Anthropogenic nutrient inputs enhance microbial respiration within many coastal ecosystems, driving concurrent hypoxia and acidification. During photosynthesis, Symbiodinium spp., the microalgal endosymbionts of cnidarians and other marine phyla, produce O2 and assimilate CO2, and thus potentially mitigate the exposure of the host to these stresses. However, such a role for Symbiodinium remains untested for non-calcifying cnidarians. We therefore contrasted the fitness of symbiotic and aposymbiotic polyps of a model host jellyfish (Cassiopea sp.) under reduced O2 (~2.09mgL−1) and pH (~pH 7.63) scenarios in a full factorial experiment. Host fitness was characterised as asexual reproduction and their ability to regulate internal pH and Symbiodinium performance characterised by maximum photochemical efficiency, chla content, and cell density. Acidification alone resulted in 58% more asexual reproduction of symbiotic polyps than aposymbiotic polyps (and enhanced Symbiodinium cell density) suggesting Cassiopea sp. fitness was enhanced by CO2-stimulated Symbiodinium photosynthetic activity. Indeed, greater CO2 drawdown (elevated pH) was observed within host tissues of symbiotic polyps under acidification regardless of O2 conditions. Hypoxia alone produced 22% fewer polyps than ambient conditions regardless of acidification and symbiont status, suggesting Symbiodinium photosynthetic activity did not mitigate its effects. Combined hypoxia and acidification, however, produced similar numbers of symbiotic polyps compared with aposymbiotic kept under ambient conditions, demonstrating that the presence of Symbiodinium was key for mitigating the combined effects of hypoxia and acidification on asexual reproduction. We hypothesise that this mitigation occurred because of reduced photorespiration under elevated CO2 conditions where increased net O2 production ameliorates oxygen debt. We show that Symbiodinium play an important role in facilitating enhanced fitness of Cassiopea sp. polyps, and perhaps also other non-calcifying cnidarian hosts, to the ubiquitous effects of ocean acidification. Importantly we highlight that symbiotic, non-calcifying cnidarians may be particularly advantaged in productive coastal waters that are subject to simultaneous hypoxia and acidification.
Posts Tagged 'cnidaria'
Symbiodinium mitigate the combined effects of hypoxia and acidification on a non-calcifying cnidarian
Published 28 April 2017 Science ClosedTags: biological response, cnidaria, communityMF, laboratory, mortality, multiple factors, oxygen, photosynthesis, physiology, protists, reproduction, respiration, South Pacific
Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment
Published 19 April 2017 Science ClosedTags: abundance, BRcommunity, cnidaria, community composition, crustaceans, field, laboratory, mesocosms, morphology, North Atlantic, otherprocess, physiology, reproduction, respiration, zooplankton
Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.
Entering the Anthropocene: How ocean acidification and warmer temperatures affect the symbiotic sea anemone Exaiptasia pallida
Published 28 February 2017 Science ClosedTags: biological response, cnidaria, laboratory, morphology, multiple factors, performance, photosynthesis, phytoplankton, respiration, temperature
Here I report the effects of long-term elevated CO2 combined with two subsequent elevated temperature intervals on the model symbiotic anemone Exaiptasia pallida. A central goal of this thesis was to investigate how altered CO2 and temperature affect the symbiotic relationship while this anemone hosted three different strains of endosymbiotic dinoflagellates (Symbiodinium minutum, Symbiodinium A4a, and Symbiodinium A4b). Exposure to elevated CO2 (930μatm) alone for 42 days led to no significant changes in either the anemone or the algae physiological response, with the exception of some separation between the photosynthesis to respiration ratio of S. A4a and S. A4b control and treatment animals. Exposure to both elevated CO2 (930μatm) and a moderate elevation in temperature (29°C) for 49 days led to a significant increase in the net maximal photosynthesis (normalized to algal cell density) between the treatment and controls of all three holobionts. Exposure to both elevated CO2 (930μatm) and an even higher temperature (33°C) for up to 20 days led to a significant decrease in photobiology and algal cell density, along with visible bleaching in the S. minutum holobiont. All three holobionts displayed a significant decrease in the photosynthesis to respiration ratio, thereby providing evidence for temperature having a greater impact on the phototrophic response of these anemones. However, anemones harboring the two A4 Symbiodinium did not show as large of a negative response in photosystem II photochemistry when compared to anemones with S. minutum. The high temperature treatment also resulted in juvenile mortality in all three holobionts, with the greatest mortality seen in the S. minutum holobiont. The differential response to both elevated CO2 and elevated temperature between the three holobionts highlights the thermal sensitivity of the S. minutum symbiosis, and the thermal tolerance of the S. A4 holobionts. Thermal tolerance may enable these anemones to survive and thrive in future climate change conditions, while the effects of higher CO2 appear to be more neutral.
