Posts Tagged 'communitymodeling'

Cascading effects augment the direct impact of CO2 on phytoplankton growth in a biogeochemical model

Atmospheric and oceanic CO2 concentrations are rising at an unprecedented rate. Laboratory studies indicate a positive effect of rising CO2 on phytoplankton growth until an optimum is reached, after which the negative impact of accompanying acidification dominates. Here, we implemented carbonate system sensitivities of phytoplankton growth into our global biogeochemical model FESOM-REcoM and accounted explicitly for coccolithophores as the group most sensitive to CO2. In idealized simulations in which solely the atmospheric CO2 mixing ratio was modified, changes in competitive fitness and biomass are not only caused by the direct effects of CO2, but also by indirect effects via nutrient and light limitation as well as grazing. These cascading effects can both amplify or dampen phytoplankton responses to changing ocean pCO2 levels. For example, coccolithophore growth is negatively affected both directly by future pCO2 and indirectly by changes in light limitation, but these effects are compensated by a weakened nutrient limitation resulting from the decrease in small-phytoplankton biomass. In the Southern Ocean, future pCO2 decreases small-phytoplankton biomass and hereby the preferred prey of zooplankton, which reduces the grazing pressure on diatoms and allows them to proliferate more strongly. In simulations that encompass CO2-driven warming and acidification, our model reveals that recent observed changes in North Atlantic coccolithophore biomass are driven primarily by warming and not by CO2. Our results highlight that CO2 can change the effects of other environmental drivers on phytoplankton growth, and that cascading effects may play an important role in projections of future net primary production.

Continue reading ‘Cascading effects augment the direct impact of CO2 on phytoplankton growth in a biogeochemical model’

Crustacean decapods are models to describe the general trends of biodiversity according to ocean acidification

A remarkable lack of punctual and comparable data on the availability of trophic resources characterizes most studies relating biodiversity and food webs, but decapod crustaceans will help, in this study, finding some peculiar common trends of ecosystems. Structural properties of networks, as statistically investigated, affect their stability and food webs are ultimately considered as complex networks of biotic interactions. Fixed mathematical limits constrain the number of species naturally assembled in a community, even if species composition was progressively modified by climate changes: the biodiversity has space constraints. Consequently, since there is less space at higher latitudes than at lower ones, less species may be predicted to globally co-exist, as the planet warms up and the oceans acidify. Here, according to some key mathematical relationships of networks, we forecast an inverse relationship between connectance (a specific feature of food webs) and species diversity. In this chapter, we will apply these relationships to test a general model of biodiversity trends based on the responses of crustacean decapods to the abundance of feeding sources, in a range of environments variably impacted by O.A. The conclusions reached within this chapter will demonstrate consistent properties characterizing the assemblages of aquatic creatures, and extensible to various structural levels, from single cells to the largest ecosystems.

Continue reading ‘Crustacean decapods are models to describe the general trends of biodiversity according to ocean acidification’

Rates of future climate change in the Gulf of Mexico and the Caribbean Sea: implications for coral reef ecosystems

Rising temperatures and ocean acidification due to anthropogenic climate change pose ominous threats to coral reef ecosystems in the Gulf of Mexico (GoM) and the western Caribbean Sea. Unfortunately, the once structurally complex coral reefs in the GoM and Caribbean have dramatically declined since the 1970s; relatively few coral reefs still exhibit a mean live coral cover of > 10%. Additional work is needed to characterize future climate stressors on corals reefs in the GoM and the Caribbean Sea. Here, we use climate model simulations spanning the period of 2015-2100 to partition and assess the individual impacts of climate stressors on corals in the GoM and the western Caribbean Sea. We use a top-down modeling framework to diagnose future projected changes in thermal stress and ocean acidification and discuss its implications for coral reef ecosystems. We find that ocean temperatures increase by 2-3°C over the 21st century, and surpass reported regional bleaching thresholds by mid-century. Whereas ocean acidification occurs, the rate and magnitude of temperature changes outpace and outweigh the impacts of changes in aragonite saturation state. A framework for quantifying and communicating future risks in the GoM and Caribbean using reef risk projection maps is discussed. Without substantial mitigation efforts, the combined impact of increasing ocean temperatures and acidification are likely to stress most existing corals in the GoM and the Caribbean, with widespread economic and ecological consequences.

