Effects of ocean acidification (OA) on the plant phenology and colonization/settlement pattern of the hydrozoan epibiont community of the leaves of the seagrass Posidonia oceanica have been studied at volcanic CO2 vents off Ischia (Italy). The study was conducted in shallow Posidonia stands (2.5–3.5 m depth), in three stations on the north and three on the south sides of the vent’s area (Castello Aragonese vents), distributed along a pH gradient. At each station, 10–15 P. oceanica shoots were collected every three months for one-year cycle (Sept 2009–2010). The shoot density of Posidonia beds in the most acidified stations along the gradient (pH < 7.4) was significantly higher than that in the control area (pH = 8.10). On the other hand, we recorded lower leaf lengths and widths in the acidified stations in the whole year of observations, compared to those in the control stations. However, the overall leaf surface (Leaf Area Index) available for epiphytes under ocean acidification conditions was higher on the south side and on both the most acidified stations because of the higher shoot density under OA conditions. The hydrozoan epibiont community on the leaf canopy accounted for seven species, three of which were relatively abundant and occurring all year around (Sertularia perpusilla, Plumularia obliqua, Clytia hemisphaerica). All hydroids species showed a clear tolerance to low pH levels, including chitinous and non-calcifying forms, likely favoured also by the absence of competition for substratum with the calcareous forms of epiphytes selected against OA.
Continue reading ‘Epiphytic hydroids on Posidonia oceanica seagrass meadows are winner organisms under future ocean acidification conditions: evidence from a CO2 vent system (Ischia Island, Italy)’Posts Tagged 'phanerogams'
Epiphytic hydroids on Posidonia oceanica seagrass meadows are winner organisms under future ocean acidification conditions: evidence from a CO2 vent system (Ischia Island, Italy)
Published 26 April 2021 Science ClosedTags: abundance, adaptation, biological response, BRcommunity, chemistry, cnidaria, community composition, field, growth, Mediterranean, morphology, otherprocess, phanerogams, vents
Alkalinity cycling and carbonate chemistry decoupling in seagrass mystify processes of acidification mitigation
Published 23 April 2021 Science ClosedTags: biological response, chemistry, field, mitigation, North Pacific, phanerogams
The adverse conditions of acidification on sensitive marine organisms has led to the investigation of bioremediation methods as a way to abate local acidification. This phytoremediation, by macrophytes, is expected to reduce the severity of acidification in nearshore habitats on short timescales. Characterizing the efficacy of phytoremediation can be challenging as residence time, tidal mixing, freshwater input, and a limited capacity to fully constrain the carbonate system can lead to erroneous conclusions. Here, we present in situ observations of carbonate chemistry relationships to seagrass habitats by comparing dense (DG), patchy (PG), and no grass (NG) Zostera marina pools in the high intertidal experiencing intermittent flooding. High-frequency measurements of pH, alkalinity (TA), and total-CO2 elucidate extreme diel cyclicity in all parameters. The DG pool displayed frequent decoupling between pH and aragonite saturation state (Ω arg ) suggesting pH-based inferences of acidification remediation by seagrass can be misinterpreted as pH and Ω arg can be independent stressors for some bivalves. Estimates show the DG pool had an integrated ΔTA of 550 μmol kg -1 over a 12 h period, which is ~60 % > the PG and NG pools. We conclude habitats with mixed photosynthesizes (i.e., PG pool) result in less decoupling between pH and Ωarg.
Continue reading ‘Alkalinity cycling and carbonate chemistry decoupling in seagrass mystify processes of acidification mitigation’Coast‐wide evidence of low pH amelioration by seagrass ecosystems
Published 1 April 2021 Science ClosedTags: abundance, biological response, chemistry, field, mitigation, morphology, North Pacific, phanerogams
Global‐scale ocean acidification has spurred interest in the capacity of seagrass ecosystems to increase seawater pH within crucial shoreline habitats through photosynthetic activity. However, the dynamic variability of the coastal carbonate system has impeded generalization into whether seagrass aerobic metabolism ameliorates low pH on physiologically and ecologically relevant timescales. Here we present results of the most extensive study to date of pH modulation by seagrasses, spanning seven meadows (Zostera marina) and 1000 km of U.S. west coast over 6 years. Amelioration by seagrass ecosystems compared to non‐vegetated areas occurred 65% of the time (mean increase 0.07 ± 0.008 SE). Events of continuous elevation in pH within seagrass ecosystems, indicating amelioration of low pH, were longer and of greater magnitude than opposing cases of reduced pH or exacerbation. Sustained elevations in pH of >0.1, comparable to a 30% decrease in [H+], were not restricted only to daylight hours but instead persisted for up to 21 days. Maximal pH elevations occurred in spring and summer during the seagrass growth season, with a tendency for stronger effects in higher latitude meadows. These results indicate that seagrass meadows can locally alleviate low pH conditions for extended periods of time with important implications for the conservation and management of coastal ecosystems.
Continue reading ‘Coast‐wide evidence of low pH amelioration by seagrass ecosystems’Boosted fish abundance associated with Posidonia oceanica meadows in temperate shallow CO2 vents
Published 1 February 2021 Science ClosedTags: abundance, algae, biological response, BRcommunity, chemistry, field, fish, mollusks, otherprocess, phanerogams, vents
Highlights
- Ocean acidification (OA) may induce shifts in the structure and function of coastal marine ecosystems
- CO2 vents were used to assess the effects of OA on fish assemblages associated with Posidonia oceanica
- Posidonia structure and associated fish assemblages were compared at vents and off-vents using underwater visual census
- Posidonia density increases and fish show boosted abundance but not reduced diversity at vents
- Mediterranean Posidonia fish assemblages may cope with OA under near-future acidification level
Abstract
Ocean acidification (OA) may induce major shifts in the structure and function of coastal marine ecosystems. Studies in volcanic CO2 vents, where seawater is naturally acidified, have reported an overall simplification of fish assemblages structure, while some primary producers are likely to increase their biomass under elevated concentration of CO2. Here we used temperate shallow CO2 vents located around the coast of Ischia island (Italy) to assess the effects of OA on necto-benthic fish assemblages associated with the foundation seagrass species Posidonia oceanica in the Mediterranean Sea. We compared P. oceanica meadow structure, its epiphytic community and the associated fish assemblage structure and diversity at vents with low pH sites and reference sites with ambient pH using underwater visual census strip transects, in two seasons (fall 2018 and summer 2019). Data were analysed using both univariate and multivariate statistical techniques. Results showed greater P. oceanica habitat complexity (i.e. shoot density) and lower abundance of epiphytic calcareous species (e.g. coralline algae) at the vents than reference sites. Total abundance of adult and juvenile fish was higher at vents than reference sites, while no differences were found for species richness and composition. Overall, the herbivore Sarpa salpa stands out among the species contributing the most to dissimilarity between vents and reference sites, showing higher abundances under OA conditions. This pattern could be explained by the combined effect of a positive response to the higher structural meadows complexity and the greater seagrasses palatability / nutritional value occurring at the vents, which may help herbivores to withstand the higher energetic cost to live under high pCO2 / low pH conditions. Our results indicate that necto-benthic fish assemblages associated with the Mediterranean P. oceanica ecosystem may cope with OA under the CO2 emission scenarios forecasted for the end of this century.
Continue reading ‘Boosted fish abundance associated with Posidonia oceanica meadows in temperate shallow CO2 vents’Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states
Published 13 January 2021 Science ClosedTags: biological response, chemistry, mitigation, modeling, North Pacific, phanerogams, phytoplankton, primary production, regionalmodeling, zooplankton
Highlights
- Harmonized simulation of DO, pH, and Y2095 climate change impacts in the Salish Sea
- A 52-fold increase in exposure and near-bed pelagic species to hypoxic waters in Y2095
- Ocean acidification projections for Y2095 indicate ≈ 20 −114% increase in water column (ΩA) <1)
- Primary productivity propagation to zooplankton projected for Y2095 with ≈ 13%−25% increases.
- Eelgrass sensitive to stressors and potential for loss of eelgrass biomass in the future.
Abstract
Future projections based on the IPCC high emissions scenario RCP8.5 have previously shown that the Pacific Northwest coastal waters will be subjected to altered ocean states in the upwelled shelf waters, resulting in higher primary productivity and increased regions of hypoxia and acidification in the inner estuarine waters such as the Salish Sea. However, corresponding effects on the lower trophic levels and submerged aquatic vegetation have not yet been quantified. Supported by new synoptic field data, explicit coupled simulation of algae, zooplankton, and eelgrass biomass was accomplished for the first time in the Salish Sea. We re-applied the improved model to evaluate future ecological response and examined potential algal species shift, but with the effects of zooplankton production, metabolism, and predation-prey interactions included. We also evaluated the role of eelgrass with respect to potential for improvements to dissolved oxygen and pH levels and as a mitigation measure against hypoxia and ocean acidification. The results re-confirm the possibility that there could be a substantial area-days increase (≈52-fold) in exposure of benthic and near-bed pelagic species to hypoxic waters in 2095. The projections for ocean acidification similarly indicate ≈ 20 -114% increase in exposure to lower pH corrosive waters with aragonite saturation state ΩA <1. Importantly, projected increase in primary productivity was shown to propagate to higher trophic levels, with ≈ 13% and 25% increases in micro and mesozooplankton biomass levels. However, the preliminary results also point to sensitivity of the eelgrass model to environmental stressor and potential loss eelgrass biomass in the future.
Continue reading ‘Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states’Leaf proteome modulation and cytological features of seagrass Cymodocea nodosa in response to long-term high CO2 exposure in volcanic vents
Published 29 December 2020 Science ClosedTags: adaptation, biological response, field, Mediterranean, otherprocess, phanerogams, physiology, vents
Seagrass Cymodocea nodosa was sampled off the Vulcano island, in the vicinity of a submarine volcanic vent. Leaf samples were collected from plants growing in a naturally acidified site, influenced by the long-term exposure to high CO2 emissions, and compared with others collected in a nearby meadow living at normal pCO2 conditions. The differential accumulated proteins in leaves growing in the two contrasting pCO2 environments was investigated. Acidified leaf tissues had less total protein content and the semi-quantitative proteomic comparison revealed a strong general depletion of proteins belonging to the carbon metabolism and protein metabolism. A very large accumulation of proteins related to the cell respiration and to light harvesting process was found in acidified leaves in comparison with those growing in the normal pCO2 site. The metabolic pathways linked to cytoskeleton turnover also seemed affected by the acidified condition, since a strong reduction in the concentration of cytoskeleton structural proteins was found in comparison with the normal pCO2 leaves. Results coming from the comparative proteomics were validated by the histological and cytological measurements, suggesting that the long lasting exposure and acclimation of C. nodosa to the vents involved phenotypic adjustments that can offer physiological and structural tools to survive the suboptimal conditions at the vents vicinity.
Continue reading ‘Leaf proteome modulation and cytological features of seagrass Cymodocea nodosa in response to long-term high CO2 exposure in volcanic vents’Volcanic CO2 seep geochemistry and use in understanding ocean acidification
Published 15 December 2020 Science ClosedTags: abundance, algae, annelids, biogeochemistry, BRcommunity, bryozoa, chemistry, cnidaria, community composition, corals, crustaceans, echinoderms, field, fish, Mediterranean, mollusks, otherprocess, phanerogams, phytoplankton, polychaetes, protists, review, vents
Ocean acidification is one of the most dramatic effects of the massive atmospheric release of anthropogenic carbon dioxide (CO2) that has occurred since the Industrial Revolution, although its effects on marine ecosystems are not well understood. Submarine volcanic hydrothermal fields have geochemical conditions that provide opportunities to characterise the effects of elevated levels of seawater CO2 on marine life in the field. Here, we review the geochemical aspects of shallow marine CO2-rich seeps worldwide, focusing on both gas composition and water chemistry. We then describe the geochemical effects of volcanic CO2 seepage on the overlying seawater column. We also present new geochemical data and the first synthesis of marine biological community changes from one of the best-studied marine CO2 seep sites in the world (off Vulcano Island, Sicily). In areas of intense bubbling, extremely high levels of pCO2 (> 10,000 μatm) result in low seawater pH (< 6) and undersaturation of aragonite and calcite in an area devoid of calcified organisms such as shelled molluscs and hard corals. Around 100–400 m away from the Vulcano seeps the geochemistry of the seawater becomes analogous to future ocean acidification conditions with dissolved carbon dioxide levels falling from 900 to 420 μatm as seawater pH rises from 7.6 to 8.0. Calcified species such as coralline algae and sea urchins fare increasingly well as sessile communities shift from domination by a few resilient species (such as uncalcified algae and polychaetes) to a diverse and complex community (including abundant calcified algae and sea urchins) as the seawater returns to ambient levels of CO2. Laboratory advances in our understanding of species sensitivity to high CO2 and low pH seawater, reveal how marine organisms react to simulated ocean acidification conditions (e.g., using energetic trade-offs for calcification, reproduction, growth and survival). Research at volcanic marine seeps, such as those off Vulcano, highlight consistent ecosystem responses to rising levels of seawater CO2, with the simplification of food webs, losses in functional diversity and reduced provisioning of goods and services for humans.
Continue reading ‘Volcanic CO2 seep geochemistry and use in understanding ocean acidification’Ocean acidification alters the composition of decapod crustacean communities associated to Posidonia oceanica beds
Published 14 December 2020 Science ClosedTags: abundance, biological response, BRcommunity, community composition, crustaceans, field, Mediterranean, otherprocess, phanerogams
Ocean Acidification (OA) produces manifest changes in the species assemblages of stable marine ecosystems, although the general levels of biodiversity may be partially conserved. In the case of decapod crustaceans, that represent an interesting taxon because it reacts both to direct and indirect effects of OA, a lowering of pH induces clear changes in the structure of species assemblages. In this study we collected decapod crustaceans at two sites at low pH located at Castello d’Ischia, two control sites at normal pH located at Castello d’Ischia and one external control site. The results confirm that a lower biodiversity characterizes the acidified zones over the year and indicate that key species, normally very abundant in normal conditions all over the year, exhibit impoverished populations associated to the Posidonia oceanica beds off the island of Ischia.
Continue reading ‘Ocean acidification alters the composition of decapod crustacean communities associated to Posidonia oceanica beds’A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: implications for ocean acidification buffering
Published 13 November 2020 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific, phanerogams, tracheophyta
In contrast to most seagrass meadows where seawater carbonate chemistry generally shows strong diel variations with a higher pH during the daytime and a lower pH during nighttime due to the alternation in photosynthesis and respiration, the seagrass meadows of the inner lagoon on Dongsha Island had a unique diel pattern with an extremely high pH across a diel cycle. We suggest that this distinct diel pattern in pH was a result of a combination of total alkalinity (TA) production through the coupling of aerobic/anaerobic respiration and carbonate dissolution in the sediments and dissolved inorganic carbon consumption through the high productivity of seagrasses in overlying seawaters. The confinement of the semienclosed inner lagoon may hamper water exchange and seagrass detritus export to the adjacent open ocean, which may provide an ideal scenario for sedimentary TA production and accumulation, thereby forming a strong capacity for seagrass meadows to buffer ocean acidification.
Continue reading ‘A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: implications for ocean acidification buffering’Scaling up: predicting the impacts of climate change on seagrass ecosystems
Published 5 November 2020 Science ClosedTags: biological response, phanerogams, review
Since Susan Williams and I started our scientific careers in the mid-1970s, seagrass science has been transformed from a largely descriptive field to an increasingly quantitative and predictive endeavor that requires a mechanistic understanding of environmental influence on metabolic networks that control energy assimilation, growth, and reproduction. Although the potential impacts of environment on gene products are myriad, important phenotypic responses are often regulated by a few key points in metabolic networks where externally supplied resources or physiological substrates limit reaction kinetics. Environmental resources commonly limiting seagrass productivity, survival, and growth include light, temperature, and CO2 availability that control carbon assimilation and sucrose formation, and regulate stress responses to environmental change. Here I present a systems approach to quantify the responses of seagrasses to shifts in environmental factors that control fundamental physiological processes and whole plant performance in the context of a changing climate. This review shows that our ability to understand the past and predict the future trajectory of seagrass-based ecosystems can benefit from a mechanistic understanding of the responses of these remarkable plants to the simultaneous impacts of ocean acidification, climate warming, and eutrophication that are altering ecosystem function across the globe.
Continue reading ‘Scaling up: predicting the impacts of climate change on seagrass ecosystems’Metabolic profiling reveals biochemical pathways responsible for eelgrass response to elevated CO2 and temperature
Published 23 September 2020 Science ClosedTags: laboratory, North Atlantic, phanerogams, physiology
As CO2 levels in Earth’s atmosphere and oceans steadily rise, varying organismal responses may produce ecological losers and winners. Increased ocean CO2 can enhance seagrass productivity and thermal tolerance, providing some compensation for climate warming. However, the metabolic shifts driving the positive response to elevated CO2 by these important ecosystem engineers remain unknown. We analyzed whole-plant performance and metabolic profiles of two geographically distinct eelgrass (Zostera marina L.) populations in response to CO2 enrichment. In addition to enhancing overall plant size, growth and survival, CO2 enrichment increased the abundance of Calvin Cycle and nitrogen assimilation metabolites while suppressing the abundance of stress-related metabolites. Overall metabolome differences between populations suggest that some eelgrass phenotypes may be better suited than others to cope with an increasingly hot and sour sea. Our results suggest that seagrass populations will respond variably, but overall positively, to increasing CO2 concentrations, generating negative feedbacks to climate change.
The challenges of detecting and attributing ocean acidification impacts on marine ecosystems
Published 12 August 2020 Science ClosedTags: biological response, corals, mollusks, phanerogams, review, zooplankton
A substantial body of research now exists demonstrating sensitivities of marine organisms to ocean acidification (OA) in laboratory settings. However, corresponding in situ observations of marine species or ecosystem changes that can be unequivocally attributed to anthropogenic OA are limited. Challenges remain in detecting and attributing OA effects in nature, in part because multiple environmental changes are co-occurring with OA, all of which have the potential to influence marine ecosystem responses. Furthermore, the change in ocean pH since the industrial revolution is small relative to the natural variability within many systems, making it difficult to detect, and in some cases, has yet to cross physiological thresholds. The small number of studies that clearly document OA impacts in nature cannot be interpreted as a lack of larger-scale attributable impacts at the present time or in the future but highlights the need for innovative research approaches and analyses. We summarize the general findings in four relatively well-studied marine groups (seagrasses, pteropods, oysters, and coral reefs) and integrate overarching themes to highlight the challenges involved in detecting and attributing the effects of OA in natural environments. We then discuss four potential strategies to better evaluate and attribute OA impacts on species and ecosystems. First, we highlight the need for work quantifying the anthropogenic input of CO2 in coastal and open-ocean waters to understand how this increase in CO2 interacts with other physical and chemical factors to drive organismal conditions. Second, understanding OA-induced changes in population-level demography, potentially increased sensitivities in certain life stages, and how these effects scale to ecosystem-level processes (e.g. community metabolism) will improve our ability to attribute impacts to OA among co-varying parameters. Third, there is a great need to understand the potential modulation of OA impacts through the interplay of ecology and evolution (eco–evo dynamics). Lastly, further research efforts designed to detect, quantify, and project the effects of OA on marine organisms and ecosystems utilizing a comparative approach with long-term data sets will also provide critical information for informing the management of marine ecosystems.
Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps
Published 3 August 2020 Science ClosedTags: abundance, biological response, chemistry, field, growth, Mediterranean, otherprocess, phanerogams, vents
We used population reconstruction techniques to assess for the first time the population dynamics of a seagrass, Cymodocea nodosa, exposed to long-term elevated CO2 near three volcanic seeps and compare them with reference sites away from the seeps. Under high CO2, the density of shoots and of individuals (apical shoots), and the vertical and horizontal elongation and production rates, were higher. Nitrogen effects on rhizome elongation and production rates and on biomass, were stronger than CO2 as these were highest at the location where the availability of nitrogen was highest. At the seep where the availability of CO2 was highest and nitrogen lowest, density of shoots and individuals were highest, probably due to CO2 effects on shoot differentiation and induced reproductive output, respectively. In all three seeps there was higher short- and long-term recruitment and growth rates around zero, indicating that elevated CO2 increases the turnover of C. nodosa shoots.
A meta-analysis of multiple stressors on seagrasses in the context of marine spatial cumulative impacts assessment
Published 30 July 2020 Science ClosedTags: biological response, multiple factors, phanerogams, review
Humans are placing more strain on the world’s oceans than ever before. Furthermore, marine ecosystems are seldom subjected to single stressors, rather they are frequently exposed to multiple, concurrent stressors. When the combined effect of these stressors is calculated and mapped through cumulative impact assessments, it is often assumed that the effects are additive. However, there is increasing evidence that different combinations of stressors can have non-additive impacts, potentially leading to synergistic and unpredictable impacts on ecosystems. Accurately predicting how stressors interact is important in conservation, as removal of certain stressors could provide a greater benefit, or be more detrimental than would be predicted by an additive model. Here, we conduct a meta-analysis to assess the prevalence of additive, synergistic, and antagonistic stressor interaction effects using seagrasses as case study ecosystems. We found that additive interactions were the most commonly reported in seagrass studies. Synergistic and antagonistic interactions were also common, but there was no clear way of predicting where these non-additive interactions occurred. More studies which synthesise the results of stressor interactions are needed to be able to generalise interactions across ecosystem types, which can then be used to improve models for assessing cumulative impacts.
Porewater carbonate chemistry dynamics in a temperate and a subtropical seagrass system
Published 26 May 2020 Science ClosedTags: biogeochemistry, biological response, BRcommunity, chemistry, community composition, field, North Atlantic, North Pacific, otherprocess, phanerogams
Seagrass systems are integral components of both local and global carbon cycles and can substantially modify seawater biogeochemistry, which has ecological ramifications. However, the influence of seagrass on porewater biogeochemistry has not been fully described, and the exact role of this marine macrophyte and associated microbial communities in the modification of porewater chemistry remains equivocal. In the present study, carbonate chemistry in the water column and porewater was investigated over diel timescales in contrasting, tidally influenced seagrass systems in Southern California and Bermuda, including vegetated (Zostera marina) and unvegetated biomes (0–16 cm) in Mission Bay, San Diego, USA and a vegetated system (Thallasia testudinium) in Mangrove Bay, Ferry Reach, Bermuda. In Mission Bay, dissolved inorganic carbon (DIC) and total alkalinity (TA) exhibited strong increasing gradients with sediment depth. Vertical porewater profiles differed between the sites, with almost twice as high concentrations of DIC and TA observed in the vegetated compared to the unvegetated sediments. In Mangrove Bay, both the range and vertical profiles of porewater carbonate parameters such as DIC and TA were much lower and, in contrast to Mission Bay where no distinct temporal signal was observed, biogeochemical parameters followed the semi-diurnal tidal signal in the water column. The observed differences between the study sites most likely reflect a differential influence of biological (biomass, detritus and infauna) and physical processes (e.g., sediment permeability, residence time and mixing) on porewater carbonate chemistry in the different settings.
Continue reading ‘Porewater carbonate chemistry dynamics in a temperate and a subtropical seagrass system’Effects of ocean acidification on phenology and epiphytes of the seagrass Posidonia oceanica at two CO2 vent systems of Ischia (Italy)
Published 28 April 2020 Science ClosedTags: biological response, community composition, field, Mediterranean, morphology, otherprocess, phanerogams, vents
Morphological features of the seagrass Posidonia oceanica (L.) Delile and its epiphyte community were studied in three acidified stations located in two CO2 vents systems and one control station under normal pH conditions off the island of Ischia (Italy) to highlight the possible effects of ocean acidification. Plant phenology was analyzed every two months for a year cycle (June 2016–April 2017), while epiphytes were studied in the period of highest development of both the leaf canopy and the epiphytic community (June, August, and October 2016). The shoot density of Posidonia beds in the acidified stations of the studied sites was significantly higher than that in the control area. Significant differences in the mean leaf length according to the pH condition, month, and the interaction of these two factors were observed (PERMANOVA); the mean leaf width differed also among pH conditions and months. We recorded lower leaf lengths and widths in the acidified stations in all the considered months, compared to those in the control station. These differences are consistent with the higher impact of grazing by the herbivorous fish Sarpa salpa observed on the leaves in the acidified stations. However, the overall leaf surface available for epiphytes was similar among stations because of the higher shoot density under ocean acidification conditions. Overall, the composition and structure of the epiphytic community on the Posidonia leaves showed significant differences in relation to acidification: in both acidified sites, all the calcareous forms, both encrusting red algae (Corallinales) and animals (bryozoans, foraminiferans, and spirorbids), disappeared or were strongly reduced, in favor of encrusting or erect fleshy algae, and non-calcifying invertebrates (hydrozoans, tunicates) which dominated the assemblage. Coralline algae are early species in the epiphytic colonization of P. oceanica and therefore their absence can further modify the pattern of leaf colonization by other species. Therefore, the changes found in the epiphyte community in low pH areas could have potential cascading effects on the seagrass trophic network and the functioning of the system.
Resistance of seagrass habitats to ocean acidification via altered interactions in a tri-trophic chain
Published 27 March 2020 Science ClosedTags: abundance, algae, biological response, BRcommunity, echinoderms, field, fish, Mediterranean, morphology, otherprocess, performance, phanerogams, physiology, vents
Despite the wide knowledge about prevalent effects of ocean acidification on single species, the consequences on species interactions that may promote or prevent habitat shifts are still poorly understood. Using natural CO2 vents, we investigated changes in a key tri-trophic chain embedded within all its natural complexity in seagrass systems. We found that seagrass habitats remain stable at vents despite the changes in their tri-trophic components. Under high pCO2, the feeding of a key herbivore (sea urchin) on a less palatable seagrass and its associated epiphytes decreased, whereas the feeding on higher-palatable green algae increased. We also observed a doubled density of a predatory wrasse under acidified conditions. Bottom-up CO2 effects interact with top-down control by predators to maintain the abundance of sea urchin populations under ambient and acidified conditions. The weakened urchin herbivory on a seagrass that was subjected to an intense fish herbivory at vents compensates the overall herbivory pressure on the habitat-forming seagrass. Overall plasticity of the studied system components may contribute to prevent habitat loss and to stabilize the system under acidified conditions. Thus, preserving the network of species interactions in seagrass ecosystems may help to minimize the impacts of ocean acidification in near-future oceans.
Does ocean acidification benefit seagrasses in a mesohaline environment? a mesocosm experiment in the northern Gulf of Mexico
Published 12 March 2020 Science ClosedTags: biological response, field, laboratory, mesocosms, morphology, North Atlantic, phanerogams, physiology, respiration
Ocean acidification is thought to benefit seagrasses because of increased carbon dioxide (CO2) availability for photosynthesis. However, in order to truly assess ecological responses, effects of ocean acidification need to be investigated in a variety of coastal environments. We tested the hypothesis that ocean acidification would benefit seagrasses in the northern Gulf of Mexico, where the seagrasses Halodule wrightii and Ruppia maritima coexist in a fluctuating environment. To evaluate if benefits of ocean acidification could alter seagrass bed composition, cores of H. wrightii and R. maritima were placed alone or in combination into aquaria and maintained in an outdoor mesocosm. Half of the aquaria were exposed to either ambient (mean pH of 8.1 ± 0.04 SD on total scale) or high CO2 (mean pH 7.7 ± 0.05 SD on total scale) conditions. After 54 days of experimental exposure, the δ13C values were significantly lower in seagrass tissue in the high CO2 condition. This integration of a different carbon source (either: preferential use of CO2, gas from cylinder, or both) indicates that plants were not solely relying on stored energy reserves for growth. Yet, after 41 to 54 days, seagrass morphology, biomass, photo-physiology, metabolism, and carbon and nitrogen content in the high CO2 condition did not differ from those at ambient. There was also no indication of differences in traits between the homospecific or heterospecific beds. Findings support two plausible conclusions: (1) these seagrasses rely heavily on bicarbonate use and growth will not be stimulated by near future acidification conditions or (2) the mesohaline environment limited the beneficial impacts of increased CO2 availability.
Global environmental changes negatively impact temperate seagrass ecosystems
Published 14 February 2020 Science ClosedTags: biological response, BRcommunity, crustaceans, field, fish, flow, laboratory, mesocosms, morphology, multiple factors, North Atlantic, phanerogams, photosynthesis, physiology, respiration, temperature
The oceans are increasingly affected by multiple aspects of global change, with substantial impacts on ecosystem functioning and food-web dynamics. While the effects of single factors have been extensively studied, it has become increasingly evident that there is a need to unravel the complexities related to a multiple stressor environment. In a mesocosm experimental study, we exposed a simplified, multi-trophic seagrass ecosystem (composed of seagrass, two shrimp species, and two intermediate predatory fish species) to three global change factors consisting of simulated storm events (Storms), heat shocks (Heat), and ocean acidification (OA), and the combination of all three factors (All). The most striking result indicated that when all factors were combined, there was a negative influence at all trophic levels, while the treatments with individual factors revealed species-specific response patterns. It appeared, however, that single factors may drive the multi-stressor response. All single factors (i.e., Storms, Heat, and OA) had either negative, neutral, or positive effects on fish and shrimp, whereas no effect was recorded for any single stressor on seagrass plants. The findings demonstrate that when several global change factors appear simultaneously, they can have deleterious impacts on seagrass ecosystems, and that the nature of factors and food-web composition may determine the sensitivity level of the system. In a global change scenario, this may have serious and applicable implications for the future of temperate seagrass ecosystems.
Continue reading ‘Global environmental changes negatively impact temperate seagrass ecosystems’
Carbon budgets in coastal estuaries of the northwestern Gulf of Mexico under hydrologic control
Published 4 October 2019 Science ClosedTags: biogeochemistry, biological response, chemistry, field, North Atlantic, phanerogams, photosynthesis, physiology, respiration
Globally, estuaries are considered as important CO2 sources to the atmosphere. However, previous studies on estuarine carbon fluxes have mostly focused on temperate and high latitude regions, leaving a significant knowledge gap in subtropical and tropical estuaries. In addition, the drivers that cause large spatiotemporal variability in estuarine inorganic and organic carbon fluxes remain insufficiently explored. In this dissertation, carbon budgets in four northwestern Gulf of Mexico (nwGOM) estuaries along a climatic gradient, Lavaca-Colorado Estuary (LCE), Guadalupe Estuary (GE), Mission-Aransas Estuary (MAE), and Nueces Estuary (NE), were evaluated. All these estuaries, with annual CO2 emission ranging 2.7—35.9 mol·C·m-2·y-1, are moderate to strong CO2 sources. However, there was large spatiotemporal variability that corresponded to changes in hydrologic conditions. The two northern estuaries (LCE and GE), due to larger riverine discharges, had an order of magnitude higher CO2 emissions than the
southern estuaries (MAE and NE). In addition, episodic flooding made the entire regional CO2 fluxes differ significantly under dry (-0.7—20.9 mmol·C·m-2·d-1) and wet (11.6—170.0 mmol·C·m-2·d-1) conditions. A mass balance model for carbon budget predicted lateral transport of total organic matter (TOC) and dissolved inorganic carbon (DIC) from tidal wetlands, which accounted for ~95% and 70% of total TOC and DIC inputs to the open estuarine water, respectively. However, the loss of coastal saltmarsh-mangrove habitats due to sea level rise could result in ~1% per year decline in estuarine CO2 fluxes at the expense of decreasing lateral carbon transport. Finally, this dissertation suggested that the average estuarine CO2 flux from nwGOM was about 8 times higher than previously estimated North America estuarine CO2 flux. Additionally, flooding condition was estimated to elevate CO2 emission and lateral fluxes by 10 times in this region.
