Drivers of global mangrove loss and gain in social-ecological systems.

Mangrove forests store high amounts of carbon, protect communities from storms, and support fisheries. Mangroves exist in complex social-ecological systems, hence identifying socioeconomic conditions associated with decreasing losses and increasing gains remains challenging albeit important. The impact of national governance and conservation policies on mangrove conservation at the landscape-scale has not been assessed to date, nor have the interactions with local economic pressures and biophysical drivers. Here, we assess the relationship between socioeconomic and biophysical variables and mangrove change across coastal geomorphic units worldwide from 1996 to 2016. Globally, we find that drivers of loss can also be drivers of gain, and that drivers have changed over 20 years. The association with economic growth appears to have reversed, shifting from negatively impacting mangroves in the first decade to enabling mangrove expansion in the second decade. Importantly, we find that community forestry is promoting mangrove expansion, whereas conversion to agriculture and aquaculture, often occurring in protected areas, results in high loss. Sustainable development, community forestry, and co-management of protected areas are promising strategies to reverse mangrove losses, increasing the capacity of mangroves to support human-livelihoods and combat climate change.

Adult incontinence products are a larger and faster growing waste issue than disposable infant nappies (diapers) in Australia.

The environmental issues relating to disposable of infant nappies have received considerable attention. However, adult absorbent hygiene products (AHPs) receive less attention, despite having comparable or greater environmental impact. Here we quantify and compare current and future flows of continence related AHPs entering waste streams from both infant and adult populations. Importantly our study accounts for current waste management and landfilling practices across Australia and the environmental implications of AHP disposal. Absorbent hygiene product use from infants and adults was modelled from 2020 to 2030 for Australia, and it's predicted that AHP waste generated by adults will account for between 4 and 10 times that of infants by 2030 due to an aging population. Our results indicate that 50% of used AHPs end up in landfill with both leachate and biogas collection, the remainder going to landfills without biogas collection or without both leachate and biogas collection, based on the most recent national data set, which is over a decade old. The average composition of used absorbent hygiene product (including 60% urine and faeces by mass) is estimated to contain 20% non-biodegradable material, which may complicate the biodegradability of absorbent hygiene products in landfill. Without additional regulatory incentive, the current waste management practices in Australia are likely to continue, with absorbent hygiene products typically entering landfill as municipal solid waste, rather than industrial composting or recycling facilities. More accurate estimation of environmental implications from these disposal pathways requires further work including biodegradation experiments currently unavailable in the literature.

Connecting targets for catchment sediment loads to ecological outcomes for seagrass using multiple lines of evidence.

Catchment impacts on downstream ecosystems are difficult to quantify, but important for setting management targets. Here we compared 12 years of monitoring data of seagrass area and biomass in Cleveland Bay, northeast Australia, with discharge and associated sediment loads from nearby rivers. Seagrass biomass and area exhibited different trajectories in response to river inputs. River discharge was a slightly better predictor of seagrass indicators than total suspended solid (TSS) loads, indicating that catchment effects on seagrass are not restricted to sediment. Linear relationships between Burdekin River TSS loads delivered over 1-4 years and seagrass condition in Cleveland Bay generated Ecologically Relevant Targets (ERT) for catchment sediment inputs. Our predicted ERTs were comparable to those previously estimated using mechanistic models. This study highlights the challenges of linking catchment inputs to condition of downstream ecosystems, and the importance of integrating a variety of metrics and approaches to increase confidence in ERTs.

Synthesising wave attenuation for seagrass: Drag coefficient as a unifying indicator.

An estimated 100 million people inhabit coastal areas at risk from flooding and erosion due to climate change. Seagrass meadows, like other coastal ecosystems, attenuate waves. Due to inconsistencies in how wave attenuation is measured results cannot be directly compared. We synthesised data from laboratory and field experiments of seagrass-wave attenuation by converting measurements to drag coefficients (CD). Drag coefficients varied from 0.02-5.12 with CD¯ = 0.74 for studies conducted in turbulent flow in non-storm conditions. A statistical model suggested that seagrass species affects CD although the exact mechanism remains unclear. A wave model using the estimated CD¯ as an input parameter demonstrated that wave attenuation increased with meadow length, shoot density, shoot width and canopy height. Findings can be used to estimate wave attenuation by seagrass, in any given set of conditions.

