Ocean acidification (OA) and associated shifts in carbonate chemistry represent major threats to marine organisms, particularly calcifiers. OA effects can be influenced by other environmental variables, including the biotic environment. This study investigated the individual and interactive effects of OA and algal density, acting through biofilm composition, on post-larval and juvenile abalone (Haliotis tuberculata). In a three-month factorial experiment, abalone were exposed from metamorphosis onward to two pH conditions (ambient 8.0 and reduced 7.7) and two initial densities of the green alga Ulvella lens on settlement plates. Biofilm biomass and composition were characterised using spectral reflectance and HPLC pigment analysis. Biological (density, length), physiological (respiration rate), behavioural (hiding response) and shell parameters (colour, surface corrosion, strength) of abalone were measured throughout the experiment. Biofilm biomass and composition remained relatively stable under both pH conditions, though greater variability in algal biomass occurred at low initial Ulvella density. Post-larval density and total length decreased significantly under low pH, while high Ulvella density reduced juvenile length at 80 days, likely due to competition between algal groups. A pH × Ulvella interaction affected shell fracture resistance and colouration, but not metabolism or behaviour, indicating that juvenile abalone maintained vital functions. Overall, the results confirm the sensitivity of early H. tuberculata stages to moderate OA (−0.3 pH units) and highlight indirect macroalgal effects through changes in diatom communities. In natural environments, the capacity of abalone to cope with future OA will depend on complex trade-offs between direct acidification effects and food-related biotic interactions.
Continue reading ‘Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata’Posts Tagged 'communityMF'
Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata
Published 23 December 2025 Science ClosedTags: biological response, communityMF, laboratory, mollusks, morphology, multiple factors, North Atlantic, performance, phytoplankton, reproduction, respiration
Impact of crustose coralline algae, ocean acidification, and ocean warming on larval pinto abalone settlement and juvenile survival
Published 11 November 2025 Science ClosedTags: algae, biological response, BRcommunity, communityMF, laboratory, mollusks, morphology, mortality, multiple factors, North Pacific, reproduction, temperature
Highlights
- Ocean acidification reduced pinto abalone settlement and survival in the hatchery.
- Ocean acidification is likely a greater threat than warming to Washington pinto abalone.
- Use of a natural settlement inducer improves abalone settlement and survival.
- Coralline algae may improve survival of pinto abalone under ocean acidification.
Abstract
Since 1994, Washington State (USA) has experienced a 97 % drop in the native pinto abalone population. Since 2007, conservation aquaculture initiatives have been underway to return the population to a self-sustaining level. Successful restoration, however, depends on both the ability to successfully raise juveniles in hatchery settings and the capacity of outplanted pinto abalone to survive and reproduce in the wild as threats of ocean acidification and warming continue to increase. Crustose coralline algae (CCA) can play an important role in restoration efforts by acting as natural inducers of larval settlement. Additionally, studies have shown that CCA can create a boundary layer with elevated pH, potentially providing a refuge for benthic species. We examined the settlement of pinto abalone under different environmental conditions (7.90 pH/14 °C (ambient), 7.90 pH/18 °C, 7.55 pH/14 °C; and 7.55 pH/18 °C) using two substrates: CCA-covered rocks and clean rocks with GABA (a chemical settlement inducer). Low pH negatively impacted larval settlement. Though settlement was higher with CCA than with GABA, this difference was not statistically significant. Juvenile survival was negatively impacted by low pH, but positively impacted by CCA presence, demonstrating the potential of CCA to increase juvenile pinto abalone survival and ameliorate the negative effects of low pH. Using CCA in hatchery culture and selecting sites with CCA cover for pinto abalone outplants may improve the efficiency of restoration in Washington.
Continue reading ‘Impact of crustose coralline algae, ocean acidification, and ocean warming on larval pinto abalone settlement and juvenile survival’Quantifying the impacts of multiple stressors on the production of marine benthic resources
Published 11 March 2024 Science ClosedTags: abundance, algae, biogeochemistry, biological response, BRcommunity, chemistry, communityMF, laboratory, mesocosms, methods, modeling, mollusks, morphology, mortality, multiple factors, North Atlantic, nutrients, otherprocess, performance, physiology, regionalmodeling, temperature
Coastal ecosystems are among the most heavily affected by climate change and anthropogenic activities, which impacts their diversity, productivity and functioning and puts many of the key ecosystem services that they provide at risk. Although empirical studies have moved beyond single-stressor-single-species experiments with limited extrapolation potential and have increasingly investigated the cumulative effects of simultaneously occurring multiple stressors, consistent generalities have not yet been identified. Upscaling from controlled experiments to natural ecosystems, therefore, remains an unsolved challenge. Disentangling the independent and cumulative effects of multiple stressors across different levels of biological complexity, revealing the underlying mechanisms and understanding how coastal ecosystems may respond to predicted scenarios of global change is critical to manage and protect our natural capital.