Plain Language Summary

Coral reefs are among the most diverse and valuable ecosystems on Earth, and the coral reefs in the Gulf of Mexico (GoM) and the Caribbean Sea are no exception. In this region, coral reefs support vibrant recreation, tourism, and fishing industries. However, climate change, including rising temperatures and ocean acidification, threaten the future health of corals. To asses climate-change related risks to coral reefs in the Gulf of Mexico and the Caribbean Sea, this study uses climate model simulations spanning 2015-2100 to understand future changes in temperature and ocean acidification. Although many regions of the Gulf of Mexico and the western Caribbean Sea will cross the critical coral reef bleaching thresholds by mid-century, we hope that this work will inform and streamline mitigation efforts to protect vulnerable coral reef ecosystems and the valuable benefits and resources they provide to local communities.

Key Points

  • Sea-surface temperatures (SSTs) surpass critical coral bleaching thresholds by mid-century in the Gulf of Mexico (GoM) and Caribbean Sea
  • The rate and magnitude of SST changes in the GoM/Caribbean more strongly influence future coral reef vulnerability than ocean acidification
  • Future climate projections with high greenhouse gas forcing underscore the need for mitigation to ensure long-term coral reef preservation
Continue reading ‘Rates of future climate change in the Gulf of Mexico and the Caribbean Sea: implications for coral reef ecosystems’

Role of coral symbiont in coral resilience under future ocean conditions

Anthropogenic climate change is leading to severe consequences for coral reefs because it disrupts the mutualistic partnership between the coral host and their dinoflagellate endosymbionts (Family: Symbiodiniaceae). Ocean acidification (OA) and ocean warming lead to reduced coral growth, causes coral bleaching, and increases coral mortality. One mechanism of long-term acclimatization to thermal stress by corals is to acquire more thermally tolerant symbiont lineages or increase the proportion of thermally tolerant lineages in the symbiont community. Using a combination of field and long-term mesocosm experiments this research investigated the main drivers of Symbiodiniaceae community composition in some of the main corals in Hawai‘i. The first chapter elucidates the baseline symbiont community composition of 600 colonies of Montipora capitata sampled from 30 reefs across the range of environmental conditions that occur in Kāne‘ohe Bay. Symbiodiniaceae community differed markedly across sites, with M. capitata in the most open-ocean (northern) site hosting few or none of the genus Durusdinium, whereas individuals at other sites had a mix of Durusdinium and Cladocopium. The second chapter then investigates how the symbiont composition of those same individually marked colonies responded to the 2019 bleaching event. The relative proportion of the heat-tolerant symbiont Durusdinium increased in most parts of the bay, but despite this significant increase in abundance, the overall algal symbiont community composition was largely unchanged. Rather than bleaching stress, symbiont community composition was driven by environmentally designated regions across the bay, and remained differentiated and similar to pre-bleaching composition. Among measured variables, depth and variability in temperature were the most significant drivers of Symbiodiniaceae community composition among sites, regardless of bleaching intensity or change in relative proportion of Durusdinium. The final chapter investigates the role of specificity in the symbiont community composition for eight of the main Hawaiian corals sampled from six different locations around O‘ahu. Corals were then maintained for ~2.5 years under temperature and acidification conditions predicted by the end of the century in a mesocosm experiment to determine the response of their symbiont communities to climate change and test for environmental memory. Symbiodiniaceae communities were highly specific in each of the eight coral species-, and site-specific differences in community composition were lost by the end of the experiment in the common garden ambient treatment. Future ocean conditions lead to an increase in stress resilient symbionts (e.g., Durusdinium) in some species, whereas others became more vulnerable to the infection of opportunistic symbionts (e.g., Symbiodinium or Breviolum). Temperature was found to be the main driver of change, whereas there was no significant effect of acidification on symbiont community composition. Provenance of corals mattered, because corals from some locations responded differently than conspecifics from other locations confirming an environmental memory effect. Together these results highlight the complexity in predicting coral response to future ocean conditions. Algal symbiont community composition of corals changes in response to their environment, and that this response is dependent on both the coral species and their site of origin, highlighting the role of symbiont specificity and environmental memory in shaping coral resilience.

