The Ocean Acidification (OA) Workshop for the for the Western Indian Ocean was successfully organized in Dar es Salaam, Tanzania on 27 January 2025. The review meeting of the proposed Ocean Acidification Action Plan by the Nairobi Convention was supported by the Nairobi Convention component in the ACP MEA Phase 3 Programme. The technical meeting will lead to a validation and endorsement of the regional ocean acidification action plan by the contracting Member States to the Nairobi Convention.
Technical experts, government officials, and OA stakeholders amplified the greater need for stronger regional collaboration to address the impacts of emerging environmental and economic challenges posed by ocean acidification. The OA review workshop addressed local drivers, and the significant impacts of OA on fishery resources amongst ocean dependent coastal livelihoods.
Ocean Acidification workshop in Dar es Salaam, Tanzania.
The OA action plan highlighted the region’s ocean acidification monitoring data and existing data gaps, notable trends that are enhancing ocean acidification, and the necessity for regional, national, and community advocacy. Participants called for the urgent need to integrate OA into climate change policies, strategies, into nationally determined contributions, and to enhance measures to mitigate ocean acidification.
Ocean acidification (OA) stands out as one of the main threats to marine ecosystems. OA leads to a reduction in the availability of carbonate ions, which are essential for marine calcifiers such as echinoderms. We aim to understand the physiological responses of two sea urchin species, Paracentrotus lividus and Arbacia lixula to low pH conditions and determine whether their responses result from phenotypic plasticity or local adaptation. The study is divided into two parts: plasticity response over time, measuring respiration rates of individuals from the Mediterranean Sea exposed to low pH over seven days, and adaptation and plasticity under changing pH, analyzing individuals inhabiting a pH gradient in a natural CO2 vent system located in La Palma Island, Spain. Over the seven days of low pH exposure, distinct patterns in respiration rates were revealed, with both species demonstrating potential for acclimatization. Notably, P. lividus and A. lixula displayed unsynchronized acidosis/alkalosis cycles, suggesting different physiological mechanisms. Additionally, environmental history seemed to influence adaptive capacity, as specimens from fluctuating pH environments exhibited respiration rates similar to those from stable environments with heightened phenotypic plasticity. Overall, our results suggest that both species possess the capacity for metabolic plasticity, which may enhance their resilience to future OA scenarios but likely involve energetic costs. Moreover, CO2 vent systems may serve as OA refugia, facilitating long-term survival. Understanding the plastic responses versus adaptations is crucial for predicting the effects of OA on species distribution and abundance of marine organisms in response to ongoing climate change.
Central carbon and fatty acid metabolism up-regulated after warming adaptation.
High CO2 acted antagonistically with warming to slow down these pathways.
Amino acid synthesis accelerated after high CO2 and warming adaptation.
Abstract
While it is known that warming and rising CO2 level might interactively affect the long-term adaptation of marine diatoms, the molecular and physiological mechanisms underlying these interactions in the marine diatom Thalassiosira weissflogii on an evolutionary scale remain largely unexplored. In this study, we investigated the changes in metabolic pathways and physiological responses of T. weissflogii under long-term ocean acidification and/or warming conditions (∼3.5 years), integrating proteomics analyses and physiological measurements. Our findings reveal that proteins involved in central carbon metabolisms (e.g., tricarboxylic acid cycle and glycolysis) and fatty acid metabolism were significantly up-regulated in the long-term warming-adapted populations. However, the long-term adaptation to high CO2 acted antagonistically with warming, slowing down the central carbon metabolism and fatty acid metabolism by down-regulating protein expressions in the key metabolic pathways of the glycolysis and tricarboxylic acid cycle. Additionally, amino acid synthesis was accelerated in the long-term warming and its combination with high CO2-adapted populations. Physiological measurements further supported these findings, showing altered growth rates and metabolic activity under the combined warming and high CO2 conditions. Our results provide new insights into the molecular mechanisms underpinning the antagonistic interaction between high CO2 and warming on marine phytoplankton in the context of global change.
