Many asexual animal populations comprise a mixture of genetically different lineages, but to what degree this genetic diversity leads to ecological differences remains often unknown. Here, we test whether genetically different clonal lineages of Aptinothrips grass thrips differ in performance on a range of plants used as hosts in natural populations. We find a clear clone‐by‐plant species interactive effect on reproductive output, meaning that clonal lineages perform differently on different plant species and thus are characterized by disparate ecological niches. This implies that local clonal diversities can be driven and maintained by frequency‐dependent selection and that resource heterogeneity can generate diverse clone assemblies.
<p>The abyssal seafloor is at some locations covered with polymetallic nodules that provide hard substrate for sessile organisms. Extraction of these mineral-rich nodules will likely severely modify the trophic and non-trophic interactions within the abyssal food web, but the importance of nodules and their associated sessile fauna in supporting this food web remains unclear. Here, we present highly resolved interaction webs with ~200 (Peru Basin) and ~450 (Clarion-Clipperton Zone, CCZ) food-web compartments based on an extensive literature research. Compartments were connected with ~3,100 (Peru Basin) and ~8,500 (CCZ) trophic and non-trophic (e.g. substrate-providing nodules) links. The webs were used to assess how nodule extraction would modify the number of network compartments, number of links, link density and web connectance. We showed that nodule removal would reduce the number of food-web compartments and links by ~25% and ~35%, respectively, in the Peru Basin and by 21% and 20%, respectively, in the CCZ. Subsequent analysis identified stalked sponges, living attached to the nodules, as key structural species that support a high diversity of commensal and mutualistic fauna. We conclude that nodules are critical for food-web integrity and suggest the deployment of artificial sponge stalks as a potential mitigation strategy for deep-sea mining.</p>
Abstract. Mercury (Hg) is a pollutant of global concern. Due to anthropogenic emissions, the global Hg burden has been ever increasing since preindustrial times. Hg emitted into the atmosphere gets transported on a global scale and ultimately reaches the oceans. There it is transformed into highly toxic methylmercury (MeHg) that effectively accumulates in the food web. The international community has recognized this serious threat to human health and in 2017 regulated Hg under the UN Minamata Convention. Currently, the first effectiveness evaluation of the Minamata Convention is being prepared and, in addition to observations, models play a major role in understanding environmental Hg pathways and in predicting the impact of policy decisions and external drivers (e.g. climate, emission, and land-use change) on Hg pollution. Yet, the available model capabilities are mainly limited to atmospheric models covering the Hg cycle from emission to deposition. With the presented model MERCY v2.0 we want to contribute to the currently ongoing effort to further our understanding of Hg and MeHg transport, transformation, and bioaccumulation in the marine environment with the ultimate goal of linking anthropogenic Hg releases to MeHg in sea food. Here, we present the governing equations and parameters implemented in the MERCY model and evaluate the model performance for two European shelf seas, the North-and Baltic Sea. With the presented model evaluation we want to establish a set of general quality criteria that can be used for evaluation of marine Hg models. The evaluation is based on a rigid statistical framework developed for the quantitative evaluation of atmospheric chemistry transport models. Using the approach, we show that the MERCY model can reproduce observed average concentrations of individual Hg species (normalized mean bias: HgT 17 %, Hg0 2 %, MeHg -28 %) in two complex coastal oceans. Moreover, it is able to reproduce the observed seasonality and spatial patterns. We find that the model error for HgT(aq) is mainly driven by the limitations of the physical model setup in the coastal zone and the poor quality of data on Hg in major rivers (i.e.: Schelde and Elbe). In addition, the model error in calculating vertical mixing and stratification contributes to the total HgT model error. For the vertical transport we find that the widely used particle partitioning coefficient for organic matter of log(kd)=5.6 is too low for the coastal systems. For Hg0 the model performance is at a level where further model improvements will be difficult to detect. For MeHg, there is still a lack in the basic understanding of the processes governing methylation and demethylation. While the model can reproduce average MeHg concentrations this lack in understanding hampers our ability to reproduce the observed value range. Finally, we evaluate Hg and MeHg concentrations in biota and show, that modelled values are within the range of observed levels of accumulation in phytoplankton, zooplankton, and fish. The results of the model evaluation prove the feasibility of developing marine Hg models with similar predictive capability as established atmospheric chemistry transport models. Our findings also highlight important knowledge gaps in the dynamics controlling methylation and bioaccumulation that, if closed, could lead to important improvements of the model performance.
<p>Mercury is a pollutant of global concern due to its ability for long-range atmospheric transport, combined with its capability to be methylated into the neurotoxin methylmercury in the marine environment. The consumption of methylmercury in seafood is the primary hazard of mercury to humans, but most mercury emissions are in the form of atmospheric inorganic mercury. The link between inorganic atmospheric mercury and organic mercury in biota is poorly understood. &#160;Here we present our newly developed mercury bioaccumulation model for the North and Baltic Sea based on a fully resolved biogeochemical hydrodynamic model. The modelled bioaccumulation falls well in the range of observations and works by combining a new bioaccumulation model combined with the MERCY Hg speciation model and the ECOSMO ecosystem model. In phytoplankton, bioaccumulated mercury is mostly inorganic. In zooplankton inorganic and organic mercury is roughly equal and it originates in similar amounts from direct uptake from the water column and dietary interactions. In planktivorous fish organic mercury originating from trophic interactions is by far the dominant contaminant, interestingly omnivorous have a higher fraction (~20%) of methylmercury from passive uptake than planktivorous fish, this likely due to the longevity (10~15 years) of these high trophic predatorial fish. Notable interactions between bioaccumulation and Hg speciation in the model are that the cyanobacterial uptake of Hg2+ and MMHg on the shallow sea surface layer decreased mercury release into the atmosphere and lead to a higher buildup of both organic and inorganic mercury throughout the water column, additionally, POC is a major factor transporting Hg to deep anoxic bottom water increasing the amount of methylmercury. Our results indicate that the ecosystem plays an essential role in marine Hg cycling and should not be carelessly ignored in models.&#160;</p>
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