In this thesis, I advance multiple stressor research by applying complementary approaches to quantify the impact of multiple stressors on marine benthic resources and thereby help predict the consequences of expected climate change for coastal habitats. First, I present the newly developed experimental platform QIMS (Quantifying the Impacts of Multiple Stressors) that overcomes some of the shortfalls of previous multiple stressor research (Chapter 2). Second, in a novel empirical study, I investigate the independent and combined effects of moderate ocean warming and acidification on the functioning and production of mussels and algae, considering the effects of interspecific interactions in the presence or absence of the respective other species (Chapter 3). Third, I synthesise monitoring data from Dublin Bay (representative of a typical metropolitan estuary) using conditional interference and a Bayesian Network model and provide alternative system trajectories according to different climate change scenarios. From this new model, I deepen the understanding of the complex linkages between environmental conditions and the diversity and functioning of Dublin Bay to support local decision making and management (Chapter 4).
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Continue reading ‘Quantifying the impacts of multiple stressors on the production of marine benthic resources’Turf algae drives coral bioerosion under high CO2
Published 20 February 2024 Science ClosedTags: abundance, algae, biogeochemistry, biological response, BRcommunity, calcification, chemistry, communityMF, corals, dissolution, field, laboratory, morphology, multiple factors, North Pacific, otherprocess, photosynthesis, respiration, temperature, vents
Turf algal prevalence will increase in coral ecosystems under ocean acidification yet their contribution towards the ongoing and projected degradation of reefs is often overlooked. Turf algal settlement was induced on exposed coral skeleton adjacent to live coral tissue to investigate coral-turf algal interactions through a combination of laboratory and field transplantation (shallow volcanic CO2 seep) experiments across two temperature regimes. Here, we show that turf algae are competitively favored over corals under high pCO2 conditions. Turf algae-associated biological activity locally acidified the microenvironment overlying the exposed coral skeleton, leading to its bioerosion. Increases in coral-turf algal interactions could shift coral ecosystems towards net dissolution and should be integrated into global accretion models when considering future carbonate budgets under climate change.
Continue reading ‘Turf algae drives coral bioerosion under high CO2’Hidden cost of pH variability in seagrass beds on marine calcifiers under ocean acidification
Published 9 February 2024 Science ClosedTags: biological response, calcification, chemistry, communityMF, echinoderms, growth, laboratory, light, mortality, multiple factors, North Atlantic
Highlights
- The presence of seagrass creates variability in pH/pCO2.
- High pCO2/low pH negatively impacts growth and calcification of sea urchin larvae.
- The variability associated with the presence of seagrass negatively impacts growth under ocean acidification.
- Two different calcification strategies are observed in presence and absence of seagrass.
Abstract
Coastal ecosystems experience large environmental variability leading to local adaptation. The key role of variability and adaptation in modulating the biological sensitivity to ocean acidification is increasingly acknowledged. Monitoring and understanding the ecological niche at the right spatio-temporal scale is key to understand the sensitivity of any organism and ecosystems. However, the role of the variability in relevant carbonate chemistry parameters as a driver is often overlooked. For example, the balance between photosynthesis and respiration over the day/night cycle is leading to high pH/pCO2 variability in seagrass beds. We hypothesized that (i) the calcifying larvae of the sea urchin Echinus esculentus exposed to seagrass-driven variability would have some physiological mechanisms to respond to such variability; and (ii) these mechanisms would reach their limit under ocean acidification. We compared the presence and absence of the seagrass Zostera marina in flow through mesocosms fed with seawater with 4 pHs. The carbonate chemistry was monitored and biological response of a sea urchin larvae was documented over 3 weeks. Growth and net calcification rates were measured twice a day to encompass diurnal variability. Our results show that larvae growth rate significantly decreased with decreasing average pHT in both absence and presence of seagrass. Moreover, sea urchin larvae showed a slower growth rate in presence of seagrass, only visible in the lowest pH conditions. In addition, larvae raised in presence of seagrass, maximized calcification during the day, and lower their calcification during the night. In contrast, no significant difference was observed between day and night for the net calcification rate in larvae raised in absence of seagrass. Our results demonstrate the limit of local adaptation to the present range of variability under ocean acidification conditions. It also demonstrates that photosynthetic ecosystems such as seagrass may not play a role of refuge against future ocean acidification.