The ocean carbonate system consists of pH, alkalinity, inorganic carbon and the partial pressure of carbon dioxide, and during the current era of anthropogenic change, its dynamics are key for understanding changes in the ocean and its ecosystem over time. The focus of this study is to estimate the carbonate system in the Labrador Sea with time series methods, using direct observations from the ocean surface and interior, and chemical relationships between variables. Interior ocean observations are minimal for some of these variables, however, connections between the variables rooted in chemistry were used to create pseudo-observations using CO2SYS, increasing the information available. A state space model was designed that combined GLODAP and SOCAT observations along with pseudo-observations in a time series estimate of the carbonate system. The Labrador Sea between 1993 and 2016 shows increasing rates for DIC (0.57-1.16 µmol kg−1 year−1) and fCO2 (0.70-2.45 µatm year−1), as well as acidification via pH trends (0.0007-0.0018 year−1). These ranges describe the scale of rates that are occurring at various depths through the water column, though they do not change linearly with depth. Largest rates are found at the surface for DIC, 500-1500 m for fCO2, and 500-1500 m for pH. Total alkalinity also decreased and is correlated with the freshening of salinity. With the core carbonate variables estimated, other aspects of the carbonate system are calculated using CO2SYS, such as the aragonite and calcite saturation states, the Revelle factor, and the carbonate species. Our method also calculates uncertainties that vary over time and depth based on the availability of observations and their variance, which has lowered the uncertainty for pH by 71% and for fCO2 by 64% compared to time-independent methods.
Introduction: This study investigated the variability and main drivers of the carbonate system in Gayraca Bay and Chengue Bay, located on the northeastern Caribbean coast of Colombia, through monthly measurements of partial pressure of CO2 (pCO2), pH, total alkalinity (TA), and dissolved inorganic carbon (DIC) from 2017 to 2022. Statistical analyses and Taylor series decomposition were employed to determine the seasonal and interannual contributions of sea surface temperature, salinity, TA, and DIC to changes in pCO2, pH, and calcium carbonate saturation state (Ω).
Results: The results showed significant seasonal variability influenced by annual changes in coastal upwelling, rainfall, and river runoff. Low/high pH and Ω values were associated with high/low DIC and TA values during the dry and wet seasons, respectively, while pCO2 exhibited an opposite pattern. During El Niño, negative anomalies in coastal upwelling produced negative anomalies in pCO2 and positive anomalies in Ω, DIC, and TA. Conversely, during La Niña, alternating periods of positive rainfall and upwelling anomalies were observed. Higher rainfall corresponded to negative anomalies in pCO2, DIC, and TA and positive anomalies in Ω, whereas stronger upwelling led to opposite trends. In early 2022, undersaturated levels of Ωcalc and Ωarag (<1) were observed, which could affect coral calcification and pose risks in future climate change scenarios. Taylor series decomposition analysis identified TA and DIC as primary drivers of carbonate system variability, modulated by seasonal and interannual changes in rainfall and river runoff, which are influenced by ENSO events. The observed trends in pH and pCO2 were driven by a decrease in DIC and TA, attributed to increased river runoff, contrasting with typical ocean acidification trends driven by rising atmospheric CO2 levels.
Discussion: This highlights the region’s unique dynamics and underscores the importance of local studies. This study provides a novel 6-year time-series dataset for the carbonate system in the Colombian Caribbean, offering a valuable baseline for assessing the impacts of global warming and ocean acidification in the region.
Understanding the effects of global change, including temperature, pH, and oxygen availability, on commercially important species is crucial for anticipating consequences for these resources and their ecosystems. In the Gulf of St. Lawrence (GSL), redfish (Sebastes spp.) have been under moratorium from 1995 to 2024, with a massive recruitment observed in 2011–2013. However, little is known about their metabolic and thermal physiology, making predictions of their response to changing GSL conditions challenging. To address this, we quantified the effects of four acclimatation temperatures (2.5, 5.0, 7.5, and 10.0 ℃) and two pH levels (7.35 and 7.75) on standard and maximum metabolic rates (SMR and MMR), aerobic scope (AS), hypoxia tolerance (O2crit), food consumption, and growth in redfish. SMR, MMR, and AS increased with temperature, but growth decreased at the highest temperature, likely due to increased metabolic demand, with food consumption similar across 5.0 to 10.0 °C treatments. O2crit was lower for fish acclimated to 2.5 and 5.0 ℃, making redfish less hypoxia-tolerant at higher temperatures. Except from SMR, no significant effect of pH was observed. These results suggest that future changes in the GSL will challenge redfish, with potential long-term effects on their growth due to increased energy requirements.
