Christian Möllmann

University of Hamburg | UHH · Institute for Marine Ecosystem and Fisheries Science

Collapses and regime changes are pervasive in complex systems (such as marine ecosystems) governed by multiple stressors. The demise of Atlantic cod (Gadus morhua) stocks constitutes a text book example of the consequences of overexploiting marine living resources, yet the drivers of these nearly synchronous collapses are still debated. Moreover, i...

Understanding tipping point dynamics in harvested ecosystems is of crucial importance for sustainable resource management because ignoring their existence imperils social-ecological systems that depend on them. Fisheries collapses provide the best known examples for realizing tipping points with catastrophic ecological, economic and social conseque...

Fish represent a politically regulated, scientifically researched, industrially processed, commercially marketed and socially contested living marine resource. Related to this, the incorporation of resource users and stakeholders into fisheries management is particularly important. Such involvement has recently improved in terms of frequency, but i...

Zusammenfassung Dem Dorsch der Westlichen Ostsee geht es schlecht und die von ihm abhängige Fischerei ist in Gefahr. Neueste Abschätzungen des Internationalen Rates für Mee-resforschung (ICES) zeigen einen katastrophalen Zustand des Bestands. In einem wissenschaftlichen Artikel haben wir mit weiteren Kolleg:innen die historische Ent-wicklung des Be...

Human impacts can induce ecosystems to cross tipping points and hence unexpected and sudden changes in ecosystem services that are difficult or impossible to reverse. The world´s oceans suffer from cumulative anthropogenic pressures like overexploitation and climate change and are especially vulnerable to such regime shifts. Yet an outstanding ques...

Worldwide, fisheries face the consequences of climate change and compete with expanding human activities at sea, which may trigger unforeseen reactions of fishers. Hence, knowledge on drivers of fishing behavior is crucial for management and needs to be integrated in resource management policies. In this study, we identify factors influencing fishi...

Recovery of depleted fish stocks is an important goal for fisheries management and crucial to sustain important ecosystem functions as well as global food security. Successful recovery requires adjusting fishing mortality to stock productivity but can be prevented or inhibited by additional anthropogenic impacts such as climate change. Despite mana...

1. Cumulative human pressures and climate change can induce nonlinear discontinuous dynamics in ecosystems, known as regime shifts. Regime shifts typically imply hysteresis, a lacking or delayed system response when pressures are reverted, which can frustrate restoration efforts. 2.Here, we investigate whether the northern Adriatic Sea fish and mac...

Recently, the rights of small-scale fishers have increasingly been acknowledged in ocean governance because coastal development and various maritime activities have reduced traditional fishing grounds. More specifically, small-scale fisheries (SSF) are increasingly being threatened by ocean grabbing, pollution, and a lack of inclusiveness in decisi...

The operational principle of offshore wind farms (OWF) is to extract kinetic energy from the atmosphere and convert it into electricity. Consequently, a region of reduced wind speed in the shadow zone of an OWF, the so-called wind-wake, is generated. As there is a horizontal wind speed deficit between the wind-wake and the undisturbed neighboring r...

Die westliche Ostsee steht unter massivem Druck. Bedingt durch negativen anthropogene Effekte wie Klimawandel, Eutrophierung und Überfischung folgt eine Veränderung der Ökosysteme entlang der Küste sowie der Fischerei und ihrer Kultur. Weitere Gründe für diesen Strukturwandel sind ein relativ sinkendes Einkommen in der Fischerei aufgrund starker Fa...

Background and aim Billfish are epipelagic marine predators facing increasing pressures such as overfishing and rising global temperatures. Overfishing is a major concern, as they are caught by industrial longline fishers targeting tuna. Billfish are targeted by multiple fishing sectors, which provides food, socio‐economic and cultural benefits. To...

With recent advances in Machine Learning techniques based on Deep Neural Networks (DNNs), automated plankton image classification is becoming increasingly popular within the marine ecological sciences. Yet, while the most advanced methods can achieve human-level performance on the classification of everyday images, plankton image data possess prope...

Quantifying the morphology of organisms remains fundamental in ecology given the form-function relationship. Morphology is quantifiable in traits, landmarks, and outlines, and the choice of approach may influence ecological conclusions to an unknown extent. Here, we apply these three approaches to 111 individual coral reef fish of 40 species common...

We present estimates of length‐weight relationships (LWRs) of 55 mesopelagic fish species of 13 taxonomic families based on data collected in the eastern tropical North Atlantic (ETNA) in March/April 2015. Our data include novel records for 19 species, while for 25 species, LWRs are based on the most robust sample sizes and for 21 species, based on...

