Symbiont-bearing Foraminifera Research Articles

Resilience of reefal foraminifera to anthropogenic influences from reef areas (Pirangi, Maracajaú, and Açu) in Rio Grande do Norte (RN, Brazil)

We have studied seven symbiont-bearing foraminiferal species to evaluate the condition of sedimentary reef areas (Pirangi, Maracajaú, and Açu) in Rio Grande do Norte (RN, Brazil). The species are: Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Borelis schlumbergeri, Heterostegina antillarum, Peneroplis carinatus, and Laevipeneroplis proteus. This paper focuses on the quantitative distributions of the first two species in Maracajaú and Pirangi, considering micro-habitat variation, shelf zonation, and anthropogenic disturbances. Amphistegina gibbosa, which is more abundant than A. hemprichii, is prevalent in coral or coral-rubble substrates, whereas Amphisorus hemprichii is better represented in seagrass habitats. Our dataset from Pirangi and Maracajaú is based on 123 samples collected over three years through diver collection, grab samples, and underwater videographic surveys. Compared to other Brazilian reefs, species diversity at Pirangi is low, and the community is impoverished near tourism sites. These areas, especially Pirangi, may also be affected by pollution from domestic sewage and industrial waste. In Maracajaú, the community appears healthier, except in sites heavily impacted by tourism. Data from 84 foraminiferal samples from Açu show well-preserved symbiont-bearing foraminifera (SBF), indicating good water quality, with microhabitat variations likely due to natural factors. A quantitative examination of the foraminiferal species revealed the presence of a Caribbean-type reef community, including Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Heterostegina antillarum, Homotrema rubra, Peneroplis carinatus, and Laevipeneroplis proteus. Additionally, among 65 species, living Buccella peruviana were found with a very restricted distribution in organic-rich sediments associated with upwelling wind events, highlighting areas of cold water upwelling on the outer shelf. The spatial distribution of this species indicates that cold waters are bringing nutrients through tidal currents perpendicular to the shelf edge, likely using canyons and valleys to transport nutrients and cold water masses into the partially filled incised valley of the ancient Açu River. Changes in diversity appear to be primarily induced by anthropogenic influences on the inner shelf rather than the outer shelf.

Environmental monitoring of the Kavaratti lagoon, Lakshadweep Islands, Arabian Sea using larger foraminiferal distribution

Coral reef environments are known for the proliferation of algal symbiont-bearing foraminifera, which are sensitive indicators of water-quality conditions that support reef development. Keeping this in mind, 18 sediment samples were collected in the Kavaratti lagoon of Lakshadweep in 2004. The foraminiferal distribution and abundance of the major genera Amphistegina, Calcarina, Amphisorus and miliolids were compared with those reported nearly three decades ago. The aim was to identify changes in the foraminiferal data within the lagoon over time, through time-gap-sampling, to be able to assess environmental stress if any. The total foraminiferal number (TFN) in the lagoon ranges between 45 and 983 specimens per gram of dry sediments. The average TFN in the northern part of the lagoon (506/g) is lower than that in the southern part of the lagoon (612/g). Amphistegina and Calcarina, both being algal-symbiont-bearing foraminifera, show the tendency to occupy shallower depths of the lagoon. Amphisorus prefer the northern part of the lagoon, due to the prevalence of comparatively stronger currents. Over the past three decades, TFN in the lagoon has on an average gone down from 65,667 in 1976 to 56,100 (present study) specimens per 100 g of sediments. The larger foraminiferal distribution in the Kavaratti lagoon has slightly but undisputedly undergone quantitative and distributional changes over the past three decades. The FORAM Index suggests conducive environment for coral growth in the lagoon. However, definite deterioration due to dredging in the northern lagoon is indicated by the assemblage. The study also records signatures of domestic discharge and predicts a larger impact on the corals since 2004 to 2024.