Effects of ocean acidification on benthic organisms in the Mediterranean Sea under realistic climatic scenarios: A meta-analysis
Published 12 January 2017 Science ClosedTags: abundance, algae, biological response, bryozoa, calcification, cnidaria, corals, echinoderms, Mediterranean, methods, mollusks, morphology, mortality, otherprocess, photosynthesis, review
Ocean acidification is expected to cause significant changes in the marine environment over the coming century. The effects of acidification on organisms’ physiology have been studied over the past two decades. However, the experimental findings are not always easily comparable because of differences in experimental design, and comparable experiments do not always produce similar results. To rigorously integrate the current knowledge, we performed a meta-analysis of published studies focused on benthic organisms in the Mediterranean Sea, both in controlled manipulative experiments and in situ experiments near vent areas. In each experiment, the effect of acidification was calculated as the log-transformed response ratio (LnRR) of experimental versus control conditions. The quantitative results obtained by the meta-analysis highlight: (a) an increase in fleshy algae cover, which may lead to a competitive advantage over calcifying macroalgae; (b) a reduction of calcification by both algae and corals; (c) an increase in seagrass shoot density under low pH; and (d) a general increase in the photosynthetic activity of macrophytes.
The stable microbiome of inter and sub-tidal anemone species under increasing pCO2
Published 30 November 2016 Science ClosedTags: abundance, biological response, chemistry, cnidaria, community composition, field, Mediterranean, molecular biology, morphology, otherprocess, prokaryotes
Increasing levels of pCO2 within the oceans will select for resistant organisms such as anemones, which may thrive under ocean acidification conditions. However, increasing pCO2 may alter the bacterial community of marine organisms, significantly affecting the health status of the host. A pH gradient associated with a natural volcanic vent system within Levante Bay, Vulcano Island, Italy, was used to test the effects of ocean acidification on the bacterial community of two anemone species in situ, Anemonia viridis and Actinia equina using 16 S rDNA pyrosequencing. Results showed the bacterial community of the two anemone species differed significantly from each other primarily because of differences in the Gammaproteobacteria and Epsilonproteobacteria abundances. The bacterial communities did not differ within species among sites with decreasing pH except for A. viridis at the vent site (pH = 6.05). In addition to low pH, the vent site contains trace metals and sulfide that may have influenced the bacteria community of A. viridis. The stability of the bacterial community from pH 8.1 to pH 7.4, coupled with previous experiments showing the lack of, or beneficial changes within anemones living under low pH conditions indicates that A. viridis and A. equina will be winners under future ocean acidification scenarios.
