Posts Tagged 'mesocosms'



Seagrass can mitigate negative ocean acidification effects on calcifying algae

The ultimate effect that ocean acidification (OA) and warming will have on the physiology of calcifying algae is still largely uncertain. Responses depend on the complex interactions between seawater chemistry, global/local stressors and species-specific physiologies. There is a significant gap regarding the effect that metabolic interactions between coexisting species may have on local seawater chemistry and the concurrent effect of OA. Here, we manipulated CO2 and temperature to evaluate the physiological responses of two common photoautotrophs from shallow tropical marine coastal ecosystems in Brazil: the calcifying alga Halimeda cuneata, and the seagrass Halodule wrightii. We tested whether or not seagrass presence can influence the calcification rate of a widespread and abundant species of Halimeda under OA and warming. Our results demonstrate that under elevated CO2, the high photosynthetic rates of H. wrightii contribute to raise H. cuneata calcification more than two-fold and thus we suggest that H. cuneata populations coexisting with H. wrightii may have a higher resilience to OA conditions. This conclusion supports the more general hypothesis that, in coastal and shallow reef environments, the metabolic interactions between calcifying and non-calcifying organisms are instrumental in providing refuge against OA effects and increasing the resilience of the more OA-susceptible species.

Continue reading ‘Seagrass can mitigate negative ocean acidification effects on calcifying algae’

Implicações fisiológicas e ecológicas de interações interespecíficas nos bentos marinho-subsídio para o entendimento de cenários atuais e futuros (in Portuguese)

Biotic interactions are increasingly known to shape ecosystem community structure. Recently, there has been a renewed focus on species interactions in light of global change, especially ocean warming (OW) and ocean acidification (OA) in marine ecosystems. In coastal environments, macroalgae are among the most important taxa as they are often the most abundant primary producers and form the base of food webs. However, due to their sedentary nature, they are also vulnerable to the effects of climate change. In order to better understand how species interactions will be affected by climate change stressors, a solid understanding of how interspecies interactions operate under present-day conditions is needed. The first chapter of this thesis attempts to characterize seasonal variation in macroalgal physiology and biochemistry, and how interspecific interactions might affect algal fitness and palatability to a sea urchin herbivore (Echinometra lucunter). Specimens of Jania rubens, Sargassum cymosum, and Ulva lactuca were collected from monospecific patches or from associations , where individuals were in physical contact with another species, in both summer and winter. Net photosynthesis, nitrogen reductase activity, and pigment, phenolic and carbonate content of algae were evaluated among different associations across the two seasons. The results indicate that in addition to seasonal variation in most parameters measured, interactions between algae could change in both magnitude and sign (positive, negative or neutral) in different seasons. The no-choice herbivory assay (conducted in winter) revealed that both Jania and Ulva were consumed at higher rates when they were associated with each other, whereas Sargassum was not affected. These results suggest that macroalgae may influence the physiology and biochemical composition of neighboring species and subsequently affect their palatability, which may influence local community structure. To further evaluate effects of species interactions under climate change stressors, an experiment was performed to assess algal-herbivore interactions under OW and OA conditions. The most preferentially consumed algae from the first experiment (Jania rubens) and the sea urchin E. lucunter were evaluated in a 21-day mesocosm study with treatments of control, OW, OA, and OW+OA. Algal physiology was unaffected by increased temperature (+4°C) and pCO2 (1,000 ppm), but changes in the biochemical composition of the algal tissue were found. Metabolic rates of the sea urchin E. lucunter were higher in the ambient temperature, high pCO2 treatment, and feeding assays showed that this influenced consumption, with increased feeding rates in this treatment. The results here show that although algal biochemical composition was affected by future pCO2, at least in the short term, direct effects to sea urchin metabolism were more important for impacting this algae-herbivore interaction.

Continue reading ‘Implicações fisiológicas e ecológicas de interações interespecíficas nos bentos marinho-subsídio para o entendimento de cenários atuais e futuros (in Portuguese)’

Context-dependence of abiotic and biotic factors influencing performance of juvenile clams

Highlights

• We found site-level variability in performance of two sizes of juvenile Manila clams.

• Field experiments concurrently assessed the roles of biotic and abiotic variables.

• Performance was particularly impaired at one site with hot summer porewater temperatures.

• Under greater abiotic stress, smaller clams suffered more losses than large.

• Salinity, elevation, and pH were less important to survival than was predator density.

Abstract

Post-settlement survival and growth of bivalves can be limited by abiotic and biotic factors, both of which are spatially variable. Rarely has the importance of these factors been tested concurrently in the field. Our study spanned three spatial scales in estuarine waters of Washington state (Region: north vs. south; Within-region: fresher vs. saline; Within-site: mid- vs. low-tidal elevation). Predator access and sediment conditions were manipulated in a crossed experimental design, with juvenile (3-mm and 6-mm) Manila clams (Ruditapes philippinarum) outplanted in open- or closed-top mesh tubes. We found differences between treatments that appeared only at sites with cancrid crabs, suggesting that predators, rather than emigration, likely reduced numbers of clams in open tubes. We had hypothesized that clams at lower tidal elevations, which experience longer immersion times, would show improved growth but reduced survivorship because of greater exposure to marine predators. However, these patterns were evident at only one of three sites (lower-elevation treatments were lost at the fourth). The larger size class of clams was more tolerant of abiotic stressors at all sites, but the magnitude of difference in survival between size classes was sometimes dependent on other treatments. The maximum predator effect on survival was 74% (north, high salinity, low-intertidal site), whereas the maximum abiotic effect appeared as 62% lower survival and 59% slower growth for 3-mm clams at another site (north, fresher). In laboratory trials, high water temperatures (28–32 °C) and low salinity (5–15) acted synergistically to cause juvenile clam (6–12 mm) mortality, whereas clams tolerated each of these stressors alone. Context-dependence in the relative importance of predation and abiotic stressors was apparent in our results, but contrary to expectations, abiotic stressors did not characterize southern or fresher sites. Instead, extreme high temperatures occurred at the site with the wide tidal flat rather than in the south, and the within-region salinity differences appeared not to exceed tolerances of juvenile clams.

Continue reading ‘Context-dependence of abiotic and biotic factors influencing performance of juvenile clams’

Future climate change is predicted to affect the microbiome and condition of habitat-forming kelp

Climate change is driving global declines of marine habitat-forming species through physiological effects and through changes to ecological interactions, with projected trajectories for ocean warming and acidification likely to exacerbate such impacts in coming decades. Interactions between habitat-formers and their microbiomes are fundamental for host functioning and resilience, but how such relationships will change in future conditions is largely unknown. We investigated independent and interactive effects of warming and acidification on a large brown seaweed, the kelp Ecklonia radiata, and its associated microbiome in experimental mesocosms. Microbial communities were affected by warming and, during the first week, by acidification. During the second week, kelp developed disease-like symptoms previously observed in the field. The tissue of some kelp blistered, bleached and eventually degraded, particularly under the acidification treatments, affecting photosynthetic efficiency. Microbial communities differed between blistered and healthy kelp for all treatments, except for those under future conditions of warming and acidification, which after two weeks resembled assemblages associated with healthy hosts. This indicates that changes in the microbiome were not easily predictable as the severity of future climate scenarios increased. Future ocean conditions can change kelp microbiomes and may lead to host disease, with potentially cascading impacts on associated ecosystems.

Continue reading ‘Future climate change is predicted to affect the microbiome and condition of habitat-forming kelp’

Molecular mechanisms underpinning transgenerational plasticity in the green sea urchin Psammechinus miliaris

The pre-conditioning of adult marine invertebrates to altered conditions, such as low pH, can significantly impact offspring outcomes, a process which is often referred to as transgenerational plasticity (TGP). This study describes for the first time, the gene expression profiles associated with TGP in the green sea urchin Psammechinus miliaris and evaluates the transcriptional contribution to larval resilience. RNA-Seq was used to determine how the expression profiles of larvae spawned into low pH from pre-acclimated adults differed to those of larvae produced from adults cultured under ambient pH. The main findings demonstrated that adult conditioning to low pH critically pre-loads the embryonic transcriptional pool with antioxidants to prepare the larvae for the “new” conditions. In addition, the classic cellular stress response, measured via the production of heat shock proteins (the heat shock response (HSR)), was separately evaluated. None of the early stage larvae either spawned in low pH (produced from both ambient and pre-acclimated adults) or subjected to a separate heat shock experiment were able to activate the full HSR as measured in adults, but the capacity to mount an HSR increased as development proceeded. This compromised ability clearly contributes to the vulnerability of early stage larvae to acute environmental challenge.

Continue reading ‘Molecular mechanisms underpinning transgenerational plasticity in the green sea urchin Psammechinus miliaris’

Effects of higher CO2 and temperature on exopolymer particle content and physical properties of marine aggregates

We investigated how future ocean conditions, and specifically the interaction between temperature and CO2, might affect marine aggregate formation and physical properties. Initially, mesocosms filled with coastal seawater were subjected to three different treatments of CO2 concentration and temperature: (1) 750 ppm CO2, 16°C, (2) 750 ppm CO2, 20°C, and (3) 390 ppm CO2, 16°C. Diatom-dominated phytoplankton blooms were induced in the mesocosms by addition of nutrients. In aggregates produced in roller tanks using seawater taken from the mesocosms during different stages of the bloom, we measured sinking velocity, size, chlorophyll a, particulate organic carbon and nitrogen, and exopolymer particle content; excess density and mass were calculated from the sinking velocity and size of the aggregates. As has been seen in previous experiments, no discernable differences in overall nutrient uptake, chlorophyll-a concentration, or exopolymer particle concentrations could be related to the acidification treatment in the mesocosms. In addition, in the aggregates formed during the roller tank experiments (RTEs), we observed no statistically significant differences in chemical composition among the treatments during Pre-Bloom, Bloom, and Post-Bloom periods. However, physical characteristics were different and showed a synergistic effect of warmer temperature and higher CO2 during the Pre-Bloom period; at this time, temperature had a larger effect than CO2 on aggregate sinking velocity. In RTEs with warmer and acidified treatment (future conditions), aggregates were larger, heavier, and settled faster than aggregates formed at present-day or only acidified conditions. During the Post-Bloom, however, aggregates formed under present and future conditions had similar physical properties. In acidified tanks at ambient temperature, aggregates were slower, smaller and less dense than those formed at the same temperature but under present CO2 or under warmer and acidified conditions. Thus, the sinking velocity of aggregates formed in acidified tanks at ambient temperature was slower than the other two cases. Our findings point out the potential of ocean acidification and warming to modify physical properties of sinking aggregates but also emphasize the need of future experiments investigating multiple environmental stressors to clarify the importance of each factor.

Continue reading ‘Effects of higher CO2 and temperature on exopolymer particle content and physical properties of marine aggregates’

A continuous-flow and on-site mesocosm for ocean acidification experiments on benthic organisms

Mesocosm experiments conducted for ecological purposes have become increasingly popular because they can provide a holistic understanding of the biological complexities associated with natural systems. This paper describes a new outdoor mesocosm designed for CO2 perturbation experiments of benthos. Manipulated the carbonate chemistry in a continuous flow-through system can be parallelized with diurnal changes, while irradiance, temperature, and nutrients can vary according to the local environment. A target hydrogen ion activity (pH) of seawater was sufficiently stabilized and maintained within 4 h after dilution, which was initiated by the ratio of CO2-saturated seawater to ambient seawater. Specifically, pH and CO2partial pressure (pCO2) levels gradually varied from 8.05–7.28 and 375–2,691 μatm, respectively, over a range of dilution ratios. This mesocosm can successfully manipulate the pH and pCO2 of seawater, and it demonstrates suitability for ocean acidification experiments on benthic communities.

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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book