Open Water Habitats Research Articles

Impact of invasive Typha and wetland interspersion on muskrat declines in North America

Muskrat (Ondatra zibethicus) populations are declining in North America. The exact cause of these declines is largely unknown. Along a similar timeframe, wetlands have been experiencing an invasion of cattail (Typha) throughout the continent. Specifically, T. x glauca, a hybrid of native T. latifolia and non-native T. angustifolia, has been increasing in range and abundance. This hybrid is associated with many negative impacts on wetland ecosystems, including reductions in biodiversity, open water habitat, and interspersion of water and emergent vegetation, the latter of which is an important habitat feature for muskrats. We sought to determine the impact of invasive T. x glauca on muskrat populations. We sampled 39 Typha-dominated marshes in southern Ontario, Canada to test the hypotheses that muskrats are declining in North America due to: (1) the increased relative abundance of T. x glauca in marshes, and (2) reduced wetland interspersion, which is associated with T. x glauca invasions. We estimated muskrat population density using house counts, sampled Typha communities to determine the relative abundance of T. x glauca, and measured interspersion using remote sensing techniques. We found that muskrat population density was positively associated with interspersion, but not associated with the relative abundance of T. x glauca. However, most sites were highly dominated by T. x glauca, limiting our inference. Our findings suggest that changing wetland structure may be contributing to muskrat population declines in North America, but more research is needed to determine the full impact of T. x glauca invasions on muskrat population declines.

Evolution and Prospects of Freshwater Fish Species and Aquaculture in Colombia: A Historical Perspective

Since the 1970s Colombia has been aware of the importance of aquaculture and inland fisheries in the future of its economy due to the constant increase of a population that is increasingly in need of protein of animal origin. In 1972, a joint project between the Government of Colombia and the Food and Agriculture Organization of the United Nations was approved and aimed at studying inland fishing and developing aquaculture in the country. The work of the project is described, as are the fish culture and fisheries research activities starting with the situation in the 1970s but comparing it with recent findings. A list of the main capture and culture fish species is given. Colombian fishing production has had great variations, but first inland water fishing was more important than marine. For instance, in 1972 total fish catch was 104,390 tons and 79% of that originated from inland waters. After the continental fisheries went down, the marine fisheries accounted in 2019 already 78 per cent of the total catch of the country. Mean standing fish crop estimates in 1975‒76 from the bay, open water and vegetation habitats in four floodplain lakes were 118, 12 and 251 kg/ha indicating clearly that the fish productivity on the Magdalena floodplain was relatively low. The aquaculture sector has been growing rapidly, reflecting global trends, and producing more than capture fisheries. Aquaculture produced 88,000 tons in 2013, which was a three-fold increase from the mid-1990s. Again twofold increase took place before 2020 when the production was almost 180,000 tons. Future development prospects of inland fisheries and aquaculture are discussed and a mention is made of the present situation of ornamental fish cultivation and trade in Colombia.

Multi-decadal floodplain classification and trend analysis in the Upper Columbia River valley, British Columbia

Abstract. Floodplain wetland ecosystems experience significant seasonal water fluctuation over the year, resulting in a dynamic hydroperiod, with a range of vegetation community responses. This paper assesses trends and changes in land cover and hydroclimatological variables, including air temperature, river discharge, and water level in the Upper Columbia River Wetlands (UCRW), British Columbia, Canada. A land cover classification time series from 1984 to 2022 was generated from the Landsat image archive using a random forest algorithm. Peak river flow timing, duration, and anomalies were examined to evaluate temporal coincidence with observed land cover trends. The land cover classifier used to segment changes in wetland area and open water performed well (kappa of 0.82). Over the last 4 decades, observed river discharge and air temperature have increased, precipitation has decreased, the timing of peak flow is earlier, and the flow duration has been reduced. The frequency of both high-discharge events and dry years have increased, indicating a shift towards more extreme floodplain flow behavior. These hydrometeorological changes are associated with a shift in the timing of snowmelt, from April to mid-May, and with seasonal changes in the vegetative communities over the 39-year period. Thus, woody shrubs (+6 % to +12 %) have expanded as they gradually replaced marsh and wet-meadow land covers with a reduction in open-water area. This suggests that increasing temperatures have already impacted the regional hydrology, wetland hydroperiod, and floodplain land cover in the Upper Columbia River valley. Overall, there is substantial variation in seasonal and annual land cover, reflecting the dynamic nature of floodplain wetlands, but the results show that the wetlands are drying out with increasing areas of woody/shrub habitat and loss of aquatic habitat. The results suggest that floodplain wetlands, particularly marsh and open-water habitats, are vulnerable to climatic and hydrological changes that could further reduce their areal extent in the future.