Continue reading ‘Hidden cost of pH variability in seagrass beds on marine calcifiers under ocean acidification’Effects of ocean acidification and warming on physiological and behavioural responses of an herbivore snail to waterborne predator cues
Published 30 October 2023 Science ClosedTags: biological response, communityMF, laboratory, mollusks, morphology, multiple factors, performance, respiration, South Pacific, temperature
Ocean Acidification (OA) and Ocean Warming (OW) represent major climate stressors that may disrupt species interactions. However, despite the knowledge about the impacts of OA and OW on the performance of individual species, it is still unclear how biological interactions can be modified by the combined effects of these stressors. Consequently, in this study, we assess the effects of changes in temperature (12 °C and 20 °C) and pCO2 (500 and 1600 μatm) levels in seawater, along with the presence/absence of waterborne cues from the predator crab Homalaspis plana on the physiological and behavioural performance of the snail Tegula atra. Snail consumption rate was positively affected by OW and negatively by predator cues whereas absorption efficiency (AE) was positively affected by OW without interactions among these stressors. Oxygen uptake of snails reared in OW conditions was greater than those in control conditions, but only at control pCO2 levels. When pCO2 level was also raised, the positive effect of warmer temperature on oxygen uptake was reduced. While biomass was negatively affected by OW, OA and predator cues, without interactions. In the presence of predator cues the self-righting times of snails were significantly slower in individuals reared at OW conditions. Additionally, OA and OW conditions do not affect the prey hunting, efficiency (consumption) and preference, and claw strength of the predatory crab. These results indicate that OA and OW affect physiological and behavioral traits of snails but no the predatory behavior of crab. This environmentally-induced decoupling of co-evolutionary predator-prey dynamics may have important consequences on the structure and stability of coastal communities and ecosystems under the influence of climate change.
Continue reading ‘Effects of ocean acidification and warming on physiological and behavioural responses of an herbivore snail to waterborne predator cues’Ocean acidification and predation risk, in isolation and in combination, show strong effects on marine mussels
Published 27 October 2023 Science ClosedTags: biological response, communityMF, laboratory, mesocosms, mollusks, morphology, multiple factors, performance
Carbon dioxide-induced ocean acidification is producing a range of new selection pressures on marine calcifying organisms that show phenotypic plasticity in their shell morphology in response to predators. Although there are numerous studies on the effects of ocean acidification and predation risk on marine bivalves in isolation, information concerning their combined effects is still lacking. To bridge this gap, we conducted a long-term mesocosm experiment using mussel populations with different histories of predator exposure: crab-experienced and crab-naïve. Mussels were exposed to either lower pH or crab cues and the combination of both of these treatments for 4 mo. We demonstrate that both crab-experienced and crab-naïve mussels have heavier, thicker, rounder and, thus, stronger shells in response to crab cues, whereas low pH significantly decreased shell mass, thickness and strength. Mussels with previous crab experience showed greater plasticity in response to crab cues than crab-naïve mussels. However, the differences in plasticity between naïve and crab-experienced mussels to crab cues disappeared in the acidification treatment. Exposure to low pH and crab cues resulted in antagonistic interactions for all traits, except for shell length, where the combined effect was additive. However, there was no difference between populations in the interaction type for any of the traits. Our study provides increased understanding of potential implications for mussel populations under climate change.
Continue reading ‘Ocean acidification and predation risk, in isolation and in combination, show strong effects on marine mussels’Optimizing marine macrophyte capacity to locally ameliorate ocean acidification under variable light and flow regimes: insights from an experimental approach
Published 19 October 2023 Science ClosedTags: biological response, chemistry, communityMF, communitymodeling, flow, laboratory, light, modeling, multiple factors, North Atlantic, photosynthesis
The urgent need to remediate ocean acidification has brought attention to the ability of marine macrophytes (seagrasses and seaweeds) to take up carbon dioxide (CO2) and locally raise seawater pH via primary production. This physiological process may represent a powerful ocean acidification mitigation tool in coastal areas. However, highly variable nearshore environmental conditions pose uncertainty in the extent of the amelioration effect. We developed experiments in aquaria to address two interconnected goals. First, we explored the individual capacities of four species of marine macrophytes (Ulva lactuca, Zostera marina, Fucus vesiculosus and Saccharina latissima) to ameliorate seawater acidity in experimentally elevated pCO2. Second, we used the most responsive species (i.e., S. latissima) to assess the effects of high and low water residence time on the amelioration of seawater acidity in ambient and simulated future scenarios of climate change across a gradient of irradiance. We measured changes in dissolved oxygen, pH, and total alkalinity, and derived resultant changes to dissolved inorganic carbon (DIC) and calcium carbonate saturation state (Ω). While all species increased productivity under elevated CO2, S. latissima was able to remove DIC and alter pH and Ω more substantially as CO2 increased. Additionally, the amelioration of seawater acidity by S. latissima was optimized under high irradiance and high residence time. However, the influence of water residence time was insignificant under future scenarios. Finally, we applied predictive models as a function of macrophyte biomass, irradiance, and residence time conditions in ambient and future climatic scenarios to allow projections at the ecosystem level. This research contributes to understanding the biological and physical drivers of the coastal CO2 system.