Invasion success of a Lessepsian symbiont-bearing foraminifera linked to high dispersal ability, preadaptation and suppression of sexual reproduction

Among the most successful Lessepsian invaders is the symbiont-bearing benthic foraminifera Amphistegina lobifera. In its newly conquered habitat, this prolific calcifier and ecosystem engineer is exposed to environmental conditions that exceed the range of its native habitat. To disentangle which processes facilitated the invasion success of A. lobifera into the Mediterranean Sea we analyzed a ~ 1400 bp sequence fragment covering the SSU and ITS gene markers to compare the populations from its native regions and along the invasion gradient. The genetic variability was studied at four levels: intra-genomic, population, regional and geographical. We observed that the invasion is not associated with genetic differentiation, but the invasive populations show a distinct suppression of intra-genomic variability among the multiple copies of the rRNA gene. A reduced genetic diversity compared to the Indopacific is observed already in the Red Sea populations and their high dispersal potential into the Mediterranean appears consistent with a bridgehead effect resulting from the postglacial expansion from the Indian Ocean into the Red Sea. We conclude that the genetic structure of the invasive populations reflects two processes: high dispersal ability of the Red Sea source population pre-adapted to Mediterranean conditions and a likely suppression of sexual reproduction in the invader. This discovery provides a new perspective on the cost of invasion in marine protists: The success of the invasive A. lobifera in the Mediterranean Sea comes at the cost of abandonment of sexual reproduction.

The distribution of benthic foraminifera in coral reefs ecosystem of East Penjaliran Island, Seribu Islands, Indonesia

Abstract. Natsir SM. 2022. ­­The distribution of benthic foraminifera in coral reefs ecosystem of East Penjaliran Island, Seribu Islands, Indonesia. Biodiversitas 23: 3073-3080. East Penjaliran Island is located in the core zone of Seribu Islands Marine National Park and is included in the protected green area. The research shows the close relationship between benthic foraminifera and coral reef. Certain foraminifera has the same environmental requirement to live with coral reefs. Therefore, the study of foraminiferal assemblages is also very important to shed light on the environmental conditions for the growth of coral reefs through calculating the Foraminifera in Reef Assessment and Monitoring Index (FORAM Index/FI). Sampling was conducted in December 2016 around the coral reef ecosystems of East Penjaliran Island, Seribu Islands. A total of 37 species of benthic foraminifera were collected from the island with a diverse abundance. Based on the FI gained values on average of 3.18. It indicates that East Penjaliran Island is classified as an environmental change for coral reefs' growth. The condition was feasible for the growth of coral reefs, but it tends to be an unfavorable environment for their recovery. The benthic foraminifera assemblages can be classified into three major groups based on the Shannon diversity index and FI (i.e., Group A, Group B, and Group C) with their specific characteristics. Group A was characterized by coarse sand sediment and dwelled dominantly by opportunistic foraminifers such as Elphidium advenum, Elphidium crispum, and Flintina bradyana. Groups B and C have very fine sand sediment, but they dwelled by foraminiferal assemblages in different compositions. Group B was dominated by E. crispum and followed by several species of Peneroplis, but Group C dwelled abundantly by E. advenum, E. crispum, Elphidium depressulum and followed by symbiont-bearing foraminifera such as Peneroplis planatus.

The combined effects of rising temperature and salinity may halt the future proliferation of symbiont-bearing foraminifera as ecosystem engineers

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.

Distribution of benthic foraminifera in an oceanic (Darwinian) barrier reef lagoon, Bora Bora, French Polynesia

