Freshwater cyanobacterial harmful algae blooms (cHABs) are a major threat to human and environmental health and are increasing globally in frequency and severity. To manage this threat in a timely ...manner, science must focus on increasing our ability to predict the growth and toxigenicity of specific taxa of cyanobacteria.
Recent molecular research has revealed striking genomic and metabolic diversity among the many morphologically indistinguishable sub‐species and strains of cyanobacteria. Assemblage‐level molecular metabolic capability surveys promise to improve our ability to predict cyanobacterial responses to environmental forcing, but many of these cutting‐edge techniques are not widely available or cost‐effective enough to be employed in routine monitoring programmes to support management decisions. Taxonomic ambiguity, cryptic functional specialisation, incongruence between genomic capability and phylogeny, and genomic flexibility impose severe challenges to our ability to ascribe autecological attributes at a level of taxonomic resolution that is attainable under current management strategies (i.e. Linnaean species). This lack of knowledge prohibits reliable predictions of species' responses to environmental stressors.
Cyanobacterial species comprise consortia of metabolically diverse, morphologically indistinct strains that span a range of ecological specialisation. Under current, broadly applied taxonomic concepts, these species functionally embody a generalist ecological strategy—persisting and/or proliferating where other specialised competitors are negatively impacted.
We postulate that within current management frameworks, characterising of cyanobacterial species as competing generalists, as well as considering abundance trajectories of well‐characterised, non‐cyanobacterial specialist phytoplankton will generate more scalable, mechanistic, and management‐relevant insight into increasing cHAB frequency and severity in suitable time frames.
Here we recommend that cHAB management considers the competitive framework of phytoplankton communities, including cyanobacteria, wherein diverse environmental changes lead to deterministic responses by readily identifiable, documented specialist taxa. Characterising these changes in community structure will quantify the relative importance of altered stressors and resource availability that can be exploited by metabolically flexible cyanobacteria.
Abstract
Frozen winters define life at high latitudes and altitudes. However, recent, rapid changes in winter conditions have highlighted our relatively poor understanding of ecosystem function in ...winter relative to other seasons. Winter ecological processes can affect reproduction, growth, survival, and fitness, whereas processes that occur during other seasons, such as summer production, mediate how organisms fare in winter. As interest grows in winter ecology, there is a need to clearly provide a thought-provoking framework for defining winter and the pathways through which it affects organisms. In the present article, we present nine maxims (concise expressions of a fundamentally held principle or truth) for winter ecology, drawing from the perspectives of scientists with diverse expertise. We describe winter as being frozen, cold, dark, snowy, less productive, variable, and deadly. Therefore, the implications of winter impacts on wildlife are striking for resource managers and conservation practitioners. Our final, overarching maxim, “winter is changing,” is a call to action to address the need for immediate study of the ecological implications of rapidly changing winters.
We present the first evidence of biological change in all of the pelagic Laurentian Great Lakes associated with recent climatic warming. We hypothesized that measured changes in lake temperature, and ...the resulting physical changes to water columns, were affecting diatom communities in the Great Lakes. A paleolimnological analysis of 10 sediment cores collected from deep locations throughout the Great Lakes basin indicates a recent (30–50 yr) reorganization of the diatom community to one characterized by elevated abundances of several species from the group Cyclotella sensu lato, coinciding with rising atmospheric and water temperatures. These Cyclotella increases are a probable mechanistic result of new physical regimes such as changing stratification depths and longer ice-free periods, and possibly water quality shifts. Efforts to understand the mechanisms of these changes are ongoing, but this compositional reorganization in primary producers could have important implications to Great Lakes food webs.
As global surface temperatures continue to rise as a result of anthropogenic climate change, effects in temperate lakes are likely to be more pronounced than in other ecosystems. Decreases in snow ...and ice cover extent and duration and extended periods of summer stratification have been observed in temperate lake systems throughout the Anthropocene. However, the effects of changing snow and ice cover on lacustrine communities remain largely uninvestigated. We examined underwater light climate and associated primary productivity patterns under snow-covered and clear-lake ice in 6 inland lakes in Minnesota, USA, spanning gradients of water column optical properties (blue, green, brown) associated with trophic status and organic material content. In all lakes, snow cover influenced not only the intensity, but also the spectral signature of light penetrating into the water column. Specifically, the wavelength of maximum penetration was shifted towards longer wavelengths under snow cover in green (eutrophic) lakes but was shifted towards shorter wavelengths in blue and brown lakes. Volumetric primary productivity was often higher than anticipated (e.g., ∼1200 mg m
−3
d
−1
; Lake Minnetonka, snow-covered ice). Carbon assimilation rates were lower under snow-covered ice throughout the water column in all lake types except immediately under cleared ice in eutrophic lakes, where phytoplankton were likely photoinhibited because of the penetration of intense, short-wavelength light. These findings suggest that changes to snow and ice cover under ongoing climate change scenarios can affect patterns of phytoplankton primary productivity in sensitive aquatic ecosystems.
We review the literature on species flocks in diatoms. Past descriptions of species flocks in diatoms are of few species and do not demonstrate monophyly of the taxa explicitly. The genus
Tetralunata
..., with 19 taxa described from Lake Toba, Indonesia, may be the best example to date of species flocks in freshwater diatoms. Other examples for this group are evaluated, from ancient lakes, river drainages and islands, to more geologically short-lived areas and habitats. Other examples may reside in the Rift Valley lakes of East Africa, Amazonia, lakes Baikal, and Ohrid, and some islands such as New Caledonia, Sulawesi, and Madagascar. It would appear that the phenomenon is not expressed in Hawaii, which has endemic, but very few, species. It is interesting to note that nearly all of the examples of species flocks of extant diatoms are of those groups that possess a raphe system. The role of molecular studies to study species flocks is discussed. Other features not traditionally examined to recognize species-level distinctions (physiology, ecology) which may be useful in the future to help identify species flocks in freshwater diatoms.
Among its many impacts, climate warming is leading to increasing winter air temperatures, decreasing ice cover extent, and changing winter precipitation patterns over the Laurentian Great Lakes and ...their watershed. Understanding and predicting the consequences of these changes is impeded by a shortage of winter‐period studies on most aspects of Great Lake limnology. In this review, we summarize what is known about the Great Lakes during their 3–6 months of winter and identify key open questions about the physics, chemistry, and biology of the Laurentian Great Lakes and other large, seasonally frozen lakes. Existing studies show that winter conditions have important effects on physical, biogeochemical, and biological processes, not only during winter but in subsequent seasons as well. Ice cover, the extent of which fluctuates dramatically among years and the five lakes, emerges as a key variable that controls many aspects of the functioning of the Great Lakes ecosystem. Studies on the properties and formation of Great Lakes ice, its effect on vertical and horizontal mixing, light conditions, and biota, along with winter measurements of fundamental state and rate parameters in the lakes and their watersheds are needed to close the winter knowledge gap. Overcoming the formidable logistical challenges of winter research on these large and dynamic ecosystems may require investment in new, specialized research infrastructure. Perhaps more importantly, it will demand broader recognition of the value of such work and collaboration between physicists, geochemists, and biologists working on the world's seasonally freezing lakes and seas.
Plain Language Summary
The Laurentian Great Lakes are the world's largest freshwater ecosystem and provide diverse ecosystem services to millions of people. Affected by multiple interacting stressors, this system is the target of extensive restoration and management efforts that demand robust scientific knowledge. Winter limnology represents a key knowledge gap that limits understanding and prediction of the function of the Great Lakes and other large temperate lakes. Here, we summarize what is known about the Great Lakes during their 3–6 months of winter, identify key questions that must be addressed to improve understanding of the physical, chemical, and biological functioning of large lakes in winter, and suggest ways to address these questions. We show that ice cover is a “master variable” that controls numerous aspects of large temperate lake ecology and that the effects of the ongoing reduction in ice cover extent and duration cannot be predicted without improved knowledge of winter limnology.