Continue reading ‘Optimizing marine macrophyte capacity to locally ameliorate ocean acidification under variable light and flow regimes: insights from an experimental approach’Seagrass meadows as ocean acidification refugia for sea urchin larvae
Published 12 October 2023 Science ClosedTags: biological response, chemistry, communityMF, echinoderms, laboratory, Mediterranean, mesocosms, morphology, multiple factors
Higlights
- Sea urchin larvae were grown at ambient or low pH in tanks with or without plants.
- Plant photosynthesis increased pH and altered seawater chemistry at both pH levels.
- Positive effects of plant metabolism on larval development and growth at low pH
- Seagrass meadows as a tool against climate-driven loss of calcifying species
Abstract
Foundation species have been widely documented to provide suitable habitats for other species by ameliorating stressful environmental conditions. Nonetheless, their role in rescuing stress-sensitive species from adverse conditions due to climate change remains often unexplored. Here, we performed a mesocosm experiment to assess whether the seagrass, Posidonia oceanica, through its photosynthetic activity, could mitigate the negative effects of ocean acidification on larval development and growth of the calcifying sea urchin, Paracentrotus lividus. Sea urchin larvae at early and late developmental stages that are generally associated to benthic habitats, were grown in aquaria with or without P. oceanica plants, under ambient or low pH conditions predicted by the end of the century under the worst climate scenario (RCP8.5). The percentage of abnormal larvae and their total body length under different experimental conditions were assessed on early- (i.e., pluteus; 72 h post-fertilization) and final-developmental stages (i.e., echinopluteus; 30 days post-fertilization), respectively. The presence of P. oceanica increased mean daily pH values of ∼0.1 and ∼0.15 units at ambient and low pH conditions, respectively, compared with tanks without plants. When grown at low pH in association with P. oceanica, plutei showed a ∼23 % reduction of malformations and echinoplutei a ∼34 % increase in total body length, respectively, compared with larvae developing in tanks without plants. Our results suggest that P. oceanica, by increasing pH and altering seawater carbonate chemistry through its metabolic activity, could buffer the negative effects of ocean acidification on calcifying organisms and could, thus, represent a tool against climate-driven loss of biodiversity.
Continue reading ‘Seagrass meadows as ocean acidification refugia for sea urchin larvae’Direct and indirect impacts of ocean acidification and warming on algae-herbivore interactions in intertidal habitats
Published 29 September 2023 Science ClosedTags: algae, biological response, BRcommunity, communityMF, laboratory, mollusks, multiple factors, performance, physiology, temperature
Highlights
- Ocean acidification (OA) and warming (OW) alter algae-herbivore interactions
- OA and OW modify biochemical composition of the kelp Lessonia spicata.
- Changes in kelp biochemical composition affect snail’s feeding behaviour.
- OW and OA conditions increased snail’s metabolic stress.
- Nutritional quality of food plays a key role on grazers’ physiological energetics.
Abstract
Anthropogenically induced global climate change has caused profound impacts in the world ocean. Climate change related stressors, like ocean acidification (OA) and warming (OW) can affect physiological performance of marine species. However, studies evaluating the impacts of these stressors on algae-herbivore interactions have been much more scarce. We approached this issue by assessing the combined impacts of OA and OW on the physiological energetics of the herbivorous snail Tegula atra, and whether this snail is affected indirectly by changes in biochemical composition of the kelp Lessonia spicata, in response to OA and OW. Our results show that OA and OW induce changes in kelp biochemical composition and palatability (organic matter, phenolic content), which in turn affect snails’ feeding behaviour and energy balance. Nutritional quality of food plays a key role on grazers’ physiological energetics and can define the stability of trophic interactions in rapidly changing environments such as intertidal communities.