Die westliche Ostsee und ihre Fischerei durchleben aktuell eine umfassende Transformation. Sinkende Fangquoten für die Hauptzielfischarten Dorsch und Hering als Folge von Überfischung und Klimawandel führen zu einem Rückgang der Beschäftigung in der Fischerei. Hinzu komm das generelle Fehlen von Nachwuchs in der Fischerei. Ein transdisziplinärer Bl...

Sustainable environmental management needs to consider multiple ecological and societal objectives simultaneously while accounting for the many uncertainties arising from natural variability, insufficient knowledge about the system's behaviour leading to diverging model projections, and changing ecosystem. In this paper we demonstrate how a Bayesia...

Mesopelagic sound scattering layers (SSLs) are predominantly associated with mesopelagic fish taxa with gas-inflated swimbladders that perform active nocturnal diel vertical migration (DVM), like species of the families Myctophidae, Gonostomatidae, Sternoptychidae and Phosichthyidae. Larger-sized species with limited, partial, asynchronous and non-...

Spatially explicit records of fishing activities’ distribution are fundamental for effective marine spatial planning (MSP) because they can help to identify principal fishing areas. However, in numerous case studies, MSP has ignored fishing activities due to data scarcity. The vessel monitoring system (VMS) and the automatic identification system (...

The concept of social–ecological knowledge diversity (SEKD) provides a novel way of examining coupled human–environment interactions—it acknowledges differences in knowledge, values, and beliefs of stakeholder groups within social–ecological systems (SES). Thus, understanding and measuring SEKD is an essential component of sustainable management wi...

Winter has long been regarded as a period of minor importance in marine zooplankton ecology with static, low concentrations and growth rates of organisms. Yet, there is growing evidence that winter conditions influence spring bloom strength. With rising water temperatures, growing importance of fish larvae survival during winter and the lack of dat...

Abstract Improving the health of coastal and open sea marine ecosystems represents a substantial challenge for sustainable marine resource management, since it requires balancing human benefits and impacts on the ocean. This challenge is often exacerbated by incomplete knowledge and lack of tools that measure ocean and coastal ecosystem health in a...

Global environmental changes have accelerated at an unprecedented rate in recent decades due to human activities. As a consequence, the incidence of novel abiotic conditions and biotic communities, which have been continuously emerging in the Earth system, has rapidly risen. Despite growing attention to the incidence and challenges posed by novelty...

This study presents the diet composition of western Baltic cod Gadus morhua based on 3150 stomachs sampled year-round between 2016 and 2017 using angling, gillnetting and bottom trawling, which enhanced the spatio-temporal coverage of cod habitats. Cod diet composition in shallow areas (<20 m depth) was dominated by benthic invertebrate species, ma...

Conflict is a common feature in conservation and resource management. Environmental conflicts are frequently attributed to differences in values; however, variability in the perception of facts, rooted in social and cultural differences also underlies conflicts. Such differences in perception have been termed the Rashomon effect after the Kurosawa...

Predators not only have direct impact on biomass but also indirect, non-consumptive effects on the behavior their prey organisms. A characteristic response of zooplankton in aquatic ecosystems is predator avoidance by diel vertical migration (DVM), a behavior which is well studied on the population level. A wide range of behavioral diversity and pl...

One of the most applied tools to create ecosystem models to support management decisions in the light of ecosystem-based fisheries management is Ecopath with Ecosim (EwE). Recently, its spatial routine Ecospace has evolved due to the addition of the Habitat Foraging Capacity Model (HFCM), a spatial-temporal dynamic niche model to drive the foraging...

Practical and applied knowledge of local fishers can help to improve our understanding of target species ecology and fisheries management decisions. In the Western Baltic Sea (WBS), the spatio-temporal distribution of cod is still largely unknown despite decades of research. We studied changes in cod distribution by obtaining information on tempora...

Identifying key indicator species, their life cycle dynamics and the multiple driving forces they are affected by is an important step in ecosystem-based management. Similarly important is understanding how environmental changes and trophic interactions shape future trajectories of key species with potential implications for ecosystem state and ser...

The ecology of vertically migrating mesopelagic micronekton is affected by physical properties of their environment. Increased light attenuation in particle-rich productive waters, as well as low oxygen conditions decrease the migration amplitude. This likely has implications on the trophic organisation of micronekton communities, which are predomi...

