate the combined thermohaline tolerance of one of the most common LBF species and carbonate producer, Amphistegina lobifera. The experiments were done under ambient (39 psu) and modified (30, 45, 50 psu) salinities and at optimum (25 °C) and warm temperatures (32 °C). Calcification of the A. lobifera holobiont was evaluated by measuring alkalinity loss in the culturing seawater, as an indication of carbonate ion uptake. The vitality of the symbionts was determined by monitoring pigment loss of the holobiont and their photosynthetic performances by measuring dissolved oxygen. We further evaluated the growth of Peneroplis (P. pertusus and P. planatus), a Rhodophyta bearing LBF, which is known to tolerate high temperatures, under elevated salinities. The results show that the A. lobifera holobiont exhibits optimal performance at 39 psu and 25 °C, and its growth is significantly reduced upon exposure to 30, 45, 50 psu and under all 32 °C treatments. Salinity and temperature exhibit a significant interaction, with synergic effects observed in most treatments. Our results confirm that Peneroplis has a higher tolerance to elevated temperature and salinity compared to A. lobifera, implying that a further increase of salinity and temperatures may result in a regime shift from Amphistegina- to Peneroplis-dominated assemblages., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The accelerated release of heavy metals into the coastal environments due to increasing anthropogenic activities poses a severe threat to local marine ecosystems and food chains. Although some heavy metals are essential nutrients for plants and animals, higher concentrations can be toxic and hazardous. To mitigate this threat, developing quantifiable proxies for monitoring heavy metal concentrations in near-shore marine environments is essential. Here, we describe culture experiments to quantify uptake of some heavy metals using live juvenile specimens of the large benthic foraminifera (LBF) Amphisorus hemprichii collected from the subtropical waters of Rottnest Island located ~20 km offshore Perth, South West Australia. The uptake of Mn, Ni, Cd, and Pb in the newly precipitated chambers of Amphisorus hemprichii in the laboratory was characterized using the micro-analytical technique, laser ablation inductively coupled plasma mass spectrometry. We found no significant increase in Mn, Ni, Cd, and Pb incorporation in the tests of Amphisorus hemprichii with increasing temperature and light intensities. Importantly, we found that changes in the concentrations of Mn, Ni, and Cd in the A. hemprichii tests are directly proportional to those in the culture solution over a wide range of concentrations. The calculated partition coefficients for Mn, Ni, and Cd from our culture experiments are 1.3±0.2, 0.3±0.04, 2.6±0.3, respectively. These multi-element calibration studies now enable A. hemprichii to be utilized as a naturally occurring bio-archive to quantitatively monitor the anthropogenic pollution of Mn, Ni, and Cd in coastal waters., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Anthropogenic lead (Pb) contamination resulting from the rapid growth of industrialization in coastal environments poses significant challenges. In this study, we report a novel approach utilising the large benthic foraminifera Amphisorus hemprichii as a biogeochemical archive for monitoring Pb pollution in tropical to warm-temperate coastal waters. Live juvenile specimens of A. hemprichii were cultured in the laboratory for 16 weeks with a range of seawater Pb concentrations. Lead uptake in both newly grown and pre-existing chambers of individual specimens was characterised using the microanalytical technique, Laser ablation-ICP mass spectrometry. We found that Pb concentration in the tests of cultured foraminifera in the laboratory is proportional to seawater [Pb] with the lead partition coefficient (K D Pb ) of 8.37 ± 0.3. This calibration together with a new biomineralisation model now enables A. hemprichii to be utilised as a naturally occurring bio-archive to quantitatively monitor anthropogenic Pb pollution in coastal waters., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Symbiosis is a phenomenon that allows organisms to colonise a wide range of environments and occupy a variety of ecological niches in marine environments. Large benthic foraminifera (LBF) are crucial marine calcifiers that rely on photo-endosymbionts for growth and calcification, yet the influence of environmental conditions in shaping their interactions with prokaryotic and eukaryotic associates is poorly known., Results: Here, we used next-generation sequencing to identify eukaryotic photosynthesizing and prokaryotic microbes associated with the common LBF Amphistegina lobifera across a physio-chemical gradient on the Great Barrier Reef (GBR). We collected samples from three reef sites located in the inner-, mid- and outer-shelf regions of the northern section of the GBR. Results showed the consistent presence of Bacillaryophyta as the main eukaryotic taxa associated with A. lobifera across all reef sites analysed; however, the abundance and the diversity of prokaryotic organisms varied among reef sites. Inner-shelf specimens showed the highest diversity of prokaryote associates, with a total of 231 genotypes in their core microbiome. A total of 30 taxa were identified in the core microbiome across all reef sites. Within these taxa, Proteobacteria was the most abundant bacteria present. The presence of groups such as Actinobacteria was significantly correlated with inner-shelf populations, whereas the abundance of Bacteroidetes and Firmicutes was associated with A. lobifera collected from mid- and outer-shelf reef sites., Conclusions: We found that benthic foraminifera form stable and persistent symbiosis with eukaryotic partners, but flexible and site-specific associations with prokaryotic microbes that likely influence the ecological success of these crucial calcifying organisms on the GBR.