Six Decades of Changes in Pool Characteristics on a Concentric-Patterned Raised Bog

AbstractRaised bogs are wetland ecosystems which, under the right climatic conditions, feature patterns of pool hollows and hummock ridges. The relative cover and the spatial arrangement of pool and ridge microforms are thought to be influential on peatland atmosphere carbon gas fluxes and plant biodiversity. The mechanisms responsible for the formation and maintenance of pools, and the stability of these features in response to warming climates, remain topics of ongoing research. We employed historical aerial imagery, combined with a contemporary uncrewed aerial vehicle survey, to study 61 years of changes in pools at a patterned raised bog in central Sweden. We used a pool inheritance method to track individual pools between image acquisition dates throughout the time series. These data show a rapid loss of open-water pool area during the study period, primarily due to overgrowth of open-water pools by Sphagnum. We postulate that these changes are driven by ongoing climate warming that is accelerating Sphagnum colonisation. Open-water pool area declined by 26.8% during the study period, equivalent to a loss of 1001 m2 y−1 across the 150-hectare site. This is contradictory to an existing theory that states pools are highly stable, once formed, and can only convert to a terrestrial state through catastrophic drainage. The pool inheritance analysis shows that smaller pools are liable to become completely terrestrialised and expire. Our findings form part of a growing body of evidence for the loss of open-water habitats in peatlands across the boreal and elsewhere.

A continuous fish fossil record reveals key insights into adaptive radiation

Adaptive radiations have been instrumental in generating a considerable amount of life’s diversity. Ecological opportunity is thought to be a prerequisite for adaptive radiation1, but little is known about the relative importance of species’ ecological versatility versus effects of arrival order in determining which lineage radiates2. Palaeontological records that could help answer this are scarce. In Lake Victoria, a large adaptive radiation of cichlid fishes evolved in an exceptionally short and recent time interval3. We present a rich continuous fossil record extracted from a series of long sediment cores along an onshore–offshore gradient. We reconstruct the temporal sequence of events in the assembly of the fish community from thousands of tooth fossils. We reveal arrival order, relative abundance and habitat occupation of all major fish lineages in the system. We show that all major taxa arrived simultaneously as soon as the modern lake began to form. There is no evidence of the radiating haplochromine cichlid lineage arriving before others, nor of their numerical dominance upon colonization; therefore, there is no support for ecological priority effects. However, although many taxa colonized the lake early and several became abundant, only cichlids persisted in the new deep and open-water habitats once these emerged. Because these habitat gradients are also known to have played a major role in speciation, our findings are consistent with the hypothesis that ecological versatility was key to adaptive radiation, not priority by arrival order nor initial numerical dominance.

Infection with swim bladder nematode Anguillicola crassus in relation to European eel growth, age, and habitat along the German Baltic coast.

One possible reason for the European eel (Anguilla anguilla) population decline is the neozoan eel swim bladder nematode Anguillicola crassus. To investigate whether the prevalence of A. crassus and the associated swim bladder pathology is related to eel habitat, growth rate, and age, 728 yellow eels from 6 habitats differing in salinity and located along the German Baltic coast were examined between 2005 and 2009. The prevalence of A. crassus varied between habitats, ranging from 9 to 57%. Infection prevalence and the percentage of eels with a damaged swim bladder were significantly higher in inner coastal waters compared to more saline open coastal water. In infected eels, 1 to 32 adult and preadult individuals of A. crassus were observed. The mean infection intensity varied between habitats from 2 to 7 nematodes per eel but did not significantly differ between inner and open coastal waters. Infection prevalence and intensity decreased significantly with age when all open coastal waters and all habitats were combined. Both the lower prevalence of A. crassus and the swim bladder damage of older eels and of eels originating from open coastal water habitats suggest that these eels have a higher fitness for spawning migrations than eels from inner coastal waters. The present study underlines the importance of eel screening on a sufficiently small geographical scale for the accurate estimation of eel recruitment and the identification of priority areas that are likely to produce healthy silver eels.

