Major Environmental Disturbances Research Articles

Loss and replacement of macroalgal standing stock and productivity after a major environmental disturbance

AbstractHabitat‐forming macroalgae are widely recognized as one of the most productive ecosystems on earth. However, relatively little is known about the variation in productivity over large spatiotemporal scales and the relative importance of environmental and biotic factors in influencing the quantity of carbon fixed. Here we leverage a large tectonic event to understand how fluctuations in the biomass of habitat‐forming macroalgae and changes in light availability influence primary productivity along 130 km of coastline over 5 years. We also quantify the effects of changes to species composition on primary productivity. This study revealed significant implications of a compromised light environment for the biomass of macroalgae and productivity rates. Immediately post‐earthquake, there was a substantial loss of biomass (an average of −83%) of a previously dominant large brown alga, Durvillaea spp., and very limited recovery of biomass over the next 5 years. Reductions in biomass coupled with changes in light attenuation resulted in average net primary production (NPP) from Durvillaea decreasing from 1130 g C m−2 year−1 before the earthquake to 192 g C m−2 year−1 after 5 years. Partial compensation of reduced NPP was facilitated by increases in the biomass of a smaller fucoid Carpophyllum maschalocarpum, but its productivity was considerably less on average, resulting in a reduction in carbon fixation. Overall, reductions in biomass resulted in a 2‐fold to 10‐fold drop in carbon fixation by canopy‐forming macroalgae over at least 5 years, while a degradation of the light environment further compromised primary productivity, and most likely detrital subsidies of organic matter to the nearshore ecosystem.

Emergent governance responses to shocks to critical provisioning systems

The structure and functioning of formal and informal governance arrangements and associated infrastructure prior to major environmental disturbance play a central role in how cities experience and respond to such events. This paper considers how city managers, businesses, and residents responded to two disturbances experienced in the City of Cape Town—a drought-induced water crisis and a pandemic crisis (COVID-19) that followed a year later—and the consequences of these actions for infrastructural assets and governance innovations. Our analysis suggests that efforts aimed at transformative change in these provisioning systems require attention to the existing and potential roles and responsibilities of private and public sector actors, as well as the associated distribution of risks and rewards. Furthermore, polycentric and decentralized governance arrangements, which are often thought to be most flexible in the face of shocks, are not always feasible or desirable to actors with a stake in resource governance.

Disentangling the impact of anthropogenic and natural processes on the environment in a subtropical subalpine lake catchment in northeastern Taiwan over the past 150 years

Human activities impose significant changes on sedimentation processes and vegetation cover within lake catchments. However, the needed time for an anthropogenically disturbed natural state to be reversed back to its natural state by environmental protection programs is still ambiguous. Here we employ a multi-proxy approach to delineate major environmental disturbances such as logging and forest fires on the catchment in Cueifong Lake, a subtropical subalpine lake in northeastern Taiwan. X-ray Fluorescence (XRF) core scanning, bulk total organic carbon (TOC), bulk total nitrogen (TN), stable carbon isotope (δ13Corg) analysis, and macro-charcoal counting were utilized to reconstruct changes in the catchment environment based on a sediment core from Cueifong Lake. The results show that the element content changed distinctly around 1975 CE, which coincided with the onset of profound deforestation in the lake vicinity recorded in historical documents and aerial photos. After the cessation of the logging event, the detrital input increased, accompanied by decreasing C/N ratios and increasing δ13Corg values. This suggests that increased terrestrial nutrient input promoted algae growth. After the deforestation phase, our results imply a gradual recovery of elemental composition in the catchment environment. By extrapolating the XRF element records, we suggest that it might take >50 years for the sedimentary regime to reach its pre-logging baseline. In contrast to the depositional system, the C/N and δ13Corg shifted significantly - potentially irreversibly - towards an algae-dominant environment instead of recovering to the pre-logging condition. This could be due to both 1) the changes in the different vegetation species used for reforestation and/or 2) anthropogenically introduced fishes in the 1980s. This study proposes the first assessment of the needed recovery time for subtropical Asian subalpine forests after large-scale logging activity and thus provides an apparent reference for policy decisions on natural resource development and environmental protection.

IS ABERRANCY A RELIABLE INDICATOR FOR MAJOR PALEOCLIMATIC DISTURBANCE?