Large benthic foraminifera are significant contributors to sediment formation on coral reefs, yet they are vulnerable to ocean acidification. Here, we assessed the biochemical and morphological impacts of acidification on the calcification of Amphistegina lessonii and Marginopora vertebralis exposed to different pH conditions. We measured growth rates (surface area and buoyant weight) and Ca-ATPase and Mg-ATPase activities and calculated shell density using micro-computer tomography images. In A. lessonii, we detected a significant decrease in buoyant weight, a reduction in the density of inner skeletal chambers, and an increase of Ca-ATPase and Mg-ATPase activities at pH 7.6 when compared with ambient conditions of pH 8.1. By contrast, M. vertebralis showed an inhibition in Mg-ATPase activity under lowered pH, with growth rate and skeletal density remaining constant. While M. vertebralis is considered to be more sensitive than A. lessonii owing to its high-Mg-calcite skeleton, it appears to be less affected by changes in pH, based on the parameters assessed in this study. We suggest difference in biochemical pathways of calcification as the main factor influencing response to changes in pH levels, and that A. lessonii and M. vertebralis have the ability to regulate biochemical functions to cope with short-term increases in acidity., (© 2015 The Author(s) Published by the Royal Society. All rights reserved.)

The Eocene Large Benthic Foraminiferal limestones of the Tethyan margins are proven hydrocarbon reservoirs. This study examines the controls on porosity and permeability development of the producing Middle Eocene Pirkoh Member of the Eastern Tethys using well core data from Well Zx-01 from the Punjab Platform area, Central Indus Basin, Pakistan. The standard petrographic and core analysis techniques were adopted to determine these controls. Petrographic studies revealed three microfacies comprising bioclastic packstone to floatstone, bioclastic wackestone and mud-wackestone microfacies. The allochems belong to benthic foraminifera including Nummulites sp., Discocyclinids sp.., Coralline algae, Assilina sp., Lockhartia sp., Coralline algae and Gastropods along with the other bioclastic debris. These allochems were found embedded in the micritic matrix with extensive cementation of calcite. The diagenetic events included cementation, compaction, dolomitization, fracture filling and neomorphism. Based on microfacies, the environment of deposition is interpreted to be a high-energy zone of the middle ramp in shallow marine environment. Subsurface core indicates that the porosity of the reservoir is low to high ranging between 6 to 27.47% and permeability is found low to fair ranging between 0.03 to 7.73 mD, found closely related to microfacies and diagenetic modifications. This study is a first attempt to document the reservoir facies of the non-reefal carbonates of the Pirkoh limestone that would help to exploit the reservoir's potential of the carbonate platforms developed in similar settings worldwide. [ABSTRACT FROM AUTHOR]

The lithium (Li) isotopic composition of carbonates is considered to be a reliable archive of past seawater Li isotopic compositions, which are useful as a tracer of silicate weathering. However, δ7Li values have been shown to be dependent on either pH or DIC in two studies using similar species of large, benthic foraminifera from the genus Amphistegina. To resolve this issue, we conducted culture experiments on Amphistegina lessonii in decoupled pH–DIC conditions, under two different light treatments, and with normal or Li-enriched seawater. The δ7Li values and Li/Ca ratios in the foraminifera tests were analysed by ion microprobe and LA-ICP-MS, respectively. No links between either the pH or DIC and δ7Li or Li/Ca values were observed for any of the treatments, and growth rates also did not seem to influence the Li incorporation or isotopic fractionation, contrary to observations from inorganic carbonate-precipitation experiments. Overall, these findings appear to support the use of Li isotopes in large benthic foraminifera to reconstruct past seawater chemistry and to infer changes in chemical weathering during carbon-cycle perturbations. [ABSTRACT FROM AUTHOR]

