Leibniz Centre for Tropical Marine Research (ZMT)

The South Indian Ocean, one of the least explored ocean regions, is dominated by the Indian Ocean subtropical gyre (IOSG), one of the five extensive oligotrophic areas in the world’s oceans. Here, we present results from a comprehensive study on physical water column data (e.g., temperature, salinity and sigma-theta), nutrient and stable isotope data, and long-time sinking particulate matter collection retrieved between 2014 and 2019 by sediment trap moorings in the INDEX (Indian Ocean Exploration) area. Our research contributes to the main understanding of key processes of the N and C cycle and provides the first multidisciplinary approach of water mass interfingering, N sources and transformation processes and the quantity, quality and variability of sediment trap-based sinking particulate matter fluxes. With this knowledge, future impacts from deep-sea mining activities on persisting biogeochemical cycles in the South Indian Ocean will be better understood and evaluated. Numerous water samples along 3°S to 28°S allow detailed water mass analyses accompanied by a comprehensive study of nitrogen sources and cycling processes. We demonstrate the convergence and mixing of water masses of Antarctic and Subantarctic origin with water masses from the North Indian Ocean and track the changes in nutrient distribution and signatures of stable isotopes (N and O of nitrate) along these diverse water masses. This provides evidence for the injection of preformed nutrients from the Subantarctic and the Arabian Sea. Furthermore, dinitrogen (N2) fixation evidently accounts for a significant proportion of primary production, and we calculate that ~32–34% of the nitrified nitrate is contributed by N2 fixation in surface waters of the IOSG at ~20–24°S. Nevertheless, the IOSG is a strongly nutrient-limited ocean realm and is characterised by low primary production rates and hence very low sinking particulate matter fluxes. Sinking particulate matter considered here was collected during the 5-year sediment trap deployment experiment between 2014 and 2019 to provide new information on the major factors that control the particle export out of the biologically active zone, its transfer into the ocean’s interior and its potential storage in pelagic sediments of the South Indian Ocean. Comparing particulate organic carbon (POC) fluxes to global data, the IOSG reveals the lowest fluxes worldwide (0.52 ± 0.18 mg m−2 d−1 at 500 m.a.b.), even compared to other oligotrophic areas. Preliminary estimates indicate an average POC export efficiency of ε ≈ 0.02. Based on net primary production (NPP) data in surface waters of the IOSG only 0.17% of the POC produced at the sea surface reaches the sea floor. Due to intense degradation at the sediment–water interface, less than 0.01% (~0.02 mg POC m−2 d−1) accumulates in surface sediments. Assuming that the IOSG, as well as comparable ocean regions, will expand under climate warming, it is of major importance to investigate POC export fluxes and its final carbon storage in the sediments in order to study the organic carbon pump and potential changes in the global C cycle. Furthermore, we present the seasonal variability of particle fluxes in the IOSG that shows a decoupling between NPP and the amount of exported particles. In the winter season, the external nutrient supply via gyre boundaries and/or subsurface waters elevate NPP and favour a complex zooplankton-dominated food web. In a first step, this enhances the organic matter production but, on the other hand, reduces the export of particles by increasing their fragmentation into free/unprotected particles, vulnerable to remineralisation/degradation. In comparison, during the low productive summer season, a foraminifera-dominated zooplankton community increases the particle export efficiency by ballast-minerals (here CaCO3). Consequently, the final export of particulate matter is anti-correlated to NPP rates. Various factors, such as variations in the ocean mixed layer depth, impacts of physical mixing (surface wind stress, cyclonic eddies), changes in the plankton community structure and concomitant changes, impact the vertical transfer of particles to the sea floor. Understanding these complex mechanisms is challenging, but they have to be studied in detail to make robust statements about global climate predictions.

Global coral reef degradation has precipitated phase shifts toward macroalgal-dominated communities. Despite the negative repercussions for reefscapes, higher abundances of primary producers have the potential to positively impact the physicochemical environment and mitigate negative impacts of ocean acidification (OA). In this study, we investigated the influence of macroalgal (cf. Sargassum vulgare) density on coral (Acropora millepora and A. hemprichii) calcification rates under current and future OA conditions. Corals were resistant to OA up to ~ 1100 µatm, with no changes in calcification rates. However, the presence of (low and high density) algae reduced calcification rates by ~ 41.8%, suggesting either a chemical defense response due to algal metabolites or potential physical impacts from shading or abrasion. Documented beneficial buffering effects of macroalgae in OA may also elicit negative impacts on coral calcification, suggesting further work is needed to elucidate how species interactions influence responses to projected climate change.

