Posts Tagged 'algae'

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Salinity-dependent effects of seawater acidification on growth, photosynthetic physiology and biochemistry of the invasive macroalga Codium fragile

Published 25 March 2025 Science Closed
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Highlights

  • Decreased and increased salinity adversely affect the growth and photosynthetic physiology of Codium fragile under ambient pCO2 conditions.
  • Ocean acidification could help Codium fragile to encounter moderate salinity stress by up-regulating photosynthetic ability.
  • The deleterious effect of progressively decreased salinity on growth of Codium fragile was magnified when pCO2 increased.

Abstract

Ocean acidification (OA) and seawater salinity are two major environmental factors that influence the growth and distribution of macroalgae in coastal ecosystems. To investigate the effects of OA and salinity on the invasive macroalga Codium fragile, the growth, Chlorophyll a fluorescence, and biochemical compositions (pigment and soluble carbohydrate contents, the superoxide dismutase (SOD) activity, and malondialdehyde (MDA) contents) were studied after exposure to two pCO2 levels (400 ppmv, LC; and 1000 ppmv, HC) and four salinity regimes (high salinity, 40 psu; control salinity, 30 psu; medium salinity, 20 psu; low salinity, 10 psu). The results showed that, except for SOD activity at 20 psu, the growth, maximum and effective quantum yield of PSII, and maximum relative electron transport, pigment and soluble carbohydrate contents, SOD activity, and the MDA content were adversely impacted by both hypo- and hypersaline under LC conditions. Similarly, under HC conditions, the growth, photosynthetic physiology and biochemistry were negatively impacted by low salinity, while high salinity enhanced pigment contents and chlorophyll fluorescence parameters but inhibited SOD activity and MDA contents. Furthermore, higher pCO2 significantly promoted growth, pigment contents, and photosynthetic performance at 20 and 40 psu, while it amplified the depression in growth at 10 psu. These findings suggest that OA may enhance the potential invasive ability and salinity tolerance of C. fragile under medium hyposaline and hypersaline conditions by alleviating the negative effects of salinity stress on growth, photosynthesis, and pigments synthesis. However, it may also synergistically reduce algal growth at further reduced salinity. These data collected herein are valuable for understanding C. fragile cultivation and predicting its future distribution in response to changing ocean conditions.

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Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions

Published 25 March 2025 Science Closed
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Highlights

  • The decomposition of mixed and single detrital sources was assessed in current and future ocean conditions.
  • The identity of detrital sources significantly influenced decomposition rates, and carbon and nutrient release.
  • Detrital mixing significantly decreased variation in mass loss and nitrogen release.
  • Ocean warming sometimes increased rates of decomposition of macrophyte detritus.
  • Ocean acidification did not significantly influence detrital mass loss or nutrient release.

Abstract

The complex interactions between detrital diversity and ocean climate change are not well understood. Here, we used sixteen outdoor raceways to test the hypothesis that ocean warming, and acidification would increase rates of decomposition and nutrient release from detritus of common macroalgae, but the magnitude of change would vary for single detrital sources compared to mixed sources. Our litter-bag experiment to test this hypothesis had six types of macroalgal detritus: (i) Ecklonia radiata, (ii) Sargassum vestitum, (iii) Caulerpa filiformis, (iv) Ecklonia and Sargassum mix, (v) Ecklonia and Caulerpa mix, and (vi) Sargassum and Caulerpa mix. The experimental design also had an orthogonal set of treatments testing effects of ocean warming and acidification, individually and combined, based on the RCP 8.5 climate model for 2081–2100. The identity of detrital sources significantly influenced decomposition rates, carbon liberation and nutrient release. The treatments with two detrital sources did not have increased rates of decomposition and nutrient release compared to single sources. However, detrital source mixing significantly moderated variation in decomposition and nutrient release rates. While ocean acidification had little effect on the decomposition of macroalgal detritus, ocean warming tended to increase rates of decomposition. Given that excessive decomposition can lead to severe anoxia, the results suggest the risk of this occurring will be greater in the warmer oceans of coming decades. In such circumstances, the moderating force of detrital diversity may become increasingly important in maintaining benthic oxygen concentrations and detritus-based production.

