Marine ecosystems face unprecedented challenges in the Anthropocene, an age characterized by escalating environmental stressors such as ocean acidification, warming and the intrusion of human infrastructure into coastal seascapes. As we hasten to understand the ecological consequences of these mounting pressures, much attention has been devoted to characterizing the traits of individual taxa that are likely to dictate their response to future conditions. However, we are increasingly recognizing the pivotal role that habitat may play in shaping the response of communities to such broad-scale changes. In this thesis, I present empirical evidence of the capacity of habitat-level responses to stress to propagate upwards through the broader ecosystem, inducing substantial and meaningful changes in supported fish assemblages. In my first project, I trace the indirect effects of ocean acidification from the habitat level through to the structure of an assemblage of small-bodied reef fish. I use the natural laboratory provided by a volcanic seep in Papua New Guinea to approximate future acidification conditions under current climate change projections. Here, coral communities chronically exposed to elevated CO2 exhibit a shift in competitive interactions that favours fast-growing, morphologically simple taxa, with the implication that other coral reefs globally may undergo an equivalent structural simplification in coming decades in response to ocean acidification. I show that several common, ecologically important reef fishes display strong and relatively inflexible associations with branching corals, with some even preferencing structure over living tissue when selecting habitat. I then demonstrate that acidified and structurally simplified reefs show a drastically reduced capacity to support healthy populations of these fishes. This chapter contributes two important findings: first, that simplification of coral morphology in response to ocean acidification can induce substantial negative changes in supported reef fish assemblages, even if the total cover of live coral remains unchanged; and secondly, that reef fish may be more vulnerable to these indirect, habitat level changes than to the simple direct effects wrought by acidification. Shifting focus to temperate ecosystems, my second project examines how warming, coastal urbanisation and marine protection interact to influence the distributions and assemblage structures of rangeshifting tropical fishes as they venture poleward in response to ocean warming. Using breakwalls as a ubiquitous and readily accessible test case, I reveal that the structural complexity and shelter from wave action offered by coastal infrastructure can render these environments hotspots for tropical fish recruitment. Importantly, this chapter both identifies coastal infrastructure as potentially significant contributors to the process of tropicalisation, highlighting the need for further research attention and monitoring, but also recognises that marine protected areas can offer an effective means of mitigating the effects of coastal urbanisation. Together, the two projects presented in this thesis demonstrate the power of both the direct and indirect effects of habitat changes. In light of the ongoing and accelerating accumulation of anthropogenically induced stressors, my research underscores the necessity of accounting for habitat-level responses when projecting future fish assemblages, and frames habitat protection as a vital element of safeguarding healthy ecosystems.
Continue reading ‘Bottom’s up – focusing on habitat shifts as mediators of anthropogenic impacts on marine ecosystems’Posts Tagged 'community composition'
Bottom’s up – focusing on habitat shifts as mediators of anthropogenic impacts on marine ecosystems
Published 16 July 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, corals, fish, otherprocess, South Pacific
Out of shape: ocean acidification simplifies coral reef architecture and reshuffles fish assemblages
Published 3 July 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, corals, fish, otherprocess, performance, physiology, South Pacific
- Climate change stressors are progressively simplifying biogenic habitats in the terrestrial and marine realms, and consequently altering the structure of associated species communities.
- Here, we used a volcanic CO2 seep in Papua New Guinea to test in situ if altered reef architecture due to ocean acidification reshuffles associated fish assemblages.
- We observed replacement of branching corals by massive corals at the seep, with simplified coral architectural complexity driving abundance declines between 60% and 86% for an assemblage of damselfishes associated with branching corals. An experimental test of habitat preference for a focal species indicated that acidification does not directly affect habitat selection behaviour, with changes in habitat structural complexity consequently appearing to be the stronger driver of assemblage reshuffling. Habitat health affected anti-predator behaviour, with P. moluccensis becoming less bold on dead branching corals relative to live branching corals, irrespective of ocean acidification.
- We conclude that coral reef fish assemblages are likely to be more sensitive to changes in habitat structure induced by increasing pCO2 than any direct effects on behaviour, indicating that changes in coral architecture and live cover may act as important mediators of reef fish community structures in a future ocean.
Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates
Published 3 July 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, echinoderms, mollusks, otherprocess, performance, sediment
Climate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour—a key process mediating nutrient cycling—associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO2]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing.
Continue reading ‘Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates’Sulphate reduction and carbonate precipitation in a high-energy algal rim framework
Published 24 June 2024 Science ClosedTags: biogeochemistry, biological response, BRcommunity, chemistry, community composition, corals, laboratory, otherprocess, prokaryotes, South Pacific
Algal ridges are protective features for coral reefs that form through the accretion and encrustation of reef rubble and debris by crustose coralline algae (CCA) and processes of diagenetic cementation. Carbonate precipitation and dissolution dynamics on and within algal ridge frameworks are poorly understood. We studied the surface and subsurface geochemistry of the algal ridge framework at One Tree Island, Australia. Measurable quantities of hydrogen sulphide were detected in most porewater samples collected from bores, indicating a largely anoxic ridge framework. Total alkalinity (TA) and pH measurements indicate that the precipitation of carbonate minerals within the interior of the ridge framework occurs under largely anoxic conditions and is likely to be driven by TA changes associated with sulphate-reducing bacteria. Modelling of porewater hydrogen sulphide concentrations in combination with TA and dissolved inorganic carbon (DIC) indicates anoxic respiration processes produce alkalinity within the algal ridge framework. However, significantly more TA is removed via the precipitation of mineral carbonate, resulting in porewater TA concentrations falling below the open seawater values. The precipitation of mineral carbonate also lowers interstitial water pH, such that pH changes are not solely from organic carbon diagenesis. The simultaneous precipitation and dissolution of carbonate minerals within the algal ridge framework are key to forming and cementing algal ridges, which are important physical protective features for coral reefs.
