Posts Tagged 'phanerogams'

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Who wins or loses matters: strongly interacting consumers drive seagrass resistance under ocean acidification

Published 8 December 2021 Science Closed
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Highlights

  • Ocean acidification (OA) directly facilitated algal epiphyte and seagrass.
  • Co-occurring grazers variably controlled algal overgrowth on seagrass.
  • pH-tolerant, strongly interacting grazers maintained overall grazing pressure.
  • Grazing and OA additively increased seagrass productivity.

Abstract

Global stressors are increasingly altering ecosystem resistance, resilience, and functioning by reorganizing vital species interactions. However, our predictive understanding of these changes is hindered by failures to consider species-specific functional roles and stress responses within communities. Stressor-driven loss or reduced performance of strongly interacting species may generate abrupt shifts in ecosystem states and functions. Yet, empirical support for this prediction is scarce, especially in marine climate change research. Using a marine assemblage comprising a habitat-forming seagrass (Phyllospadix torreyi), its algal competitor, and three consumer species (algal grazers) with potentially different functional roles and pH tolerance, we investigated how ocean acidification (OA) may, directly and indirectly, alter community resistance. In the field and laboratory, hermit crabs (Pagurus granosimanus and P. hirsutiusculus) and snails (Tegula funebralis) displayed distinct microhabitat use, with hermit crabs more frequently grazing in the area of high algal colonization (i.e., surfgrass canopy). In mesocosms, this behavioral difference led to hermit crabs exerting ~2 times greater per capita impact on algal epiphyte biomass than snails. Exposure to OA variably affected the grazers: snails showed reduced feeding and growth under extreme pH (7.3 and 7.5), whereas hermit crabs (P. granosimanus) maintained a similar grazing rate under all pH levels (pH 7.3, 7.5, 7.7, and 7.95). Epiphyte biomass increased more rapidly under extreme OA (pH 7.3 and 7.5), but natural densities of snails and hermit crabs prevented algal overgrowth irrespective of pH treatments. Finally, grazers and acidification additively increased surfgrass productivity and delayed the shoot senescence. Hence, although OA impaired the function of the most abundant consumers (snails), strongly interacting and pH-tolerant species (hermit crabs) largely maintained the top-down pressure to facilitate seagrass dominance. Our study highlights significant within-community variation in species functional and response traits and shows that this variation has important ecosystem consequences under anthropogenic stressors.

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A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: the enhancement of metabolic carbonate dissolution in a semienclosed lagoon

Published 15 November 2021 Science Closed
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In contrast to other seagrass meadows where seawater carbonate chemistry generally shows strong diel variations with higher pH but lower partial pressure of CO2 (pCO2) during the daytime and lower pH but higher pCO2 during nighttime due to the alternation in photosynthesis and respiration, the seagrass meadows of the inner lagoon (IL) on Dongsha Island had a unique diel pattern with extremely high pH and low pCO2 across a diel cycle. We suggest that this distinct diel pattern in pH and pCO2 could be associated with the enhancement of total alkalinity (TA) production coupled to carbonate sediment dissolution in a semienclosed lagoon. The confinement of the IL may hamper water exchange and seagrass detritus export to the adjacent open ocean, which may result in higher organic matter loading to the sediments, and longer residence time of the water in the IL, accompanied by microbial respiration (both aerobic and anaerobic) that may reduce carbonate saturation level to drive carbonate dissolution and thus TA elevation, thereby forming such a unique diel pattern in carbonate chemistry. This finding further highlights the importance of considering TA production through metabolic carbonate dissolution when evaluating the potential of coastal blue carbon ecosystems to buffer ocean acidification and to absorb atmospheric CO2, in particular in a semienclosed setting.