ABSTRACT Aberrant forms of many different spore and pollen taxa (sporomorphs) are often used to assess timings and extent of environmental stress at major extinction/climate events. However, little is known about the normal level of malformations in these taxa. Malformation can manifest in several different ways, including significant size differences (± from the accepted range for the species), retention of pollen/spores within tetrads, and unusual and inconsistent morphological aberrations. This study analyses one commonly used pollen genus, Classopollis, and its aberrant forms, from the Bajocian of Argentina. Tetrads, including those incorporating malformed/aborted pollen grains, are found to be common, showing that tetrads of Classopollis are not a reliable signal of major environmental disturbance. The results and discussion presented here emphasize why palynological data must be interpreted in context of the depositional dynamics, facies changes and how they affect the assemblages in conjunction with understanding variations in the strategies of individual flora.

Glacial kettles as archives of early human settlement along the Northern Rocky Mountain Front

AbstractThe Northern Rocky Mountain Front (hereafter Northern Front) is a prominent geographic feature in archaeological models of human dispersal in the terminal Pleistocene and Early Holocene of North America. Testing those models has been arduous because of local geomorphological factors that tend to obliterate or otherwise limit access to archaeological finds of relevant age. In this paper, we present well-stratified archaeological and environmental records dating back to 14,000–13,000 cal yr BP from the site of Billy Big Spring (Blackfeet Indian Reservation, Montana), located on a glacial kettle, a type of landform that has been largely ignored by regional archaeological research to date. Findings from Billy Big Spring show the continuous use of the Northern Front foothills throughout the major climatic and environmental disturbances of the Early Holocene, and possibly the terminal Pleistocene as well. As such, Billy Big Spring contributes to refining several archaeological models of early settlement of the Northern Front, particularly those that posit differential use of foothills versus plains settings during the midst of the Holocene Thermal Maximum. The record at Billy Big Spring also suggests that kettles, regardless of physiographic setting, provide a yet unsuspected and unsampled potential for preserving high-quality and easily accessible early archaeological and paleoenvironmental records.

Multitemporal Analysis of Land Use Changes and Their Effect on the Landscape of the Jerte Valley (Spain) by Remote Sensing

In recent years, the interest of institutions in land use has increased, creating the need to determine the changes in use through spatial-temporal and statistical analysis. This study analyzes the changes over the last 40 years, based on a cartography of landscape units obtained from the study of geo-environmental parameters in the Jerte Valley (Spain) with satellite images, Landsat 5 and 7. Subsequently, through the analysis of spatial patterns and diversity and fragmentation indices, and with the Fragstat software, the landscape was characterized from 1994 to the present. The results show that wooded areas decreased slightly, crops increased in altitude and major environmental disturbances (mainly forest fires) negatively affected the environmental mosaic. Land uses affect the landscape by developing larger tesserae (+5 ha), which are less fragmented (−0.15), but more isolated (0.12). This study demonstrates that landscape metrics can be used to understand changes in spatial pattern, help in decision making to implement appropriate management measures in the conservation of traditional land uses, and allow the maintenance of connecting areas between fragments to avoid the loss of natural corridors to increase landscape quality.

Environment, Biodiversity and Soil Security: A New Dimension in the Era of COVID-19

Undoubtedly, COVID-19 pandemic is one of the most devastating pandemics in the recent era and major problem for sustainability of life. This virus has severely impacted both environmental and human health. Moreover, it has become the top priority among other challenging global issues including pollution, climate change, urbanization, and unsustainable consumption, which have led to major environmental disturbances and biodiversity loss. The COVID-19 may have long-lasting impacts on the environment health, biodiversity, and soil security, consequently, will raising several scientific questions to be investigated in near future including the expected environmental impacts of COVID-19 on soil, water and air, connecting the missing links between environmental pollutions and COVID-19. Most importantly, unraveling the role of soil in spreading or reducing transmission of the COVID-19 pandemic, and soil xenobiotics status under the COVID-19 outbreak. Understanding the projected management scenario of soil and freshwater pollution in the post-COVID-19 era and the potential impact of COVID-19 on food and soil security would be of immense aid in the preparation of future pandemics. This opinion article aims to analyze and foresee some of the major issues for meeting the United Nation’s Sustainable Development Goals.

Ocean warming affected faunal dynamics of benthic invertebrate assemblages across the Toarcian Oceanic Anoxic Event in the Iberian Basin (Spain).