Symbiont-bearing perforated large benthic foraminifers are vital to the formation of coral reef islands in the Pacific Ocean and are affected by the deterioration of reefal water quality in urbanized atolls. Recently, road traffic was identified as a notable source of heavy-metal pollution in the densely populated area of Majuro atoll in the Marshall Islands. However, the effects of polycyclic aromatic hydrocarbons (PAHs) on LBFs have not been investigated so far. In the present study, pyrene, a PAH, was selected, and its effects on photosynthesis were examined by using Calcarina gaudichaudii. The organisms were exposed to 0.02, 2.0, and 200 µg L−1 of pyrene for 8 d. The effective and maximum quantum yields did not change (p > 0.05). Chlorophyll-a content too remained constant (p > 0.05). The results indicate that pyrene does not damage the photosystem II and symbiotic algal cell in C. gaudichaudii. Although a previous study reported that the cell density of a marine diatom decreased on exposure to 125 µg L−1 of pyrene, the Langmuir adsorption isotherm model confirmed that pyrene was sufficiently adsorbed on the dried shell of C. gaudichaudii. Through visual observation, sticky materials such as the extracellular organic matrix around C. gaudichaudii were identified under exposure to pyrene. This extracellular organic matrix likely acted as a protective layer against the toxic effects of pyrene with different defense mechanisms found in coral. We conclude that C. gaudichaudii can tolerate short-term exposure to pyrene. [ABSTRACT FROM AUTHOR]

Coral reefs are in global decline and anomalously hot temperatures shoulder the blame. Foraminferal bioindicators are important because they record historical reef stress over periods of centuries to millennia, as compared to the few decades offered by diver surveys. For a region lacking systematic long-term reef monitoring programs, the use of bioindicators in the Red Sea is compelling. Whereas foraminfera-based indices exist to reconstruct histories of nutrient stress on reefs, there is a paucity of equivalent bioindicators that respond to temperature. Capitalizing on a portfolio of surficial sediment samples collected along the eastern margin of the N. Red Sea and Gulf of Aqaba, this study shows that the relative abundance of Amphisteginidae foraminifera—specifically Amphistegina lobifera—closely track heat stress, as has recently been reported for this family in the S. Pacific. This result is consequential for at least three reasons. First, the Red Sea hosts some of the most northerly coral reefs on Earth. Establishment of a thermal bioindicator here confirms the strategy can be deployed on high latitudes reefs, which are disproportionally afflicted with heat extremes. Second, the considered reefs, and the foraminifera they host, are famed for their thermal resilience. Foraminiferal bioindicators have not previously been trialed on reefs that have adapted in this way. Finally, as a restricted offshoot of the Indian Ocean, the level of endemism in the Red Sea is especially high. The bioindicator that we propose is apparently not compromised by endemism. Our findings advocate for an expanded deployment of Amphistegina-based reef bioindicators. [ABSTRACT FROM AUTHOR]

Global warming permits range expansions of tropical marine species into mid-latitude habitats, where they are, however, faced with cold winter temperatures. Therefore, tolerance to cold temperatures may be the key adaptation controlling zonal range expansion in tropical marine species. 2. Here we investigated the molecular and physiological response to cold and heat stress in a tropical symbiont-bearing foraminifera that has successfully invaded the Eastern Mediterranean. 3. Our physiological measurements indicate thermal tolerance of the diatom symbionts but a decrease in growth for the foraminifera host under both cold and warm stress. 4. The combined ('holobiont') transcriptome revealed an asymmetric response in short-term gene expression under cold versus warm stress. Cold stress induced major reorganization of metabolic processes, including regulation of genes involved in photosynthesis. Analyses limited to genes that are inferred to belong to the symbionts confirm that the observed pattern is due to changes in the regulation of photosynthesis-related genes and not due to changes in the abundance of the symbionts. 5. In contrast to cold stress, far fewer genes change expression under heat stress and those that do are primarily related to movement and cytoskeleton. This implies that under cold stress, cellular resources are allocated to the maintenance of photosynthesis, and the key to zonal range shifts of tropical species could be the cold tolerance of the symbiosis. [ABSTRACT FROM AUTHOR]