Heterotrophic aquatic metabolism and sustained carbon dioxide emissions in a mineral-soil wetland restored with treated effluent

Wetlands are economically valuable ecosystems, in part because they purify wastewater by retaining and processing nutrients, organic matter (OM), and other pollutants. While natural wetlands are highly productive and sequester large pools of carbon (C), it is unclear whether the C cycle of restored treatment wetlands is functionally consistent with natural systems. This knowledge gap limits our appreciation for the role that wetland restoration can play as a natural solution to climate change. Here, we quantified metabolic and C cycling patterns of a restored, multi-basin wetland (Frank Lake, Alberta, Canada) receiving municipal and beef processing plant effluents rich in nutrients and OM. We conducted metabolic measurements in all three basins using dissolved oxygen sensors deployed under ice and in open water. Extreme production and respiration indicated that effluent was largely mineralized and replaced with wetland OM in transit. The heterotrophic status of all basins aligned with a published mass budget demonstrating the aquatic habitat of the wetland was an OM sink under current drought conditions that lengthen effluent processing time. Floating chamber measurements in open water zones confirmed that the wetland was a source of CO2 to the atmosphere. From input to outflow, sustained emissions led to declining pCO2 and a decline in the ratio of dissolved inorganic to organic C. Over 30 years post-restoration, the open water habitats in Frank Lake remain heterotrophic and a net source of CO2, suggesting that the trajectory of aquatic C cycling may be distinct from wetlands restored with non-effluent water sources.

Future Wetland Loss in Louisiana Threatens the Carbon Sequestration Potential of the Coastal Habitats

Photo 1. Scientists collecting aboveground biomass in a saline wetland (light green is smooth cordgrass, Spartina alterniflora and dark green are black mangroves, Avicennia germinans) located in coastal Louisiana. Aboveground net primary productivity, soil carbon accumulation rates, and greenhouse gas emissions can be used to estimate the net ecosystem carbon balance of coastal habitats like this saline wetland. Our estimates suggest that existing saline wetland habitats are a net sink of greenhouse gases. Photo credit: The Water Institute of the Gulf. Photo 2. Saline wetland habitat (dominated by black mangroves, Avicennia germinans) and saline open water habitat in coastal area of Louisiana. The 2017 Coastal Master Plan model output projects that at year 2050, the highest area of habitat will be the saline open water. Photo credit: The Water Institute of the Gulf. Photo 3. Fresh forested wetlands (dominated by cypress trees, Taxodium distichum) are commonly observed in the Atchafalaya Basin in the Louisiana coast area. Our net ecosystem carbon balance estimates suggest that existing fresh forested wetland habitats are a net sink of greenhouse gases. Photo credit: The Water Institute of the Gulf. These photographs illustrate the article “Climate Change Mitigation Potential of Louisiana's Coastal Area: Current Estimates and Future Projections” by Baustian, Melissa M, Bingqing Liu, Leland Moss, Alyssa Dausman, and James W. Pahl published in Ecological Applications. https://doi.org/10.1002/eap.2847

Spatial and Temporal Variations in Waterfowl Assemblage Structures in Mongolian Lakes and the Changes Linked to the Gradient of Lake Surface Areas

Lakes and wetlands provide top-priority hotspots that play a key role in maintaining and protecting threatened and migratory waterfowl. Identifying seasonal and spatial variations in aquatic bird communities and their responses to environmental factors is vital conservation efforts. However, there is a lack of information on waterfowl in Mongolian lakes and their associated wetlands. The purpose of this study was to investigate the spatial–seasonal changes in waterfowl assemblage structures in Mongolian lakes, as well as to determine how they respond to various environmental factors (lake surface area, elevation, and geographical distribution). Statistical analyses were performed using seasonal data (May, July, and September) for 28 waterfowl collected from 54 lakes across the country between 2016 and 2018. Seasonal heterogeneity in species richness and abundance was observed in lakes in each geographical region (Eastern, Central, and Western Mongolia). The composition of waterfowl in the lake was also relatively similar between May and September compared to July. This was due to the overlapping migration seasons in spring and autumn. Regionally, the number of waterfowl was much higher in the Eastern Mongolian lakes, followed by Central Mongolian lakes and then Western Mongolian lakes. This is likely due to differences in habitat availability and water levels between the regions. Eastern Mongolian lakes tend to have more wetlands and shallow water habitats, while Central and Western Mongolian lakes tend to have deeper open-water habitats. These differences in habitat types could contribute to the observed differences in waterfowl abundance among the regions. Additionally, some small lakes and the group of small lakes supported a greater abundance and diversity of waterfowl compared to some medium-sized and large lakes, suggesting that they are important for conservation. Indices of diversity (H’) and species dominance (D’) showed positive and negative correlations with lake surface area, respectively. Perhaps the increased surface area of the lake decreases the habitat overlap for designated waterfowl due to habitat heterogeneity. Accordingly, the indices (H’ and EH) increased as the waterfowl species composition became relatively equivalent in large lakes. Overall, spatial variations among the lakes were primarily attributable to the individual features of the lakes (shallowness, small lake groupings, and surface area), and seasonal variation in the lakes depended majorly on the compositional changes of the waterfowl due to migration.

