abundance Archives - Page 2 of 48

Posts Tagged 'abundance'

Mollusc epifaunal assemblages are simplified due to habitat shifts under ocean acidification

Published 14 July 2025 Science Closed
Tags: abundance, biological response, BRcommunity, community composition, field, mollusks, North Atlantic, otherprocess, vents

Highlights

Ocean acidification can modify the structure of marine communities.
The macroalga Halopteris sp. supports a rich community of associated molluscs.
Halopteris sp. from an acidified site support fewer and less diverse assemblages.
Most abundant species were present both at the acidified and reference sites.
Biodiversity of molluscs will be simplified under acidified conditions.

Abstract

Ocean acidification can have profound effects on marine organisms, particularly those that rely on calcium carbonate for shell and skeleton formation, resulting in structural changes to marine ecosystems. Here, we contrast the structure of marine mollusc communities (epifauna) associated with an abundant shallow-water macroalga, Halopteris scoparia, in an area with seawater carbonated by natural CO₂ seeps and three reference sites, off the Azores archipelago. Epifaunal mollusc abundance and diversity were significantly lower at the CO₂ seep compared to reference sites whilst species accumulation curves and Jaccard multivariate analyses showed that the mollusc assemblage was consistently less diverse at the CO₂ seep. Most of the abundant epifaunal species that were present at the CO₂ seep were also found at reference sites, but less common or rare species were generally absent from the former. We conclude that while some molluscs are likely to cope with ocean acidification, the overall biodiversity of epifaunal molluscs will be simplified under these conditions in a future ocean.

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CO2 enrichment enhances biomass density and C:N:P ratios in phytoplankton assemblage in the coastal water of the Taiwan Strait

Published 3 July 2025 Science Closed
Tags: abundance, biogeochemistry, biological response, community composition, laboratory, North Pacific, otherprocess, phytoplankton

Seawater CO₂ concentrations are steadily increasing in the Taiwan Strait of the Southeast China, while the effects of rising CO₂ on carbon fixation and elemental composition of phytoplankton assemblages in this area are still poorly understood. Here, we enriched the seawater CO₂ concentrations to 808 μatm and above to simulate the CO₂–induced ocean acidification, and investigated the effects of CO₂ enrichment on concentrations of chlorophyll (Chl) a, particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), the C:N:P ratio, and phytoplankton community composition in the coastal surface seawaters of the northwest Taiwan Strait in autumn 2023 and spring 2024 through an outdoor incubation experiment. After three days of incubation, CO₂ enrichment increased the concentrations of Chl a by 1–14%, POC by 21–32% and PON by 21–56%, whereas reduced the POP concentrations by 1–37%, leading to elevated ratios of POC:POP and PON:POP. Furthermore, elevated CO₂ level enhanced cell abundances of the dominant diatom genera at three stations. These results suggest that phytoplankton has the potential to buffer against rising atmospheric CO₂ level and can help us to understand the elemental biogeochemistry in the Taiwan Strait under future ocean acidification scenarios.

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Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans

Published 2 July 2025 Science Closed
Tags: abundance, biogeochemistry, biological response, community composition, growth, Indian, laboratory, multiple factors, North Pacific, otherprocess, physiology, phytoplankton

Abstract

Key roles of marine dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS₂) in the sulfur cycle and/or atmospheric chemistry, alongside the rapid environmental changes in marine ecosystems, underscore the need to understand their responses to dynamic ecosystem shifts. We conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans to explore how dust deposition, ocean acidification, and microplastic exposure impact these compounds. Our results demonstrate that these stressors not only alter phytoplankton community but also modify per-cell DMSP production capacity and DMSP degradation pathways, subsequently influencing DMSP, DMS, and MeSH concentrations. CS₂‘s response closely mirrors phytoplankton abundance and species. Initial physical-chemical conditions, such as carbonate system and nutrient availability, may mediate the sensitivity of phytoplankton and sulfur compounds to environmental shifts. This study enhances our understanding of biogenic sulfur responses in dynamic marine ecosystems and provides essential basis for future climate modeling.

Key Points

External stressors alter algal communities and production and degradation of dimethyl sulfoniopropionate, thus affecting biogenic sulfides
Response of carbon disulfide to different environmental stressors is closely linked to algal abundance
Initial physical-chemical conditions of seawater mediate algae and biogenic sulfides’ sensitivity to environmental stressors

Plain Language Summary

Biogenic sulfur-containing compounds in the ocean, such as dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS₂), play critical roles in the global sulfur cycle and have the potential to influence the Earth’s climate. For instance, DMS released from the ocean into the atmosphere contributes to cloud formation, which in turn affects weather patterns. Over recent decades, rapid environmental changes in marine ecosystems may have significantly impacted marine biogeochemical processes. To investigate how these compounds respond to such changes, we conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans. We assessed the effects of dust deposition, ocean acidification (due to increased carbon dioxide), and microplastic pollution on the production of DMSP, DMS, MeSH, and CS₂ by marine organisms. Our results demonstrate that these stressors alter phytoplankton growth and community composition and impact the pathways through which DMSP is degraded. Consequently, the concentrations of sulfur compounds in seawater are affected. Notably, changes in CS₂ levels were more closely related to shifts in phytoplankton abundance. These findings enhance our understanding of how marine sulfur compounds may respond to future oceanic changes and offer valuable data for improving climate models.

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Antarctic macroalgal-associated amphipod assemblages exhibit long-term resistance to ocean acidification

Published 19 June 2025 Science Closed
Tags: abundance, algae, Antarctic, biological response, BRcommunity, community composition, crustaceans, laboratory, mortality, otherprocess

The pH of the world’s oceans has decreased since the Industrial Revolution due to the oceanic uptake of increased atmospheric CO₂ in a process called ocean acidification. Low pH has been linked to negative impacts on the calcification, growth, and survival of calcifying invertebrates. Along the Western Antarctic Peninsula, dominant brown macroalgae often shelter large numbers of diverse invertebrate mesograzers, many of which are calcified. Mesograzer assemblages in this region are often composed of large numbers of amphipods which have key roles in Antarctic macroalgal communities. Understanding the impacts of acidification on amphipods is vital for understanding how these communities will be impacted by climate change. To assess how long-term acidification may influence the survival of different members in these assemblages, mesograzers, particularly amphipods, associated with the brown alga Desmarestia menziesii were collected from the immediate vicinity of Palmer Station, Antarctica (S64°46′, W64°03′) in January 2020 and maintained under three different pH treatments simulating ambient conditions (approximately pH 8.1), near-future conditions for 2100 (pH 7.7), and distant future conditions (pH 7.3) for 52 days then enumerated. Total assemblage number and the relative proportion of each species in the assemblage were found to be similar across the pH treatments. These results suggest that amphipod assemblages associated with D. menziesii may be resistant to long-term exposure to decreased pH.

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Microzooplankton community dynamics under ocean acidification: key observations and insights

Published 30 April 2025 Science Closed
Tags: abundance, biological response, BRcommunity, community composition, Indian, laboratory, otherprocess, phytoplankton, prokaryotes, zooplankton

Microzooplankton (MZP) community dynamics under ocean acidification were studied through pH manipulated microcosm experiments conducted in the coastal waters of the Bay of Bengal (off Vishakhapatnam) during the months of July and October 2022 (Experiment 1 and Experiment 2). The total abundance of phytoplankton and microzooplankton (MZP) communities was varied from 3.66 × 10⁴ to 5.27 × 10⁵ Cells. L⁻¹ and 0.06 × 10³ to 1.53 × 10³ Cells. L⁻¹, respectively, and a significant difference in phytoplankton and MZP abundance was found between the initial and final day of the entire experimental samples (control and acidified). The initial seawater samples were dominated with centric diatom species Dactyliosolen fragilissimus (Experiment 1 and Experiment 2: 72–82%) and shifted to pennate diatoms such as Pseudo-nitzschia sp. (Experiment 1: 60–68%) and Amphora sp. (Experiment 2: 80–94%) at the end of the experiments (all acidified and control samples). The initial MZP community composition consisted of four different groups LC: loricate ciliates, ALC: aloricate ciliates (heterotrophy and mixotrophy), HDS: heterotrophic dinoflagellates and copepod nauplii, and at the end of the experiments, it was shifted entirely to the dominance of aloricate ciliates (16–73%) and heterotrophic dinoflagellates (67–100%) in all the samples (control and acidified) in Experiments 1 and 2, respectively. Statistical analysis (Spearman’s rank correlation) results showed a relative and significant inverse relation of MZP with phytoplankton biomass and abundance and heterotrophic bacterial counts in all the samples (control and acidified). Besides, the LC showed a weak correlation with Chl-a, and the HDS showed a significant correlation with LC, phytoplankton biomass and abundance, and bacterial counts (picocyanobacteria and heterotrophic bacteria). These results indicate that the MZP may graze on both picocyanobacteria and heterotrophic bacteria, and also, HDS may graze on their relative community like LC. Canonical correlation analysis (CCA) revealed that prey abundance such as phytoplankton biomass (Chl-a), picocyanobacteria, and heterotrophic bacterial communities are most influencing variables on the MZP assemblages than other environmental variables such as pH, temperature, and salinity. Thus, these findings show that the MZP community dynamics under ocean acidification may vary with different species and groups due to their food availability (indirect effect) and individual competence (direct effect) to different environmental conditions, such as pH variations.

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Investigating the effects of environmental stress on coastal zooplankton populations: from mechanistic drivers to trophic impacts

Published 29 January 2025 Science Closed
Tags: abundance, biological response, BRcommunity, crustaceans, field, laboratory, mortality, multiple factors, otherprocess, oxygen, performance, zooplankton

Environmental stressors, such as hypoxia and acidification, are increasing in intensity, duration, and extent in coastal waters and estuaries. Environmental stressors are known to affect a wide range of marine species, including zooplankton. Zooplankton are a critical link in marine food webs, connecting phytoplankton to higher trophic levels such as economically important fish, and are thought to be informative indicators of ecosystem change. For this reason, increased attention has been paid to understanding the mechanisms shaping zooplankton populations. Previous studies have shown that zooplankton exhibit both lethal and sublethal responses to changes in dissolved oxygen and pH. However, there is a range of species-specific responses to stressors. Different responses across species alter zooplankton community composition and spatial distributions, directly impacting predator-prey interactions and the trophic dynamics in coastal environments. This dissertation integrates laboratory experiments, in situ observations, and field work to understand how environmental stressors affect coastal zooplankton populations and nearshore food webs. In Chapter 1, I conducted laboratory experiments to investigate whether the copepod, Calanus pacificus, showed behavioral responses to stressors, and whether these responses lead to changes in vertical population distributions. Our laboratory experiments demonstrated significant effects of bottom water hypoxia and acidification on behavioral avoidance, swimming statistics, and apparent mortality rates in C. pacificus. In Chapter 2, I used a remote camera system to quantify in situ behavioral responses of zooplankton to stressors, using results from Chapter 1 to generate hypotheses about observations in the field. Our in situ videos revealed that copepods in stressful conditions exhibited significantly slower swimming speeds than copepods in non-stressful conditions, while amphipods showed significantly decreased abundances within stressful conditions. Finally, in Chapter 3, I collected zooplankton net tows in an intertidal estuary to investigate the transport of pelagic species into eelgrass beds and the role of eelgrass beds as potential sinks of pelagic zooplankton over the tidal cycle, potentially due to predation by juvenile fish. We found evidence of transport of pelagic species into intertidal habitats and measured large spatial and temporal variability, highlighting the need for sampling programs that can capture small-scale variability. This dissertation provides insight into the mechanisms that link the effects of environmental stressors across individual responses to population, community, and ecosystem level scales and suggests novel methodologies to help advance our understanding of changing zooplankton dynamics.

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Migrating is not enough for modern planktonic foraminifera in a changing ocean

Published 20 November 2024 Science Closed
Tags: abundance, globalmodeling, modeling, mortality, otherprocess, phytoplankton

Rising carbon dioxide emissions are provoking ocean warming and acidification^1,2, altering plankton habitats and threatening calcifying organisms³, such as the planktonic foraminifera (PF). Whether the PF can cope with these unprecedented rates of environmental change, through lateral migrations and vertical displacements, is unresolved. Here we show, using data collected over the course of a century as FORCIS⁴ global census counts, that the PF are displaying evident poleward migratory behaviours, increasing their diversity at mid- to high latitudes and, for some species, descending in the water column. Overall foraminiferal abundances have decreased by 24.2 ± 0.1% over the past eight decades. Beyond lateral migrations⁵, our study has uncovered intricate vertical migration patterns among foraminiferal species, presenting a nuanced understanding of their adaptive strategies. In the temperature and calcite saturation states projected for 2050 and 2100, low-latitude foraminiferal species will face physicochemical environments that surpass their current ecological tolerances. These species may replace higher-latitude species through poleward shifts, which would reduce low-latitude foraminiferal diversity. Our insights into the adaptation of foraminifera during the Anthropocene suggest that migration will not be enough to ensure survival. This underscores the urgent need for us to understand how the interplay of climate change, ocean acidification and other stressors will impact the survivability of large parts of the marine realm.

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Changes in gill neuroepithelial cells and morphology of threespine stickleback (Gasterosteus aculeatus) to hypoxia and simulated ocean acidification

Published 7 August 2024 Science Closed
Tags: abundance, biological response, chemistry, fish, laboratory, morphology, North Pacific, otherprocess, physiology, respiration

Coastal marine environments are characterized by daily, seasonal and long-term changes in both O₂ and CO₂, driven by local biotic and abiotic factors. The neuroepithelial cells (NECs) of fish are thought to be the putative chemoreceptors for sensing oxygen and CO₂, and, thus, NECs play a key role in detecting these environmental changes. However, the role of NECs as chemosensors in marine fish remains largely understudied. In this study, the NECs of marine threespine sticklebacks (Gasterosteus aculeatus) were characterized using immunohistochemistry. We then determined if there were changes in NEC size and density, and in gill morphology in response to either mild (10 kPa) or moderate (6.8 kPa) hypoxia and two levels of elevated CO₂ (1,500 and 3,000 µatm). We found that the NECs of stickleback contained synaptic vesicles and were innervated, and were 50–300% larger and 2 to 4 times more abundant than in other similar sized freshwater fishes. NEC size and density were largely unaffected by exposure to hypoxia, but there was a 50% decrease in interlamellar cell mass (ILCM) in response to mild and moderate hypoxia. NECs increased in size, but not abundance in response to elevated CO₂. Moreover, fish exposed to moderate or elevated CO₂ had 53–78% larger ILCMs compared to control fish. Our results demonstrated that adult marine sticklebacks have NECs that can respond to environmentally relevant pCO₂ and likely hypoxia, which highlights the importance of NECs in marine fishes under the heterogeneity of environmental conditions in coastal areas.

Continue reading ‘Changes in gill neuroepithelial cells and morphology of threespine stickleback (Gasterosteus aculeatus) to hypoxia and simulated ocean acidification’

Assessing the effects of warming and carbonate chemistry parameters on marine microbes in the Gulf of Mexico through basin-scale DNA metabarcoding

Published 2 August 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, laboratory, molecular biology, North Atlantic, otherprocess, physiology, prokaryotes

Ocean acidification and warming threaten marine life, yet the impact of these processes on microbes remains unclear. Here, we performed basin-scale DNA metabarcoding of prokaryotes (16S V4–V5) and protists (18S V9) in the Gulf of Mexico and applied generalized linear models to reveal group-specific environmental correlates of functionally diverse microbes. Models supported prior physiological trends for some groups, like positive temperature effects on SAR11 and SAR86, and a positive effect of pH on Prochlorococcus that implied a negative response to decreasing pH. New insights were revealed for protists, like Syndiniales and Sagenista (e.g., positive pH effects), which offset positive relationships with temperature and reinforced the importance of considering multiple stressors simultaneously. Indicator analysis revealed phytoplankton, like Ostreococcus sp. and Emiliania huxleyi, that were associated with more acidic waters and may reflect candidate indicators of ocean change. Our findings highlight the need for sustained microbial sampling in marine systems, with implications for carbon export, nutrient cycling, and ecosystem health.

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From nutrients to fish: impacts of mesoscale processes in a global CESM-FEISTY eddying ocean model framework

Published 26 July 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, fish, globalmodeling, modeling, otherprocess, phytoplankton, review, zooplankton

The ocean sustains ecosystems that are essential for human livelihood and habitability of the planet. The ocean holds an enormous amount of carbon, and serves as a critical source of nutrition for human societies worldwide. Climate variability and change impacts marine biogeochemistry and ecosystems. Thus, having state-of-the-art simulations of the ocean, which include marine biogeochemistry and ecosystems, is critical for understanding the role of climate variability and change on the ocean biosphere. Here we present a novel global eddy-resolving (0.1° horizontal resolution) simulation of the ocean and sea ice, including ocean biogeochemistry, performed with the Community Earth System Model (CESM). The simulation is forced by the atmospheric dataset based on the Japanese Reanalysis (JRA-55) product over the 1958 – 2021 period. We present a novel configuration of the CESM marine ecosystem model in this simulation which includes two zooplankton classes: microzooplankton and mesozooplankton. This novel planktonic food web structure facilitates “offline” coupling with the Fisheries Size and Functional Type (FEISTY) model. FEISTY is a size- and trait-based model of fish functional types contributing to fisheries. We present an evaluation of the ocean biogeochemistry, marine ecosystem (including fish types), and sea ice in this high-resolution simulation compared to available observations and a corresponding low resolution (nominal 1°) simulation. Our analysis offers insights into environmental controls on trophodynamics within the ocean. We find that this high resolution simulation provides a realistic reconstruction of nutrients, oxygen, sea ice, plankton and fish distributions over the global ocean. On global and large regional scales the high-resolution simulation is comparable to the standard 1° simulation, but on smaller scales, explicitly resolving the mesoscale dynamics is shown to be important for accurately capturing trophodynamic structuring, especially in coastal ecosystems. We show that fine scale ocean features leave imprints on ocean ecosystems, from plankton to fish, from the tropics to polar regions. This simulation also offers insights on ocean acidification over the past 64 years, as well as how large scale climate variations may impact upper trophic levels. The data generated by the simulations are publicly available and will be a fruitful community resource for a large variety of oceanographic science questions.

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Organic matter decay and bacterial community succession in mangroves under simulated climate change scenarios

Published 24 July 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, laboratory, molecular biology, morphology, otherprocess, physiology, prokaryotes, sediment, South Atlantic

Mangroves are coastal environments that provide resources for adjacent ecosystems due to their high productivity, organic matter decomposition, and carbon cycling by microbial communities in sediments. Since the industrial revolution, the increase of Greenhouse Gases (GHG) released due to fossil fuel burning led to many environmental abnormalities such as an increase in average temperature and ocean acidification. Based on the hypothesis that climate change modifies the microbial diversity associated with decaying organic matter in mangrove sediments, this study aimed to evaluate the microbial diversity under simulated climate change conditions during the litter decomposition process and the emission of GHG. Thus, microcosms containing organic matter from the three main plant species found in mangroves throughout the State of São Paulo, Brazil (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) were incubated simulating climate changes (increase in temperature and pH). The decay rate was higher in the first seven days of incubation, but the differences between the simulated treatments were minor. GHG fluxes were higher in the first ten days and higher in samples under increased temperature. The variation in time resulted in substantial impacts on α-diversity and community composition, initially with a greater abundance of Gammaproteobacteria for all plant species despite the climate conditions variations. The PCoA analysis reveals the chronological sequence in β-diversity, indicating the increase of Deltaproteobacteria at the end of the process. The GHG emission varied in function of the organic matter source with an increase due to the elevated temperature, concurrent with the rise in the Deltaproteobacteria population. Thus, these results indicate that under the expected climate change scenario for the end of the century, the decomposition rate and GHG emissions will be potentially higher, leading to a harmful feedback loop of GHG production. This process can happen independently of an impact on the bacterial community structure due to these changes.

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Impact of ocean acidification on the intestinal microflora of Sinonovacula constricta

Published 23 July 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, laboratory, molecular biology, mollusks, morphology, North Pacific, otherprocess, physiology, prokaryotes

The intestinal microflora of host, vital for nutrient absorption and immune regulation, can experience dysbiosis under environmental stress, thereby potentially enhancing host susceptibility to pathogenic invasion. The impact of ocean acidification on bivalves is substantial, yet its effects on the intestinal microflora remain poorly understood. This study employed high-throughput 16S rRNA sequencing technology to investigate the variations in the intestinal microflora of Sinonovacula constricta between the control group (CON) and the seawater acidification group (OA) at different time points.After exposure to OA, changes in the composition of the intestinal microflora of S. constricta were observed, with no significant difference in α-diversity between the acidified and control groups. At the phylum level, there was an increase in the abundance of Proteobacteria, while Cyanobacteria decreased in the OA14d and OA35d groups. Additionally, the relative abundance of Firmicutes increased in the OA7d and OA35d groups. At the genus level, the relative content of Pseudomonas was lower than that in the control group, while the relative content of Flavobacterium, Acinetobacter, and Enterobacter showed a gradual increasing trendin the OA14d and OA35d groups.. LEfSe analysis identified Serpens as discriminative biomarkers in the OA7d group, while Enterobacteriales, Rhodobacteraceae and Martvita were biomarker in the OA14d group, and Serpens, Acidibacteria and Aeromonadaceae were biomarker in the OA35d group. Functional prediction results indicated significant enrichment in metabolic pathways at different time points following ocean acidification stress… The pathways involved in biosynthesis in the OA14d group and in sucrose degradation in the OA35d group were significantly disrupted. These results suggest that OA stress can have adverse effects on the intestinal microflora of S. constricta, but it does not cause obvious damage to the digestive system. This study provides new insights into the intestinal microflora of marine bivalves under acidification stress.

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Uptake of dissolved inorganic nitrogen and N2 fixation by Crocosphaera watsonii under climate change scenarios

Published 22 July 2024 Science Closed
Tags: abundance, biological response, chemistry, growth, laboratory, multiple factors, nitrogen fixation, otherprocess, physiology, prokaryotes, temperature

The response of N₂ fixation to projected future conditions in the ocean cannot be reliably predicted to date. We conducted a minicosm experiment with pre-acclimated cultures of the globally significant diazotroph Crocosphaera watsonii strain WH8501 (“Crocosphaera”). PH and temperature were altered simultaneously to match the RCP scenarios 4.5 and 6 and investigate a more realistic future scenario compared to studies that focus on changes of a single stressor only. The cell abundance and nitrogen metabolism of Crocosphaera was monitored over 5 days. Our results imply that Crocosphaera is able to simultaneously perform N₂ fixation and assimilate dissolved inorganic nitrogen (DIN, i.e., nitrate and ammonium) under all the conditions tested and implies a competition with non-diazotrophic phytoplankton for DIN, which should be further investigated. Using NanoSIMS analysis of single cells, our results point towards a preference for DIN assimilation over N₂ fixation under more acidic and warmer conditions. Overall, our results show that while the combined alteration of pH and temperature had a negative effect on the diazotroph’s growth and N₂ fixation, Crocosphaera is likely to cope well with conditions in the future ocean. The high intra-population variability in nitrogen assimilation pathways may give this species the flexibility to quickly react to environmental changes.

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Unveiling the secrets of diatom-mediated calcification: implications for the biological pump

Published 19 July 2024 Science Closed
Tags: abundance, biological response, chemistry, laboratory, North Pacific, otherprocess, performance, photosynthesis, phytoplankton

Siliceous diatoms are one of the most prominent actors in the oceans, and they account for approximately 40% of the primary production and particulate organic carbon export flux. It is believed that changes in carbon flux caused by variations in diatom distribution can lead to significant climate shifts. Although the fundamental pathways of diatom-driven carbon sequestration have long been established, there are no reports of CaCO₃ precipitation induced by marine diatom species. This manuscript introduces novel details regarding the enhancement of aragonite precipitation during photosynthesis in Skeletonema costatum in both artificial and natural seawater. Through direct measurements of cell surfaces via a pH microelectrode and zeta potential analyzer, it was determined that the diatom-mediated promotion of CaCO₃ precipitation is achieved through the creation of specific microenvironments with concentrated [CO₃²⁻] and [Ca²⁺] and/or the dehydrating effect of adsorbed Ca²⁺. Based on this mechanism, it is highly plausible that diatom-mediated calcification could occur in the oceans, an assertion that was supported by the significant deviation of total alkalinity (TA) from the conservative TA-salinity mixing line during a Skeletonema costatum bloom in the East China Sea and other similar occurrences. The newly discovered calcification pathway establishes a link between particulate inorganic and organic carbon flux and thus helps in the reassessment of marine carbon export fluxes and CO₂ sequestration efficiency. This discovery may have important ramifications for assessing marine carbon cycling and predicting the potential effects of future ocean acidification.

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Bottom’s up – focusing on habitat shifts as mediators of anthropogenic impacts on marine ecosystems

Published 16 July 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, corals, fish, otherprocess, South Pacific

Marine ecosystems face unprecedented challenges in the Anthropocene, an age characterized by escalating environmental stressors such as ocean acidification, warming and the intrusion of human infrastructure into coastal seascapes. As we hasten to understand the ecological consequences of these mounting pressures, much attention has been devoted to characterizing the traits of individual taxa that are likely to dictate their response to future conditions. However, we are increasingly recognizing the pivotal role that habitat may play in shaping the response of communities to such broad-scale changes. In this thesis, I present empirical evidence of the capacity of habitat-level responses to stress to propagate upwards through the broader ecosystem, inducing substantial and meaningful changes in supported fish assemblages. In my first project, I trace the indirect effects of ocean acidification from the habitat level through to the structure of an assemblage of small-bodied reef fish. I use the natural laboratory provided by a volcanic seep in Papua New Guinea to approximate future acidification conditions under current climate change projections. Here, coral communities chronically exposed to elevated CO2 exhibit a shift in competitive interactions that favours fast-growing, morphologically simple taxa, with the implication that other coral reefs globally may undergo an equivalent structural simplification in coming decades in response to ocean acidification. I show that several common, ecologically important reef fishes display strong and relatively inflexible associations with branching corals, with some even preferencing structure over living tissue when selecting habitat. I then demonstrate that acidified and structurally simplified reefs show a drastically reduced capacity to support healthy populations of these fishes. This chapter contributes two important findings: first, that simplification of coral morphology in response to ocean acidification can induce substantial negative changes in supported reef fish assemblages, even if the total cover of live coral remains unchanged; and secondly, that reef fish may be more vulnerable to these indirect, habitat level changes than to the simple direct effects wrought by acidification. Shifting focus to temperate ecosystems, my second project examines how warming, coastal urbanisation and marine protection interact to influence the distributions and assemblage structures of rangeshifting tropical fishes as they venture poleward in response to ocean warming. Using breakwalls as a ubiquitous and readily accessible test case, I reveal that the structural complexity and shelter from wave action offered by coastal infrastructure can render these environments hotspots for tropical fish recruitment. Importantly, this chapter both identifies coastal infrastructure as potentially significant contributors to the process of tropicalisation, highlighting the need for further research attention and monitoring, but also recognises that marine protected areas can offer an effective means of mitigating the effects of coastal urbanisation. Together, the two projects presented in this thesis demonstrate the power of both the direct and indirect effects of habitat changes. In light of the ongoing and accelerating accumulation of anthropogenically induced stressors, my research underscores the necessity of accounting for habitat-level responses when projecting future fish assemblages, and frames habitat protection as a vital element of safeguarding healthy ecosystems.

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Out of shape: ocean acidification simplifies coral reef architecture and reshuffles fish assemblages

Published 3 July 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, corals, fish, otherprocess, performance, physiology, South Pacific

Climate change stressors are progressively simplifying biogenic habitats in the terrestrial and marine realms, and consequently altering the structure of associated species communities.
Here, we used a volcanic CO₂ seep in Papua New Guinea to test in situ if altered reef architecture due to ocean acidification reshuffles associated fish assemblages.
We observed replacement of branching corals by massive corals at the seep, with simplified coral architectural complexity driving abundance declines between 60% and 86% for an assemblage of damselfishes associated with branching corals. An experimental test of habitat preference for a focal species indicated that acidification does not directly affect habitat selection behaviour, with changes in habitat structural complexity consequently appearing to be the stronger driver of assemblage reshuffling. Habitat health affected anti-predator behaviour, with P. moluccensis becoming less bold on dead branching corals relative to live branching corals, irrespective of ocean acidification.
We conclude that coral reef fish assemblages are likely to be more sensitive to changes in habitat structure induced by increasing pCO₂ than any direct effects on behaviour, indicating that changes in coral architecture and live cover may act as important mediators of reef fish community structures in a future ocean.

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Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates

Published 3 July 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, community composition, echinoderms, mollusks, otherprocess, performance, sediment

Climate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour—a key process mediating nutrient cycling—associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO₂]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing.

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Impact of ocean acidification on microzooplankton grazing dynamics

Published 28 June 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, laboratory, North Pacific, otherprocess, performance, phytoplankton, zooplankton

This study examines the potential impacts of projected atmospheric carbon dioxide (pCO₂) levels reaching 800 ppm by the end of the century, focusing on ocean acidification effects on marine ecosystems in the coastal areas of Bohai. We investigated how acidification affects the grazing patterns of microzooplankton using dilution techniques and ecophysiological methods. Our findings indicate that acidic conditions shift the phytoplankton community structure, changing dominant species. Elevated CO₂ concentrations reduced grazing pressure on phytoplankton, with less steep declines in growth rates at 800 ppm CO₂ (spring: 2.43 d⁻¹ vs. 2.16 d⁻¹, summer: −0.46 d⁻¹ vs. −0.73 d⁻¹, autumn: −0.45 d⁻¹ vs. −0.90 d⁻¹) and significant decreases in grazing pressure percentages (%Pp from 0.84 to 0.58 and %Pi from 0.64 to 0.46). Short-term acid exposure significantly increased superoxide dismutase activity in both microplankton (from 0.03 to 0.08 U mg⁻¹, p<0.01) and nanoplankton (from 0.05 to 0.09 U mg⁻¹, p<0.001), indicating an adaptive response to oxidative stress. These results highlight that elevated CO₂ levels primarily boost phytoplankton growth by reducing microzooplankton grazing pressure, resulting in higher growth rates and a shift towards smaller-sized phytoplankton, reflecting complex short-term ecological responses to acidification. Further research is needed to understand the long-term effects of ocean acidification on microzooplankton and their role in marine secondary productivity.

Continue reading ‘Impact of ocean acidification on microzooplankton grazing dynamics’

Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons

Published 20 June 2024 Science Closed
Tags: abundance, biological response, BRcommunity, calcification, chemistry, community composition, corals, dissolution, laboratory, morphology, North Atlantic, otherprocess, primary production, protists, respiration

As the balance between erosional and constructive processes on coral reefs tilts in favor of framework loss under human-induced local and global change, many reef habitats worldwide degrade and flatten. The resultant generation of coral rubble and the beds they form can have lasting effects on reef communities and structural complexity, threatening the continuity of reef ecological functions and the services they provide. To comprehensively capture changing framework processes and predict their evolution in the context of climate change, heavily colonized rubble fragments were exposed to ocean acidification (OA) conditions for 55 days. Controlled diurnal pH oscillations were incorporated in the treatments to account for the known impact of diel carbonate chemistry fluctuations on calcification and dissolution response to OA. Scenarios included contemporary pH (8.05 ± 0.025 diel fluctuation), elevated OA (7.90 ± 0.025), and high OA (7.70 ± 0.025). We used a multifaceted approach, combining chemical flux analyses, mass alteration measurements, and computed tomography scanning images to measure total and chemical bioerosion, as well as chemically driven secondary calcification. Rates of net carbonate loss measured in the contemporary conditions (1.36 kg m⁻² year⁻¹) were high compared to literature and increased in OA scenarios (elevated: 1.84 kg m⁻² year⁻¹ and high: 1.59 kg m⁻² year⁻¹). The acceleration of these rates was driven by enhanced chemical dissolution and reduced secondary calcification. Further analysis revealed that the extent of these changes was contingent on the density of the coral skeleton, in which the micro- and macroborer communities reside. Findings indicated that increased mechanical bioerosion rates occurred in rubble with lower skeletal density, which is of note considering that corals form lower-density skeletons under OA. These direct and indirect effects of OA on chemical and mechanical framework-altering processes will influence the permanence of this crucial habitat, carrying implications for biodiversity and reef ecosystem function.

Continue reading ‘Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons’

Ocean acidification alters microeukaryotic and bacterial food web interactions in a eutrophic subtropical mesocosm

Published 4 June 2024 Science Closed
Tags: abundance, biological response, BRcommunity, chemistry, mesocosms, otherprocess, photosynthesis, phytoplankton, prokaryotes, zooplankton

Highlights

The communities were strongly affected by phytoplankton bloom stages.
Ocean acidification (OA) affected some taxa as the phytoplankton bloom stages progressed.
OA changed the co-occurrence network complexity and stability of microeukaryotes.
OA altered the proportions of potential interactions between phytoplankton and their predators.

Abstract

Ocean acidification (OA) is known to influence biological and ecological processes, mainly focusing on its impacts on single species, but little has been documented on how OA may alter plankton community interactions. Here, we conducted a mesocosm experiment with ambient (∼410 ppmv) and high (1000 ppmv) CO₂ concentrations in a subtropical eutrophic region of the East China Sea and examined the community dynamics of microeukaryotes, bacterioplankton and microeukaryote-attached bacteria in the enclosed coastal seawater. The OA treatment with elevated CO₂ affected taxa as the phytoplankton bloom stages progressed, with a 72.89% decrease in relative abundance of the protist Cercozoa on day 10 and a 322% increase in relative abundance of Stramenopile dominated by diatoms, accompanied by a 29.54% decrease in relative abundance of attached Alphaproteobacteria on day 28. Our study revealed that protozoans with different prey preferences had differing sensitivity to high CO₂, and attached bacteria were more significantly affected by high CO₂ compared to bacterioplankton. Our findings indicate that high CO₂ changed the co-occurrence network complexity and stability of microeukaryotes more than those of bacteria. Furthermore, high CO₂ was found to alter the proportions of potential interactions between phytoplankton and their predators, as well as microeukaryotes and their attached bacteria in the networks. The changes in the relative abundances and interactions of microeukaryotes between their predators in response to high CO₂ revealed in our study suggest that high CO₂ may have profound impacts on marine food webs.

Continue reading ‘Ocean acidification alters microeukaryotic and bacterial food web interactions in a eutrophic subtropical mesocosm’

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