Posts Tagged 'North Atlantic'



The future of marine biodiversity and marine ecosystem functioning in UK coastal and territorial waters (including UK Overseas Territories) – with an emphasis on marine macrophyte communities

Marine biodiversity and ecosystem functioning – including seaweed communities – in the territorial waters of the UK and its Overseas Territories are facing unprecedented pressures. Key stressors are changes in ecosystem functioning due to biodiversity loss caused by ocean warming (species replacement and migration, e.g. affecting kelp forests), sea level rise (e.g. loss of habitats including salt marshes), plastic pollution (e.g. entanglement and ingestion), alien species with increasing numbers of alien seaweeds (e.g. outcompeting native species and parasite transmission), overexploitation (e.g. loss of energy supply further up the food web), habitat destruction (e.g. loss of nursery areas for commercially important species) and ocean acidification (e.g. skeletal weakening of ecosystem engineers including coralline algal beds). These stressors are currently affecting biodiversity, and their impact can be projected for the future. All stressors may act alone or in synergy. Marine biodiversity provides crucial goods and services. Climate change and biodiversity loss pose new challenges for legislation. In particular, there are implications of climate change for the designation and management of Marine Protected Areas and natural carbon storage by marine systems to help control the global climate system. The UK currently has legal obligations to protect biodiversity under international and European law.

Continue reading ‘The future of marine biodiversity and marine ecosystem functioning in UK coastal and territorial waters (including UK Overseas Territories) – with an emphasis on marine macrophyte communities’

Role of host genetics and heat tolerant algal symbionts in sustaining populations of the endangered coral Orbicella faveolata in the Florida Keys with ocean warming

Identifying which factors lead to coral bleaching resistance is a priority given the global decline of coral reefs with ocean warming. During the second year of back‐to‐back bleaching events in the Florida Keys in 2014 and 2015, we characterized key environmental and biological factors associated with bleaching resilience in the threatened reef‐building coral Orbicella faveolata. Ten reefs (five inshore, five offshore, 179 corals total) were sampled during bleaching (September 2015) and recovery (May 2016). Corals were genotyped with 2bRAD and profiled for algal symbiont abundance and type. O. faveolata at the inshore sites, despite higher temperatures, demonstrated significantly higher bleaching resistance and better recovery compared to offshore. The thermotolerant Durusdinium trenchii (formerly Symbiondinium trenchii) was the dominant endosymbiont type region‐wide during initial (78.0% of corals sampled) and final (77.2%) sampling; > 90% of the non‐bleached corals were dominated by D. trenchii. 2bRAD host genotyping found no genetic structure among reefs, but inshore sites showed a high level of clonality. While none of the measured environmental parameters were correlated with bleaching, 71% of variation in bleaching resistance and 73% of variation in the proportion of D. trenchii was attributable to differences between genets, highlighting the leading role of genetics in shaping natural bleaching patterns. Notably, D. trenchii was rarely dominant in O. faveolata from the Florida Keys in previous studies, even during bleaching. The region‐wide high abundance of D. trenchii was likely driven by repeated bleaching associated with the two warmest years on record for the Florida Keys (2014 and 2015). On inshore reefs in the upper Florida Keys, O. faveolata was most abundant, had the highest bleaching resistance, and contained the most corals dominated by D. trenchii, illustrating a causal link between heat tolerance and ecosystem resilience with global change.

Continue reading ‘Role of host genetics and heat tolerant algal symbionts in sustaining populations of the endangered coral Orbicella faveolata in the Florida Keys with ocean warming’

Effects of ocean acidification on the transcriptome of larval Atlantic cod and impacts of parental acclimation

Ocean acidification, caused by the uptake of carbon dioxide (CO2) from the atmosphere, is impacting many marine organisms. This dissertation investigated the effects of direct exposure and parental acclimation to simulated ocean acidification on the larval stages of Atlantic cod (Gadus morhua, L.). For this, ocean acidification levels predicted for the year 2100 were applied on cod eggs from hatch to 36 days post hatch in in vivo laboratory experiments. The direct exposure experiment clearly showed that Atlantic cod larvae were severely affected by simulated ocean acidification on a phenotypic level (chapter 1). Changes in growth, bone and gill development as well as increased frequency of organ damages were observed under predicted ocean acidification levels compared to controls. Then, the underlying molecular phenotype was assessed, using whole transcriptome sequencing (RNA-Seq), to couple transcriptomic mechanisms to the observed phenotypes (chapter 2). Transcriptome analysis revealed 1413 differentially expressed genes in late larval stages, corresponding to the observed changes in growth and developmental patterns, leading to the conclusion that these changes represent an accelerated development under ocean acidification. Surprisingly, only few genes (3 and 16, respectively) were differentially expressed in the early larval stages. An experiment set to address the effects of long-term parental acclimation (5 month) was performed to assess whether or not this kind of acclimation can mediate the identified detrimental direct effects on the larvae (chapter 3). However, none of the previously observed phenotypes under ocean acidification were found in this experiment, making it impossible to draw any conclusion on the effectiveness of parental acclimation on larval susceptibility to simulated ocean acidification. A concluding meta-analysis between experiments shows that the larvae of Atlantic Cod are to be considered vulnerable to simulated ocean acidification.