Continue reading ‘Sulphate reduction and carbonate precipitation in a high-energy algal rim framework’Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons
Published 20 June 2024 Science ClosedTags: abundance, biological response, BRcommunity, calcification, chemistry, community composition, corals, dissolution, laboratory, morphology, North Atlantic, otherprocess, primary production, protists, respiration
As the balance between erosional and constructive processes on coral reefs tilts in favor of framework loss under human-induced local and global change, many reef habitats worldwide degrade and flatten. The resultant generation of coral rubble and the beds they form can have lasting effects on reef communities and structural complexity, threatening the continuity of reef ecological functions and the services they provide. To comprehensively capture changing framework processes and predict their evolution in the context of climate change, heavily colonized rubble fragments were exposed to ocean acidification (OA) conditions for 55 days. Controlled diurnal pH oscillations were incorporated in the treatments to account for the known impact of diel carbonate chemistry fluctuations on calcification and dissolution response to OA. Scenarios included contemporary pH (8.05 ± 0.025 diel fluctuation), elevated OA (7.90 ± 0.025), and high OA (7.70 ± 0.025). We used a multifaceted approach, combining chemical flux analyses, mass alteration measurements, and computed tomography scanning images to measure total and chemical bioerosion, as well as chemically driven secondary calcification. Rates of net carbonate loss measured in the contemporary conditions (1.36 kg m−2 year−1) were high compared to literature and increased in OA scenarios (elevated: 1.84 kg m−2 year−1 and high: 1.59 kg m−2 year−1). The acceleration of these rates was driven by enhanced chemical dissolution and reduced secondary calcification. Further analysis revealed that the extent of these changes was contingent on the density of the coral skeleton, in which the micro- and macroborer communities reside. Findings indicated that increased mechanical bioerosion rates occurred in rubble with lower skeletal density, which is of note considering that corals form lower-density skeletons under OA. These direct and indirect effects of OA on chemical and mechanical framework-altering processes will influence the permanence of this crucial habitat, carrying implications for biodiversity and reef ecosystem function.
Continue reading ‘Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons’Functional diversity and metabolic response in benthic communities along an ocean acidification gradient
Published 1 May 2024 Science ClosedTags: abundance, annelids, biological response, BRcommunity, chemistry, community composition, crustaceans, echinoderms, field, Mediterranean, mollusks, otherprocess, vents
Highlights
- Ocean acidification (OA) affect the distribution of traits within a community leading to the selection of specific functional traits.
- Along with the selection of traits, OA led to differences in oxygen consumption between benthic communities following acidification gradient.
- Altered acidified condition have a negative effect on the stability of the community resulting from changes in functional evennes of benthic communities.
Abstract
Altered ocean chemistry caused by ocean acidification (OA) is expected to have negative repercussions at different levels of the ecological hierarchy, starting from the individual and scaling up to the community and ultimately to the ecosystem level. Understanding the effects of OA on benthic organisms is of primary importance given their relevant ecological role in maintaining marine ecosystem functioning. The use of functional traits represents an effective technique to investigate how species adapt to altered environmental conditions and can be used to predict changes in the resilience of communities faced with stresses associated with climate change. Artificial supports were deployed for 1-y along a natural pH gradient in the shallow hydrothermal systems of the Bottaro crater near Panarea (Aeolian Archipelago, southern Tyrrhenian Sea), to explore changes in functional traits and metabolic rates of benthic communities and the repercussions in terms of functional diversity. Changes in community composition due to OA were accompanied by modifications in functional diversity. Altered conditions led to higher oxygen consumption in the acidified site and the selection of species with the functional traits needed to withstand OA. Calcification rate and reproduction were found to be the traits most affected by pH variations. A reduction in a community’s functional evenness could potentially reduce its resilience to further environmental or anthropogenic stressors. These findings highlight the ability of the ecosystem to respond to climate change and provide insights into the modifications that can be expected given the predicted future pCO2 scenarios. Understanding the impact of climate change on functional diversity and thus on community functioning and stability is crucial if we are to predict changes in ecosystem vulnerability, especially in a context where OA occurs in combination with other environmental changes and anthropogenic stressors.