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Marine macrophytes as carbon sinks: comparison between seagrasses and the non-native alga Halimeda incrassata in the Western Mediterranean (Mallorca)

Published 11 November 2021 Science Closed
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Seagrass species play a critical role in the mitigation of climate change by acting as valuable carbon sinks and storage sites. Another important ecosystem service of this coastal vegetation is nutrient removal. However, coastal ecosystems are under increasing pressure of global warming and associated establishment of invasive species. To elucidate the respective contributions of seagrass species Posidonia oceanica and Cymodocea nodosa and the non-native macroalga Halimeda incrassata as primary producers and nutrient sinks in coastal habitats we conducted in-situ incubations in the North-western Mediterranean Sea. Measured metabolic activity and nutrient removal as well as calcification rates in these habitats over a 24 h period in spring and summer confirmed that the endemic seagrass P. oceanica represents a valuable ecosystem with high O2 production and considerable carbon capture. The documented regression of P. oceanica meadows with higher temperatures and decline in autotrophy as measured here causes concern for the continuity of ecosystem services rendered by this habitat throughout the Mediterranean Sea with progressing climate warming. In contrast, the enhanced performance of C. nodosa and the calcifying alga H. incrassata with increasing temperatures, under expected rates of future warming is uncertain to mitigate loss of productivity in case of a potential shift in marine vegetation. This could ultimately lead to a decline in ecosystem services, decreased carbon storage and mitigation of climate change. Furthermore, this study provides a first estimate for the growth rate of H. incrassata in the Mediterranean Sea, supporting evidence for the mechanism of its rapid extension.

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Overstated potential for seagrass meadows to mitigate coastal ocean acidification

Published 3 November 2021 Science Closed
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Ricart et al. (2021, R21) explored the potential for seagrass meadows to act as a buffer of coastal ocean acidification (OA). This work relied largely on sensor-based pH measurements during 29 separate instrument deployments along the California coast, arguing that (1) seagrass aerobic metabolism consistently enhances local pH, and that (2) this OA-amelioration can persist for lengths of up to 21 days. While pH was often greater in seagrass meadows than in adjacent unvegetated regions, we are concerned with the extent to which this is attributed to seagrass ecosystem metabolism, and the interpretation that this OA-amelioration is sustained over daily and tidal timescales. By incompletely considering alternative explanations for elevated pH, irrespective of seagrass productivity, R21 offers insufficient support of OA-mitigation as a reliable ecosystem service of seagrasses. We therefore see the authors’ claim that seagrass ecosystems could be “leveraged as local management tools to mitigate the consequences of OA” as worthy of critical inspection.

First, there is a fundamental issue in R21 with the mathematical treatment of ΔpH (ΔpH = pHseagrass – pHnonvegetated), stemming from the fact that pH is on a logarithmic scale. To illustrate this issue, it is a simple fact that a ΔpH of 0.1 involves a change in [H+] that is 10 times larger when starting at pH = 7 than at pH=8. This effect is made abundantly clear by the linear relationship between pH and ΔpH (Figure 1A) present in the R21 dataset. As expected, pH also varies with salinity, with slopes that vary across sites (Figure 1B) and seasons (Figure 5 in R21). Such comparisons of ΔpH across sites, seasons, etc., are mathematically inappropriate, when made without also considering Δ[H+] (Fassbender et al., 2021). We therefore find the interpretation of ΔpH in R21 to be misleading because it does not consider the impact of initial pH on the size of ΔpH.

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In situ experiments on the effect of low pH on the ultrastructure of the seagrasses Cymodocea nodosa and Posidonia oceanica

Published 29 October 2021 Science Closed
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The present study investigates the impacts of low pH on the cell structure of the seagrasses Posidonia oceanica (L.) Delile and Cymodocea nodosa (Ucria) Ascherson. The study was applied with in situ experiments at the Castello Aragonese of Ischia (Naples, Italy), where shallow submarine vents, lowering the pH, can be used as natural laboratories. Shoots of the seagrasses were transferred from the control area (pH 8.1) to the two venting areas (pH 7.8 and 6.8) for different times. Epidermal cells of young leaves were examined using transmission electron microscopy (TEM) and tubulin immunofluorescence. After one week at pH 7.8, the cell structure of Posidonia oceanica was normal, while in Cymodocea nodosa microtubule (MT) network and cell structure were affected. In addition, in C. nodosa, ultrastructural analysis revealed a gradual degradation of the nuclei, a disorganization of the chloroplasts, and an increase in the number of mitochondria and dictyosomes. The exposure of both plants for 3 weeks at pH 6.8 resulted in the aggregation and finally in the dilation of the endoplasmic reticulum (ER) membranes. Tubulin immunofluorescence revealed that after three weeks, the MT cytoskeleton of both plants was severely affected. All these alterations can be considered as indications of an apoptotic like programmed cell death (AL-PCD) which may be executed in order to regulate stress response.