Identification of compounds from terrestrial dissolved organic matter toxic to cyanobacteria.

There is emerging evidence for the phytotoxicity of terrestrial dissolved organic matter (DOM), however its sources, transformations and ecological effects in aquatic ecosystems are poorly understood. DOM characterization by Nuclear Magnetic Resonance (NMR) spectroscopy has typically involved solid-state techniques, but poor resolution has often precluded identification of individual components. This study is the first to directly identify individual phytotoxic components using a novel combined approach of preparative HPLC fractionation of DOM (obtained from leaves of two common riparian trees, Casuarina cunninghamiana and Eucalyptus tereticornis). This was followed by chemical characterization of fractions, using one-dimensional (1D) and two-dimensional (2D) solution-state 1H NMR analyses. Additionally, the phytotoxic effect of the fractions was determined using cultures of the cyanobacteria Raphidiopsis (Cylindrospermopsis) raciborskii. The amino acid, proline, from Casuarina leachate was identified as phytotoxic, while for Eucalyptus leachate, it was gallic acid and polyphenols. These phytotoxicants remained in the leachates when they were incubated in sunlight or the dark conditions over 5 days. Our study identifies phytotoxic compounds with the potential to affect algal species composition, and potentially control nuisance R. raciborskii blooms.

Are laboratory growth rate experiments relevant to explaining bloom-forming cyanobacteria distributions at global scale?

Predicting algal population dynamics using models informed by experimental data has been used as a strategy to inform the management and control of harmful cyanobacterial blooms. We selected toxic bloom-forming species Microcystis spp. and Raphidiopsis raciborskii (basionym Cylindrospermopsis raciborskii) for further examination as they dominate in 78 % and 17 %, respectively, of freshwater cyanobacterial blooms (cyanoHABs) reported globally over the past 30 years. Field measurements of cyanoHABs are typically based on biomass accumulation, but laboratory experiments typically measure growth rates, which are an important variable in cyanoHAB models. Our objective was to determine the usefulness of laboratory studies of these cyanoHAB growth rates for simulating the species dominance at a global scale. We synthesized growth responses of M. aeruginosa and R. raciborskii from 20 and 16 culture studies, respectively, to predict growth rates as a function of two environmental variables, light and temperature. Predicted growth rates of R. raciborskii exceeded those of M. aeruginosa at temperatures ≳ 25 °C and light intensities ≳ 150 µmol photons m-2 s-1. Field observations of biomass accumulation, however, show that M. aeruginosa dominates over R. raciborskii, irrespective of climatic zones. The mismatch between biomass accumulation measured in the field, and what is predicted from growth rate measured in the laboratory, hinders effective use of culture studies to predict formation of cyanoHABs in the natural environment. The usefulness of growth rates measured may therefore be limited, and field experiments should instead be designed to examine key physiological attributes such as colony formation, buoyancy regulation and photoadaptation. Improving prediction of cyanoHABs in a changing climate requires a more effective integration of field and laboratory approaches, and an explicit consideration of strain-level variability.

Effects of photochemical and microbiological changes in terrestrial dissolved organic matter on its chemical characteristics and phytotoxicity towards cyanobacteria.