Concurrent anthropogenic global climate change and ocean acidification are expected to have a negative impact on calcifying marine organisms. While knowledge of biological responses of organisms to oceanic stress has emerged from single‐species experiments, these do not capture ecologically relevant scenarios where the potential for multi‐organism physiological interactions is assessed. Marine algae provide an interesting case study, as their photosynthetic activity elevates pH in the surrounding microenvironment, potentially buffering more acidic conditions for associated epiphytes. We present findings that indicate increased tolerance of an important epiphytic foraminifera, Marginopora vertebralis, to the effects of increased temperature (±3°C) and pCO2 (~1,000 µatm) when associated with its common algal host, Laurencia intricata. Specimens of M. vertebralis were incubated for 15 days in flow‐through aquaria simulating current and end‐of‐century temperature and pH conditions. Physiological measures of growth (change in wet weight), calcification (measured change in total alkalinity in closed bottles), photochemical efficiency (Fv/Fm), total chlorophyll, photosynthesis (oxygen flux), and respiration were determined. When incubated in isolation, M. vertebralis exhibited reduced growth in end‐of‐century projections of ocean acidification conditions, while calcification rates were lowest in the high‐temperature, low‐pH treatment. Interestingly, association with L. intricata ameliorated these stress effects with the growth and calcification rates of M. vertebralis being similar to those observed in ambient conditions. Total chlorophyll levels in M. vertebralis decreased when in association with L. intricata, while maximum photochemical efficiency increased in ambient conditions. Net production estimates remained similar between M. vertebralis in isolation and in association with L. intricata, although both production and respiration rates of M. vertebralis were significantly higher when associated with L. intricata. These results indicate that the association with L. intricata increases the resilience of M. vertebralis to climate change stress, providing one of the first examples of physiological buffering by a marine alga that can ameliorate the negative effects of changing ocean conditions. [ABSTRACT FROM AUTHOR]

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Adaptation, acclimatization and symbiont diversity are known to regulate thermal tolerance in corals, but the role of these mechanisms remains poorly constrained in other photosymbioses, such as large benthic foraminifera (LBFs), which are known to bleach at temperatures that are likely to be exceeded in the near future. LBFs inhabit a broad range of shallow-water settings. Within species, differences in thermal tolerance have been found among populations from different habitats, but it is not clear whether such differences occur among LBFs inhabiting similar habitats, but differing in other aspects, such as symbiont type. To this end, we compared responses to thermal stress in specimens from a population of Amphistegina lessonii, an abundant Indo-Pacific species, to specimens of Amphistegina gibbosa, its Atlantic counterpart, from a similar environment but two different water depths (5 and 18 m). Test groups of each species were exposed in a common experiment to three thermal stress scenarios over a four-week period. Growth, respiration, mortality and motility were measured to characterize the holobiont response. Coloration, photosynthesis and chlorophyll a content were measured to determine the response of the endosymbiotic diatoms. The photosymbionts were characterized by genetic fingerprinting. Our results show that, although groups of A. gibbosa were collected from different habitats, their responses were similar, indicating only marginally higher tolerance to thermal peaks in specimens from the shallower site. In contrast, species-specific differences were stronger, with A. lessonii showing higher tolerance to episodic stress and less pronounced impacts of chronic stress on motility, growth and photosymbiont performance. These interspecies variations are consistent with the presence of different and more diverse symbiont assemblages in A. lessonii compared with A. gibbosa. This study demonstrates the importance of considering symbiont diversity in the assessment of intra- and interspecific variations in stress responses in LBFs. [ABSTRACT FROM AUTHOR]

Fellowes, T.E.; Gacutan, J.; Harris, D.L.; Vila-Concejo, A.; Webster, J.M., and Byrne, M., 2017. Patterns of sediment transport using foraminifera tracers across sand aprons on the Great Barrier Reef. Sediment dynamics exert large control over coral reef geomorphological evolution and are vital to understanding past and present geomorphic responses. Large benthic foraminifera (LBF) live in the algal reef flats, and their tests (shells) are transported post-mortem by waves and currents onto back-reef environments, including sand aprons. This study investigated the patterns of transport linking surficial and downcore sediments in samples from three sand aprons with different wave exposures at One Tree Reef on the southern Great Barrier Reef (Australia). Six LBF genera represented up to 32% of the sediments analysed. Lagoonward transport increased LBF test abrasion and sediment bulk density. Sediment grain size and LBF abundance in sediments also decreased with lagoonward transport. Sediment transport patterns indicated by LBF species used as tracer were consistent with the prominent E-SE wave environment. A novel taphofacies approach was used to describe stratigraphic layers in downcore sediments based on LBF test abrasion and abundance. Varied sediment deposition rates did not affect the LBF test abrasion signature downcore. It appears that Baculogypsina sphaerulata has been the dominant species for at least 3 ka. Tests that were deposited slowly exhibited less or the same levels of abrasion than those that were rapidly deposited. It appears that test abrasion is primarily determined by the distance travelled rather than the influence of increased age or chemical dissolution. [ABSTRACT FROM AUTHOR]