Continue reading ‘Functional diversity and metabolic response in benthic communities along an ocean acidification gradient’Geochemical evidence of temporal ecosystem photosynthetic plasticity within a pristine coral atoll
Published 29 April 2024 Science ClosedTags: algae, biological response, chemistry, community composition, laboratory, photosynthesis, South Pacific
The impacts of ocean acidification on coral reef macroalgal community composition and metabolism have implications for the habitat supporting capacity of future reefs. In this pilot study, we use co-located semi-hourly measurements of total dissolved inorganic carbon (DIC), total alkalinity, and the stable carbon isotope composition of DIC (δ13CDIC) over a 27 + h period from Tetiaroa Atoll, French Polynesia, to investigate the potential for reef carbonate chemistry to record information related to benthic photosynthetic community composition and response to natural gradients in ambient acidity and dissolved carbon dioxide. The results of this preliminary sampling and modeling exercise suggest that Tetiaroa’s macroalgal communities express plastic carbon-concentrating mechanisms (CCMs) over daily cycles of productivity but may potentially vary this expression as a function of ambient CO2 and acidity within the ecosystem. Additional studies are, therefore, underway to investigate the implications of these observations for reef macroalgal compositional differences under rapidly acidifying oceans.
Continue reading ‘Geochemical evidence of temporal ecosystem photosynthetic plasticity within a pristine coral atoll’Meiobenthos and ocean acidification: effects on meiobenthic communities inhabiting Mediterranean cold shallow CO2-vents
Published 5 April 2024 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, field, Mediterranean, nematodes, otherprocess, sediment, vents
Highlights
- Ocean acidification modify the composition of marine communities.
- Meiobenthos around Castello Aragonese is influenced by CO2 emissions.
- Nematofauna inhabiting CO2 vents is adapted to pH variability.
- Acidification influences nematode diversity and functional diversity.
- Sediment type and O2 are major factors affecting the nematofauna.
Abstract
Ocean acidification is causing major changes in marine ecosystems, with varying levels of impact, depending both on the habitat and the studied organisms. Here, we investigated for the first time the meiobenthos and nematode fauna inhabiting the sediments around Castello Aragonese (Ischia, Italy), characterized by variable pH values due to coastal volcanic CO2 venting. In this scenario, nematode functional diversity changed according to different pH levels and grain size: maturity index was higher at most acidic stations and trophic composition spanned from the dominance of predators in the acidic stations, to the high abundance of non-selective deposit feeders and epistrate feeders in the ambient-pH stations. Overall, the present study revealed a relatively high tolerance of meiobenthos and nematodes to lower pH conditions. However, an in-depth analysis of nematode fauna showed differences in their assemblages at different pH levels with few nematode genera rather adapted to the extreme environmental conditions at the acidic stations.
Continue reading ‘Meiobenthos and ocean acidification: effects on meiobenthic communities inhabiting Mediterranean cold shallow CO2-vents’A laboratory study of the increasing competitiveness of Karenia mikimotoi under rising CO2 scenario
Published 3 April 2024 Science ClosedTags: algae, biological response, community composition, laboratory, morphology, multiple factors, North Pacific, otherprocess, physiology, phytoplankton, temperature
Highlights
- Rising CO2 level promoted the growth of Karenia mikimotoi.
- Rising CO2 weakened allelopathic effects of Ulva pertusa on K. mikimotoi.
- High CO2 level disturbed the synthesis of free fatty acids in U. pertusa, decreasing its allelopathic effects.
- Rising CO2 increases the outbreak risk of K. mikimotoi.
Abstract
Ocean acidification (OA) driven by elevated carbon dioxide (CO2) levels is expected to disturb marine ecological processes, including the formation and control of harmful algal blooms (HABs). In this study, the effects of rising CO2 on the allelopathic effects of macroalgae Ulva pertusa to a toxic dinoflagellate Karenia mikimotoi were investigated. It was found that high level of CO2 (1000 ppmv) promoted the competitive growth of K. mikimotoi compared to the group of present ambient CO2 level (420ppmv), with the number of algal cell increased from 32.2 × 104 cells/mL to 36.75 × 104 cells/mL after 96 h mono-culture. Additionally, rising CO2 level weakened allelopathic effects of U. pertusa on K. mikimotoi, as demonstrated by the decreased inhibition rate (50.6 % under the original condition VS 34.3 % under the acidified condition after 96 h co-culture) and the decreased reactive oxygen species (ROS) level, malondialdehyde (MDA) content, antioxidant enzymes activity (superoxide dismutase (SOD), peroxidase (POD), glutathione peroxidase (GPX), glutathione reductase (GR) and catalase (CAT) and non-enzymatic antioxidants (glutathione (GSH) and ascorbic acid (ascorbate, vitamin C). Indicators for cell apoptosis of K. mikimotoi including decreased caspase-3 and -9 protease activity were observed when the co-cultured systems were under rising CO2 exposure. Furthermore, high CO2 level disturbed fatty acid synthesis in U. pertusa and significantly decreased the contents of fatty acids with allelopathy, resulting in the allelopathy weakening of U. pertusa. Collectively, rising CO2 level promoted the growth of K. mikimotoi and weakened allelopathic effects of U. pertusa on K. mikimotoi, indicating the increased difficulties in controlling K. mikimotoi using macroalgae in the future.
