Posts Tagged 'protists'

The Bouraké semi-enclosed lagoon (New Caledonia). A natural laboratory to study the life-long adaptation of a coral reef ecosystem to climate change-like conditions

According to current experimental evidence, coral reefs could disappear within the century if CO2 emissions remain unabated. However, recent discoveries of diverse and high cover reefs that already thrive under extreme conditions seem to contradict these projections. Volcanic CO2 vents, semi-enclosed lagoons and mangrove estuaries are unique study sites where one or more ecologically relevant parameters for life in the oceans are close or even worse than currently projected for the year 2100. These natural analogues of future conditions hold new hope for the future of coral reefs and provide unique natural laboratories to explore how reef species could keep pace with climate change. To achieve this, it is essential to characterize their environment as a whole, and accurately consider all possible environmental factors that may differ from what is expected in the future and that may possibly alter the ecosystem response.

In this study, we focus on the semi-enclosed lagoon of Bouraké (New Caledonia, SW Pacific Ocean) where a healthy reef ecosystem thrives in warm, acidified and deoxygenated water. We used a multi-scale approach to characterize the main physical-chemical parameters and mapped the benthic community composition (i.e., corals, sponges, and macroalgae). The data revealed that most physical and chemical parameters are regulated by the tide, strongly fluctuate 3 to 4 times a day, and are entirely predictable. The seawater pH and dissolved oxygen decrease during falling tide and reach extreme low values at low tide (7.2 pHT and 1.9 mg O2 L−1 at Bouraké, vs 7.9 pHT and 5.5 mg O2 L−1 at reference reefs). Dissolved oxygen, temperature, and pH fluctuates according to the tide of up to 4.91 mg O2 L−1, 6.50 °C, and 0.69 pHT units on a single day. Furthermore, the concentration of most of the chemical parameters was one- to 5-times higher at the Bouraké lagoon, particularly for organic and inorganic carbon and nitrogen, but also for some nutrients, notably silicates. Surprisingly, despite extreme environmental conditions and altered seawater chemical composition, our results reveal a diverse and high cover community of macroalgae, sponges and corals accounting for 28, 11 and 66 species, respectively. Both environmental variability and nutrient imbalance might contribute to their survival under such extreme environmental conditions. We describe the natural dynamics of the Bouraké ecosystem and its relevance as a natural laboratory to investigate the benthic organism’s adaptive responses to multiple stressors like future climate change conditions.

Continue reading ‘The Bouraké semi-enclosed lagoon (New Caledonia). A natural laboratory to study the life-long adaptation of a coral reef ecosystem to climate change-like conditions’

Effects of ocean acidification on carbon and nitrogen fixation in the hermatypic coral Galaxea fascicularis

The supply of metabolites from symbionts to scleractinian corals is crucial to coral health. Members of the Symbiodiniaceae can enhance coral calcification by providing photosynthetically fixed carbon (PFC) and energy, whereas dinitrogen (N2)-fixing bacteria can provide additional nutrients such as diazotrophically-derived nitrogen (DDN) that sustain coral productivity especially when alternative external nitrogen sources are scarce. How these mutualistic associations benefit corals in the future acidifying ocean is not well understood. In this study, we investigated the possible effects of ocean acidification (OA; pHs 7.7 and 7.4 vs. 8.1) on calcification in the hermatypic coral Galaxea fascicularis with respect to PFC and DDN assimilation. Our measurements based on isotopic tracing showed no significant differences in the assimilation of PFC among different pH treatments, but the assimilation of DDN decreased significantly after 28 days of stress at pH 7.4. The decreased DDN assimilation suggests a nitrogenous nutrient deficiency in the coral holotiont, potentially leading to reduced coral calcification and resilience to bleaching and other stressful events. This contrasting impact of OA on carbon and N flux demonstrates the flexibility of G. fascicularis in coping with OA, apparently by sustaining a largely undamaged photosystem at the expense of N2 fixation machinery, which competes with coral calcification for energy from photosynthesis. These findings shed new light on the critically important but more vulnerable N cycling in hospite, and on the trade-off between coral hosts and symbionts in response to future climate change.

