Posts Tagged 'performance'

Warming and CO2 enhance Arctic heterotrophic microbial activity

Ocean acidification and warming are two main consequences of climate change that can directly affect biological and ecosystem processes in marine habitats. The Arctic Ocean is the region of the world experiencing climate change at the steepest rate compared with other latitudes. Since marine planktonic microorganisms play a key role in the biogeochemical cycles in the ocean it is crucial to simultaneously evaluate the effect of warming and increasing CO2 on marine microbial communities. In 20 L experimental microcosms filled with water from a high-Arctic fjord (Svalbard), we examined changes in phototrophic and heterotrophic microbial abundances and processes [bacterial production (BP) and mortality], and viral activity (lytic and lysogenic) in relation to warming and elevated CO2. The summer microbial plankton community living at 1.4°C in situ temperature, was exposed to increased CO2 concentrations (135–2,318 μatm) in three controlled temperature treatments (1, 6, and 10°C) at the UNIS installations in Longyearbyen (Svalbard), in summer 2010. Results showed that chlorophyll a concentration decreased at increasing temperatures, while BP significantly increased with pCO2 at 6 and 10°C. Lytic viral production was not affected by changes in pCO2 and temperature, while lysogeny increased significantly at increasing levels of pCO2, especially at 10°C (R2 = 0.858, p = 0.02). Moreover, protistan grazing rates showed a positive interaction between pCO2 and temperature. The averaged percentage of bacteria grazed per day was higher (19.56 ± 2.77% d-1) than the averaged percentage of lysed bacteria by virus (7.18 ± 1.50% d-1) for all treatments. Furthermore, the relationship among microbial abundances and processes showed that BP was significantly related to phototrophic pico/nanoflagellate abundance in the 1°C and the 6°C treatments, and BP triggered viral activity, mainly lysogeny at 6 and 10°C, while bacterial mortality rates was significantly related to bacterial abundances at 6°C. Consequently, our experimental results suggested that future increases in water temperature and pCO2 in Arctic waters will produce a decrease of phytoplankton biomass, enhancement of BP and changes in the carbon fluxes within the microbial food web. All these heterotrophic processes will contribute to weakening the CO2 sink capacity of the Arctic plankton community.

Continue reading ‘Warming and CO2 enhance Arctic heterotrophic microbial activity’

Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation

Change in the nutritional quality of phytoplankton is a key mechanism through which ocean acidification can affect the function of marine ecosystems. Copepods play an important role transferring energy from phytoplankton to higher trophic levels, including fatty acids (FA)—essential macronutrients synthesized by primary producers that can limit zooplankton and fisheries production. We investigated the direct effects of pCO2 on phytoplankton and copepods in the laboratory, as well as the trophic transfer of effects of pCO2 on food quality. The marine cryptophyte Rhodomonas salina was cultured at 400, 800, and 1200 μatm pCO2 and fed to adult Acartia hudsonica acclimated to the same pCO2 levels. We examined changes in phytoplankton growth rate, cell size, carbon content, and FA content, and copepod FA content, grazing, respiration, egg production, hatching, and naupliar development. This single-factor experiment was repeated at 12°C and at 17°C. At 17°C, the FA content of R. salina responded non-linearly to elevated pCO2 with the greatest FA content at intermediate levels, which was mirrored in A. hudsonica; however, differences in ingestion rate indicate that copepods accumulated FA less efficiently at elevated pCO2. A. hudsonica nauplii developed faster at elevated pCO2 at 12°C in the absence of strong food quality effects, but not at 17°C when food quality varied among treatments. Our results demonstrate that changes to the nutritional quality of phytoplankton are not directly translated to their grazers, and that studies that include trophic links are key to unraveling how ocean acidification will drive changes in marine food webs.

Continue reading ‘Direct and indirect effects of elevated CO2 are revealed through shifts in phytoplankton, copepod development, and fatty acid accumulation’

Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues

Florida Bay is home to a network of shallow mud-banks which act as barriers to circulation creating small basins that are often subject to extremes in temperature and salinity. Florida bay is also important juvenile habitat for the Caribbean spiny lobster Panulirus argus. While our understanding of the effect of environmental changes on the survival, growth, and movement of spiny lobsters is growing, the effect on their chemosensory abilities has not yet been investigated. Lobsters rely heavily on chemical cues for many biological and ecological activities, and here we report on the effect of extreme environmental events in temperature (32 °C), salinity (45ppt), and pH (7.65 pH) on social behavior and sheltering preference in P. argus. Under normal conditions, chemical cues from conspecifics are used by spiny lobsters to identify suitable shelter and cues from stone crabs and diseased individuals are used to determine shelters to be avoided. In all altered conditions, lobsters lost the ability to aggregate with conspecifics and avoid stone crabs and diseased conspecifics. Thus, seasonal extreme events, and potentially future climate change conditions, alter the chemosensory-driven behavior of P. argus and may result in decreased survivorship due to impaired shelter selection or other behaviors.

Continue reading ‘Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues’

A negative correlation between behavioural and physiological performance under ocean acidification and warming

Many studies have examined the average effects of ocean acidification and warming on phenotypic traits of reef fishes, finding variable, but often negative effects on behavioural and physiological performance. Yet the presence and nature of a relationship between these traits is unknown. A negative relationship between phenotypic traits could limit individual performance and even the capacity of populations to adapt to climate change. Here, we examined the relationship between behavioural and physiological performance of a juvenile reef fish under elevated CO2 and temperature in a full factorial design. Behaviourally, the response to an alarm odour was negatively affected by elevated CO2, but not elevated temperature. Physiologically, aerobic scope was significantly diminished under elevated temperature, but not under elevated CO2. At the individual level, there was no relationship between behavioural and physiological traits in the control and single-stressor treatments. However, a statistically significant negative relationship was detected between the traits in the combined elevated CO2 and temperature treatment. Our results demonstrate that trade-offs in performance between behavioural and physiological traits may only be evident when multiple climate change stressors are considered, and suggest that this negative relationship could limit adaptive potential to climate change.

Continue reading ‘A negative correlation between behavioural and physiological performance under ocean acidification and warming’

Insensitivities of a subtropical productive coastal plankton community and trophic transfer to ocean acidification: results from a microcosm study

Highlights
• Lower apparent growth was observed under elevated CO2 of 1000 μatm.

• Primary production and trophic transfer were unaffected by high CO2.

• Fatty acid profiles of phyto-/zooplankton were unaffected by ocean acidification.

Abstract
Ocean acidification (OA) has potential to affect marine phytoplankton in ways that are partly understood, but there is less knowledge about how it may alter the coupling to secondary producers. We investigated the effects of OA on phytoplankton primary production, and its trophic transfer to zooplankton in a subtropical eutrophic water (Wuyuan Bay, China) under present day (400 μatm) and projected end-of-century (1000 μatm) pCO2 levels. Net primary production was unaffected, although OA did lead to small decreases in growth rates. OA had no measurable effect on micro-/mesozooplankton grazing rates. Elevated pCO2 had no effect on phytoplankton fatty acid (FA) concentrations during exponential phase, but saturated FAs increased relative to the control during declining phase. FA profiles of mesozooplankton were unaffected. Our findings show that short-term exposure of plankton communities in eutrophic subtropical waters to projected end-of-century OA conditions has little effect on primary productivity and trophic linkage to mesozooplankton.

Continue reading ‘Insensitivities of a subtropical productive coastal plankton community and trophic transfer to ocean acidification: results from a microcosm study’

A triple trophic boost: how carbon emissions indirectly change a marine food chain

The pervasive enrichment of CO2 in our oceans is a well‐documented stressor to marine life. Yet, there is little understanding about how CO2 affects species indirectly in naturally complex communities. Using natural CO2 vents, we investigated the indirect effects of CO2 enrichment through a marine food chain. We show how CO2 boosted the biomass of three trophic levels: from the primary producers (algae), through to their grazers (gastropods), and finally through to their predators (fish). We also found that consumption by both grazers and predators intensified under CO2 enrichment, but, ultimately, this top‐down control failed to compensate for the boosted biomass of both primary producers and herbivores (bottom‐up control). Our study suggests that indirect effects can buffer the ubiquitous and direct, negative effects of CO2 enrichment by allowing the upward propagation of resources through the food chain. Maintaining the natural complexity of food webs in our ocean communities could, therefore, help minimize the future impacts of CO2 enrichment.

Continue reading ‘A triple trophic boost: how carbon emissions indirectly change a marine food chain’

Early development and metabolic physiology of the temperate lesser spotted shark (Scyliorhinus canicula) under high CO2 levels

Although sharks thrive in many different kinds of habitats and evolved to fill many ecological niches across a wide range of habitats, these animals are characterized by the limited capability to adapt rapidly to future climate change. Thus, the objective of the present dissertation was to analyze the potential impact of seawater acidification (OA, high CO2 levels ~1000 μatm) on the early development and physiology of the temperate shark Scyliorhinus canicula. More specifically, we evaluated OA effects on: i) development time and first feed, ii) Fulton condition of the newborns, iii) survival, iv) routine metabolic rate (RMR), v) maximum metabolic rate (MMR), and vi) aerobic scope (AS). The duration of embrygenesis ranged from 118 to 125 days, and after hatching, the mean number of days to start feeding (i.e. first feeding) varied between 4 and 6 days. In both endpoints there were no significant differences among treatments (i.e. normocapnia and hypercapnia; p >0.05). Juvenile survival (after 150 days post-hatching) also did no change significantly under high CO2 levels (p >0.05). Regarding energy expenditure rates and aerobic window, there were no significant differences in RMR, MMR, and AS among treatments (p-value > 0.005). In the overall, we argue that these findings are associated to the fact that S. canicula is a benthic, cosmopolitan and temperate shark usually exposed to great variations of abiotic factors, like those experienced in the highly-dynamic western Portuguese coast (with seasonal upwelling events). Although the present dissertation only investigated acclimation processes, it is plausible to assume that this shark species will not be greatly affected by future acidification conditions.

Continue reading ‘Early development and metabolic physiology of the temperate lesser spotted shark (Scyliorhinus canicula) under high CO2 levels’


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Ocean acidification in the IPCC AR5 WG II

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