Ongoing climatic shifts and increasing anthropogenic pressures demand an efficient delineation of conservation units and accurate predictions of populations' resilience and adaptive potential. Molecular tools involving DNA sequencing are nowadays routinely used for these purposes. Yet, most of the existing tools focusing on sequence‐level information have shortcomings in detecting signals of short‐term ecological relevance. Epigenetic modifications carry valuable information to better link individuals, populations, and species to their environment. Here, we discuss a series of epigenetic monitoring tools that can be directly applied to various conservation contexts, complementing already existing molecular monitoring frameworks. Focusing on DNA sequence‐based methods (e.g. DNA methylation, for which the applications are readily available), we demonstrate how (a) the identification of epi‐biomarkers associated with age or infection can facilitate the determination of an individual's health status in wild populations; (b) whole epigenome analyses can identify signatures of selection linked to environmental conditions and facilitate estimating the adaptive potential of populations; and (c) epi‐eDNA (epigenetic environmental DNA), an epigenetic‐based conservation tool, presents a non‐invasive sampling method to monitor biological information beyond the mere presence of individuals. Overall, our framework refines conservation strategies, ensuring a comprehensive understanding of species' adaptive potential and persistence on ecologically relevant timescales.

Submarine groundwater discharge (SGD) dynamically links land‐ and ocean‐derived chemical constituents, such as metals, in the coastal ocean. While many metals are sediment‐bound, changing environmental conditions, particularly along the coast, may lead to increased release of metals to their dissolved and more bioavailable form. Here, we review metal behavior, speciation, and drivers of mobilization in the coastal environment under anthropogenic influence. We also model global metal contamination risk to the coastal ocean via SGD considering anthropogenic and hydrogeologic pressures, where tropical regions with high population density, SGD, and acid sulfate soils (4% of the global coast) present the highest risk. Although most SGD studies focus on other analytes, such as nutrients, this review demonstrates the importance of considering SGD as a critical pathway for metals to reach the coastal ocean under rapidly changing environmental conditions.

Marine carbon dioxide removal (mCDR) and geological carbon storage in the marine environment (mCS) promise to contribute to the mitigation of global climate change in combination with drastic emission reductions. However, the implementable potential of mCDR and mCS depends, apart from technology readiness, also on site-specific conditions. In this paper, we explore different options for mCDR and mCS, using the German context as a case study. We challenge each option to remove 10 Mt CO2 yr-1, which accounts for 8-22% of projected hard-to-abate and residual emissions of Germany in 2045. We focus on the environmental, resource, and infrastructure requirements of individual mCDR and mCS options at a specific site, within the German jurisdiction when possible. Furthermore, we discuss main uncertainty factors and research needs, and, where possible, cost estimates, expected environmental effects, and monitoring approaches. In total, we describe ten mCDR and mCS options; four aim at enhancing the chemical carbon uptake of the ocean through alkalinity enhancement, four aim at enhancing blue carbon ecosystems’ sink capacity, and two employ geological off-shore storage. Our results indicate that five out of ten options would potentially be implementable within German jurisdiction, and three of them could potentially rise to the challenge. This exercise provides a basis for further studies to assess the socio-economic, ethical, political, and legal aspects for such implementations.

Terrestrial groundwater travels through subterranean estuaries before reaching the sea. Groundwater‐derived nutrients drive coastal water quality, primary production, and eutrophication. We determined how dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved organic nitrogen (DON) are transformed within subterranean estuaries and estimated submarine groundwater discharge (SGD) nutrient loads compiling > 10,000 groundwater samples from 216 sites worldwide. Nutrients exhibited complex, nonconservative behavior in subterranean estuaries. Fresh groundwater DIN and DIP are usually produced, and DON is consumed during transport. Median total SGD (saline and fresh) fluxes globally were 5.4, 2.6, and 0.18 Tmol yr⁻¹ for DIN, DON, and DIP, respectively. Despite large natural variability, total SGD fluxes likely exceed global riverine nutrient export. Fresh SGD is a small source of new nutrients, but saline SGD is an important source of mostly recycled nutrients. Nutrients exported via SGD via subterranean estuaries are critical to coastal biogeochemistry and a significant nutrient source to the oceans.