Ocean acidification (OA) is one of the greatest threats to marine species, with widespread impacts on their physiological functions. However, the adaptive capacities of many marine species to OA and the underlying mechanisms remain unclear. In this study, we investigated the effects of short-term (4 days) and medium-term (30 days) CO2 exposure (pH 8.0, 7.6, and 7.3) on black rockfish (Sebastes schlegelii), focusing on histopathological changes in gill tissues, ion transport biomarkers, oxidative stress indicators, and transcriptomic responses. The results showed that both short-term and medium-term OA induced significant morphological changes in gill tissues, including epithelial lifting, hyperplasia, hypertrophy, and lamellar clubbing, which are likely adaptive mechanisms for maintaining homeostasis. Both Na+/K+-ATPase and carbonic anhydrase (CA) activities increased significantly in both short- and medium-term exposure, while Ca2+-ATPase activity was elevated only in the short-term, suggesting differential enzyme regulation over time to sustain ionic balance. Additionally, oxidative stress indicators (superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), reduced glutathione (GSH) and glutathione peroxidase (GPx)) were significantly elevated after both exposure durations, indicating that the antioxidant defense system was activated. Moreover, the integrated biomarker response (IBR) index further indicated that the stress response was more pronounced during short-term exposure. Transcriptomic analysis reveals significant alterations in pathways related to calcium signaling, cytoskeletal structure, energy metabolism, and oxidative stress following short-term exposure. In contrast, medium-term exposure leads to significant enrichment of pathways associated with cell-environment interactions, highlighting the molecular adaptations of S. schlegelii to OA-induced stress. These findings provide valuable insights into the mechanisms of OA tolerance in S. schlegelii and contribute to understanding the adaptability of marine species in future ocean environments.
Dr. Richard Feely (NOAA/PMEL) presents on “The Combined Effects of Ocean Acidification and Hypoxia” (Part 1) with Dr. Nina Bednarsek (Oregon State University) at our December 5th, 2024 Partnerships for Tribal Carbon Solutions workshop: Can Rocks Fix the Climate and Heal the Sea? Richard Feely from NOAA’s Pacific Marine Environmental Laboratory discusses ocean acidification in the Pacific Northwest, one of the most vulnerable regions globally. He explains how rising atmospheric CO₂ leads to ocean acidification through chemical reactions that increase hydrogen ion concentration, lowering pH and reducing carbonate availability, which threatens calcifying marine organisms. He highlights how coastal upwelling and biological respiration amplify acidification, making subsurface waters particularly susceptible. Using models and observational data, he demonstrates that acidification is progressing rapidly, with pH declines exceeding EPA water quality criteria in some areas. He emphasizes that adding ocean alkalinity could counteract these changes, offering a potential strategy to mitigate acidification’s impacts.
Submarine groundwater discharge impacts on tropical coastal waters were studied.
Nutrient sourced SGD input stimulate the growth of diatoms in the coastal waters.
Acidification may alter the balance between plankton communities.
Long term monitoring studies of interactive effects of potential drivers needed.
Abstract
Submarine groundwater discharge (SGD) is a significant contributor to effect phytoplankton community shift and marine ecosystem changes, yet little information is available about its influence in the Indian coastal waters. This microcosm study assessed the impact of groundwater input on carbonate chemistry changes, plankton community structuring and marine ecosystem dynamics in coastal waters off Kochi, southeastern Arabian Sea (SEAS), southwest India. The relatively high nutrient content (nitrate and silicate) and low nitrate to silicate ratio (N/Si < 1) in the groundwater favoured the growth and fast abundance of diatom species (Thalassiosira sp.). The increased growth rate of diatoms in coastal groundwater additions shifts the community composition towards higher microphytoplankton relative to picoplankton proportion. Increased heterotrophic thecate dinoflagellates such as Protoperidinium species with SGD might become the significant consumers of bloom forming diatoms in the coastal waters. The SGD driven acidification with increased nutrient supply may alter the balance between autotrophic and heterotrophic plankton communities, which becomes intense with the effective increase in atmospheric aerosols and anthropogenic inputs, amplifying the scope of coastal ocean acidification.
Enjoyed at raw bars across the world with a squeeze of lemon, nearly every farmed oyster starts its journey the same way: in a hatchery.
“When hatcheries make baby oysters they start with the moms and pops and they end up with billions of tiny, microscopic oyster larvae that hang out in suspension for a couple of weeks in the seawater, feeding on phytoplankton,” explains Gary Fleener, a scientist-turned-director at Hog Island Oyster Co. Based in California, Hog Island is one of the largest oyster businesses in the US – operating five restaurants, selling wholesale and shipping its oysters directly to homes across the country via their website.
