ALBERT

Description: Simulation models have a broad potential as decision-support tools for resource management by mechanistically representing and projecting complex ecological processes. In the case of socioeconomically and biologically important coral reef ecosystems, models have been used to address important questions regarding the effects of human impacts on their ecological dynamics and to inform management approaches. However, few of the models integrate benthic and fish dynamics with the influence of external anthropogenic stressors, and virtually none is available as a user-friendly platform for non-scientist managers to easily access. We propose a new ecological model to assess the effects of simultaneous stressors on coral reef ecosystems which includes a dynamic representation of benthic and fish spatial processes, linked by their ecological feedbacks. SEAMANCORE is a two-dimensional model representing the dynamics of local coral reefs which can be used to explore the influence of bleaching, eutrophication, and fishing, including destructive fishing such as bomb and cyanide fishing. The model is coupled with a menu-based interface that allows users with no programming experience to simulate numerous scenarios in specific contexts that can be customized with depth profile maps and initial coral reef conditions of fish and benthos functional group abundance. This study includes SEAMANCORE’s description and shows the model’s sensitivity to its parameters by means of sensitivity analyses. Its utility is exemplified by exploring various scenarios of no stressors, fishing and bleaching regimes in a theoretical coral reef. We expect that linking fish demographics with changing habitat quality will prove insightful for fisheries management.

Description: The factors regulating phytoplankton community composition play a crucial role in structuring aquatic food webs. However, consensus is still lacking about the mechanisms underlying the observed biogeographical differences in cell size composition of phytoplankton communities. Here we use a trait-based model to disentangle these mechanisms in two contrasting regions of the Atlantic Ocean. In our model, the phytoplankton community can self-assemble based on a trade-off emerging from relationships between cell size and (1) nutrient uptake, (2) zooplankton grazing and (3) phytoplankton sinking. Grazing ‘pushes’ the community towards larger cell sizes, whereas nutrient uptake and sinking ‘pull’ the community towards smaller cell sizes. We find that the stable environmental conditions of the tropics strongly balance these forces leading to persistently small cell sizes and reduced size diversity. In contrast, the seasonality of the temperate region causes the community to regularly reorganize via shifts in species composition and to exhibit, on average, bigger cell sizes and higher size diversity than in the tropics. Our results raise the importance of environmental variability as a key structuring mechanism of plankton communities in the ocean and call for a reassessment of the current understanding of phytoplankton diversity patterns across latitudinal gradients.

Description: Recent studies have analysed valuable compilations of data for the size-scaling of phytoplankton traits, but these cannot be employed directly in most large-scale modelling studies, which typically do not explicitly resolve the relevant trait values. Although some recent large-scale modelling studies resolve species composition and sorting within communities, most do not account for the observed flexible response of phytoplankton communities, such as the dynamic acclimation often observed in laboratory experiments. In order to derive a simple yet flexible model of phytoplankton growth that can be useful for a wide variety of ocean modelling applications, we combine two trade-offs, one for growth and the other for nutrient uptake, under the optimality assumption, i.e. that intracellular resources are dynamically allocated to maximize growth rate. This yields an explicit equation for growth as a function of nutrient concentration and daily averaged irradiance. We furthermore show how with this model effective Monod parameter values depend on both the underlying trait values and environmental conditions. We apply this new model to two contrasting time-series observation sites, including idealized simulations of size diversity. The flexible model responds differently compared with an inflexible control, suggesting that acclimation by individual species could impact models of plankton diversity.

Description: Chemical pollution is a growing issue for ocean ecosystems, threatening especially apex predators because they bioaccumulate persistent chemical pollutants such as non-essential trace elements. The trophic position is thus a key aspect when assessing the impacts of environmental pollution in marine organisms. Here we investigate the differences in the concentrations of essential (Cu, Cr, Se, and Zn) and non-essential elements (Hg, Al, As, Cd, and Sr), in muscular and hepatic tissues of four sympatric non-migratory seabirds (namely Sula leucogaster, Larus dominicanus, Fregata magnificens, and Thalasseus acuflavidus), which were found stranded along the Brazilian coast. The observed hepatic and muscular interspecific differences in elemental concentrations indicated that these sympatric seabirds are differently exposed to persistent contaminants circulating in the food web due to differences with respect to known feeding behaviours and prey preferences. Moreover, we found a consistent co-accumulative relationship between Se and Hg molar levels in liver tissues with mean Se:Hg molar ratio above 1. This relationship supports previous studies indicating that Se, via the formation of Sesingle bondHg complexes, plays an essential biochemical role in the detoxification process of methyl mercury in seabirds. Our results suggest that feeding behaviour is an important factor associated to the interspecific differences of trace element concentrations in seabirds. However, traits other than feeding preferences (e.g. age) may also play an important role in the accumulation of these elements.

Description: Mismanaged plastic waste is transported via rivers or city drains into the ocean where it accumulates in coastal sediments, ocean gyres and the deep ocean. Plastic harms marine biota and may ultimately return to humans via the food chain. Private initiatives proposing to collect plastic from the sea and rivers have gained widespread attention, especially in the media. However, few of these methods are proven concepts and it remains unclear how effective they are. Here we estimate the amount of plastic in the global surface ocean to assess the long-term legacy of plastic mass production, calculate the time required to clean up the oceans with river barriers and clean up devices, and explore the fate of collected plastic waste. We find that the projected impact of both single and multiple clean up devices is very modest. A significant reduction of plastic debris in the ocean can be only achieved with collection at rivers or with a combination of river barriers and clean up devices. We also show that the incineration and production of plastic has a significant long-term effect on the global atmospheric carbon budget. We conclude that a combination of reduced plastic emissions and reinforced collection is the only way to rid the ocean of plastic waste.

Description: Biodiversity is one of the key mechanisms that facilitate the adaptive response of planktonic communities to a fluctuating environment. How to allow for such a flexible response in marine ecosystem models is, however, not entirely clear. One particular way is to resolve the natural complexity of phytoplankton communities by explicitly incorporating a large number of species or plankton functional types. Alternatively, models of aggregate community properties focus on macroecological quantities such as total biomass, mean trait, and trait variance (or functional trait diversity), thus reducing the observed natural complexity to a few mathematical expressions. We developed the PhytoSFDM modelling tool, which can resolve species discretely and can capture aggregate community properties. The tool also provides a set of methods for treating diversity under realistic oceanographic settings. This model is coded in Python and is distributed as open-source software. PhytoSFDM is implemented in a zero-dimensional physical scheme and can be applied to any location of the global ocean. We show that aggregate community models reduce computational complexity while preserving relevant macroecological features of phytoplankton communities. Compared to species-explicit models, aggregate models are more manageable in terms of number of equations and have faster computational times. Further developments of this tool should address the caveats associated with the assumptions of aggregate community models and about implementations into spatially resolved physical settings (one-dimensional and three-dimensional). With PhytoSFDM we embrace the idea of promoting open-source software and encourage scientists to build on this modelling tool to further improve our understanding of the role that biodiversity plays in shaping marine ecosystems.

Description: Ecosystem models need to capture biodiversity, because it is a fundamental determinant of food web dynamics and consequently of the cycling of energy and matter in ecosystems. In oceanic food webs, the plankton compartment encompasses by far most of the biomass and diversity. Therefore, capturing plankton diversity is paramount for marine ecosystem modelling. In recent years, many models have been developed, each representing different aspects of plankton diversity, but a systematic comparison remains lacking. Here we present established modelling approaches to study plankton ecology and diversity, discussing the limitations and strengths of each approach. We emphasize their different spatial and temporal resolutions and consider the potential of these approaches as tools to address societal challenges. Finally, we make suggestions as to how better integration of field and experimental data with modelling could advance understanding of both plankton biodiversity specifically and more broadly the response of marine ecosystems to environmental change, including climate change.

Description: The interplay between tectonics and climate is known to impact the evolution and distribution of life forms, leading to present-day patterns of biodiversity. Numerical models that integrate the co-evolution of life and landforms are ideal tools to investigate the causal links between these earth system components. Here, we present a tool that couples an ecological–evolutionary model with a landscape evolution model (LEM). The former is based on the adaptive speciation of functional traits, where these traits can mediate ecological competition for resources, and includes dispersal and mutation processes. The latter is a computationally efficient LEM (FastScape) that predicts topographic relief based on the stream power law, hillslope diffusion, and orographic precipitation equations. We integrate these two models to illustrate the coupled behaviour between tectonic uplift and eco-evolutionary processes. Particularly, we investigate how changes in tectonic uplift rate and eco-evolutionary parameters (i.e. competition, dispersal, and mutation) influence speciation and thus the temporal and spatial patterns of biodiversity.

Description: 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.