Bora Bora, French Polynesia, represents the classic oceanic (Darwinian) barrier reef system, complete with a deep and extensive lagoon. The foraminiferal faunas of such oceanic barrier reef lagoons have never been studied in detail. How they relate to atoll lagoons and more broadly to coral reef lagoons in general is not known. Back-reef lagoon samples from Bora Bora were studied for their foraminiferal content. The fauna contains sparse larger symbiont bearing foraminifera, and most samples are dominated by a textulariid fauna of mainly Textularia gr. sp. 1, Textularia gr. foliacea and Textularia oceanica. Statistical analyses revealed three main assemblages, a Textularia-dominated deep central lagoon assemblage, an outer shallow lagoon assemblage characterised by abundant porcelaneous taxa, and a narrow embayment assemblage with abundant Elphidium. Although the species at Bora Bora are common to the Pacific Ocean, the Textularia-dominated assemblages are markedly different from the lagoon assemblages reported from atoll and non-oceanic barrier reef lagoons in the Pacific. These unique assemblages are hypothesised to have evolved due to interactions of the central volcanic island with the lagoon system, likely via the run-off of fine sediment and nutrients. Thereby, the prerequisites for abundant larger, symbiont-bearing foraminifera, which prefer clear, nutrient-poor waters, are largely unavailable. Despite similar substrates and facies, differences between species compositions indicate subtly different disconnected western and eastern deep lagoon environments, possibly due to differences in connectivity to the open ocean. This study provides the first detailed account of the foraminifera from the lagoon of an oceanic barrier reef lagoon.

Using past interglacial temperature maxima to explore transgressions in modern Maldivian coral and Amphistegina bleaching thresholds

Tropical corals and Amphistegina, an example genus of symbiont-bearing larger benthic foraminifera, are presently living close to their thermal bleaching thresholds. As such, these essential reef-building organisms are vulnerable to the future prospect of more frequent sea surface temperature (SST) extremes. Exploring the earth’s paleo-climatic record, including interglacials warmer than present, may provide insights into future oceanographic conditions. We analyse foraminiferal shell geochemical compositions, from Recent surface sediments and Marine Isotope stage (MIS) 9e and MIS11c aged sediments, from the International Ocean Discovery Program Expedition 359 Site U1467 drilled in the Inner Sea of the Maldives. We illustrate through traditional (pooled) geochemical analysis (δ18O, Mg/Ca) that tropical temperatures were indeed marginally warmer during MIS9e and MIS11c in comparison to the modern ocean. Individual foraminiferal analysis (IFA) from the Recent (representing the last few hundred years) and MIS9e samples shows SSTs occasionally breached the coral bleaching threshold similarly to the modern-day. Significantly, the number of transgressions was four times higher during MIS11c, a recognised analogue for a warmer modern world. This new knowledge and novel IFA insight and application is invaluable given thermal stress is already obvious today with an increasing number of bleaching events over the last few decades.

Research Article: Study of coral reef benthic foraminiferal assemblages in Qeshm Island, Persian Gulf

Benthic foraminifera are important in sediment production of coral reef environments and are excellent indicators of water quality and reef health. There is a lack of precise information about the foraminifer’s fauna of the coral reefs in the Persian Gulf. In this study, sediment sampling was performed in June 2019 from two coral stations of Naz Island and Zeytoon Park. The surface sediment with three replicates for each location was collected using a mini corer and then were fixed in 70% ethanol. In this study, thirty species belong to 23 genera and 19 families of foraminifer's assemblages were identified based on morphological characters. Our results indicated that Foraminiferal assemblages were similar in both sampling localities. Quinqueloculina was the most abundant genera for both Naz Island and Zeytoon Park. Foraminifer's frequency of Zeytoon Park was higher than Naz Island. Symbiont-bearing foraminifera (e.g. Peneroplis) were observed just in Zeytoon Park. Higher frequency and the presence of symbiont-bearing foraminifera possibly indicate that Zeytoon Park has a more favorable condition for the coral reef growth in the future. Finally, we recommend that the structure of the foraminifer’s community could be used as an early warning system for water quality around coral reefs and in particular, would help resource managers make better decisions about protecting coral habitats.