Continue reading ‘Effects of ocean acidification on carbon and nitrogen fixation in the hermatypic coral Galaxea fascicularis’

Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming

Ocean chemistry is changing as a result of human activities. Atmospheric carbon dioxide (CO2) concentrations are increasing, causing an increase in oceanic pCO2 that drives a decrease in oceanic pH, a process called ocean acidification (OA). Higher CO2 concentrations are also linked to rising global temperatures that can result in more stratified surface waters, reducing the exchange between surface and deep waters; this stronger stratification, along with nutrient pollution, contributes to an expansion of oxygen-depleted zones (so called hypoxia or deoxygenation). Determining the response of marine organisms to environmental changes is important for assessments of future ecosystem functioning. While many studies have assessed the impact of individual or paired stressors, fewer studies have assessed the combined impact of pCO2, O2, and temperature. A long-term experiment (∼10 months) with different treatments of these three stressors was conducted to determine their sole or combined impact on the abundance and survival of a benthic foraminiferal community collected from a continental-shelf site. Foraminifera are well suited to such study because of their small size, relatively rapid growth, varied mineralogies and physiologies. Inoculation materials were collected from a ∼77-m deep site south of Woods Hole, MA. Very fine sediments (<53 μm) were used as inoculum, to allow the entire community to respond. Thirty-eight morphologically identified taxa grew during the experiment. Multivariate statistical analysis indicates that hypoxia was the major driving factor distinguishing the yields, while warming was secondary. Species responses were not consistent, with different species being most abundant in different treatments. Some taxa grew in all of the triple-stressor samples. Results from the experiment suggest that foraminiferal species’ responses will vary considerably, with some being negatively impacted by predicted environmental changes, while other taxa will tolerate, and perhaps even benefit, from deoxygenation, warming and OA.

Continue reading ‘Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming’

Effects of ocean acidification on bleaching, survival, and calcification of Porites porites and P. astreoides in Cartagena, Colombia

Estimations of the ocean acidification-OA effects on marine environments indicate that coral reefs’ structure will collapse. This study aimed to determine the effects of OA, and its associated carbon chemistry in the sea water, on corals near the Colombian Caribbean city of Cartagena, taking as model organisms of the species Porites astreoides and P. porites. For each species, the effect of OA on bleaching, survival, and calcification was determined using artificial systems with pH of 7.879 ± 0.004 and 7.789 ± 0.007. The results showed that under the first pH, the bleaching of P. astreoides increased by 24.92% and its survival decreased by 80.56%, while at lowest pH, bleaching increased in 32.78% and survival decreased by 87.5%. In the case of P. porites, at first pH bleaching increased by 29.42% and survival decreased by 30.56% and at the lowest, bleaching increased in 37.32% and survival decreased by 13.39%. In both species, calcification was reduced in more than 90% at 7.879 ± 0.004 and their skeleton began to dissolve at 7.789 ± 0.007. This study represents the first effort to determine OA effects on Colombian Caribbean’s marine biota.

Continue reading ‘Effects of ocean acidification on bleaching, survival, and calcification of Porites porites and P. astreoides in Cartagena, Colombia’

Partner preference in the intertidal: possible benefits of ocean acidification to sea anemone-algal symbiosis

Ocean acidification (OA) threatens many marine species and is projected to become more severe over the next 50 years. Areas of the Salish Sea and Puget Sound that experience seasonal upwelling of low pH water are particularly susceptible to even lower pH conditions. While ocean acidification literature often describes negative impacts to calcifying organisms, including economically important shellfish, and zooplankton, not all marine species appear to be
threatened by OA. Photosynthesizing organisms, in particular, may benefit from increased levels of CO2. The aggregating anemone (Anthopleura elegantissima), a common intertidal organism throughout the northeast Pacific, hosts two photosynthetic symbionts: Symbiodinium muscatinei (a dinoflagellate) and Elliptochloris marina (a chlorophyte). The holobiont, therefore, consists of both a cnidarian host and a photosymbiont that could be affected differently by the changing levels of environmental CO2. To determine the effects of OA on this important marine organism, A. elegantissima in each of four symbiotic conditions (hosting S. muscatinei, hosting E. marina, hosting mixed symbiont assemblages, or symbiont free) were subjected to one of three pCO2 levels (800 ppm, 1200 ppm, or 1800 ppm) of OA for 10 weeks. At regular intervals, gross photosynthesis and density of the symbionts, respiration rate of the hosts, levels of reactive oxygen species (ROS) in the host, and percent of organic carbon received by the host from the symbiont (CZAR) were measured. Over the 10-week period of the experiment, the densities of symbionts responded differently to an increase in pCO2, increasing in anemones hosting S. muscatinei but decreasing for those hosting E. marina. Similarly, anemones of mixed symbiont complement that started with approximately 50% of each symbiont type shifted toward a higher percentage of S. muscatinei with higher pCO2. Both gross photosynthesis and dark respiration were significantly affected by pCO2 and symbiont state, though we cannot say that the symbiontsv responded differently to increased OA. Symbiont state was a significant predictor for ROS concentration, with greatest levels seen in anemones hosting E. marina and for CZAR score, with greatest levels in anemones hosting S. muscatinei, our linear models did not reveal pCO2 as a significant factor in these responses. Together, these results suggest that S. muscatinei may benefit from elevated pCO2 levels and that A. elegantissima hosting that symbiont may have a competitive advantage under some future scenarios of ocean acidification.

