Macroalgae, with their various morphologies, are ubiquitous throughout the world’s oceans and provide ecosystem services to a multitude of organisms. Water motion is a fundamental physical parameter controlling the mass transfer of dissolved carbon and nutrients to and from the macroalgal surface, but measurements of flow speed and turbulence within and above macroalgal canopies are lacking. This information is becoming increasingly important as macroalgal canopies may act as refugia for calcifying organisms from ocean acidification (OA); and the extent to which they act as refugia is driven by water motion. Here we report on a field campaign to assess the flow speed and turbulence within and above natural macroalgal canopies at two depths (3 and 6 m) and two sites (Ninepin Point and Tinderbox) in Tasmania, Australia in relation to the canopy height and % cover of functional forms. Filamentous groups made up the greatest proportion (75%) at both sites and depth while foliose groups were more prevalent at 3 than at 6 m. Irrespective of background flows, depth or site, flow speeds within the canopies were <0.03 m s–1 – a ∼90% reduction in flow speeds compared to above the canopy. Turbulent kinetic energy (TKE) within the canopies was up to two orders of magnitude lower (<0.008 m2 s–2) than above the canopies, with higher levels of TKE within the canopy at 3 compared to 6 m. The significant damping effect of flow and turbulence by macroalgae highlights the potential of these ecosystems to provide a refugia for vulnerable calcifying species to OA.
Continue reading ‘Safe in my garden: reduction of mainstream flow and turbulence by macroalgal assemblages and implications for refugia of calcifying organisms from ocean acidification’Posts Tagged 'algae'
Safe in my garden: reduction of mainstream flow and turbulence by macroalgal assemblages and implications for refugia of calcifying organisms from ocean acidification
Published 24 September 2021 Science ClosedTags: algae, field, Indian
Biotic habitats as refugia under ocean acidification
Published 22 September 2021 Science ClosedTags: algae, phanerogams, review
Habitat-forming organisms have an important role in ameliorating stressful conditions and may be of particular relevance under a changing climate. Increasing CO2 emissions are driving a range of environmental changes, and one of the key concerns is the rapid acceleration of ocean acidification and associated reduction in pH. Such changes in seawater chemistry are anticipated to have direct negative effects on calcifying organisms, which could, in turn, have negative ecological, economic and human health impacts. However, these calcifying organisms do not exist in isolation, but rather are part of complex ecosystems. Here, we use a qualitative narrative synthesis framework to explore (i) how habitat-forming organisms can act to restrict environmental stress, both now and in the future; (ii) the ways their capacity to do so is modified by local context; and (iii) their potential to buffer the effects of future change through physiological processes and how this can be influenced by management adopted. Specifically, we highlight examples that consider the ability of macroalgae and seagrasses to alter water carbonate chemistry, influence resident organisms under current conditions and their capacity to do so under future conditions, while also recognizing the potential role of other habitats such as adjacent mangroves and saltmarshes. Importantly, we note that the outcome of interactions between these functional groups will be context dependent, influenced by the local abiotic and biotic characteristics. This dependence provides local managers with opportunities to create conditions that enhance the likelihood of successful amelioration. Where individuals and populations are managed effectively, habitat formers could provide local refugia for resident organisms of ecological and economic importance under an acidifying ocean.
Continue reading ‘Biotic habitats as refugia under ocean acidification’Influence of seawater acidification on biochemical composition and oxidative status of green algae Ulva compressa
Published 21 September 2021 Science ClosedTags: algae, biological response, Indian, laboratory, photosynthesis, physiology, primary production
Highlights
- Seawater acidification improved primary productivity, pigments and carbon storage.
- No significant change in the cellular redox status of U. compressa under acidification.
- Elevated level of essential amino acids and polyunsaturated fatty acids.
- Possible benefits to U. compressa in future predicted acidified waters.
Abstract
The sequestration of elevated atmospheric CO2 levels in seawater results in increasing acidification of oceans and it is unclear what the consequences of this will be on seaweed ecophysiology and ecological services they provide in the coastal ecosystem. In the present study, we examined the physiological and biochemical response of intertidal green seaweed Ulva compressa to elevated pCO2 induced acidification. The green seaweed was exposed to control (pH 8.1) and acidified (pH 7.7) conditions for 2 weeks following which net primary productivity, pigment content, oxidative status and antioxidant enzymes, primary and secondary metabolites, and mineral content were assessed. We observed an increase in primary productivity of the acidified samples, which was associated with increased levels of photosynthetic pigments. Consequently, primary metabolites levels were increased in the thalli grown under lowered pH conditions. There was also richness in various minerals and polyunsaturated fatty acids, indicating that the low pH elevated the nutritional quality of U. compressa. We found that low pH reduced malondialdehyde (MDA) content, suggesting reduced oxidative stress. Consistently we found reduced total antioxidant capacity and a general reduction in the majority of enzymatic and non-enzymatic antioxidants in the thalli grown under acidified conditions. Our results indicate that U. compressa will benefit from seawater acidification by improving productivity. Biochemical changes will affect its nutritional qualities, which may impact the food chain/food web under future acidified ocean conditions.
Continue reading ‘Influence of seawater acidification on biochemical composition and oxidative status of green algae Ulva compressa’The Bouraké semi-enclosed lagoon (New Caledonia) – a natural laboratory to study the lifelong adaptation of a coral reef ecosystem to extreme environmental conditions (update)
Published 17 September 2021 Science ClosedTags: abundance, algae, biogeochemistry, biological response, BRcommunity, chemistry, community composition, corals, field, otherprocess, protists, South Pacific
According to current experimental evidence, coral reefs could disappear within the century if CO2 emissions remain unabated. However, recent discoveries of diverse and high cover reefs that already live under extreme conditions suggest that some corals might thrive well under hot, high-pCO2, and deoxygenated seawater. Volcanic CO2 vents, semi-enclosed lagoons, and mangrove estuaries are unique study sites where one or more ecologically relevant parameters for life in the oceans are close to or even worse than currently projected for the year 2100. Although they do not perfectly mimic future conditions, these natural laboratories offer unique opportunities to explore the mechanisms that reef species could use to keep pace with climate change. To achieve this, it is essential to characterize their environment as a whole and accurately consider all possible environmental factors that may differ from what is expected in the future, possibly altering the ecosystem response.
This study focuses on the semi-enclosed lagoon of Bouraké (New Caledonia, southwest Pacific Ocean) where a healthy reef ecosystem thrives in warm, acidified, and deoxygenated water. We used a multi-scale approach to characterize the main physical-chemical parameters and mapped the benthic community composition (i.e., corals, sponges, and macroalgae). The data revealed that most physical and chemical parameters are regulated by the tide, strongly fluctuate three to four times a day, and are entirely predictable. The seawater pH and dissolved oxygen decrease during falling tide and reach extreme low values at low tide (7.2 pHT and 1.9 mg O2 L−1 at Bouraké vs. 7.9 pHT and 5.5 mg O2 L−1 at reference reefs). Dissolved oxygen, temperature, and pH fluctuate according to the tide by up to 4.91 mg O2 L−1, 6.50 ∘C, and 0.69 pHT units on a single day. Furthermore, the concentration of most of the chemical parameters was 1 to 5 times higher at the Bouraké lagoon, particularly for organic and inorganic carbon and nitrogen but also for some nutrients, notably silicates. Surprisingly, despite extreme environmental conditions and altered seawater chemical composition measured at Bouraké, our results reveal a diverse and high cover community of macroalgae, sponges, and corals accounting for 28, 11, and 66 species, respectively. Both environmental variability and nutrient imbalance might contribute to their survival under such extreme environmental conditions. We describe the natural dynamics of the Bouraké ecosystem and its relevance as a natural laboratory to investigate the benthic organism’s adaptive responses to multiple extreme environmental conditions.
Continue reading ‘The Bouraké semi-enclosed lagoon (New Caledonia) – a natural laboratory to study the lifelong adaptation of a coral reef ecosystem to extreme environmental conditions (update)’Increased CO2 relevant to future ocean acidification alleviates the sensitivity of a red macroalgae to solar ultraviolet irradiance by modulating the synergy between photosystems II and I
Published 16 September 2021 Science ClosedTags: algae, biological response, laboratory, North Pacific, photosynthesis, physiology
While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO2 levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO2 concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O2-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (Fk) of Kautsky curves relative to the amplitude of FJ−Fo (Wk) and a decrease of the maximum quantum yield of PSII (Fv/Fm). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO2 assimilation. When the algal thalli were grown under increased CO2 and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO2 levels and OA.
Continue reading ‘Increased CO2 relevant to future ocean acidification alleviates the sensitivity of a red macroalgae to solar ultraviolet irradiance by modulating the synergy between photosystems II and I’The role of algal blooms and community respiration in controlling the temporal and spatial dynamics of hypoxia and acidification in eutrophic estuaries
Published 10 September 2021 Science ClosedTags: algae, chemistry, field, North Atlantic, photosynthesis
While hypoxia and acidification can be common occurrences in eutrophic coastal zones, the precise, coupled temporal and spatial dynamics of these conditions are poorly described. Here, continuous measurements of water column pH, pCO2, carbonate chemistry, and dissolved oxygen (DO) concentrations were made from spring through fall across two, temperate eutrophic estuaries, western Long Island Sound (LIS) and Jamaica Bay, NY, USA. Vertical dynamics were resolved using an underway towing profiler and an automated stationary profiling unit. During the study, high rates of respiration in surface and bottom waters (> -0.2 mg O2 L-1 h-1) yielded strongly negative rates of net ecosystem metabolism during the summer (-4 to -8 g O2 m-2 d-1). Ephemeral surface algal blooms caused brief periods (< one week) of basification and supersaturation of DO that were succeeded by longer periods of acidification and hypoxia. In deeper regions, hypoxia (< 2 mg L-1 DO) and acidic water (pH < 7; total scale; pCO2 levels >2000 μatm) that persisted continuously for >40 days in both estuaries was often overlain by water with higher DO and pH. Diurnal vertical profiles demonstrated that oxic surface waters saturated with respect to calcium carbonate and DO during the day transitioned to unsaturated and hypoxic at night. Evidence is presented that, beyond respiration, nitrification in surface water promoted by sewage discharge and oxidation processes in sediments also contribute to acidification in these estuaries. Collectively, this study demonstrates the pervasive, persistent, and dynamic nature of hypoxia and acidification in eutrophic estuaries are likely to shape marine food webs.
Continue reading ‘The role of algal blooms and community respiration in controlling the temporal and spatial dynamics of hypoxia and acidification in eutrophic estuaries’Approaches and involved principles to control pH/pCO2 stability in algal cultures
Published 6 September 2021 Science ClosedTags: algae, biological response, BRcommunity, community composition, laboratory, otherprocess, photosynthesis, physiology, phytoplankton, prokaryotes
Experimental cultures of both microalgae and macroalgae are commonly carried out by phycologists or environmental biologists to look into morphological, physiological, and molecular responses to aquatic environmental changes. However, the species of inorganic carbon in algae cultures is often altered by algal photosynthetic CO2 removal and/or bicarbonate utilization. The pH changes associated with altered carbonate chemistry in cultures impact physiological processes in microalgae and macroalgae even at their exponential growth phases, since extra energy is required to sustain intracellular acid–base homeostasis. Usually, pH increases during light period due to inorganic carbon uptake and utilization for photosynthesis and decreases during dark period because of respiratory CO2 release. Therefore, to obtain relevant data aimed for physiological and/or molecular responses of algae to changed levels of environmental factors, stability of pH/pCO2 in the cultures should be considered and controlled to rule out impacts of carbonate chemistry and pH changes. In this work, principles involved in changing pH processes in algal cultures are mechanistically analyzed and several approaches to control pH and pCO2 are introduced. In order to sustain stability of pH/pCO2, the principles underline the following key points: (1) maintaining the rate of photosynthetic C removal less than or equal to the rate of CO2 dissolution into the cultures which are aerated; or (2) sustaining dilute cultures with very low cell density without aeration, so that photosynthetic C removal is small enough not to cause significant pH/pCO2 changes; or (3) stabilizing the changes in micro-environments surrounding the cells or thallus. To maintain pH drift < 1% in growing typical unicellular microalgae, the recommended cell concentration ranges from 50 × 103 to 200 × 103 mL−1 with aeration (air replacement rate of ca 500–1000 mL L−1 min−1) in semi-continuous cultures of < 1 L, and it ranges from 100 to 5000 cells mL−1 for diatoms and from 100 to 100 × 103 cells mL−1 for coccolithophores in dilute cultures without aeration, respectively. For macroalgae, maintaining the thalli in flowing through- system or in semi-continuous cultures (continuously control algal biomass density) is recommended.
Continue reading ‘Approaches and involved principles to control pH/pCO2 stability in algal cultures’Rate and fate of dissolved organic carbon release by seaweeds: a missing link in the coastal ocean carbon cycle
Published 31 August 2021 Science ClosedTags: algae, biogeochemistry, biological response, physiology
Dissolved organic carbon (DOC) release by seaweeds (marine macroalgae) is a critical component of the coastal ocean biogeochemical carbon cycle but is an aspect of seaweed carbon physiology that we know relatively little about. Seaweed-derived DOC is found throughout coastal ecosystems and supports multiple food web linkages. Here, we discuss the mechanisms of DOC release by seaweeds and group them into passive (leakage, requires no energy) and active release (exudation, requires energy) with particular focus on the photosynthetic “overflow” hypothesis. The release of DOC from seaweeds was first studied in the 1960s, but subsequent studies use a range of units hindering evaluation: we convert published values to a common unit (μmol C · g DW−1 · h−1) allowing comparisons between seaweed phyla, functional groups, biogeographic region, and an assessment of the environmental regulation of DOC production. The range of DOC release rates by seaweeds from each phylum under ambient environmental conditions was 0–266.44 μmol C · g DW−1 · h−1 (Chlorophyta), 0–89.92 μmol C · g DW−1 · h−1 (Ochrophyta), and 0–41.28 μmol C · g DW−1· h−1 (Rhodophyta). DOC release rates increased under environmental factors such as desiccation, high irradiance, non-optimal temperatures, altered salinity, and elevated dissolved carbon dioxide (CO2) concentrations. Importantly, DOC release was highest by seaweeds that were desiccated (<90 times greater DOC release compared to ambient). We discuss the impact of future ocean scenarios (ocean acidification, seawater warming, altered irradiance) on DOC release rates by seaweeds, the role of seaweed-derived DOC in carbon sequestration models, and how they inform future research directions.
Continue reading ‘Rate and fate of dissolved organic carbon release by seaweeds: a missing link in the coastal ocean carbon cycle’The brown algae Saccharina japonica and Sargassum horneri exhibit species-specific responses to synergistic stress of ocean acidification and eutrophication
Published 19 August 2021 Science ClosedTags: algae, biological response, laboratory, morphology, multiple factors, North Pacific, nutrients, photosynthesis, physiology, respiration
Ocean acidification and eutrophication are two important environmental stressors. They inevitably impact marine macroalgae, and hence the coastal ecosystem of China. Saccharina japonica, as the main culture species in China, is suffering the harmful golden tide caused by Sargassum horneri. However, it remains unclear whether the detrimental effects of S. horneri on S. japonica cultivation become more severe in future acidified and eutrophic scenario. In this study, we respectively investigated the effects of pCO2 (400 µatm and 1000 µatm) and nutrients (non-enriched and enriched seawater) on the growth, photosynthesis, respiration, chlorophyll contents, and tissue nitrogen of S. japonica and S. horneri. Results indicated that enrichment of nutrients contributed S. horneri to utilize HCO3−. The carbon acquisition pathway shifted from HCO3− to CO2 in S. japonica, while S. horneri remained using HCO3− regulated by nutrient enrichment. S. horneri exhibited better photosynthetic traits than S. japonica, with a higher level of net photosynthetic rate and chlorophyll contents at elevated pCO2 and enriched nutrients. Tissue nitrogen also accumulated richly in the thalli of S. horneri under higher pCO2 and nutrients. Significant enhancement in growth was only detected in S. horneri under synergistic stress. Together, S. horneri showed competitive dominance in current study. These findings suggest that increasing risk of golden tide in acidified and eutrophic ocean can most likely result in great damage to S. japonica cultivation.
Continue reading ‘The brown algae Saccharina japonica and Sargassum horneri exhibit species-specific responses to synergistic stress of ocean acidification and eutrophication’Elevated CO2 accelerated the bloom of three Ulva species after one life cycle culture
Published 11 August 2021 Science ClosedTags: algae, biological response, BRcommunity, laboratory, molecular biology, multiple factors, North Pacific, nutrients, photosynthesis, physiology
Human activities and the resulting global climate change have profound effects on ecosystems, and economic and social systems, including those dependent on the ocean. Increasing concentrations of atmospheric CO2 have led to gradual changes in the marine carbonate system. It is well known that environmental changes determine the composition and abundance of algal populations. In the present study, we evaluated the growth, photosynthesis, nutrient uptake rates, tissue C and N content, nitrate reductase activity, and nitrate transporter gene expression of Ulva prolifera, Ulva linza, and Ulva compressa exposed to 400, 1000, and 2000 ppm CO2 levels after one life cycle culture. Elevated CO2 promoted the rapid propagation of three Ulva species, which can result in the formation of a green tide. This was due to enhanced photosynthetic and respiration efficiency, reductions in energy requirements for biosynthesis and metabolism for maintaining external pH, and promotion of NO3− uptake by increased NO3− gene expression level and NO3− reductase activity.
Continue reading ‘Elevated CO2 accelerated the bloom of three Ulva species after one life cycle culture’DNA metabarcoding to examine the biodiversity of coral reef cryptobiota
Published 3 August 2021 Science ClosedTags: algae, annelids, biological response, BRcommunity, cnidaria, community composition, corals, echinoderms, laboratory, mesocosms, molecular biology, mollusks, multiple factors, North Pacific, porifera, reproduction, temperature
Coral reefs are among the most biologically diverse, complex, and productive of ecosystems. The vast majority of coral reef biodiversity is made up of the small and cryptic organisms living unseen by most within the reef matrix. This hidden community, the cryptobiota, are a critical component of coral reef trophic dynamics and play an essential role in nutrient recycling that enable reefs to thrive in oligotrophic environments. Despite their ecological importance, the cryptobiota are often ignored because they live deep within the reef matrix and require significant taxonomic expertise and time to collect and identify. As a result, our perceptions of coral reef biodiversity across marine gradients and how it will respond to climatic change is based on observable surface-dwelling taxa, such as corals and fish. Using DNA metabarcoding technology, this research fills an extensive knowledge gap about the diversity and distribution of the important and understudied coral reef cryptobiota community. The objectives of this dissertation were to (i) evaluate metabarcoding performance on marine sponges, a prominent and ecologically vital member of the cryptobenthos that is one of the most difficult metazoans to identify to species using both taxonomic and molecular methods; (ii) investigate the individual and combined effects of ocean warming and acidification on cryptobiota biodiversity; and (iii) examine cryptobiota diversity along the most striking macrospatial diversity gradient in the marine tropics. Contrary to expectations, this research (i) demonstrated that the metabarcoding approach performs much better than expected in capturing sponge richness; (ii) discovered that diversity shuffles but does not decline under the combined stressors of ocean warming and acidification; and (iii) cryptobiotic diversity undermines the tropical Pacific longitudinal diversity gradient defined by corals and fish. These results contribute towards reshaping the way we consider coral reef biodiversity under different oceanographic, geographic and climatic regimes.
Continue reading ‘DNA metabarcoding to examine the biodiversity of coral reef cryptobiota’Rate and fate of dissolved organic carbon release by seaweeds: a missing link in the coastal ocean carbon cycle
Published 29 July 2021 Science ClosedTags: algae, biogeochemistry, biological response, review
Dissolved organic carbon (DOC) release by seaweeds (marine macroalgae) is a critical component of the coastal oceans biogeochemical carbon cycle but is an aspect of seaweed carbon physiology that we know relatively little about. Seaweed-derived DOC is found throughout coastal ecosystems and supports multiple food web linkages. Here we discuss the mechanisms of DOC release by seaweeds and group them into passive (leakage, requires no energy) and active release (exudation, requires energy) with particular focus on the photosynthetic ‘overflow’ hypothesis. The release of DOC from seaweeds was first studied in the 1960’s but subsequent studies use a range of units hindering evaluation: we convert published values to a common unit (μmol C · g DW-1 · h-1) allowing comparisons between seaweed phyla, functional groups, biogeographic region, and an assessment of the environmental regulation of DOC production. The range of DOC release rates by seaweeds from each phylum under ambient environmental conditions was: 0 – 266.44 μmol C · g DW-1 · h-1 (Chlorophyta), 0 – 89.92 μmol C · g DW-1 · h-1 (Ochrophyta) and 0 – 41.28 μmol C · g DW-1· h-1 (Rhodophyta). DOC release rates increased under environmental factors such as desiccation, high irradiance, non-optimal temperatures, altered salinity and elevated dissolved carbon dioxide (CO2) concentrations. Importantly DOC release was highest by seaweeds which were desiccated (<90 times greater DOC release compared to ambient). We discuss the impact of future ocean scenarios (ocean acidification, seawater warming, altered irradiance) on DOC release rates by seaweeds, the role of seaweed-derived DOC in carbon sequestration models, and how they inform future research directions.
Continue reading ‘Rate and fate of dissolved organic carbon release by seaweeds: a missing link in the coastal ocean carbon cycle’Major loss of coralline algal diversity in response to ocean acidification
Published 23 July 2021 Science ClosedTags: abundance, algae, biological response, community composition, laboratory, Mediterranean, molecular biology, mortality, North Pacific, otherprocess
Calcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO2 conditions. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition; it is less diverse today and was the most sensitive to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO2; it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO2 highlighted their lower fitness in response to ocean acidification. Reductions in CO2 emissions are needed to limit the risk of losing coralline algal diversity.
Continue reading ‘Major loss of coralline algal diversity in response to ocean acidification’Low irradiance amplifies negative effects of ocean acidification on recruitment of coralline algae communities
Published 23 July 2021 Science ClosedTags: algae, biological response, laboratory, light, multiple factors, reproduction
Coralline algae play foundational roles in coastal ecosystems and are globally significant components of benthic habitats down to the limits of the photic zone. Despite their vulnerability to ocean acidification (OA) and importance in low light environments, there is a limited understanding of how the interplay between irradiance and OA influences coralline reproduction and recruitment. To better understand this interaction, a 212-day experiment was run exposing coralline communities to two pH(T) levels (present-day pH(T) 8.07/ OA pH(T) 7.65) and a gradient of daily light dose (0.35, 0.17 and 0.1 mol m-2 d-1), based on in situ measurements. In the highest light dose treatment, lowered seawater pH projected for 2100 (pH(T) 7.65) reduced recruitment by 56%. This OA-driven reduction in recruitment was amplified under reduced light, with recruitment near zero in the lowest light treatment. This study shows, for the first time, the increased vulnerability of coralline community recruitment to OA under low light. Coralline algae are known to be the deepest growing macroalgae and thus, in these low light zones, OA many have the potential to reduce coralline depth distribution.
Continue reading ‘Low irradiance amplifies negative effects of ocean acidification on recruitment of coralline algae communities’Impacts of large-scale aquaculture activities on the seawater carbonate system and air-sea CO2 flux in a subtropical mariculture bay, southern China
Published 23 July 2021 Science ClosedTags: algae, biogeochemistry, chemistry, field, fish, fisheries, laboratory, mollusks, North Pacific, photosynthesis, socio-economy
In this study, the variations of the seawater carbonate system parameters and air-sea CO2 flux (FCO2) of Shen’ao Bay, a typical subtropical aquaculture bay located in China, were investigated in spring 2016 (March to May). Parameters related to the seawater carbonate system and FCO2 were measured monthly in 3 different aquaculture areas (fish, oyster and seaweed) and in a non-culture area near the bay mouth. The results showed that the seawater carbonate system was markedly influenced by the biological processes of the culture species. Total alkalinity was significantly lower in the oyster area compared with the fish and seaweed areas, mainly because of the calcification process of oysters. Dissolved inorganic carbon (DIC) and CO2 partial pressure ( pCO2) were highest in the fish area, followed by the oyster and non-culture areas, and lowest in the seaweed area. Oysters and fish can have indirect influences on DIC and pCO2by releasing nutrients, which facilitate the growth of seaweed and phytoplankton and therefore promote photosynthetic CO2 fixation. For these reasons, Shen’ao Bay acts as a potential CO2 sink in spring, with an average FCO2 ranging from -1.2 to -4.8 mmol m-2 d-1. CO2 fixation in the seaweed area was the largest contributor to CO2 flux, accounting for ca. 58% of the total CO2 sink capacity of the entire bay. These results suggest that the carbonate system and FCO2 of Shen’ao Bay were significantly affected by large-scale mariculture activities. A higher CO2 sink capacity could be acquired by extending the culture area of seaweed.
Continue reading ‘Impacts of large-scale aquaculture activities on the seawater carbonate system and air-sea CO2 flux in a subtropical mariculture bay, southern China’Species turnover underpins the effect of elevated CO2 on biofilm communities through early succession
Published 22 July 2021 Science ClosedTags: algae, biological response, community composition, field, laboratory, molecular biology, mortality, North Pacific, otherprocess, photosynthesis, prokaryotes
Highlights
- High CO2 conditions profoundly affected biofilm community composition
- Species turnover explained differences in community composition
- Biofilm communities were more homogeneous under high CO2 conditions
- Toxin producing and turf-forming algae were enriched under high CO2 conditions
Abstract
Biofilms harbour a wealth of microbial diversity and fulfil key functions in coastal marine ecosystems. Elevated carbon dioxide (CO2) conditions affect the structure and function of biofilm communities, yet the ecological patterns that underpin these effects remain unknown. We used high-throughput sequencing of the 16S and 18S rRNA genes to investigate the effect of elevated CO2 on the early successional stages of prokaryotic and eukaryotic biofilms at a CO2 seep system off Shikine Island, Japan. Elevated CO2 profoundly affected biofilm community composition throughout the early stages of succession, leading to greater compositional homogeneity between replicates and the proliferation of the potentially harmful algae Prymnesium sp. and Biddulphia biddulphiana. Species turnover was the main driver of differences between communities in reference and high CO2 conditions, rather than differences in richness or evenness. Our study indicates that species turnover is the primary ecological pattern that underpins the effect of elevated CO2 on both prokaryotic and eukaryotic components of biofilm communities, indicating that elevated CO2 conditions represent a distinct niche selecting for a distinct cohort of organisms without the loss of species richness.
Continue reading ‘Species turnover underpins the effect of elevated CO2 on biofilm communities through early succession’Simplification, not “tropicalization”, of temperate marine ecosystems under ocean warming and acidification
Published 22 July 2021 Science ClosedTags: algae, biological response, calcification, chemistry, community composition, corals, field, growth, light, morphology, multiple factors, North Pacific, otherprocess, photosynthesis, physiology
Ocean warming is altering the biogeographical distribution of marine organisms. In the tropics, rising sea surface temperatures are restructuring coral reef communities with sensitive species being lost. At the biogeographical divide between temperate and tropical communities, warming is causing macroalgal forest loss and the spread of tropical corals, fishes and other species, termed “tropicalization”. A lack of field research into the combined effects of warming and ocean acidification means there is a gap in our ability to understand and plan for changes in coastal ecosystems. Here, we focus on the tropicalization trajectory of temperate marine ecosystems becoming coral-dominated systems. We conducted field surveys and in situ transplants at natural analogues for present and future conditions under (i) ocean warming and (ii) both ocean warming and acidification at a transition zone between kelp and coral-dominated ecosystems. We show that increased herbivory by warm-water fishes exacerbates kelp forest loss and that ocean acidification negates any benefits of warming for range extending tropical corals growth and physiology at temperate latitudes. Our data show that, as the combined effects of ocean acidification and warming ratchet up, marine coastal ecosystems lose kelp forests but do not gain scleractinian corals. Ocean acidification plus warming leads to overall habitat loss and a shift to simple turf-dominated ecosystems, rather than the complex coral-dominated tropicalized systems often seen with warming alone. Simplification of marine habitats by increased CO2 levels cascades through the ecosystem and could have severe consequences for the provision of goods and services.
Continue reading ‘Simplification, not “tropicalization”, of temperate marine ecosystems under ocean warming and acidification’Environmental legacy effects and acclimatization of a crustose coralline alga to ocean acidification
Published 15 July 2021 Science ClosedTags: adaptation, algae, biological response, calcification, chemistry, field, individualmodeling, laboratory, modeling, morphology, North Pacific, otherprocess
Prior exposure to variable environmental conditions is predicted to influence the resilience of marine organisms to global change. We conducted complementary 4-month field and laboratory experiments to understand how a dynamic, and sometimes extreme, environment influences growth rates of a tropical reef-building crustose coralline alga and its responses to ocean acidification (OA). Using a reciprocal transplant design, we quantified calcification rates of the Caribbean coralline Lithophyllum sp. at sites with a history of either extreme or moderate oxygen, temperature, and pH regimes. Calcification rates of in situ corallines at the extreme site were 90% lower than those at the moderate site, regardless of origin. Negative effects of corallines originating from the extreme site persisted even after transplanting to more optimal conditions for 20 weeks. In the laboratory, we tested the separate and combined effects of stress and variability by exposing corallines from the same sites to either ambient (Amb: pH 8.04) or acidified (OA: pH 7.70) stable conditions or variable (Var: pH 7.80-8.10) or acidified variable (OA-Var: pH 7.45-7.75) conditions. There was a negative effect of all pH treatments on Lithophyllum sp. calcification rates relative to the control, with lower calcification rates in corallines from the extreme site than from the moderate site in each treatment, indicative of a legacy effect of site origin on subsequent response to laboratory treatment. Our study provides ecologically relevant context to understanding the nuanced effects of OA on crustose coralline algae, and illustrates how local environmental regimes may influence the effects of global change.
Continue reading ‘Environmental legacy effects and acclimatization of a crustose coralline alga to ocean acidification’Macroalgal calcification and the effects of ocean acidification and global warming
Published 14 July 2021 Science ClosedTags: algae, biological response, calcification, molecular biology, physiology, review
Calcification by calcified marine macroalgae is crucial to algal growth, and the formation and maintenance of coral reefs. It involves complex processes, such as the uptake, transport and storage of Ca2+, HCO3- or CO32-, and formation of crystals responsible for calcium depositions. Calcification is vulnerable to changes in global climate, including ocean acidification (OA) and warming (OW). Studies investigating the mechanisms of macroalgal calcification are limited and restricted to the physiology level; however, the application of new approaches, i.e. genomics, provide avenues for new understanding. We review the literature on macroalgal calcification from the physiological to the molecular level, and present in a list of key issues to be resolved in order to understand the mechanism of calcification. The review offers insights into the potential impacts of changing climate conditions on algal calcification to provide an accurate prediction of future changes in the reef ecosystems.
Continue reading ‘Macroalgal calcification and the effects of ocean acidification and global warming’