Resilience to ocean acidification: decreased carbonic anhydrase activity in sea anemones under high pCO2 conditions
Published 16 November 2016 Science ClosedTags: biological response, cnidaria, field, laboratory, Mediterranean, morphology, photosynthesis, physiology
Non-calcifying photosynthetic anthozoans have emerged as a group that may thrive under high carbon dioxide partial pressure ( pCO2) conditions via increased productivity. However, the physiological mechanisms underlying this potential success are unclear. Here we investigated the impact of high pCO2 on the dissolved inorganic carbon (DIC) use in the temperate sea anemone Anemonia viridis. We assessed the impacts of long-term exposure to high pCO2, i.e. sampling in situ natural CO2 vents (Vulcano, Italy), and short-term exposure, i.e. during a 3 wk controlled laboratory experiment. We focused on photo-physiological parameters (net photosynthesis rates, chlorophyll a content and Symbiodinium density) and on carbonic anhydrase (CA) activity, an enzyme involved in the energy-demanding process of DIC absorption. Long-term exposure to high pCO2 had no impact on Symbiodinium density and chlorophyll a content. In contrst, short-term exposure to high pCO2 induced a significant reduction in Symbiodinium density, which together with unchanged net photosynthesis resulted in the increase of Symbiodinium productivity per cell. Finally, in both in situ long-term and laboratory short-term exposure to high pCO2, we observed a significant decrease in the CA activity of sea anemones, suggesting a change in DIC use (i.e. from an HCO3- to a CO2 user). This change could enable a shift in the energy budget that may increase the ability of non-calcifying photosynthetic anthozoans to cope with ocean acidification.
Survey of Cnidarian gene expression profiles in response to environmental stressors: summarizing 20 years of research, what are we heading for?
Published 15 September 2016 Science ClosedTags: biological response, cnidaria, individualmodeling, modeling, molecular biology, review
Coral research has come a long way since the pioneering coral biology studies of thermal tolerance dating back to the turn of the previous century. In great contrast, at the present time, the currently available in silico technologies enable the entire transcriptome to be surveyed in a high-throughput manner following an array of stress manipulations. Deep-sequencing is expected to revolutionize the way we study gene expression and holds the potential to answer prominent questions regarding cnidarian cellular pathways following global change scenarios. In this review we focus on cnidarian responses to environmental stressors in general and to global climate change in particular, focusing on the gene expression levels. A wide characterization of studies conducted in cnidarians following environmental stress revealed that most of the studies investigated a single stress factor and mostly thermal stress, were short-term and focused on branching corals. Subsequently, there is a lack of gene expression knowledge concerning massive corals that are known to be less susceptible to bleaching comparing to branching corals. In this review, we present a detailed list of differentially expressed genes in branching/massive corals under eight types of environmental stress. A conceptual model was constructed of the main processes occurring within the coral host cell under heat, ocean acidification and UV stress. The tables and the pathways of this review emphasize gaps in knowledge and can assist in guiding future research as they suggests which genes/processes one should look at in order to achieve a greater understanding of the cnidarians molecular processes affected by global anthropogenic stress.
Withstanding multiple stressors: ephyrae of the moon jellyfish (Aurelia aurita, Scyphozoa) in a high-temperature, high-CO2 and low-oxygen environment
Published 25 August 2016 Science ClosedTags: biological response, cnidaria, laboratory, morphology, mortality, multiple factors, oxygen, performance, temperature, zooplankton
Global change is affecting marine ecosystems through a combination of different stressors such as warming, ocean acidification and oxygen depletion. Very little is known about the interactions among these factors, especially with respect to gelatinous zooplankton. Therefore, in this study we investigated the direct effects of pH, temperature and oxygen availability on the moon jellyfish Aurelia aurita, concentrating on the ephyral life stage. Starved one-day-old ephyrae were exposed to a range of pCO2 (400–4000 ppm) and three different dissolved oxygen levels (from saturated to hypoxic conditions), in two different temperatures (5 and 15 °C) for 7 days. Carbon content and swimming activity were analysed at the end of the incubation period, and mortality noted. General linearized models were fitted through the data, with the best fitting models including two- and three-way interactions between pCO2, temperature and oxygen concentration. The combined effect of the stressors was small but significant, with the clearest negative effect on growth caused by the combination of all three stressors present (high temperature, high CO2, low oxygen). We conclude that A. aurita ephyrae are robust and that they are not likely to suffer from these environmental stressors in a near future.
Ocean acidification alters fish–jellyfish symbiosis
Published 30 June 2016 Science ClosedTags: biological response, cnidaria, fish, laboratory, performance
Symbiotic relationships are common in nature, and are important for individual fitness and sustaining species populations. Global change is rapidly altering environmental conditions, but, with the exception of coral–microalgae interactions, we know little of how this will affect symbiotic relationships. We here test how the effects of ocean acidification, from rising anthropogenic CO2 emissions, may alter symbiotic interactions between juvenile fish and their jellyfish hosts. Fishes treated with elevated seawater CO2 concentrations, as forecast for the end of the century on a business-as-usual greenhouse gas emission scenario, were negatively affected in their behaviour. The total time that fish (yellowtail scad) spent close to their jellyfish host in a choice arena where they could see and smell their host was approximately three times shorter under future compared with ambient CO2 conditions. Likewise, the mean number of attempts to associate with jellyfish was almost three times lower in CO2-treated compared with control fish, while only 63% (high CO2) versus 86% (control) of all individuals tested initiated an association at all. By contrast, none of three fish species tested were attracted solely to jellyfish olfactory cues under present-day CO2 conditions, suggesting that the altered fish–jellyfish association is not driven by negative effects of ocean acidification on olfaction. Because shelter is not widely available in the open water column and larvae of many (and often commercially important) pelagic species associate with jellyfish for protection against predators, modification of the fish–jellyfish symbiosis might lead to higher mortality and alter species population dynamics, and potentially have flow-on effects for their fisheries.
Continue reading ‘Ocean acidification alters fish–jellyfish symbiosis’
Reduced pH affects pulsing behaviour and body size in ephyrae of the moon jellyfish, Aurelia aurita
Published 25 April 2016 Science ClosedTags: biological response, cnidaria, laboratory, morphology, North Pacific, performance
Our understanding of how reduced seawater pH affects the behaviour and growth of scyphozoan jellyfish is poor. Here, we investigated the effects of simulated Ocean Acidification (OA) (pH = 7.6 for 7 d) on pulsing behaviour (as an index of swimming behaviour) and aspects of the morphology of ephyrae of the moon jellyfish Aurelia aurita. Ephyrae exposed to reduced pH had a significantly smaller surface area, central disc area, and lappet length and width than controls. Pulsation rate was significantly lower, and the mean pulse-to-pulse period shorter, in the reduced pH treatment. There was, however, no significant treatment effect on either the maximum or minimum pulse-to-pulse period, suggesting that the ability for rapid pulsations was maintained. Ephyrae from the reduced pH treatment displayed a more variable pulsation behaviour, with an elevated standard deviation and root mean square of successive difference (RMSSD) in pulse-to-pulse period. In summary, reduced pH simulating future predicted Ocean Acidification conditions, had important effects on aspects of swimming behaviour and size of A. aurita ephyra, which may have consequences for survival and the population dynamics of field populations.
Differences in the responses of three scleractinians and the hydrocoral Millepora platyphylla to ocean acidification
Published 2 March 2016 Science ClosedTags: biological response, calcification, cnidaria, corals, laboratory, multiple factors, South Pacific, temperature
We tested the hypothesis that taxonomically diverse cnidarians display dissimilar responses to ocean acidification (OA), and did so by comparing the individual responses to OA of one hydrocoral and three scleractinians. The hydrocoral Millepora platyphylla and the scleractinians massive Porites spp., Acropora pulchra and Pocillopora meandrina provided a contrast of three clades of calcifying cnidarian (Milleporidae, Robusta, and Complexa). Corals were collected from the shallow back reef of Moorea, French Polynesia, and were incubated under orthogonal contrasts of 408 and 913 μatm pCO2, and 28.0 and 30.1 °C. After 19 days in these treatments, calcification of P. meandrina was reduced 55 % at 913 μatm pCO2 and 30.1 °C, but the calcification of the other three taxa was unaffected by high pCO2 at 30.1 °C; the calcification of all taxa was unaffected by high pCO2 at 28.0 °C. These results show that P. meandrina (Robusta) was strongly and negatively affected by OA, whereas A. pulchra and massive Porites spp. (Complexa) and M. platyphylla (milleporine) were unaffected by OA. The assignment of these taxa to different clades suggests that evolutionary constraints could play a role in determining the sensitivity of cnidarian calcification to OA.
Species-specific photosynthetic responses of symbiotic zoanthids to thermal stress and ocean acidification
Published 16 December 2015 Science ClosedTags: biological response, BRcommunity, cnidaria, communityMF, laboratory, multiple factors, photosynthesis, protists, temperature
Increasing sea-surface temperatures and ocean acidification (OA) are impacting physiologic processes in a variety of marine organisms. Many sea anemones, corals and jellies in the phylum Cnidaria form endosymbiotic relationships with Symbiodinium spp. (phylum Dinoflagellata) supply the hosts with fixed carbon from photosynthesis. Much work has focused on the generally negative effects of rising temperature and OA on calcification in Symbiodinium-coral symbioses, but has not directly measured symbiont photosynthesis in hospite or fixed carbon translocation from symbiont to host. Symbiodinium species or types vary in their environmental tolerance and photosynthetic capacity; therefore, primary production in symbiotic associations can vary with symbiont type. However, symbiont type has not been identified in a large portion of Symbiodinium−cnidarian studies. Future climate conditions and OA may favor non-calcifying, soft-bodied cnidarians, including zoanthids. Here we show that two zoanthid species, Palythoa sp. and Zoanthus sp., harboring different symbiont types (C1 and A4), had very different responses to increased temperature and increased partial pressure of CO2 (pCO2), or dissolved CO2, and low pH. Thermal stress did not affect carbon fixation or fixed carbon translocation in the Zoanthus sp./A4 association, and high pCO2/low pH increased carbon fixation. In contrast, both thermal stress and high pCO2/low pH greatly inhibited carbon fixation in the Palythoa sp./C1 association. However, the combined treatment of high temperature and high pCO2 increased carbon fixation relative to the treatment of high temperature alone. Our observations support the growing body of evidence that demonstrates that the response of symbiotic cnidarians to thermal stress and OA must be considered on a host-specific and symbiont-specific basis. In addition, we show that the effects of increased temperature and pCO2 on photosynthesis may change when these two stressors are combined. Understanding how carbon fixation and translocation varies among different host−symbiont combinations is critical to predicting which Symbiodinium associations may persist in warm, acidified oceans.
The impact of CO2 emissions on ‘nuisance’ marine species (video & text)
Published 6 November 2015 Science ClosedTags: algae, biological response, chordata, cnidaria, crustaceans, echinoderms, fish, mollusks, review
Anthropogenic CO2 emissions are being taken up from the atmosphere by the oceans, increasing the availability of dissolved inorganic carbon but reducing both the carbonate saturation and pH of seawater. This ocean acidification affects biological processes in a wide range of marine taxa. Here, we assess the likely responses of ‘nuisance’ species to ocean acidification, meaning those organisms that have undesirable effects from a human perspective. Based on a synthesis of evidence available to date, we predict increased growth and toxicity in harmful algal bloom species, and a significant increase in invasive algae in response to increased CO2 availability. Blooms of stinging jellyfish are also expected to increase since they are highly resilient to acidification. The effects of ocean acidification on invasive molluscs (eg, oyster drills), damaging echinoderms (eg, crown-of-thorns starfish), and a wide range of nuisance taxa will vary depending on species and location. In the USA, for example, the invasive crab Carcinus maenas is resilient to projected increases in CO2 and its impact on marine communities is expected to increase since it feeds on organisms that respond to ocean acidification with weaker defensive traits and lower recruitment. Conversely, the Red King Crab, Paralithodes camtschaticus, is adversely affected by acidification and so is expected to die back in the Barents Sea which it has invaded. Overall, we suspect that there will be an increase in nuisance species, as many have traits that are resilient to the combined warming and acidification caused by rising CO2 levels; region-specific assessments are needed to understand responses of nuisance species in local habitats. Finally, we highlight the need for targeted studies of the effects of global change on particularly harmful marine taxa such as the seaweed Caulerpa taxifolia, the starfish Asterias amurensis, several invasive ascidians, and the lionfish Pterois volitans.
Continue reading ‘The impact of CO2 emissions on ‘nuisance’ marine species (video & text)’
Carbonic anhydrase activity changes in response to increased temperature and pCO2 in Symbiodinium–zoanthid associations
Published 29 September 2015 Science ClosedTags: abundance, biological response, cnidaria, laboratory, multiple factors, North Atlantic, otherprocess, physiology, temperature
Carbon dioxide (CO2) makes up less than 1% of dissolved inorganic carbon (DIC) in the ocean. To acquire carbon dioxide for photosynthesis, many marine autotrophs rely on the enzyme carbonic anhydrase (CA) to catalyze the conversion of bicarbonate ions (HCO3−) to CO2. In zoanthids and other cnidarians with Symbiodinium spp. endosymbionts, CA is essential for transporting CO2 to symbionts for photosynthesis. Temperature and ambient DIC affect CA activity, therefore, increased sea water temperatures and ocean acidification (OA) will alter CO2 transport in symbiotic cnidarians. However, these effects are likely to be species specific for both host and symbiont, as different cnidarians and Symbiodinium spp. vary in their mechanisms of DIC transport and utilization of CA. In this study, host and symbiont CA activity in the zoanthids Palythoa sp. and Zoanthus sp. varied with thermal stress and low pH. Increased temperature inhibited algal, but not host CA activity in Zoanthus sp. polyps with A4 Symbiodinium, while temperature had no effect on CA activity in Palythoa sp. with C1 Symbiodinium. High pCO2/low pH altered algal CA activity in both zoanthid species, but host CA activity changed in Zoanthus sp. polyps only. This study shows that thermal stress and OA induce species-specific changes in CA activity, and thus DIC transport in symbiotic zoanthids. These observations suggest that CA activity in symbiotic cnidarians will be altered by climate conditions predicted for the future, and for some cnidarians, changes in CA activity may inhibit photosynthesis.
Differential carbon utilization and asexual reproduction under elevated pCO2 conditions in the model anemone, Exaiptasia pallida, hosting different symbionts
Published 16 September 2015 Science ClosedTags: biological response, cnidaria, laboratory, otherprocess, photosynthesis, primary production, protists, reproduction
Here we report the effects of elevated pCO2 on the model symbiotic anemone Exaiptasia pallida and how its association with three different strains of the endosymbiotic dinoflagellate Symbiodinium minutum (ITS2-type B1) affects its response. Exposure to elevated pCO2 (70.9 Pa) for 28 d led to an increased effective quantum yield of PSII in actinic light within two of the alga-anemone combinations. Autotrophic carbon fixation, along with the rate of carbon translocated to the animal, were significantly elevated with high pCO2. Elevated pCO2 exposure also coincided with significantly greater asexual budding rates in all tested anemones. Further, differences in photochemistry and carbon translocation rates suggest subtle differences in the response to pCO2 among the three strains of S. minutum and their host anemones. This illustrates the potential for physiological diversity at the subspecies level for this ecologically important dinoflagellate. Positive alterations in photosynthesis, carbon utilization, and fitness within this model symbiosis suggest a potential benefit from ocean acidification (OA) not yet observed within corals, which may enable these anthozoans to gain a greater ecological presence under future OA conditions.
