Posts Tagged 'morphology'

Ocean warming has a greater effect than acidification on the early life history development and swimming performance of a large circumglobal pelagic fish

Ocean warming and acidification are serious threats to marine life; however, their individual and combined effects on large pelagic and predatory fishes are poorly understood. We determined the effects of projected future temperature and carbon dioxide (CO2) levels on survival, growth, morphological development and swimming performance on the early life stages of a large circumglobal pelagic fish, the yellowtail kingfish Seriola lalandi. Eggs, larvae and juveniles were reared in cross‐factored treatments of temperature (21 and 25°C) and pCO2 (500 and 985 μatm) from fertilisation to 25 days post hatching (dph). Temperature had the greatest effect on survival, growth and development. Survivorship was lower, but growth and morphological development were faster at 25°C, with surviving fish larger and more developed at 1, 11 and 21 dph. Elevated pCO2 affected size at 1 dph, but not at 11 or 21 dph, and did not affect survival or morphological development. Elevated temperature and pCO2 had opposing effects on swimming performance at 21 dph. Critical swimming speed (Ucrit) was increased by elevated temperature but reduced by elevated pCO2. Additionally, elevated temperature increased the proportion of individuals that responded to a startle stimulus, reduced latency to respond and increased maximum escape speed, potentially due to the more advanced developmental stage of juveniles at 25°C. By contrast, elevated pCO2 reduced the distance moved and average speed in response to a startle stimulus. Our results show that higher temperature is likely to be the primary driver of global change impacts on kingfish early life history; however, elevated pCO2 could affect critical aspects of swimming performance in this pelagic species. Our findings will help parameterise and structure fisheries population dynamics models and improve projections of impacts to large pelagic fishes under climate change scenarios to better inform adaptation and mitigation responses

Continue reading ‘Ocean warming has a greater effect than acidification on the early life history development and swimming performance of a large circumglobal pelagic fish’

The interactive effects of ocean acidification, food availability, and source location on the growth and physiology of the California mussel

Research shows ocean acidification (OA) can have largely negative impacts on marine organisms and ecosystems. Prior laboratory studies show that shelled marine invertebrates (e.g., molluscs) exhibit reduced growth rates and weaker shells when experiencing OA-related stress. However, populations of the critical intertidal mussel species, Mytilus californianus, which experience naturally acidic water due to upwelling in certain parts of Northern California have been observed to have relatively stronger and thicker shells and higher growth rates than those that experience less frequent exposure to upwelling. To address the discrepancies between negative effects of OA exposure in the laboratory and seemingly positive effects off OA exposure in the field we collected juvenile mussels from four separate locations on the northern California coast that vary in exposure to upwelling-driven OA and raised them under ambient, constantly acidified, or intermittently acidified seawater conditions. Half of the mussels in each of the experimental treatments were given access to either ambient or elevated food concentrations. Although higher food availability increased shell and overall mussel growth, variation in mussel life-history traits among locations appears to be driven primarily by inherent differences (i.e. genetics or epigenetics). In particular, overall growth, soft tissue mass, and shell dissolution in mussels were associated with source-specific upwelling strength while adductor muscle mass along with shell growth and strength of mussels were associated with source-specific levels of predation risk. Oxygen consumption of mussels did not significantly vary among food, pH or source location treatments, suggesting that differences in growth rates were not due to differences in differences in metabolic or energetic efficiencies between individuals. Although not statistically significant, mussels from areas of high crab predation risk tended to survive crab attacks in the lab better than mussels from other areas. My data suggests that the adaptive potential of M. californianus to respond to future OA conditions is dependent on local environmental factors such as upwelling strength, food availability, and predation risk. My study addresses a significant gap in our understanding of the mechanism behind conflicting observations of increased growth in the field associated with low pH and previous laboratory results, demonstrating the importance of environmental context in shaping the organismal response to current and future OA conditions.

Continue reading ‘The interactive effects of ocean acidification, food availability, and source location on the growth and physiology of the California mussel’

A simple role of coral-algal symbiosis in coral calcification based on multiple geochemical tracers