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Rapid enhancement of multiple ecosystem services following the restoration of a coastal foundation species

Published 26 October 2021 Science Closed
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The global decline of marine foundation species (kelp forests, mangroves, salt marshes, and seagrasses) has contributed to the degradation of the coastal zone and threatens the loss of critical ecosystem services and functions. Restoration of marine foundation species has had variable success, especially for seagrasses, where a majority of restoration efforts have failed. While most seagrass restorations track structural attributes over time, rarely do restorations assess the suite of ecological functions that may be affected by restoration. Here we report on the results of two small-scale experimental seagrass restoration efforts in a central California estuary where we transplanted 117 0.25-m2 plots (2,340 shoots) of the seagrass species Zostera marina. We quantified restoration success relative to persistent reference beds, and in comparison to unrestored, unvegetated areas. Within three years, our restored plots expanded ˜8,500%, from a total initial area of 29 to 2,513 m2. The restored beds rapidly began to resemble the reference beds in (1) seagrass structural attributes (canopy height, shoot density, biomass), (2) ecological functions (macrofaunal species richness and abundance, epifaunal species richness, nursery function), and (3) biogeochemical functions (modulation of water quality). We also developed a multifunctionality index to assess cumulative functional performance, which revealed restored plots are intermediate between reference and unvegetated habitats, illustrating how rapidly multiple functions recovered over a short time period. Our comprehensive study is one of few published studies to quantify how seagrass restoration can enhance both biological and biogeochemical functions. Our study serves as a model for quantifying ecosystem services associated with the restoration of a foundation species and demonstrates the potential for rapid functional recovery that can be achieved through targeted restoration of fast-growing foundation species under suitable conditions.

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Biotic habitats as refugia under ocean acidification

Published 22 September 2021 Science Closed
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Habitat-forming organisms have an important role in ameliorating stressful conditions and may be of particular relevance under a changing climate. Increasing CO2 emissions are driving a range of environmental changes, and one of the key concerns is the rapid acceleration of ocean acidification and associated reduction in pH. Such changes in seawater chemistry are anticipated to have direct negative effects on calcifying organisms, which could, in turn, have negative ecological, economic and human health impacts. However, these calcifying organisms do not exist in isolation, but rather are part of complex ecosystems. Here, we use a qualitative narrative synthesis framework to explore (i) how habitat-forming organisms can act to restrict environmental stress, both now and in the future; (ii) the ways their capacity to do so is modified by local context; and (iii) their potential to buffer the effects of future change through physiological processes and how this can be influenced by management adopted. Specifically, we highlight examples that consider the ability of macroalgae and seagrasses to alter water carbonate chemistry, influence resident organisms under current conditions and their capacity to do so under future conditions, while also recognizing the potential role of other habitats such as adjacent mangroves and saltmarshes. Importantly, we note that the outcome of interactions between these functional groups will be context dependent, influenced by the local abiotic and biotic characteristics. This dependence provides local managers with opportunities to create conditions that enhance the likelihood of successful amelioration. Where individuals and populations are managed effectively, habitat formers could provide local refugia for resident organisms of ecological and economic importance under an acidifying ocean.

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Dwarf eelgrass (Zostera noltii) fatty acid remodelling induced by climate change

Published 11 August 2021 Science Closed
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Highlights

  • Seagrasses are marine founding species threatened by climate change.
  • These plants are sources of essential fatty acids (FAs) for the marine heterotrophic life.
  • Leaf saturated and polyunsaturated FAs in response to warming and acidification.
  • Changes in FAs suggest a membrane composition rearrangement to maintain membrane fluidity.
  • Linolenic acid decrease appears to be connected to reactive oxygen species quenching.
  • Seagrass FAs profile appear as good candidate biomarkers for climate change related stress.