Benthic foraminifera as bio-indicator of Mangrove ecosystem quality: A case study from Abu Ghoson area, Red Sea Coast, Egypt

The assemblages of benthic foraminifera were studied in surface sediment samples collected along two transects from the mangrove swamp and the intertidal flat zone in Abu Ghoson area, the Red Sea coast of Egypt, to validate and support their use as bio-indicators of ecosystem quality. Using Q-mode and R-mode cluster analyses, three biotopes following the bathymetric and environmental gradients have been documented. The seaward intertidal flat stations were dominated by larger symbiont-bearing foraminifera (Peneroplis planatus, Peneroplis pertusus, Sorites orbiculus, Coscinospira spp., and Amphisorous spp.). This biotope reflects the oligotrophic environment. Assemblage of smaller miliolids and rotaliids is diversified and characterized the swamp stations and the closest intertidal stations. The assemblage from the most landward semi-closed swamp station was distinguished by stress-tolerant taxa, especially Ammonia tepida, found in high percentages, though relatively low diversity.

Imprint of Regional Oceanography on Foraminifera of Eastern Pacific Coral Reefs

ABSTRACT The marginal marine environments of the eastern tropical Pacific (ETP) serve as an ideal natural laboratory to study how oceanographic and climatic variability influence coral-reef ecosystems. Reefs along the Pacific coast of Panamá span a natural gradient of nutrients, pH, and temperature as a result of stronger seasonal upwelling in the Gulf of Panamá relative to the Gulf of Chiriquí. The ecosystems are not only influenced by spatial and seasonal variations in oceanography but are affected by the climatic variability of the El Niño-Southern Oscillation (ENSO). Foraminifera can be robust indicators of ecosystem condition because the composition of their assemblages and the geochemistry of their tests can change rapidly in response to environmental variability. We studied benthic foraminifera in sediment samples collected from 3 m below mean sea level in the Gulf of Panamá and the Gulf of Chiriquí. Temperature loggers deployed from 2016 to 2019 showed that average temperatures were lower and more variable in the Gulf of Panamá due to seasonal upwelling. All sites in both gulfs were dominated by heterotrophic foraminifera, which was likely the result of nutrient enrichment due to upwelling, combined with ENSO effects. However, the Gulf of Chiriquí was characterized by higher abundances of symbiont-bearing foraminifera than the Gulf of Panamá. The orders Miliolida and Rotaliida dominated the foraminiferal assemblages in both gulfs, with Quinqueloculina and Rosalina being the most abundant genera in the two orders, respectively. Miliolids were less abundant in the Gulf of Panamá than in the Gulf of Chiriquí, whereas rotaliid densities were not significantly different between the two gulfs. Lower pH in the Gulf of Panamá as a result of upwelling may have contributed to the lower abundance of miliolids, which secrete tests of high-magnesium calcite. Geochemical analysis of tests of the symbiont-bearing miliolid Sorites marginalis revealed that foraminiferal Mg/Ca ratios were lower in the Gulf of Panamá than in the Gulf of Chiriquí. The offset in foraminiferal Mg/Ca is consistent with the lower mean annual temperature observed in the Gulf of Panamá due to stronger seasonal upwelling. Because the geochemistry and assemblages of foraminifera reflect differences in environmental conditions, they could potentially be used in tandem with coral proxies to reconstruct past environmental change and project the future of coral-reef systems within the ETP.

Symbiont-bearing foraminifera as health proxy in coral reefs in the equatorial margin of Brazil.