Airborne dispersal of microorganisms is a ubiquitous migration mechanism, allowing otherwise independent microbial habitats to interact via biomass exchange. Here, we study the ecological implications of such advective transport using a simple spatial model for bacteria–phage interactions: the population dynamics at each habitat are described by classical Lotka–Volterra equations; however, species populations are taken as integer, that is, a discrete, positive extinction threshold exists. Spatially, species can spread from habitat to habitat by stochastic airborne dispersal. In any given habitat, the spatial biomass exchange causes incessant population density oscillations, which, as a consequence, occasionally drive species to extinction. The balance between local extinction events and dispersal-induced migration allows species to persist globally, even though diversity would be depleted by competitive exclusion, locally. The disruptive effect of biomass dispersal thus acts to increase microbial diversity, allowing system-scale coexistence of multiple species that would not coexist locally.

Opinion dynamics are affected by cognitive biases and noise. While mathematical models have focused extensively on biases, we still know surprisingly little about how noise shapes opinion patterns. Here, we use an agent-based opinion dynamics model to investigate the interplay between confirmation bias—represented as bounded confidence—and different types of noise. After analysing where noise can enter social interaction, we propose a type of noise that has not been discussed so far, ambiguity noise. While previously considered types of noise acted on agents either before, after or independent of social interaction, ambiguity noise acts on communicated messages, assuming that socially transmitted opinions are inherently noisy. We find that noise can induce agreement when confirmation bias is moderate, but different types of noise require quite different conditions for this effect to occur. An application of our model to the climate change debate shows that at just the right mix of confirmation bias and ambiguity noise, opinions tend to converge to high levels of climate change concern. This result is not observed with the other types. Our findings highlight the importance of considering and distinguishing between the various types of noise and the unique role of ambiguity in opinion formation.

Black band disease (BBD) is one of the oldest recognized diseases of scleractinian corals. This disease is little known on the variation of progression rates across relatively small spatial scales and how local variations in the environment can impact prevalence and spread. The purpose of this study was to explore the progression of BBD on genus Montipora in relation to spatio-temporal environmental parameters in two islands of the Seribu Islands, North Jakarta, Indonesia during dry season and rainy season. Monthly underwater pictures were taken for determining the progress of disease level. Interestingly, the progression rate of the disease recorded at Pramuka Island was higher (8.10 cm² day⁻¹) than the one at Pari Island (3.79 cm² day⁻¹). In Pramuka Island, the infected corals had almost 89% of the dead surface, compared to only 68% at Pari Island. Similar to other studies in the region, we confirmed that the disease progressed faster during the dry season, where the environmental parameters, such as temperature, light intensity, and phosphate, were starting to increase, while total organic matter, current flow rates, and turbidity were lower. Progression of the disease was significantly different between seasons (p<0.001), but not between sites (p=0.118). Therefore, the progress of BBD has a higher impact at the more populated Pramuka island than at the less populated Pari Island, in addition to the influence of environmental parameters on coral vulnerability to diseases.

The re-establishment of mangrove forests is necessary to increase the quantity of sequestered carbon that would help to mitigate climate change. Determining long-term patterns of mangrove chronosequences is needed to develop a predictive capacity of carbon sequestration. We conducted a global meta-analysis of aboveground, belowground, sediment, and total ecosystem organic carbon (C ORG ) stocks and C ORG burial rates (SCBR) in reforested, afforested, and naturally regenerated mangroves. Global patterns were detected for aboveground and belowground biomass C ORG and ecosystem C ORG stocks but not for sediment C ORG stocks or SCBR. Mangrove trees increase carbon storage for up to a century, although they begin to plateau after 30-50 yr. Statistical analyses identified multiple variables as possible drivers and strong relationships between (1) mangrove biomass C ORG stocks and forest age, (2) sediment and ecosystem C ORG stocks, and (3) dominant mangrove species and environmental variables. Lack of a significant relationship between mangrove biomass and sediment blue carbon may be attributable to differences in environmental timescales and life histories between vegetation, sediment C ORG , and subsurface sedimentary deposits. Sediment burial rates were nearly identical between those measured in re-established and natural forests, indicating that re-establishment of mangrove forests is a viable and predictable means of increasing long-term blue carbon sequestration. The global patterns suggest that predictive models can be constructed to improve forecasting of mangrove carbon sequestration, assisting in the sustainable development of mangrove plantations and mitigating climate change through market-based approaches.

There is a need to synthesize the vast amount of empirical case study research on social‐ecological systems (SES) to advance theory. Innovative methods are needed to identify patterns of system interactions and outcomes at different levels of abstraction. Many identifiable patterns may only be relevant to small sets of cases, a sector or regional context, and some more broadly. Theory needs to match these levels while still retaining enough details to inform context‐specific governance. Archetype analysis offers concepts and methods for synthesizing and explaining patterns of interactions across cases. At the most basic level, there is a need to identify two and three independent variable groupings (i.e. dyads and triads) as a starting point for archetype identification (i.e. as theoretical building blocks). The causal explanations of dyads and triads are easier to understand than larger models, and once identified, can be used as building blocks to construct or explain larger theoretical models. We analyse the recurrence of independent variable interactions across 71 quantitative SES models generated from qualitative case study research applying Ostrom's SES framework and examine their relationships to specific outcomes (positive or negative, social or ecological). We use hierarchical clustering, principal component analysis and network analysis tools to identify the frequency and recurrence of dyads and triads across models of different sizes and outcome groups. We also measure the novelty of model composition as models get larger. We support our quantitative model findings with illustrative visual and narrative examples in four case study boxes covering deforestation in Indonesia, pollution in the Rhine River, fisheries management in Chile and renewable wind energy management in Belgium. Findings indicate which pairs of two (dyads) and three (triads) variables are most frequently linked to either positive or negative, social or ecological outcomes. We show which pairs account for most of the variation of interactions across all the models (i.e. the optimal suite). Both the most frequent and optimal suite sets are good starting points for assessing how dyads and triads can fulfil the role of explanatory archetype candidates. We further discuss challenges and opportunities for future SES modelling and synthesis research using archetype analysis. Read the free Plain Language Summary for this article on the Journal blog.

Mangroves are one of the most carbon‐dense forests on the Earth and have been highlighted as key ecosystems for climate change mitigation and adaptation. Hundreds of studies have investigated how mangroves fix, transform, store, and export carbon. Here, we review and synthesize the previously known and emerging carbon pathways in mangroves, including gains (woody biomass accumulation, deadwood accumulation, soil carbon sequestration, root and litterfall production), transformations (food web transfer through herbivory, decomposition), and losses (respiration as CO 2 and CH 4 , litterfall export, particulate and dissolved carbon export). We then review the technologies available to measure carbon fluxes in mangroves, their potential, and their limitations. We also synthesize and compare mangrove net ecosystem productivity (NEP) with terrestrial forests. Finally, we update global estimates of carbon fluxes with the most current values of fluxes and global mangrove area. We found that the contributions of recently investigated fluxes, such as soil respiration as CH 4 , are minor (<1 Tg C year ⁻¹ ), while the contributions of deadwood accumulation, herbivory, and lateral export are significant (>35 Tg C year ⁻¹ ). Dissolved inorganic carbon exports are an order of magnitude higher than the other processes investigated and were highly variable, highlighting the need for further studies. Gross primary productivity (GPP) and ecosystem respiration (ER) per area of mangroves were within the same order of magnitude as terrestrial forests. However, ER/GPP was lower in mangroves, explaining their higher carbon sequestration. We estimate the global mean mangrove NEP of 109.1 Tg C year ⁻¹ (7.4 Mg C ha ⁻¹ year ⁻¹ ) or through a budget balance, accounting for lateral losses, a global mean of 66.6 Tg C year ⁻¹ (4.5 Mg C ha ⁻¹ year ⁻¹ ). Overall, mangroves are highly productive, and despite losses due to respiration and tidal exchange, they are significant carbon sinks.