Large benthic foraminifera (LBF) are prolific producers of calcium carbonate sediments in shallow, tropical environments that are being influenced by ocean acidification (OA). Two LBF species, Amphistegina gibbosa (Order Rotaliida) with low-Mg calcite tests and Archaias angulatus (Order Miliolida) with high-Mg calcite tests, were studied to assess the effects of pH 7.6 on oxygen and carbon isotopic fractionation between test calcite and ambient seawater. The δ18O and δ13C values of terminal chambers and of whole adult tests of both species after 6 weeks were not significantly different between pH treatments of 8.0 and 7.6. However, tests of juveniles produced during the 6-week treatments showed significant differences between δ18O and δ13C values from control (pH 8.0) when compared with the treatment (pH 7.6) for both species. Although each individual's growth was photographed and measured, difficulty in distinguishing and manually extracting newly precipitated calcite from adult specimens likely confounded any differences in isotopic signals. However, juvenile specimens that resulted from asexual reproduction that occurred during the experiments did not contain old carbonate that could confound the new isotopic signals. These data reveal a potential bias in the design of OA experiments if only adults are used to investigate changes in test chemistries. Furthermore, the results reaffirm that different calcification mechanisms in these two foraminiferal orders control the fractionation of stable isotopes in the tests and will reflect decreasing pH in seawater somewhat differently. [ABSTRACT FROM AUTHOR]

Intra-test variability in Mg/Ca and other (trace) elements within large benthic foraminifera (LBF) of the family Nummulitidae have been investigated using laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). These foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to ‘surface-dwelling’ planktic foraminifera. Coupled with their abundance in climatically important periods such as the Paleogene, this means that this family of foraminifera are an important but under-utilised source of palaeoclimatic information. We have calibrated the relationship between Mg/Ca and temperature in modern Operculina ammonoides and observe a increase in Mg/Ca °C−1. O. ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling us to reconstruct mid-Eocene tropical sea surface temperature seasonality by applying our calibration to fossil Nummulites djokdjokartae from Java. Our results indicate a 5–6 °C annual temperature range, implying greater than modern seasonality in the mid-Eocene (Bartonian). This is consistent with seasonal surface ocean cooling facilitated by enhanced Eocene tropical cyclone-induced upper ocean mixing, as suggested by recent modelling results. Analyses of fossil N. djokdjokartae and Operculina sp. from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera, within error. Using previously published test–seawater alkaline earth metal distribution coefficients derived from an LBF of the same family (Raitzsch et al., 2010) and inorganic calcite, with appropriate correction systematics for secular Mg/Casw variation (Evans and Müller, 2012), we use our fossil data to produce a more accurate foraminifera-based Mg/Casw reconstruction and an estimate of seawater Sr/Ca. We demonstrate that mid-Eocene Mg/Casw was , which is in contrast to the model most commonly used to correct deep-time Mg/Ca data from foraminifera, but in agreement with most other Paleogene proxy and model data. This indicates that Mg/Casw has undergone a substantial ( ) rise over the last . [ABSTRACT FROM AUTHOR]

Abstract: Calcium carbonate shells produced by large benthic foraminifers (LBF) are major components in sediments on coral reef islands. Quantifying growth patterns of LBFs is important for accurate estimation of calcium carbonate production. To quantify the growth pattern of Baculogypsina sphaerulata in a tropical area, we developed a novel rearing method with high survival rate (>90%) by creating constant disturbance with the combination of a floating chamber and coral sand. Through the rearing experiments, coral sand has a significant inhibitory effect on lethal epiphyte infestation on B. sphaerulata in a rearing chamber. This implies that the inhibitory effect by such disturbance on the epiphyte may be one of the reason that B. sphaerulata prefer the most exposed areas among LBFs. The novel rearing method allowed the quantification of the relationship between size and growth rate. The growth rate of B. sphaerulata showed size dependence with a peak at 0.8–1.2mm2, and development time to adult size was estimated at 1.3year with substantial variation induced by variability in growth parameters. The estimated development time is similar to that reported in subtropical areas (1.5year). This quantified growth pattern of the species will apply to the analysis of population dynamics and estimation of CaCO3 productions of the species in a tropical area. [Copyright &y& Elsevier]