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Quantifying coral-algal interactions in an acidified ocean: Sargassum spp. exposure mitigates low pH effects on Acropora cervicornis health

Published 3 March 2025 Science Closed
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Increasingly frequent large-scale pelagic Sargassum algae blooms in the Atlantic have become a problem for coastal ecosystems. The mass decay of these blooms reduces water quality for coastal flora and fauna. However, the effects of living Sargassum blooms on seawater quality and consequently coral reef ecosystems that rely on delicately balanced carbonate chemistry are more ambiguous. Future oceans are predicted to be more acidic as additional anthropogenic CO2 emissions are absorbed, potentially tipping the balance in favor of algal blooms at the cost of coral survival. This study aimed to simulate the indirect interaction between pelagic Sargassum spp. and Acropora cervicornis coral fragments from the Florida Reef in current-day and future ocean pH conditions over the course of 70 days in a mesocosm experimental system. Measurements of coral growth and health via buoyant weight and Pulse Amplitude Modulated (PAM) fluorescence measurements reveal an unexpected coral-algal interaction. After 1 month, coral growth was significantly reduced under ocean acidification conditions and exposure to Sargassum; at the same time quantum yield and maximum electron transport rate of photosynthesis were increased relative to control counterparts in ambient and future pH scenarios by up to 14% and 18% respectively. These improvements in photosynthetic efficiency did not translate to significant differences in growth by the final measurement time point. In addition, the presence of Sargassum spp. did not raise seawater pH in the system, raising questions about how it benefited photosynthetic efficiency in exposed corals. Heterotrophy of detrital algal matter is suspected to compensate for impaired photosynthesis of pH stressed corals. Therefore, despite their current negative reputation, Sargassum blooms could provide short term localized benefits to corals in present and future ocean conditions.

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Impacts of ocean acidification on the palatability of two Antarctic macroalgae and the consumption of a grazer

Published 27 February 2025 Science Closed
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Increases in atmospheric CO2 have led to more CO2 entering the world’s oceans, decreasing the pH in a process called ’ocean acidification’. Low pH has been linked to impacts on macroalgal growth and stress, which can alter palatability to herbivores. Two common and ecologically important macroalgal species from the western Antarctic Peninsula, the unpalatable Desmarestia menziesii and the palatable Palmaria decipiens, were maintained under three pH treatments: ambient (pH 8.1), near future (7.7) and distant future (7.3) for 52 days and 18 days, respectively. Discs of P. decipiens or artificial foods containing extracts of D. menziesii from each treatment were presented to the amphipod Gondogeneia antarctica in feeding choice experiments. Additionally, G. antarctica exposed to the different treatments for 55 days were used in a feeding assay with untreated P. decipiens. For D. menziesii, extracts from the ambient treatment were eaten significantly more by weight than the other treatments. Similarly, P. decipiens discs from the ambient and pH 7.7 treatments were eaten more than those from the pH 7.3 treatment. There was no significant difference in the consumption by treated G. antarctica. These results suggest that ocean acidification may decrease the palatability of these macroalgae to consumers but not alter consumption by G. antarctica.

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CO2 fertilisation counteracts the negative effect of poor water quality on the growth and photosynthesis of a Great Barrier Reef coralline alga

Published 10 February 2025 Science Closed
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The global problem of ocean acidification and localised decline in water quality are major threats to coral reefs worldwide. This study examined the individual and interactive impacts of global and local stressors by investigating the effects of increased seawater pCO2, elevated nutrient concentrations and reduced light levels on linear growth and metabolic rates of the common branching crustose coralline alga Lithophyllum cf. pygmaeum. We found complex interactions between factors on algal growth and photosynthetic rates, but overall, growth was significantly enhanced by pCO2 enrichment under all light and nutrient combinations. This is the first study to report a positive growth response in coralline algae to elevated pCO2 using linear extension methods. In contrast, the combination of reduced light levels and high nutrient concentrations simulating poor water quality conditions reduced algal growth rates by up to 67% (compared to individuals exposed to high light, low nutrients and elevated pCO2). Decreased light levels reduced linear growth, Pgross and Pnet rates by 33%, 18% and 24%, respectively, highlighting the critical role of light in coralline algal physiology. We suggest that poor water quality may counteract any CO2 fertilisation effect under ocean acidification conditions on the growth of coralline algae, and this has implications for coral reef conservation as it emphasises the importance of improving water quality to maintaining coral reef functions. These results further highlight the need for multifactorial experiments to better understand the interplay between global and local processes on coralline algae growth.