The Toarcian Oceanic Anoxic Event (TOAE; Early Jurassic, ca. 182 Ma ago) represents one of the major environmental disturbances of the Mesozoic and is associated with global warming, widespread anoxia, and a severe perturbation of the global carbon cycle. Warming-related dysoxia-anoxia has long been considered the main cause of elevated marine extinction rates, although extinctions have been recorded also in environments without evidence for deoxygenation. We addressed the role of warming and disturbance of the carbon cycle in an oxygenated habitat in the Iberian Basin, Spain, by correlating high resolution quantitative faunal occurrences of early Toarcian benthic marine invertebrates with geochemical proxy data (δ18O and δ13C). We find that temperature, as derived from the δ18O record of shells, is significantly correlated with taxonomic and functional diversity and ecological composition, whereas we find no evidence to link carbon cycle variations to the faunal patterns. The local faunal assemblages before and after the TOAE are taxonomically and ecologically distinct. Most ecological change occurred at the onset of the TOAE, synchronous with an increase in water temperatures, and involved declines in multiple diversity metrics, abundance, and biomass. The TOAE interval experienced a complete turnover of brachiopods and a predominance of opportunistic species, which underscores the generality of this pattern recorded elsewhere in the western Tethys Ocean. Ecological instability during the TOAE is indicated by distinct fluctuations in diversity and in the relative abundance of individual modes of life. Local recovery to ecologically stable and diverse post-TOAE faunal assemblages occurred rapidly at the end of the TOAE, synchronous with decreasing water temperatures. Because oxygen-depleted conditions prevailed in many other regions during the TOAE, this study demonstrates that multiple mechanisms can be operating simultaneously with different relative contributions in different parts of the ocean.

Risk perception, media exposure, and visitor’s behavior responses to Florida Red Tide

ABSTRACT Florida’s Red Tide outbreak, a major environmental disturbance in 2018, not only garnered nationwide attention but also affected both in-state and out-of-state visitors. Guided by the Social Amplification of Risk Framework (SARF), this study examined the relationships between media exposure, risk perception, and visitors’ behavioral responses. Data were gathered from two surveys in late 2018. The findings validate the practicality of applying SARF to the current context. This study also found that both perceived consequences and access to the community are significant predictors of visitor behavior. This study further discussed how to market destinations during turbulent times.

Biodiversity‐mediated effects on ecosystem functioning depend on the type and intensity of environmental disturbances

Environmental disturbances affect ecosystem functioning through changes in organisms’ metabolism (direct effect) and biodiversity loss (indirect or biodiversity‐mediated effect). It is still a challenge to separate direct and biodiversity‐mediated effects of environmental changes on ecosystem functioning due to the difficulties in isolating ‘true’ biodiversity loss effects. Furthermore, it is still unclear whether biodiversity‐mediated effects are as important as direct effects. In this study, we performed an experiment in artificial microcosms to disentangle biodiversity‐mediated and direct effects of two major environmental disturbances on the functioning of aquatic ecosystems: increases in temperature and salinity. The ecosystem function analyzed was the microalgae predation by the zooplankton community (zooplankton grazing rates). Temperature and salinity increases affected the zooplankton grazing rates due to changes in community composition and abundance, as well as organism performance. The impact of salinity changes on community structure was higher than that of temperature; however, the importance of biodiversity‐mediated and direct effects was similar to regulating the ecosystem functioning, albeit they have presented different directions and magnitude across the treatments. At a moderate level of temperature increase, we observed that the biodiversity‐mediated effect was more relevant than the direct effect, with negative effects on the overall grazing rates. Our results suggest that disturbances can affect the functioning of aquatic environments through a set of complex biological mechanisms that balance direct and biodiversity‐mediated effects. We concluded that the relative importance of biodiversity‐mediated effects depends on the type and intensity of the disturbance.

Environmental conditions of deposition of the Lower Cretaceous lacustrine carbonates of the Barra Velha Formation, Santos Basin (Brazil), based on stable carbon and oxygen isotopes: A continental record of pCO2 during the onset of the Oceanic Anoxic Event 1a (OAE 1a) interval?