Continue reading ‘Role of coral symbiont in coral resilience under future ocean conditions’

Marine gastropods at higher trophic level show stronger tolerance to ocean acidification

Climate change and anthropogenic activities are producing a range of new selection pressures, both abiotic and biotic, on marine organisms. Although it is known that climate change can differentially affect fitness-related traits at different trophic levels of the food web, it is not clear if different trophic levels will respond via phenotypic plasticity in the form of maintenance of phenotypes in the face of abiotic and biotic environmental stress similarly. To answer this question, we combined a mesocosm experiment (120 days) using a food web comprising three gastropod species from two trophic levels (grazers and meso-predators) and a meta-analysis including 38 studies to address whether different trophic levels exhibit similar phenotypic responses to abiotic and biotic variables. Abiotic (ocean acidification) and biotic (predation) stress significantly influenced body mass, shell mass, shell thickness and shell strength in both grazers and meso-predators in the mesocosm experiment, with the magnitude of OA effects greater on the meso-predator than the grazers; a result supported by the meta-analysis. In contrast, both mesocosm experiment and meta-analysis found that predation risk induced stronger responses in shell morphology for grazers compared to meso-predators. Together, our findings indicate that higher trophic level species are better able to maintain aspects of their phenotype under OA, suggesting that they may show greater tolerance to climate change effects in general, while lower trophic levels express higher levels of plastic inducible defences to maintain function when under threat of predation. By using marine snails as a model, our study provides new knowledge for understanding how changing environmental conditions may alter biological interactions, and increases our understanding of how climate change may affect ecological communities in which gastropods play a key role.

Continue reading ‘Marine gastropods at higher trophic level show stronger tolerance to ocean acidification’

The influence of climate change on marine bacterioplankton communities and greenhouse gases in New Zealand waters

Bacterioplankton communities play a fundamental role in the cycling of carbon and nitrogen in the oceans. Cycling of these nutrients by bacterioplankton also contributes to the production of nitrous oxide and methane, resulting in the oceans being a net source of both these greenhouse gases. Climate change is impacting the oceans through warming and acidification resulting in alteration of planktonic ecosystems, via changes in productivity, biomass, and species composition. The response of marine bacterioplankton communities to the direct effects of ocean warming and lowered pH, and to the indirect effects of changes in phytoplankton and zooplankton, has implications for biogeochemical cycling and therefore the production of nitrous oxide and methane. This thesis investigates the impact of both direct and indirect climate pressures by determining the influence of ocean warming and lowered pH on bacterioplankton and the production of methane and nitrous oxide in New Zealand coastal waters. It also assesses how open ocean bacterioplankton communities and dissolved methane and nitrous oxide are influenced by water mass properties and, in particular, how they may be affected by climate-induced changes in the distribution and abundance of salps, a dominant group of zooplankton.

To determine the impact of lower pH and warming on bacterioplankton community, production and abundance, coastal water was manipulated in three mesocosm experiments to projected future ocean temperature and pH. The experiments ran for 18-21 days using 4000-Litre mesocosms filled with coastal water and associated plankton communities, with pH and temperature continuously regulated. High-throughput sequencing of the 16S rRNA gene was used to determine bacterioplankton community composition and leucine incorporation was used to measure bacterial production during the experiments. Minor but significant increases in alpha diversity were seen under low pH and warming. However, overall results from the mesocosm experiments indicate resilience to ocean warming and low pH in coastal bacterioplankton communities, with no significant impacts on production, abundance or beta-diversity found. Bacterioplankton communities in coastal sites are likely to experience high natural variability, which may result in lack of sensitivity to projected climate change.