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Short-term negative effects of seawater acidification on the rhodolith holobionts metatranscriptome

Published 7 February 2025 Science Closed
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Highlights

  • Cyanobacteria dominate the microbial community in living rhodoliths.
  • Vibrionales dominate dead rhodolith skeletons.
  • Short-term (1 h) acidification affects the microbial community structure.
  • Diverse functional genes modulate microbe-host interactions.

Abstract

Rhodolith holobionts are formed by calcareous coralline algae (e.g., Corallinales) and associated microbiomes. The largest rhodolith bank in the South Atlantic is located in the Abrolhos Bank, in southwestern Brazil, covering an area of 22,000 km2. Rhodoliths serve as nurseries for marine life. However, ocean acidification threatens them with extinction. The acute effects of high pCO₂ levels on rhodolith metatranscriptomes remain unknown. This study investigates the transcriptomic profiles of rhodoliths exposed to short-term (96-h) high pCO₂ levels (up to 1638 ppm). Metatranscriptomes were generated for both dead and alive rhodoliths (15.48 million Illumina reads in total). Alive rhodoliths showed an enrichment of gene transcripts related to environmental stress responses and photosynthesis (Cyanobacteria). In contrast, the metatranscriptomes of dead rhodoliths were dominated by heterotrophic (Proteobacteria and Bacteroidetes) metabolism and virulence factors. The rhodolith holobiont metatranscriptomes respond rapidly to short-term acidification (within 1 h), suggesting that these holobionts may have some capacity to cope with acute acidification effects. However, the negative impacts of prolonged ocean acidification on rhodolith health cannot be overlooked. Rhodoliths exposed to low pH (7.5) for 96 h exhibited a completely altered transcriptomic profile compared to controls. This study highlights the plasticity of rhodolith transcriptomes in the face of ocean acidification and climate change.

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The effect of water motion and elevated carbon on two green algae Ulva intestinalis and Cladophora glomerata DIC acquisition and DOC release in the brackish Baltic Sea

Published 31 January 2025 Science Closed
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Macrophytes play a key role in coastal environments, acting to transform inorganic carbon into biologically available organic matter. This process supports the marine food web at large, however, the dynamics behind macrophyte carbon acquisition are not fully understood with factors influencing their ability to utilize different carbon forms (HCO3− and/or CO2) and subsequent release mechanics of this carbon remaining rather poorly understood. This study aims to investigate the physiological responses of two important Baltic Sea macrophytes, Ulva intestinalis and Cladophora glomerata. By examining the effects of pH drift inhibitors, coupled with carbon-concentrating mechanisms (CCMs) and dissolved organic carbon (DOC) dynamics, we provide insights into the complex adaptations of these macroalgae to changing environmental conditions. The results demonstrate that both species exhibit distinct capabilities to adapt their carbon concentration mechanisms (CCMs) but suggest that C. glomerata may potentially gain a photosynthetic advantage in future high CO2. The observed differences between pH and water motion highlight species-specific nuances in the regulation of dissolved organic carbon (DOC) release, aligning with current theories on DOC dynamics. This research underscores the importance of understanding macroalgal adaptation and fitness in both present and future coastal ecosystems, particularly as environmental changes continue to evolve. By examining these factors, the study contributes valuable insights into how macroalgae may respond to future climate shifts.

