Posts Tagged 'morphology'

Lipid biochemistry and physiology of Antarctic krill (Euphausia superba) in the present day and under future ocean acidification scenarios

Antarctic krill (Euphausia superba, hereafter ‘krill’) are lipid-rich euphausiids with an important role in the Southern Ocean, including as the primary prey of Antarctic megafauna (whales, seals, penguins), fish, squid and seabirds. They contain high levels of nutritious long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA), specifically eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). The sheer abundance of krill in the Southern Ocean means that the ecosystem is largely driven by energy derived from krill lipids. In addition to their ecological importance, a Scotia Sea krill fishery harvests krill, including for commercial use of their LC-PUFA. The existence of this year-round krill fishery provides a unique opportunity to collect krill samples for research over large spatial and temporal scales, which is unfeasible using scientific research vessels.

In this thesis, fishery caught krill samples were used to investigate the fatty acid content and composition of krill, during all seasons and over consecutive years (2013 – 2016). This research (presented in Chapter 2) aimed to fill knowledge gaps on the seasonal diet of krill (particularly in winter) in the Scotia Sea region, using fatty acids as dietary biomarkers. Krill were primarily herbivorous in summer (higher levels of 20:5n-3 and 22:6n-3, and low 18:1n-9c/18:1n-7c ratios) and became more omnivorous from autumn to spring (increasing ratios of 18:1n-9c/18:1n-7c and percentages of Σ 20:1 + 22:1 isomers). Seasonal proportions of herbivory and omnivory differed between years, and fatty acid composition differed between fishing locations. Selected samples were also used to investigate the composition of fatty acids in the structural (phospholipids) and storage lipids (triacylglycerols) of krill (Chapter 3). Triacylglycerol fatty acids (thought to better represent recent diet), reflected omnivorous feeding with highest percentages of flagellate biomarkers (18:4n-3) occurring in summer, diatom biomarkers (16:1n-7c) from autumn-spring, and greater carnivory (higher Σ 20:1 + 22:1 and 18:1n-9c/18:1n-7c ratios) in autumn. Phospholipid fatty acids were less variable and were higher in the essential membrane fatty acids 20:5n-3 and 22:6n-3. Percentages of the major krill sterol, cholesterol, were significantly higher in winter and spring compared with summer and autumn. Results presented in Chapters 2 and 3 highlighted the dynamic nature of krill lipids, and the flexible diet of krill, which likely contributes to their huge biomass and success as one of the most abundant organisms on Earth.

Because krill are so important in the Southern Ocean food web, any decreases in krill biomass could result in a major ecological regime shift. Very little is known about how climate change will affect krill. Increasing anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification, as absorption of atmospheric CO2 in seawater alters ocean chemistry. Ocean acidification increases mortality and negatively affects physiological functioning in some marine invertebrates, and is predicted to occur most rapidly at high latitudes. Long-term laboratory studies are needed to understand how keystone species such as krill may respond to predicted future pCO2 levels. A long term experiment was conducted to test whether rising ocean pCO2 is likely to impact krill physiology and biochemistry (Chapters 4 and 5). Adult krill were exposed to near-future ocean acidification (1000 – 2000 μatm pCO2) for one year in the laboratory. Krill reared in near-future pCO2 conditions were able to survive, grow, store fat, mature, and maintain normal respiration rates. Haemolymph pH, lipid and fatty acid composition were also maintained at the same levels as krill in ambient pCO2 (400 μatm). Negative effects on physiology and lipid biochemistry were only observed in extreme pCO2 conditions (4000 μatm), which krill will not experience in the wild. These results place adult krill among the most resilient species in ocean acidification studies to date.

In summary, results in this thesis highlight the remarkable adaptability of krill in a changing environment, from short-term seasonal or annual scales, to longer-term decadal scales. Their flexible phenotype may aid their survival in an ocean that is rapidly changing with increasing anthropogenic CO2 emissions. The data obtained in this thesis can be used for fisheries management to guide fishing activities, and in fisheries models to predict how krill biomass may be affected by climate change. Krill lipid energy fuels the Southern Ocean ecosystem and to date, lipid data has not been included in Antarctic ecosystem models. The large scale of lipid data in this study makes it ideal for inclusion in such models, and it has important implications for the health of the wider Southern Ocean ecosystem.

Continue reading ‘Lipid biochemistry and physiology of Antarctic krill (Euphausia superba) in the present day and under future ocean acidification scenarios’

Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth


• Elevated CO2 and reduced dissolved oxygen have opposite effects on otolith (earstone) development in juvenile copper and blue rockfish.

• Increased CO2 levels resulted in otoliths being larger in area for a relative fish body size in blue rockfish.

• Reduced dissolved oxygen levels results in otoliths being smaller in area for a relative fish body size in both species.