Well-preserved, isolated specimens of Pseudotaberina were found at three localities in Indonesia, thus enabling the study of the relationships between this genus and Caribbean Archaiasinae. The internal architecture of the chambers of Pseudotaberina consists of four layers of stolon planes, each of which is divided by superposed septula into chamberlets. The chamberlets are connected to the next chambers by foramina opposing the septula. The stolons are Y-shaped. All other Archaiasinae have radial stolon axes combined with an initial involute growth stage, whereas the Soritinae have cross-wise oblique stolon axes, but with evolute growth in the early stages. Pseudotaberina shows a combination of the characters of these two subfamilies, confirming the need to study more Tethyan material to elucidate phylogenetic relationships within this group of large benthic foraminifera. [ABSTRACT FROM AUTHOR]

Knowledge of the assemblage composition of large benthic foraminifera (LBF) in relation to environmental conditions is needed to interpret fossil records. In this study the assemblage composition of LBF is described for a carbonate shelf with a barrier reef system and some reefs outside the barrier. In a total of 140 samples, 34-35 species of LBF were found. Four clusters, roughly corresponding to substrate type were identified. Several small groups of samples were recognized that were collected locally inside, on, or outside the barrier. Microscale environmental gradients within the substrate or in the benthic boundary layer resulted in spatial differentiation of the microhabitat of each species. [ABSTRACT FROM AUTHOR]

Lepidocyclinids are one of the most common group of Cenozoic large benthic foraminifera and, thanks to their clear evolutionary patterns, they are extensively used in biostratigraphy. They originated during the Eocene in the American region and then spread eastward, reaching a worldwide distribution in the Oligocene. This paper investigates the southernmost population of lepidocyclinids ever found along the Pacific coast of South America, located in the lower part of the Paracas Formation (Los Choros Member) of the East Pisco Basin of Peru. The examined Los Choros strata are composed of mixed siliciclastic-bioclastic coarse-grained deposits. The skeletal assemblage is dominated by large benthic foraminifera and mollusks with subordinate echinoids and barnacles, suggesting a deposition in a shallow, tropical, shelf environment with a moderate nutrient supply. The large benthic foraminiferal assemblage is largely dominated by Lepidocyclina rdouvillei. This species is extremely primitive, exhibiting ancestral characters such as a straight wall separating the protoconch and deuteroconch, very large principal auxiliary chambers and a poorly organized equatorial plane. The presence of common and primitive L. rdouvillei , supported by the associated occurrence of Polylepidina , suggests an age comprised between 43.6 Ma and 40.5 Ma for the Los Choros Member in the study area. This range is confirmed by nannofossil assemblages that indicate an age between 42.37 Ma and 40.34 Ma for the base of the overlying Yumaque Member of the Paracas Formation. These results highlight the potential of lepidocyclinids for biostratigraphy and paleoenvironmental reconstructions in South America. • Large benthic foraminifera of the Los Choros Member, Paracas Fm., East Pisco Basin. • Southernmost lepidocyclinids population of the Pacific Coast of South American. • The age of the Los Choros Member is constrained to the late Lutetian. • The association indicates tropical climate during the deposition of the Los Choros Member. [ABSTRACT FROM AUTHOR]

Large benthic foraminifera are significant contributors to sediment formation on coral reefs, yet they are vulnerable to ocean acidification. Here, we assessed the biochemical and morphological impacts of acidification on the calcification of Amphistegina lessonii and Marginopora vertebralis exposed to different pH conditions. We measured growth rates (surface area and buoyant weight) and Ca-ATPase and Mg-ATPase activities and calculated shell density using micro-computer tomography images. In A. lessonii, we detected a significant decrease in buoyant weight, a reduction in the density of inner skeletal chambers, and an increase of Ca-ATPase and Mg-ATPase activities at pH 7.6 when compared with ambient conditions of pH 8.1. By contrast, M. vertebralis showed an inhibition in Mg-ATPase activity under lowered pH, with growth rate and skeletal density remaining constant. While M. vertebralis is considered to be more sensitive than A. lessonii owing to its high-Mg-calcite skeleton, it appears to be less affected by changes in pH, based on the parameters assessed in this study. We suggest difference in biochemical pathways of calcification as the main factor influencing response to changes in pH levels, and that A. lessonii and M. vertebralis have the ability to regulate biochemical functions to cope with short-term increases in acidity. [ABSTRACT FROM AUTHOR]