Continue reading ‘The influence of climate change on marine bacterioplankton communities and greenhouse gases in New Zealand waters’

Enhanced silica export in a future ocean triggers global diatom decline

Diatoms account for up to 40% of marine primary production and require silicic acid to grow and build their opal shell3. On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification. Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 ± 6 per cent under pCO2 conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13–26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system.

Continue reading ‘Enhanced silica export in a future ocean triggers global diatom decline’

Sinking diatoms trap silicon in deep seawater of acidified oceans

The seas are acidifying as a result of carbon dioxide emissions. It now emerges that this will alter the solubility of the shells of marine organisms called diatoms — and thereby change the distribution of nutrients and plankton in the ocean.

The ecologically dominant phytoplankton in much of the ocean are a group of unicellular organisms known as diatoms. Writing in Nature, Taucher et al. present a study that uses a combination of experimental, observational and modelling approaches to examine how the diatom-driven effects of ocean acidification — a consequence of rising carbon dioxide concentrations in seawater — will affect biogeochemical cycles. The separate lines of evidence suggest that ocean acidification will have far-reaching effects on the export of elements to the deep ocean.

Diatoms are highly efficient at converting dissolved CO2 into organic carbon through photosynthesis, whereupon this organic carbon becomes incorporated into particles that sink rapidly to the deep ocean. Diatoms therefore serve as primary engines of a ‘biological pump’ that exports carbon to the deep ocean for sequestration. Each diatom cell is enclosed in a shell of silica (SiO2, where Si is silicon), and the solubility of the silicon in this biomineral is pH-sensitive — it becomes less soluble as seawater acidity rises. Although these features of diatoms are familiar to marine scientists, their combined implications for future biogeochemical cycles in the context of ocean acidification had not been explored.

Enter Taucher and colleagues. They carried out a series of five experiments in various parts of the ocean in which natural phytoplankton communities were grown in large enclosures (with volumes of 35–75 cubic metres) known as mesocosms, which simulated future ocean acidification. When the authors measured the elemental composition of the diatom-derived debris at the bottom of the mesocosms, they observed much higher ratios of silicon to nitrogen than the ratios of particles suspended near the surface. This suggested that, at low seawater pH, diatom silica shells were dissolving much more slowly than nitrogen-containing compounds in the same sinking material. In other words, silicon was being exported from the surface to deeper waters preferentially to nitrogen. The authors validated this finding using records of silicon-to-nitrogen ratios in sinking biological detritus in the open ocean, measured as a function of seawater pH, and obtained from particle-collecting sediment traps deployed by research vessels.

Continue reading ‘Sinking diatoms trap silicon in deep seawater of acidified oceans’

Coral symbiosis carbon flow: a numerical model study spanning cellular to ecosystem levels

Corals rely on a symbiotic relationship with algae (zooxanthellae), which reside in the host tissue and play a critical role for host metabolism through photosynthesis, respiration, carbon translocation, and calcification. These processes affect coral reefs on different scales from cellular to organismal and ecosystem levels. A process-based dynamic model was developed and coupled with a one-dimensional (1-D) biogeochemical model to describe coral photosynthesis, respiration, and carbon translocation at the cellular level, calcification and ion transport in different coral polyp components (i.e., coelenteron, calcifying fluid) at the organismal level; and the exchange of material between corals and the ambient seawater at the ecosystem level. Major processes controlling the carbon budget in internal symbiosis were identified. For the symbiont, photosynthesis is the primary carbon source and translocation to the host is the major sink. For the host, most of the carbon translocated from the symbiont is lost through mucus leakage. In the host dissolved inorganic carbon (DIC) pool, most of the carbon is obtained from the surrounding seawater through uptake; photosynthesis and calcification are the major sinks of DIC. Based on a series of scenario studies, the model produced increase of photosynthesis rate with decline of calcification rate under higher air pCO2 and associated carbonate chemistry variabilities in different polyp components. The model results support the hypothesis that elevated pCO2 stimulates photosynthesis, resulting in a reduced supply of DIC to calcification. Such coupled models allow the exploration of process-based mechanisms, complementing laboratory and field studies.

