Posts Tagged 'biological response'

Changes in fish communities due to benthic habitat shifts under ocean acidification conditions

Highlights

• Ocean acidification-mediated habitat shifts and decreased complexity affect associated fish communities.

• Altered fish traits and reduced diversity occurred under near-future ocean acidification levels.

• Ocean acidification may oppose the poleward-shift of tropical fish species under warming.

Abstract

Ocean acidification will likely change the structure and function of coastal marine ecosystems over coming decades. Volcanic carbon dioxide seeps generate dissolved CO2 and pH gradients that provide realistic insights into the direction and magnitude of these changes. Here, we used fish and benthic community surveys to assess the spatio-temporal dynamics of fish community properties off CO2 seeps in Japan. Adding to previous evidence from ocean acidification ecosystem studies conducted elsewhere, our findings documented shifts from calcified to non-calcified habitats with reduced benthic complexity. In addition, we found that such habitat transition led to decreased diversity of associated fish and to selection of those fish species better adapted to simplified ecosystems dominated by algae. Our data suggest that near-future projected ocean acidification levels will oppose the ongoing range expansion of coral reef-associated fish due to global warming.

Continue reading ‘Changes in fish communities due to benthic habitat shifts under ocean acidification conditions’

The effects of mining tailings in the physiology of benthic algae: understanding the relation between mud’s inductive acidification and the heavy metal’s toxicity

Highlights

• Mariana’s mud was evaluated for toxic effects of heavy metals and acidification.

• Sargassum cymosum and Hypnea musciformis were evaluated for physiological responses.

• The presence of mud and acidic conditions caused lethality and metabolic damages.

• The acidified condition had the greatest impact over physiology of both species.

• The toxicity effects of mining tailings are intensified by abiotic changes.

Abstract

The direct and indirect effects of mining tailing on macroalgae were evaluated in vitro to determine the relationship between heavy metals toxicity and pH alterations caused by the presence of pollutants. The marine brown seaweed Sargassum cymosum (C. Hagard 1820) and its main epiphytic alga, the red seaweed Hypnea pseudomusciformis (Nauer, Cassano, Oliveira, 2015), were exposed to Mariana’s mud in cross treatments, including presence or absence of mud, and normal (˜8.0) or acidic (˜7.0) pH conditions. The effects of different biological conditions were also evaluated in two treatments, with seaweed in isolated or associative conditions, for a seven-day period. The measured variables were growth rates and metabolic descriptors, such as chlorophyll a, phenolic compounds, total proteins, and the analysis of enzymatic activity, e.g. catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD). Kruskal-Wallis and post-hoc Dunn’s test were performed to evaluate the significant differences among treatments and biological conditions. Decreased growth rates in treatments with presence of mud or in acidic conditions were detected and probably related to deviations of metabolic energy towards the synthesis of defensive metabolites. Especially in the acidified culture medium, both algae species presented significant declines in pigments concentration, antioxidant compounds and an accentuated inhibition of enzymatic activity. The algal association was not beneficial for either species and H. pseudomusciformis was responsible for reducing the defensive ability of Sargassum against stressors. Considering the results, we infer that the physiological ability of both algae to resist metals and/or acidified conditions was affected not only by their mutual interference in each other, but also by the interaction between the abiotic parameters evaluated in this study.

Continue reading ‘The effects of mining tailings in the physiology of benthic algae: understanding the relation between mud’s inductive acidification and the heavy metal’s toxicity’

Effects of ocean acidification on the larval settlement and metamorphosis of marine invertebrates

Future Ocean acidification (OA) has the potential to negatively affect marine ecosystems and the organisms they support, with the early life-history stages particularly sensitive to reduced seawater pH and carbonate saturation states. Most marine organisms reproduce through an indirect lifecycle, which includes a free-swimming larval stage. In benthic or sessile taxa, the lifecycle is marked by the larval settlement and metamorphosis processes. Here, at the end of the free-living (generally planktonic) stage, larvae selectively search for a preferred settlement substrate for attachment, with metamorphosis occurring before or after it. Larval settlement and metamorphosis are arguably the most important processes in the life cycle of marine invertebrates, since they determine and optimize the final location of the organisms. Altered larval settlement rates will therefore influence the ecology, abundances and distributions of future coastal communities.

The aim of this thesis was to investigate whether OA could affect the larval settlement success of marine invertebrates, and whether these impacts would be mediated through direct, indirect or carry-over mechanisms. Three key New Zealand coastal marine invertebrates were used as model organisms: the sea urchin Evechinus chloroticus, the black-footed abalone (Haliotis iris) or pāua and the serpulid polychaete Galeolaria hystrix.

Continue reading ‘Effects of ocean acidification on the larval settlement and metamorphosis of marine invertebrates’

Ocean acidification interacts with variable light to decrease growth but increase particulate organic nitrogen production in a diatom

Highlights

• Variable light decreased growth rate and pigmentation contents in both LC and HC.

• Cells grown under variable light appeared more tolerant of high light.

• HC and varying light decreased carbon fixation rate but increased POC and PON.

• HC and varying light lead to less primary productivity but more PON per biomass.

Abstract

Phytoplankton in the upper oceans are exposed to changing light levels due to mixing, diurnal solar cycles and weather conditions. Consequently, effects of ocean acidification are superimposed upon responses to variable light levels. We therefore grew a model diatom Thalassiosira pseudonana under either constant or variable light but at the same daily photon dose, with current low (400 μatm, LC) and future high CO2 (1000 μatm, HC) treatments. Variable light, compared with the constant light regime, decreased the growth rate, Chl a, Chl c, and carotenoid contents under both LC and HC conditions. Cells grown under variable light appeared more tolerant of high light as indicated by higher maximum relative electron transport rate and saturation light. Light variation interacted with high CO2/lowered pH to decrease the carbon fixation rate, but increased particulate organic carbon (POC) and particularly nitrogen (PON) per cell, which drove a decrease in C/N ratio, reflecting changes in the efficiency of energy transfer from photo-chemistry to net biomass production. Our results imply that elevated pCO2 under varying light conditions can lead to less primary productivity but more PON per biomass of the diatom, which might improve the food quality of diatoms and thereby influence biogeochemical nitrogen cycles.

Continue reading ‘Ocean acidification interacts with variable light to decrease growth but increase particulate organic nitrogen production in a diatom’

Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming

Ocean acidification and warming (OA-W) result mainly from the absorption of carbon dioxide and heat by the oceans, altering its physical and chemical properties and affecting carbonate secretion by marine calcifiers such as gastropods. These processes are ongoing, and the projections of their aggravation are not encouraging. This work assesses the concomitant effect of the predicted pH decrease and temperature rise on early life stages of the neogastropod Tritia reticulata (L.), a common scavenger of high ecological importance on coastal ecosystems of the NE Atlantic. Veligers were exposed for 14 days to 12 OA-W experimental scenarios generated by a factorial design of three pH levels (targeting 8.1, 7.8 and 7.5) at four temperatures (16, 18, 20 and 22 °C). Results reveal effects of both pH and temperature (T °C) on larval development, growth, shell integrity and survival, individually or interactively at different exposure times. All endpoints were initially driven by pH, with impaired development and high mortalities being recorded in the first week, constrained by the most acidic scenarios (pHtarget 7.5). Development was also significantly driven by T °C, and its acceleration with warming was observed for the remaining exposure time. Still, by the end of this 2-weeks trial, larval performance and survival were highly affected by the interaction between pH and T °C: growth under warming was evident but only for T °C ≤ 20 °C and carbonate saturation (pHtarget ≥ 7.8). In fact, carbonate undersaturation rendered critical larval mortality (100%) at 22 °C, and the occurrence of extremely vulnerable, unshelled specimens in all other tested temperatures. As recruitment cohorts are the foundation for future populations, our results point towards the extreme vulnerability of this species in case tested scenarios become effective that, according to the IPCC, are projected for the northern hemisphere, where this species is ubiquitous, by the end of the century. Increased veliger mortality associated with reduced growth rates, shell dissolution and loss under OA-W projected scenarios will reduce larval performance, jeopardizing T. reticulata subsistence.

Continue reading ‘Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming’

Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)

Species interactions are crucial for the persistence of ecosystems. Within vegetated habitats, early life stages of plants and algae must survive factors such as grazing to recover from disturbances. However, grazing impacts on early stages, especially under the context of a rapidly changing climate, are largely unknown. Here we examine interaction strengths between juvenile giant kelp (Macrocystis pyrifera) and four common grazers under hypoxia and ocean acidification using short-term laboratory experiments and field data of grazer abundances to estimate population-level grazing impacts. We found that grazing is a significant source of mortality for juvenile kelp and, using field abundances, estimate grazers can remove on average 15.4% and a maximum of 73.9% of juveniles per m2 per day. Short-term exposure to low oxygen, not acidification, weakened interaction strengths across the four species and decreased estimated population-level impacts of grazing threefold, from 15.4% to 4.0% of juvenile kelp removed, on average, per m2 per day. This study highlights potentially high juvenile kelp mortality from grazing. We also show that the effects of hypoxia are stronger than the effects of acidification in weakening these grazing interactions over short timescales, with possible future consequences for the persistence of giant kelp and energy flow through these highly productive food webs.

Continue reading ‘Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)’

A sediment trap evaluation of B/Ca as a carbonate system proxy in asymbiotic and nondinoflagellate hosting planktonic foraminifera

The ratio of boron to calcium (B/Ca) in a subset of foraminifera has been shown to covary with seawater carbonate chemistry, making this geochemical signature a promising proxy for carbon cycle science. Some studies suggest complications with the B/Ca proxy in photosymbiont‐bearing planktonic foraminifera, while relatively few studies have investigated B/Ca in species that lack large dinoflagellate symbionts. For the first time, we use a sediment trap time series to evaluate B/Ca of subtropical and subpolar planktonic foraminifera species that are asymbiotic (Globigerina bulloides and Neogloboquadrina incompta) and a species that hosts small intrashell photosymbionts (Neogloboquadrina dutertrei). We find that B/Ca measurements across size fractions indicate overall little to no size‐dependent uptake of boron that has previously been reported in some symbiont‐bearing foraminifera. Neogloboquadrina incompta and N. dutertrei B/Ca are strongly correlated with calcite saturation, pH, and carbonate ion concentration, which is in good agreement with the limited number of published core top results. While G. bulloides B/Ca trends with seasonal fluctuations in carbonate chemistry, during discrete periods considerable B/Ca offsets occur when a cryptic G. bulloides species is known to be seasonally present within the region. We confirm presence and significant B/Ca offset between cryptic species by individual LA‐ICP‐MS analyses. This finding calls into question the use of traditional morphological classification to lump what might be genetically distinct species for geochemical analyses. Our overall results highlight the utility of G. bulloides, N. incompta, and N. dutertrei B/Ca while bringing to light new considerations regarding divergent geochemistry of cryptic species.

Continue reading ‘A sediment trap evaluation of B/Ca as a carbonate system proxy in asymbiotic and nondinoflagellate hosting planktonic foraminifera’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book