Speciation can be mediated by a variety of reproductive barriers, and the interaction among different barriers has often been shown to enhance overall reproductive isolation, a process referred to as 'coupling'. Here, we analyze a population genetics model to study the establishment of linkage disequilibrium (LD) among loci involved in multiple premating barriers, an aspect that has received little theoretical attention to date. We consider a simple genetic framework underlying two distinct premating barriers, each encoded by a preference locus and its associated mating trait locus. We show that their interaction can lead to a decrease in overall reproductive isolation relative to a situation with a single barrier, a process we call 'negative coupling'. More specifically, in our model, negative coupling results either from sexual selection that reduces divergence at all loci, or from reduced LD that occurs because the presence of many females with “mismatched” preferences causes the mating success of recombinant males to become high. Interestingly, the latter effect may even cause LD among preference loci to become negative when recombination rates among loci are low. We conclude that coincident reproductive barriers may not necessarily reinforce each other, and that the underlying loci may not necessarily develop a positive association.

We analyze archetypes of farmer groups conducting pond aquaculture across the province of Nusa Tenggara Barat, Indonesia using Ostrom’s social-ecological systems framework. Pond aquaculture farmers share coastal irrigation infrastructure as common property, among other resources, and are encouraged by the government to organize into groups with varying sets of evolved rules, norms, social practices and environmental conditions shaping what they produce, how and how much. Yet little is known about the diversity of these pond aquaculture communities, or what factors – both social and ecological – shape production trends and sustainability outcomes. We designed a standardized survey to collect data on 26 indicators from 85 diverse community-based fish farmer groups across the province. Data included indicators on ownership, rules, history, production trends, demographics, government involvement, livelihood dependence, environmental characteristics and risks. Clustering analysis was applied to identify five unique archetypes of pond aquaculture communities, each distinguished by a different set of development challenges and opportunities. Our findings highlight the need to move beyond a “one-size-fits-all” policy approach. We suggest moving towards a locally adapted capacity building strategy that can recognize contextual needs so that policy programs can better target and differentiate between farmer groups that face similar challenges. We further discuss how empowering collective action among the farmers can reduce risks associated with producing blue food for local consumption and regional markets.

Plain Language Summary Convective cold pools form when rain evaporates underneath thunderstorm clouds. The evaporation causes the air to cool and sink toward the ground, where it is deflected horizontally. Cold pools are thus associated with strong gusty winds, and over tropical land, they can be especially vigorous. Cold pools are also suggested to contribute to the organization of thunderstorm clouds into large clusters of rain‐producing areas. The widespread, heavy rainfall can then cause flooding. To better predict such flooding in numerical weather models, having a precise observational basis for cold pool properties is essential — yet currently missing in equatorial Africa. We here provide such an observational benchmark by analyzing thousands of cold pools using timeseries of near‐surface temperature, wind, humidity and precipitation. We additionally show that the cold pools can even be detected from satellite data when analyzing abrupt changes in cloud top temperature. Such satellite‐based detection could open for cold pool studies across all tropical land areas — of great practical relevance to the prediction of thunderstorm clusters.

Properly predicting the rapid transition from shallow to precipitating atmospheric convection within a diurnal cycle over land is of great importance for both weather prediction and climate projections. In this work, we consider that a cumulus cloud is formed due to the transport of water mass by multiple updrafts during its life-time. Cumulus clouds then locally create favorable conditions for the subsequent convective updrafts to reach higher altitudes, leading to deeper precipitating convection. This mechanism is amplified by the cold pools formed by the evaporation of precipitation in the sub-cloud layer. Based on this conceptual view of cloud-cloud interactions which goes beyond the one cloud equals one-plume picture, it is argued that precipitating clouds may act as predators that prey on the total cloud population, such that the rapid shallow-to-deep transition can be modeled as a simple predator-prey system. This conceptual model is validated by comparing solutions of the Lotka-Volterra system of equations to results obtained using a high-resolution large-eddy simulation model. Moreover, we argue that the complete diurnal cycle of deep convection can be seen as a predator-prey system with varying food supply for the prey. Finally, we suggest that the present model can be applied to weather and climate models, which may lead to improved representations of the transition from shallow to precipitating continental convection.