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Seagrass influence on mitigating ocean acidification and warming impacts on tropical calcifying macroalgae

Published 28 January 2025 Science Closed
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Highlights

  • OA and warming reduce calcium carbonate for marine calcifiers.
  • Seagrass can capture excess carbon, possibly mitigating OA effects.
  • 12-week study tested algae with/without seagrass under increasing stress.
  • M. rosea was affected by OA and warming; H. opuntia by temperature alone.
  • Mesophyllum sp. was resilient, and seagrass did not reduce OA impacts.
  • Light, flow, combining OA and warming, likely to impact coralline algae

Abstract

Ocean acidification (OA) and warming pose significant threats to marine ecosystems, particularly by reducing calcium carbonate availability for marine calcifiers. Given that seagrasses can capture and store excess carbon, this study aimed to investigate whether seagrasses can mitigate the impacts of OA and elevated temperatures on three calcifying macroalgae: Mastophora rosea, Halimeda opuntia, and Mesophyllum sp. A 12-week mesocosm experiment was conducted, where the algae were cultured with and without seagrass under gradually increasing stress conditions: ambient conditions, OA alone for four weeks, OA combined with elevated (but non-stressful) temperatures (28°C) for four weeks, and OA plus a stress-inducing temperature (31°C) for two weeks. Results indicated that OA and warming negatively affected M. rosea, while H. opuntia was more strongly impacted by temperature alone. Mesophyllum sp. exhibited resilience to both OA and elevated temperatures. Contrary to expectations, the presence of seagrass did not mitigate the negative effects of OA and warming on these calcifying macroalgae species.

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The response mechanisms of kelp Macrocystis pyrifera holobiont to elevated temperature and CO2 concentration

Published 17 January 2025 Science Closed
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The kelp Macrocystis pyrifera, a crucial component of marine ecosystems, is significantly impacted by climate change and environmental stresses. Macrocystis pyrifera and its associated bacteria form a holistic functional unit (holobiont), yet the regulatory roles of bacteria in stress responses and acclimation are often overlooked. This study investigates the diversity of M. pyrifera associated bacteria and their chemical interactions under high temperature and elevated CO2 conditions. Our findings indicate that high temperatures significantly reduce associated bacterial diversity, while elevated CO2 does not alter community structure. Key microbial biomarkers identified include Pseudomonas, Sulfitobacter, and Olleya. However, it is unknown how they function in M. pyrifera. In metabolite analysis, we identified 18 metabolites with significant differences. These metabolites included phospholipids, antibacterial compounds, signaling molecules, and various compounds of unclear function. The changes in these compounds are probably connected to how M. pyrifera respond to climate change. These results will enrich the baseline data related to the chemical interactions between the microbiota and M. pyrifera and provide clues for predicting the resilience of M. pyrifera to future climate change.

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Impacts of climate change on members of shallow water Antarctic communities

Published 16 January 2025 Science Closed
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Human-derived CO2 emissions have lowered the ocean’s pH and increased global temperatures. Low seawater pH can decrease the calcification, growth, and survival of calcifying invertebrates. Furthermore, low pH changes macroalgal growth and stress, possibly altering palatability to consumers. Global warming has decreased sea ice coverage, profoundly influencing photosynthetic organisms by altering subsurface irradiance. Shallow, hard-bottom communities along the Western Antarctic Peninsula are characterized by large macroalgal forests that shelter large numbers of mesograzers. Amphipods and macroalgae have a community-wide mutualistic relationship where macroalgae provide refuge from predatory fish while amphipods remove competing epiphytes. To understand how climate change could impact members of this relationship, macroalgal-associated mesograzers were collected near Palmer Station, Antarctica (64°46′S, 64°03′W) and maintained under three different pH treatments [ambient (pH 8.1), near-future (pH 7.7), and distant-future conditions (pH 7.3)] for 52 days. Total assemblage number and the relative proportion of each species were similar across the treatments, indicating possible resistance to short-term low pH exposure. The amphipods Djberboa furcipes, Gondogeneia antarctica, and Prostebbingia gracilis were maintained under the pH treatments for 8 weeks. No difference in biochemical composition or survival was found between the treatments for any of the species. However, each species decreased molt activity between the ambient and pH 7.3 treatment. These results suggest that amphipods may maintain their survival in decreased pH by reallocating energy into compensatory behaviors and away from energy-expensive processes like molting. The palatability of the unpalatable Desmarestia menziesii and the palatable Palmaria decipiens were maintained under three pH treatments and then presented to the amphipod Gondogeneia antarctica in a feeding choice assay. Decreased seawater pH generally lowered the consumption of both species, suggesting that acidification may decrease the palatability of these macroalgae to consumers. Finally, biochemical composition, carbon and nitrogen percentages, and C:N were correlated with sea ice indices for the macroalgae D. menziesii, Himantothallus grandifolius, Sarcopeltis antarctica, and Iridaea sp. from a sea ice gradient. Surprisingly, most of the chemical components were not correlated with sea ice cover, indicating sea ice coverage does not change the nutritional contributions of macroalgae to food webs.