This method of spawning oysters in tanks that are aerated with a mix of fresh seawater and oxygen is similar across the world and is why farmed oysters have a 71 percent higher survival rate than their wild counterparts: hatcheries work.
But in 2007, west coast hatcheries in the United States were shaken. From Washington State to California, entire generations of larvae were dying. And hatchery technicians couldn’t figure out why it was happening. That year, most west coast oyster farmers were left without any seed for their upcoming season.
Describing it as “series of fairly catastrophic die-offs of larvae,” Fleener says that “the complete die off… was a little bit baffling.” At first, hatcheries thought that it was a bacterial outbreak but it turned out to be a product of increased ocean acidity or declining ocean pH. Upwellings of deep ocean water with a pH of 7.8 were too acidic for the oyster larvae. Surface ocean pH is typically above 8.0. Although it was a small difference in alkalinity, for larvae working to create shells, it was too great.
“It ended up serving as a foreshadowing of… [what] the future might do to the shellfish industry,” says Fleener. “The waters that were upwelling at the time that killed all those larvae are what they model for 50 years down the road.”
“The changes in ocean chemistry associative with rising human-caused carbon dioxide emissions actually change the building blocks that organisms use to make their shells. We’ve seen evidence of smaller, weaker shells in animals such as oysters and mussels,” she explains.
After the die-off, Hog Island invested in building their own hatchery and created a vertically integrated business, a move that they say has helped them become one of the country’s most successful oyster businesses. By 2012, they had acquired a seawater pumping permit from the California Coastal Commission and now mix their intake ocean water with ash, to make it more alkaline and ensure that the larvae oysters are not damaged by declining ocean pH.
Although hatcheries and farmers figured out a workaround, the event sparked many questions for marine scientists and ocean observers. If farmed larvae were struggling under these new conditions, what did it mean for wild species?
The SDGs-EYES webinar “Eutrophication and acidification in the North Sea: Advancing on SDGs indicators monitoring, reporting and accounting” will provide an in-depth exploration of critical environmental challenges and solutions. This webinar highlights the innovative Copernicus-based tool delivering advanced mapping of SDG indicators for the North Sea, supporting local and European policy-making processes in sustainable marine resource management.
Participants will gain insights into the pilot‘s advanced tools and datasets, designed to enhance stakeholders’ understanding and response strategies to sustainable management of marine resources and ecosystems. The webinar will foster discussions on potential applications, align solutions with user needs, and encourage the adoption of the pilot’s outcomes to address real-world challenges.
Key Highlights:
Advancing SDG14 – Life Below Water: Explore how the pilot contributes to monitoring and managing marine ecosystems, addressing eutrophication and acidification to promote the sustainable use of ocean resources.
Innovative Marine Indicators: Learn how the Copernicus-based tools generate high-resolution maps of SDG14 indicators for the North Sea, supporting policy-making and sustainable management of vulnerable marine areas.
Mitigating Anthropogenic Pressures: Understand how the pilot supports knowledge of the impacts of human activities, such as marine ecosystems changes under recent climate conditions, helping to safeguard biodiversity.
Global Sustainability and Marine Protection: Discuss the role of this initiative in supporting global efforts to achieve SDG 14 targets and contribute to the post-2030 United Nations agenda for ocean health.
Discuss the role of this pilot in supporting global efforts, as the United Nations shapes the post-2030 agenda to advance sustainability goals.
Unlike many vertebrates, oysters do not possess fixed sex chromosomes that dictate whether they develop as male or female at the moment of fertilization. Instead, they utilize a sophisticated biological mechanism known as environmental sex determination, where the surrounding environmental conditions influence their sexual development. Previous investigations have largely concentrated on factors such as temperature and food availability as drivers of sex ratios within aquatic populations; however, the role of fluctuating pH levels remained largely unexamined until now. The recent study led by researchers Xin Dang and Vengatesen Thiyagarajan breaks new ground in understanding how ocean acidification might modify the sex ratio of oysters across multiple generations, both in controlled hatchery environments and in natural habitats.
In their experiment, the researchers began with a collection of wild oysters to serve as the foundational population for their study. These oysters were divided into two groups, one maintained in water with a neutral pH and the other introduced to conditions simulating ocean acidification, characterized by a slightly more acidic pH. The results of this initial phase were revealing. The offspring of oysters that were spawned in the acidic environment exhibited a significantly higher ratio of females to males compared to the offspring of those raised in a neutral pH tank. This implies that the acidification of ocean waters could skew reproductive outputs towards female progeny, potentially altering population structures over time.