Variability of Echolocation Clicks in Beluga Whales (Delphinapterus leucas) Within Shallow Waters

While echolocation is vital to the sensory ecology of odontocetes, we have few data characterizing the signals of most species, limiting our understanding of key attributes of these animals, especially for those with a diverse range of habitats. Beluga whales (Delphinapterus leucas) have successfully overcome the pressures of living in both shallow and deep open water habitats. We characterized the echolocation clicks of 13 wild beluga whales during temporary capture-and-release events in Bristol Bay, Alaska (USA). We extracted and examined 556 high-quality clicks from approximately 22 hours of recordings. As a group, the duration (41.1 ± 17.3 µs; mean ± SD), peak frequency (97.9 ± 34.4 kHz), centroid frequency (101.9 ± 23.9 kHz), -3 dB bandwidth (29.1 ± 14.4 kHz), -10 dB bandwidth (67.7 ± 31.8 kHz), and root mean square (RMS) bandwidth (27.8 ± 8.1 kHz) were assessed. These are the first on-axis data from wild belugas in their natural shallow water habitat within 1 m. Beluga whales emit clicks with high frequency and high source level in extremely shallow waters regardless of the potential strong reverberations and clutter. These results provide a foundation for future studies on how this species manipulates its sonar to successfully operate in acoustically challenging shallow waters.

Microdebris Abundance, Distribution, and Ingestion by Sargassum-Associated Juvenile Fishes in the Gulf of Mexico

Holopelagic Sargassum is a critical nursery habitat for the early life stages of many marine fishes, including several federally managed species in the United States and Caribbean. Sargassum is often aggregated along surface convergence features where microdebris (synthetic, semi—synthetic, and naturally—derived particles size) have also been found in relatively high concentrations. In this study, we collected microdebris from Sargassum and adjacent open water habitats (in 2018), and juvenile fishes from Sargassum (in 2017 and 2018) in the northern Gulf of Mexico to quantify habitat—specific microdebris concentrations and the degree to which Sargassum—associated juvenile fishes ingest microdebris. Microdebris concentrations within Sargassum habitats were, on average, 180 times greater than those found within adjacent open water habitats. Microdebris concentrations decreased with distance from shore in both Sargassum and open water habitats, and generally increased with Sargassum biomass. Microdebris ingestion by juvenile (9–320 mm SL) fishes (n = 846) varied by year (all taxa: 24.7% in 2017; 14.7% in 2018) and by taxa, and generally decreased with distance from shore. Small fibers were the dominant type of microdebris observed in stomach contents. The structural complexity of Sargassum provides a mechanism for microdebris capture and concentration in surface waters. Since 2011, massive blooms of Sargassum have inundated regions in the central Atlantic Ocean and Caribbean Sea. The role of Sargassum as a microdebris “sink” has major implications for the transport of microdebris as Sargassum drifts within and across basins and eventually strands on beaches and coastal habitats, or subsides to benthic environments.