Climate change is predicted to alter ocean chemistry through warming temperatures, increases in CO2 (i.e., ocean acidification), and reductions in dissolved oxygen (DO) (i.e., hypoxia). Past research has shown that early life stages of marine fishes are sensitive to all three stressors, but with sometimes different directions of response. In this study, we examined the separate effects of ocean acidification and hypoxia on otolith growth in two species of juvenile rockfish (copper rockfish, Sebastes caurinus, and blue rockfish, Sebastes mystinus). Fishes were collected at settlement stage from kelp forests on the central California coast and reared in the laboratory for up to 6 months in 4 separate pH treatments (pH = 7.3, 7.6, 7.8, and a control of 8.0), simulating the effects of ocean acidification through the addition of CO2, and 4 separate dissolved oxygen treatments (DO = 2.2, 4.1, 6.0, and a control of 8.7 mg/L), simulating the effects of hypoxia. For both species, otoliths were smaller for a given fish length in response to hypoxia but were larger (trend was non-significant for copper rockfish) in response to elevated CO2. The results suggest that otolith growth may respond differently to ocean acidification and hypoxia for some species, which has implications for sensory development, ecological performance, and interpretations of the permanent record of fish growth in hard parts such as otoliths.

Continue reading ‘Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth’

Independent effects of ocean warming versus acidification on the growth, survivorship and physiology of two Acropora corals

Climate change is the greatest threat to coral reef ecosystems. Importantly, gradual changes in seawater chemistry compounds upon increasing temperatures leading to declines in calcification and survivorship of reef-building corals. To assess relative versus synergistic effects of warming versus ocean acidification, Acropora muricata and Acropora hyacinthus were subjected to three temperature treatments (26 °C, 28.5 °C, 31 °C) crossed with three levels of pCO2 (410 μatm, 652 μatm, 934 μatm), representing current, mid and end-of-century scenarios for 12 weeks. Temperature increased gradually in the tanks from 26 °C to target temperatures over 5 weeks. Once stress was evident in the 31 °C (+ 2.5 °C above historical summer max) tanks, water temperature was decreased to normal summertime levels (29 °C) to assess recovery. pCO2 was gradually changed from control values (410 μatm) to target values over a 3 week period where they remained constant until the end of the experiment at 12 weeks. Temperature stress (31 °C) significantly impacted survivorship (90–95% decline), and over the long-term, there was a 50–90% decline in calcification across both coral species. Negative effects of mid and end-of-century pCO2 were largely independent of temperature and caused moderate reductions (36–74%) in calcification rates compared to temperature, over the long-term. Corals that survived temperature stress had higher lipid and protein content, showing that enhanced physiological condition provides an increased capacity to tolerate adverse temperatures. This study demonstrates that given the mortality rates in response to + 2.5 °C temperature stress, warming oceans (as opposed to ocean acidification) throughout the remainder of this century poses the greatest threat to reef-building corals.

Continue reading ‘Independent effects of ocean warming versus acidification on the growth, survivorship and physiology of two Acropora corals’

Futuristic ocean acidification levels reduce growth and reproductive viability in the Pacific Oyster (Crassostrea gigas)

In this study, we investigated the effects of futuristic pH because of climate change on the growth and reproductive viability of the Pacific oysters. The futuristic pH levels to which adult oysters were exposed are 7.5 and 7.8 (as extreme case) and 8.1 (as moderate case), with pH 8.2 serving as the control. We monitored growth and reproductive viability over a four-week exposure period. The reproductive viability of the oysters exposed to each pH level were assessed based on the sperm motility and egg viability. Throughout the exposure period, the induced acidified nature of each treatment aquaria was maintained. Data obtained from this investigation revealed significant decrease in weight of oysters exposed to pH 7.5 and 7.8 compared to the groups exposed to pH levels 8.1 and 8.2 (p < 0.05). Groups of oysters exposed to pH 7.5 recorded as much as 10.49% decrease in weight, with specific growth rate (SGR) of -0.4 %/day. Reproductive viability was significantly compromised in groups exposed to pH 7.5 and 7.8 as evident with reduced sperm motility and percentage of ruptured eggs in these groups of oysters. We therefore postulate that climate change will have significant impact on the recruitment of oysters in coastal waters as growth and reproduction will be impaired at extreme levels of futuristic ocean acidification.

Continue reading ‘Futuristic ocean acidification levels reduce growth and reproductive viability in the Pacific Oyster (Crassostrea gigas)’

The planktonic stages of the salmon louse (Lepeophtheirus salmonis) are tolerant of end-of-century pCO2 concentrations

The copepod Lepeophtheirus salmonis is an obligate ectoparasite of salmonids. Salmon lice are major pests in salmon aquaculture and due to its economic impact Lepeophtheirus salmonis is one of the most well studied species of marine parasite. However, there is limited understanding of how increased concentration of pCO2 associated with ocean acidification will impact host-parasite relationships. We investigated the effects of increased pCO2 on growth and metabolic rates in the planktonic stages, rearing L. salmonis from eggs to 12 days post hatch copepodids under three treatment levels: Control (416 µatm), Mid (747 µatm), and High (942 µatm). The pCO2 treatment had a significant effect on oxygen consumption rate with the High treatment animals exhibiting the greatest respiration. The treatments did not have a significant effect on the other biological endpoints measured (carbon, nitrogen, lipid volume, and fatty acid content). The results indicate that L. salmonis have mechanisms to compensate for increased concentration of pCO2and that populations will be tolerant of projected future ocean acidification scenarios. The work reported here also describes catabolism during the lecithotrophic development of L. salmonis, information that is not currently available to parameterize models of dispersal and viability of the planktonic free-living stages.

Continue reading ‘The planktonic stages of the salmon louse (Lepeophtheirus salmonis) are tolerant of end-of-century pCO2 concentrations’

Ocean warming and acidification alter the behavioral response to flow of the sea urchin Paracentrotus lividus

Ocean warming (OW) and acidification (OA) are intensively investigated as they pose major threats to marine organism. However, little effort is dedicated to another collateral climate change stressor, the increased frequency, and intensity of storm events, here referred to as intensified hydrodynamics. A 2‐month experiment was performed to identify how OW and OA (temperature: 21°C; pHT: 7.7, 7.4; control: 17°C‐pHT7.9) affect the resistance to hydrodynamics in the sea urchin Paracentrotus lividus using an integrative approach that includes physiology, biomechanics, and behavior. Biomechanics was studied under both no‐flow condition at the tube foot (TF) scale and flow condition at the individual scale. For the former, TF disk adhesive properties (attachment strength, tenacity) and TF stem mechanical properties (breaking force, extensibility, tensile strength, stiffness, toughness) were evaluated. For the latter, resistance to flow was addressed as the flow velocity at which individuals detached. Under near‐ and far‐future OW and OA, individuals fully balanced their acid‐base status, but skeletal growth was halved. TF adhesive properties were not affected by treatments. Compared to the control, mechanical properties were in general improved under pHT7.7 while in the extreme treatment (21°C‐pHT7.4) breaking force was diminished. Three behavioral strategies were implemented by sea urchins and acted together to cope with flow: improving TF attachment, streamlining, and escaping. Behavioral responses varied according to treatment and flow velocity. For instance, individuals at 21°C‐pHT7.4 increased the density of attached TF at slow flows or controlled TF detachment at fast flows to compensate for weakened TF mechanical properties. They also showed an absence of streamlining favoring an escaping behavior as they ventured in a riskier faster movement at slow flows. At faster flows, the effects of OW and OA were detrimental causing earlier dislodgment. These plastic behaviors reflect a potential scope for acclimation in the field, where this species already experiences diel temperature and pH fluctuations.

Continue reading ‘Ocean warming and acidification alter the behavioral response to flow of the sea urchin Paracentrotus lividus’

Specific dynamic action of mussels exposed to TiO2 nanoparticles and seawater acidification


• Low pH can enhance the toxicity of TiO2 NPs to mussels.

• The feeding and metabolism of mussels are impaired by TiO2 NPs and low pH.

• TiO2 NPs and low pH have significant interactions and carry-over effects on mussels.


Both nanoparticles (NPs) and ocean acidification (OA) pose threats to marine animals as well as marine ecosystems. The present study aims to evaluate the combined effects of NPs and OA on specific dynamic action (SDA) of mussels. The thick shell mussels Mytilus coruscus were exposed to two levels of pH (7.3 and 8.1) and three concentrations of TiO2 NPs (0, 2.5, and 10 mg L−1) for 14 days followed by a 7-day recovery period. The SDA parameters, including standard metabolic rate, peak metabolic rate, aerobic metabolic scope, SDA slope, time to peak, SDA duration and SDA, were measured. The results showed that TiO2 NPs and low pH significantly affected all parameters throughout the experiment. When the mussels were exposed to seawater acidification or TiO2 NPs conditions, standard metabolic rate, aerobic metabolic scope, SDA slope and SDA significantly decreased, whereas peak metabolic rate, time to peak and SDA duration significantly increased. In addition, interactive effects between TiO2 NPs and pH were observed in SDA parameters except time to peak and SDA. Therefore, the synergistic effect of TiO2 NPs and low pH can adversely affect the feeding metabolism of mussels.

Continue reading ‘Specific dynamic action of mussels exposed to TiO2 nanoparticles and seawater acidification’

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Ocean acidification in the IPCC AR5 WG II

OUP book