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Anthropogenic structures (e.g. weirs and dams) fragment river networks and restrict the movement of migratory fish. Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures. This study aimed to assess the effect of flow constriction and associated flow patterns on eel behaviour during downstream migration. In a field experiment, we tracked the movements of 40 tagged adult European eels (Anguilla anguilla) through the forebay of a redundant hydropower intake under two manipulated hydrodynamic treatments. Interrogation of fish trajectories in relation to measured and modelled water velocities provided new insights into behaviour, fundamental for developing passage technologies for this endangered species. Eels rarely followed direct routes through the site. Initially, fish aligned with streamlines near the channel banks and approached the intake semi-passively. A switch to more energetically costly avoidance behaviours occurred on encountering constricted flow, prior to physical contact with structures. Under high water velocity gradients, fish then tended to escape rapidly back upstream, whereas exploratory ‘search’ behaviour was common when acceleration was low. This study highlights the importance of hydrodynamics in informing eel behaviour. This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening. Fish_detections_UL_CHFish positions derived from acoustic telemetry contained within excel file with 5 columns. 'Record' denotes tag detection numbered consecutively in sequence; 'tag_number' denotes the fish identification number; ‘PosX’ denotes fish x coordinate in UTM; ‘PosY’ denotes fish y coordinate in UTM, ‘Treatment’ denotes experimental treatment

AbstractClimate change is a major threat to global biodiversity. Antarctic ecosystems are no exception. Investigating past species responses to climatic events can distinguish natural from anthropogenic impacts. Climate change produces ‘winners’, species that benefit from these events and ‘losers’, species that decline or become extinct. Using molecular techniques, we assess the demographic history and population structure of Pygoscelis penguins in the Scotia Arc related to climate warming after the Last Glacial Maximum (LGM). All three pygoscelid penguins responded positively to post-LGM warming by expanding from glacial refugia, with those breeding at higher latitudes expanding most. Northern (Pygoscelis papua papua) and Southern (Pygoscelis papua ellsworthii) gentoo sub-species likely diverged during the LGM. Comparing historical responses with the literature on current trends, we see Southern gentoo penguins are responding to current warming as they did during post-LGM warming, expanding their range southwards. Conversely, Adélie and chinstrap penguins are experiencing a ‘reversal of fortunes’ as they are now declining in the Antarctic Peninsula, the opposite of their response to post-LGM warming. This suggests current climate warming has decoupled historic population responses in the Antarctic Peninsula, favoring generalist gentoo penguins as climate change ‘winners’, while Adélie and chinstrap penguins have become climate change ‘losers’.

Significance As they grow, die, and sink into the ocean’s interior, oceanic phytoplankton drive the so-called biological carbon pump, one of the main biological processes regulating atmospheric carbon concentrations. The biological carbon pump is, therefore, key to climate regulation. Its efficiency is largely determined by the coupling of marine biology to ocean geochemistry through the C:N:P:Fe stoichiometry of phytoplankton biomass, yet what determines this stoichiometry remains poorly understood. Based on a model of plankton biology, we characterize control mechanisms of the C:N ratio of phytoplankton biomass in the North Atlantic, which explain extensive sets of apparently conflicting observations. These findings could improve the predictive ability of global ocean models regarding climate change and the role of marine biology in its mitigation/aggravation.

Changes in biomass and elemental composition (dry mass, W; carbon, C; nitrogen, N; hy- drogen, H) were studied in the laboratory during complete larval and early juvenile development of the southern stone crab Paralomis granulosa (Jacquinot). At 6 ± 0.5°C; total larval development from hatching to metamorphosis lasted ca. 56 d, comprising 2 demersal zoeal stages and a benthic mega- lopa, with mean stage durations of 5, 11 and 45 d, respectively. All larval stages of P. granulosa are lecithotrophic, and first feeding and growth were consistently observed immediately after meta- morphosis to the first juvenile crab stage. Regardless of presence or absence of food, W, C, N, and H decreased throughout larval development. Also the C:N mass ratio decreased significantly, from 7.2 at hatching to 4.2 at metamorphosis, indicating that a large initial lipid store remaining from the egg yolk was gradually utilised as an internal energy source. In total, about 68% of the initial quantities of C and H present at hatching, and 44% of N were lost during non-feeding larval development to meta- morphosis. Approximately 10% of the initially present C, N and H were lost with larval exuviae, half of which was lost in the megalopa stage alone. Hence, metabolic biomass degradation accounted for losses of ca. 59% in C and H, but for only 33% in N. Most of the losses in C and H reflected metabolic energy consumption (primarily lipid degradation), while ca. 1 /4 of the losses in N and 2 /3 of those in W were due to larval exuviation. Complete larval lecithotrophy is based on an enhanced maternal energy investment per offspring, and on energy-saving mechanisms such as low larval locomotory activity and low exuvial losses. These traits are interpreted as bioenergetic adaptations to food-limited condi- tions in subantarctic regions, where a pronounced seasonality limits the period of primary production.