Continue reading ‘Coral symbiosis carbon flow: a numerical model study spanning cellular to ecosystem levels’

Predictive model for gross community production rate of coral reefs using ensemble learning methodologies

Coral reefs play a vital role in maintaining the ecological balance of the marine ecosystem. Various marine organisms depend on coral reefs for their existence and their natural processes. Coral reefs provide the necessary habitat for reproduction and growth for various exotic species of the marine ecosystem. In this article, we discuss the most important parameters which influence the lifecycle of coral and coral reefs such as ocean acidification, deoxygenation and other physical parameters such as flow rate and surface area. Ocean acidification depends on the amount of dissolved Carbon dioxide (CO2). This is due to the release of H+ ions upon the reaction of the dissolved CO2 gases with the calcium carbonate compounds in the ocean. Deoxygenation is another problem that leads to hypoxia which is characterized by a lesser amount of dissolved oxygen in water than the required amount for the existence of marine organisms. In this article, we highlight the importance of physical parameters such as flow rate which influence gas exchange, heat dissipation, bleaching sensitivity, nutrient supply, feeding, waste and sediment removal, growth and reproduction. In this paper, we also bring out these important parameters and propose an ensemble machine learning-based model for analyzing these parameters and provide better rates that can help us to understand and suitably improve the ocean composition which in turn can eminently improve the sustainability of the marine ecosystem, mainly the coral reefs

Continue reading ‘Predictive model for gross community production rate of coral reefs using ensemble learning methodologies’

Environmental vulnerability of the global ocean epipelagic plankton community interactome

Marine plankton form complex communities of interacting organisms at the base of the food web, which sustain oceanic biogeochemical cycles and help regulate climate. Although global surveys are starting to reveal ecological drivers underlying planktonic community structure and predicted climate change responses, it is unclear how community-scale species interactions will be affected by climate change. Here, we leveraged Tara Oceans sampling to infer a global ocean cross-domain plankton co-occurrence network—the community interactome—and used niche modeling to assess its vulnerabilities to environmental change. Globally, this revealed a plankton interactome self-organized latitudinally into marine biomes (Trades, Westerlies, Polar) and more connected poleward. Integrated niche modeling revealed biome-specific community interactome responses to environmental change and forecasted the most affected lineages for each community. These results provide baseline approaches to assess community structure and organismal interactions under climate scenarios while identifying plausible plankton bioindicators for ocean monitoring of climate change.

Continue reading ‘Environmental vulnerability of the global ocean epipelagic plankton community interactome’

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

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 echinataAlvania lineataAlvania sp. juv, Eatonina fulgidaHiatella arcticaMytilys galloprovincialisMusculus subpictusPhorcus 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.

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

Environmental DNA metabarcoding reveals winners and losers of global change in coastal waters

Studies of the ecological effects of global change often focus on one or a few species at a time. Consequently, we know relatively little about the changes underway at real-world scales of biological communities, which typically have hundreds or thousands of interacting species. Here, we use COI mtDNA amplicons from monthly samples of environmental DNA to survey 221 planktonic taxa along a gradient of temperature, salinity, dissolved oxygen and carbonate chemistry in nearshore marine habitat. The result is a high-resolution picture of changes in ecological communities using a technique replicable across a wide variety of ecosystems. We estimate community-level differences associated with time, space and environmental variables, and use these results to forecast near-term community changes due to warming and ocean acidification. We find distinct communities in warmer and more acidified conditions, with overall reduced richness in diatom assemblages and increased richness in dinoflagellates. Individual taxa finding more suitable habitat in near-future waters are more taxonomically varied and include the ubiquitous coccolithophore Emiliania huxleyi and the harmful dinoflagellate Alexandrium sp. These results suggest foundational changes for nearshore food webs under near-future conditions.