Differential abundance, composition and mesohabitat use by aquatic macroinvertebrate taxa in ponds with and without fish

Fish are known to pose strong effects on invertebrate abundance, species richness and assemblage structure. Littoral vegetation may play a crucial role as a refuge for invertebrates vulnerable to fish predation. We studied relative densities and taxonomic composition of water mites, aquatic beetles and bugs in large lake-like ponds with different fish status (fish-free and containing fish) and mesohabitats (emergent littoral vegetation and open water zone). The macroinvertebrate taxa differed in their responses to the fish presence and in mesohabitat preferences. The density and species richness of water mites were greater in fish-containing ponds, while no differences were found between littoral and open-water habitats. In contrast, beetles were far more numerous and species-rich in fish-free ponds and in littoral vegetation. Total densities of aquatic bugs were non-significantly higher in fish-containing ponds, and they preferred littoral areas, but species richness was independent of fish presence and mesohabitat. No statistical interactions between fish presence and the densities of individual macroinvertebrate groups in the littoral habitat were detected, indicating that their use of emergent littoral vegetation was not an antipredator response to fish. The assemblages of the three macroinvertebrate taxa exhibited nested structures of a different order, consistent with their species richness patterns. Our research stresses the importance of littoral vegetation for the distribution and abundance of aquatic insects; however, high fish presence may not affect or may even benefit ecologically important macroinvertebrate groups, such as water mites or bugs.

Ontogenetic and spatial variability in parasite communities of white shrimp Penaeus setiferus (Decapoda: Penaeidae).

Understanding the combined effects of multi-parasite infections on their hosts is necessary for documenting parasite impacts and is particularly important for developing effective management strategies for economically important organisms. The white shrimp Penaeus setiferus supports important recreational and commercial fisheries along the southeastern and Gulf coasts of the United States and occupies an important ecological niche in estuarine and offshore habitats throughout these regions. The goal of this study was to identify and assess ontogenetic and spatial variation in white shrimp parasite communities and their relation to shrimp health. We used a series of trawl surveys in tidal creek and open water habitats of an estuary in the southeastern USA to collect and identify parasites of white shrimp using morphological and DNA sequencing techniques. Parasite communities in white shrimp were composed of organisms belonging to 6 classes: Conoidasida (gregarines), Oligohymenophorea (apostome and sessilid ciliates), Microsporea (meiodihaplophasids), Chromadorea (rhabditids), Cestoda (cyclophyllideans, lecanocephalideans and trypanorhynchs) and Trematoda (plagiorchiids). Parasite communities differed significantly among white shrimp life stages and localities. Furthermore, the health condition known as black gill occurred in some shrimp and was significantly related to parasite community structure. Infection metrics for the apostome ciliate Hyalophysa lynni, the trypanorhynch larvae Prochristianella sp. and the rhabditid larvae Hysterothylacium sp. were significantly different between shrimp exhibiting and not exhibiting black gill. These results highlight the importance of understanding parasite communities and the potential interactive effects of multiple parasite infections on shrimp health.

Assessing the core microbial symbionts of jellyfish in Indonesian and Vietnamese marine lakes

AbstractJellyfish are a well-known component of marine ecosystems. Here, we aimed to assess whether populations of the jellyfish species Mastigias cf. papua and Cassiopea ornata inhabiting different marine lakes and jellyfish species from open water habitat host ‘core’ symbionts and if there is evidence of species-specific host-microbial associations. Compositionally, jellyfishes hosted prokaryotic communities distinct from those found in water samples. All jellyfish samples across habitats and species exhibited a core OTU, assigned to the genus Endozoicomonas. This OTU was particularly abundant (>90% of all sequences) in C. ornata from one Papuan marine lake. Additionally, an OTU assigned to the Entomoplasmatales order was found in all but two jellyfish specimens, and was particularly abundant in marine lake specimens from Berau and Papua, Indonesia. Given the well-known relationship between Endozoicomonas and Symbiodinium spp., we tested for Symbiodinium presence in pooled specimens of M. papua from Berau. Our results showed that OTUs assigned to the genus Symbiodinium accounted for >99% of all sequences in jellyfish-associated microeukaryotic communities; these were closely related to organisms from Symbiodinium clade C. These results suggest the existence of a widespread and abundant jellyfish core symbiont, which may interact with symbiotic Symbiodinium populations to influence host fitness.