Continue reading ‘Direct and indirect impacts of ocean acidification and warming on algae-herbivore interactions in intertidal habitats’Brown seaweed Nemacystus decipiens intensifies the effects of ocean acidification on coral Montipora digitata
Published 22 August 2023 Science ClosedTags: algae, biological response, calcification, communityMF, corals, laboratory, multiple factors, North Pacific, photosynthesis
Photosynthetic marine macrophytes such as seaweeds have been proposed to provide habitat refugia for marine calcifiers against ocean acidification (OA) by increasing the local pH. However, the effectiveness of seaweed as a potential habitat refugia for marine calcifiers such as corals remains to be investigated. This study focused on the seaweed Nemacystus decipiens, which are widely farmed in the shallow reef lagoon of Okinawa coral reefs, Japan, and aimed to evaluate their response to high pCO2 and whether they can mitigate the effect of high pCO2 on the coral Montipora digitata. Corals were cultured with and without seaweed under control (300–400 μatm) or high pCO2 conditions (OA, 900–1000 μatm) for 2 weeks. Results showed that all photo-physiological parameters examined in the seaweed N. decipiens were not affected by high pCO2, suggesting that OA will not positively affect their productivity. The calcification rate of the coral M. digitata was found to decrease under OA and the effect was further exaggerated by the presence of seaweed. The present study suggests that farming seaweeds will not act as a potential habitat refugia for adjacent corals under future OA, but instead can exaggerate the negative effect of OA on coral calcification.
Continue reading ‘Brown seaweed Nemacystus decipiens intensifies the effects of ocean acidification on coral Montipora digitata’Effects of pH, eelgrass, and settlement substrate on the growth of juvenile magallana (crassostrea) gigas, a commercially important oyster species
Published 6 July 2023 Science ClosedTags: biogeochemistry, biological response, chemistry, communityMF, field, laboratory, mollusks, morphology, multiple factors, North Pacific, performance
Worsening ocean acidification (OA), resulting from ongoing absorption of atmospheric carbon dioxide (CO2) by the oceans, threatens marine life globally. Calcifying organisms, especially their early life stages, are particularly vulnerable; this includes the economically important Pacific oyster, Magallana (Crassostrea) gigas. Uptake of dissolved CO2 through photosynthesis by seagrasses, like eelgrass (Zostera marina), may benefit calcifying organisms by increasing pH and carbonate availability. I conducted laboratory and field experiments to quantify carbonate chemistry modification by eelgrass and potential mitigation of OA impacts on growth in juvenile Pacific oysters. In the laboratory experiment, daytime net photosynthesis by eelgrass increased seawater pH, while nighttime net respiration reduced pH though to a lesser extent; both effects grew stronger as the pH of incoming seawater decreased. This is consistent with the expectation that eelgrass will benefit from increased aqueous CO2 levels and suggests that the importance of carbonate chemistry modification by eelgrass and its role as a refugium may increase as OA proceeds. Under the conditions tested, however, eelgrass effects on pH were modest and did not affect oyster growth in the lab or field. In the lab, oysters settled on shell flour grew faster than those on shell chunks, but unlike those on chunks, the growth rate of oysters on flour decreased significantly in low pH treatments. One hypothesis consistent with these results is that the boundary layer around shell chunks may have slowed oyster growth by limiting food availability but that it also reduced sensitivity to low pH via enhanced carbonate saturation.
Continue reading ‘Effects of pH, eelgrass, and settlement substrate on the growth of juvenile magallana (crassostrea) gigas, a commercially important oyster species’Effect of ocean acidification on the growth, response and hydrocarbon degradation of coccolithophore-bacterial communities exposed to crude oil
Published 12 April 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, communityMF, laboratory, molecular biology, mortality, multiple factors, otherprocess, photosynthesis, phytoplankton, prokaryotes, toxicants
Hydrocarbon-degrading bacteria, which can be found living with eukaryotic phytoplankton, play a pivotal role in the fate of oil spillage to the marine environment. Considering the susceptibility of calcium carbonate-bearing phytoplankton under future ocean acidification conditions and their oil-degrading communities to oil exposure under such conditions, we investigated the response of non-axenic E. huxleyi to crude oil under ambient versus elevated CO2 concentrations. Under elevated CO2 conditions, exposure to crude oil resulted in the immediate decline of E. huxleyi, with concomitant shifts in the relative abundance of Alphaproteobacteria and Gammaproteobacteria. Survival of E. huxleyi under ambient conditions following oil enrichment was likely facilitated by enrichment of oil-degraders Methylobacterium and Sphingomonas, while the increase in relative abundance of Marinobacter and unclassified Gammaproteobacteria may have increased competitive pressure with E. huxleyi for micronutrient acquisition. Biodegradation of the oil was not affected by elevated CO2 despite a shift in relative abundance of known and putative hydrocarbon degraders. While ocean acidification does not appear to affect microbial degradation of crude oil, elevated mortality responses of E. huxleyi and shifts in the bacterial community illustrates the complexity of microalgal-bacterial interactions and highlights the need to factor these into future ecosystem recovery projections.
