Ecological Regime Research Articles

Long-term transients and complex dynamics of a stage-structured population with time delay and the Allee effect

Traditionally, mathematical modeling in population ecology is mainly focused on asymptotic behavior of the model, i.e. as given by the system attractors. Recently, however, transient regimes and especially long-term transients have been recognized as playing a crucial role in the dynamics of ecosystems. In particular, long-term transients are a potential explanation of ecological regime shifts, when an apparently healthy population suddenly collapses and goes extinct. In this paper, we show that the interplay between delay in maturation and a strong Allee effect can result in long-term transients in a single species system. We first derive a simple ‘conceptual’ model of the population dynamics that incorporates both a strong Allee effect and maturation delay. Unlike much of the previous work, our approach is not empirical since our model is derived from basic principles. We show that the model exhibits a high complexity in its asymptotic dynamics including multi-periodic and chaotic attractors. We then show the existence of long-term transient dynamics in the system, when the population size oscillates for a long time between locally stable stationary states before it eventually settles either at the persistence equilibrium or goes extinct. The parametric space of the model is found to have a complex structure with the basins of attraction corresponding to the persistence and extinction states being of a complicated shape. This impedes the prediction of the eventual fate of the population, as a small variation in the maturation delay or the initial population size can either bring the population to extinction or ensure its persistence.

ЗАЛЕЖНІСТЬ СИСТЕМАТИЧНОЇ ТА ЕКОЛОГІЧНОЇ СТРУКТУРИ ТРАВ’ЯНОГО ПОКРИВУ ЛІСОВИХ ЕКОСИСТЕМ ВІД АНТРОПОГЕННОГО ВПЛИВУ

<p>Pine forests Chigirinsky Bor grow on fresh sod-podzolic soils formed on ancient alluvial deposits. Pine forests are characterized by stringent moisture regimes and constantly suffer from lack of productive moisture in soil. Industrial development of Cherkasy in 60th years of ХХ century leaded air pollution and emissions of SO2, NOx, NH3, and dust. This contributed to significant negative influence on the surrounding forest ecosystems from enterprises of Cherkassy industrial agglomeration.</p> <p>The grass cover in pine stands of Chigirinsky Bor transforms into xerophytic grasses and ruderal communities under the impact of negative biotic and abiotic factors. They are namely the anthropogenic violation of forest conditions, stands decline, recreational and industrial tree crowns understocking, xerophytic and heliophytic transformations of forest conditions. All the above mentioned caused strong ruderal and adventive transformation of grass cover. We registered the changes in nitrophilous plant spread regards the Cherkasy industrial agglomeration approaching which emits toxic with nitrogen-containing gases. Adventive and other non-forest species displace ferns and mosses, the ratio of ecomorfs is also changes due to increase of the quantity and development activation of annuals, xerophytic, ruderal, and nitrofil plants. The <em>Asteraceae</em>/<em>Brassicaceae</em> 3:1 ratio indicates significant anthropogenic violations in the region.</p> <p>We fixed the xerophytic, ruderal, and adventive transformation of grass cover in forest ecosystems. It is also founded the tendency of expanding the fraction of mesophilic plant species due to alterations in water regime (creation of Kremenchug reservoir and draining of floodplain Tyasmyn). When approaching the Cherkasy industrial agglomeration the grass cover degradation is clearly observed on the environmental profile. All this causes the forest ecosystem degradation and gradual loss of forest vegetation typical characteristics. We revealed the domination of plant species that are tolerant to transformed forest conditions due to drastic anthropogenic changes of ecological regimes in Chygyryn's Bor.</p> <p><em>Key words:</em><em> grass cover, Chigirin's Bor, anthropogenic impact, forest ecosystem, industrial transformation and degradation of grass cover.</em></p>

Abundance and Biogeography of Picoprasinophyte Ecotypes and Other Phytoplankton in the Eastern North Pacific Ocean.

Eukaryotic algae within the picoplankton size class (≤2 μm in diameter) are important marine primary producers, but their spatial and ecological distributions are not well characterized. Here, we studied three picoeukaryotic prasinophyte genera and their cyanobacterial counterparts, Prochlorococcus and Synechococcus, during two cruises along a North Pacific transect characterized by different ecological regimes. Picoeukaryotes and Synechococcus reached maximum abundances of 1.44 × 10(5) and 3.37 × 10(5) cells · ml(-1), respectively, in mesotrophic waters, while Prochlorococcus reached 1.95 × 10(5) cells · ml(-1) in the oligotrophic ocean. Of the picoeukaryotes, Bathycoccus was present at all stations in both cruises, reaching 21,368 ± 327 18S rRNA gene copies · ml(-1). Micromonas and Ostreococcus clade OI were detected only in mesotrophic and coastal waters and Ostreococcus clade OII only in the oligotrophic ocean. To resolve proposed Bathycoccus ecotypes, we established genetic distances for 1,104 marker genes using targeted metagenomes and the Bathycoccus prasinos genome. The analysis was anchored in comparative genome analysis of three Ostreococcus species for which physiological and environmental data are available to facilitate data interpretation. We established that two Bathycoccus ecotypes exist, named here BI (represented by coastal isolate Bathycoccus prasinos) and BII. These share 82% ± 6% nucleotide identity across homologs, while the Ostreococcus spp. share 75% ± 8%. We developed and applied an analysis of ecomarkers to metatranscriptomes sequenced here and published -omics data from the same region. The results indicated that the Bathycoccus ecotypes cooccur more often than Ostreococcus clades OI and OII do. Exploratory analyses of relative transcript abundances suggest that Bathycoccus NRT2.1 and AMT2.2 are high-affinity NO3 (-) and low-affinity NH4 (+) transporters, respectively, with close homologs in multiple picoprasinophytes. Additionally, in the open ocean, where dissolved iron concentrations were low (0.08 nM), there appeared to be a shift to the use of nickel superoxide dismutases (SODs) from Mn/Fe/Cu SODs closer inshore. Our study documents the distribution of picophytoplankton along a North Pacific ecological gradient and offers new concepts and techniques for investigating their biogeography.

Detecting regime shifts in marine systems with limited biological data: An example from southeast Australia

The ability to detect ecological regime shifts in a data-limited setting was investigated, using southeast Australian ecosystems as a model. Community variability was summarized for 1968–2008 with the first two principal components (PCs) of recruitment estimates for six fish stocks and reproductive parameters for four seabird species; regional climate was summarized for 1953–2008 with the first two PCs for three parameters (sea surface temperature [SST], sea surface salinity, surface nitrate) measured at two stations; and basin-scale climate variability was summarized for 1950–2012 with mean South Pacific SST and the first two PCs of detrended South Pacific SST. The first two biology PCs explained 45% of total community variability. The first two PCs of basin-scale SST showed abrupt shifts similar to “regime” behavior observed in other ocean basins, and the first PC of basin-scale SST showed significant covariation with the first PC of regional climate. Together, these results are consistent with the strong community variability and decadal-scale red noise climatic variability associated with Northern Hemisphere regime shifts. However, statistical model selection showed that the first two PCs of regional climate and the first PC of biology time series all exhibited linear change, rather than abrupt shifts. This result is consistent with previous studies documenting rapid linear change in the climate and biology of southeast Australian shelf ecosystems, and we conclude that there is no evidence for regime shift behavior in the region’s ecology. However, analysis of a large set of previously-published biological time series from the North Pacific (n=64) suggests that studies using fewer than ∼30 biological time series, such as this one, may be unable to detect regime shifts. Thus we conclude that the nature of ecological variability in the region cannot be determined with available data. The development of additional long-term biological observations is needed for understanding change in southeast Australia and in many other marine ecosystems globally.