Light-enhanced calcification of reef-building corals, which eventually create vast coral reefs, is well known and based on coral-algal symbiosis. Several controversial hypotheses have been proposed as possible mechanisms for connecting symbiont photosynthesis and coral calcification, including pH rise in the internal pool, role of organic matrix secretion, and enzyme activities. Here, based on the skeletal chemical and isotopic compositions of symbiotic and asymbiotic primary polyps of Acropora digitifera corals, we show a simple pH increase in the calcification medium as the predominant contribution of symbionts to calcification of host corals. We used the symbiotic and asymbiotic primary polyps reared for 10 days at four temperatures (27, 29, 31, and 33 °C), five salinities (34, 32, 30, 28, and 26), and four pCO2 levels (< 300, 400, 800, and 1000 µatm). As a result of analyzing multiple geochemical tracers (U/Ca, Mg/Ca, Sr/Ca, δ18O, δ 13C, and δ 44Ca), a clear and systematic decrease in skeletal U/Ca ratio (used as a proxy for calcification fluid pH) was observed, indicating a higher pH of the fluid in symbiotic compared to asymbiotic polyps. In contrast, Mg/Ca ratios (used as a tentative proxy for organic matrix secretion) and δ 44Ca (used as an indicator of Ca2+ pathway to the fluid) did not differ between symbiotic and asymbiotic polyps. This suggests that organic matrix secretion related to coral calcification is controlled mainly by the coral host itself, and a transmembrane transport of Ca2+ does not vary according to symbiosis relationship. Skeletal δ 18O values of the both symbiotic and asymbiotic polyps showed offsets between them with identical temperature dependence for the both polyps. Based on a newly proposed model, behavior of δ 18O in the present study seems to reflect the rate of CO2 hydration in the calcifying fluid. Since CO2 hydration is promoted by enzyme carbonic anhydrase, the offset of δ 18O values between symbiotic and asymbiotic polyp is attributed to the differences of enzyme activity, although the enzyme is functional even in the asymbiotic polyp. Symbiotic δ 13C values in the temperature and salinity experiments were higher compared to those in the asymbiotic polyps due to photosynthesis, although photosynthetic δ 13C signals in the pCO2 experiment were masked by the dominant δ 13C gradient in dissolved inorganic carbon in seawater caused by 13C-depletd CO2 gas addition in the higher pCO2 treatments. Sr/Ca ratios showed a negligible relationship according to variation of temperature, salinity, and pCO2, although it might be attributed to relatively large deviations of replicates of Sr/Ca ratios in the present study. Overall, only the U/Ca ratio showed a significant difference between symbiotic and asymbiotic polyps throughout all experiments, indicating that the critical effect on coral calcification caused by symbiotic algae is the increase of pH of the calcifying fluid by photosynthesis.

Continue reading ‘A simple role of coral-algal symbiosis in coral calcification based on multiple geochemical tracers’

Boosted nutritional quality of food by CO2 enrichment fails to offset energy demand of herbivores under ocean warming, causing energy depletion and mortality

Highlights

• We tested if energy transfer via feeding is boosted under future seawater conditions.
• Energy budget of herbivores and nutritional quality of their food were determined.
• Energy budget raised by feeding on the more nutritious food under ocean acidification.
• When combined with warming, however, mass mortality occurred due to energy depletion.
• Enhanced food quality inadequately offsets the energy demand under ocean warming.

Abstract

The CO2-boosted trophic transfer from primary producers to herbivores has been increasingly discovered at natural CO2 vents and in laboratory experiments. Despite the emerging knowledge of this boosting effect, we do not know the extent to which it may be enhanced or dampened by ocean warming. We investigated whether ocean acidification and warming enhance the nutritional quality (C:N ratio) and energy content of turf algae, which is speculated to drive higher feeding rate, greater energy budget and eventually faster growth of herbivores. This proposal was tested by observing the physiological (feeding rate, respiration rate and energy budget) and demographic responses (growth and survival) of a common grazing gastropod (Phasianella australis) to ocean acidification and warming in a 6-month mesocosm experiment. Whilst we observed the boosting effect of ocean acidification and warming in isolation on the energy budget of herbivores by either increasing feeding rate on the more nutritious algae or increasing energy gain per feeding effort, their growth and survival were reduced by the sublethal thermal stress under ocean warming, especially when both climate change stressors were combined. This reduced growth and survival occurred as a consequence of depleted energy reserves, suggesting that the boosting effect via trophic transfer might not sufficiently compensate for the increased energy demand imposed by ocean warming. In circumstances where ocean acidification and warming create an energy demand on herbivores that outweighs the energy enhancement of their food (i.e. primary producers), the performance of herbivores to control their blooming resources likely deteriorates and thus runaway primary production ensues.

Continue reading ‘Boosted nutritional quality of food by CO2 enrichment fails to offset energy demand of herbivores under ocean warming, causing energy depletion and mortality’

Ocean warming has greater and more consistent negative effects than ocean acidification on the growth and health of subtropical macroalgae