Previous studies have shown that under laboratory conditions, dissolved organic matter (DOM) leached from plants can be differentially more phytotoxic to cyanobacteria, compared to green algae. This study examined how DOM source and transformation processes (microbial and photochemical) affect its chemical composition and phytotoxicity towards a cultured species of cyanobacteria (Raphidiopsis raciborskii) using a factorial experimental design. To complement cyanobacterial bioassays, the chemical composition and associated changes in DOM were determined using spectroscopic (nuclear magnetic resonance (NMR) and absorbance) and elemental analyses. Sunlight exposed DOM from leaves of the terrestrial plants, Casuarina cunninghamiana and Eucalyptus tereticornis had the most phytotoxic effect compared to DOM not exposed to sunlight. This phytotoxic DOM was characterised by relatively low nitrogen content, containing highly coloured and relatively high molecular mass constituents. Both mixed effect model and PCA approaches to predict inhibition of photosynthetic yield indicated phytotoxicity could be predicted (P < 0.001) based upon the following parameters: C: N ratio; gilvin, and lignin-derived phenol content of DOM. Parallel proton-detected 1D and 2D NMR techniques showed that glucose anomers were the major constituents of fresh leachate. With ageing, glucose anomers disappeared and products of microbial transformation appeared, but there was no indication of the appearance of additional phytotoxic compounds. This suggests that reactive oxygen species may be responsible, at least partially, for DOM phytotoxicity. This study provides important new information highlighting the characteristics of DOM that link with phytotoxic effects.

What Is Gender Equality in Science?

Why do inequalities persist between male and female scientists, when the causes are well-researched and widely condemned? In part, because equality has many dimensions. Presenting eight definitions of gender equality, we show each is important but incomplete. Rigid application of any single equality indicator can therefore have perverse outcomes.

Losing a winner: thermal stress and local pressures outweigh the positive effects of ocean acidification for tropical seagrasses.

Seagrasses are globally important coastal habitat-forming species, yet it is unknown how seagrasses respond to the combined pressures of ocean acidification and warming of sea surface temperature. We exposed three tropical species of seagrass (Cymodocea serrulata, Halodule uninervis, and Zostera muelleri) to increasing temperature (21, 25, 30, and 35°C) and pCO2 (401, 1014, and 1949 µatm) for 7 wk in mesocosms using a controlled factorial design. Shoot density and leaf extension rates were recorded, and plant productivity and respiration were measured at increasing light levels (photosynthesis-irradiance curves) using oxygen optodes. Shoot density, growth, photosynthetic rates, and plant-scale net productivity occurred at 25°C or 30°C under saturating light levels. High pCO2 enhanced maximum net productivity for Z. muelleri, but not in other species. Z. muelleri was the most thermally tolerant as it maintained positive net production to 35°C, yet for the other species there was a sharp decline in productivity, growth, and shoot density at 35°C, which was exacerbated by pCO2 . These results suggest that thermal stress will not be offset by ocean acidification during future extreme heat events and challenges the current hypothesis that tropical seagrass will be a 'winner' under future climate change conditions.

Seagrass ecosystem trajectory depends on the relative timescales of resistance, recovery and disturbance.

Seagrass ecosystems are inherently dynamic, responding to environmental change across a range of scales. Habitat requirements of seagrass are well defined, but less is known about their ability to resist disturbance. Specific means of recovery after loss are particularly difficult to quantify. Here we assess the resistance and recovery capacity of 12 seagrass genera. We document four classic trajectories of degradation and recovery for seagrass ecosystems, illustrated with examples from around the world. Recovery can be rapid once conditions improve, but seagrass absence at landscape scales may persist for many decades, perpetuated by feedbacks and/or lack of seed or plant propagules to initiate recovery. It can be difficult to distinguish between slow recovery, recalcitrant degradation, and the need for a window of opportunity to trigger recovery. We propose a framework synthesizing how the spatial and temporal scales of both disturbance and seagrass response affect ecosystem trajectory and hence resilience.

Variation within and between cyanobacterial species and strains affects competition: Implications for phytoplankton modelling.

Cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii are two harmful species which co-occur and successively dominate in freshwaters globally. Within-species strain variability affects cyanobacterial population responses to environmental conditions, and it is unclear which species/strain would dominate under different environmental conditions. This study applied a Monte Carlo approach to a phytoplankton dynamic growth model to identify how growth variability of multiple strains of these two species affects their competition. Pairwise competition between four M. aeruginosa and eight C. raciborskii strains was simulated using a deterministic model, parameterized with laboratory measurements of growth and light attenuation for all strains, and run at two temperatures and light intensities. 17 000 runs were simulated for each pair using a statistical distribution with Monte Carlo approach. The model results showed that cyanobacterial competition was highly variable, depending on strains present, light and temperature conditions. There was no absolute 'winner' under all conditions as there were always strains predicted to coexist with the dominant strains, which were M. aeruginosa strains at 20°C and C. raciborskii strains at 28°C. The uncertainty in prediction of species competition outcomes was due to the substantial variability of growth responses within and between strains. Overall, this study demonstrates that within-species strain variability has a potentially large effect on cyanobacterial population dynamics, and therefore this variability may substantially reduce confidence in predicting outcomes of phytoplankton competition in deterministic models, that are based on only one set of parameters for each species or strain.

Optimum Temperatures for Net Primary Productivity of Three Tropical Seagrass Species.

Rising sea water temperature will play a significant role in responses of the world's seagrass meadows to climate change. In this study, we investigated seasonal and latitudinal variation (spanning more than 1,500 km) in seagrass productivity, and the optimum temperatures at which maximum photosynthesis and net productivity (for the leaf and the whole plant) occurs, for three seagrass species (Cymodocea serrulata, Halodule uninervis, and Zostera muelleri). To obtain whole plant net production, photosynthesis, and respiration rates of leaves and the root/rhizome complex were measured using oxygen-sensitive optodes in closed incubation chambers at temperatures ranging from 15 to 43°C. The temperature-dependence of photosynthesis and respiration was fitted to empirical models to obtain maximum metabolic rates and thermal optima. The thermal optimum (Topt) for gross photosynthesis of Z. muelleri, which is more commonly distributed in sub-tropical to temperate regions, was 31°C. The Topt for photosynthesis of the tropical species, H. uninervis and C. serrulata, was considerably higher (35°C on average). This suggests that seagrass species are adapted to water temperature within their distributional range; however, when comparing among latitudes and seasons, thermal optima within a species showed limited acclimation to ambient water temperature (Topt varied by 1°C in C. serrulata and 2°C in H. uninervis, and the variation did not follow changes in ambient water temperature). The Topt for gross photosynthesis were higher than Topt calculated from plant net productivity, which includes above- and below-ground respiration for Z. muelleri (24°C) and H. uninervis (33°C), but remained unchanged at 35°C in C. serrulata. Both estimated plant net productivity and Topt are sensitive to the proportion of below-ground biomass, highlighting the need for consideration of below- to above-ground biomass ratios when applying thermal optima to other meadows. The thermal optimum for plant net productivity was lower than ambient summer water temperature in Z. muelleri, indicating likely contemporary heat stress. In contrast, thermal optima of H. uninervis and C. serrulata exceeded ambient water temperature. This study found limited capacity to acclimate: thus the thermal optima can forewarn of both the present and future vulnerability to ocean warming during periods of elevated water temperature.

Phytotoxic effects of terrestrial dissolved organic matter on a freshwater cyanobacteria and green algae species is affected by plant source and DOM chemical composition.

Here we link plant source phylogeny to its chemical characteristics and determine parameters useful for predicting DOM phytotoxicity towards algal monocultures. We found that DOM characterised using UV-visible spectroscopic indices and elemental analysis is useful for distinguishing DOM plant sources. Specifically, combined values of absorbance at 440 nm and coefficients for the spectral slope ratio, were used to distinguish between gymnosperm-leached DOM and that from angiosperms. In our bioassays, DOM leached from 4 g leaf L-1 resulted in over 40% inhibition of photosynthetic yield for the cyanobacterium, Cylindrospermopsis raciborskii, for eight of the nine plants tested. Significant variables for predicting inhibition of yield were DOM exposure time and plant source, or using an alternate model, exposure time and spectroscopic and elemental measures. Our study proposes spectroscopic indices which can estimate a plant source's contribution to aquatic DOM, may provide insights into ecological outcomes, such as phytotoxicity to algae. The cyanobacterium (C. raciborskii) was more sensitive to DOM than a green algae (Monoraphidium spp.), as identified in a subsequent dose-response experiment with five different DOM plant sources. Low level additions of angiosperm derived-DOM (i.e. 0.5 g L-1) were slight phytotoxic to Monoraphidium spp. causing 30% inhibition of yield, while C. raciborskii was not affected. Higher DOM additions (i.e. 2 g L-1) caused 100% inhibition of yield for C. raciborskii, while Monoraphidium spp. inhibition remained under 30%. The divergence in algal sensitivity to DOM indicates that in aquatic systems, DOM derived from catchment vegetation has the potential to affect algal assemblages.

On the Long-term Stability of Clines in Some Metabolic Genes in Drosophila melanogaster.

Very little information exists for long-term changes in genetic variation in natural populations. Here we take the unique opportunity to compare a set of data for SNPs in 15 metabolic genes from eastern US collections of Drosophila melanogaster that span a large latitudinal range and represent two collections separated by 12 to 13 years. We also expand this to a 22-year interval for the Adh gene and approximately 30 years for the G6pd and Pgd genes. During these intervals, five genes showed a statistically significant change in average SNP allele frequency corrected for latitude. While much remains unchanged, we see five genes where latitudinal clines have been lost or gained and two where the slope significantly changes. The long-term frequency shift towards a southern favored Adh S allele reported in Australia populations is not observed in the eastern US over a period of 21 years. There is no general pattern of southern-favored or northern-favored alleles increasing in frequency across the genes. This observation points to the fluid nature of some allelic variation over this time period and the action of selective responses or migration that may be more regional than uniformly imposed across the cline.

Model fit versus biological relevance: Evaluating photosynthesis-temperature models for three tropical seagrass species.

When several models can describe a biological process, the equation that best fits the data is typically considered the best. However, models are most useful when they also possess biologically-meaningful parameters. In particular, model parameters should be stable, physically interpretable, and transferable to other contexts, e.g. for direct indication of system state, or usage in other model types. As an example of implementing these recommended requirements for model parameters, we evaluated twelve published empirical models for temperature-dependent tropical seagrass photosynthesis, based on two criteria: (1) goodness of fit, and (2) how easily biologically-meaningful parameters can be obtained. All models were formulated in terms of parameters characterising the thermal optimum (Topt) for maximum photosynthetic rate (Pmax). These parameters indicate the upper thermal limits of seagrass photosynthetic capacity, and hence can be used to assess the vulnerability of seagrass to temperature change. Our study exemplifies an approach to model selection which optimises the usefulness of empirical models for both modellers and ecologists alike.

The fundamental role of ecological feedback mechanisms for the adaptive management of seagrass ecosystems - a review.

Seagrass meadows are vital ecosystems in coastal zones worldwide, but are also under global threat. One of the major hurdles restricting the success of seagrass conservation and restoration is our limited understanding of ecological feedback mechanisms. In these ecosystems, multiple, self-reinforcing feedbacks can undermine conservation efforts by masking environmental impacts until the decline is precipitous, or alternatively they can inhibit seagrass recovery in spite of restoration efforts. However, no clear framework yet exists for identifying or dealing with feedbacks to improve the management of seagrass ecosystems. Here we review the causes and consequences of multiple feedbacks between seagrass and biotic and/or abiotic processes. We demonstrate how feedbacks have the potential to impose or reinforce regimes of either seagrass dominance or unvegetated substrate, and how the strength and importance of these feedbacks vary across environmental gradients. Although a myriad of feedbacks have now been identified, the co-occurrence and likely interaction among feedbacks has largely been overlooked to date due to difficulties in analysis and detection. Here we take a fundamental step forward by modelling the interactions among two distinct above- and belowground feedbacks to demonstrate that interacting feedbacks are likely to be important for ecosystem resilience. On this basis, we propose a five-step adaptive management plan to address feedback dynamics for effective conservation and restoration strategies. The management plan provides guidance to aid in the identification and prioritisation of likely feedbacks in different seagrass ecosystems.

Comparison of water-energy trajectories of two major regions experiencing water shortage.