Trajectory of an anthropogenically induced ecological regime shift in a New Zealand shallow coastal lake

This study examines environmental change over the post-colonial period at Wainono (South Canterbury, New Zealand), a coastal lagoon and wetland of national and international significance for native birds and fish, currently targeted for restoration. In order to better understand the recent trajectory of this ecosystem, a multi-proxy palaeolimnological approach was adopted, including the analysis of core composition, and diatom and macrofossil assemblages in sedimentary archives. Results indicated that a combination of land-use changes in the catchment and water-level control, by an artificial connection to the sea, transformed this shallow lake from a freshwater macrophyte-dominated state to a brackish, hypertrophic system with little or no macrophytes. The reconstruction corroborates the trajectory of stressors gleaned from historical reports of changes in and around Wainono Lagoon, as well as reported trajectories from other coastal lakes and lagoons of the east coast of the South Island of New Zealand and elsewhere around the world. This study adds to the evidence that such ecosystems are ecologically vulnerable and in need of careful management to safeguard the important biodiversity and provisioning values that they afford. It also highlights the usefulness of the palaeolimnological approach in providing substantial information for improving sustainable management and restoration strategies for shallow lakes.

Response of the Baltic and North Seas to river runoff from the Baltic watershed – Physical and biological changes

Selected Baltic Sea watershed River Runoff (BSRR) events during 1970–2000 were used as predictor in Generalised Linear Mixed Models (GLIMMIX) for evidence of simultaneous changes/chain of events (including possible time lags) in some chemical, physical and biological variables in the Baltic and North Sea ecosystems. Our aim was to explore for climatic-based explanation for ecological regime shifts that were documented semi-simultaneously in both ecosystems. Certain similarities were identified in the North Sea and the Baltic Sea salinity, oxygen concentration, temperature and phyto- and zooplankton parameters. These findings suggest that BSRR events which originate in the Baltic Sea catchment area modify and contribute to large scale ecosystem changes not only in the Baltic Sea, but also in the adjacent parts of the North Sea. However, the Baltic Sea inter-annual and inter-decadal variabilities of physical and biological parameters are driven by direct atmospheric forcing, typically with a relatively short lag. In contrast, such changes in the North Sea are influenced by both local and direct atmospheric forcing, typically with a longer lag than in the Baltic, and a more regional, indirect forcing from changes in the North Atlantic. We suggest that this interactive system partially is behind large scale ecosystem regime shifts found in both Seas. During our study period two such shifts have been identified independently from us in a study earlier in the Southern and Central Baltic in 1980s and 1990s and a later one in 2001/2002 in the North Sea. As a post hoc test we compared the 0+ year class strength of the North Sea herring with BSRR intensity, and found evidence for higher herring production in high BSRR periods, which further corroborates the idea of a remote effect from the large watershed area of the Baltic. Regime shifts as well as their semi-synchronous appearance in two neighbouring sea areas could be identified. GLIMMIX models provide opportunities for determining and understanding the mechanisms behind marine ecosystem long-term and large-scale changes. Many studies have shown the importance of climatic factors (identified by the air pressure index, North Atlantic Oscillation) to the physical and biological changes over the North Atlantic. Our study enlarges the areal and temporal scope of these observations, and provides further support and explanation for climate as the pacemaker for marine ecological changes.

An empirical model of the Baltic Sea reveals the importance of social dynamics for ecological regime shifts

Regime shifts triggered by human activities and environmental changes have led to significant ecological and socioeconomic consequences in marine and terrestrial ecosystems worldwide. Ecological processes and feedbacks associated with regime shifts have received considerable attention, but human individual and collective behavior is rarely treated as an integrated component of such shifts. Here, we used generalized modeling to develop a coupled social-ecological model that integrated rich social and ecological data to investigate the role of social dynamics in the 1980s Baltic Sea cod boom and collapse. We showed that psychological, economic, and regulatory aspects of fisher decision making, in addition to ecological interactions, contributed both to the temporary persistence of the cod boom and to its subsequent collapse. These features of the social-ecological system also would have limited the effectiveness of stronger fishery regulations. Our results provide quantitative, empirical evidence that incorporating social dynamics into models of natural resources is critical for understanding how resources can be managed sustainably. We also show that generalized modeling, which is well-suited to collaborative model development and does not require detailed specification of causal relationships between system variables, can help tackle the complexities involved in creating and analyzing social-ecological models.

SYNPHYTOINDICATION REKREATIONAL ECOLOGICAL CHANGES CONDITIONS OF PLANT FORMATION IN PROTECTED AREAS «BORZHAVA", ZAKARPATSKA LOWLAND

Phytocoenoses sensitively respond to changes of ecological regimes and objectively reflect changes in the structure of ecosystems at different levels of organisation.The aim of the research was to estimate the condition of vegetation of the foresr ecosystem of the protected area at the ecosystem level by gradient of recreational transformation.The River Borzhava flows in the protected area and is a favourite place of rest; it starts on the south-west slope of Borzhava meadows, which are located on the Polonynskii ridge.The comparative estimation of the ecological profile areas showed that with approach to the River Borzhava the territory of the protected area becomes more attractive for tourists and is subjected to more intensive recrearional impact. On the whole the analysis showed that dependence of plants on the edaphotope conditions undergoes the greatesr changes, which is caused by different degree of recreational load on phytocoenoses. By the gradient of recreational transformation of the ecoprofile increased contribution of euribionts and hemi-euribionts in the formation of the grass cover on the most transformed sites was detected.It was detected that peculiarities of change of the grass layer of the forest ecosystem of the protected area is characterised by processes of reduction of the level of the soil moistening and increase of the level of illumination under the stand shed on the most degraded sites.It was shown that recreational changes of ecological regimes condition change of the species composition of the grass cover and domination of the species which are more tolerant to transformed forest conditions.The performed analysis at the synecological level testifies that local recreational impact on the forest ecosystem of the protected area results in certain disruption of the integrity and structure of vegetation, reduction of ecological role of the forest in the floodplain.

Vulnerability of Antarctic shallow invertebrate‐dominated ecosystems

AbstractHuman impacts threaten not only species, but also entire ecosystems. Ecosystems under stress can collapse or transition into different states, potentially reducing biodiversity at a variety of scales. Here we examine the vulnerability of Antarctic shallow invertebrate‐dominated ecosystems, which may be threatened for several reasons. These unique shallow‐water communities mostly consist of dark‐adapted invertebrates, and rely on sea ice to create low‐light marine environments. Climate change is likely to cause early breakout of seasonal sea ice in parts of Antarctica, which will dramatically increase the amount of light reaching shallow seabed. This is predicted to result in ecological regime shifts, in which invertebrate‐dominated communities are replaced by macroalgal beds. Habitat for these endemic Antarctic ecosystems is globally rare, and the fragmented nature of their distribution along Antarctic coast increases their sensitivity to change. Concurrently, human activities in Antarctica are concentrated in areas where these habitats occur, compounding potential impacts. While there are clear mechanisms of threat to these ecosystems, lack of knowledge about their spatial distribution obscures predictions of potential ecosystem loss, and the likelihood of recovery. In this paper we describe these ecosystems, their association with the environment and the reasons for their vulnerability. We estimate their spatial distribution around Antarctica using sea ice and bathymetric data, and apply the International Union for Conservation of Nature Red List of Ecosystems criteria to assess their vulnerability. Best available data suggest that shallow ice‐covered ecosystems are likely Near Threatened to Vulnerable in places, although the magnitude of risk is spatially variable and requires additional data to strengthen the assessment.

Power and politics of social–ecological regime shifts in the Chilika lagoon, India and Tam Giang lagoon, Vietnam

Analyses of ecological regime shifts primarily focus on abrupt, long-term and significant changes that trigger fundamental reorganisation in ecosystem structure and function. There remains limited empirical work on the relationship between regime shifts and social inequities, power imbalances, and social and environmental injustices. Inadequate attention to this social context restricts our ability to predict and avert impending regime shifts, or to effectively navigate where thresholds have been crossed. In this paper, we offer an initial empirical assessment of politics and power in two coastal lagoons in India and Vietnam experiencing abrupt change. We adopt a realist view of power to: (1) assess the social relations structuring human–environment interactions in both lagoons; (2) characterise the dominant framings and narratives that influence if and how regime shifts are understood; (3) consider who wins and loses if and when regime shifts and other forms of rapid environmental change take place; and (4) reflect on the implications of power and politics for the governance of regime shifts in linked human–ocean settings.

