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As a part of the project "Melting at Thwaites grounding zone and its control on sea level" (MELT), we developed a compact 750-MHz ice-penetrating radar for phase-sensitive measurements to infer basal melt and ice layer displacement using multiple passes. The radar operates with 300-MHz bandwidth and a peak output power of 400 W. It is equipped with a small antenna array designed to fit within the limited space underneath the floor of a Twin Otter aircraft (without out-of-mold-line protuberances). The radar was installed and deployed onboard a Twin Otter airplane from the British Antarctic Survey (BAS) as a part of the ongoing International Thwaites Glacier Collaboration (ITGC). We conducted multiple radar survey flights during two consecutive austral summer seasons, collecting ~5 TB of raw data. In this paper, we present an overview of the radar system and antenna implementations. We provide a summary of our field operations and present sample data products to illustrate the instrument capabilities to sound ice as thick as ~1,400 m and map internal reflecting horizons near the grounding line of TG with sub-m vertical resolution. We also discuss the utility of our repeat pass data for inferring ice shelf basal melt rates.

Restoration projects often rely on the assumption that a local intervention will restore diminished populations, without fully understanding the constraints that limit the target species in the first place. In rivers, one common restoration technique is to place large structures, such as wood and boulders, on the bed, with the assumption that fish will subsequently arrive and use them. Nonetheless, providing large habitat structure may not overcome demographic or resource constraints on fish populations, and thus may not aid recovery. We aimed to test if resource constraints (food and cover) are limiting local densities of fishes in a degraded stream by experimentally alleviating these constraints. If the abundance of one or more species is constrained by resource availability, then local numbers of these species should increase following an increase in resources. To test our prediction, we increased the availability of food and microhabitat complexity (cover) at sites in Hughes Creek, a degraded stream in south‐east Australia that has extensive accumulations of sand and limited in‐stream structure. At treatment sites, we hammered pairs of wooden stakes (25 cm apart) into the stream bed so that the ends of stakes protruded just above the water surface at moderate flows. Stakes effectively trapped passing sticks and leaves, which increased local detrital densities and, subsequently, invertebrate densities, hence providing food and cover for fish. Over the course of a year, we compared the changes in fish abundances at treatment sites to unmanipulated control sites. Fish responded quickly to enhanced retention of detritus, with assemblage differences observed between treatment and control sites. We caught more river blackfish (Gadopsis marmoratus), southern pygmy perch (Nannoperca australis), Macquarie perch (Macquaria australasica), and mountain galaxias (Galaxias olidus) at treatment sites on some occasions, indicating that these species may be subject to r

The Western Antarctic Peninsula (WAP) is a rapidly changing region with receding sea-ice cover. This region generally has increased phytoplankton productivity on the continental slope with a decrease observed in off-shelf waters located further northward. This study aims to improve the understanding of the distribution of iron (Fe) in this climatically important oceanic region during early sea-ice retreat, as well as the impact of receding ice cover on Fe concentrations and the importance of Fe and its sources at the beginning of the phytoplankton growth season. Five ocean transects were sampled along the Palmer Long Term Ecological Research (Pal-LTER) grid with an additional oceanward extension to access off-shelf waters during the austral spring (October and November) of 2014. High Fe inputs into the entire water column from ice melt as well as from sediments increased dissolved Fe (DFe) and total dissolvable Fe (TDFe) concentrations across the shelf (off-shelf DFe: 0.38 ± 0.30 nmol/L and TDFe: 2.23 ± 2.95 nmol/L versus shelf DFe: 1.54 ± 1.38 nmol/L and TDFe: 19.47 ± 23.82 nmol/L). The combination of meteoric meltwater and shallow sedimentary sources is strongest over the shelf and increased landward towards the WAP. Additionally, a winter sea-ice formation signature was detected in inner shelf waters that appeared to contribute to DFe concentrations. Relatively warm Circumpolar Deep Water (CDW) that flows onto the shelf through troughs is likely modified by non-reductive sedimentary input of Fe into the water column. The increase in Fe concentrations in WAP waters in early spring could trigger enhanced phytoplankton productivity across the shelf, although the highest productivity levels were observed in off-shelf waters, likely related to improved light conditions following receding sea-ice cover. The relatively high productivity levels in WAP off-shelf waters are presumably caused by two factors: (1) supply from below, and (2) the transport of Fe from the shelf