Abstract

Dwarf eelgrass Zostera noltii meadows are found in estuarine coastal areas across the north-eastern Atlantic, where they provide key ecosystem services, including nursery grounds, sediment stabilization, nutrient cycling and carbon sequestration. These blue carbon ecosystems are being subjected to several anthropogenic pressures, including climate change-related effects. In the present study, we investigated the biochemical changes (fatty acid profiling) under different climate change scenarios (present-day conditions, ocean acidification, ocean warming and combined warming and acidification), following IPCC RCP scenario 8.5. Significant modifications in the percentage of saturated (SFA) and polyunsaturated fatty acids (PUFAs) in response to warming and low pH levels were detected. The changes suggest a rearrangement of membrane composition to maintain membrane fluidity, especially under warming conditions. Individuals under warming treatment showed higher plastidial pathway activity, while acidification induced a shift in the fatty acid synthesis pathway towards the extra-plastidial pathway, indicating a need to readjust the chloroplastidial monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) lipids under thermal stress to counteract excessive membrane fluidity. Regarding PUFA fatty acids, α-linolenic acid (ALA, C18:3, n-3) showed a pronounced decrease under the combined treatment, a tendency that can be connected to reactive oxygen species (ROS) quenching and membrane remodelling. Thus, and observing the changes in the fatty acid profile, these essential molecules appear as good candidate biomarkers to detect changes in seagrass ecophysiology under acute climate change-related events. Our findings suggest that future global warming will pose a serious threat to these already endangered blue ecosystems.

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Ocean warming and acidification modify top-down and bottom-up control in a tropical seagrass ecosystem

Published 26 July 2021 Science Closed
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Seagrass ecosystem is one of the most productive ecosystems in coastal waters providing numerous ecological functions and supporting a large biodiversity. However, various anthropogenic stressors including climate change are impacting these vulnerable habitats. Here, we investigated the independent and combined effects of ocean warming and ocean acidification on plant–herbivore interactions in a tropical seagrass community. Direct and indirect effects of high temperature and high pCO2 on the physiology of the tropical seagrass Thalassia hemprichii and sea urchin Tripneustes gratilla were evaluated. Productivity of seagrass was found to increase under high pCO2, while sea urchin physiology including feeding rate decreased particularly under high temperature. The present study indicated that future climate change will affect the bottom-up and top-down balance, which potentially can modify the ecosystem functions and services of tropical seagrass ecosystems.

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Ocean acidification and mollusc settlement in Posidonia oceanica meadows: does the seagrass buffer lower pH effects at CO2 vents?

Published 12 July 2021 Science Closed
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Ocean acidification has been broadly recognised to have effects on the structure and functioning of marine benthic communities. The selection of tolerant or vulnerable species can also occur during settlement phases, especially for calcifying organisms which are more vulnerable to low pH–high pCO2 conditions. Here, we use three natural CO2 vents (Castello Aragonese north and south sides, and Vullatura, Ischia, Italy) to assess the effect of a decrease of seawater pH on the settlement of Mollusca in Posidonia oceanica meadows, and to test the possible buffering effect provided by the seagrass. Artificial collectors were installed and collected after 33 days, during April–May 2019, in three different microhabitats within the meadow (canopy, bottom/rhizome level, and dead matte without plant cover), following a pH decreasing gradient from an extremely low pH zone (pH < 7.4), to ambient pH conditions (pH = 8.10). A total of 4659 specimens of Mollusca, belonging to 57 different taxa, were collected. The number of taxa was lower in low and extremely low pH conditions. Reduced mollusc assemblages were reported at the acidified stations, where few taxa accounted for a high number of individuals. Multivariate analyses revealed significant differences in mollusc assemblages among pH conditions, microhabitat, and the interaction of these two factors. Acanthocardia echinata, Alvania lineata, Alvania sp. juv, Eatonina fulgida, Hiatella arctica, Mytilys galloprovincialis, Musculus subpictus, Phorcus sp. juv, and Rissoa variabilis were the species mostly found in low and extremely low pH stations, and were all relatively robust to acidified conditions. Samples placed on the dead matte under acidified conditions at the Vullatura vent showed lower diversity and abundances if compared to canopy and bottom/rhizome samples, suggesting a possible buffering role of the Posidonia on mollusc settlement. Our study provides new evidence of shifts in marine benthic communities due to ocean acidification and evidence of how P. oceanica meadows could mitigate its effects on associated biota in light of future climate change.