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Natural fluctuation of pH in shallow-water macrophyte habitats in the brackish Baltic Sea

Published 15 January 2025 Science Closed
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The pH declines caused by increasing atmospheric CO2 as defined term “ocean acidification”, are more predictable in open ocean surface waters than in coastal seas. The pH of coastal waters is inherently more variable due to the effects of different factors, for example, temperature, biological uptake and respiration, pollution, and terrestrial run-off. Benthic macrophytes are important structural components in coastal ecosystems, playing crucial roles as primary producers and habitat formers. In this coastal ecosystem, the daily pH fluctuation is also strongly affected by algal photosynthesis (increasing pH) and respiration (lowering pH). In this study, we investigated the diurnal fluctuations in pH in shallow-water macroalgal habitats in July and August 2023 in the Estonian coastal waters, NE Baltic Sea. The study sites were chosen to represent different compositions of macrophyte species and environmental conditions. Measurements were carried out at each site for a full 24-hour cycle at a 5-meter depth during the active growth period. In addition, water temperature, and photosynthetically active radiation (PAR) were measured continuously at each site. Biomass samples were collected by scuba divers from surrounding macrophyte communities. Our results showed that the pH values at different study sites exhibited large daily variations as well as large variations during the study period. Within the study period, the pH fluctuations in different sites exceeded 1 unit, which is higher than pH changes owing to ocean acidification predicted for surface ocean waters by 2100. Our results suggested that besides local environmental conditions, the magnitude of pH changes in shallow coastal waters depends on the carbon use strategies of macrophytes as well as the community biomass. Overall, this natural fluctuation in pH in shallow coastal waters is important to incorporate into future climate change prediction scenarios.

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Response of the photosynthetic physiology of Ulva lactuca to Cu toxicity under ocean acidification

Published 8 January 2025 Science Closed
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Highlights

  • Low Cu concentrations promote the growth of Ulva lactuca.
  • The growth of Ulva lactuca was decreased with Cu increase under low CO2 condition.
  • Ocean acidification can exacerbate the adverse effects of Cu on Ulva lactuca.

Abstract

Ocean acidification can significantly affect the physiological performance of macroalgae. While copper (Cu) is an essential element for macroalgae and has been extensively studied, the interactive effects of ocean acidification and Cu on these organisms remain less understood. In this study, we measured the photosynthetic characteristics of Ulva lactuca exposed to varying Cu concentrations at two CO2 levels (415 ppmv, low concentration; 1000 ppmv, high concentration). The results indicated that during chronic toxicity testing, the growth of juvenile U. lactuca significantly increased at Cu concentrations of 0.001 μM, 0.01 μM, and 0.1 μM regardless of low CO2 concentrations or high CO2 concentrations condition. In acute toxicity tests, elevated Cu concentrations negatively impacted the growth rate, yield, and photosynthetic rate of U. lactuca under low CO2 concentrations. Conversely, high CO2 concentrations enhanced the photosynthetic capacity of U. lactuca with increased Cu concentrations, while the growth rate significantly decreased at Cu concentration of 1.5 μM. Additionally, the activities of peroxidase (POD) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) increased, with an enhancement of malondialdehyde (MDA) content at 1.5 μM Cu under high CO2 conditions. However, the structure of the chloroplast thylakoid was disrupted by elevated Cu concentrations. These findings suggest that low Cu concentrations promote the growth of U. lactuca, whereas high Cu concentrations inhibit algal growth, and ocean acidification may exacerbate the adverse effects of Cu on U. lactuca in acute toxicity tests.