Continue reading ‘Partner preference in the intertidal: possible benefits of ocean acidification to sea anemone-algal symbiosis’

Will community calcification reflect reef accretion on future, degraded coral reefs?

Coral bleaching events continue to drive the degradation of coral reefs worldwide, causing a shift in the benthic community from coral to algae dominated ecosystems. Critically, this shift may decrease the capacity of degraded coral reef communities to maintain net positive accretion during warming-driven stress events (e.g., reef-wide coral bleaching). Here we measured rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) on a degraded coral reef lagoon community (coral cover < 10 % and algae cover > 20 %) during a reef-wide bleaching event in February of 2020 at Heron Island on the Great Barrier Reef. We found that during this bleaching event, rates of community NEP and NEC across replicate transects remained positive and did not change in response to bleaching. Repeated benthic surveys over a period of 20 d indicated an increase in the percent area of bleached coral tissue, corroborated by relatively low Symbiodiniaceae densities (~0.6 × 106 cm−2) and dark-adapted photosynthetic yields in photosystem II of corals (~0.5) sampled along each transect over this period. Given that a clear decline in coral health was not reflected in the overall community NEC estimates, it is possible that elevated temperatures in the water column that compromise coral health enhanced the thermodynamic favourability for calcification in other, ahermatypic benthic calcifiers. These data suggest that positive NEC on degraded reefs may not equate to the net positive accretion of reef structure in a future, warmer ocean. Critically, our study highlights that if coral cover continues to decline as predicted, NEC may no longer be an appropriate proxy for reef growth as the proportion of the community NEC signal owed to ahermatypic calcification increases and coral dominance on the reef decreases.

Continue reading ‘Will community calcification reflect reef accretion on future, degraded coral reefs?’

Ocean temperature, but not acidification, causes sea anemone bleaching under a near-future climate scenario

Climate change is causing ocean temperature and partial pressure of carbon dioxide (pCO(2)) to increase. For sea anemones that have Symbiodiniaceae, high temperatures induce bleaching, whereas rises in pCO(2) can enhance photosynthesis and increase host growth and abundance. It is, however, not clear how the interaction of these two stressors impacts sea anemones that provide habitat for anemonefishes. Here, we investigated the bleaching response of the sea anemone Entacmaea quadricolor, under four conditions: (i) current temperature and current pCO(2) (control); (ii) future pCO(2); (iii) future temperature; and (iv) future temperature and future pCO(2). After 16 days of exposure, future temperature, but not pCO(2) nor their interaction, significantly reduced the Symbiodiniaceae density and total chlorophyll Symbiodiniaceae cell(-1). Colour score was lower in the sea anemones exposed to future temperature than current temperature from day 4 onwards. In contrast, total chlorophyll symbiont cell(-1) increased in the future temperature treatments, and light-adapted effective quantum yield remained similar in all treatments. Although pCO(2) had no impact within the time frame of our experiment, the predicted future temperature induced bleaching in E. quadricolor. As bleaching events increase in frequency and severity, this will likely impact the abundance of host sea anemones and their symbiotic anemonefishes.

Continue reading ‘Ocean temperature, but not acidification, causes sea anemone bleaching under a near-future climate scenario’

Divergent proteomic responses offer insights into resistant physiological responses of a reef-foraminifera to climate change scenarios

Reef-dwelling calcifiers face numerous environmental stresses associated with anthropogenic carbon dioxide emissions, including ocean acidification and warming. Photosymbiont-bearing calcifiers, such as large benthic foraminifera, are particularly sensitive. To gain insight into their resistance and adaptive mechanisms to climate change, Amphistegina lobifera from the Gulf of Aqaba were cultured under elevated pCO2 (492, 963, and 3182 ppm) fully-crossed with elevated temperature (28°C and 31°C) for two months. Differential protein abundances in host and photosymbionts amongst treatments were investigated alongside physiological responses and microenvironmental pH variations. Over 1000 proteins were identified, of which one-third varied significantly between treatments. Thermal stress induced protein depletions, along with reduced holobiont growth. Elevated pCO2 caused only minor proteomic alterations and color changes. However, combined stressors reduced pore sizes and increased microenvironmental pH, indicating adaptive modifications to gas exchange. Notably, substantial proteomic variations at moderate-pCO2 and 31°C indicate cellular stress, while stable physiological performance at high-pCO2 and 31°C is scrutinized by putative decreases in test stability. Our experiment shows that the effects of climate change can be missed when stressors are assessed in isolation, and that physiological responses should be assessed across organismal levels to make more realistic predictions for the fate of reef calcifiers.