Key Points
Winter limnology is a key knowledge gap that limits understanding and management of the Great Lakes and other large, seasonally frozen lakes
We review the winter physics, chemistry, and biology of the Great Lakes and identify priority questions for winter research on large lakes
Ice cover is a “master variable” for many large lake limnological processes, making a better understanding of its role a research priority
Winter conditions impose dramatic constraints on temperate, boreal, and polar ecosystems, and shape the abiotic and biotic interactions underpinning these systems. At high latitudes, winter can last ...longer than the growing season and may have a disproportionately large impact on organisms and ecosystems. Even so, our understanding of the ecological implications of winter is often lacking. Indeed, even what exactly defines winter is currently unclear, and boundaries that delineate this season are blurred across marine, freshwater, and terrestrial realms and fields of biology. Here, we discuss the complexity of defining winter, and highlight the importance of maintaining the capacity to test hypotheses across seasons, realms, and domains of life. We then outline questions drawn from diverse fields of research that address current gaps in our understanding of winter ecology and how winter influences multiple levels of biological organization, from individuals to ecosystems. Finally, we highlight the potential consequences of changes to both the length and severity of winter due to climate change, and discuss the role winter may play in mediating ecosystem function in the future.
We compared size and colour characteristics of rocks used by male cutlip minnows Exoglossum maxillingua to build nests to those of streambed background materials. We found that materials used to ...construct conspicuous, mound‐shaped nests were uniform in size and darker and more colour‐saturated than background materials of the same size. To our knowledge, this phenomenon is the first reported example of fish selecting nest materials based on colour and has important implications for the conservation of mound‐nesting stream cyprinid species.
Abstract
The Laurentian Great Lakes are among the planet’s fastest-warming lakes. Recent paleolimnological studies have shown changes in the diatom community of the system, including shifts towards ...taxa characteristic of strongly stratified systems and ongoing cell-size diminution. Relationships between species’ cell size and establishment in—or extirpation from—the system have not been addressed. Examining patterns of establishment and extirpation provides insight into the effects of multiple stressors at the ecosystem scale. We evaluate the timing of the establishment or extirpation of diatom taxa from fossil records post-European settlement within the Great Lakes as a function of cell size. Relationships between establishment or extirpation date and cell size were not random, and were best expressed as cubic curves. Generally, large taxa became established early in the record, while establishments of smaller taxa continued apace until the late 20th century. Extirpations of taxa of all sizes accelerated in the late 20th and early 21st centuries, and large-celled taxa were disproportionately extirpated over the last two decades. We discuss the implications of these relationships on the overall cell-size characteristics of the community, and consider the influences of propagule pressure, nutrient status, species invasions, and climate change upon diatom establishment and extirpation.
Habitat homogenization, nutrient enrichment and loss of biodiversity are broadly recognized as the consequences of human activity in aquatic systems. Diatoms (Bacillariophyceae) are frequently used ...in aquatic environmental assessment and impact monitoring, but in unique habitats dominated by endemic taxa, traditional approaches may not be appropriate. We examined the impacts of long term anthropogenic impacts upon the littoral episammic diatom community around the town of Soroako, located on Lake Matano, an ancient tropical lake. Lake Matano is located on central Sulawesi Island, Indonesia, and socio-economic conditions are typical of developing nations. Although differences in nutrient concentrations were undetectable with field-based spectroscopy approaches, mean Shannon diversity was decreased in association with proximity the town-site. However, mean ß-diversity was maintained despite several decades of shoreline modification at Soroako. Elevated abundances of early-successional diatom taxa in the disturbed area drove differences between areas immediately offshore of Soroako and those farther away. These findings suggest that increased physical disturbance and TSS loads around Soroako, rather than increased nutrient loading, influenced shifts in the diatom community. These results suggest that microscopy-based biomonitoring approaches are sensitive indicators of environmental modification that could be useful in areas where access to cutting-edge analytical equipment is limited.
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