Movement is a key driver of the distribution of animals and the structure of populations, communities, and ecosystems. Habitat loss and fragmentation can compromise movement and contribute to population declines. However, there is often insufficient knowledge about when, why, and where animals move, particularly in highly modified environments. We present results from an 8‐year study on the movement behavior of Murray cod Maccullochella peelii, an Australian freshwater fish species that has undergone major declines due in part to river flow regulations. We studied movement within and between different habitat types in a highly modified floodplain ecosystem in the lower Murray River to (1) identify the key environmental conditions associated with movement, (2) examine how a new regulating structure can be managed to influence movement behavior, and (3) explore movement mediated recovery following a hypoxic event. Movement within and between an anabranch and main river channel habitats increased during the core spawning period and during elevated discharge. The likelihood of Murray cod moving to an anabranch system from the Murray River declined substantially following construction of a new flow regulating structure (a weir and vertical slot fishway). Managed flows delivered through the anabranch after regulator construction in accordance with targeted recommendations (time‐of‐year and magnitude of discharge) increased the movement of adult fish within and between habitats. Finally, a hypoxic event caused not only high mortality but also resulted in a high proportion of fish migrating outside of the study reach, before returning to the system over several years. These results demonstrate how flow management can help a keystone species access habitats required to complete critical life history requirements including recovery from disturbance events. Importantly, the work provides an example of how timely and robust applied research has informed a major interve

As efforts to restore coastal habitats accelerate, it is critical that investments are targeted to most effectively mitigate and reverse habitat loss and its impacts on biodiversity. One likely but largely overlooked impediment to effective restoration of habitat-forming organisms is failing to explicitly consider non-habitat-forming animals in restoration planning, implementation, and monitoring. These animals can greatly enhance or degrade ecosystem function, persistence, and resilience. Bivalves, for instance, can reduce sulfide stress in seagrass habitats and increase drought tolerance of saltmarsh vegetation, whereas megaherbivores can detrimentally overgraze seagrass or improve seagrass seed germination, depending on the context. Therefore, understanding when, why, and how to directly manipulate or support animals can enhance coastal restoration outcomes. In support of this expanded restoration approach, we provide a conceptual framework, incorporating lessons from structured decision-making, and describe potential actions that could lead to better restoration outcomes using case studies to illustrate practical approaches.

Humans are altering marine ecosystems at unprecedented rates, and these changes can result in animals selecting poor‐quality habitats if the cues they use become misleading. Such “ecological traps” increase extinction risk, reduce ecosystem resilience, and are a consequence of human‐induced rapid environmental change. Although there is growing evidence for traps impacting terrestrial species, the phenomenon has so far received little attention from marine scientists. To explore why so few studies have attempted to identify traps in the ocean, we conducted a literature review of the major drivers of marine environmental change to determine how their impacts on habitat choice and species fitness are being assessed. From this we summarize the current evidence for marine traps, present case studies to show why the phenomenon is potentially common in the ocean, highlight ways to advance awareness and understanding of traps, and demonstrate how this information can help improve management of marine environments.

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22-30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.

Understanding how and why the size of populations varies is critical knowledge for conservation and management. While considerable work has explored how different demographic parameters affect population growth, less is known the drivers of variability in these parameters. Long-term time series tracking population size that are coupled with empirical data to examine the relative importance of different drivers are rare, especially in freshwater systems. Even rarer are studies that collect this information concurrently from multiple species with contrasting life history strategies in the same system to assess whether population size and the relative importance of drivers also vary. We studied changes in the abundance and size structure of four native freshwater fish species in the Murray River, southeastern Australia, over a continuous 19-yr period. Two species with traits typical of "equilibrium" species (Murray cod Maccullochella peelii and trout cod Maccullochella macquariensis) and two with traits of "periodic" species (golden perch Macquaria ambigua and silver perch Bidyanus bidyanus) were sampled annually and capture-mark-recapture modeling was used to ask (1) how did population size change during this period, (2) how were changes in population size related to variability in hydrology, and (3) how were changes in population size driven by different processes (local recruitment or migration events)? Populations of all four species varied throughout the study, and our results are consistent with the notion that local recruitment is an important driver of this variability for Murray cod and trout cod, whereas immigration is more important for the two other species. Increases in spring river discharge strongly influenced these responses for trout cod and golden perch. Our study provides fundamental insights into the population dynamics of these valued species, and how management strategies might differ based on their life histories. Management should focus on allow

Over half of global rivers and streams lack perennial flow, and understanding the distribution and drivers of their flow regimes is critical for understanding their hydrologic, biogeochemical, and ecological functions. We analyzed nonperennial flow regimes using 540 U.S. Geological Survey watersheds across the contiguous United States from 1979 to 2018. Multivariate analyses revealed regional differences in no‐flow fraction, date of first no flow, and duration of the dry‐down period, with further divergence between natural and human‐altered watersheds. Aridity was a primary driver of no‐flow metrics at the continental scale, while unique combinations of climatic, physiographic and anthropogenic drivers emerged at regional scales. Dry‐down duration showed stronger associations with nonclimate drivers compared to no‐flow fraction and timing. Although the sparse distribution of nonperennial gages limits our understanding of such streams, the watersheds examined here suggest the important role of aridity and land cover change in modulating future stream drying.