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The photosynthetic quotient (PQ) of Ulva ohnoi (Chlorophyta) under future ocean conditions

Published 2 January 2025 Science Closed
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Recently there has been a rapid increase in interest regarding the CO2 removal capacity of seaweed, leading to a focus on photosynthesis research. Because direct measuring the dissolved inorganic carbon (CT) uptake rate is challenging, the use of the photosynthetic quotient (PQ), which converts oxygen evolution to carbon fixation, has proven effective. However, PQ is highly sensitive to various environmental factors, including climate change (warming and acidification). This study aimed to investigate the impact of climate change conditions on the PQ of Ulva ohnoi, namely, control (CONT: 271 µatm CO2 & 20°C), acidification (OA: 526 µatm CO2 & 20°C), warming (OW: 307 µatm CO2 & 25°C), and greenhouse (GR: 634 µatm CO2 & 25°C). The PQ was determined through an incubation experiment, where simultaneous measurements of O2 evolution and CT uptake rates were conducted in a seawater medium. The average PQ values were consistently above 1 across all treatments, with the highest PQ values observed in the CONT (1.67 ± 0.03) and the lowest in the OW (1.16 ± 0.04). While increased CO2 levels and light intensity did not affect the PQ value, higher temperatures had a significant impact on the PQ of U. ohnoi. Consequently, it can be expected that increased temperatures will lead to a decrease in PQ, resulting in increased CT uptake compared to O2 evolution. Estimating CT uptake based on O2 evolution may, therefore, lead to an overestimation of the CT uptake rate when applying theoretical PQ.

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Effects of pH, temperature, and light on the inorganic carbon uptake strategies in early life stages of Macrocystis pyrifera (Ochrophyta, Laminariales)

Published 1 January 2025 Science Closed
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The responses of seaweed species to increased CO2 and lowered pH (Ocean Acidification: OA) depend on their carbon concentrating mechanisms (CCMs) and inorganic carbon (Ci) preferences. However, few studies have described these mechanisms in the early life stages of seaweeds or assessed the effects of OA and its interactions with other environmental drivers on their functionality and photophysiology. Our study evaluated the effects of pH, light (PAR), temperature, and their interactions on the Ci uptake strategies and photophysiology in the early stages of Macrocystis pyrifera. Gametophytes were cultivated under varying pH (7.80 and 8.20), light (20 and 50 µmol photons m−2s−1), and temperature (12 and 16 °C) conditions for 25 days. We assessed photophysiological responses and CCMs (in particular, the extracellular dehydration of HCO3− to CO2 mediated by the enzyme carbonic anhydrase (CA) and direct HCO3− uptake via an anion exchange port). This study is the first to describe the Ci uptake strategies in gametophytes of M. pyrifera, demonstrating that their primary CCM is the extracellular conversion of HCO3− to CO2 mediated by CA. Additionally, our results indicate that decreased pH can positively affect their photosynthetic efficiency and maximum quantum yield; however, this response is dependent on the light and temperature conditions.

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Characterization of coral communities in the shallow hydrothermal vents of Mabini, Batangas, Philippines

Published 31 December 2024 Science Closed
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The existence of shallow hydrothermal vents in Mabini, Batangas, Philippines, has been recognized to contribute to CO2-rich submarine groundwater discharges. However, little is known about the existing coral community structure in the area which provides valuable ecosystem goods and ecological services. We characterized the reef community in this unique microenvironment falls within the predicted future reef condition with low pH and aragonite saturation using coral recruitment tiles, examined coral life-history strategies and size frequency distribution, and measured calcification of transplanted fragments from the genus Goniopora sp., Pectinia sp., and Porites sp. The availability of larval supply has proven that corals can still settle (45–73 recruits m−2) due to the presence of hard substrate and settlement cues such as the crustose coralline algae. The existing coral colonies were mostly dominated by stress-tolerant groups and sizes ranging from 5 to 20 cm. Deployed coral fragments showed growth via extension, and calcification was negatively affected by local conditions, such as Porites sp. fragments. Higher nutrient input may have promoted coral growth, but combined with low carbonate chemistry, it likely made the corals more susceptible to physical damage, as seen on the fragments. This study highlights the importance of naturally occurring extreme environments to determine climate-resilient corals that can adapt to changing conditions and recover from disturbances over time.