The follow-up experiments were equally illuminating. The second-generation oysters from the acidic environment were transplanted into two contrasting natural settings: one with a neutral pH and another with an acidic pH. Remarkably, regardless of whether these third-generation oysters were placed in an acidic or neutral pH habitat, they still exhibited an increased female-to-male ratio. This observation strongly suggests that the effects of ocean acidity on sex determination are not merely a transient phenomenon; rather, they can persist across generations. Such findings provide deeper insights into the transgenerational impacts of environmental stressors on marine life.
This study investigates the interaction between δ¹³C and δ¹¹B with terrigenous carbon dynamics in the Singapore Strait, a region characterized by distinct monsoon patterns and significant terrigenous input from surrounding peatlands. We hypothesized that elevated levels of colored dissolved organic matter (CDOM) during the Southwest Monsoon would decrease light penetration, leading to more negative δ¹³C values in coral skeletons. Additionally, we expected that remineralization of terrigenous dissolved organic matter (tDOM) would acidify seawater, resulting in more negative δ¹¹B values in corals. Analysis of Porites spp. corals from two plug cores (KUK and KUL) and seawater data from Kusu Island (2017-2020) revealed no significant correlation between CDOM and coral δ¹³C anomalies— deviations between coral skeletal δ¹³C values and the δ¹³C values of dissolved inorganic carbon (DIC) in seawater— contradicting our hypothesis. Instead, variations in coral δ¹³C appear to be related to a reservoir effect associated with negative δ¹³C in seawater DIC, influenced by tDOC remineralization. Although not statistically significant, the positive correlation pattern observed between δ¹¹B and seawater pH in the KUL core suggests that δ¹¹B might serve as a useful proxy for historical seawater pH and acidification. This finding also supports the idea that Porites corals may regulate their internal pH in response to changes in seawater acidity, potentially influenced by tDOC remineralization. Inconsistencies in the KUK core could be attributed to data offsets from our age-depth model. Further research with extended sampling is needed to confirm δ¹¹B’s sensitivity to pH changes and understand its impact on coral physiology. This study highlights the complex interplay between seasonal changes, carbon dynamics, and coral isotopic records.
Ocean acidification is a growing topic of interest and concern for Alaska communities. Alaska has been identified as a hotspot, and the effects of ocean acidification are likely to have serious implications for fisheries, food security and the economy. Researchers with the University of Alaska Fairbanks and the National Oceanic and Atmospheric Administration (NOAA) are monitoring ocean acidification in coastal waters around Alaska, and are also exploring ecological and socio-economic impacts. In recent years, Tribes, coastal communities and industry groups have joined the monitoring effort. The Alaska Ocean Acidification Network brings together these diverse entities and more to share and expand the understanding of ocean acidification processes and consequences, as well as explore potential adaptation and mitigation strategies. These conversations include “what is the data telling us and how can it help to inform local community decisions?” This presentation will include a refresher on ocean acidification, the primary information needs voiced by Alaskans, and what we’ve learned from recent research and monitoring about conditions and species response.
Arctic Research Consortium of the United States, 4 February 2025. More information.
Ocean acidification describes the decline in pH of marine environments as they continue to absorb anthropogenically derived carbon dioxide (CO2). Research over the past ~15 years has reported that levels of ocean acidification forecasted for the end of the century (CO2 ~800-1000 μatm; pH ~7.6-7.7) can severely impair behaviours of marine animals, including fishes and invertebrates. Impaired behaviours of most concern are those linked with neural and sensory systems, such as the capacity to respond appropriately to predators. However, after an initial proliferation of studies reporting dire behavioural disturbances, studies finding negligible effects of end-of-century ocean acidification began to accumulate. We have now reached a point where there is little consensus on whether, and how much, ocean acidification will impact animal behaviour. Here, we outline existing knowledge regarding the effects of ocean acidification on animal behaviour, discuss the chronology of discoveries and controversies in the field, and provide guidance for improving rigour and transparency in behavioural ecology more broadly.