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Global review of the impact of naturally occurring shallow water CO2 seeps

Published 1 July 2021 Science Closed
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Studying the local impacts of natural marine discharges can help in understanding the local impacts of large-scale restoration programs. This paper reviews studies of naturally occurring CO2 rich hydrothermal vents to understand how nature responds. Venting CO2 raises both total DIC, and the CO2 partial pressure by a factor of 10 or 20 times, lowering the pH and the saturation state of calcium carbonate, impeding calcification by calcifying organisms.

The ocean is a relatively stable environment and significant changes to water chemistry caused by high levels of CO2 input impacts marine organisms. Many algae are able to survive and photosynthesise at low pH levels, and some may actually benefit from an increase in dissolved CO2. However, coralline and calcareous algae that form carbonate skeletons are negatively impacted at low pH. Ecologically and economically valuable marine flora such as kelp, seagrass and certain seaweeds can benefit from increased DIC, exhibiting increases in photosynthetic and growth rates. Kelp and seagrass may also increase local pH levels, creating refuges for calcifying marine species.

The calcification rates of Many marine invertebrates decrease with increasing pCO2. At sites closer to vent openings, with lower pH, the abundance and diversity of invertebrates is significantly reduced. This can impact species valuable to the fishery and aquaculture industry by directly affecting recruitment, growth and survivorship of species such as mussels and oysters and indirectly through reduced abundance of invertebrate prey for herring and mackerel. Corals are also negatively impacted by declining pH and calcium carbonate saturation, yet not all hard corals respond evenly. More resilient genera such as Porites can survive pH drops to approximately 7.8, however below this value reef development is virtually absent and the habitat is dominated by algae and soft corals.

Naturally occurring low pH sites are relatively common in the marine environment and though they clearly alter species composition and abundance, the locally lower pH does not kill marine life, and beyond dispersion zones species are unaffected. Global ocean acidification is a serious problem, however the impacts of local releases of CO2 are relatively limited, resulting in community shifts towards low pH tolerant species. Reversal of global ocean acidification is essential, and restoration of the oceans will require huge carbon dioxide removal (CDR) processes.

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Rising temperature is a more important driver than increasing carbon dioxide concentrations in the trait responses of Enhalus acoroides seedlings

Published 21 June 2021 Science Closed
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Increasing temperature and CO2 concentration are among the most important factors affecting marine ecosystems under climate change. We investigated the morphological, biochemical, and physiological trait responses of seedlings of the tropical seagrass Enhalus acoroides under experimental conditions. Trait responses were greater under temperature effects than increasing CO2 concentration. Seedlings under rising temperatures showed enhanced leaf growth, lower leaf nutrient content, and stimulated down-regulating mechanisms in terms of photo-physiology. Increasing CO2 concentrations did not show any significant effects independently. There was a significant interaction for some of the trait responses considered, such as leaf number and carbon content in the roots, and trends of higher starch concentrations in the leaves and lower rETRmax under combined enriched CO2 and high temperature, even though none of these interactions were synergistic. Understanding the single and interactive trait responses of seagrass seedlings to increasing temperature and CO2 concentration is of importance to determine the relative responses of early life stages of seagrasses, which may differ from adult plants, in order to form a more holistic view of seagrass ecosystem health under climate change.