Geophysical conceptualization of a fractured sedimentary bedrock riverbed using ground-penetrating radar and induced electrical conductivity

Summary Bedrock rivers exhibit very different hydraulic and ecological regimes compared to alluvial rivers. Groundwater–surface water interaction in rivers that flow directly on sedimentary bedrock surfaces with exposed fracture and conduit networks is generally based on alluvial river conceptual models. However, the dual and triple porosity systems of sedimentary rock (e.g., matrix, fractures and vugs) leads to highly variable hydraulic pathways and groundwater velocities that, in turn, result in processes that are very different than those derived from alluvial concepts. Relative to alluvial rivers there has been very little direct examination of dynamic interactions, such as fluxes, groundwater velocities, and mechanisms affecting water quality across the channel interface; this is largely because bedrock rivers are difficult to instrument and monitor given their heterogeneous and anisotropic flow systems. In this study, we evaluate the capacity of non-invasive, low impact ground-penetrating radar and frequency-domain electromagnetic induction methods capable of detecting discrete fracture and conduit features, mapping complex distributions of lithostratigraphic interfaces, and providing information about formation properties along a partially exposed section of the Eramosa River located in Ontario, Canada. Geophysical data are supported by direct hydrogeologic and geologic information obtained from a nearby borehole piezometer cluster and a continuous 15 m rock core. Valuable insights were gained into the lateral extent and geometry of structurally-controlled whydrostratigraphic units (e.g., dissolution-enhanced fractures, epikarst and karst features), which are expected to strongly influence groundwater and surface water interaction along the channel. An integrated application of GPR and EMI methods was necessary to fully understand the complex geometry of geologic boundaries and karst features within the shallow bedrock aquifer. The identification of epikarst below fluvial sediment and its relationship to the formation of dissolution features, exposed fracture conduit networks and sinkholes represents the basis for understanding the dynamic hydraulic responses between the surface water and the shallow bedrock aquifer.

Richards-like two species population dynamics model.

The two-species population dynamics model is the simplest paradigm of inter- and intra-species interaction. Here, we present a generalized Lotka-Volterra model with intraspecific competition, which retrieves as particular cases, some well-known models. The generalization parameter is related to the species habitat dimensionality and their interaction range. Contrary to standard models, the species coupling parameters are general, not restricted to non-negative values. Therefore, they may represent different ecological regimes, which are derived from the asymptotic solution stability analysis and are represented in a phase diagram. In this diagram, we have identified a forbidden region in the mutualism regime, and a survival/extinction transition with dependence on initial conditions for the competition regime. Also, we shed light on two types of predation and competition: weak, if there are species coexistence, or strong, if at least one species is extinguished.

Identifying the key water levels in reservoir operation on ecological objectives

This paper investigates the influences of reservoir water level variations of the operation rule curves on different objectives, especially on ecological objectives. Five representative ecological objectives are selected besides industrial and domestic (I&D) and agricultural water supply objectives. They can reflect the impacts of reservoir operation on different attributes of ecological flow regime in the Biliuhe Reservoir case study, Northeastern China. Sensitivities of water supply and ecological objectives caused by water level variations of I&D and agricultural operation rule curves are analyzed by using a variance-based sensitivity analysis method – Sobol's method. Results show that impacts of individual water levels and their interactions on ecological objectives are very different. Also the ecological objectives do not always conflict with water supply objectives. This study provides new insights for reservoir managers to improve downstream aquatic ecosystem by adjusting water levels not only at individual time periods but also at some interacting time periods. Furthermore, it helps us better understand the influence mechanism of water level changes on different objectives, and provides guidance for the development of reservoir operation rules.

Reconceptualizing Environmental Challenges Is Resilience the New Narrative?

We need to reexamine both our thinking about and our relationship to environmental and natural resource challenges. This includes facing the emerging realities of the Anthropocene: unprecedented and irreversible rates of biodiversity loss, exponential increases in per-capita resource consumption, and global climate change. Combined, these and other factors are increasing the likelihood of rapid, non-linear, social and ecological regime changes. New policy directions and orientations are needed to provide the necessary capacity to deal with challenges in a meaningful and equitable ways. This article posits that the concept of “resilience” is emerging as a new narrative in both scholarly literature and policy discussions that has potential in this regard. After first situating resilience thinking within current and historical narratives regarding social-ecological relations, it examines the potential for resilience to shift the environmental governance paradigm in helpful ways.

Elucidating multidecadal saltwater intrusion and vegetation dynamics in a coastal floodplain with artificial neural networks and aerial photography

AbstractSaltwater intrusion has been recognized as a major driver of ecological regime shifts in coastal wetlands, but few studies have incorporated long‐term salinity modelling data into the understanding of vegetation dynamics. This study uniquely combined artificial neural network (ANN) modelling and time series of aerial photographs to elucidate saltwater intrusion and mangrove encroachment into the freshwater floodplain of the Loxahatchee River over a period of six decades. Three ANN models were developed to simulate river salinity on a daily time step using freshwater inflow, rainfall and tide as inputs. With 8 years of measured data for training and testing, the ANN models demonstrated comparable or superior model performance for salinity simulation to their hydrodynamic counterparts. Modelling of historical salinity (1948–2011) using the ANNs indicated that the intensity of saltwater intrusion clearly correlated with watershed hydrology, which, in turn, was linked to historical watershed alterations and regional rainfall variability. Interpretation of the 1940, 1953, 1964, 1979, 1985 and 1995 aerial photographs revealed the progressive encroachment of mangroves and displacement of bald cypress and freshwater communities in the floodplain. The spatial extent of mangrove encroachment was related to the increasing mortality of bald cypress under the chronic effect of cumulative salinity exposure. The ecohydrological controls over vegetation changes in the Loxahatchee River support the ongoing ecosystem restoration programme, which aims to achieve incremental freshwater flow targets to protect and restore the floodplain ecosystem. Copyright © 2014 John Wiley & Sons, Ltd.

The End of Sustainability

It is time to move past the concept of sustainability. The realities of the Anthropocene warrant this conclusion. They include unprecedented and irreversible rates of human-induced biodiversity loss, exponential increases in per-capita resource consumption, and global climate change. These factors combine to create an increasing likelihood of rapid, nonlinear, social and ecological regime changes. The recent failure of the Rio + 20 provides an opportunity to collectively reexamine—and ultimately move past—the concept of sustainability as an environmental goal. We must face the impossibility of defining—let alone pursuing—a goal of “sustainability” in a world characterized by such extreme complexity, radical uncertainty and lack of stationarity. After briefly examining sustainability's failure, we propose resilience thinking as one possible new orientation and point to the challenges associated with translating resilience theory into policy application.

Assessing the distribution of social–ecological resilience and risk: Ireland as a case study of the uneven impact of famine

Explanations for the causes of famine and food insecurity often reside at a high level of aggregation or abstraction. Popular models within famine studies have often emphasised the role of prime movers such as population stress, or the political-economic structure of access channels, as key determinants of food security. Explanation typically resides at the macro level, obscuring the presence of substantial within-country differences in the manner in which such stressors operate. This study offers an alternative approach to analyse the uneven nature of food security, drawing on the Great Irish famine of 1845–1852. Ireland is often viewed as a classical case of Malthusian stress, whereby population outstripped food supply under a pre-famine demographic regime of expanded fertility. Many have also pointed to Ireland's integration with capitalist markets through its colonial relationship with the British state, and country-wide system of landlordism, as key determinants of local agricultural activity. Such models are misguided, ignoring both substantial complexities in regional demography, and the continuity of non-capitalistic, communal modes of land management long into the nineteenth century. Drawing on resilience ecology and complexity theory, this paper subjects a set of aggregate data on pre-famine Ireland to an optimisation clustering procedure, in order to discern the potential presence of distinctive social–ecological regimes. Based on measures of demography, social structure, geography, and land tenure, this typology reveals substantial internal variation in regional social–ecological structure, and vastly differing levels of distress during the peak famine months. This exercise calls into question the validity of accounts which emphasise uniformity of structure, by revealing a variety of regional regimes, which profoundly mediated local conditions of food security. Future research should therefore consider the potential presence of internal variations in resilience and risk exposure, rather than seeking to characterise cases based on singular macro-dynamics and stressors alone.

Biofilm community dynamics in bench-scale annular reactors simulating arrestment of chloraminated drinking water nitrification.

Annular reactors (ARs) were used to study biofilm community succession and provide ecological insight during nitrification arrestment through simultaneously increasing monochloramine (NH2Cl) and chlorine to nitrogen mass ratios, resulting in four operational periods (I-IV). Analysis of 16S rRNA-encoding gene sequence reads (454-pyrosequencing) examined viable and total biofilm communities and found total samples were representative of the underlying viable community. Bacterial community structure showed dynamic changes corresponding with AR operational parameters. Period I (complete nitrification and no NH2Cl residual) was dominated by Bradyrhizobium (total cumulative distribution: 38%), while environmental Legionella-like phylotypes peaked (19%) during Period II (complete nitrification and minimal NH2Cl residual). Nitrospira moscoviensis (nitrite-oxidizing bacteria) was detected in early periods (2%) but decreased to <0.02% in later periods, corresponding to nitrite accumulation. Methylobacterium (19%) and members of Nitrosomonadaceae (42%) dominated Period III (complete ammonia and partial nitrite oxidation and low NH2Cl residual). An increase in Afipia (haloacetic acid-degrading bacteria) relative abundance (<2% to 42%) occurred during Period IV (minimal nitrification and moderate to high NH2Cl residual). Microbial community and operational data provided no evidence of taxa-time relationship, but rapid community transitions indicated that the system had experienced ecological regime shifts to alternative stable states.

Investigation of nutrient thresholds to guide restoration and management of two impounded rivers in south-western Australia

Hysteresis between macrophyte and phytoplankton dominant ecological regimes has been observed in shallow lakes between 50 and 150μg/L total phosphorus (TP). This paper explores the capacity of these thresholds, initially proposed for European systems, to guide management and the successful restoration of macrophytes in two eutrophic rivers, the Canning River and the Lower Vasse River in Western Australia. Investigation of long-term nutrient data (1996–2007), revealed alternating macrophyte and phytoplankton dominance in the Canning River at TP concentrations in the spring and summer months of 152μg/L (±20μg/L SE) prior to remediation. Management interventions, including the application of Phoslock™, were successful in reducing TP to approximately 100μg/L and resulted in persistent macrophyte dominance. Despite reductions from approximately 400 to 150μg/L TP in the Lower Vasse River, phytoplankton blooms persisted. Transplantation of four native, perennial macrophyte species simultaneously in the Canning River and Lower Vasse River resulted in only Vallisneria australis surviving within a nutrient regime of 130–300μg/L TP, concurrent with very high epiphyte loads. This research supports guidelines to managers of 150μg/L TP (high risk macrophyte loss), 100μg/L TP for maintenance of existing macrophyte beds, and less than 100μg/L TP for restoration of transplanted species other than V. australis. The efficacy of these thresholds is dependent on P limitation and we suggest optimum molar total nitrogen to total phosphorus ratio greater than 20:1 and maximum total nitrogen concentration of 2000μg/L for macrophyte dominance.

A review of factors contributing to the decline of Newfoundland and Labrador snow crab (Chionoecetes opilio)

The Newfoundland and Labrador (NL) snow crab resource, presently the basis of the most important commercial fishery in the region, is in decline. Short-, mid-, and long-term recruitment prospects are deemed poor in most areas. Fishery declines have been most apparent in the north, beginning in the mid- to late 2000s, but are expected to begin in the more productive southern areas in the near future. A multitude of emergent theories to explain the resource decline have been hypothesized as contributing factors, including fishing, trawling impacts, seismic activities, disease, predation, and increasing temperature. This study comprehensively reviews and qualitatively relates the results of recent research and literature on each of these factors. We find that several factors may be contributing to a lack of recruitment in the stock, but diminishing produc- tivity resulting from a warming oceanographic regime is the primary cause of the resource decline. Further, we postulate that trends occurring in the snow crab stock are indicative of a broader-scale ecological regime shift occurring along the NL shelf.