Unveiling the intricate relationships between animal movement ecology, feeding behavior, and internal energy budgeting is crucial for a comprehensive understanding of ecosystem functioning, especially on coral reefs under significant anthropo-genic stress. Here, herbivorous fishes play a vital role as mediators between algae growth and coral recruitment. Our research examines the feeding preferences, bite rates, inter-bite distances, and foraging energy expenditure of the Brown surgeonfish (Acanthurus nigrofuscus) and the Yellowtail tang (Zebrasoma xanthurum) within the fish community on a Red Sea coral reef. To this end, we used advanced methods such as remote underwater stereo-video, AI-driven object recognition, species classification, and 3D tracking. Despite their comparatively low biomass, the two surgeonfish species significantly influence grazing pressure on the studied coral reef. A. nigrofuscus exhibits specialized feeding preferences and Z. xanthurum a more generalist approach, highlighting niche differentiation and their importance in maintaining reef ecosystem balance. Despite these differences in their foraging strategies, on a population level, both species achieve a similar level of energy efficiency. This study highlights the transformative potential of cutting-edge technologies in revealing the functional feeding traits and energy utilization of keystone species. It facilitates the detailed mapping of energy seascapes, guiding targeted conservation efforts to enhance ecosystem health and biodiversity.

Although the general impacts of zooplankton grazing on phytoplankton communities are clear, we know comparatively less about how specific grazing strategies interact with environmental conditions to shape the size structure of phytoplankton communities. Here, we present a new data‐driven, size‐based model that describes changes in the size composition of lake phytoplankton under various environmental constraints. The model includes an ecological trade‐off emerging from observed allometric relationships between (1) phytoplankton cell size and phytoplankton growth and (2) phytoplankton cell size and zooplankton grazing. In our model, phytoplankton growth is nutrient‐dependent and zooplankton grazing varies according to specific grazing strategies, namely, specialists (targeting a narrow range of the size‐feeding spectrum) vs. generalists (targeting a wide range of the size‐feeding spectrum). Our results indicate that grazing strategies shape the size composition of the phytoplankton community in nutrient‐rich conditions, whereas inorganic nutrient concentrations govern phytoplankton biomass. Under oligotrophic regimes, the phytoplankton community is dominated by small cell sizes and the grazers have little to no impact. Under eutrophic regimes, dominating specialist grazers push phytoplankton towards small cells, whereas dominating generalist grazers push phytoplankton towards large cells. Our work highlights that trait‐based modeling, based on realistic eco‐physiological trade‐offs, represents a valuable tool for disentangling the interactive roles played by nutrient regimes and grazing strategies in determining the size compositions of lake phytoplankton. Ultimately, our study offers a quantitative basis for understanding how communities of lake phytoplankton may reorganize in the future in response to changes in nutrient levels and zooplankton grazing strategies.

Small pelagic fish (SPF) are important forage species and a target of major fisheries within diverse ecosystems. SPF are a critical link between plankton and higher trophic levels. Understanding the network of dependencies among species and fisheries supported by SPF is required for effective resource management and assessment of risks posed by environmental and anthropogenic stressors. Food-web models represent a synthesis of knowledge of these dependencies and are a platform for evaluating the consequences of change in SPF productivity. From Ecopath food-web models archived within EcoBase (www.ecobase.ecopath.org) and from peer-reviewed literature, we compiled physiological parameters, biomasses, diets, and fishery catch rates that define SPF characteristics. From 199 models, metrics characterizing demand on ecosystem production, contribution to predators and fisheries, and sensitivities to changes in SPF were calculated. Across all models, globally, SPF represented 43% of total fish production and were supported by 8% of total primary production (14% in open ocean and 10% in upwelling models). In turn, SPF represented 18% of total fish and invertebrate catch (53% in upwelling models). From a services perspective, considering all direct and indirect trophic pathways, SPF were major contributors to predators and fisheries. On average, SPF supported 22% of seabird production, 15% of mammal production, and 34% of total fisheries catch. Support to upper trophic levels was greater in upwelling models (33% of seabird, 41% of mammal, and 62% of fishery production). These analyses show the importance of accounting for direct and indirect support by SPF to predators and fisheries when making management decisions.