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Impacts of seagrass on benthic microalgae and phytoplankton communities in an experimentally warmed coral reef mesocosm

Published 10 June 2021 Science Closed
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The effects of seagrass on microalgal assemblages under experimentally elevated temperatures (28°C) and CO2 partial pressures (pCO2; 800 μatm) were examined using coral reef mesocosms. Concentrations of nitrate, ammonium, and benthic microalgal chlorophyll a (chl-a) were significantly higher in seagrass mesocosms, whereas phytoplankton chl-a concentrations were similar between seagrass and seagrass-free control mesocosms. In the seagrass group, fewer parasitic dinoflagellate OTUs (e.g., Syndiniales) were found in the benthic microalgal community though more symbiotic dinoflagellates (e.g., Cladocopium spp.) were quantified in the phytoplankton community. Our results suggest that, under ocean acidification conditions, the presence of seagrass nearby coral reefs may (1) enhance benthic primary productivity, (2) decrease parasitic dinoflagellate abundance, and (3) possibly increase the presence of symbiotic dinoflagellates.

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Impact of ocean carbonation on long-term regulation of light harvesting in eelgrass Zostera marina

Published 7 June 2021 Science Closed
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Seagrasses account for approximately 10% of the ocean’s total carbon storage, although photosynthesis of seagrasses is carbon-limited at today’s oceanic pH. Therefore, increasing atmospheric CO2 concentration, which results in ocean acidification/carbonation, is predicted to have a positive impact on seagrass productivity. Previous studies have confirmed the positive influence of increasing CO2 on photosynthesis and survival of the temperate eelgrass Zostera marina, but the acclimation of photoprotective mechanisms in this context has not been characterized. This study aimed to quantify the long-term impacts of ocean acidification on photochemical control mechanisms that promote photosynthesis while simultaneously protecting eelgrass from photodamage. Eelgrass were grown in controlled outdoor aquaria at different aqueous CO2 concentrations ranging from ~50 to ~2100 μM from May 2013 to October 2014 and examined for differences in leaf optical properties. Even with daily and seasonal variations of temperature and light, CO2 enrichment consistently increased plant size, leaf thickness and chlorophyll use efficiency, and decreased pigment content and the package effect while maintaining similar light harvesting efficiency. These acclimation responses suggest a common photosynthetic sensory function, such as redox regulation, can be manipulated by CO2 availability, as well as light, and may serve to optimize photosynthetic carbon gain by seagrasses into the anthropocene.

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Reviews and syntheses: spatial and temporal patterns in metabolic fluxes inform potential for seagrass to locally mitigate ocean acidification

Published 1 June 2021 Science Closed
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As global change continues to progress, there is a growing interest in assessing any local levers that could be used to manage the social and ecological impacts of rising CO2 concentrations. While habitat conservation and restoration have been widely recognized for their role in carbon storage and sequestration at a global scale, the potential for managers to use vegetated habitats to mitigate CO2 concentrations at local scales in marine ecosystems facing the accelerating threat of ocean acidification (OA) has only recently garnered attention. Early studies have shown that submerged aquatic vegetation, such as seagrass beds, can locally draw down CO2 and raise seawater pH in the water column through photosynthesis, but empirical studies of local OA mitigation are still quite limited. Here, we leverage the extensive body of literature on seagrass community metabolism to highlight key considerations for local OA management through seagrass conservation or restoration. In particular, we synthesize the results from 62 studies reporting in situ rates of seagrass gross primary productivity, respiration, and/or net community productivity to highlight spatial and temporal variability in carbon fluxes. We illustrate that daytime net community production is positive overall, and similar across seasons and geographies. Full-day net community production rates, which illustrate the potential cumulative effect of seagrass beds on seawater biogeochemistry integrated over day and night, were also positive overall, but were higher in summer months in both tropical and temperate ecosystems. Although our analyses suggest seagrass meadows are generally autotrophic, the modeled effects on seawater pH are relatively small in magnitude. In addition, we illustrate that periods when full-day net community production is highest could be associated with lower nighttime pH and increased diurnal variability in seawater pCO2/pH. Finally, we highlight important areas for future research to inform the next steps for assessing the utility of this approach for management.