Continue reading ‘A laboratory study of the increasing competitiveness of Karenia mikimotoi under rising CO2 scenario’Adverse environmental perturbations may threaten kelp farming sustainability by exacerbating enterobacterales diseases
Published 25 March 2024 Science ClosedTags: algae, biological response, community composition, field, laboratory, light, molecular biology, morphology, mortality, multiple factors, North Pacific, otherprocess, physiology, prokaryotes, protists, reproduction
Globally kelp farming is gaining attention to mitigate land-use pressures and achieve carbon neutrality. However, the influence of environmental perturbations on kelp farming remains largely unknown. Recently, a severe disease outbreak caused extensive kelp mortality in Sanggou Bay, China, one of the world’s largest high-density kelp farming areas. Here, through in situ investigations and simulation experiments, we find indications that an anomalously dramatic increase in elevated coastal seawater light penetration may have contributed to dysbiosis in the kelp Saccharina japonica’s microbiome. This dysbiosis promoted the proliferation of opportunistic pathogenic Enterobacterales, mainly including the genera Colwellia and Pseudoalteromonas. Using transcriptomic analyses, we revealed that high-light conditions likely induced oxidative stress in kelp, potentially facilitating opportunistic bacterial Enterobacterales attack that activates a terrestrial plant-like pattern recognition receptor system in kelp. Furthermore, we uncover crucial genotypic determinants of Enterobacterales dominance and pathogenicity within kelp tissue, including pathogen-associated molecular patterns, potential membrane-damaging toxins, and alginate and mannitol lysis capability. Finally, through analysis of kelp-associated microbiome data sets under the influence of ocean warming and acidification, we conclude that such Enterobacterales favoring microbiome shifts are likely to become more prevalent in future environmental conditions. Our study highlights the need for understanding complex environmental influences on kelp health and associated microbiomes for the sustainable development of seaweed farming.
Continue reading ‘Adverse environmental perturbations may threaten kelp farming sustainability by exacerbating enterobacterales diseases’Acidification offset warming-induced increase in N2O production in estuarine and coastal sediments
Published 22 March 2024 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, field, laboratory, molecular biology, North Pacific, otherprocess, prokaryotes, sediment
Global warming and acidification, induced by a substantial increase in anthropogenic CO2 emissions, are expected to have profound impacts on biogeochemical cycles. However, underlying mechanisms of nitrous oxide (N2O) production in estuarine and coastal sediments remain rarely constrained under warming and acidification. Here, the responses of sediment N2O production pathways to warming and acidification were examined using a series of anoxic incubation experiments. Denitrification and N2O production were largely stimulated by the warming, while N2O production decreased under the acidification as well as the denitrification rate and electron transfer efficiency. Compared to warming alone, the combination of warming and acidification decreased N2O production by 26 ± 4%, which was mainly attributed to the decline of the N2O yield by fungal denitrification. Fungal denitrification was mainly responsible for N2O production under the warming condition, while bacterial denitrification predominated N2O production under the acidification condition. The reduced site preference of N2O under acidification reflects that the dominant pathways of N2O production were likely shifted from fungal to bacterial denitrification. In addition, acidification decreased the diversity and abundance of nirS-type denitrifiers, which were the keystone taxa mediating the low N2O production. Collectively, acidification can decrease sediment N2O yield through shifting the responsible production pathways, partly counteracting the warming-induced increase in N2O emissions, further reducing the positive climate warming feedback loop.
Continue reading ‘Acidification offset warming-induced increase in N2O production in estuarine and coastal sediments’Effects of reduced seawater pH and oil contamination on bacterial communities and biochemical markers of estuarine animal hosts
Published 18 March 2024 Science ClosedTags: annelids, biological response, chemistry, community composition, laboratory, molecular biology, mollusks, mortality, North Atlantic, otherprocess, performance, physiology, toxicants
Ecosystem functioning depends on complex interactions between microorganisms, hosts, and the environment. Changes in environmental conditions (e.g., ocean acidification) in combination with anthropogenic pollution have been shown to affect the composition and function of free-living microbial communities, but little is known about the effects these stressors on host-associated communities. This study aims to characterize the response of host-associated bacterial communities of the bottom-dwelling polychaete Hediste diversicolor and the epibenthic gastropod Peringia ulvae to oil contamination and reduced seawater pH. The independent and interactive effects of both stressors were simulated under controlled conditions. The response of host-associated bacterial communities was assessed using the high-throughput sequencing of the 16S rRNA gene and several biochemical markers related to host metabolic pathways, e.g., neurotransmission, anaerobic metabolism, biotransformation, oxidative stress, and energy consumption. In H. diversicolor, reduced seawater pH was associated with a high relative abundance of Cyanobacteria, while in P. ulvae oil contamination was associated with a reduction in the relative abundance of Chitinophagales. In P. ulvae, enrichment with oil hydrocarbon-degrading bacteria suggests a possible role of these organisms in the dispersion of oil hydrocarbon degraders. Furthermore, oil supplementation shifted some specific biochemical markers of gastropods related to oxidative stress and energy consumption, which suggests host stress. In general, the bacterial communities and biochemical markers of the gastropod were more affected by stressors than those of the polychaete. Overall, this study contributes to a better understanding of the response of host-associated bacterial communities of benthic macrofauna to anthropogenic contamination and environmental change.