Continue reading ‘Effects of ocean acidification on the transcriptome of larval Atlantic cod and impacts of parental acclimation’

Feeding plasticity more than metabolic rate drives the productivity of economically important filter feeders in response to elevated CO2 and reduced salinity

Climate change driven alterations in salinity and carbonate chemistry are predicted to have significant implications particularly for northern costal organisms, including the economically important filter feeders Mytilus edulis and Ciona intestinalis. However, despite a growing number of studies investigating the biological effects of multiple environmental stressors, the combined effects of elevated pCO2 and reduced salinity remain comparatively understudied. Changes in metabolic costs associated with homeostasis and feeding/digestion in response to environmental stressors may reallocate energy from growth and reproduction, affecting performance. Although these energetic trade-offs in response to changes in routine metabolic rates have been well demonstrated fewer studies have investigated how these are affected by changes in feeding plasticity. Consequently, the present study investigated the combined effects of 26 days’ exposure to elevated pCO2 (500 µatm and 1000 µatm) and reduced salinity (30, 23, and 16) on the energy available for growth and performance (Scope for Growth) in M. edulis and C. intestinalis, and the role of metabolic rate (oxygen uptake) and feeding plasticity [clearance rate (CR) and absorption efficiency] in this process. In M. edulis exposure to elevated pCO2 resulted in a 50% reduction in Scope for Growth. However, elevated pCO2 had a much greater effect on C. intestinalis, with more than a 70% reduction in Scope for Growth. In M. edulis negative responses to elevated pCO2 are also unlikely be further affected by changes in salinity between 16 and 30. Whereas, under future predicted levels of pCO2C. intestinalis showed 100% mortality at a salinity of 16, and a >90% decrease in Scope for Growth with reduced biomass at a salinity of 23. Importantly, this work demonstrates energy available for production is more dependent on feeding plasticity, i.e. the ability to regulate CR and absorption efficiency, in response to multiple stressors than on more commonly studied changes in metabolic rates.

Continue reading ‘Feeding plasticity more than metabolic rate drives the productivity of economically important filter feeders in response to elevated CO2 and reduced salinity’

Distinct bleaching resilience of photosynthetic plastid-bearing mollusks under thermal stress and high CO2 conditions

The impact of temperature on photo-symbiotic relationships has been highly studied in the tropical reef-forming corals but overlooked in less charismatic groups such as solar-powered sacoglossan sea slugs. These organisms display one of the most puzzling symbiotic features observed in the animal kingdom, i.e., their mollusk-plastid association, which enables them to retain photosynthetic active chloroplasts (i.e., kleptoplasts) retrieved from their algae feed sources. Here we analyze the impact of thermal stress (+4∘C) and high pCO2 conditions (ΔpH = 0.4) in survival, photophysiology (i.e., bleaching, photosynthetic efficiency, and metabolism) and stress defense mechanisms (i.e., heat shock and antioxidant response) of solar-powered sacoglossan sea slugs, from tropical (Elysia crispata) and temperate (E. viridis) environments. High temperature was the main factor affecting the survival of both species, while pH only affected the survival of the temperate model. The photobiology of E. viridis remained stable under the combined scenario, while photoinhibition was observed for E. crispata under high temperature and high pCO2. In fact, bleaching was observed within all tropical specimens exposed to warming (but not in the temperate ones), which constitutes the first report where the incidence of bleaching in tropical animals hosting photosynthetic symbionts, other than corals, occurs. Yet, the expulsion of kleptoplasts by the tropical sea slug, allied with metabolic depression, constituted a physiological response that did not imply signs of vulnerability (i.e., mortality) in the host itself. Although the temperate species revealed greater heat shock and antioxidant enzyme response to environmental stress, we argue that the tropical (stenotherm) sea slug species may display a greater scope for acclimatization than the temperate (eurytherm) sea slug. E. crispata may exhibit increased capacity for phenotypic plasticity by increasing fitness in a much narrower thermal niche (minimizing maintenance costs), which ultimately may allow to face severe environmental conditions more effectively than its temperate generalist counterpart (E. viridis).

Continue reading ‘Distinct bleaching resilience of photosynthetic plastid-bearing mollusks under thermal stress and high CO2 conditions’

Climate change effects on copepod physiology and trophic transfer

Increased anthropogenic carbon dioxide (CO2) emissions have led to an increasingly acidified ocean and higher average global sea surface temperatures. This alteration of abiotic conditions is directly affecting aquatic organisms through physiological stress and indirectly through reductions in trophic transfer efficiency. Less efficient trophic transfer at the base of the food web would reduce the overall energy available to support higher trophic levels and could be detrimental to the dependent ecosystem. Estuarine ecosystems are subject to harmful algal blooms (HABs). They are also characterized by low species diversity, which lowers ecosystem resilience to environmental perturbations. This results in a system where changes in phytoplankton and their consumers can dramatically impact the health of the local community. Increased temperature and pCO2 are predicted to change nutritional adequacy and/or toxicity of some HAB species and their copepod consumers. Interactions between Karlodinium veneficum, a HAB species present in the Delaware Inland Bays, and its consumer Acartia tonsa, a locally-dominant copepod, were used to assess direct changes to physiology and/or indirect changes to trophic transfer. Acartia tonsa, toxic prey K. veneficum, and non-toxic prey Storeatula major were grown in multi-generational laboratory cultures at both ambient conditions (25 °C/400 ppm pCO2) and those predicted for year 2100 (29 °C/ 1000 ppm pCO2). Physiological changes were assessed using grazing, respirometry, egg production, and egg hatching success. Grazing experiments indicated there was not a direct toxic effect of the prey on A. tonsa. Respiration rates did not change significantly at higher temperature and pCO2 values, indicating physiological compensation. Egg production did not significantly differ between treatments, but a significant reduction in egg hatching success was found when A. tonsa were fed exclusively K. veneficum. Significant reduction of egg production and hatching also occurred as a result of higher temperature and pCO2. Significant reductions in efficiency of carbon transfer from prey to consumer offspring were found when A. tonsa ingested K. veneficum, and when A. tonsa ingested S. major at elevated temperature and pCO2. In summary, A. tonsa acclimated to the elevated pCO2 and temperature conditions, but changes in resource partitioning led to a lowered transfer of carbon to their offspring. Ingestion of K. veneficum also led to a lowered trophic transfer efficiency, irrespective of temperature and pCO2 level. This indicates that both HABs and increased temperature and pCO2 from climate change have the potential to alter ecosystem dynamics by reducing trophic transfer efficiency at the base of the food chain.

Continue reading ‘Climate change effects on copepod physiology and trophic transfer’

Carbonate ion concentrations in seawater: Spectrophotometric determination at ambient temperatures and evaluation of propagated calculation uncertainties

Highlights

• A new model is presented for direct determination of [CO32−] in seawater.
• The model is appropriate for temperature 3 to 40 °C and salinity 20 to 40.
• Measured [CO32−] is best paired with CT and AT in CO2 system calculations.
• Measured [CO32−] alone can yield reliable estimates of CaCO3 saturation states.
• [CO32−] can be used in a variety of ways as a fifth measured CO2 system variable.

Abstract

In ocean waters, the carbonate ion is of crucial importance to benthic and pelagic organisms that build their physical support structures out of calcium carbonate (CaCO3). Marine carbonate ion concentrations ([CO32−]) are measurable through spectrophotometric observations of the ultraviolet (UV) light absorbed by lead carbonate in Pb-enriched seawater, but previous characterizations of the Pb UV-absorption model have been applicable only at a fixed temperature of 25 °C. In this paper, the model is extended to a temperature range of 3 to 40 °C and a salinity range of 20 to 40. This advancement allows for determinations of [CO32−] with temperature measurement rather than temperature control, thus decreasing the required financial investment and instrumental complexity. The extended model also represents a significant step toward the development of automated inline or in situ [CO32−] sensors and promotes the utility of [CO32−] as a fifth measured variable for inclusion in studies of the marine carbon dioxide (CO2) system. Therefore, a quantitative evaluation of propagated uncertainties in CO2 system calculations based on [CO32−] as an input variable was also performed. The results show that total dissolved inorganic carbon (CT) and total alkalinity (AT) are the most suitable measured variables to pair with measured [CO32−] as input to such calculations. Pairing [CO32−] with the partial pressure of CO2 yields relatively low uncertainty in calculated pH — comparable to that resulting from conventional input pairs — but relatively high uncertainties in calculated AT and CT. Pairing [CO32−] with pH results in relatively high uncertainties in all calculated variables. CaCO3 saturation states (Ω) determined from measured [CO32−] (alone) can circumvent some sources of uncertainty inherent to conventional (two-variable) calculations. Simpler, more direct ways of measuring [CO32−] open up new opportunities for marine researchers and others interested in monitoring CaCO3 saturation states in seawater.

Continue reading ‘Carbonate ion concentrations in seawater: Spectrophotometric determination at ambient temperatures and evaluation of propagated calculation uncertainties’


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Ocean acidification in the IPCC AR5 WG II

OUP book