Climate Change Vulnerability Assessment for the Major Habitats and Species in Lung Ngoc Hoang Nature Reserve, Vietnamese Mekong Delta

The study assessed the vulnerability of habitats and species to climate change in Lung Ngoc Hoang Nature Reserve (NR), Vietnam. The vulnerability assessment tools for habitat and species were developed by the International Union for Conservation of Nature (IUCN). Community members, NR managers and experts in the fields of environment, economic and rural development were involved in this study. The results showed that saltwater intrusion and inundation could cause serious threats to habitats (i.e., open water, Lung, agricultural and Melaleuca habitats) and freshwater species. The combined impacts of drought and high temperature potentially increase forest fires for the Melaleuca habitat and decrease the quantity and quality of open water habitats. The Melaleuca and Lung habitats have a high baseline conservation status, in which Melaleuca habitats are more vulnerable than Lung habitats. Conversely, open water and agricultural habitats are at low baseline conservation status, but open water habitats are more vulnerable. In addition, the proliferation of invasive alien species, encroachment on agricultural cultivation, and the degradation of water quality are also great threats to the NR. Key species, including Melaleuca cajuputi, Elaeocarpus hygrophilus, Chitala ornate, Channa micropeltes, were at low threat of climate change. However, C. ornate and C. micropeltes are seriously endangered by seawater intrusion, drought and poor water quality. The findings of this study can provide essential information for NR managers to formulate water management plans for the protection and management of the habitats and species in Lung Ngoc Hoang NR.

Efficacy and Fate of Fluridone Applications for Control of Invasive Submersed Aquatic Vegetation in the Estuarine Environment of the Sacramento-San Joaquin Delta

Estuaries are ecologically and economically important ecosystems but are threatened by non-native invasive species, including many species of submersed aquatic vegetation (SAV). Herbicides are the primary tool used to control SAV, but most field evaluations of herbicides have been conducted in lentic systems. Therefore, managers working in estuaries must base their SAV control programs largely on findings from systems fundamentally different from their own. We conducted a study in the Sacramento-San Joaquin Delta to determine efficacy of the widely used herbicide fluridone in an estuarine ecosystem. The primary goal of SAV removal was restoration of open water habitat for endangered Hypomesus transpacificus (Delta Smelt). Over 18 months and multiple sets of multi-week fluridone applications, we monitored concentrations of fluridone and responses by SAV across pairs of treated and reference sites. Fluridone concentrations in the water were generally below the 2–5 parts per billion required for SAV control. Monitoring demonstrated that these low water concentrations were likely due to dissipation by tides, despite use of pelleted fluridone formulations marketed for flowing water environments. Fluridone did, however, accumulate in sediment at concentrations hundreds of times higher than those measured in the water. Nonetheless, we did not observe lasting reductions in SAV abundance or changes in SAV community composition. By demonstrating lack of efficacy of one of the few herbicides permitted for use in this estuary, this study highlights the need for development of SAV management tools tailored to the challenges of hydrologically complex environments like estuaries.

Artificial aquatic habitats impoverish amphibian diversity in agricultural landscapes of central Argentina

Abstract In central Argentina, agro‐ecosystems constitute the dominant landscape, representing the replacement of extensive grassland areas by crops and pastures. Agriculture has caused the loss of extensive areas of Pampean inland wetlands through drainage and the construction of artificial aquatic habitats such as ditches and ponds. This study evaluated the availability and amphibian breeding use of 194 natural and artificial open water habitats and identified those attributes that affect amphibian diversity (richness, abundance and species occurrence). Interviews with farmers revealed that all artificial ditches, drainage channels and ponds were constructed directly or indirectly to support agricultural activities, and 61.5% of them were created at the expense of natural wetlands. The results from generalized linear mixed models) indicated a significant decrease (P < 0.05) in amphibian richness (14.2–35.7%) and abundance (35.3–86.6%) in artificial habitats compared with natural habitats. Overall, vegetation cover, average depth and edge slope emerged as the most important attributes affecting amphibian diversity in artificial open water habitats. Vegetation cover had a significant (P < 0.05) positive influence on species richness and abundance, whereas average depth and edge slope had the opposite effect. Given the substantial modification of inland wetlands in central Argentina, natural aquatic habitats should be considered top priorities for conservation, and law enforcement is urgently needed to control the drainage and levelling of lagoons, ponds and low‐lying areas. The appropriate design and planning of constructed wetlands, including shallow depth and slightly sloping edges, could greatly improve the ability of artificial wetlands to favour native amphibians in these altered landscapes. Artificial wetlands could offer complementary habitats to natural habitats for amphibians and aquatic wildlife if actions leading to sustainable management and territorial planning are applied.