Continue reading ‘Effects of reduced seawater pH and oil contamination on bacterial communities and biochemical markers of estuarine animal hosts’Fouling communities from the South African west coast are vulnerable to cooling and ocean acidification
Published 15 March 2024 Science ClosedTags: abundance, annelids, biological response, BRcommunity, bryozoa, chordata, community composition, crustaceans, fish, mollusks, multiple factors, otherprocess, prokaryotes, South Atlantic, temperature
Changing temperature and ocean acidification are well-recognised consequences of climate change in marine systems. In contrast to global trends, the South African west coast is experiencing cooling due to increased frequency and intensity of upwelling. The implications of concurrent cooling and acidification for marine biota are poorly understood, particularly at the community level. This laboratory study assessed how cooling and acidification might affect fouling communities along the South African west coast. Communities were experimentally exposed to two temperatures, 13℃ (current) and 9℃ (cooling), and three pH treatments, 7.9 (current), 7.6 and 7.4, for 18 days. Cooling and acidification altered community structure. Species diversity declined in response to acidification but was not affected by cooling. This was driven by greatest loss of species at 7.4 pH. Notably, acidification reduced the abundance of both calcifying and soft-bodied taxa, highlighting the vulnerability of taxa like ascidians to acidification. Overall, these results highlight the dominant threat posed by acidification, even for alien taxa that are often perceived as resilient to climate change. Additionally, in regions experiencing cooling, acidification may pose a greater threat to fouling communities than thermal changes.
Continue reading ‘Fouling communities from the South African west coast are vulnerable to cooling and ocean acidification’Marine phytoplankton and heterotrophic bacteria rapidly adapt to future pCO2 conditions in experimental co-cultures
Published 7 March 2024 Science ClosedTags: abundance, biological response, BRcommunity, community composition, growth, laboratory, molecular biology, otherprocess, phytoplankton, prokaryotes
The CO2 content of Earth’s atmosphere is rapidly increasing due to human consumption of fossil fuels. Models based on short-term culture experiments predict that major changes will occur in marine phytoplankton communities in the future ocean, but these models rarely consider how the evolutionary potential of phytoplankton or interactions within marine microbial communities may influence these changes. Here we experimentally evolved representatives of four phytoplankton functional types (silicifiers, calcifiers, coastal cyanobacteria, and oligotrophic cyanobacteria) in co-culture with a heterotrophic bacterium, Alteromonas, under either present-day or predicted future pCO2 conditions. Growth rates of cyanobacteria generally increased under both conditions, and the growth defects observed in ancestral Prochlorococcus cultures at elevated pCO2 and in axenic culture were diminished after evolution, possibly due to regulatory mutations in antioxidant genes. Except for Prochlorococcus, mutational profiles suggested phytoplankton experienced primarily purifying selection, but most Alteromonas lineages showed evidence of directional selection, especially when co-cultured with eukaryotic phytoplankton, where evolution appeared to favor a broad metabolic switch from growth on small organic acids to catabolism of more complex carbon substrates. Evolved Alteromonas were also poorer “helpers” for Prochlorococcus, supporting the assertion that the interaction between Prochlorococcus and heterotrophic bacteria is not a true mutualism but rather a competitive interaction stabilized by Black Queen processes. This work provides new insights on how phytoplankton will respond to anthropogenic change and on the evolutionary mechanisms governing the structure and function of marine microbial communities.
Continue reading ‘Marine phytoplankton and heterotrophic bacteria rapidly adapt to future pCO2 conditions in experimental co-cultures’Marine benthic communities of the future: use of acidified natural systems
Published 5 March 2024 Science ClosedTags: adaptation, biological response, BRcommunity, chemistry, community composition, echinoderms, field, molecular biology, morphology, North Atlantic, otherprocess, vents
Ocean acidification (OA) is one of the most significant threats to marine organisms and is linked to climate change. It occurs when anthropogenic CO2 is absorbed by the oceans, resulting in a decrease in seawater pH and the dissolution of calcium carbonate. Projections indicate that OA will exacerbate in the future, highlighting the need to understand its impact on marine ecosystems. Much of our knowledge about the effects of OA comes from laboratory experiments, as predicting responses in natural conditions is challenging. Therefore, studies focusing on species living in naturally acidified systems, such as shallow CO2 seeps or vents, are becoming increasingly popular to obtain more realistic predictions.
This doctoral thesis, consisting of 5 chapters, explores the effects of ocean acidification on benthic communities in the subtropical Atlantic Ocean, using the naturally acidified CO2 vent system off the southern coast of La Palma Island in the Canary Islands, Spain, as a natural laboratory. Chapter 1 serves as an introduction to this thesis, explaining what naturally acidified systems are and discussing the research conducted in various locations worldwide where they have been discovered. Specifically, it focuses on studies that have utilized CO2 vents, which originate from volcanic activity. This chapter provides an overview of the importance, advantages, and disadvantages of using these acidified systems as natural laboratories to study OA in situ. It highlights that although there is no perfect analogue for future oceans, these systems help us to better understand the direct and indirect impacts of OA on different marine communities.
Among all the CO2 vents in the world, one of the few naturally acidified shallow systems in the Atlantic Ocean, and the only one with subtropical communities is located off the southern coast of Fuencaliente municipality in La Palma Island, Canary Islands. Chapter 2 of the thesis characterizes the chemical properties of this natural CO2 system in La Palma. It provides information about its volcanic and hydrological origins, as well as the different emission points along the Punta de Fuencaliente. Furthermore, it describes the carbon dynamics of the system, including variations in total inorganic carbon (CT) from 2120.10 to 10784.84 μmol kg-1, alkalinity (AT) from 2415.20 to 10817.12 μmol kg-1, pH from 7.12 to 8.07, aragonite saturation state (Ω) from 0.71 to 4.15, and calcite Ω from 1.09 to 6.49 units. A high CO2 emission flux ranging from 2.8 to 28 kg of CO2 d-1 has also been detected, making this zone an important natural carbon source. Due to its origins, this acidified system presents disadvantages as a natural laboratory for studying OA, such as natural fluctuations caused by tides or additional input of alkaline substances. Nevertheless, it creates a natural gradient of CO2 or pH along the coast with chemical characteristics very similar to those predicted for future scenarios, making it an exceptional location for studying the long-term and multi-level effects of acidification on marine ecosystems.
Chapter 3 explores rocky benthic communities along the natural pH gradient generated by the CO2 vent system in front of Punta de Fuencaliente. The objective of this chapter was to understand the direct and indirect effects of OA on the diversity and species composition of these subtropical marine communities. The study utilized a high-resolution molecular technique called DNA metabarcoding, which sequences fragments of the mitochondrial gene Cytochrome C Oxidase subunit I (COI) to detect the actual species diversity in each area. In this chapter, metabarcoding analysis reveals, for the first time, high levels of taxonomic diversity in a naturally acidified area. These high levels of diversity are attributed to the detection of small and cryptic species that are undetectable by traditional techniques and are tolerant to natural acidification. The results of this chapter unveil that future subtropical communities could maintain high taxonomic diversity values under an acidification scenario, although they will tend toward miniaturization due to the dominance of small algae and invertebrate species. This will have significant consequences for benthic subtropical communities, leading to important changes in ecosystem functions.
It is not the first time that an increase in species diversity related to environmental variations has been detected. In 1978, Connell first proposed the “Intermediate Disturbance Hypothesis” (IDH), which suggests that ecosystems are more diverse when disturbances occur at intermediate scales.
Chapter 4 investigates whether the IDH can be applied to a naturally acidified system at different biological organization levels (from organisms to communities) using molecular data. In La Palma’s acidified system, a fluctuating pH gradient caused by tides can act as a physical disturbance to marine ecosystems. This chapter utilizes sequenced fragments of the mitochondrial COI gene from two species of sea urchins (Arbacia lixula and Paracentrotus lividus) and metabarcoding analyses of benthic communities from the previous chapter. High levels of genetic and taxonomic diversity were detected at both biological organization levels under intermediate pH fluctuation, respectively. Therefore, the results of this chapter support the validity of the IDH in marine ecosystems affected by natural pH fluctuations and at different biological organization levels. Among the species living under natural acidification in the CO2 vents of La Palma, the sea urchin Arbacia lixula stands out. This is because sea urchins, like other calcareous organisms, should be susceptible to acidification due to their calcareous skeletons, however, this species has been found to live apparently unaffected in both Mediterranean and Atlantic CO2 vents.
The final chapter 5 explores the adaptation potential of A. lixula populations along the natural pH gradient of La Palma Island. Using the 2bRADseq molecular technique, a total of 14,883 SNPs (Single Nucleotide Polymorphisms) were detected in 74 individuals, of which 432 loci were correlated with the pH gradient of La Palma and are considered potential SNPs under selection. Analysis of these SNPs demonstrates that despite the short distance between the studied A. lixula populations, significant differences exist in the genomic structure of the populations correlated with the pH gradient. Additionally, these sequences are aligned and compared with available A. lixula transcriptomes, revealing 17 annotated genes involved in biological functions related to growth, development, membrane functions, and calcification. This chapter suggests that A. lixula can adapt to acidification and, therefore, able to withstand future changes anticipated for the oceans.
This thesis is the first to be developed at the Marine Observatory of Climate Change in Punta de Fuencaliente (OMaCC), where the naturally acidified system of La Palma is located. It emphasizes the importance of these natural laboratories in overcoming the experimental limitations of laboratory studies and contributes to understand how subtropical benthic ecosystems may change in the future. Moreover, it has uncovered evidence of local adaptation to ocean acidification in populations living in these natural laboratories. This thesis highlights the importance of these special environments and observatories for future research on the effects of OA.
Continue reading ‘Marine benthic communities of the future: use of acidified natural systems’The impact of extreme weather events exceeds those due to global-change drivers on coastal phytoplankton assemblages
Published 1 March 2024 Science ClosedTags: abundance, biological response, BRcommunity, community composition, flow, laboratory, light, multiple factors, nutrients, otherprocess, photosynthesis, phytoplankton, South Atlantic, temperature
Highlights
- Extreme wind and rainfall events have become frequent phenomena in coastal ecosystems.
- We simulated these events under global change for five phytoplankton assemblages.
- Extreme events were responsible for the bulk of variability on photosynthesis efficiency.
- The impact of extreme events is low in assemblages with high diversity and evenness
- Extreme events should be considered in global change studies.
Abstract
Extreme wind and rainfall events have become more frequent phenomena, impacting coastal ecosystems by inducing increased mixing regimes in the upper mixed layers (UML) and reduced transparency (i.e. browning), hence affecting phytoplankton photosynthesis. In this study, five plankton assemblages from the South Atlantic Ocean, from a gradient of environmental variability and anthropogenic exposure, were subjected to simulated extreme weather events under a global change scenario (GCS) of increased temperature and nutrients and decreased pH, and compared to ambient conditions (Control). Using multiple linear regression (MLR) analysis we determined that evenness and the ratio of diatoms/ (flagellates + dinoflagellates) significantly explained the variations (81–91 %) of the photosynthesis efficiency (i.e. Pchla/ETRchla ratio) for each site under static conditions. Mixing speed and the optical depth (i.e. attenuation coefficient * depth, kdz), as single drivers, explained 40–76 % of the variability in the Pchla/ETRchla ratio, while GCS drivers <9 %. Overall, assemblages with high diversity and evenness were less vulnerable to extreme weather events under a GCS. Extreme weather events should be considered in global change studies and conservation/management plans as even at local/regional scales, they can exceed the predicted impacts of mean global climate change on coastal primary productivity.
Continue reading ‘The impact of extreme weather events exceeds those due to global-change drivers on coastal phytoplankton assemblages’Effect of increased pCO2 and temperature on the phytoplankton community in the coastal of Yellow Sea
Published 26 February 2024 Science ClosedTags: abundance, biological response, BRcommunity, community composition, growth, laboratory, multiple factors, North Pacific, otherprocess, physiology, phytoplankton, primary production, temperature
Highlights
- Elevated pCO2 and temperature impact phytoplankton abundance and structure.
- High temperature boosts phytoplankton growth.
- Species vary in response to pCO2 and temperature.
Abstract
In order to study the dynamics of marine phytoplankton communities in response to anticipated in temperature and CO2, a shipboard continuous culture experiment (Ecostat) was conducted. The experiment involved simulations under current atmospheric CO2 concentrations (400 ppm) and projected year-2100 CO2 levels (1000 ppm), as well as varying temperature under present (22 °C) versus increased temperature (26 °C) in the Yellow Sea during the summer of 2020. The results showed that both the increased pCO2 and temperature had significant effects on microphytoplankton and picophytoplankton, with the warming effect proving to be more significant. The different responses of various species to acidification and warming and their coupling effect led to the changes in microphytoplankton and picophytoplankton community structure. Elevated temperature and greenhouse treatments promoted the growth of dominant diatoms and Synechococcus, such as Guinardia flaccida and Pseudo-nitzschia delicatissima. This phenomenons widened the ecological niche, and the changes in the growth patterns of dominant species consequently influenced the content of cellular elements. Mantel’s analysis further demonstrated that both warming and greenhouse promoted the growth of diatoms and Synechococcus. Projections of marine phytoplankton community trends by the end of the century based on Growth Rate Ratio (GRR), indicated that not only would species with GRR < 1 decrease, but also numerous species with growth rates >1 at elevated pCO2 levels would be ousted from competition. This experiment demonstrates the need to investigate whether extended exposure to increased pCO2 and temperature over more extended time scales would similarly induce shifts in the biological and biogeochemical dynamics of the Yellow Sea.
Continue reading ‘Effect of increased pCO2 and temperature on the phytoplankton community in the coastal of Yellow Sea’Divergent morphological and microbiome strategies of two neighbor sponges to cope with low pH in Mediterranean CO2 vents
Published 14 February 2024 Science ClosedTags: abundance, biological response, BRcommunity, community composition, field, Mediterranean, molecular biology, morphology, otherprocess, porifera, prokaryotes, vents
Highlights
- Sponges are seen as winner taxa of future OA, yet not all species respond equally.
- Neighbor sponges had different morphology and microbiome patterns in CO2 vents.
- Vent S. cunctatrix displayed morphology changes and incipient microbial dysbiosis.
- C. reniformis microbiomes were normobiotic, diverse and functionally flexible.
- Symbioses supplying C–N–S cycles, vitamins and probiotics uphold resilience to OA.
Abstract
Ocean Acidification (OA) profoundly impacts marine biochemistry, resulting in a net loss of biodiversity. Porifera are often forecasted as winner taxa, yet the strategies to cope with OA can vary and may generate diverse fitness status. In this study, microbial shifts based on the V3–V4 16S rRNA gene marker were compared across neighboring Chondrosia reniformis sponges with high microbial abundance (HMA), and Spirastrella cunctatrix with low microbial abundance (LMA) microbiomes. Sponge holobionts co-occurred in a CO2 vent system with low pH (pHT ~ 7.65), and a control site with Ambient pH (pHT ~ 8.05) off Ischia Island, representing natural analogues to study future OA, and species’ responses in the face of global environmental change. Microbial diversity and composition varied in both species across sites, yet at different levels. Increased numbers of core taxa were detected in S. cunctatrix, and a more diverse and flexible core microbiome was reported in C. reniformis under OA. Vent S. cunctatrix showed morphological impairment, along with signs of putative stress-induced dysbiosis, manifested by: 1) increases in alpha diversity, 2) shifts from sponge related microbes towards seawater microbes, and 3) high dysbiosis scores. Chondrosia reniformis in lieu, showed no morphological variation, low dysbiosis scores, and experienced a reduction in alpha diversity and less number of core taxa in vent specimens. Therefore, C. reniformis is hypothesized to maintain an state of normobiosis and acclimatize to OA, thanks to a more diverse, and likely metabolically versatile microbiome. A consortium of differentially abundant microbes was identified associated to either vent or control sponges, and chiefly related to carbon, nitrogen and sulfur-metabolisms for nutrient cycling and vitamin production, as well as probiotic symbionts in C. reniformis. Diversified symbiont associates supporting functional convergence could be the key behind resilience towards OA, yet specific acclimatization traits should be further investigated.
Continue reading ‘Divergent morphological and microbiome strategies of two neighbor sponges to cope with low pH in Mediterranean CO2 vents’Seasonal resilience of temperate estuarine fish in response to climate change
Published 31 January 2024 Science ClosedTags: biological response, BRcommunity, community composition, fish, modeling, North Pacific, otherprocess, performance, regionalmodeling
Highlights
- The suitability of fish habitat is threatened by falling pH, especially in spring.
- Seasonality provides resilience against climate change for estuarine fish and assemblages.
- Centroids respond by shifting northeast in spring and southeast in autumn.
- Support for estuary ecosystem management under climate change is offered.
Abstract
To date, the intricacies and efficacy of how periodic seasonal environmental fluctuations affect fish populations in biogeography in the context of profound climate change remain to be elucidated. Collected monitoring data on fish resources in the temperate estuary provide an excellent opportunity to assess the effects of seasonal environmental fluctuations on populations and functional assemblages under climate change. We first developed a framework for predicting habitat suitability under different climate change scenarios (SSP1-2.6 and SSP5-8.5) for 12 fish populations in the Yangtze estuary by examining the seasonal environmental affinities of temperate estuarine fishes. We then summarized the multidimensional habitat suitability responses (HSRs) of populations and functional assemblages and discussed the possible drivers and mechanisms underlying these changes. The results suggest that the acidity of the Yangtze estuary may decline in the future as the climate warms, endangering the ecosystem that many fish species depend on. Prospective climate change may have an impact on fish population HSRs through redistribution, area changes, and centroid migration of suitable habitats; nevertheless, affinity for environmental factors may be limited to distinguishing patterns of population response in the spring. Fish (5 populations) and functional assemblages (11 assemblages) may exhibit robust adaptations or non-adaptations to climate change when seasons change, given their suitable habitat area. Furthermore, projections indicate that the majority of fish habitat centroids exhibit seasonal responses, migrating northeast in the spring and southeast in the autumn. By decentralizing climate risk to seasonal scales, seasonal resilience in the multidimensional HSRs of several fish populations (5/12) and their functional assemblages (11/16) is revealed for the first time. Efforts to mitigate climate risks and safeguard resources should take these seasonal forecasts and indicative information into account.
Continue reading ‘Seasonal resilience of temperate estuarine fish in response to climate change’Early stage ecological communities on artificial algae showed no difference in diversity and abundance under ocean acidification
Published 24 January 2024 Science ClosedTags: abundance, algae, annelids, biological response, BRcommunity, calcification, chemistry, community composition, crustaceans, echinoderms, field, Mediterranean, mesocosms, mitigation, mollusks, otherprocess, photosynthesis, protists, respiration
Marine habitat-forming species create structurally complex habitats that host macroinvertebrate communities characterized by remarkable abundance and species richness. These habitat-forming species also play a fundamental role in creating favourable environmental conditions that promote biodiversity. The deployment of artificial structures is becoming a common practice to help offset habitat loss although with mixed results. This study investigated the suitability of artificial flexible turfs mimicking the articulated coralline algae (mimics) as habitat providers and the effect of ocean acidification (OA) on early stage ecological communities associated to flexible mimics and with the mature community associated to Ellisolandia elongata natural turfs. The mimics proved to be a suitable habitat for early stage communities. During the OA mesocosms experiment, the two substrates have been treated and analysed separately due to the difference between the two communities. For early stage ecological communities associated with the mimics, the lack of a biologically active substrate does not exacerbate the effect of OA. In fact, no significant differences were found between treatments in crustaceans, molluscs and polychaetes diversity and abundance associated with the mimics. In mature communities associated with natural turfs, buffering capability of E. elongata is supporting different taxonomic groups, except for molluscs, greatly susceptible to OA.
Continue reading ‘Early stage ecological communities on artificial algae showed no difference in diversity and abundance under ocean acidification’