Structured, systematic processes for decision-making can facilitate implementation of ecosystem-based fisheries management (EBFM). In U.S. fisheries management, existing Fishery Ecosystem Plans (FEPs) are primarily descriptive documents – not action-oriented planning processes. “Next-generation” FEPs extend existing FEPs by translating ecosystem pr...

Sustainability in the provision of ecosystem services requires understanding of the vulnerability of social-ecological systems (SES) to tipping points (TPs). Assessing SES vulnerability to abrupt ecosystem state changes remains challenging, however, because frameworks do not operationally link ecological, socio-economic and cultural elements of the...

A fundamental challenge in ecology is to understand why species are found where they are and predict where they are likely to occur in the future. Trait-based approaches may provide such understanding, because it is the traits and adaptations of species that determine which environments they can inhabit. It is therefore important to identify key tr...

The ability of organisms to adapt their foraging behaviour to spatial variations in food availability and habitat quality is crucial to maximize energy intake and hence fitness. Under ideal conditions, habitat selection should result in a spatial distribution of individuals such that their fitness (energy reserves or condition) is roughly equal acr...

The ICES Working Group on comparative analyses between European Atlantic and Mediterra-nean Ecosystems to move towards an Ecosystem-based Approach to Fisheries (WGCOMEDA) recently completed its second three-year cycle. WGCOMEDA was established in 2014 and works in cooperation with other groups within the ICES Integrated Ecosystem Assessments Steeri...

Ecological communities are constantly being reshaped in the face of environmental change and anthropogenic pressures. Yet, how food webs change over time remains poorly understood. Food web science is characterized by a trade-off between complexity (in terms of the number of species and feeding links) and dynamics. Topological analysis can use comp...

linearity in stock-recruitment relationships of Atlantic cod: insights from a multi-model approach. The stock-recruitment relationship is the basis of any stock prediction and thus fundamental for fishery management. Traditional parametric stock-recruitment models often poorly fit empirical data, nevertheless they are still the rule in fish stock a...

The Eastern Mediterranean Sea (EMS) is an ultraoligotrophic semi-enclosed sea with low nutrient levels, low primary production rate, impoverished phytoplankton populations and low zooplankton standing stocks. The Cretan Passage in the western Levantine Sea is one of the least explored areas of the EMS. We measured the mesozooplankton biomass, abund...

Combined analyses of Fatty Acid Trophic Markers (FATM) and Stable Isotopes (SI) were used to characterize food preferences among copepod species/taxa and to trace their food sources in the ultra-oligotrophic Cretan Passage of the Eastern Mediterranean Sea (EMS). FATMs are based on the conservation and transfer of specific source Fatty Acids (FAs) t...

Marine social-ecological systems (SES) are vulnerable to regime shifts, triggered at multiple scales by a combination of anthropogenic stressors, e.g. climate change, overfishing. These abrupt and unexpected changes threaten living marine resource populations and their sustainable exploitation with adverse social and economic consequences for human...

Overfishing and global warming are threatening the sustainability of marine social-ecological systems (SES) worldwide. In this study, we focused on the particular case of Western Baltic cod fishery which has shown a decreasing trend over the last fifteen years inducing substantial social and economic consequences. To understand the conflicts arose...

U.S. fisheries management has made tremendous strides under the current management framework, which centers on single stocks rather than ecosystems. However, conventional management focuses on one fishing sector at a time, considers a narrow range of issues, and is separated into individual fishery management plans often leaving little opportunity...

The relationship, if any, between diversity and stability has puzzled ecologists for decades. Most studies use taxonomic classifications to understand why and under what conditions the community is more stable than the sum of its parts. However, fish populations, for example, are known for their strong ontogenetic-trophic niche shift, suggesting a...

Trait‐based approaches are increasingly popular in ecology to describe communities and their responses to natural or anthropogenic changes. Morphology is an integrative trait that combines functional and evolutionary information. However, the objective and quantitative description of the morphological diversity is quite challenging. Modern morphome...

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Quantitative analysis of the predation impact of planktivores on zooplankton is essential for proper understanding of energy flow and trophic coupling in ecosystems. To quantify trophic dynamics between zooplankton and small pelagic fish in the Baltic Sea, we conducted a temporally resolved investigation on the diet, feeding and predation impact of...

Fisheries and marine ecosystem-based management requires a holistic understanding of the dynamics of fish communities and their responses to changes in environmental conditions. Environmental conditions can simultaneously shape the spatial distribution and the temporal dynamics of a population, which together can trigger changes in the functional s...

Converging water masses and mesoscale eddies shape habitats for larval fish assemblages in upwelling ecosystems. In the Canary Current Upwelling Ecosystem, two water masses, the North Atlantic Central Water (NACW) and South Atlantic Central Water (SACW) converge. The resulting Cape Verde Frontal Zone (CVFZ) is located off the Banc d'Arguin, Maurita...