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Seagrass-driven changes in carbonate chemistry enhance oyster shell growth

Published 31 May 2021 Science Closed
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Quantifying the strength of non-trophic interactions exerted by foundation species is critical to understanding how natural communities respond to environmental stress. In the case of ocean acidification (OA), submerged marine macrophytes, such as seagrasses, may create local areas of elevated pH due to their capacity to sequester dissolved inorganic carbon through photosynthesis. However, although seagrasses may increase seawater pH during the day, they can also decrease pH at night due to respiration. Therefore, it remains unclear how consequences of such diel fluctuations may unfold for organisms vulnerable to OA. We established mesocosms containing different levels of seagrass biomass (Zostera marina) to create a gradient of carbonate chemistry conditions and explored consequences for growth of juvenile and adult oysters (Crassostrea gigas), a non-native species widely used in aquaculture that can co-occur, and is often grown, in proximity to seagrass beds. In particular, we investigated whether increased diel fluctuations in pH due to seagrass metabolism affected oyster growth. Seagrasses increased daytime pH up to 0.4 units but had little effect on nighttime pH (reductions less than 0.02 units). Thus, both the average pH and the amplitude of diel pH fluctuations increased with greater seagrass biomass. The highest seagrass biomass increased oyster shell growth rate (mm day−1) up to 40%. Oyster somatic tissue weight and oyster condition index exhibited a different pattern, peaking at intermediate levels of seagrass biomass. This work demonstrates the ability of seagrasses to facilitate oyster calcification and illustrates how non-trophic metabolic interactions can modulate effects of environmental change.

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Ocean acidification and carbon limitation affect photosynthetic capacity of the seagrass (Amphibolis antarctica) and its calcifying epiphytes

Published 26 May 2021 Science Closed
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Amphibolis antarctica seagrass meadows, and their associated calcifying epiphytes, are abundant on Australia’s west coast, but have declined in recent years due to anthropogenic factors such as marine heatwaves, damaging fishing practices and increased turbidity resulting from eutrophication which causes light limitation. Burning fossil fuels has increased the flux of CO2 in to the ocean, lowering surface seawater pH, and making more carbon available for photosynthetic life. There are benefits of increasing CO2 for those seagrasses that are carbon limited, as this alleviates their energetic use of carbon concentrating mechanisms (CCM’S) which are less efficient, and more energy costly than passive diffusion of CO2 across cell walls. This study used pulse amplitude modulation fluorometry to quantify relative electron transport rates (rETR) at a range of pH levels both above and below current ocean pH of 8.1, and found that A. antarctica has significantly decreased rETR at pH treatments of 7.81 and 7.61. Calcifying epiphytes on A. antarctica also had a significant drop in rETR at the lower pH treatments. There was also significantly lowered rETR at higher pH treatments, likely the result of carbon limitation. These results from the lower pH tests may have profound implications for A. antarctica meadows under ocean acidification. A decline in these meadows would cause the loss of ecosystem services provided by them, such as carbon storage and sequestration, commercial fisheries and a decline the abundance of biodiversity that they support.

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Everything is everywhere: physiological responses of the Mediterranean sea and Eastern Pacific ocean Epiphyte Cobetia Sp. to varying nutrient concentration

Published 25 May 2021 Science Closed
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Bacteria are essential in the maintenance and sustainment of marine environments (e.g., benthic systems), playing a key role in marine food webs and nutrient cycling. These microorganisms can live associated as epiphytic or endophytic populations with superior organisms with valuable ecological functions, e.g., seagrasses. Here, we isolated, identified, sequenced, and exposed two strains of the same species (i.e., identified as Cobetia sp.) from two different marine environments to different nutrient regimes using batch cultures: (1) Cobetia sp. UIB 001 from the endemic Mediterranean seagrass Posidonia oceanica and (2) Cobetia sp. 4B UA from the endemic Humboldt Current System (HCS) seagrass Heterozostera chilensis. From our physiological studies, both strains behaved as bacteria capable to cope with different nutrient and pH regimes, i.e., N, P, and Fe combined with different pH levels, both in long-term (12 days (d)) and short-term studies (4 d/96 h (h)). We showed that the isolated strains were sensitive to the N source (inorganic and organic) at low and high concentrations and low pH levels. Low availability of phosphorus (P) and Fe had a negative independent effect on growth, especially in the long-term studies. The strain UIB 001 showed a better adaptation to low nutrient concentrations, being a potential N2-fixer, reaching higher growth rates (μ) than the HCS strain. P-acquisition mechanisms were deeply investigated at the enzymatic (i.e., alkaline phosphatase activity, APA) and structural level (e.g., alkaline phosphatase D, PhoD). Finally, these results were complemented with the study of biochemical markers, i.e., reactive oxygen species (ROS). In short, we present how ecological niches (i.e., MS and HCS) might determine, select, and modify the genomic and phenotypic features of the same bacterial species (i.e., Cobetia spp.) found in different marine environments, pointing to a direct correlation between adaptability and oligotrophy of seawater.

