Footprints of climate change in the Arctic marine ecosystem

In this article, we review evidence of how climate change has already resulted in clearly discernable changes in marine Arctic ecosystems. After defining the term ‘footprint’ and evaluating the availability of reliable baseline information we review the published literature to synthesize the footprints of climate change impacts in marine Arctic ecosystems reported as of mid‐2009. We found a total of 51 reports of documented changes in Arctic marine biota in response to climate change. Among the responses evaluated were range shifts and changes in abundance, growth/condition, behaviour/phenology and community/regime shifts. Most reports concerned marine mammals, particularly polar bears, and fish. The number of well‐documented changes in planktonic and benthic systems was surprisingly low. Evident losses of endemic species in the Arctic Ocean, and in ice algae production and associated community remained difficult to evaluate due to the lack of quantitative reports of its abundance and distribution. Very few footprints of climate change were reported in the literature from regions such as the wide Siberian shelf and the central Arctic Ocean due to the limited research effort made in these ecosystems. Despite the alarming nature of warming and its strong potential effects in the Arctic Ocean the research effort evaluating the impacts of climate change in this region is rather limited.     

Learning from the past: Diatoms as palaeoecological indicators of changes in marine environments

The North Sea is seriously threatened by a variety of pollution sources. Terrestrially derived effluents are causing extensive environmental damage and changes to ecosystems of both the offshore and coastal waters. Coastal and estuarine communities are being lost to reclamation projects, and there is the future threat of rising sea level associaed with global warming. The spatial and temporal extent of recent anthropogenic changes are largely unknown due to the paucity of background information. The possible role of palaeoecological methodology in providing ‘reference levels’ against which current status can be compared, and their importance for restoration and policy decisions, are presented. The usefulness of diatoms as environmental indicators is illustrated. The extent of natural and anthropogenic changes on coastal habitats are demonstrated by reference to the Holocene evolution of the coastline of The Netherlands. Possible profitable areas for further research are outlined,e.g. a diatom nutrient calibration data set for shallow marine embayments.     

Specialization of bone structure in Pachyvaranus crassispondylus Arambourg, 1952, an aquatic squamate from the Late Cretaceous of the southern Tethyan margin

The histological organization of the vertebrae of the Maastrichtian squamate Pachyvaranus crassispondylus Arambourg, 1952 , was compared to that of various extant squamates, in order to further document the causes and functional consequences of the so-called 'pachyostosis', frequently observed in Late Cretaceous squamates. The vertebrae of Pachyvaranus are composed of the same basic bone tissue types as those of extant lizards and snakes. In particular, periosteal cortices are made of a pseudolamellar (or 'parallel-fibred') tissue, with radial vascular canals, Sharpey's fibres and conspicuous cyclic growth marks that are strictly identical to that found in extant varanids. Conversely, the vertebrae of Pachyvaranus are extremely compact, whereas those of extant squamates are very cancellous and lightly built. This difference is due to the absence in Pachyvaranus of a broad internal resorption field that, in extant lizards and snakes, transforms compact cortices into loose spongy formations. This absence of inner bone resorption typically corresponds to an osteosclerotic process. In Pachyvaranus , cortical hyperplasy, or pachyostosis stricto sensu , was restricted to the walls of the neural spine. Extreme vertebral porosity is likely to be a primitive condition in squamates, because all lizards and snakes examined in this study display this feature. Therefore, the high vertebral compactness observed in Pachyvaranus would be a derived condition arising from the loss (or de-differentiation) of a morphogenetic process: the broad internal resorption of the vertebrae. Possible palaeoecological bearings of these results are discussed.     

Development of indicators of ecosystem functioning in a temperate shelf sea: a combined fieldwork and modelling approach

A conceptual model of the main carbon and nitrogen flows through pelagic and benthic food webs was used to identify the key biogeochemical processes representing ecosystem functioning, and to select indicators of each of these processes. A combined fieldwork and modelling approach was used to provide the data required to evaluate the indicators in terms of their suitability for assessing and managing the impacts of climate change and demersal trawling. Four of our 16 proposed indicators (phytoplankton production and productivity, near-bed oxygen concentrations and oxygen penetration of the seabed) met the majority of criteria we used for evaluating indicators. Five indicators (depth of anoxic sediment, zoobenthos biomass, production, productivity and bioturbation potential) did not comply with sufficient criteria to be considered as good indicators. Six of our proposed indicators (zooplankton biomass, size structure, production and productivity; ecosystem productivity; ecosystem balance) could not be assessed for sensitivity and specificity using our models, and therefore need to be addressed in future work aimed at improving both the models and the fieldwork. Our results indicate that evaluation of indicators is difficult, because of the number and variety of human pressures which need to be considered in reality, and the interactions between these pressures and the ecosystem components which they affect. The challenge will be to establish if there are indeed any indicators which are able to meet the majority of criteria for good indicators in holistic ecosystem-based assessments.     