Continue reading ‘Effect of ocean acidification on the growth, response and hydrocarbon degradation of coccolithophore-bacterial communities exposed to crude oil’Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica
Published 4 February 2021 Science ClosedTags: abundance, algae, biological response, communityMF, field, laboratory, morphology, multiple factors, nitrogen fixation, North Atlantic, nutrients
Coastal ecosystems are prone to multiple anthropogenic and natural stressors including eutrophication, acidification, and invasive species. While the growth of some macroalgae can be promoted by excessive nutrient loading and/or elevated pCO2, responses differ among species and ecosystems. Native to the western Pacific Ocean, the filamentous, turf-forming rhodophyte, Dasysiphonia japonica, appeared in estuaries of the northeastern Atlantic Ocean during the 1980s and the northwestern Atlantic Ocean during the late 2000s. Here, we report on the southernmost expansion of the D. japonica in North America and the effects of elevated nutrients and elevated pCO2 on the growth of D. japonica over an annual cycle in Long Island, New York, USA. Growth limitation of the macroalga varied seasonally. During winter and spring, when water temperatures were < 15 °C, growth was significantly enhanced by elevated pCO2 (p < 0.05). During summer and fall, when the water temperature was 15–24 °C, growth was significantly higher under elevated nutrient treatments (p < 0.05). When temperatures reached 28 °C, the macroalga grew poorly and was unaffected by nutrients or pCO2. The δ13C content of regional populations of D. japonica was −30‰, indicating the macroalga is an obligate CO2-user. This result, coupled with significantly increased growth under elevated pCO2 when temperatures were < 15 °C, indicates this macroalga is carbon-limited during colder months, when in situ pCO2 was significantly lower in Long Island estuaries compared to warmer months when estuaries are enriched in metabolically derived CO2. The δ15N content of this macroalga (9‰) indicated it utilized wastewater-derived N and its N limitation during warmer months coincided with lower concentrations of dissolved inorganic N in the water column. Given the stimulatory effect of nutrients on this macroalga and that eutrophication can promote seasonally elevated pCO2, this study suggests that eutrophic estuaries subject to peak annual temperatures < 28 °C may be particularly vulnerable to future invasions of D. japonica as ocean acidification intensifies. Conversely, nutrient reductions would serve as a management approach that would make coastal regions more resilient to invasions by this macroalga.
Continue reading ‘Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica’Keystone predators govern the pathway and pace of climate impacts in a subarctic marine ecosystem
Published 14 September 2020 Science ClosedTags: algae, biological response, communityMF, echinoderms, multiple factors, North Pacific
Predator loss and climate change are hallmarks of the Anthropocene yet their interactive effects are largely unknown. Here, we show that massive calcareous reefs, built slowly by the alga Clathromorphum nereostratum over centuries to millennia, are now declining because of the emerging interplay between these two processes. Such reefs, the structural base of Aleutian kelp forests, are rapidly eroding because of overgrazing by herbivores. Historical reconstructions and experiments reveal that overgrazing was initiated by the loss of sea otters, Enhydra lutris (which gave rise to herbivores capable of causing bioerosion), and then accelerated with ocean warming and acidification (which increased per capita lethal grazing by 34 to 60% compared with preindustrial times). Thus, keystone predators can mediate the ways in which climate effects emerge in nature and the pace with which they alter ecosystems.
Continue reading ‘Keystone predators govern the pathway and pace of climate impacts in a subarctic marine ecosystem’Predator populations differ in their foraging responses to acute seawater acidification
Published 13 August 2020 Science ClosedTags: biological response, communityMF, laboratory, mollusks, multiple factors, North Pacific, performance
Local adaptation can cause predator populations to vary in traits and their effects on prey, but few studies have tested whether divergent predator populations respond differently to acute environmental stressors. We tested how Nucella dogwhelks from 3 populations with natural exposure to distinct environmental regimes in the California Current System altered consumption of mussel prey (Mytilus californianus) in ambient (pH 8.0, 429 µatm partial pressure of CO2 [pCO2]) and acidified (pH 7.6, 1032 µatm pCO2) seawater. Overall, experimental acidification increased the variation in consumption time observed among populations. We found reduced consumption time for the population that experienced more frequent exposure to low pH conditions in nature but not for populations with less prior exposure. Exposure to acidification also altered the individual components of consumption time—search time and handling time—depending on source population. These results indicate that impaired predator performance is not a universal response to acidification, that predation responses to acute acidification can be population specific, and that individual population responses may relate to prior exposure. Our study highlights how population-specific responses to climate change can lead to differences in ecological effects that may restructure prey communities at local scales.
Epiphytes provide micro-scale refuge from ocean acidification
Published 12 August 2020 Science ClosedTags: algae, biogeochemistry, biological response, calcification, communityMF, field, laboratory, Mediterranean, mesocosms, multiple factors, photosynthesis, physiology, respiration
Highlights
• OA induced bleaching and reduced metabolism in non-epiphytized coralline.
• Epiphytized corallines were less susceptible to the detrimental effects of OA.
• Epiphytized corallines had thicker diffusive boundary layer than non-epiphytized.
• Non-calcifying epiphytes provide small scale refuge from OA.
• Epiphytic refugia may protect corallines under future OA conditions.
Abstract
Coralline algae, a major calcifying component of coastal shallow water communities, have been shown to be one of the more vulnerable taxonomic groups to ocean acidification (OA). Under OA, the interaction between corallines and epiphytes was previously described as both positive and negative. We hypothesized that the photosynthetic activity and the complex structure of non-calcifying epiphytic algae that grow on corallines ameliorate the chemical microenvironmental conditions around them, providing protection from OA. Using mesocosm and microsensor experiments, we showed that the widespread coralline Ellisolandia elongata is less susceptible to the detrimental effects of OA when covered with non-calcifying epiphytic algae, and its diffusive boundary layer is thicker than when not covered by epiphytes. By modifying the microenvironmental carbonate chemistry, epiphytes, facilitated by OA, create micro-scale shield (and refuge) with more basic conditions that may allow the persistence of corallines associated with them during acidified conditions. Such ecological refugia could also assist corallines under near-future anthropogenic OA conditions.
Continue reading ‘Epiphytes provide micro-scale refuge from ocean acidification’
Amelioration of ocean acidification and warming effects through physiological buffering of a macroalgae
Published 22 July 2020 Science ClosedTags: algae, biological response, calcification, communityMF, laboratory, morphology, multiple factors, photosynthesis, protists, respiration, temperature
Concurrent anthropogenic global climate change and ocean acidification are expected to have a negative impact on calcifying marine organisms. While knowledge of biological responses of organisms to oceanic stress has emerged from single‐species experiments, these do not capture ecologically relevant scenarios where the potential for multi‐organism physiological interactions is assessed. Marine algae provide an interesting case study, as their photosynthetic activity elevates pH in the surrounding microenvironment, potentially buffering more acidic conditions for associated epiphytes. We present findings that indicate increased tolerance of an important epiphytic foraminifera, Marginopora vertebralis , to the effects of increased temperature (±3°C) and p CO2 (~1,000 µatm) when associated with its common algal host, Laurencia intricata . Specimens of M. vertebralis were incubated for 15 days in flow‐through aquaria simulating current and end‐of‐century temperature and pH conditions. Physiological measures of growth (change in wet weight), calcification (measured change in total alkalinity in closed bottles), photochemical efficiency (Fv/Fm ), total chlorophyll, photosynthesis (oxygen flux), and respiration were determined. When incubated in isolation, M. vertebralis exhibited reduced growth in end‐of‐century projections of ocean acidification conditions, while calcification rates were lowest in the high‐temperature, low‐pH treatment. Interestingly, association with L. intricata ameliorated these stress effects with the growth and calcification rates of M. vertebralis being similar to those observed in ambient conditions. Total chlorophyll levels in M. vertebralis decreased when in association with L. intricata , while maximum photochemical efficiency increased in ambient conditions. Net production estimates remained similar between M. vertebralis in isolation and in association with L. intricata , although both production and respiration rates of M. vertebralis were significantly higher when associated with L. intricata . These results indicate that the association with L. intricata increases the resilience of M. vertebralis to climate change stress, providing one of the first examples of physiological buffering by a marine alga that can ameliorate the negative effects of changing ocean conditions.