Macrophytes play a key role in coastal environments, acting to transform inorganic carbon into biologically available organic matter. This process supports the marine food web at large, however, the dynamics behind macrophyte carbon acquisition are not fully understood with factors influencing their ability to utilize different carbon forms (HCO3− and/or CO2) and subsequent release mechanics of this carbon remaining rather poorly understood. This study aims to investigate the physiological responses of two important Baltic Sea macrophytes, Ulva intestinalis and Cladophora glomerata. By examining the effects of pH drift inhibitors, coupled with carbon-concentrating mechanisms (CCMs) and dissolved organic carbon (DOC) dynamics, we provide insights into the complex adaptations of these macroalgae to changing environmental conditions. The results demonstrate that both species exhibit distinct capabilities to adapt their carbon concentration mechanisms (CCMs) but suggest that C. glomerata may potentially gain a photosynthetic advantage in future high CO2. The observed differences between pH and water motion highlight species-specific nuances in the regulation of dissolved organic carbon (DOC) release, aligning with current theories on DOC dynamics. This research underscores the importance of understanding macroalgal adaptation and fitness in both present and future coastal ecosystems, particularly as environmental changes continue to evolve. By examining these factors, the study contributes valuable insights into how macroalgae may respond to future climate shifts.
Land-based inputs, such as runoff, rivers, and submarine groundwater, can alter biologic processes on coral reefs. While the abiotic factors associated with land-based inputs have strong effects on corals, corals are also affected by biotic interactions, including other neighboring corals. The biologic responses of corals to changing environmental conditions and their neighbors are likely interactive; however, few studies address both biotic and abiotic interactions in concert. In a manipulative field experiment, we tested how the natural environmental gradient created by submarine groundwater discharge (SGD) affected holobiont and symbiont metabolic rates and endosymbiont physiology of Porites rus. We further tested how the effect of SGD on the coral was mediated by intra and interspecific interactions. SGD is a natural land-sea connection that delivers nutrients, inorganic carbon, and other solutes to coastal ecosystems worldwide. Our results show that a natural gradient of nutrient enrichment and pH variability as a result of acute SGD exposure generally benefited P. rus, increasing gross photosynthesis, respiration, endosymbiont densities, and chlorophyll a content. Conspecifics in direct contact with the a neighboring coral, however, altered the relationship between coral physiology and SGD, lowering the photosynthetic and respiration rates from expected values when the coral had no neighbor. We show that the response of corals to environmental change is dependent on the types of nearby neighbor corals and how neighbors alter the chemical or physical environment around the coral. Our study underscores the importance of considering biotic interactions when predicting the physiologic responses of corals to the environment.
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.
We used semi-parametric Bayesian regression to determine whether ocean acidification or climate warming could explain declining productivity for southeast Bering Sea red king crab (Paralithodes camtchaticus). Negative effects of acidification explained ~21% of recruitment variability over 1980-2023, and ~45% since 2000. Ocean warming had a negligible effect in our analysis. Model-estimated annual mean bottom pH in the region has fallen from ~8.03 in 1980 to ~7.89 in 2023, approaching levels that reduce juvenile survival in laboratory studies. Improved model validation and better understanding of potential threshold effects on red king crab are needed to better understand the possible population-level acidification effect that we demonstrate.
Ocean acidification estimated in the Mozambique Basin and the African coastal zone.
These regions act as a CO2 sink
The decrease of pH was faster in recent decade
It was driven by anthropogenic CO2 uptake with about 10% due to the ocean warming
Abstract
We describe new observations of the oceanic carbonate system in the South-Western Indian Ocean obtained in January 2021 (OISO-31 cruise) and May 2022 (RESILIENCE cruise). To evaluate the decadal trends and drivers of fugacity of CO2 (fCO2), air-sea CO2 fluxes, dissolved inorganic carbon (CT) and pH, we used available data in this region over 1963-2023 and compared the results in the Mozambique Basin and in the Agulhas region near the African coast. Over 1995-2023, we found a faster fCO2 increase in the Mozambique basin (2.03 ±0.07 μatm.yr-1) compared to the coastal zone (1.37 ±0.07 μatm.yr-1). The temporal change of anthropogenic CO2 concentrations estimated in subsurface enables to reconstruct the carbonate system properties since the 1960s. In the Mozambique Basin the CO2 sink increased slightly over 1960-2022 with a maximum observed in May 2022 (-2.4 mmolC.m-2.d-1). In the coastal zone, the ocean CO2 sink increased from near equilibrium in the 1960s to a maximum observed in May 2022 (-4.2 mmolC.m-2.d-1). In both regions, we found a decrease of pH, most pronounced in the open ocean zone (-0.020 ±0.001.decade-1 over 1995-2023). The lowest pH of 8.04 was observed in January 2021, 0.11 lower than in the 1960s. The increase of the CO2 sink and the decrease of pH were mainly driven by anthropogenic CO2 uptake, with about 10% due to the ocean warming.