Macroalgae are the major habitat-forming organisms in many coastal temperate and subtropical marine systems. Although climate change has been identified as a major threat to the persistence of macroalgal beds, the combined effects of ocean warming and ocean acidification on algal performance are poorly understood. Here we investigate the effects of increased temperature and acidification on the growth, calcification and nutritional content of 6 common subtropical macroalgae; Sargassum linearifolium, Ulva sp., Amphiroa anceps, Corallina officinalis, Delisea pulchra and Laurencia decussata. Algae were reared in a factorial cross of 3 temperatures (23°C [ambient], 26°C and 28°C) and 3 pH levels (8.1 [ambient], 7.8 and 7.6) for 2 wk. The highest (28°C) temperature decreased the growth of all 6 macroalgal species, irrespective of the pH levels. In contrast, the effect of decreased pH on growth was variable. The growth of Ulva sp. and C. officinalis increased, L. decussata decreased, while the remaining 3 species were unaffected. Interestingly, the differential responses of macroalgae to ocean acidification were unrelated to whether or not a species was a calcifying alga, or their carbon-uptake mechanism—2 processes that are predicted to be sensitive to decreased pH. The growth of the calcifying algae (C. officinalis and A. anceps) was not affected by reduced pH but calcification of these 2 algae was reduced when exposed to a combination of reduced pH and elevated temperature. The 3 species capable of uptake of bicarbonate, S. linearifolium, L. decussata and Ulva sp., displayed positive, negative and neutral changes in growth, respectively, in response to reduced pH. The C:N ratio for 5 of the 6 species was unaffected by either pH or temperature. The consistent and predictable negative effects of temperature on the growth and calcification of subtropical macroalgae suggests that this stressor poses a greater threat to the persistence of subtropical macroalgal populations than ocean acidification under ongoing and future climate change.

Continue reading ‘Ocean warming has greater and more consistent negative effects than ocean acidification on the growth and health of subtropical macroalgae’

Residing at low pH matters, resilience of the egg jelly coat of sea urchins living at a CO2 vent site

The sea urchin egg jelly coat is important in fertilisation as a source of sperm activating compounds, in species-specific gamete recognition and in increasing egg target size for sperm. The impact of ocean acidification (− 0.3 to 0.5 pHT units) on the egg jelly coat of Arbacia lixula was investigated comparing populations resident in a control (pHT 8.00) and a CO2 vent site (mean pHT 7.69) in Ischia. Measurements of egg and jelly coat size showed no significant differences between sea urchins from the different sites; however, sensitivity of the jelly coat to decreased pH differed depending on the origin of the population. Acidification to pHT 7.7 and 7.5 significantly decreased egg jelly coat size of control urchins by 27 and 23%, respectively. In contrast, the jelly coat of the vent urchins was not affected by acidification. For the vent urchins, there was a significant positive relationship between egg and jelly coat size, a relationship not seen for the eggs of females from the control site. As egg and jelly coat size was similar between both populations, vent A. lixula jelly coats are likely to be chemically fine-tuned for the low pH environment. That the egg jelly coat of sea urchins from the vent site was robust to low pH shows intraspecific variation in this trait, and that this difference may be a maternal adaptive strategy or plastic response. If this is a common response in sea urchins, this would facilitate the maintenance of gamete function, facilitating fertilisation success in a low pH ocean.

Continue reading ‘Residing at low pH matters, resilience of the egg jelly coat of sea urchins living at a CO2 vent site’

Ocean acidification modulates the incorporation of radio-labeled heavy metals in the larvae of the Mediterranean sea urchin Paracentrotus lividus

Highlights

• The radionuclide method allowed accurate tracing of the metal incorporation within this microscopic planktonic species.
• Metal incorporation in sea urchin larvae strongly correlates with the indirect delaying effect of acidification on larval size.
• Independently of the size effect, acidification directly affects the incorporation behavior of four metals (Mn, Ag, Se, Zn).
• The nature of the modulation is specific to each metallic element (see graphical abstract).
• Relationships between speciation, bioaccumulation and toxicity in the context of changing seawater pH requires more research.

Abstract

The marine organisms which inhabit the coastline are exposed to a number of anthropogenic pressures that may interact. For instance, the accumulation of toxic metals present in coastal waters is expected to be modified by ocean acidification through e.g. changes in physiological performance and/or elements availability. Changes in bioaccumulation due to lowering pH are likely to be differently affected depending on the nature (essential vs. non-essential) and speciation of each element. The Mediterranean is of high concern for possible cumulative effects due to strong human influences on the coastline.

The aim of this study was to determine the effect of ocean acidification (from pH 8.1 down to −1.0 pH units) on the incorporation kinetics of six trace metals (Mn, Co, Zn, Se, Ag, Cd, Cs) and one radionuclide (241Am) in the larvae of an economically- and ecologically-relevant sea urchin of the Mediterranean coastline: Paracentrotus lividus. The radiolabelled metals and radionuclides added in trace concentrations allowed precise tracing of their incorporation in larvae during the first 74 h of their development.

Independently of the expected indirect effect of pH on larval size/developmental rates, Paracentrotus lividus larvae exposed to decreasing pHs incorporated significantly more Mn and Ag and slightly less Cd. The incorporation of Co, Cs and 241Am was unchanged, and Zn and Se exhibited complex incorporation behaviors. Studies such as this are necessary prerequisites to the implementation of metal toxicity mitigation policies for the future ocean. We discuss possible reasons and mechanisms for the specific effect of pH on each metals.

Continue reading ‘Ocean acidification modulates the incorporation of radio-labeled heavy metals in the larvae of the Mediterranean sea urchin Paracentrotus lividus’


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