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Chapter 21 – Coral reefs: globally predicted climate change impact mitigation, mediated by the marine flora and their ecosystem connectivity, with a case study from Neil Island (the Andamans)

Published 25 May 2021 Science Closed
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Mangrove–coral habitat is characterized by heterogeneity in the physical environment that allows it to be out of equilibrium with open ocean conditions, resulting in differentiation of local physical, chemical, and biological attributes. This chapter highlights how some mangrove habitats can act as alternate refuges for corals during climate threats, particularly increasing seawater temperature, high levels of solar radiation, and ocean acidification. Coastal ecosystems are interconnected and so any change in one coastal ecosystem will have an impact on other ecosystems. Similarly, recovery and resilience of coastal ecosystems like coral reefs depend on the degree of connectivity and support from the neighboring coastal ecosystems such as seagrass beds. Therefore, healthy seagrass beds are especially vital for the resilience of coral reefs, as they support the coral communities to adapt to climate change impacts. Corals compete with seaweeds for space on the reef. When corals are healthy, the coral–seaweed competition reaches a balance. But, if the corals are not able to do well because of smothering like eutrophication or climate change induced impacts, then seaweeds can take over. Our study results suggest that coral reefs may become increasingly susceptible to seaweed proliferation under ocean acidification. Though the functional links of mangroves, seagrasses, and coral reefs have been studied, their conservation and management aspects due to connectivity and their importance for humans is yet to be understood. Importance of interconnectivity in biodiversity richness is illustrated by presenting the bioresource availability in the existing heterogeneous coral reef, seagrass, and mangrove habitats of the Neil Island, the Andamans and studies on the interactions among them are essential for conservation and management of such precious ecosystems.

Continue reading ‘Chapter 21 – Coral reefs: globally predicted climate change impact mitigation, mediated by the marine flora and their ecosystem connectivity, with a case study from Neil Island (the Andamans)’

Chapter 5 – Effect of climate change on marine ecosystems

Published 18 May 2021 Science Closed
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The impacts of anthropogenic climate change are already discernible throughout the ocean, from the equator to the poles, and from the surface to abyssal depths. Further climate change impacts are inevitable; however, their damage to marine organisms and ecosystems, and the services they provide, can be greatly reduced if greenhouse gas emissions are rapidly reduced. This review covers six main climate-related drivers (warming, acidification, deoxygenation, sea level rise and storm events, sea ice loss, stratification, and nutrient supply) and their impacts on 13 marine ecosystems, broadly defined. Seven of these are near-shore (coral reefs, kelp ecosystems, seagrass meadows, rocky and sandy intertidal, saltmarshes, estuaries, and mangroves) and six are in shelf seas and the open ocean (shelf sea benthos, upper ocean plankton, fish and fisheries, cold water corals, ice-influenced ecosystems, and the deep seafloor). Three cross-cutting issues are emphasized: that climate change impacts are not single factors, but interact together and with other human pressures in a multistressor context; that there are fast and slow climate processes in the ocean, with overall temporal uncertainties relating to future societal behavior; and that there can be high spatial heterogeneity in marine ecosystem impacts and vulnerabilities.

Continue reading ‘Chapter 5 – Effect of climate change on marine ecosystems’

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