This study presents new stable carbon and oxygen isotope data from Lower Cretaceous lacustrine carbonate rock samples recovered from a well drilled in the Santos Basin, offshore southeast Brazil. These samples represent a record of a continental environment just prior to the opening of the South Atlantic Ocean and the ultimate break-up of Gondwanaland. The geochemical data, along with carbonate mineralogy, indicate repeated cycles of lake level variation that could be attributed to climatic oscillations. Despite the absence of correlations between δ13C and δ18O values, facies analysis and the isotopic and mineralogical data suggest that lake hydrology was essentially closed for most of the depositional interval studied here. The existence of persisting trends of nearly constant δ13C values with a spread in δ18O values though, suggests long water residence times in the palaeolake, equilibrium between atmosphere and lake water CO2, as well as significant evaporation of water. The overall geological model that emerges unveils a more comprehensive picture of the depositional conditions that favoured the continuity of a significant carbonate factory in the middle of the Gondwanan continent, corroborating previous studies that suggested the lasting existence of a large and somewhat shallow endorheic lake in the area during the Early Cretaceous. As a result of this recorded trend strongly suggesting equilibrium between lake waters DIC (dissolved inorganic carbon) reservoir and atmospheric CO2, the data are most consistent with lacustrine deposition rather than precipitation of travertine, contrasting with some suggestions for the genesis of the carbonates of the Barra Velha Formation. Finally, this apparent equilibrium with the atmosphere likely left a preserved record in the continental carbonates of the final stages that preceded a major global environmental disturbance associated with an increase in atmospheric CO2, known for this time as the Oceanic Anoxic Event (OAE) 1a. If this is correct, it also helps to put further time constraints on this studied interval, which should not be younger than Barremian age, and to provide a regional continental perspective on a global event.

Robust stabilization of spacecraft attitude motion under magnetic control through time‐varying integral sliding mode

SummaryMagnetic spacecraft attitude control is suitable for missions with moderate pointing and stabilization requirements. It would be especially preferable if an implemented three‐axis magnetic control law guarantees global and moreover robust stabilization. Motivated by this consideration, in this work, the integral sliding mode control method is successfully applied to the purely magnetic attitude control problem for the first time in literature. The resulting magnetic integral sliding mode control system, which is designed via Lyapunov's direct method by taking the four major environmental disturbance torques and the full inertia matrix uncertainty into account, has the expected insensitivity against environmental disturbances in the plane of continuous actuation. Along the instantaneous direction of underactuation, which continuously varies in control space as the satellite moves along the orbit, there is no counteraction to perturbations. However, as seen in the results of the high‐fidelity simulation, state trajectories are ultimately bounded in the vicinity of the reference state independently from the initial state thanks to the proven robustness of the global stability. Performance robustness of the obtained control system against disturbances and model uncertainty is evaluated to be superior through a couple of comparisons with existing control laws even though it is partial due to the intrinsic underactuation in the system.

A 7000-year environmental history and soil erosion record inferred from the deep sediments of Lake Pavin (Massif Central, France)

A 14-m long sedimentary sequence (core PAV12) was collected in the deepest part of Lake Pavin, a maar lake located in the French Massif Central. The PAV12 sedimentary sequence documents the lake's environmental evolution since its formation 7000 years ago. The relationships between the catchment's vegetation cover, erosion processes and changes in trophic status were shown using a multi-proxy characterization of mineral and organic fractions supported by palynological data. The record shows a succession of lithological units starting at the base with volcanoclastic material corresponding to the early stage of Lake Pavin. The deposition of organic-rich and diatomaceous sedimentary units above volcanoclastic material indicates an evolution toward a pristine lacustrine state. The Late Holocene environmental history of this lake is marked by two tipping points reflecting major environmental disturbances at ca. 4000 cal BP and after the deposition of erosive mass-wasting deposits (MWDs) at 1350 cal BP (AD 600) and 650 cal BP (AD 1300). The upper unit of core PAV12, which corresponds to the past 700 years, indicates that one of these MWDs was likely the driving force behind a major limnological change marked by a shift in redox-sensitive elements (i.e., current meromictic lacustrine state). The palynological diagram indicates a forested catchment where woodland clearances and agro-pastoral activities have remained limited except over the last 700 years. These findings suggest restricted human impact within the watershed compared to other regional archives. The reconstruction of the Lake Pavin erosion record determined from titanium and red amorphous particle fluxes highlights phases of enhanced erosion at ca. 6.5–5.5, 4.1–3.8, 3.5, 2.8–2.6, 1.6–1.4 cal kyr BP and during the Little Ice Age (LIA). A comparison between this erosion record, palaeoenvironmental archives from Western Europe and palaeoclimatic data supports an Atlantic signal driving precipitation patterns over Lake Pavin at centennial to millennial timescales. The influence of local human activities, even on a small scale, cannot be completely discounted as their impact on erosional processes may be amplified in a steep catchment such as that found in Lake Pavin.