Water shortage, increased demand and rising energy costs are major challenges for the water sector worldwide. Here we use a comparative case study to explore the long-term changes in the system-wide water and associated energy use in two different regions that encountered water shortage. In Australia, South East Queensland (SEQ) encountered a drought from 2001 to 2009, while Perth has experienced a decline in rainfall since the 1970s. This novel longitudinal study quantifies and compares the urban water consumption and the energy use of the water supply systems in SEQ and Perth during the period 2002 to 2014. Unlike hypothetical and long-term scenario studies, this comparative study quantifies actual changes in regional water consumption and associated energy, and explores the lessons learned from the two regions. In 2002, Perth had a similar per capita water consumption rate to SEQ and 48% higher per capita energy use in the water supply system. From 2002 to 2014, a strong effort of water conservation can be seen in SEQ during the drought, while Perth has been increasingly relying on seawater desalination. By 2014, even though the drought in SEQ had ended and the drying climate in Perth was continuing, the per capita water consumption in SEQ (266 L/p/d) was still 28% lower than that of Perth (368 L/p/d), while the per capita energy use in Perth (247 kWh/p/yr) had increased to almost five times that of SEQ (53 kWh/p/yr). This comparative study shows that within one decade, major changes in water and associated energy use occurred in regions that were similar historically. The very different "water-energy" trajectories in the two regions arose partly due to the type of water management options implemented, particularly the different emphasis on supply versus demand side management. This study also highlights the significant energy saving benefit of water conservation strategies (i.e. in SEQ, the energy saving was sufficient to offset the total energy use for seawater desalination and water recycling during the period.). The water-energy trajectory diagram provides a new way to illustrate and compare longitudinal water consumption and associated energy use within and between cities.

Comparative population genomics of latitudinal variation in Drosophila simulans and Drosophila melanogaster.

Examples of clinal variation in phenotypes and genotypes across latitudinal transects have served as important models for understanding how spatially varying selection and demographic forces shape variation within species. Here, we examine the selective and demographic contributions to latitudinal variation through the largest comparative genomic study to date of Drosophila simulans and Drosophila melanogaster, with genomic sequence data from 382 individual fruit flies, collected across a spatial transect of 19 degrees latitude and at multiple time points over 2 years. Consistent with phenotypic studies, we find less clinal variation in D. simulans than D. melanogaster, particularly for the autosomes. Moreover, we find that clinally varying loci in D. simulans are less stable over multiple years than comparable clines in D. melanogaster. D. simulans shows a significantly weaker pattern of isolation by distance than D. melanogaster and we find evidence for a stronger contribution of migration to D. simulans population genetic structure. While population bottlenecks and migration can plausibly explain the differences in stability of clinal variation between the two species, we also observe a significant enrichment of shared clinal genes, suggesting that the selective forces associated with climate are acting on the same genes and phenotypes in D. simulans and D. melanogaster.

How to Break the Cycle of Low Workforce Diversity: A Model for Change.

Social justice concerns but also perceived business advantage are behind a widespread drive to increase workplace diversity. However, dominance in terms of ethnicity, gender or other aspects of diversity has been resistant to change in many sectors. The different factors which contribute to low diversity are often hotly contested and difficult to untangle. We propose that many of the barriers to change arise from self-reinforcing feedbacks between low group diversity and inclusivity. Using a dynamic model, we demonstrate how bias in employee appointment and departure can trap organizations in a state with much lower diversity than the applicant pool: a workforce diversity "poverty trap". Our results also illustrate that if turnover rate is low, employee diversity takes a very long time to change, even in the absence of any bias. The predicted rate of change in workforce composition depends on the rate at which employees enter and leave the organization, and on three measures of inclusion: applicant diversity, appointment bias and departure bias. Quantifying these three inclusion measures is the basis of a new, practical framework to identify barriers and opportunities to increasing workforce diversity. Because we used a systems approach to investigate underlying feedback mechanisms rather than context-specific causes of low workforce diversity, our results are applicable across a wide range of settings.