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Rhodolith beds in a shifting world: a palaeontological perspective

Published 16 December 2024 Science Closed
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The occurrence of rhodolith beds in the stratigraphic record from the Cretaceous to the Pleistocene was analysed from published papers. Most data refer to low-mid latitude records of rhodolith beds described in the Tethyan-Paratethyan-Mediterranean domain. The first putative rhodolith beds are from Albian (uppermost Lower Cretaceous) deposits. These rhodolith beds are made up mostly of unattached loose branching corallines as well as of nodular structures. From the Coniacian (Upper Cretaceous) to the Langhian (Middle Miocene), abundance of rhodolith beds shows a generally increasing fluctuating trend with two significant expansions in the Priabonian (late Eocene) and during the Aquitanian-Langhian (Early-Middle Miocene). After the Langhian maximum, rhodolith beds sharply declined to a minimum in the Zanclean (Early Pliocene). During the Pleistocene, they recovered to values similar to those reached in the Langhian. The general increase in rhodolith beds up the Langhian maximum correlates well with global temperature and pCO2 declines and with an ocean pH increase. The tectonic activity leading to important palaeogeographic changes in the Tethyan-Parathetyan-Mediterranean realm might account for the Serravallian-Zanclean downfall of rhodolith-dominated deposits. The Cretaceous-Pleistocene record of rhodolith beds shows that these ecosystems withstood successfully a highly changing world. The rapid acclimation of particular taxa to environmental changes and the variable reaction of taxa distributed at different water depths can be crucial to understand their success. In this regard, it would be interesting to analyse how different taxa in modern deep rhodolith beds respond to changing oceanic conditions.

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Resource homogenisation drives niche convergence between generalists and specialists in a future ocean

Published 13 December 2024 Science Closed
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Highlights

  • Do marine herbivores adjust their trophic niches under climate change?.
  • Specialist and generalist herbivore niches and their food were tested using stable isotopes.
  • Food resources were dominated by turf algae and SOM under climate change.
  • Niche breath of generalists narrowed under climate stress but widened in specialists.
  • Generalists and specialists appear to converge their trophic niches under climate change.

Abstract

When humans drive rapid environmental change, is it favourable to be a generalist or specialist? To address this question, we compare how specialist and generalist marine herbivores adjust their isotopic niches (used as proxy for trophic niche) in response to predicted resource alterations under the simulated effects of ocean warming and acidification (based on a 6-month mesocosm experiment). Here, we show that when exposed to multiple climate stressors, food resources homogenized towards dominance of turf algae and suspended organic matter, with generalists and specialists adjusting their trophic niches in opposing ways. Whilst the niche breath of most generalists narrowed under climate stressors, those of specialists generally broadened, causing increasing overlap between their niches. The magnitude of this change was such that some generalists turned into specialists, and vice versa. Under ocean acidification, there was a greater probability of generalists increasing and specialists maintaining their biomass, respectively, but under warming the biomass of both specialists and generalists had a greater probability of collapse. For specialists, this collapse occurred even though they had adequate thermal tolerance and the capacity to expand their trophic niche. Climate change constrains or liberates resources, but where they are homogenized, generalists and specialists are likely to converge their trophic niches so they can exploit transforming environments for their survival or adaptive advantage.