Comparative analysis of European wide marine ecosystem shifts: a large-scale approach for developing the basis for ecosystem-based management

Abrupt and rapid ecosystem shifts (where major reorganizations of food-web and community structures occur), commonly termed regime shifts, are changes between contrasting and persisting states of ecosystem structure and function. These shifts have been increasingly reported for exploited marine ecosystems around the world from the North Pacific to the North Atlantic. Understanding the drivers and mechanisms leading to marine ecosystem shifts is crucial in developing adaptive management strategies to achieve sustainable exploitation of marine ecosystems. An international workshop on a comparative approach to analysing these marine ecosystem shifts was held at Hamburg University, Institute for Hydrobiology and Fisheries Science, Germany on 1-3 November 2010. Twenty-seven scientists from 14 countries attended the meeting, representing specialists from seven marine regions, including the Baltic Sea, the North Sea, the Barents Sea, the Black Sea, the Mediterranean Sea, the Bay of Biscay and the Scotian Shelf off the Canadian East coast. The goal of the workshop was to conduct the first large-scale comparison of marine ecosystem regime shifts across multiple regional areas, in order to support the development of ecosystem-based management strategies.     

Life on the margin: genetic isolation and diversity loss in a peripheral marine ecosystem, the Baltic Sea

Marginal populations are often isolated and under extreme selection pressures resulting in anomalous genetics. Consequently, ecosystems that are geographically and ecologically marginal might have a large share of genetically atypical populations, in need of particular concern in management of these ecosystems. To test this prediction, we analysed genetic data from 29 species inhabiting the low saline Baltic Sea, a geographically and ecologically marginal ecosystem. On average Baltic populations had lost genetic diversity compared to Atlantic populations: a pattern unrelated to dispersal capacity, generation time of species and taxonomic group of organism, but strongly related to type of genetic marker (mitochondrial DNA loci had lost c. 50% diversity, and nuclear loci 10%). Analyses of genetic isolation by geographic distance revealed clinal patterns of differentiation between Baltic and Atlantic regions. For a majority of species, clines were sigmoid with a sharp slope around the Baltic Sea entrance, indicating impeded gene flows between Baltic and Atlantic populations. Some species showed signs of allele frequencies being perturbed at the edge of their distribution inside the Baltic Sea. Despite the short geological history of the Baltic Sea (8000 years), populations inhabiting the Baltic have evolved substantially different from Atlantic populations, probably as a consequence of isolation and bottlenecks, as well as selection on adaptive traits. In addition, the Baltic Sea also acts a refuge for unique evolutionary lineages. This marginal ecosystem is thus vulnerable but also exceedingly valuable, housing unique genes, genotypes and populations that constitute an important genetic resource for management and conservation.     

Effects of recent climate change on phytoplankton phenology in a temperate lake

1. A number of long-term studies have shown that spring biological events have advanced in recent decades and that this is a response to climate change. In lentic systems, changes in phytoplankton phenology have been attributed to various directly climate-related processes including changes in the onset and duration of thermal stratification, earlier ice-break up and increased water temperature. Both indirect climatic drivers and non-climate drivers such as elevated grazing pressure and nutrient enrichment can also affect phenology.
2. This study investigated whether phenological trends in phytoplankton could be detected in a relatively short time series in a shallow, ice-free, polymictic lake with a high annual discharge and whether any such trends could be causally explained.
3. It was found that the centre of gravity of the spring chlorophyll a bloom advanced significantly by 1.6 days per year over a 15-year period. This was accompanied by a significant increase in water temperature of 0.12 °C per year which is high compared to published rates of change over longer time series. No direct effects of ice cover, stratification or water discharge rates could be linked to the advancement of the spring bloom. Instead, the shift in timing was attributed to an advance in the timing of the dominant spring diatom, Aulacoseira spp., instigated by a temperature-driven increase in replication rate leading to an earlier onset of silica (SiO₂) limitation.     