The relationship, if any, between diversity and stability has puzzled ecologists for decades. Most studies use taxonomic classifications to understand why and under what conditions the community is more stable than the sum of its parts. However, fish populations, for example, are known for their strong ontogenetic-trophic niche shift, suggesting a...

Land‐ und Forstwirtschaft sind zusammen mit der Fischerei ein wichtiger Wirtschaftsfaktor der Metropolregion Hamburg (MRH). In den dörflichen und weit von der Hansestadt entfernten Regionen ist die Landwirtschaft ein bedeutender Arbeitgeber (Schulze et al. 2011; Statistisches Amt für Hamburg und Schleswig Holstein 2013; Statistische Ämter des Bunde...

Understanding spatio-temporal dynamics of biotic communities containing large numbers of species is crucial to guide ecosystem management and conservation efforts. However, traditional approaches usually focus on studying community dynamics either in space or in time, often failing to fully account for interlinked spatio-temporal changes. In this s...

Biological characteristics of species, ordered by cluster. Information about the biogeography, the trophic level (TL), the maximum length (Lmax) are from Engelhard et al., 2011. Average Catch per Unit Effort (av CPUE) are calculated from the data itself. (PDF)

Full correlation coefficient table. Table of Pearson and RV correlation coefficient (c) with p-value (p) and adjusted p-value (ap). (PDF)

Clustering analysis of the fish species realised with K-means algorithm. (PDF)

Results of the Principal Tensor Analysis. Output of the PTA-k R-package (top) and selection of the four principal tensors (PTs) based on the scree-plot (bottom). (PDF)

Robustness analysis to data transformation and spatial scale. TD computed with (A) the method presented in the manuscript (abundance expressed in number/hour, at the scale of roundfish areas), (B) abundance expressed in biomass (catch per unit effort, expressed in kg/hour) and (C) a finer spatial resolution, at the scale of ICES rectangle (and abun...

A recent increase in the construction of Offshore Wind Farms (OWFs) has initiated numerous environmental impact assessments and monitoring programs. These focus on sea mammals, seabirds, benthos or demersal fish, but generally ignore any potential effects OWFs may have on the pelagic ecosystem. The only work on the latter has been through modelling...

European sardine (Sardina pilchardus) and round sardinella (Sardinella aurita) comprise two-thirds of total landings of small pelagic fishes in the Canary Current Eastern Boundary Ecosystem (CCEBE). Their spawning habitat is the continental shelf where upwelling is responsible for high productivity. While upwelling intensity is predicted to change...

One of the major goals in biogeography is describing and understanding species distributions. However, when focusing on taxonomy one may miss the mechanistic understanding of what underlies these distributions. Trait-based ecologists argue that traits are useful in explaining where species occur, since it is the traits that determine how species re...

Fishing is a social and economic activity, and consequently socio-economic considerations are important for resource management. While this is acknowledged in the theory of Ecosystem-Based Management (EBM) and its sector-specific development Ecosystem-Based Fisheries Management (EBFM), currently applied fishery management objectives often ignore ec...

Resource managers and policy makers have long recognized the importance of considering fisheries in the context of ecosystems; yet, movement towards widespread Ecosystem-based Fisheries Management (EBFM) has been slow. A conceptual reframing of fisheries management is occurring globally, which envisions fisheries as systems with interacting biophys...

Predictive maps of biodiversity patterns are pivotal to marine conservation and marine spatial planning alike, yet mapping of biodiversity indicators at the community-level is neither straightforward nor well-tested empirically. Two principle approaches exist. A direct approach involves calculation of indices for each sample, followed by interpolat...

Significance Whether environmental conditions, harvesting, or predation pressure primarily regulate an ecosystem is still a question of much debate in marine ecology. Using a wealth of historical records, we describe how climate and fishing interact in a complex marine ecosystem. Through an integrative evidence-based approach, we demonstrate that i...

In Europe, and around the world, the approach to management of the marine environment has developed from the management of single issues (e.g. species and/or pressures) towards holistic Ecosystem Based Management that includes aims to maintain biodiversity and protect ecosystem functioning. Within the European Union, this approach is implemented th...

Understanding how human activities and environmental conditions shape the status of marine food webs is key for making ecosystem-based management of marine resources (EBM) operational. In the Baltic Sea, for example, significant changes in the food web during the late 1980s were caused by the combined effects of changing physical oceanographic cond...