Continue reading ‘Environmental DNA metabarcoding reveals winners and losers of global change in coastal waters’

Assessing coral reef condition indicators for local and global stressors using Bayesian networks

Coral reefs are highly valued ecosystems currently threatened by both local and global stressors. Given the importance of coral reef ecosystems, a Bayesian network approach can benefit an evaluation of threats to reef condition. To this end, we used data to evaluate the overlap between local stressors (overfishing and destructive fishing, watershed‐based pollution, marine‐based pollution, and coastal development threats), global stressors (acidification and thermal stress) and management effectiveness with indicators of coral reef health (live coral index, live coral cover, population bleaching, colony bleaching and recently killed corals). Each of the coral health indicators had Bayesian networks constructed globally and for Pacific, Atlantic, Australia, Middle East, Indian Ocean, and Southeast Asia coral reef locations. Sensitivity analysis helped evaluate the strength of the relationships between different stressors and reef condition indicators. The relationships between indicators and stressors were also evaluated with conditional analyses of linear and nonlinear interactions. In this process, a standardized direct effects analysis was emphasized with a target mean analysis to predict changes in the mean value of the reef indicator from individual changes to the distribution of the predictor variables. The standardized direct effects analysis identified higher risks in the Middle East for watershed‐based pollution with population bleaching and Australia for overfishing and destructive fishing with living coral. For thermal stress, colony bleaching and recently killed coral in the Indian Ocean were found to have the strongest direct associations. For acidification threat, Australia had a relatively strong association with colony bleaching and the Middle East had the strongest overall association with recently killed coral although extrapolated spatial data were used for the acidification estimates. The Bayesian network approach helped to explore the relationships among existing databases used for policy development in coral reef management by examining the sensitivity of multiple indicators of reef condition to spatially‐distributed stress.

Continue reading ‘Assessing coral reef condition indicators for local and global stressors using Bayesian networks’

Projected expansion of Trichodesmium’s geographical distribution and increase in growth potential in response to climate change

Estimates of marine N2 fixation range from 52 to 73 Tg N/year, of which we calculate up to 84% is from Trichodesmium based on previous measurements of nifH gene abundance and our new model of Trichodesmium growth. Here, we assess the likely effects of four major climate change‐related abiotic factors on the spatiotemporal distribution and growth potential of Trichodesmium for the last glacial maximum (LGM), the present (2006–2015) and the end of this century (2100) by mapping our model of Trichodesmium growth onto inferred global surface ocean fields of pCO2, temperature, light and Fe. We conclude that growth rate was severely limited by low pCO2 at the LGM, that current pCO2 levels do not significantly limit Trichodesmium growth and thus, the potential for enhanced growth from future increases in CO2 is small. We also found that the area of the ocean where sea surface temperatures (SST) are within Trichodesmium‘s thermal niche increased by 32% from the LGM to present, but further increases in SST due to continued global warming will reduce this area by 9%. However, the range reduction at the equator is likely to be offset by enhanced growth associated with expansion of regions with optimal or near optimal Fe and light availability. Between now and 2100, the ocean area of optimal SST and irradiance is projected to increase by 7%, and the ocean area of optimal SST, irradiance and iron is projected to increase by 173%. Given the major contribution of this keystone species to annual N2 fixation and thus pelagic ecology, biogeochemistry and CO2 sequestration, the projected increase in the geographical range for optimal growth could provide a negative feedback to increasing atmospheric CO2 concentrations.