The influence of particle size distribution and composition on seasonal sedimentation rates in a temperate lake

To evaluate the effect of particle size and composition on seasonal changes in the sedimentation rate, suspended and sedimenting particles were collected from Trout Lake, Wisconsin, USA during the 2002 ice-free season. Particles were characterized with regard to particulate biogenic silicon (PBSi) concentration and distribution between four size classes. The concentration of particulate chlorophyll and chlorophyll degradation products was also measured in water column particles and sediment trap material collected during the first half of the sampling period. The highest rates of mass sedimentation during the stratified period were measured in spring and early summer. Seasonal increases in sedimentation are related to the presence of large colonial diatoms in the water column as indicated by elevated PBSi concentrations. The majority of particulate matter in the water column was found in the smallest (<20 m) size fraction while most of the mass of sediment trap material was in larger size fractions (>20 m). Smaller cells appear to carry out most of the photosynthesis in Trout Lake but larger cells are responsible for seasonal trends in sedimentation. These results may explain how pelagic photosynthesis and sedimentation rates can be quantitatively decoupled across a range of trophic conditions but appear correlated when based on mid-summer measurements.     

Cyanobacterial blooms in a temperate river-floodplain ecosystem: the importance of hydrological extremes

In the past decade, extreme hydrological events were expressed with extreme droughts and floods in temperate regions. The aim of this paper is to explain how such changes in hydrology can influence cyanobacterial populations in floodplain ecosystems. We therefore analyzed a 6-year (2003–2008) study of the phytoplankton in the Kopački Rit floodplain, one of the largest natural floodplains in the middle section of the Danube River (Europe). During the studied period, the shallow floodplain lake shifted between a state of turbid water, characterized by high phytoplankton biomass and regular appearance of cyanobacteria blooms, to a state of clear water with very low phytoplankton biomass and absence of cyanobacteria, and back to the turbid state. Apparently, the major forces driving the cyclic shift were closely related to extremely high and long-lasting flood events. Significant increase in water level, low hydraulic residence time of water, decrease in transparency and low-light climate, together with mass developed aquatic macrophyte vegetation in the whole inundated floodplain were unfavorable conditions for growth and proliferation of cyanobacteria. With the establishment of the flood regime characterized by long-lasting periods without flooding, in-lake processes prevailed leading to cyanobacterial bloom. The most successful were filamentous non-N-fixing cyanobacteria tolerant to mixed and low-light conditions (Planktothrix and Limnothrix) and invasive species Cylindrospermopsis raciborskii. Their massive development led to the establishment of a phytoplankton steady state. All our results demonstrate that the altered intensity and frequency of flood events will have pronounced effects on the appearance of cyanobacterial blooms and generally on alternative stable states in the floodplain. Relating to this, management objectives should be focused on qualifications of changes in hydrology and projecting those effects for potential floodplain restoration.     

Development of the Polar Filament-Polaroplast Complex in a Microsporidian Parasite*

SYNOPSIS. The development of the polar filament in a microsporidian parasite was studied in the electron microscope. The polar filament is a peculiar and complex organelle with intricate anatomical relationships to other structures in the mature spore. The characteristic ultrastructure of the formative and mature stages of the polar filament made it possible to trace its development and study the interactions among various organelles during its formation. In sporoblasts the polar filament develops sequentially from 3 different regions. The base of the filament appears first and is derived from a dense body. The anterior part of the filament is formed from electron dense material located in the perinuclear cisterna and in agranular endoplasmic reticulum. The base and the anterior part of the filament move toward each other and fuse. Subsequently, the posterior part of the filament develops from the posterior part of the Golgi complex. The polar sac and the polaroplast surrounding the anterior segment of the filament are formed from the anterior region of the Golgi complex.     

Spiders and subsidies: results from the riparian zone of a coastal temperate rainforest

1. Aquatic insects emerging from streams can provide an important energy subsidy to recipient consumers such as riparian web-building spiders. This subsidy has been hypothesized to be of little importance where the primary productivity of the recipient habitat exceeds that of the donor habitat. 2. To test this hypothesis, we manipulated emerging stream insect abundance in a productive riparian rainforest in a replicated design using greenhouse-type exclosures, contrasted with unmanipulated stream reaches (four exclosures on two streams). 3. Experimental exclosures resulted in a 62.9% decrease in aquatic insect abundance in exclusion reaches compared with control reaches. The overall density of riparian spiders was significantly positively correlated with aquatic insect abundances. Horizontal orb weavers (Tetragnathidae) showed a strong response to aquatic insect reduction - abundance at exclosure sites was 57% lower than at control sites. Several spider families that have not been associated with tracking aquatic insect subsidies also showed significantly decreased abundance when aquatic insects were reduced. 4. This result is contrary to predictions of weak subsidy effects where recipient net primary productivity is high. These results suggest that predicting the importance of resource subsidies for food webs requires a focus on the relative abundance of subsidy materials in recipient and donor habitats and not simply on the total flux of energy between systems.     

State-dependent risk-taking by green sea turtles mediates top-down effects of tiger shark intimidation in a marine ecosystem

1. A predictive framework of community and ecosystem dynamics that applies across systems has remained elusive, in part because non-consumptive predator effects are often ignored. Further, it is unclear how much individual-level detail community models must include. 2. Previous studies of short-lived species suggest that state-dependent decisions add little to our understanding of community dynamics. Body condition-dependent decisions made by long-lived herbivores under risk of predation, however, might have greater community-level effects. This possibility remains largely unexplored, especially in marine environments. 3. In the relatively pristine seagrass community of Shark Bay, Australia, we found that herbivorous green sea turtles (Chelonia mydas Linnaeus, 1758) threatened by tiger sharks (Galeocerdo cuvier Peron and LeSueur, 1822) select microhabitats in a condition-dependent manner. Turtles in poor body condition selected profitable, high-risk microhabitats, while turtles in good body condition, which are more abundant, selected safer, less profitable microhabitats. When predation risk was low, however, turtles in good condition moved into more profitable microhabitats. 4. Condition-dependent use of space by turtles shows that tiger sharks modify the spatio-temporal pattern of turtle grazing and their impacts on ecosystem dynamics (a trait-mediated indirect interaction). Therefore, state-dependent decisions by individuals can have important implications for community dynamics in some situations. 5. Our study suggests that declines in large-bodied sharks may affect ecosystems more substantially than assumed when non-lethal effects of these top predators on mesoconsumers are not considered explicitly.     

Opportunistic exploitation of dinosaur dung: fossil snails in coprolites from the Upper Cretaceous Two Medicine Formation of Montana

Multiple associations of fossil snails with dinosaur coprolites demonstrate that snails and dinosaurs not only shared ancient habitats but were trophically linked via dinosaur dung. Over 130 fossil snails representing at least seven different taxa have been found on or within herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana. The terrestrial snail Megomphix is the most common taxon, but three other terrestrial taxa (Prograngerella, Hendersonia and Polygyrella) and three aquatic snails (Lioplacodes, ?Viviparus and a physid) also occur in coprolites. At least 46% of the shells in the faeces are whole or nearly so, indicating that most (if not all) of the snails were not ingested by dinosaurs, but were post‐depositional visitors to the dung pats. The sizeable, moist and microbially enriched dinosaur faeces would have provided both food and roosting sites for the ancient snails, and the large number of snail–coprolite associations reflect recurring, opportunistic exploitation of dung. The terrestrial taxa in the coprolites suggest that this Late Cretaceous locality included sufficiently moist detrital or vegetative cover for snails when dinosaur dung was not present. The aquatic snails probably entered the faeces during flood events. Dinosaur dung would have provided an abundant but patchy influx of resources that was probably seasonally available in the ancient environment.     

Identification of the sea ice diatom biomarker IP25 in Arctic benthic macrofauna: direct evidence for a sea ice diatom diet in Arctic heterotrophs

Currently, the impact of declining seasonal sea ice extent in the Arctic on polar food webs remains uncertain. Previously, a range of proxy techniques has been employed to determine links between sea ice or phytoplankton primary production and the Arctic marine food web, although it is accepted that such approaches have their limitations. Here, we propose a novel approach to tracing sea ice primary production through Arctic food webs using the sea ice diatom biomarker, IP₂₅. Various benthic macrofaunal specimens were collected between March and May 2008 from Franklin Bay in the Amundsen Gulf, Arctic Canada, as part of the International Polar Year–Circumpolar Flaw Lead system study. Each specimen was analysed for the presence of the sea ice diatom biomarker IP₂₅ in order to provide evidence for feeding by benthic organisms on sea ice algae. IP₂₅ was found in nineteen out of the twenty-one specimens analysed, often as the most abundant of the highly branched isoprenoid biomarkers detected. The stable isotope composition of IP₂₅ (δ¹³C = −17.1 ± 0.5‰) in the sea urchin (Strongylocentrotus sp.) specimens was similar to that reported previously for this biomarker in Arctic sea ice, sedimenting particles and sediments. It is concluded that detection of IP₂₅ in Arctic benthic macrofauna represents a novel approach to providing convincing evidence for feeding on sea ice algae. It is also proposed that analysis of IP₂₅ may be used to trace trophic transfer of sea ice algal-derived organic matter through Arctic food webs in the future.     

Base-line variations in stable isotope values in an Arctic marine ecosystem: effects of carbon and nitrogen uptake by phytoplankton

Floods are fundamental for the maintenance of floodplain biodiversity. As a result, well-functioning floodplains are characterized by a high spatio-temporal heterogeneity. Most floodplain-organisms need this shifting landscape mosaic to fulfil their environmental requirements and display a range of adaptations to survive floods. However, in temperate areas, where winter floods are common, extraordinary floods occurring in summer, a period of high physiological activity, may seriously impact the floodplain fauna. This is especially true for guilds characterized by low mobility, such as molluscs. Here we examined the immediate and longer-term response of Elbe grassland molluscs to the extreme 2002 Elbe summer flood in terms of abundance, diversity, and community composition by comparing pre- and post-flood data collected with identical methods. The flood favoured the colonization of aquatic species and led to a shift of the community towards a more hydrophilic composition. Both diversity and abundance increased significantly in the first year following the flood but decreased later gradually to the pre-flood levels. The high spatio-temporal habitat heterogeneity played an important part in the maintenance of mollusc diversity by increasing refuge opportunities and favouring the maintenance of various mollusc communities with different environmental requirements within the floodplain. Handling editor: S. I. Dodson     

Seasonal variations of diatoms and dinoflagellates in a shallow,temperate estuary,with emphasis on neritic assemblages

Seasonal changes in the diatom and dinoflagellate assemblages were examined in the neritic zone of the Urdaibai estuary (north Spain) with regard to some major physical and chemical variables during an annual cycle. A total of 81 diatoms and 38 dinoflagellates were identified and quantified during the study period. Both groups displayed a distinctive pattern of seasonal succession. The seasonal distribution of the Shannon index showed a trend of increasing values from the upper estuary to the lower neritic segment. The diatom diversity maxima were observed in February, April and September, and dinoflagellate maxima in April–May, July and October. Diatoms dominated the assemblages, reaching 1×10⁶ cells l^–1 from April to September. A shift from large diatoms and dinoflagellates to small bloom-forming taxa was observed during winter–early spring. A spring diatom bloom composed of Rhizosolenia spp. was observed in April, while small chain-forming taxa (chiefly Chaetoceros spp.) dominated from June to September. Cell maxima for both groups in late summer were produced by the diatoms Chaetoceros salsugineum and Skeletonema costatum, and by the dinoflagellates Heterocapsa pygmaea and Peridinium quinquecorne. Silicate availability by river supply and strong tidal-mixing of the water column seem to determine the year-round dominance of diatoms over dinoflagellates.     

Food uptake and fine structure of Cryothecomonas longipes sp. nov., a marine nanoflagellate incertae sedis feeding phagotrophically on large diatoms

Cryothecomonas longipes Schnepf and Kühn sp. nov. is a colourless biflagellate organism, 9–14 μm long and 7–9 μm wide when not filled with food vacuoles. It was detected in the North Sea, feeding with pseudopodia on diatoms. It penetrates the host shell, while the main body of the flagellate remains outside the frustule. Cells are covered with a multilayered theca. The pseudopodium protrudes through a preformed slit in the theca. Each flagellum also emerges through a pit in which the theca forms a funnel of complex structure that girdles each flagellum. The anterior flagellum is 9–15 μm long and oriented forward; the ventral flagellum, posteriorly directed, is 20–24 μm long and bears fine hairs. The flagellar roots consist of microtubules that emerge at satellites around the basal bodies and run along the flagellar pits. In addition, the ventral flagellum is accompanied by a band of six microtubules. It is proximally attached to a small fibrillar band, which interconnects the basal bodies. Cryothecomonas longipes has two or three types of extrusomes which pierce the theca when discharged. Their mode of discharge is discussed. Microbody-like vesicles containing small tubules are closely associated with older digestion vacuoles. Cryothecomonas longipes is compared with other species of the genus and a diagnosis is given. Received: 4 March 1999 / Received in revised form: 28 July 1999 / Accepted: 30 August 1999     

Life history of a basal bird: morphometrics of the Early Cretaceous Confuciusornis

Confuciusornis sanctus stands out among the remarkable diversity of Mesozoic birds recently unearthed from China. Not only is this primitive beaked pygostylian (birds with abbreviated caudal vertebrae fused into a pygostyle) much more abundant than other avian taxa of this age but differences in plumage between specimens--some having a pair of long stiff tail feathers--have been interpreted as evidence for the earliest example of sexual dimorphism in birds. We report the results of a multivariate morphometric study involving measurements of more than 100 skeletons of C. sanctus. Our analyses do not show any correlation between size distribution and the presence or absence of blade-like rectrices (tail feathers), thus implying, that if these feathers are sexual characters, they are not correlated with sexual size dimorphism. Our results also provide insights into the taxonomy and life history of confuciusornithids, suggesting that these birds may have retained ancestral dinosaurian growth patterns characterized by a midlife exponential growth stage.