New Sliding Mode Attitude Controller Design Based on Lumped Disturbance Bound Equation

AbstractIn this paper, first the mathematical models of four major environmental disturbance torque components and corresponding bound equations are presented. Then the effect of the inertia matrix...

The Competitive Structure and Strategic Positioning of the Bank Industry in the Face of Major Environmental Disturbances: A Study of Brazilian Banks

ABSTRACT This work looks into the dynamics of the competitive structure and strategic positioning of Brazilian banks. Over the eighteen years covered by the study, we saw periods of strategic instability in this industry and differing structures of strategic groups, with regard to not only their number, but also their composition. Our study therefore provides empirical evidence that we will hardly find periods of full strategic stability. These findings denote that, at some moment, there is a change in the strategic positioning of these firms and provides insight with regard to the competitive patterns of an industry over the period.

Evaluation on subcellular partitioning and biodynamics of pulse copper toxicity in tilapia reveals impacts of a major environmental disturbance.

Fluctuation exposure of trace metal copper (Cu) is ubiquitous in aquatic environments. The purpose of this study was to investigate the impacts of chronically pulsed exposure on biodynamics and subcellular partitioning of Cu in freshwater tilapia (Oreochromis mossambicus). Long-term 28-day pulsed Cu exposure experiments were performed to explore subcellular partitioning and toxicokinetics/toxicodynamics of Cu in tilapia. Subcellular partitioning linking with a metal influx scheme was used to estimate detoxification and elimination rates. A biotic ligand model-based damage assessment model was used to take into account environmental effects and biological mechanisms of Cu toxicity. We demonstrated that the probability causing 50% of susceptibility risk in response to pulse Cu exposure in generic Taiwan aquaculture ponds was ~33% of Cu in adverse physiologically associated, metabolically active pool, implicating no significant susceptibility risk for tilapia. We suggest that our integrated ecotoxicological models linking chronic exposure measurements with subcellular partitioning can facilitate a risk assessment framework that provides a predictive tool for preventive susceptibility reduction strategies for freshwater fish exposed to pulse metal stressors.

Off‐reef planktivorous reef fishes respond positively to decadal‐scale no‐take marine reserve protection and negatively to benthic habitat change

AbstractThe effects of no‐take marine reserve (NTMR) protection and changes in benthic habitat on fusiliers (family Caesionidae) were investigated at four small Philippine offshore islands on time scales of 10–31 years. Fusiliers are highly mobile, schooling, medium‐sized planktivorous fish that generally feed “off‐reef.” For these reasons, and given the small size of the NTMRs (3.6–37.5 ha) in this study, it was predicted that fusilier density would be unlikely to show clear effects of NTMR protection, or to respond to changes in benthic habitat. In contrast to predictions, clear NTMR effects were observed on fusilier density at three of the four NTMRs, with durations of protection from 14 to 31 years. Furthermore, the study provided strong evidence that benthic variables, specifically cover of live hard coral and dead substratum, affect the density of fusiliers. This effect of benthic habitat on density was highlighted by several major environmental disturbances that caused shifts in the benthic habitat from live hard coral to dead substratum. For two of the three most abundant species of fusiliers individually, and for all three of them combined (Pterocaesio pisang + Caesio caerulaurea + Pterocaesio digramma/tessellata), as live hard coral cover decreased, fish density decreased. It is hypothesized that these “off‐reef” daytime feeders may have such a strong association with live hard coral cover because they use this habitat as nocturnal sleeping sites. Multivariate analyses indicated that, across all sites and times sampled, cover of live hard coral and dead substratum accounted for 38% of the variation in fish assemblage structure. These results are important as there are very few reports in the published literature of strong effects of NTMR protection or changes in benthic habitat on the density and assemblage structure of fusiliers.

Introduction: Coastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico

IntroductionCoastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico Patrick Biber* and Hyun Jung Cho* This special issue compiles original research and reviews of previous research on an important geographic constitution at the water-land interface: the seagrass/Submerged Aquatic Vegetation (SAV) beds in the Gulf of Mexico (GoM) coastal zone. SAV are a group of vascular plants that grow underwater; and seagrass is a specialized subgroup of SAV that have adapted to live in the high salinity coastal and marine waters. Presence of, types of, and seasonality of SAV beds have substantial influences on geography, ecology, landscape, culture, and economy in the coastal zone. Healthy SAV beds help shape, maintain, and modify coastal landscapes by buffering wave energy, modifying water currents, protecting shorelines from erosion, aiding sediment deposition, consolidating substrate, and changing littoral profiles and water depth. Coastal seagrass resources are among the most productive ecosystems on Earth. Seagrass beds perform numerous vital ecological functions and provide food and shelter for commercially and ecologically important organisms, including blue crabs, shrimp, turtles, manatees, and waterfowl. Therefore, assessment of SAV distribution, composition, and abundance has been of particular interest to coastal environmental managers, scientists, developers, and recreationists as this information serves as an excellent indicator of estuarine environmental quality. Coastal areas containing seagrass and SAV beds carry geographical and historical importance in the Southeast, especially throughout the GoM. The GoM and its resources have immense ecological, economical, and historic values to the U.S. but have been going through several major environmental disturbances and disasters including, but not limited to, major hurricanes (e.g., 2005 Hurricane Katrina), the 2010 Deepwater Horizon Oil Spill, red tides, rapid subsidence, marsh erosion, threats from sea level rise, and river water diversions. Man-made levees [End Page 208] along major rivers (e.g., Mississippi River) prevent natural flooding from the rivers that historically used to deliver the necessary nutrients and sediments for coastal wetland growth and delta formation. This has resulted in coastal wetland retreat and subsidence. In addition, environmental quality has been significantly degraded, which in turn, results in the loss of ecological/economical services in the region. Loss of coastal land and environmental degradation are projected to be amplified with changing global climate, which is a growing threat to coastal SAV beds (Scavia et al. 2002, Doyle et al. 2010, Unsworth et al. 2014). The low-lying coastal areas of the GoM are particularly vulnerable to natural/anthropogenic disturbances due to the effects of sea-level rise, increases in population density, extensive landscape alternation, modification, and armoring of natural shorelines, as well as natural/man-made disasters. Documentation of habitat conditions, change over time, and interactions with the human environment are critical needs to better assess current status and predict future trends for SAV/seagrass habitats, a critical component of coastal geography. However, many regionally focused relevant studies on these habitats have not been addressed in the increasingly international scope of many pertinent scientific journals. We, the Guest Editors, agreed that compiling regional studies on a unifying topic would help enhance understanding of long-term and larger scale trends in SAV/seagrass beds of the GoM. In response, requests for manuscripts on sea-grass and other SAV occurring in tidally-influenced GoM coastal habitats were sent out to several regional seagrass/SAV scientists. In order to comply with the scope of Southeastern Geographer, the papers in this issue present studies on SAV/seagrass with a regional geography focus, particularly relating to issues of temporal variation and changes related to land use change, human alteration, and climate change. The five papers published in this special issue synergistically help to summarize change occurring across the GoM. Geographically, this special issue covers coastal habitats from Texas (the Coastal Bend and Laguna Madre), Louisiana (Terrebonne Bay, the Pontchartrain basin), areas around the borders of Mississippi and Alabama (Grand Bay National Estuarine Research Reserve), and west Florida (Tampa Bay). The topics of the papers extend from (1) evaluation of SAV for nekton habitat value in comparison to marshes during one season (Jerabek et al.), (2) test of a model to assess carbon stocks in seagrass meadows in a single year (Congdon & Dunton), (3) temporal...

Biology and ecology of Zearaja maugeana, an Endangered skate restricted to two south-western Tasmanian estuaries

The Endangered Maugean skate Zearaja maugeana is a relic species restricted to two isolated estuaries, Bathurst Harbour and Macquarie Harbour, in south-western Tasmania, Australia. Over a 1-year period, dive, tagging and net surveys provided information on the biology and ecology of this species. In all, 96 Maugean skates were caught during five trips to Macquarie Harbour, with four additional individuals observed underwater; however, no animals were located in the single trip to Bathurst Harbour. Morphometrics and the sex of the animals were recorded for 95 individuals. Crustaceans dominated the diet, with the majority of animals feeding on the crab Paragrapus gaimardii. Recapture rates were very low, with only one of 82 pit-tagged skates recaptured, and that occurred on the day of release. One acoustically tagged male skate was tracked for 5km along the harbour margin for 24h, whereas a female skate tracked for 46.5h showed high site fidelity, suggesting that multiple factors potentially influence habitat utilisation. Although Macquarie Harbour represents the stronghold for this species, this estuary is also experiencing major environmental disturbance and change. Conservation management of this Endangered skate requires specific consideration of aquaculture, recreational fishing and mine drainage effects, as well as ongoing monitoring.

Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years

It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate "baseline" variability on glacial-interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations.