Posts Tagged 'biological response'

Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community

Ocean acidification and warming are likely to affect the structure and functioning of marine benthic communities. This study experimentally examined the effects of ocean acidification and warming on trophic interactions within a maerl bed community by using stable carbon and nitrogen isotope analysis. Two three‐month experiments were conducted in winter and summer seasons with four different combinations of pCO2 (ambient and elevated pCO2) and temperature (ambient and +3°C). Experimental assemblages were created in tanks held in the laboratory and were composed of calcareous (Lithothamnion corallioides) and fleshy algae (Rhodymenia ardissonei, Solieria chordalis, and Ulva sp.), gastropods (Gibbula magus and Jujubinus exasperatus), and sea urchins (Psammechinus miliaris). Our results showed higher seaweed availability for grazers in summer than winter. Therefore, grazers were able to adapt their diet seasonally. Increased pCO2 and temperature did not modify the trophic structure in winter, while shifts in the contribution of seaweed were found in summer. Combined acidification and warming increased the contribution of biofilm in gastropods diet in summer conditions. Psammechinus miliaris mostly consumed L. corallioides under ambient conditions, while the alga S. chordalis became the dominant food source under high pCO2 in summer. Predicted changes in pCO2 and temperature had complex effects on assemblage trophic structure. Direct effects of acidification and warming on seaweed metabolism may modify their abundance and biomass, affecting their availability for grazers. Climate change may also modify seaweeds’ nutritive value and their palatability for grazers. The grazers we investigated were able to change their diet in response to changes in algal assemblages, an advantage given that warming and acidification alter the composition of algal communities.

Continue reading ‘Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community’

The dynamics of rapid adaptation to ocean acidification in the Mediterranean mussel

Global climate change has intensified the need to assess if, and how, natural populations adapt to abrupt shifts in their environment. The tempo of adaptation in natural systems has been the subject of theoretical and empirical investigation for decades. Recent evidence from genome-wide sequencing approaches has indicated that evolution may proceed at a pace previously deemed theoretically impossible. Such studies, however, have largely observed these processes in the context of model systems, and the extent to which these patterns will hold in ecologically-relevant species subject to the dramatic environmental perturbations associated with global change is unclear. Accordingly, this thesis investigates the capacity for, and mechanisms by which, the Mediterranean mussel, Mytilus galloprovincialis, may rapidly adapt to expected declines in global seawater pH. Reductions in seawater pH constitute a global change stressor impacting marine species globally, with anticipated impacts altering the structure and services of numerous ecological communities. Due to its experimental tractability, as well as its ecological and economic importance, M. galloprovincialis has become a model-species for exploring the physiological and morphological impacts of low pH seawater. Yet, the extent to which evolution may offset observed phenotypic consequences is unknown. To address this knowledge gap the present thesis explores the following: (i) the processes shaping and maintaining variation in low pH tolerance across the species’ native range; (ii) the extent to which the standing variation within natural populations of M. galloprovincialis can facilitate the magnitude of evolution necessary for persistence under global change conditions; and (iii) the molecular basis of low pH adaptation in marine bivalves and beyond. My results elucidate how contemporary gradients in pH variability shape distinct patterns of low pH plasticity across natural populations. Furthermore, my findings demonstrate that the standing variation within natural populations is sufficient for rapid adaptation to even extreme reductions in seawater pH. Lastly, I provide mechanistic links between the molecular mechanisms influenced by shifts in the external seawater pH environment and fitness-related abnormalities observed in M. galloprovincialis, a finding that likely explains observed low pH sensitivity across a broad range of marine metazoans. This thesis thus lends to our conceptual understanding regarding the dynamics of rapid adaptation in natural populations, while explicitly informing the management of an ecologically and economically important marine species as global change progresses.

Continue reading ‘The dynamics of rapid adaptation to ocean acidification in the Mediterranean mussel’

Influence of iron and carbon on the occurrence of Ulva prolifera (Ulvophyceae) in the Yellow Sea

Highlights

  • Continuous, massive green tides have occurred in the Yellow Sea over the past decade (2007–2018).
  • This study integrates remote sensing, field observation, laboratory measurements and indoor cultivation.
  • Ulva prolifera blooming is influenced by higher concentrations of Fe(II) and HCO3-, and a lower pH.

Abstract

Over the past decade, massive outbreaks of Ulva prolifera have occurred in the Yellow Sea, China, and caused negative effects to the coastal environments. In response, many scientific investigations have been conducted to ascertain the origins of and reasons for the algal bloom that has resulted in continuous green tides. In this work, we explored the influences of iron and dissolved inorganic carbon (DIC) on the occurrence of green algal blooms. The moderate-resolution imaging spectroradiometer (MODIS) data showed the blooming areas and movement of U. prolifera. Field observation showed that higher Fe(II) concentrations (average 0.145 mg L−1) can be correlated with large Ulva prolifera blooms. Furthermore, lower pH might enhance the accumulation of dissolved carbon into the green algae; a premise that was supported by higher concentrations of CO2(0.037 mmol L−1), HCO3−(2.58 mmol L−1) and the lowest pH value (7.69) being found together at site H11. The indoor iron- and bicarbonate-enrichment experiments further confirmed that higher concentrations of Fe(II) and HCO3− and a lower pH can increase the growth rate of U. prolifera. This study indicates that seawater chemical factors contribute to the long term, ongoing green tides in the Yellow Sea and provides new thoughts for the causes of U. prolifera blooms.

Continue reading ‘Influence of iron and carbon on the occurrence of Ulva prolifera (Ulvophyceae) in the Yellow Sea’

Crumbling reefs and cold-water coral habitat loss in a future ocean: evidence of “coralporosis” as an indicator of habitat integrity

Ocean acidification is a threat to the net growth of tropical and deep-sea coral reefs, due to gradual changes in the balance between reef growth and loss processes. Here we go beyond identification of coral dissolution induced by ocean acidification and identify a mechanism that will lead to a loss of habitat in cold-water coral reef habitats on an ecosystem-scale. To quantify this, we present in situ and year-long laboratory evidence detailing the type of habitat shift that can be expected (in situ evidence), the mechanisms underlying this (in situ and laboratory evidence), and the timescale within which the process begins (laboratory evidence). Through application of engineering principals, we detail how increased porosity in structurally critical sections of coral framework will lead to crumbling of load-bearing material, and a potential collapse and loss of complexity of the larger habitat. Importantly, in situ evidence highlights that cold-water corals can survive beneath the aragonite saturation horizon, but in a fundamentally different way to what is currently considered a biogenic cold-water coral reef, with a loss of the majority of reef habitat. The shift from a habitat with high 3-dimensional complexity provided by both live and dead coral framework, to a habitat restricted primarily to live coral colonies with lower 3-dimensional complexity represents the main threat to cold-water coral reefs of the future and the biodiversity they support. Ocean acidification can cause ecosystem-scale habitat loss for the majority of cold-water coral reefs.

Continue reading ‘Crumbling reefs and cold-water coral habitat loss in a future ocean: evidence of “coralporosis” as an indicator of habitat integrity’

Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta

Acidification and deoxygenation are two consequences of climate change that also co-occur in eutrophied coastal zones and can have deleterious effects on marine life. While the effects of hypoxia on marine herbivores have been well-studied, how ocean acidification combined with hypoxia affects herbivory is poorly understood. This study examined how herbivory and survival by the gastropod Lacuna vincta grazing on the macroalgae Ulva rigida was influenced by hypoxia and ocean acidification, alone and in combination, with and without food limitation. Experiments exposed L. vincta to a range of environmentally realistic dissolved oxygen (0.7 – 8 mg L–1) and pH (7.3 – 8.0 total scale) conditions for 3 – 72 h, with and without a starvation period and quantified herbivory and survival. While acidified conditions (pH < 7.4) reduced herbivory when combined with food limitation, low oxygen conditions (< 4 mg L–1) reduced herbivory and survival regardless of food supply. When L. vincta were starved and grazed in acidified conditions herbivory was additively reduced, whereas starvation and hypoxia synergistically reduced grazing rates. Overall, low oxygen had a more inhibitory effect on herbivory than low pH. Shorter exposure times (9, 6, and 3 h) were required to reduce grazing at lower DO levels (∼2.4, ∼1.6, and ∼0.7 mg L–1, respectively). Herbivory ceased entirely following a three-hour exposure to DO of 0.7 mg L–1 suggesting that episodes of diurnal hypoxia disrupt grazing by these gastropods. The suppression of herbivory in response to acidified and hypoxic conditions could create a positive feedback loop that promotes ‘green tides’ whereby reduced grazing facilitates the overgrowth of macroalgae that cause nocturnal acidification and hypoxia, further disrupting herbivory and promoting the growth of macroalgae. Such feedback loops could have broad implications for estuarine ecosystems where L. vincta is a dominant macroalgal grazer and will intensify as climate change accelerates.

Continue reading ‘Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta’

Evidence for stage-based larval vulnerability and resilience to acidification in Crassostrea virginica

Using image analysis of scanning electron micrographs (SEMs), we compared differences in growth of D-stage veligers [i.e. prodissoconch I and II (PI and PII) larvae] of eastern oysters Crassostrea virginica grown in mesohaline water under high- and low-CO2 conditions. We found SEMs to reveal no evidence of dissolution or shell structure deformity for larval shells in either of the CO2 treatments but detected prominent growth lines in the PII regions of larval shells. The number of growth lines closely approximated the duration of the experiment, suggesting that growth lines are generated daily. Mean growth line interval widths were 20% greater for larval shells cultured in low- vs high-CO2 conditions. Crassostrea virginica veliger larvae were shown to tolerate high CO2 levels and aragonite saturation states (Ωarag) < 1.0, but larval growth was slowed substantially under these conditions. Differences in growth line interval width translate into substantial changes in shell area and account for previously observed differences in total shell area between the treatments, as determined by light microscopy and image analysis. Other studies have documented high mortality and malformation of D-stage larvae in bivalves when pre-veliger life stages (i.e. eggs, gastrula and trochophores) were exposed to elevated CO2. Our experiments revealed statistical differences in rates of larval survival, settlement and subsequent early-stage spat mortality for veligers reared in high- and low-CO2 conditions. Although each of these rates was measurably affected by high CO2, the magnitude of these differences was small (range across categories = 0.7–6.3%) suggesting that the impacts may not be catastrophic, as implied by several previous studies. We believe the apparent disparity among experimental results may be best explained by differential vulnerability of pre-veliger stage larvae and veligers, whereby PI and PII larvae have greater physiological capacity to withstand environmental conditions that may be thermodynamically unfavourable to calcification (i.e. Ωarag < 1.0).

Continue reading ‘Evidence for stage-based larval vulnerability and resilience to acidification in Crassostrea virginica’

pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios

The increasing atmospheric CO2 concentration in the last few decades has resulted in a decrease in oceanic pH. In this study, we assessed the natural variability of pH in coastal waters off Goa, eastern Arabian Sea. pHT showed large variability (7.6–8.1) with low pH conditions during south‐west monsoon (SWM), and the variability is found to be associated with upwelling rather than freshwater runoff. Considering that marine biota inhabiting dynamic coastal waters off Goa are exposed to such wide range of natural fluctuations of pH, an acidification experiment was carried out. We studied the impact of low pH on the local population of sea urchin Stomopneustes variolaris (Lamarck, 1816). Sea urchins were exposed for 210 days to three treatments of pHT: 7.96, 7.76 and 7.46. Our results showed that S. variolaris at pHT 7.96 and 7.76 were not affected, whereas the ones at pHT 7.46 showed adverse effects after 120 days and 50% mortality by 210 days. However, even after exposure to low pH for 210 days, 50% organisms survived. Under low pH conditions (pHT 7.46), the elemental composition of sea urchin spines exhibited deposition of excess Sr2+ as compared to Mg2+ ions. We conclude that although the sea urchins would be affected in future high CO2 waters, at present they are not at risk even during the south‐west monsoon when low pH waters reside on the shelf.

Continue reading ‘pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios’

Acclimatization drives differences in reef-building coral calcification rates

Coral reefs are susceptible to climate change, anthropogenic influence, and environmental stressors. However, corals in Kāneʻohe Bay, Hawaiʻi have repeatedly shown resilience and acclimatization to anthropogenically-induced rising temperatures and increased frequencies of bleaching events. Variations in coral and algae cover at two sites—just 600 m apart—at Malaukaʻa fringing reef suggest genetic or environmental differences in coral resilience between sites. A reciprocal transplant experiment was conducted to determine if calcification (linear extension and dry skeletal weight) for dominant reef-building species, Montipora capitata and Porites compressa, varied between the two sites and whether or not parent colony or environmental factors were responsible for the differences. Despite the two sites representing distinct environmental conditions with significant differences between temperature, salinity, and aragonite saturation, M. capitata growth rates remained the same between sites and treatments. However, dry skeletal weight increases in P. compressa were significantly different between sites, but not across treatments, with linear mixed effects model results suggesting heterogeneity driven by environmental differences between sites and the parent colonies. These results provide evidence of resilience and acclimatization for M. capitata and P. compressa. Variability of resilience may be driven by local adaptations at a small, reef-level scale for P. compressa in Kāneʻohe Bay.

Continue reading ‘Acclimatization drives differences in reef-building coral calcification rates’

Effects of temperature and food concentration on pteropod metabolism along the Western Antarctic Peninsula

Highlights

  • Measured respiration and excretion of the Antarctic pteropod Limacina.
  • Analyzed effects of future temperature and food conditions on pteropod metabolism.
  • Highest metabolism occurred under higher temperatures with less response to food.
  • Metabolic ratios of C, N, and P were all below the canonical Redfield ratio.
  • Pteropod metabolism responsive to ocean change, affecting biogeochemical cycles.

Abstract

Pteropods (pelagic snails) are abundant zooplankton in the Southern Ocean where they are important grazers of phytoplankton, prey for higher trophic levels, and sensitive to environmental change. The Western Antarctic Peninsula (WAP) is a highly dynamic and productive region that has undergone rapid warming, but little is known about how environmental changes there will affect pteropod physiology. In this study, the effects of warming seawater temperatures and shifting food availability on Limacina helicina antarctica metabolism (respiration and excretion) were determined by conducting shipboard experiments that exposed pteropods to a range of temperatures and phytoplankton (food) concentrations. Highest respiration (up to 69 μmol O2 gDW−1 h−1) and usually highest excretion rates occurred under higher temperature with more limited metabolic response to food concentration, indicating these factors do not always have an additive effect on pteropod metabolism. The proportion of dissolved organic matter (DOM) to total organic and inorganic dissolved constituents was high and was also significantly affected by shifts in temperature and food. Dissolved organic carbon, nitrogen, and phosphorus (DOC, DON, and DOP) were on average 27, 51, and 11.5% of the total C, N, and P metabolized, respectively. The proportion of total N excreted as DON and the proportion of total P excreted as DOP were significantly affected by a combination of shifting temperature and food concentrations. There were no effects of temperature or food on DOC excretion (mean 8.79 μmol C gDW−1 h−1; range 0.44 to 44) as a proportion of total C metabolized. Metabolic O2:N ratio ranged from 2 to 9 and decreased significantly with increasing temperature and food, indicating a shift toward increased protein catabolism. Metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which has implications for phytoplankton nutrient uptake and bacterial production. Respiration rates at ambient conditions of other WAP pteropods, and excretion rates for Clio pyramidata, were also measured, with respiration rates ranging from 24.39 (Spongiobranchaea australis) to 28.86 (L. h. antarctica) μmol O2 gDW−1 h−1. Finally, a CO2 perturbation experiment measuring L. h. antarctica metabolism under pre-industrial and elevated dissolved pCO2 conditions showed no significant change in mean L. h. antarctica respiration or excretion rates with higher pCO2. These insights into the metabolic response of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.

Continue reading ‘Effects of temperature and food concentration on pteropod metabolism along the Western Antarctic Peninsula’

Physiological resilience of pink salmon to naturally occurring ocean acidification

Pacific salmon stocks are in decline with climate change named as a contributing factor. The North Pacific coast of British Columbia is characterized by strong temporal and spatial heterogeneity in ocean conditions with upwelling events elevating CO2 levels up to 10-fold those of pre-industrial global averages. Early life stages of pink salmon have been shown to be affected by these CO2 levels, and juveniles naturally migrate through regions of high CO2 during the energetically costly phase of smoltification. To investigate the physiological response of out-migrating wild juvenile pink salmon to these naturally occurring elevated CO2 levels, we captured fish in Georgia Strait, British Columbia and transported them to a marine lab (Hakai Institute, Quadra Island) where fish were exposed to one of three CO2 levels (850, 1500 and 2000 μatm CO2) for 2 weeks. At ½, 1 and 2 weeks of exposure, we measured their weight and length to calculate condition factor (Fulton’s K), as well as haematocrit and plasma [Cl]. At each of these times, two additional stressors were imposed (hypoxia and temperature) to provide further insight into their physiological condition. Juvenile pink salmon were largely robust to elevated CO2 concentrations up to 2000 μatm CO2, with no mortality or change in condition factor over the 2-week exposure duration. After 1 week of exposure, temperature and hypoxia tolerance were significantly reduced in high CO2, an effect that did not persist to 2 weeks of exposure. Haematocrit was increased by 20% after 2 weeks in the CO2 treatments relative to the initial measurements, while plasma [Cl] was not significantly different. Taken together, these data indicate that juvenile pink salmon are quite resilient to naturally occurring high CO2 levels during their ocean outmigration.

Continue reading ‘Physiological resilience of pink salmon to naturally occurring ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

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