Posts Tagged 'mesocosm'

Coastal ocean acidification: dynamics and potential to affect marine mollusks

Coastal marine ecosystems are both ecologically and economically productive, and as human coastal populations expand, these critical habitats have become subject to a suite of anthropogenic stressors. During the past century, the progressive rise in levels of atmospheric carbon dioxide (CO2) entering world oceans has decreased ocean pH and caused ocean acidification. An additional and often overlooked cause of acidification in coastal zones is the production of CO2 via microbial degradation of organic matter. Nutrient loading in coastal ecosystems facilitates enhanced algal productivity and the subsequent decomposition of this algal biomass reduces oxygen levels and can promote hypoxia. The precise temporal and spatial dynamics of acidification and hypoxia as well as their potential effects on resource bivalves are not well described in most coastal waters. Here, to evaluate the status of aquatic acidification in coastal systems, I examine the seasonal, diel, and high-resolution spatiotemporal dynamics of carbonate chemistry and dissolved oxygen (DO) over a six year period in multiple northeast US estuaries and across multiple coastal habitats that host keystone marine species while concurrently quantifying the growth and survival of multiple early life stage suspension feeding bivalves. To assess the potential for acidification in eutrophic estuaries, the levels of DO, pH, the partial pressure of carbon dioxide (pCO2), and the saturation state of aragonite (ΩAr) were iv horizontally and vertically assessed during the onset, peak, and demise of low oxygen conditions in systems across the northeast US including Narragansett Bay (RI), Long Island Sound (CTNY), Jamaica Bay (NY), and Hempstead Bay (NY). Hypoxic waters and/or regions in close proximity to sewage discharge had extremely high levels of pCO2, (> 3,000 µatm), acidic pH (< 7.0), and were undersaturated with respect to aragonite (ΩAr < 1). The close spatial and temporal correspondence between DO and pH and the occurrence of extremes in these conditions in regions with the most intense nutrient loading indicated that they were driven primarily by enhanced microbial respiration relative to physical exchange processes. Next, I quantified the temporal and spatial dynamics of DO, carbonate chemistry, and net ecosystem metabolism (NEM) from spring through fall in multiple, distinct, temperate estuarine habitats: seagrass meadows, salt marshes, an open water estuary, and a shallow water habitat dominated by benthic macroalgae. All habitats displayed clear diurnal patterns of pH and DO, with minimums observed during early morning and maximums observed in the afternoon where diel ranges in pH and DO varied by site. NEM across habitats ranged from net autotrophic (macroalgae and seagrass) to metabolically balanced (open water) and net heterotrophic (salt marsh). Each habitat examined exhibited distinct buffering capacities that varied seasonally and were modulated by adjacent biological activity and variations in total alkalinity (TA) and dissolved inorganic carbon (DIC). I utilized continuous monitoring devices to characterize the diurnal dynamics of DO and carbonate chemistry from spring through fall across two, temperate eutrophic estuaries, western Long Island Sound and Jamaica Bay, NY. Vertical dynamics were resolved using an underway towing profiler and an automated stationary profiling unit. During the study, high rates of respiration in surface and bottom waters (> -0.2 mg O2 L -1 h -1 ) were observed where ephemeral surface water algal blooms caused brief periods of basification and supersaturation of DO that v were succeeded by periods of acidification and hypoxia. Diurnal vertical profiles demonstrated that oxic surface waters saturated with respect to calcium carbonate (aragonite) during the day transitioned to being unsaturated and hypoxic at night. Evidence is presented that, beyond respiration, nitrification of surface water strongly influenced by sewage discharge and oxidation processes in sediments can also contribute to acidification in these estuaries. Finally, the growth and survival of three bivalve species (Argopecten irradians, Crassostrea virginica, Mytilus edulis) were examined in an in-situ CO2 enrichment system deployed in a seagrass meadow and an open water estuary, and across a natural eutrophication gradient in Jamaica Bay, NY. In the seagrass meadow, the growth and survival of C. virginica and A. irradians significantly declined during the late summer in response to CO2 gas injection. During the open water CO2 enrichment experiment, all three species of bivalves exhibited depressed growth within the acidified chambers with no significant difference in mortality between treatments. In Jamaica Bay, dense phytoplankton blooms in the early summer decreased CO2 and increased DO creating spatial refuges for bivalves where growth rates were enhanced, but by the late summer, trends reversed as bivalve growth was depressed at these same locations due to the onset of acidification and hypoxia. Collectively, this dissertation has identified coastal ocean acidification as a symptom of eutrophication that can threaten marine bivalve populations.

Continue reading ‘Coastal ocean acidification: dynamics and potential to affect marine mollusks’

Global warming offsets the ecophysiological stress of ocean acidification on temperate crustose coralline algae

Highlights

•The ecological risk of climate change on temperate CCA has been assessed by mesocosm.

•Future change in carbonate chemistry has led to ecophysiological change of CCA.

•Oxygenic photosynthesis and growth decreased under acidified seawater.

•Negative metabolic changes in ocean acidification were offset by elevated temperature.

Abstract

Dramatic increases in the release of anthropogenic CO2 and global temperatures have resulted in alterations to seawater carbonate chemistry and metabolisms of marine organisms. There has been recent interest in the effects of these stressors on crustose coralline algae (CCA) because photosynthesis and calcification are influenced by all components of carbonate chemistry. To examine this, a mesocosm experiment was conducted to evaluate photosynthesis, calcification and growth in the temperate CCA Chamberlainium sp. under acidification (doubled CO2), warming (+5 °C), and greenhouse (doubled CO2 and +5 °C) conditions compared to present-day conditions. After 47 days of acclimation to these conditions, productivity was lowest under acidification, although photochemical properties were improved, while respiration was highest under warming. Likewise, growth was lowest under acidification, but this negative response was offset by elevated temperature under greenhouse. Together, these results suggest that warming offsets the negative effects of acidification by creating more suitable conditions for photosynthesis and growth.

Continue reading ‘Global warming offsets the ecophysiological stress of ocean acidification on temperate crustose coralline algae’

Decreased motility of flagellated microalgae long-term acclimated to CO2-induced acidified waters

Motility plays a critical role in algal survival and reproduction, with implications for aquatic ecosystem stability. However, the effect of elevated CO2 on marine, brackish and freshwater algal motility is unclear. Here we show, using laboratory microscale and field mesoscale experiments, that three typical phytoplankton species had decreased motility with increased CO2. Polar marine Microglena sp., euryhaline Dunaliella salina and freshwater Chlamydomonas reinhardtii were grown under different CO2 concentrations for 5 years. Long-term acclimated Microglena sp. showed substantially decreased photo-responses in all treatments, with a photophobic reaction affecting intracellular calcium concentration. Genes regulating flagellar movement were significantly downregulated (P < 0.05), alongside a significant increase in gene expression for flagellar shedding (P < 0.05). D. salina and C. reinhardtii showed similar results, suggesting that motility changes are common across flagellated species. As the flagella structure and bending mechanism are conserved from unicellular organisms to vertebrates, these results suggest that increasing surface water CO2 concentrations may affect flagellated cells from algae to fish.

Continue reading ‘Decreased motility of flagellated microalgae long-term acclimated to CO2-induced acidified waters’

Warming and acidification threaten glass sponge Aphrocallistes vastus pumping and reef formation

The glass sponge Aphrocallistes vastus contributes to the formation of large reefs unique to the Northeast Pacific Ocean. These habitats have tremendous filtration capacity that facilitates flow of carbon between trophic levels. Their sensitivity and resilience to climate change, and thus persistence in the Anthropocene, is unknown. Here we show that ocean acidification and warming, alone and in combination have significant adverse effects on pumping capacity, contribute to irreversible tissue withdrawal, and weaken skeletal strength and stiffness of A. vastus. Within one month sponges exposed to warming (including combined treatment) ceased pumping (50–60%) and exhibited tissue withdrawal (10–25%). Thermal and acidification stress significantly reduced skeletal stiffness, and warming weakened it, potentially curtailing reef formation. Environmental data suggests conditions causing irreversible damage are possible in the field at +0.5 °C above current conditions, indicating that ongoing climate change is a serious and immediate threat to A. vastus, reef dependent communities, and potentially other glass sponges.

Continue reading ‘Warming and acidification threaten glass sponge Aphrocallistes vastus pumping and reef formation’

The impacts of ocean acidification on marine trace gases and the implications for atmospheric chemistry and climate

Surface ocean biogeochemistry and photochemistry regulate ocean–atmosphere fluxes of trace gases critical for Earth’s atmospheric chemistry and climate. The oceanic processes governing these fluxes are often sensitive to the changes in ocean pH (or pCO2) accompanying ocean acidification (OA), with potential for future climate feedbacks. Here, we review current understanding (from observational, experimental and model studies) on the impact of OA on marine sources of key climate-active trace gases, including dimethyl sulfide (DMS), nitrous oxide (N2O), ammonia and halocarbons. We focus on DMS, for which available information is considerably greater than for other trace gases. We highlight OA-sensitive regions such as polar oceans and upwelling systems, and discuss the combined effect of multiple climate stressors (ocean warming and deoxygenation) on trace gas fluxes. To unravel the biological mechanisms responsible for trace gas production, and to detect adaptation, we propose combining process rate measurements of trace gases with longer term experiments using both model organisms in the laboratory and natural planktonic communities in the field. Future ocean observations of trace gases should be routinely accompanied by measurements of two components of the carbonate system to improve our understanding of how in situ carbonate chemistry influences trace gas production. Together, this will lead to improvements in current process model capabilities and more reliable predictions of future global marine trace gas fluxes.

Continue reading ‘The impacts of ocean acidification on marine trace gases and the implications for atmospheric chemistry and climate’

Ocean acidification reduces transfer of essential biomolecules in a natural plankton community

Ocean acidification (OA), a process of increasing seawater acidity caused by the uptake of anthropogenic carbon dioxide (CO2) by the ocean, is expected to change surface ocean pH to levels unprecedented for millions of years, affecting marine food web structures and trophic interactions. Using an in situ mesocosm approach we investigated effects of OA on community composition and trophic transfer of essential fatty acids (FA) in a natural plankton assemblage. Elevated pCO2 favored the smallest phytoplankton size class in terms of biomass, primarily picoeukaryotes, at the expense of chlorophyta and haptophyta in the nano-plankton size range. This shift in community composition and size structure was accompanied by a decline in the proportion of polyunsaturated FA (PUFA) to total FA content in the nano- and picophytoplankton size fractions. This decline was mirrored in a continuing reduction in the relative PUFA content of the dominant copepod, Calanus finmarchicus, which primarily fed on the nano-size class. Our results demonstrate that a shift in phytoplankton community composition and biochemical composition in response to rising CO2 can affect the transfer of essential compounds to higher trophic levels, which rely on their prey as a source for essential macromolecules.

Continue reading ‘Ocean acidification reduces transfer of essential biomolecules in a natural plankton community’

Ocean acidification and calcifying reef organisms: a mesocosm investigation

A long-term (10 months) controlled experiment was conducted to test the impact of increased partial pressure of carbon dioxide (pCO2) on common calcifying coral reef organisms. The experiment was conducted in replicate continuous flow coral reef mesocosms flushed with unfiltered sea water from Kaneohe Bay, Oahu, Hawaii. Mesocosms were located in full sunlight and experienced diurnal and seasonal fluctuations in temperature and sea water chemistry characteristic of the adjacent reef flat. Treatment mesocosms were manipulated to simulate an increase in pCO2 to levels expected in this century [midday pCO2 levels exceeding control mesocosms by 365 ± 130 μatm (mean ± sd)]. Acidification had a profound impact on the development and growth of crustose coralline algae (CCA) populations. During the experiment, CCA developed 25% cover in the control mesocosms and only 4% in the acidified mesocosms, representing an 86% relative reduction. Free-living associations of CCA known as rhodoliths living in the control mesocosms grew at a rate of 0.6 g buoyant weight year−1 while those in the acidified experimental treatment decreased in weight at a rate of 0.9 g buoyant weight year−1, representing a 250% difference. CCA play an important role in the growth and stabilization of carbonate reefs, so future changes of this magnitude could greatly impact coral reefs throughout the world. Coral calcification decreased between 15% and 20% under acidified conditions. Linear extension decreased by 14% under acidified conditions in one experiment. Larvae of the coral Pocillopora damicornis were able to recruit under the acidified conditions. In addition, there was no significant difference in production of gametes by the coral Montipora capitata after 6 months of exposure to the treatments.
Continue reading ‘Ocean acidification and calcifying reef organisms: a mesocosm investigation’

In situ ecosystem-based carbon dioxide perturbation experiments: Design and performance evaluation of a mesocosm facility

We describe a mesocosm facility that can be used for in situ CO2 perturbation experiments. The facility consists of a floating raft, nine impermeable cylindrical enclosures (each approximately 2400 L in volume), pCO2 regulation units, and bubble-mediated seawater mixers. Each enclosure is two-thirds filled with the seawater, and the headspace above is filled with air at a target pCO2 concentration. Each enclosure is capped with a transparent dome that transmits incoming radiation. To produce pCO2 levels higher than the ambient concentration, the mass flow controller in the pCO2 regulation unit delivers varying amounts (10-740 mL min-1) of ultra-pure CO2 into the gas mixer where it is rapidly mixed with ambient air (approximately 50 L min-1). To produce pCO2 levels lower than the ambient concentration, CO2-free air and ambient air are mixed in the gas mixer. Prior to daily seawater sampling, approximately 0.5 L min-1 of the target concentration pCO2 air stream is diverted to the seawater mixer for thorough mixing with the seawater in the enclosure, while the major fraction of the target concentration pCO2 air stream continues to flow into the enclosure headspace. A performance evaluation of the mesocosm facility assessed attainment of target pCO2 concentrations in the headspace and enclosure seawater, and the mixing efficiency of the seawater mixer. The results indicate that the facility is suitable for carrying out in situ pCO2 perturbation experiments.

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Mesocosm CO2 perturbation studies: from organism to community level

No abstract available.

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Ocean acidification in the IPCC AR5 WG II

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