Abstracts PA2

Global change: impacts and adaptation

Talks:


13:45

Abstract 164

Effects of climate change on reef communities, carbonate production and sediment systems in the remote Chagos Archipelago

by Marleen Stuhr | Aitana Gea Neuhaus | Chris T. Perry | Lea T.A. Fuchs | Ines D. Lange 

ZMT | University of Oldenburg | University of Exeter | Bremen University | University of Exeter

The complex structural framework and associated sediment production by calcifying organisms on coral reefs provide key geo-ecological functions such as coastal protection and beach nourishment that are especially important for low-lying islands. Since global coral bleaching events have substantial impacts on reef communities, even in areas characterized by minimal local human impacts, reef islands are highly vulnerable to climate change. Thus, with the ongoing degradation of coral reef ecosystems and sea-level rise, a better understanding of reef-derived carbonate production and sediment supply has become increasingly important. To assess climate impacts on benthic communities and how this affects local carbonate and sediment production, we assess variations in the reef and sediment composition along with local carbonate and sediment production states in the remote Chagos Archipelago, central Indian Ocean. This group of atolls is hardly affected by local anthropogenic impacts, but nonetheless exposed to global ocean warming. While impacts of the recent global corals bleaching event 2015/2016 have severely reduced coral cover, altered benthic communities and diminished calcium carbonate production on these reefs, all sites were on a trajectory of recovery in 2021 and several sites reached prebleaching levels in 2023. Yet, this rapid recovery varied locally between atolls and sites. Similarly, the contribution of different carbonate producers to the sediments showed spatial variability, likely reflecting the ecological transitions in local communities such as increased proportions of the calcifying algae. Long-term shifts linked to climate change impacts were also shown by comparison of recent foraminiferal communities to pre-coral bleaching assemblages. Further climate change-related impacts may progress shifts in benthic communities and related changes in carbonate and sediment production around coral reefs, with important implications for associated ecosystems and island. This highlights the need to increase our understanding of carbonate and sediment supply regimes and coastal landform development under varying conditions.


14:00

Abstract 165

Unlocking the mysteries of UCYN-A nitrogen fixation

by Subhendu Chakraborty | Agostino Merico

Systems Ecology Group, Leibniz Centre for Tropical Marine Research (ZMT) | Systems Ecology Group, Leibniz Centre for Tropical Marine Research (ZMT)

Biological N2 fixation is one of the most important processes in the ocean. It supplies bioavailable nitrogen to marine organisms with profound ecological and biogeochemical implications at a global scale. While most of the cyanobacterial N2 fixers are active within the tropical and subtropical regions, the symbiotic unicellular cyanobacterium Candidatus Atelocyanobacterium Thalassa (UCYN-A) appears as one of the most abundant N2 fixers, with a broad oceanic distribution and a potentially significant contribution to the global nitrogen budget. However, due to the unavailability of culture representatives, its biology and ecology are not well understood. Here we develop a simple cell-based mathematical model in order to (1) provide a comprehensive understanding of the cellular processes driving UCYN-A growth and N2 fixation, (2) examine the role of environmental factors regulating UCYN-A growth and N2 fixation, and (3) determine the biogeographical distribution of UCYN-A N2 fixation in the global ocean. Our results provide new insights into the physiology of UCYN-A and explain the role of environmental factors shaping the vertical and spatial distributions of UCYN-A at a global scale. Our results provide the basis for understanding and predicting global patterns of N2 fixation.


14:15

Abstract 160

Actual and Perceived Opinion Polarisation in the German Climate Change Debate

by Peter Steiglechner | Paul E. Smaldino | Agostino Merico

ZMT, Constructor University | UC Merced, Santa Fe Institute | ZMT, Constructor University

While the consensus on climate change is growing, the debate on this issue appears to be increasingly polarised, with people’s opinions seemingly more and more divided. How do these views fit together? Political sciences distinguish between (1) actual polarisation, which refers to an increase in objective differences between opinions, and (2) perceived polarisation, which refers to an increase in subjective differences between opinions. I will present a framework to extract actual and perceived opinion polarisation from survey data concerning opinions on political topics like climate change. This framework assumes that people are generally aware of the opinions of others and that people’s perception of the opinion space is determined by the opinions of others—either equally by all others or primarily by political in-group members, depending on their level of in-group bias. The way people perceive distances between opinions is thus dynamic, subjective, and asymmetric. I apply the framework to opinions on climate change among Germans obtained from two surveys conducted in 2016-2017 and 2020-2022. Not accounting for changes in the perceptions of the people, the framework yields actual polarisation on climate change opinions during this period. If we allow the perceptions to co-evolve, we find that people see less polarisation than there actually is with weak in-group bias but more polarisation (with a factor of 1.5) with strong bias. We find that this differs strongly between partisan groups. Those identifying with the Greens see polarisation increased by a factor of three, and those identifying with the FDP (liberal party) see no polarisation despite facing similar levels of actual opinion polarisation. This framework provides a new way of understanding whether we are polarised on critically relevant societal issues such as climate change or just think we are.