Coral communities worldwide are progressively more stressed by anthropogenic activities that increase fluxes of sediment and other pollutants to nearshore areas. Some nearshore coral reef environments off the Equatorial margin of Brazil, including Pirangi and Maracajaú, Rio Grande do Norte (RN, Brazil), seem to be under human-induced stress. However, the horizontal extent of this stress, its effects, and assessment of the environmental response depend on the hydrodynamic conditions (circulation and deposition patterns), sedimentary facies, and the availability of biological indicators. We investigate two Brazilian live reefal corals' communities by examining seven photosymbiont-bearing species (PSB) of Foraminifera, Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Borelis schlumbergeri, Heterostegina antillarum, Peneroplis carinatus, and Laevipeneroplis proteus, using numerical analysis FORAM Index (FI), grain size, and particulate organic and inorganic carbonate. Here, we show that coarse sand fraction followed by fine sand fraction and high hydrodynamics plays an important role in transportation and deposition of sediments and foraminiferal tests in the study area. According to FI results, conditions at Pirangi are not suitable for coral reef growth. Maracajaú has sites that are suitable for coral reef growth and sites where coral could not survive after a stress event. We need long-term assessments to improve our knowledge of the distribution and ecological importance of Brazilian reef-dwelling foraminifers and to extend the application of FI to monitoring management plans of the Pirangi and Maracajaú National Marine Parks by providing a first insight into the biodiversity patterns and a reliable tool of the reconstruction of paleo reef health.

Ecotoxicological responses of a reef calcifier exposed to copper, acidification and warming: A multiple biomarker approach

Multiple global and local stressors threat coral reefs worldwide, and symbiont-bearing foraminifera are bioindicators of reef health. The aim of this study was to investigate single and combined effects of copper (Cu) and climate change related stressors (ocean acidification and warming) on a symbiont-bearing foraminifer by means of an integrated biomarker analysis. Using a mesocosm approach, Amphistegina gibbosa were exposed for 25 days to acidification, warming and/or Cu contamination on a full orthogonal design (two levels each factor). Cu was the main factor increasing bleaching and respiration rates. Warming was the main cause of mortality and reduced growth. Calcification related enzymes were inhibited in response to Cu exposure and, in general, the inhibition was stronger under climate change. Multiple biological endpoints responded to realistic exposure scenarios in different ways, but evidenced general stress posed by climate change combined with Cu. These biological responses drove the high values found for the ‘stress index’ IBR (Integrated Biomarker Response) – indicating general organismal health impairment under the multiple stressor scenario. Our results provide insights for coral reef management by detecting potential monitoring tools. The ecotoxicological responses indicated that Cu reduces the tolerance of foraminifera to climate change (acidification + warming). Once the endpoints analysed have a high ecological relevance, and that responses were evaluated on a classical reef bioindicator species, these results highlight the high risk of climate change and metal pollution co-exposure to coral reefs. Integrated responses allowed a better effects comprehension and are pointed as a promising tool to monitor pollution effects on a changing ocean.

Evaluating the planktic foraminiferal B/Ca proxy for application to deep time paleoceanography

The Cenozoic Era has been characterized by large perturbations to the oceanic carbon cycle and global climatic changes, but quantifying the magnitude and cause of these shifts is still subject to considerable uncertainty. The boron/calcium (B/Ca) ratio of fossil planktic foraminifera shells is a promising tool for reconstructing surface ocean carbonate chemistry during such events. Previous studies indicate that symbiont-bearing, planktic foraminiferal B/Ca depends on the [B(OH)4−/DIC] ratio of seawater and potentially, when combined with foraminiferal δ11B proxy reconstructions of B(OH)4−, an opportunity to reconstruct surface ocean DIC in the geologic past. There are, however, two barriers towards interpreting records from the pre-Pleistocene era: (1) changes in seawater major ion chemistry in the past might have affected foraminiferal B/Ca; and (2) modern foraminifera species show variable B/Ca calibration sensitivities that cannot be constrained in now-extinct species. Here we address these challenges with new experiments in which we have cultured modern, symbiont-bearing foraminifera Globigerinoides ruber (pink) and Trilobatus sacculifer in seawater with simulated early Cenozoic seawater chemistry (high [Ca], low [Mg], and low [B]T). We explore mechanisms that can account for the inter-species trends that are observed in foraminiferal B/Ca, and propose a framework that can be used to apply B/Ca calibrations to now-extinct species for reconstructing climate perturbations under varying seawater chemistries.

Diverse Internal Symbiont Community in the Endosymbiotic Foraminifera Pararotalia calcariformata: Implications for Symbiont Shuffling Under Thermal Stress.