The influence of carbon load on autochthonous water microflora population distribution and diversity, and on the persistence of Campylobacter jejuni, was examined with a two-stage aquatic biofilm model. Serine was chosen since it is a carbon source utilised by C. jejuni and concentrations were chosen to reflect upper limits of amino acid load reported in surface water. The total viable count of the autochthonous biofilm microflora increased with increasing serine concentration (10-fold and 20-fold with 5 nM and 5 μM serine, respectively), as did the counts of the microflora in the planktonic phase. Differences in biofilm species distribution as determined by culture were small with changes in temperature or the addition of serine; but was markedly affected by serine as determined by light microscopy, becoming more luxuriant and dominated by long filamentous cells. The addition of serine to the water significantly and progressively reduced the persistence of C. jejuni, which decreased by 25% and 50% with serine concentrations of 5 nM and 5 μM respectively. We have demonstrated that carbon load affects the species diversity and density of both the planktonic and biofilm phase of aquatic autochthonous microflora. Although the survival of C. jejuni in water in a culturable form was sufficient for this to be an important vehicle for its transmission, carbon load significantly influenced survival; an increase in serine concentration significantly reduced survival.

AbstractAnthropogenic carbon dioxide emissions are forcing rapid ocean chemistry changes and causing ocean acidification (OA), which is of particular significance for calcifying organisms, including planktonic coccolithophores. Detailed analysis of coccolithophore skeletons enables comparison of calcite production in modern and fossil cells in order to investigate biomineralization response of ancient coccolithophores to climate change. Here we show that the two dominant coccolithophore taxa across the Paleocene–Eocene Thermal Maximum (PETM) OA global warming event (~56 million years ago) exhibited morphological response to environmental change and both showed reduced calcification rates. However, only Coccolithus pelagicus exhibits a transient thinning of coccoliths, immediately before the PETM, that may have been OA-induced. Changing coccolith thickness may affect calcite production more significantly in the dominant modern species Emiliania huxleyi, but, overall, these PETM records indicate that the environmental factors that govern taxonomic composition and growth rate will most strongly influence coccolithophore calcification response to anthropogenic change.

Mass transport phenomenon was first recognized by Stokes in 1847 using a Lagrangian description. Later, a basic theory for the mass transport in water waves in viscous fluid and of finite depth was derived by Longuet-Higgins in 1953. Theoretical solutions of mass transport in progressive waves of permanent type are subjected to the definitions of wave celerity in deriving the various finite amplitude wave theories. As it has been generally acknowledged that the Stokes wave theory can not yield a correct prediction of mass transport in the shallow depths, some new theories have been developed. Recently the authors(1974 § 1977) have derived a new finite amplitude wave theory in shallow water for quasi- Stokes and cnoidal waves by the so-called reductive perturbation method, in which the mass transport is formulated both in Lagrangian and Eulerian descriptions. On the experimental verification, Russell and 0sorio(1957) investigated and compared Longuet-Higgins' solution with experimental data of Lagrangian mass transport velocity obtained in a normal closed wave tank of finite length. Since then, many investigations, and nearly all of them, have employed the finite length of wave tank in carrying out their experiments. However, no experiment has yet been attempted at verifying the Stokes drift in progressive waves of permanent type in a wave tank of infinite length. It is not realistic nor economical in constructing such an infinitely long flume to investigate experimentally the mass transport velocity in progressive waves. Instead of using such an ideal wave tank, a new one incorporated with natural water re-circulation was equipped to carry out experiments by the authors(1978). It was confirmed from these experiments that mass transport in progressive waves of permanent type exists in the Same direction of wave propagation throughout the depth, and agrees with both the Stokes drift and the authors' new formulations, within the test range of experiments.