Posts Tagged 'temperature'



Growth of the estuarine fish Fundulus heteroclitus in response to diel-cycling hypoxia and acidification: interaction with temperature

Growth rate of Fundulus heteroclitus was examined at 25 and 30 °C in nine treatments of diel-cycling dissolved oxygen (DO) and pH. Extreme diel-cycling DO (1–11 mg O2·L−1) negatively impacted growth during 10 days at 30 °C, but not at 25 °C. Moderate DO cycles (3–9 mg O2·L−1) had no direct growth impact at either temperature. Fish did not appear to acclimate, during days 10–30, to the initial growth-limiting effects of extreme diel DO cycles at 30 °C. Diel-cycling DO interacts synergistically with temperature to impact growth. There was no evidence of an independent growth effect of either moderate pH cycles (7.2–7.8) or extreme pH cycles (6.8–8.1) at either temperature. Mean low pCO2 levels in extreme cycles were ∼32 000 and ∼47 000 μatm at 25 and 30 °C, respectively. It is noteworthy that these high mean nightly pCO2 levels are more than an order of magnitude higher than the chronic mean oceanic pCO2 of ∼1000 μatm projected by the year 2100.

Continue reading ‘Growth of the estuarine fish Fundulus heteroclitus in response to diel-cycling hypoxia and acidification: interaction with temperature’

The role of herbivores in a near future ocean: positive and negative effects of climate change on herbivore ecological function

Earth’s climate is characterised by abrupt change through its history, yet human induced climate change is warming and acidifying our oceans at unprecedented rates. Such alterations in the seawater’s chemical and physical properties are anticipated to disrupt a multitude of ecological processes leading to potential reductions in productivity and biodiversity of marine systems. Functional groups such as marine herbivores are renowned for meditating competition between benthic organisms, affecting the physical structure and primary production in marine systems, countervailing the deleterious effects of global and local disturbances. Within this context, it is important to not only understand how herbivorous species respond to climate change, but also how their overall functional role are affected and how this might have cascading effects on other species. In this thesis, I reveal that whilst populations of many species are forecast to collapse due to the effects of future climate, some herbivorous species may capitalize on environmental change and boost their densities by increasing the carrying capacity of the environment by actively modifying the habitat under an otherwise stressful condition. I also show that the modifications performed by herbivorous species trough the strengthening of positive interaction under ocean acidification can assist other species to densify, stimulating species coexistence and ecosystem function, and perhaps mitigate the deleterious effect of CO2 enrichment expected at population and community level. Therefore, under ocean warming the functional role of herbivores is eroded releasing opportunistic algae from trophic control which can potentially lead marine systems to undergo structural modification. I show that loss of this functional role, reduces the capacity of the system to control the expansion of opportunistic algae. The identification of the circumstances as to whether herbivores functional role in marine systems will strengthen or decrease provides insights into the impacts of ocean warming and acidification at local scale and their potential management.

Continue reading ‘The role of herbivores in a near future ocean: positive and negative effects of climate change on herbivore ecological function’

Functional loss in herbivores drives runaway expansion of weedy algae in a near-future ocean

Highlights

• Elevated CO2 and warming increased productivity of turf algae.

• Elevated CO2 increased per capita feeding rates of gastropods.

• Ocean warming reduced grazer diversity, density, and biomass.

• As a result, ocean warming drove a fourfold expansion of weedy algal species.

Abstract

The ability of a community to absorb environmental change without undergoing structural modification is a hallmark of ecological resistance. The recognition that species interactions can stabilize community processes has led to the idea that the effects of climate change may be less than what most considerations currently allow. We tested whether herbivory can compensate for the expansion of weedy algae triggered by CO2 enrichment and warming. Using a six-month mesocosm experiment, we show that increasing per capita herbivory by gastropods absorbs the boosted effects of CO2 enrichment on algal production in temperate systems of weak to moderate herbivory. However, under the combined effects of acidification and warming this compensatory effect was eroded by reducing the diversity, density and biomass of herbivores. This loss of functionality combined with boosted primary productivity drove a fourfold expansion of weedy algal species. Our results demonstrate capacity to buffer ecosystems against CO2 enrichment, but loss of this capacity through ocean warming either in isolation or combined with CO2, driving significant algal turf expansion. Identifying compensatory processes and the circumstances under which they prevail could potentially help manage the impacts of ocean warming and acidification, which are further amplified by local disturbances such as habitat loss and herbivore over-exploitation.

Continue reading ‘Functional loss in herbivores drives runaway expansion of weedy algae in a near-future ocean’

Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean

The Scotia Sea (Southern Ocean) is a hotspot of biodiversity, however, it is one of the fastest warming regions in the world alongside one of the first to experience ocean acidification (OA). Thecosome (shelled) pteropods are planktonic gastropods which can dominate the Scotia Sea zooplankton community, form a key component of the polar pelagic food web and are important contributors to carbon and carbonate fluxes. Pteropods have been identified as sentinel species for OA, since their aragonitic shells are vulnerable to dissolution in waters undersaturated with respect to aragonite.

In this thesis I investigate the impact of a changing ocean on the physiology and life history of pteropods in the Scotia Sea. Firstly, I culture early stage pteropods within OA and warming conditions predicted to occur in 2100 (Chapter 2). I demonstrate that larval shell morphology and survival rates are detrimentally affected in these conditions. Secondly, I constrain the life cycle and population dynamics of pteropods collected over a year from a sediment trap deployed on a moored platform (Chapter 3). I show that Limacina helicina and Limacina retroversa both have distinct life history strategies, although, spawning of both species corresponds to phytoplankton blooms. Thirdly, I establish a baseline vertical and biogeographical distribution of pteropods using historical samples (Chapter 4). I elucidate the geographical range edges of L. retroversa and L. helicina, as well as vertical migration patterns in relation to predation threat. Finally, I examine in-situ pteropod shell condition in relation to carbonate chemistry using net and oceanographic samples collected during two recent cruises (Chapter 5). I demonstrate that larval shells are susceptible to dissolution on exposure to aragonite undersaturation, however, later life stages display some resilience, since shell dissolution is confined to breaches in the periostracum. Overall, I recommend that continued monitoring, combined with bioassays and mesocosm work, will be essential in identifying the continued threat to pteropods from rapid environmental changes.

Continue reading ‘Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean’

Company matters: the presence of other genotypes alters traits and intraspecific selection in an Arctic diatom under climate change

Arctic phytoplankton and their response to future conditions shape one of the most rapidly changing ecosystems on the planet. We tested how much the phenotypic responses of strains from the same Arctic diatom population diverge and whether the physiology and intraspecific composition of multistrain populations differs from expectations based on single strain traits. To this end, we conducted incubation experiments with the diatom Thalassiosira hyalina under present‐day and future temperature and pCO2 treatments. Six fresh isolates from the same Svalbard population were incubated as mono‐ and multistrain cultures. For the first time, we were able to closely follow intraspecific selection within an artificial population using microsatellites and allele‐specific quantitative PCR. Our results showed not only that there is substantial variation in how strains of the same species cope with the tested environments but also that changes in genotype composition, production rates, and cellular quotas in the multistrain cultures are not predictable from monoculture performance. Nevertheless, the physiological responses as well as strain composition of the artificial populations were highly reproducible within each environment. Interestingly, we only detected significant strain sorting in those populations exposed to the future treatment. This study illustrates that the genetic composition of populations can change on very short timescales through selection from the intraspecific standing stock, indicating the potential for rapid population level adaptation to climate change. We further show that individuals adjust their phenotype not only in response to their physicochemical but also to their biological surroundings. Such intraspecific interactions need to be understood in order to realistically predict ecosystem responses to global change.

Continue reading ‘Company matters: the presence of other genotypes alters traits and intraspecific selection in an Arctic diatom under climate change’

Combined effects of acute temperature change and elevated pCO2 on the metabolic rates and hypoxia tolerances of clearnose skate (Rostaraja eglanteria), summer flounder (Paralichthys dentatus), and thorny skate (Amblyraja radiata)

Understanding how rising temperatures, ocean acidification, and hypoxia affect the performance of coastal fishes is essential to predicting species-specific responses to climate change. Although a population’s habitat influences physiological performance, little work has explicitly examined the multi-stressor responses of species from habitats differing in natural variability. Here, clearnose skate (Rostaraja eglanteria) and summer flounder (Paralichthys dentatus) from mid-Atlantic estuaries, and thorny skate (Amblyraja radiata) from the Gulf of Maine, were acutely exposed to current and projected temperatures (20, 24, or 28 °C; 22 or 30 °C; and 9, 13, or 15 °C, respectively) and acidification conditions (pH 7.8 or 7.4). We tested metabolic rates and hypoxia tolerance using intermittent-flow respirometry. All three species exhibited increases in standard metabolic rate under an 8 °C temperature increase (Q10 of 1.71, 1.07, and 2.56, respectively), although this was most pronounced in the thorny skate. At the lowest test temperature and under the low pH treatment, all three species exhibited significant increases in standard metabolic rate (44–105%; p < 0.05) and decreases in hypoxia tolerance (60–84% increases in critical oxygen pressure; p < 0.05). This study demonstrates the interactive effects of increasing temperature and changing ocean carbonate chemistry are species-specific, the implications of which should be considered within the context of habitat.

Continue reading ‘Combined effects of acute temperature change and elevated pCO2 on the metabolic rates and hypoxia tolerances of clearnose skate (Rostaraja eglanteria), summer flounder (Paralichthys dentatus), and thorny skate (Amblyraja radiata)’

Effects of ocean acidification and short-term light/temperature stress on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary

Ocean acidification (OA) affects marine primary productivity and community structure. Therefore, OA may influence the biogeochemical cycles of volatile biogenic dimethyl sulfide (DMS), and its precursor dimethylsulfoniopropionate (DMSP) and photochemical oxidation product dimethyl sulfoxide (DMSO). A 23-day shipboard incubation experiment investigated the short-term response of the production and cycling of biogenic sulfur compounds to OA in the Changjiang River Estuary to understand the effects of OA on biogenic sulfur compounds. Phytoplankton abundance and community composition showed a marked difference at three different pH levels at the late stage of the experiment. Significant reductions in chlorophyll a (Chl-a), DMS, particulate DMSP (DMSPp) and dissolved DMSO (DMSOd) concentrations were identified under high CO2 levels. Moreover, minimal changes were observed in the productions of dissolved DMSP (DMSPd) and particulate DMSO (DMSOp) among the treatments. The ratios of DMS, total DMSP (DMSPt) and total DMSO (DMSOt) to Chl-a were not affected by a change in pH. Furthermore, the concentrations of DMS and DMSOd were closely related to the mean bacterial abundance at the three pH levels. Additional short-term (8 h) incubation experiments on the light and temperature effects showed that the influence of pH on the production of dimethylated sulfur compounds also depended on solar radiation and temperature. Under natural and UVB light, DMS photodegradation rates increased by 1.6 to 4.2 times at low pH levels. Thus, OA may lead to decreasing DMS concentrations in surface seawater. Light and temperature conditions also play important roles in the production and cycling of biogenic sulfur compounds.

Continue reading ‘Effects of ocean acidification and short-term light/temperature stress on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book