Many shallow-water tropical and subtropical foraminifera engage in photosymbiosis with eukaryotic microalgae. Some of these foraminifera appear to harbor a diverse consortium of endosymbiotic algae within a single host. Such apparent ability to contain different symbionts could facilitate change in symbiont community composition (symbiont shuffling) and mediate the ecological success of the group in a changing environment. However, the discovery of the intra-individual symbiont diversity was thus far based on symbiont culturing, which provides strong constraints on the vitality of the identified algae but provides poor constraints on their initial abundance and thus functional relevance to the host. Here we analyze the algal symbiont diversity in Pararotalia calcariformata, a benthic foraminifera sampled at four stations, inside and outside of a thermal plume in the eastern Mediterranean coast of Israel. This species has recently invaded the Mediterranean, is unusually thermally tolerant and was described previously to host at least one different diatom symbiont than other symbiont-bearing foraminifera. Our results using genotyping and isolation of algae in culture medium, confirm multiple associations with different diatom species within the same individual. Both methods revealed spatially consistent symbiont associations and identified the most common symbiont as a pelagic diatom Minutocellus polymorphus. In one case, an alternative dominant symbiont, the diatom Navicula sp., was detected by genotyping. This diatom was the third most abundant species identified using standard algae culturing method. This method further revealed a spatially consistent pattern in symbiont diversity of a total of seventeen identified diatom species, across the studied localities. Collectively, these results indicate that P. calcariformata hosts a diverse consortium of diatom endosymbionts, where different members can become numerically dominant and thus functionally relevant in a changing environment.

Ground-truthing the planktic foraminifer-bound nitrogen isotope paleo-proxy in the Sargasso Sea

We report the nitrogen (N) isotope ratios (δ15N) of planktic foraminifera collected from upper-ocean net tows (surface to 200 m), moored sediment traps, and core-top sediments at the Bermuda Time-series Site in the northern Sargasso Sea between 2009 and 2013. Consistent with previous measurements from low-latitude core-top sediments, the annually-averaged δ15N of organic matter bound within the shells of euphotic zone-dwelling, dinoflagellate symbiont-bearing foraminifera collected in net tows (2.3‰ on average) approximates that of shallow thermocline (∼200 m) nitrate (2.6‰), the dominant source of new N to Sargasso Sea surface waters. Deeper-dwelling foraminifer species without dinoflagellate symbionts tend to have a higher δ15N (3.6‰ on average). We observe no systematic difference between the bulk tissue and shell-bound δ15N in net tow-collected foraminifera. A decline in shell N content is observed from net tows (6.8 nmol/mg) to sediment traps (5.4 nmol/mg) and surface sediment (3.0 nmol/mg). On average, shell-bound δ15N rises from net tows (3.1‰) to sediment traps (3.7‰) but does not change further upon incorporation into the sediments (3.7‰). Together, these observations are consistent with preferential loss of shells or shell portions with lower δ15N and higher N content during sinking through the upper 500 m, followed by a non-isotope fractionating decrease in N content between sinking and burial. Time-series data from sediment traps (and to a lesser extent, surface net tows) exhibit seasonal δ15N variations, with a minimum in early spring, a maximum in late spring and a decline from summer to fall. These variations appear to arise from seasonal changes in the δ15N of total upper-ocean biomass, which are, in turn, driven by early springtime nitrate supply, subsequent nitrate drawdown, and an increase in the relative importance of ammonium recycling into the late summer and early fall. The δ15N connection between total upper ocean biomass and foraminifera indicates that foraminifer-bound δ15N records the δ15N of the annual nitrate supply in oligotrophic (e.g., subtropical) environments but will also be sensitive to the degree of nitrate consumption in high-nutrient regions and possibly to changes in upper-ocean ammonium recycling under some conditions.

The sedimentary facies of Posidonia oceanica seagrass meadows from the central Mediterranean Sea

Sedimentary facies of seven Posidonia oceanica meadows of western Mediterranean Sea were investigated. Five meadows are located in the Tyrrhenian coast, two are placed in the western coast of Sardinia and Corsica. These meadows develop on soft and hard substrates, often forming “mattes”, in areas characterized by different oceanography, morphology, and terrigenous inputs produced by coastal erosion and fluvial runoff. A total of five sedimentary facies have been recognized ranging from pure terrigenous to bioclastic: terrigenous sand to gravelly sand, bioclastic sands, skeletal gravelly sands, mixed siliciclastic–carbonate sands, well to moderately sorted skeletal siliciclastic sands. All of the sedimentary facies associated with P. oceanica are in the sand grain size. The gravelly fraction is generally subordinated and variable, whereas the muddy fraction is generally low. The very low frequencies of the muddy fraction can be attributed to re-suspension processes and to the lack of carbonate mud production. The rate of epiphytic carbonate production obtained by two of the investigated meadows averages 400 g m−2 year−1. This value is in the range of temperate Mediterranean as well as of tropical and subtropical seagrasses. The epiphytic carbonate production plus the calcareous biota living on seagrass substrate contributes to form mixed siliciclastic–carbonate sediments of the nearshore environment of the Mediterranean. Lastly, the carbonate production associated with seagrass was derived by biota belonging to the heterozoan assemblage, where aphotic organisms are dominant, together with oligophotic biota such as coralline algae and symbiont-bearing foraminifera. Consequently, in the well-illuminated seagrass settings, the prevalent skeletal assemblages is represented by the heterozoan association while the components of the photozoan assemblages are absent or subordinate. This a key point for the paleoenvironmental reconstruction of the photic zone in the fossil record. Because the skeletal components of many seagrass dwellers greatly contribute to the carbonate sediment production of photic shallow-water environments, the seagrass meadows became substantial places of carbonate production and C (organic and inorganic) sequestration during the Cenozoic.

Applying Benthic Foraminiferal Assemblage to Evaluate the Coral Reef Condition in Dongsha Atoll lagoon.

Chienhsun Chen and Hui-Ling Lin (2017) Coral reefs in the South China Sea are threatened by environmental changes and anthropogenic disruptions. Foraminifera, a group of unicellular shelled protists, has been considered a reliable indicator of water quality and reef health. However, this indicator has not yet been used to study coral reefs in the South China Sea. In this study of foraminifera in the lagoon of Dongsha Atoll, both the assemblage diversity and the functional group composition were investigated. The FORAM index (FI), a numerical indicator based on functional group composition, was used to evaluate the condition of the coral reef of the Atoll lagoon. A typical assumption is that FI = 4 is the minimum index value corresponding to a suitable environment for the growth of calcifying organisms. Environments with FI values between 2 and 4 are unsuitable to marginal for recovery of coral communities after a mortality event. Data were recorded regarding a total of 287 foraminiferal species. Approximately 68% of the tests belonged to the porcelaneous taxa; the Quinqueloculina, Triloculina, and Pseudomassilina species were well represented. Hyaline foraminifera were less abundant than porcelaneous foraminifera; the agglutinated foraminifera were the least abundant. Multivariate analyses revealed four clustering groups. The functional groups were classified according to FI's definition; the heterotrophic group was the most abundant, accounting for 82% of foraminiferal abundance. The symbiont-bearing group was the second most abundant, with a relative abundance of 12%; and the stress-tolerant group was the least abundant. Two samples had FI values slightly higher than 4; Amphisorus and Calcarina were dominant, but the other symbiont-bearing foraminifera had lower values. These high FI values can be associated with seagrass meadows or relict shells in an altered environment. Eighty percent of the sediment samples had FI values lower than 4, indicating that most of the benthic habitats in the Dongsha lagoon are not suitable for coral growth and reef recovery. The present findings provide an alternative evaluation method based on foraminiferal assemblages for future studies on the environmental changes of coral reefs.