14:30

Abstract 150

A model prototype for investigating violent conflict in connection to resource scarcity

by Ago Merico | Peter Steiglechner | Subhendu Chakraborty

ZMT | ZMT | ZMT

In many areas of the world, renewable resources like fisheries show declining trends. On a backdrop of continuous human population growth, resource scarcity constitutes a likely trigger for violent conflict, especially in tropical and subtropical regions. We will present a model prototype for studying resource scarcity and conflict. The model features two rival populations both dependent on a single contested renewable resource. Each population can allocate their members between resource harvesting and resource appropriation (i.e., conflict). The model exhibits rich dynamics under a variety of human allocation decisions and resource growth development. We will present the effects that increasing uncertainties on resource growth, driven, for example, by climate change, may have on the two rival populations.

 


Poster

PA2: 11:30 – 12:00


Abstract 151

Ocean acidification and warming effects on lipid biochemistry and enzyme activities in an asterinid starfish

by Munawar Khalil | Marleen Stuhr | Andreas Kunzmann | Hildegard Westphal

Leibniz Centre for Tropical Marine Research (ZMT), Faculty of Geosciences – University of Bremen | Leibniz Centre for Tropical Marine Research (ZMT) | Leibniz Centre for Tropical Marine Research (ZMT) | Leibniz Centre for Tropical Marine Research (ZMT)

Ocean acidification and ocean warming as part of global climate change effects are altering marine ecosystems from organismal physiology on a microscale to broader functional levels. However, there is still sparse information on how they interact to affect tropical and subtropical intertidal species. Driving the environmental window of marine species away from their optimum conditions triggers stress that may affect biochemical metabolic characteristics with consequences on lipid-related biochemistry and enzyme biosynthesis; hence impacting the fitness and physiological adaptive capacity of the organism. This study aims to investigate lipids and associated fatty acids (FAs) and the activity of enzymes involved in the calcification process of asterinid starfish Aquilonastra yairi in response to near-future global change scenarios. The A. yairi in our experiment were exposed to two temperature levels (27°C, 32°C) crossed with three pCO2 concentrations (455 µatm, 1052 µatm, 2066 µatm) for 90 days. The composition of the total lipids (ΣLC) and FAs were unaffected by combined elevated temperature and pCO2. However, elevated temperature caused an increase in ΣLC, SFAs (saturated fatty acids) and PUFAs (polyunsaturated fatty acids) and a decrease in MUFAs (monounsaturated fatty acids). Furthermore, temperature alone significantly altered the SFAs composition. A. yairi appears to employ a homeoviscous adaptation strategy to reduce the impacts of elevated temperatures and pCO2. Parabolic responses and unstable Ca-ATPase and Mg-ATPase enzyme activities were detected at ambient temperature-elevated pCO2, while stable enzyme activities were observed at high- temperature-elevated pCO2. Hence, the increased temperature seems to allow the starfish to cope with the negative effect of increased pCO2 on enzyme activities (antagonistic interactive effects). Our results indicate that lipid biochemistry in starfish is resilient to elevated pCO2 but not temperature, while enzyme activities appear more sensitive to alterations in pCO2.


Abstract 166

Global distribution of non-cyanobacterial N2 fixers in sinking marine particles

by Subhendu Chakraborty | Ken Andersen | Agostino Merico | Lasse Riemann

Systems Ecology Group, Leibniz Centre for Tropical Marine Research (ZMT) | Technical University of Denmark | Systems Ecology Group, Leibniz Centre for Tropical Marine Research (ZMT) | University of Copenhagen

Biological nitrogen (N2) fixation, the conversion of inert N2 gas into ammonia by prokaryotes (diazotrophs), is crucial for maintaining ocean fertility providing bioavailable nitrogen. While cyanobacterial diazotrophs in tropical and subtropical waters were traditionally thought to be the primary contributors to marine N2 fixation, the discovery of an almost ubiquitous distribution of non-cyanobacterial diazotrophs (NCDs) in pelagic environments has challenged the notion that N2 fixation is limited to certain latitudes. However, the importance of these NCDs for nitrogen biogeochemistry in the global ocean remains unclear. Using a data-informed cell-based model, we demonstrate that NCDs can fix N2 inside sinking marine particles over a much wider range of temperatures compared to free-living cyanobacteria. This explains the observed widespread distribution of NCDs, from low to high latitudes, in the global ocean. Our result shows the highest contribution N2 fixation rates by NCDs in oxygen minimum zones. We further estimate that NCDs in sinking marine particles contribute 14-38% of the global marine N2 fixation, suggesting that the contribution of NCDs to the global nitrogen budget is substantial.


Abstract 167

Modelling competition for nutrient-uptake between diazotrophs of different cell sizes

by Sandra Marion Kam Tsemo | Subhendu Chakraborty | Ken H. Andersen | Adam C. Martiny | Agostino Merico

ZMT | ZMT | DTU AQUA | UCI | ZMT

Biologically usable forms of nitrogen and phosphorus are essential elements for phytoplankton growth and contribute to the biogeography of these organisms in the oceans. Diazotrophs, also known as nitrogen fixers, can convert nitrogen gas into ammonia, a biologically usable form of nitrogen. However, the impacts of cell size and the use of phosphonates (an organic form of phosphorus) on the competition between diazotrophs remain poorly understood. Addressing these aspects is crucial for understanding the ecological competition between diazotrophs and their biogeography. We will present a mathematical model that simulates the complex dynamics of nutrients and carbon uptakes in the diazotrophic cell. Our model provides insights into the conditions driving the competition between Trichodesmium (a colonial cyanobacterium, large cell) and UCYN-A (a unicellular cyanobacteria, group A, small cell) and highlights the advantage of small cells over their larger counterparts. Our results suggest that the ability of Trichodesmium to metabolise phosphonates gives them an advantage over UCYN-A in environments with low phosphate. Under low light conditions, high levels of iron provide a competitive edge to Trichodesmium over UCYN-A. As light intensity increases, Trichodesmium thrives under very low phosphate concentrations. In contrast, environments with elevated phosphate concentrations are more advantageous for UCYN-A. Our findings offer valuable insights on how the biogeography of nitrogen fixers may change in the future in response to changing nutrient conditions.


Abstract 171

Optimizing Silicate Rocks Weathering for CO2 Sequestration : A Global Coastal Perspective

by Murugan Ramasamy | Thorben Amann | Nils Moosdorf

ZMT | Universität Hamburg, Hamburg, Germany | ZMT

Weathering of rocks is a natural CO2-sink that has is a main balance for the global climate on geological timescales. This study investigates the potential of enhancing the rock weathering processes in coastal regions to reduce atmospheric CO2 levels over a specified 100-year timeframe. Employing geochemical kinetic modeling across 13 seas worldwide, the research offers valuable insights into the variability of CO2 sequestration rates, highlighting distinct capacities at each location based on unique environmental conditions. CO2 sequestration varies substantially between the locations, ranging from 0.13 to 0.94 metric tons (t) of CO2 per ton of distributed olivine-rich rocks over 100 years. Warmer coastal regions exhibit higher CO2 sequestration capacities compared to temperate regions, with a difference of 0.4 t per t of olivine distributed. Extrapolating this data globally shows that East Asian Seas exhibiting fast weathering (e.g., Banda Sea, South China Sea) and Northwest Pacific and North-East Atlantic coastal seas displaying relatively slower weathering but extensive coverage (e.g., Yellow Sea, East China Sea, Baltic Sea, North Seas). Additionally, the choice of grain size significantly impacts weathering rates, necessitating a 15 µm grain size for 80% sequestration efficiency in the temperate Baltic Sea and a larger 150 µm grain size in the warmer Banda Sea. By considering the CO2 costs of crushing procedures, the study establishes a theoretical maximum net-CO2 sequestration over 100 years, ranging from 0.87 t CO2 per t olivine in colder areas like the Baltic Sea to nearly stoichiometric maximum with 0.97 t CO2 per t olivine in warmer regions like the Banda Sea.


Abstract 180

DISTiC – Developing an index for the state of tropical coasts

by Jonas Geburzi | Victoria Wegner | Hauke Reuter | Martin Zimmer | Nils Moosdorf

ZMT, WG Submarine Groundwater Discharge | ZMT, WG Mangrove Ecology | ZMT, WG Spatial Ecology and Interactions | ZMT, WG Mangrove Ecology | ZMT, WG Submarine Groundwater Discharge

Coastal areas are complex systems which face particularly large challenges under ongoing global change, arising from the interactions between pressures from the land, ocean, and humans. This holds particularly true for tropical coasts, which support the livelihoods of growing coastal communities, while at the same time harboring highly diverse and functionally important ecosystems. Continuous monitoring and assessment frameworks are therefore highly needed to holistically characterize these complex systems and sense changes early. Such a framework should track spatiotemporal changes in the system and its components, depict interactions between the system’s components, identify areas of change, and allow an evaluation of the impact of interventions; in a way that is meaningful to its potential users. While several indices and assessments already exist that address components of coastal systems, an index that holistically monitors and characterizes tropical coastal systems on a globally comparable scale is still lacking. The goal of the DISTiC project is to close this gap, and we will present the current state of the index concept.