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Major threats to rhodolith beds: ocean acidification, global warming, and local stressors

Published 6 December 2024 Science Closed
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Since the industrial revolution, the human population has accelerated its magnitude of impact on the world’s oceans. The observed consequences of our rising population and globalization have expanded substantially and are expected to affect even the deepest ecosystems. The extensive rhodolith beds along the Brazilian coastline that are present from the shallows down to 133 m are predicted and already observed to suffer from the consequences of human interference. Rhodolith beds are predicted to experience a daunting diversity of anthropogenic threats, which act at different scales. Global stressors such as ocean acidification and global climate change are shown to affect fundamental metabolic processes, which over time are expected to jeopardize the integrity of these ecosystems. Local stressors such as nutrient runoff, pollution, oil/gas exploitation, predatory fishing as bottom trawling, and direct coralline mining are expected to interact with global stressors and, in multiple cases, exacerbate already negative prognosis.

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The influence of macrophytes on diurnal pH variability in subtropical estuaries: a mesocosm study

Published 4 December 2024 Science Closed
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Highlights

  • Macrophytes influence estuary water column pH levels.
  • Floating macrophytes decrease pH and submerged macrophytes increase pH.
  • Diurnal pH variability is more pronounced in submerged macroalgae.
  • Floating macrophytes exhibit lower diurnal variability.

Abstract

Coastal ecosystems are increasingly threatened by anthropogenic impacts, particularly from land-based activities that drive eutrophication. This research investigated eutrophication and the unique challenges facing southern hemisphere coastal ecosystems. We used a mesocosm study to measure the influence of a macroalga (Rhizoclonium riparium) and a floating macrophyte (Pistia stratiotes), on diurnal pH variability. Diurnal pH variability was more pronounced in the presence of macroalgae due to the direct release of metabolic byproducts into the water column during photosynthesis and respiration. In contrast, floating macrophyte treatments had lower diurnal pH variability, as metabolic byproducts are released into the atmosphere through floating foliage. Floating macrophytes influenced overall water column pH levels, resulting in an acidification effect, becoming more pronounced as macrophyte biomass increased. The study highlighted the importance of nutrient management and its association with macrophytes, to preserve the delicate balance of estuaries, and ensure the sustainable functioning of these critical ecosystems. Further in situ research is recommended to validate and expand on the mesocosm findings.

Continue reading ‘The influence of macrophytes on diurnal pH variability in subtropical estuaries: a mesocosm study’

Varying effects of climate change on the photosynthesis and calcification of crustose coralline algae: implications for settlement of coral larvae

Published 4 December 2024 Science Closed
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Highlights

  • Corals maintain settlement preferences under future climate conditions
  • Future climate conditions negatively affect crustose coralline algae physiology
  • Physiological responses to future climate conditions varied by algal species

Abstract

Coral recruitment is critical to the maintenance of healthy coral reef ecosystems. Many coral species settle preferentially on certain crustose coralline algae (CCA) (e.g., Hydrolithon boergesenii) over others (e.g., Paragoniolithon solubile). Calcifying organisms like CCA are particularly susceptible to ocean acidification (OA), and settlement behavior of larvae may be compromised as seawater temperatures increase (ocean warming; OW) and pH levels decrease as a result of climate change. Here, we examine the effects of future seawater conditions (OW and OA) on the calcification and photosynthetic efficiency of two CCA species, H. boergesenii and Pa. solubile. We also examine the effects of conditioning CCA in combined OA and OW on the settlement preferences of three coral species, Acropora palmata, A. cervicornis and Porites astreoides. Acropora palmata and Po. astreoides demonstrated a preference for H. boergesenii over Pa. solubile in choice experiments after short-term treatment (7–21 days) and this preference was not affected by future seawater conditions. A. cervicornis did not demonstrate a CCA preference under any treatment. Po. astreoides did not demonstrate a CCA preference in no-choice assays and settlement was unaffected by OW and OA even after the longest exposure (99 days). Both CCA had reduced photosynthetic efficiency after exposure to future seawater conditions. However, net calcification rate was reduced in H. boergesenii but not Pa. solubile after exposure to future seawater conditions. These results demonstrate that while climate change may differentially affect the physiological functioning of various species of CCA, coral settlement preferences are unlikely to be altered.

Continue reading ‘Varying effects of climate change on the photosynthesis and calcification of crustose coralline algae: implications for settlement of coral larvae’

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