Benthic megafauna and CO2 bubble dynamics observed by underwater photography during a controlled sub-seabed release of CO2
Published 27 July 2015 Science ClosedTags: abundance, biological response, BRcommunity, cnidaria, crustaceans, echinoderms, field, fish, mollusks, North Atlantic, otherprocess
In 2012, a controlled sub-seabed release of carbon dioxide (CO2) was conducted in Ardmucknish Bay, a shallow (12 m) coastal bay on the west coast of Scotland. During the experiment, CO2 gas was released 12 m below the seabed for 37 days, causing significant disruption to sediment and water carbonate chemistry as the gas passed up through the sediment and into the overlying water. One of the aims of the study was to investigate how the impacts caused by leakage from geological CO2 Capture and Storage (CCS) could be detected and quantified in the context of natural heterogeneity and dynamics. To do this underwater photography was used to analyze (i) the benthic megafaunal response to the CO2 release and (ii) the dynamics of the CO2 bubble streams, emerging from the seabed into the overlying water column. The frequently observed megafauna species in the study area were Virgularia mirabilis (Cnidaria), Turritella communis (Mollusca), Asterias rubens (Echinodermata), Pagurus bernhardus (Crustacea), Liocarcinus depurator (Crustacea), and Gadus morhua (Osteichthyes). No discernable abnormal behavior was observed for these megafauna, in any of the zones investigated, during or after the CO2 release. Time-lapse photography revealed that the intensity and presence of the CO2 bubble plume was affected by the tides, with the most active bubbling seen at low tides and the larger hydrostatic pressure at high tide suppressing CO2 bubbling from the seabed.
Synergistic effects of hypoxia and increasing CO2 on benthic invertebrates of the central Chilean coast
Published 6 July 2015 Science ClosedTags: biological response, cnidaria, crustaceans, echinoderms, laboratory, mollusks, multiple factors, oxygen, respiration, South Pacific
Ocean acidification and hypoxic events are an increasing worldwide problem, but the synergetic effects of these factors are seldom explored. However, this synergetic occurrence of stressors is prevalent. The coastline of Chile not only suffers from coastal hypoxia but the cold, oxygen-poor waters in upwelling events are also supersaturated in CO2, a study site to explore the combined effect of ocean acidification and hypoxia. We experimentally evaluated the metabolic response of different invertebrate species (2 anthozoans, 9 molluscs, 4 crustaceans, 2 echinoderms) of the coastline of central Chile (33°30’S, 71°37’W) to hypoxia and ocean acidification within predicted levels and in a full factorial design. Organisms were exposed to 4 different treatments (ambient, low oxygen, high CO2, and the combination of low oxygen and high CO2) and metabolism was measured after 3 and 6 days. We show that the combination of hypoxia and increased pCO2 reduces the respiration significantly, compared to a single stressor. The evaluation of synergistic pressures, a more realistic scenario than single stressors, is crucial to evaluate the effect of future changes for coastal species and our results provide the first insight on what might happen in the next 100 years.
Effects of food and CO2 on growth dynamics of polyps of two scyphozoan species (Cyanea capillata and Chrysaora hysoscella)
Published 12 June 2015 Science ClosedTags: biogeochemistry, biological response, cnidaria, laboratory, morphology, multiple factors, nutrients, respiration
Increasing anthropogenic CO2 concentration in the atmosphere is altering sea water carbonate chemistry with unknown biological and ecological consequences. Whereas some reports are beginning to emerge on the effects of ocean acidification (OA) on fish, very little is known about the impact of OA on jellyfish. In particular, the benthic stages of metagenetic species are virtually unstudied in this context despite their obvious importance for bloom dynamics. Hence, we conducted tri-trophic food chain experiments using the algae Rhodomonas salina as the primary producer, the copepod Acartia tonsa as the primary consumer and the benthic life stage of the scyphozoans Cyanea capillata and Chrysaora hysoscella as secondary consumers. Two experiments were conducted examining the effects of different levels of CO2 and food quality (experiment 1) and the effect of food quality and quantity (experiment 2) on the growth and respiration of scyphozoan polyps. Polyp growth and carbon content (µg polyp−1) were not affected by the CO2 treatments, but were significantly negatively affected by P limitation of the food in C. capillata but not in Ch. hysoscella. Growth and carbon content were reduced in low-food treatments, but increased with decreasing P limitation in high- and low-food treatments in C. capillata. Respiration was not significantly influenced by food quality and quantity in C. capillata. We conclude that phosphorus can be a limiting factor affecting the fitness of scyphopolyps and that P-limited food is of poor nutritional quality. Furthermore, OA, at least using realistic end-of-century scenarios, will have no direct effect on the growth of scyphistomae.