Continue reading ‘Divergent proteomic responses offer insights into resistant physiological responses of a reef-foraminifera to climate change scenarios’

Response of large benthic foraminifera to climate and local changes: implications for future carbonate production

Large benthic foraminifera are major carbonate components in tropical carbonate platforms, important carbonate producers, stratigraphic tools and powerful bioindicators (proxies) of environmental change. The application of large benthic foraminifera in tropical coral reef environments has gained considerable momentum in recent years. These modern ecological assessments are often carried out by micropalaeontologists or ecologists with expertise in the identification of foraminifera. However, large benthic foraminifera have been under‐represented in favour of macro reef‐builders, for example, corals and calcareous algae. Large benthic foraminifera contribute about 5% to modern reef‐scale carbonate sediment production. Their substantial size and abundance are reflected by their symbiotic association with the living algae inside their tests. When the foraminiferal holobiont (the combination between the large benthic foraminifera host and the microalgal photosymbiont) dies, the remaining calcareous test renourishes sediment supply, which maintains and stabilizes shorelines and low‐lying islands. Geological records reveal episodes (i.e. late Palaeocene and early Eocene epochs) of prolific carbonate production in warmer oceans than today, and in the absence of corals. This begs for deeper consideration of how large benthic foraminifera will respond under future climatic scenarios of higher atmospheric carbon dioxide (pCO2) and to warmer oceans. In addition, studies highlighting the complex evolutionary associations between large benthic foraminifera hosts and their algal photosymbionts, as well as to associated habitats, suggest the potential for increased tolerance to a wide range of conditions. However, the full range of environments where large benthic foraminifera currently dwell is not well‐understood in terms of present and future carbonate production, and impact of stressors. The evidence for acclimatization, at least by a few species of well‐studied large benthic foraminifera, under intensifying climate change and within degrading reef ecosystems, is a prelude to future host‐symbiont resilience under different climatic regimes and habitats than today. This review also highlights knowledge gaps in current understanding of large benthic foraminifera as prolific calcium carbonate producers across shallow carbonate shelf and slope environments under changing ocean conditions.

Continue reading ‘Response of large benthic foraminifera to climate and local changes: implications for future carbonate production’

Reduced seawater pH alters marine biofilms with impacts for marine polychaete larval settlement


• Reduced seawater pH strongly influences biofilm community composition, at both eukaryotic and prokaryotic level

• For older biofilms, biofilm age plays no role in community composition

• Incubation under different pH treatments results in variations in apparent colour and structural complexity of marine biofilms

• Incubation of marine biofilms under different pH treatments alters the settlement response in marine invertebrates

• The changes in marine biofilm community composition induced by seawater pH are most likely responsible for the changes observed in invertebrate settlement selectivity


Ocean acidification (OA) can negatively affect early-life stages of marine organisms, with the key processes of larval settlement and metamorphosis potentially vulnerable to reduced seawater pH. Settlement success depends strongly on suitable substrates and environmental cues, with marine biofilms as key settlement inducers for a range of marine invertebrate larvae. This study experimentally investigated (1) how seawater pH determines growth and community composition of marine biofilms, and (2) whether marine biofilms developed under different pH conditions can alter settlement success in the New Zealand serpulid polychaete Galeolaria hystrix. Biofilms were developed under six pH(T) treatments (spanning from 7.0 to 8.1 [ambient]) in a flow-through system for up to 14 months. Biofilms of different ages (7, 10 and 14 months) were used to assay successful settlement of competent G. hystrix larvae reared under ambient conditions. Biofilm microbiomes were characterized through amplicon sequencing of the small subunit ribosomal rRNA gene (16S and 18S). Biofilm community composition was stable over time within each pH treatment and biofilm age did not affect larval settlement selectivity. Seawater pH treatment strongly influenced biofilm community composition, as well as subsequent settlement success when biofilms were presented to competent Galeolaria larvae. Exposure to biofilms incubated under OA-treatments caused a decrease in larval settlement of up to 40% compared to the ambient treatments. We observed a decrease in settlement on biofilms relative to ambient pH for slides incubated at pH 7.9 and 7.7. This trend was reversed at pH 7.4, resulting in high settlement, comparable to ambient biofilms. Settlement decreased on biofilms from pH 7.2, and no settlement was observed on biofilms from pH 7.0. For the first time, we show that long-term incubation of marine biofilms under a wide range of reduced seawater pH treatments can alter marine biofilms in such a way that settlement success in marine invertebrates can be compromised.

Continue reading ‘Reduced seawater pH alters marine biofilms with impacts for marine polychaete larval settlement’

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Ocean acidification in the IPCC AR5 WG II

OUP book