A new boron isotope-pH calibration for Orbulina universa, with implications for understanding and accounting for ‘vital effects’

Boron isotope ratios, as measured in planktic foraminifera, can be a useful tracer of past ocean pH, and hence help to discern the concentration of CO2 in the ancient atmosphere. However, different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater pH. Therefore when applying the proxy to questions in the geological past, species-specific calibrations are preferable. Beyond the evolutionary history of a calibrated species, we must rely on our understanding of the causes of the observed “vital effects” in the modern ocean, and the applicability of that understanding to extinct species. Here we present a new open-ocean calibration of the planktic foraminifera Orbulina universa, measured via Multi-Collector Inductively Coupled Mass Spectrometry (MC-ICPMS). Unlike other symbiont-bearing foraminifera, O. universa record a δ11B (and hence pH) that is lower than its surrounding seawater, but with a pH-sensitivity roughly equal to that of aqueous borate ion. We discuss the significance of this for application of the boron isotope proxy in deep time, with recommendations for best practice and future research directions.

Extremely heat tolerant photo-symbiosis in a shallow marine benthic foraminifera.

Bleaching, the loss of algal symbionts, occurs in marine photosymbiotic organisms at water temperatures minimally exceeding average summer SST (sea surface temperatures). Pre-adaptation allows organisms to persist under warmer conditions, providing the tolerance can be carried to new habitats. Here we provide evidence for the existence of such adaptation in the benthic foraminifera Pararotalia calcariformata. This species occurs at a thermally polluted site in the Mediterranean, where water temperatures reach a maxima daily average of 36 °C during the summer. To test whether this occurrence represents a widespread adaptation, we conducted manipulative experiments exposing this species from an unpolluted site to elevated temperatures (20–42 °C). It was kept in co-culture with the more thermally sensitive foraminifera Amphistegina lobifera in two experiments (20–36 °C). Reduced photosynthetic activity in A. lobifera occurred at 32 °C whereas photochemical stress in P. calcariformata was first observed during exposure to 36 °C. Pararotalia calcariformata survived all treatment conditions and grew under 36 °C. The photosymbiosis in P. calcariformata is unusually thermally tolerant. These observations imply that marine eukaryote-eukaryote photosymbiosis can respond to elevated temperatures by drawing on a pool of naturally occurring pre-adaptations. It also provides a perspective on the massive occurrence of symbiont-bearing foraminifera in the early Cenozoic hothouse climate.

Chamber formation leads to Mg/Ca banding in the planktonic foraminifer Neogloboquadrina pachyderma

Many species of planktonic foraminifera show distinct banding in the intratest distribution of Mg/Ca. This heterogeneity appears biologically controlled and thus poses a challenge to Mg/Ca paleothermometry. The cause of this banding and its relation with chamber formation are poorly constrained and most of what we know about intratest Mg/Ca variability stems from culture studies of tropical, symbiont-bearing foraminifera. Here we present data on the non-spinose, symbiont-barren Neogloboquadrina pachyderma from the subpolar North Atlantic where wintertime mixing removes vertical gradients in temperature and salinity. This allows investigation of biologically controlled Mg/Ca intratest variability under natural conditions. We find that intratest Mg/Ca varies between <0.1 and 7 mmol/mol, even in winter specimens. High Mg/Ca bands occur at the outer edge of the laminae, indicating reduced Mg removal at the end of chamber formation. Our data thus provide new constraints on the timing of the formation of such bands and indicate that their presence is intrinsic to the chamber formation process.Additionally, all specimens are covered with an outer crust consisting of large euhedral crystals. The composition of the crust is similar to the low Mg/Ca bands in the laminar calcite in winter and summer specimens, indicating a tight biological control on crust formation and composition. Nevertheless, despite high intratest variability, the median Mg/Ca of summertime tests is higher than that of wintertime tests. This provides support for Mg/Ca paleothermometry, but to improve the accuracy of paleotemperature estimates biological effects on Mg incorporation need to be better accounted for.