Summer sea-ice variability on the Antarctic margin during the last glacial period reconstructed from snow petrel (<i>Pagodroma nivea</i>) stomach-oil deposits

Abstract. Antarctic sea ice is a critical component of the climate system affecting a range of physical and biogeochemical feedbacks and supporting unique ecosystems. During the last glacial stage, Antarctic sea ice was more extensive than today, but uncertainties in geological (marine sediments), glaciological (ice core), and climate model reconstructions of past sea-ice extent continue to limit our understanding of its role in the Earth system. Here, we present a novel archive of past sea-ice environments from regurgitated stomach oils of snow petrels (Pagodroma nivea) preserved at nesting sites in Dronning Maud Land, Antarctica. We show that by combining information from fatty acid distributions and their stable carbon isotope ratios with measurements of bulk carbon and nitrogen stable isotopes and trace metal data, it is possible to reconstruct changing snow petrel diet within Marine Isotope Stage 2 (ca. 24.3–30.3 cal kyr BP). We show that, as today, a mixed diet of krill and fish characterizes much of the record. However, between 27.4 and 28.7 cal kyr BP signals of krill almost disappear. By linking dietary signals in the stomach-oil deposits to modern feeding habits and foraging ranges, we infer the use by snow petrels of open-water habitats (“polynyas”) in the sea ice during our interval of study. The periods when consumption of krill was reduced are interpreted to correspond to the opening of polynyas over the continental shelf, which became the preferred foraging habitat. Our results show that extensive, thick, and multiyear sea ice was not always present close to the continent during the last glacial stage and highlight the potential of stomach-oil deposits as a palaeoenvironmental archive of Southern Ocean conditions.

Spatial Heterogeneity in Prey Availability, Feeding Success, and Dietary Selectivity for the Threatened Longfin Smelt

Food availability is a key determinant of the nursery value of a given habitat for larval and juvenile fishes. Growth, survival, and recruitment success are often inter-correlated and influenced by prey availability and associated feeding success. This is likely true for the threatened population of Longfin Smelt (Spirinchus thaleichthys) in the San Francisco Estuary (SFE) which has collapsed in recent decades along with its preferred prey. In years with high precipitation and freshwater outflow, larval Longfin Smelt are found in shallow wetland habitats throughout the SFE, but variation in the availability of food and feeding success in these habitats remains unexplored. To examine spatial variation in the trophic value of different rearing habitats, we quantified variation in prey availability, feeding success, and prey selection for larval and juvenile Longfin Smelt captured in restored tidal marshes, sloughs, and open-water habitats in the northern and southern SFE. Prey abundance varied spatially, with densities approximately tenfold greater in southern sloughs and restored tidal ponds relative to northern and open-water habitats. Feeding success of larval Longfin Smelt was positively correlated with both fish length and prey density. Larval Longfin Smelt fed selectively on the copepod Eurytemora affinis, with larger individuals (> 25 mm total length) exhibiting an ontogenetic diet shift to larger mysid shrimps. Our results suggest that wetland habitats across the SFE vary greatly in their trophic value, with previously unexplored habitats exhibiting the highest densities of prey and the highest foraging success for larval Longfin Smelt.

Hydroclimate Variability Affects Habitat‐Specific (Open Water and Littoral) Lake Metabolism

AbstractLakes integrate the signals of changing hydroclimate in their surrounding basin, which substantially influence gross primary production (GPP), respiration (R), and net ecosystem production (NEP). Most research focuses only on the changes to the open water habitat despite the littoral habitat's importance to lakes and its sensitivity to hydroclimatic variability. We analyze how years with different ice‐out dates and snow water equivalent (SWE) triggered different metabolism responses in the open water and littoral habitats of a subalpine lake. The dry (early ice‐out date and low SWE) and wet (late ice‐out date and high SWE) years had lower GPP and R rates in both habitats compared to the average hydroclimatic year. Furthermore, consumer biomass decreased during dry and wet years. GPP and R reduced the most in the littoral habitat. Consequently, the relative contribution to total lake GPP and R of the littoral habitat decreased, and the contribution of the open water habitat increased during the dry and wet years. We demonstrate that hydroclimatic conditions affect productivity and consumer biomass and show that within‐lake habitats do not experience equivalent responses to climate forcing. Our study has implications for how ecosystem scientists and managers quantify the absolute and relative contributions of the littoral habitat to whole lake production in the context of climate variation.