Alkaline guts contribute to immunity during exposure to acidified seawater in the sea urchin larva
Published 13 July 2020 Science ClosedTags: biological response, communityMF, echinoderms, laboratory, molecular biology, multiple factors, physiology, reproduction
Larval stages of members of the Abulacraria superphylum including echinoderms and hemichordates have highly alkaline midguts. To date, the reason for the evolution of such extreme pH conditions in the gut of these organisms remains unknown. Here, we test the hypothesis that, analogous to the acidic stomachs of vertebrates, these alkaline conditions may represent a first defensive barrier to protect from environmental pathogens. pH-optimum curves for five different species of marine bacteria demonstrated a rapid decrease in proliferation rates by 50–60% between pH 8.5 and 9.5. Using the marine bacterium Vibrio diazotrophicus, which elicits a coordinated immune response in the larvae of the sea urchin Strongylocentrotus purpuratus, we studied the physiological responses of the midgut pH regulatory machinery to this pathogen. Gastroscopic microelectrode measurements demonstrate a stimulation of midgut alkalization upon infection with V. diazotrophicus accompanied by an upregulation of acid–base transporter transcripts of the midgut. Pharmacological inhibition of midgut alkalization resulted in an increased mortality rate of larvae during Vibrio infection. Reductions in seawater pH resembling ocean acidification conditions lead to moderate reductions in midgut alkalization. However, these reductions in midgut pH do not affect the immune response or resilience of sea urchin larvae to a Vibrio infection under ocean acidification conditions. Our study addressed the evolutionary benefits of the alkaline midgut of Ambulacraria larval stages. The data indicate that alkaline conditions in the gut may serve as a first defensive barrier against environmental pathogens and that this mechanism can compensate for changes in seawater pH.
The ability of fragmented kelp forests to mitigate ocean acidification and the effects of seasonal upwelling on kelp-purple sea urchin interactions
Published 25 June 2020 Science ClosedTags: abundance, algae, biogeochemistry, biological response, chemistry, communityMF, echinoderms, field, laboratory, mesocosms, morphology, mortality, multiple factors, North Pacific, otherprocess, performance
Bull kelp (Nereocystis leutkeana) forests along the coast for northern California have decreased dramatically as a result of a ‘perfect storm’ of multiple environmental stressors. The disappearance of a predatory sea star and subsequent increase in purple sea urchins (Strongylocentrotus purpuratus) and the recurrence of marine heat waves have caused these once diverse ecosystems to be rapidly converted into relative species-depauperate urchin barrens. By examining the interactive effects of both a rapidly changing abiotic environment and the increase in urchin grazing pressure that is affecting this vital ecosystem, we can better understand its ultimate fate and make better-informed decisions to manage and protect it. As once large and persistent kelp forests are converted into fragmented landscapes of small kelp patches, kelp’s ability to take up dissolved inorganic carbon and reduce nearby acidity and increase both dissolved oxygen and bio-available calcium carbonate may be reduced, preventing it from serving as an environmental stress-free ‘oasis’ of reduced environmental stresses for local marine organisms and affecting ecosystem dynamics. In my first chapter, I examined whether small, fragmented kelp patches are able to retain their ability to alter local seawater chemistry to the same extent a large persistent kelp forests that have been studied previously. I found that in the canopies of small kelp patches, multiple parameters of carbonate chemistry fluctuated more than in the kelp benthos and in adjacent urchin barrens, consistent with metabolic activity by the kelp. Further, kelp fragments increased pH and aragonite saturation and decreased pCO2 during the day to a similar degree as large, intact kelp forests. These results suggest that small kelp patches could mitigate OA stress during the day and serve as spatial and temporal refugia for canopy-dwelling organisms. I also found that the benthic environment in kelp forests and adjacent urchin barrens is subject to unbuffered decreases in temperature, dissolved oxygen and pH. Thus, in chapter two, I assessed how current-day and future-predicted fluctuations in the duration and magnitude of these upwelling-associated stressors would impact the grazing, growth, and survivorship of purple urchins from kelp forest and urchin barren habitats. With upwelling predicted to increase in both intensity and duration with global climate change, understanding whether urchins from different habitats are differentially affected by upwelling-related stressors will give insight into how current and future stressors may be able to help ‘tip the scales’ and convert the increasing number of urchin barrens back into healthy productive kelp forests. I found condition-dependent susceptibility in urchins to increased magnitude and duration upwelling-related stressors. Grazing and gonadal development in kelp forest urchins was most negatively affected by distant future upwelling conditions, whereas in urchin barren urchins, grazing and survival were sensitive to exposure to upwelling in general, and also to increase in magnitudes of acidity, hypoxia, and temperature across both upwelling and non-upwelling events in the future. These results have important implications for population dynamics of urchins and their interactions with bull kelp, which could strongly affect ecosystem dynamics and transitions between kelp forests and urchin barrens. Taken together, the two chapters my thesis provide valuable insight into the potential resilience of bull kelp, a critical foundation species in northeastern Pacific coastal habitats, in the face of a rapidly changing multi-stressor environment.