Continue reading ‘Projected expansion of Trichodesmium’s geographical distribution and increase in growth potential in response to climate change’

Remnant kelp bed refugia and future phase-shifts under ocean acidification

Ocean warming, ocean acidification and overfishing are major threats to the structure and function of marine ecosystems. Driven by increasing anthropogenic emissions of CO2, ocean warming is leading to global redistribution of marine biota and altered ecosystem dynamics, while ocean acidification threatens the ability of calcifying marine organisms to form skeletons due to decline in saturation state of carbonate Ω and pH. In Tasmania, the interaction between overfishing of sea urchin predators and rapid ocean warming has caused a phase-shift from productive kelp beds to overgrazed sea urchin barren grounds, however potential impacts of ocean acidification on this system have not been considered despite this threat for marine ecosystems globally. Here we use automated loggers and point measures of pH, spanning kelp beds and barren grounds, to reveal that kelp beds have the capacity to locally ameliorate effects of ocean acidification, via photosynthetic drawdown of CO2, compared to unvegetated barren grounds. Based on meta-analysis of anticipated declines in physiological performance of grazing urchins to decreasing pH and assumptions of nil adaptation, future projection of OA across kelp-barrens transition zones reveals that kelp beds could act as important pH refugia, with urchins potentially becoming increasingly challenged at distances >40 m from kelp beds. Using spatially explicit simulation of physicochemical feedbacks between grazing urchins and their kelp prey, we show a stable mosaicked expression of kelp patches to emerge on barren grounds. Depending on the adaptative capacity of sea urchins, future declines in pH appear poised to further alter phase-shift dynamics for reef communities; thus, assessing change in spatial-patterning of reef-scapes may indicate cascading ecological impacts of ocean acidification.

Continue reading ‘Remnant kelp bed refugia and future phase-shifts under ocean acidification’

Combining mesocosms with models to unravel the effects of global warming and ocean acidification on temperate marine ecosystems

Ocean warming and species exploitation have already caused large-scale reorganization of biological communities across the world. Accurate projections of future biodiversity change require a comprehensive understanding of how entire communities respond to global change. We combined a time-dynamic integrated food web modelling approach (Ecosim) with a community-level mesocosm experiment to determine the independent and combined effects of ocean warming and acidification, and fisheries exploitation, on a temperate coastal ecosystem. The mesocosm enabled important physiological and behavioural responses to climate stressors to be projected for trophic levels ranging from primary producers to top predators, including sharks. We show that under current-day rates of exploitation, warming and ocean acidification will benefit most species in higher trophic levels (e.g. mammals, birds, demersal finfish) in their current climate ranges, with the exception of small pelagic fish, but these benefits will be reduced or lost when these physical stressors co-occur. We show that increases in exploitation will, in most instances, suppress any positive effects of human-driven climate change, causing individual species biomass to decrease at high-trophic levels. Species diversity at the trailing edges of species distributions is likely to decline in the face of ocean warming, acidification and exploitation. We showcase how multi-level mesocosm food web experiments can be used to directly inform dynamic food web models, enabling the ecological processes that drive the responses of marine ecosystems to scenarios of global change to be captured in model projections and their individual and combined effects to be teased apart. Our approach for blending theoretical and empirical results from mesocosm experiments with computational models will provide resource managers and conservation biologists with improved tools for forecasting biodiversity change and altered ecosystem processes due to climate change.

Continue reading ‘Combining mesocosms with models to unravel the effects of global warming and ocean acidification on temperate marine ecosystems’

Ocean acidification has impacted coral growth on the Great Barrier Reef

Ocean acidification (OA) reduces the concentration of seawater carbonate ions that stony corals need to produce their calcium carbonate skeletons, and is considered a significant threat to the functional integrity of coral reef ecosystems. However, detection and attribution of OA impact on corals in nature are confounded by concurrent environmental changes, including ocean warming. Here we use a numerical model to isolate the effects of OA and temperature, and show that OA alone has caused 13±3% decline in the skeletal density of massive Porites corals on the Great Barrier Reef since 1950. This OA‐induced thinning of coral skeletons, also evident in Porites from the South China Sea but not in the central equatorial Pacific, reflects enhanced acidification of reef water relative to the surrounding open ocean. Our finding reinforces concerns that even corals that might survive multiple heatwaves are structurally weakened and increasingly vulnerable to the compounding effects of climate change.

Continue reading ‘Ocean acidification has impacted coral growth on the Great Barrier Reef’

Effects of climate change on coastal ecosystem food webs: implications for aquaculture

Highlights

• Food web models and scenarios were used to forecast effects of climate change.

• Modeled bays were vulnerable to the effects of climate change.

• In two of three study bays the ability to support bivalve aquaculture disappeared.

Abstract

Coastal ecosystems provide important ecosystem services for millions of people. Climate change is modifying coastal ecosystem food web structure and function and threatens these essential ecosystem services. We used a combination of two new and one existing ecosystem food web models and altered scenarios that are possible with climate change to quantify the impacts of climate change on ecosystem stability in three coastal bays in Maine, United States. We also examined the impact of climate change on bivalve fisheries and aquaculture. Our modeled scenarios explicitly considered the predicted effects of future climatic change and human intervention and included: 1) the influence of increased terrestrial dissolved organic carbon loading on phytoplankton biomass; 2) benthic community change driven by synergisms between climate change, historical overfishing, and increased species invasion; and 3) altered trophic level energy transfer driven by ocean warming and acidification. The effects of climate change strongly negatively influenced ecosystem energy flow and ecosystem stability and negatively affected modeled bivalve carrying capacity in each of our models along the Maine coast of the eastern United States. Our results suggest that the interconnected nature of ecosystem food webs make them extremely vulnerable to synergistic effects of climate change. To better inform fisheries and aquaculture management, the effects of climate change must be explicitly incorporated.

Continue reading ‘Effects of climate change on coastal ecosystem food webs: implications for aquaculture’

A regional vulnerability assessment for the Dungeness crab (Metacarcinus magister) to changing ocean conditions: insights from model projections and empirical experiments

Among global coastal regions, the Northern California Current System (N-CCS) is already experiencing effects from ocean acidification and hypoxia during the summer, primarily due to the region’s seasonal upwelling, current systems, and high productivity. Oxygen, pH, and temperature conditions are expected to become more stressful with continued fossil fuel emissions under global climate change, posing a serious threat to the region’s fisheries. N-CCS fishing communities rely heavily on the economically and culturally important Dungeness crab (Metacarcinus magister). The fishery is currently sustainably managed, but potential negative impacts from changing ocean conditions on Dungeness crab life stages and populations could have adverse effects for the fishery and the communities that rely on it. To quantify the vulnerability of Dungeness crab life stages and populations to predicted future conditions, both model projections and empirical experiments need to be employed. A semi-quantitative, life stage-specific framework was adapted here to assess the vulnerability of Dungeness crab to low pH, low dissolved oxygen, and high temperature under present and future projected conditions in the seasonally dynamic N-CCS. This was achieved using a combination of regional ocean models, species distribution maps, larval transport models, a population matrix model, and a literature review. This multi-faceted approach revealed that crab vulnerability to the three climate stressors will increase in the future (year 2100) under the most intense emissions scenario, with vulnerability to low oxygen being the most severe to the N-CCS population overall. Increases in vulnerability were largely driven by the adult life stage, which contributes the most to population growth. Empirical experiments demonstrated that adult crab respiration rates increase exponentially with temperature, potentially making this life stage more susceptible to hypoxia in the future. Together, this work provides novel insights into the effects of changing ocean conditions on Dungeness crab populations, which may help inform fishery management strategies.

Continue reading ‘A regional vulnerability assessment for the Dungeness crab (Metacarcinus magister) to changing ocean conditions: insights from model projections and empirical experiments’


  • Reset

Subscribe

OA-ICC Highlights


%d bloggers like this: