Tidal action and macroalgal photosynthetic activity prevent coastal acidification in an eutrophic system within a semi-desert region (original) (raw)
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The role of macroalgal habitats as ocean acidification refugia within coastal seascapes
Cambridge Prisms: Coastal Futures
Ocean acidification (OA) is recognised as a significant aspect of global change that will have widespread impacts on marine ecosystems. There has been a recent increase in published research that acknowledges the potential for marine vegetation, such as macroalgae, to modulate local pH conditions through biotic processes and thereby serve as OA refugia for marine organisms. However, the specific role that macroalgae plays in the carbonate chemistry dynamics of shallow coastal marine environments has not yet been reviewed in detail. This review assesses the available literature documenting the distribution patterns and structural complexities of macroalgae and how this informs their role in pH modulation over various temporal and spatial extents. A wholistic understanding on the role of macroalgal marine vegetation as OA refugia can facilitate improved local OA management and protected area management to benefit impacted coastal marine species.
Macroalgal responses to ocean acidification depend on nutrient and light levels
Frontiers in Marine Science, 2015
Ocean acidification may benefit algae that are able to capitalize on increased carbon availability for photosynthesis, but it is expected to have adverse effects on calcified algae through dissolution. Shifts in dominance between primary producers will have knock-on effects on marine ecosystems and will likely vary regionally, depending on factors such as irradiance (light vs. shade) and nutrient levels (oligotrophic vs. eutrophic). Thus experiments are needed to evaluate interactive effects of combined stressors in the field. In this study, we investigated the physiological responses of macroalgae near a CO 2 seep in oligotrophic waters off Vulcano (Italy). The algae were incubated in situ at 0.2 m depth using a combination of three mean CO 2 levels (500, 700-800 and 1200 μatm CO 2), two light levels (100 and 70% of surface irradiance) and two nutrient levels of N, P, and K (enriched vs. non-enriched treatments) in the non-calcified macroalga Cystoseira compressa (Phaeophyceae, Fucales) and calcified Padina pavonica (Phaeophyceae, Dictyotales). A suite of biochemical assays and in vivo chlorophyll a fluorescence parameters showed that elevated CO 2 levels benefitted both of these algae, although their responses varied depending on light and nutrient availability. In C. compressa, elevated CO 2 treatments resulted in higher carbon content and antioxidant activity in shaded conditions both with and without nutrient enrichment-they had more Chla, phenols and fucoxanthin with nutrient enrichment and higher quantum yield (F v /F m) and photosynthetic efficiency (α ETR) without nutrient enrichment. In P. pavonica, elevated CO 2 treatments had higher carbon content, F v /F m , α ETR , and Chla regardless of nutrient levels-they had higher concentrations of phenolic compounds in nutrient enriched, fully-lit conditions and more antioxidants in shaded, nutrient enriched conditions. Nitrogen content increased significantly in fertilized treatments, confirming that these algae were nutrient limited in this oligotrophic part of the Mediterranean. Our findings strengthen evidence that brown algae can be expected to proliferate as the oceans acidify where physicochemical conditions, such as nutrient levels and light, permit.
Effects of ocean acidification on macroalgal communities
Journal of Experimental Marine …, 2011
Porzio L., Buia M. C., & Hall-Spencer J. M., in press. Effects of ocean acidification on macroalgal communities. Journal of Experimental Marine Biology and Ecology doi:10.1016/j.jembe.2011.02.011. There are high levels of uncertainty about how coastal ecosystems will be affected by rapid ocean acidification caused by anthropogenic CO2, due to a lack of data. The few experiments to date have been short-term (< 1 year) and reveal mixed responses depending on the species examined and the culture conditions used. It is difficult to carry out long-term manipulations of CO2 levels, therefore areas with naturally high CO2 levels are being used to help understand which species, habitats and processes are resilient to the effects of ocean acidification, and which are adversely affected. Here we describe the effects of increasing CO2 levels on macroalgal communities along a pH gradient caused by volcanic vents. Macroalgal habitat differed at taxonomic and morphological group levels along a pH gradient. The vast majority of the 101 macroalgal species studied were able to grow with only a 5% decrease in species richness as the mean pH fell from 8.1 to 7.8. However, this small fall in species richness was associated with shifts in community structure as the cover of turf algae decreased disproportionately. Calcitic species were significantly reduced in cover and species richness whereas a few non-calcified species became dominant. At mean pH 6.7, where carbonate saturation levels were < 1, calcareous species were absent and there was a 72% fall in species richness. Under these extremely high CO2 conditions a few species dominated the simplified macroalgal assemblage and a very few exhibited enhanced reproduction, although high CO2 levels seemed to inhibit reproduction in others. Our data show that many macroalgal species are tolerant of long-term elevations in CO2 levels but that macroalgal habitats are altered significantly as pH drops, contributing to a scant but growing body of evidence concerning the long-term effects of CO2 emissions in vegetated marine systems. Further study is now needed to investigate whether the observed response of macroalgal communities can be replicated in different seasons and from a range of geographical regions for incorporation into global modelling studies to predict effects of CO2 emissions on Earth’s ecosystems. Porzio L., Buia M. C., & Hall-Spencer J. M., in press. Effects of ocean acidification on macroalgal communities. Journal of Experimental Marine Biology and Ecology doi:10.1016/j.jembe.2011.02.011. Article (subscription required).
Acidification of subsurface coastal waters enhanced by eutrophication
Nature Geoscience, 2011
Human inputs of nutrients to coastal waters can lead to the excessive production of algae, a process known as eutrophication. Microbial consumption of this organic matter lowers oxygen levels in the water 1-3 . In addition, the carbon dioxide produced during microbial respiration increases acidity. The dissolution of atmospheric carbon dioxide in ocean waters also raises acidity, a process known as ocean acidification. Here, we assess the combined impact of eutrophication and ocean acidification on acidity in the coastal ocean, using data collected in the northern Gulf of Mexico and the East China Sea-two regions heavily influenced by nutrient-laden rivers. We show that eutrophication in these waters is associated with the development of hypoxia and the acidification of subsurface waters, as expected. Model simulations, using data collected from the northern Gulf of Mexico, however, suggest that the drop in pH since pre-industrial times is greater than that expected from eutrophication and ocean acidification alone. We attribute the additional drop in pHof 0.05 units-to a reduction in the ability of these carbon dioxide-rich waters to buffer changes in pH. We suggest that eutrophication could increase the susceptibility of coastal waters to ocean acidification.
High pH in shallow-water macroalgal habitats
Marine Ecology Progress Series, 2007
The aim of this study was to evaluate seasonal and diurnal variability in pH and inorganic carbon in shallow-water macroalgal habitats and to evaluate the importance of high pH for macroalgal photosynthesis. Seasonal variations in pH, oxygen saturation and inorganic carbon concentration were measured at an exposed and a sheltered shallow-water (0 to 1 m) macroalgal habitat. Daytime pH was significantly higher in spring, summer and autumn than in winter at both study sites. Diurnal measurements at the most exposed site showed significantly higher pH during the day than during the night. The diurnal variations were largest in shallow water and decreased with increasing water depth. High pH resulted in periodically low concentrations of available inorganic carbon in summer (as low as 1.3 mmol [CO 2 + HCO 3 -] l -1 ). Photosynthesis as a function of inorganic carbon concentrations was measured at pH 8 and 9.3 for 4 common macroalgal species (Fucus vesiculosus, F. serratus, Ceramium rubrum, Ulva sp.). Photosynthesis in these species was not limited by natural concentrations of inorganic carbon, but maximum photosynthesis and inorganic carbon concentrations at saturation were lower when measured at pH 9.3 than at pH 8. Our results suggest that pH is higher in natural shallow-water habitats than previously thought, and that high pH has a direct effect on photosynthesis that cannot be accounted for by low availability of inorganic carbon.
Water acidification: effects on the macroalgal community
2010
Recent researches, performed in a naturally acidified site (Castello Aragonese d’Ischia - Gulf of Naples, Italy) where volcanic carbon dioxide vents cause long-term changes in seawater carbonate chemistry, lowering the pH from 8.17 down to 6.57, reveal winners and losers within the benthic community. In the same site, we chose to address the impact of ocean acidification on the algal community with an integrated approach by means of ecological, physiological and molecular tools. Qualitative and quantitative changes in algal composition have been detected. Results showed a less structured community at low pH, characterized by few dominant species and the lack of calcareous taxa. Due to their different tolerance to pH variations, three target species (Sargassum vulgare, Dictyota dichotoma and Jania rubens) have been selected to carry out transplant experiments in order to detect short term stress signals. Variations in fluorometry-derived parameters of the photosynthetic performance o...
Marine pollution bulletin, 2016
The incidence and severity of extraordinary macroalgae blooms (green tides) are increasing. Here, climate change (ocean warming and acidification) impacts on life history and biochemical responses of a causative green tide species, Ulva rigida, were investigated under combinations of pH (7.95, 7.55, corresponding to lower and higher pCO2), temperature (14, 18°C) and nitrate availability (6 and 150μmolL(-1)). The higher temperature accelerated the onset and magnitude of gamete settlement. Any two factor combination promoted germination and accelerated growth in young plants. The higher temperature increased reproduction, which increased further in combination with elevated pCO2 or nitrate. Reproductive success was highest (64.4±5.1%) when the upper limits of all three variables were combined. Biochemically, more protein and lipid but less carbohydrate were synthesized under higher temperature and nitrate conditions. These results suggest that climate change may cause more severe gree...
Global Change Biology, 2000
Receiving coastal waters and estuaries are among the most nutrient-enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast-growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth-limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low-to high-nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high d 15 N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned.
Scientific Reports
Coastal ocean acidification research is dominated by laboratory-based studies that cannot necessarily predict real-world ecosystem response given its complexity. We enriched coastal sediments with increasing quantities of organic matter in the field to identify the effects of eutrophication-induced acidification on benthic structure and function, and assess whether biogenic calcium carbonate (CaCO 3) would alter the response. Along the eutrophication gradient we observed declines in macrofauna biodiversity and impaired benthic net primary productivity and sediment nutrient cycling. caco 3 addition did not alter the macrofauna community response, but significantly dampened negative effects on function (e.g. net autotrophy occurred at higher levels of organic matter enrichment in +caco 3 treatments than −caco 3 (1400 vs 950 g dw m −2)). By identifying the links between eutrophication, sediment biogeochemistry and benthic ecosystem structure and function in situ, our study represents a crucial step forward in understanding the ecological effects of coastal acidification and the role of biogenic caco 3 in moderating responses. Acidification of seawater via the increasing absorption of atmospheric CO 2 (ocean acidification; OA) is a key contemporary issue for the marine environment 1. However, eutrophication-induced acidification 2 has received comparatively little attention, despite affecting vast portions of the world's coastal zones 3. Eutrophication is defined as an increase in the rate of supply of organic carbon to an ecosystem and occurs in coastal waters primarily via the anthropogenic input of excess nutrients 4. Excess nutrients promote short-lived algal blooms which, upon collapsing, are deposited to the benthos 5 where microbially-driven aerobic respiration of organic matter releases CO 2 in approximate equivalence to O 2 consumption 6 , causing localised acidification 7. In highly productive estuarine environments, eutrophication-induced acidification adds variation to background fluctuations in pH driven by changing rates of respiration and photosynthesis 8,9 and watershed effects 10 , and occurs against a backdrop of global OA that is set to reduce seawater pH 0.3-0.4 units by 2100 11. The co-occurrence of these acidification pathways means coastal environments may experience decreases in seawater pH far exceeding those predicted from OA alone 12-14. Additionally, biogeochemical changes associated with aerobic (i.e., O 2 depletion) and anaerobic (i.e., dissimilatory N and S reduction) pathways of benthic organic matter degradation mean that acidification rarely acts in isolation, but is rather a single component in a multi-stressor setting also comprising hypoxia and increased concentrations of toxic solutes 15,16. Coastal benthic macrofauna communities exhibit predictable responses to organic matter enrichment, such as reduced abundance and diversity at high levels of loading 17. These responses are usually attributed to the onset of hypoxia 3 , however empirical evidence suggests some organisms respond more strongly to fluctuations in pH than O 2 (e.g. juvenile clams) 18. Whilst it is generally accepted that calcifying organisms will fare poorly under acidification due to calcium carbonate (CaCO 3) under-saturation and increased likelihood of dissolution 19-21 , the consequences for non-calcifying organisms are less certain and vary interspecifically 22. Understanding the response of benthic communities to decreasing pH is critical, as numerous ecosystem services (e.g. food production and nutrient cycling) are underpinned by functions (e.g. primary production and organic matter mineralisation)