• European Marine Science
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• 14. Life underwater close

It is a golden age for animal movement studies and so an opportune time to assess priorities for future work. We assembled 40 experts to identify key questions in this field, focussing on marine megafauna, which include a broad range of birds, mammals, reptiles, and fish. Research on these taxa has both underpinned many of the recent technical developments and led to fundamental discoveries in the field. We show that the questions have broad applicability to other taxa, including terrestrial animals, flying insects, and swimming invertebrates, and, as such, this exercise provides a useful roadmap for targeted deployments and data syntheses that should advance the field of movement ecology. Workshop funding was granted to M.T., A.M.M.S., and C.M.D. by the UWA Oceans Institute, the Australian Institute of Marine Science, and the Office of Sponsored Research at King Abdullah University of Science and Technology (KAUST). Hays, Graeme C. et al. Peer reviewed

Abstract The dynamics of diatoms and dinoflagellates have been monitored for many decades at the Helgoland Roads Long-Term Ecological Research site and are relatively well understood. In contrast, small-sized eukaryotic microbes and their community changes are still much more elusive, mainly due to their small size and uniform morphology, which makes them difficult to identify microscopically. By using next-generation sequencing, we wanted to shed light on the Helgoland planktonic community dynamics, including nano- and picoplankton, during a spring bloom. We took samples from March to May 2016 and sequenced the V4 region of the 18S rDNA. Our results showed that mixotrophic and heterotrophic taxa were more abundant than autotrophic diatoms. Dinoflagellates dominated the sequence assemblage, and several small-sized eukaryotic microbes like Haptophyta, Choanoflagellata, Marine Stramenopiles and Syndiniales were identified. A diverse background community including taxa from all size classes was present during the whole sampling period. Five phases with several communities were distinguished. The fastest changes in community composition took place in phase 3, while the communities from phases 1 to 5 were more similar to each other despite contrasting environmental conditions. Synergy effects of next-generation sequencing and traditional methods may be exploited in future long-term observations.

Understanding the dynamics of speciation is a central topic in evolutionary biology. Here, we investigated how morphological and genomic differentiation accumulated along the speciation continuum in the African cichlid fish Astatotilapia burtoni. While morphological differentiation was continuously distributed across different lake-stream population pairs, we found that there were two categories with respect to genomic differentiation, suggesting a “gray zone” of speciation at ~0.1% net nucleotide divergence. Genomic differentiation was increased in the presence of divergent selection and drift compared to drift alone. The quantification of phenotypic and genetic parallelism in four cichlid species occurring along a lake-stream environmental contrast revealed parallel and antiparallel components in rapid adaptive divergence, and morphological convergence in species replicates inhabiting the same environments. Furthermore, we show that the extent of parallelism was higher when ancestral populations were more similar. Our study highlights the complementary roles of divergent selection and drift on speciation and parallel evolution. African cichlid fishes reveal the dynamics of speciation and the predictability of evolution. Description

A study was conducted to evaluate variations of digestive enzyme activities in Litopenaeus vannamei (Boone) reared in commercial ponds under semi-intensive conditions. Shrimp were collected at each body weight increase of 2 g. As the shrimp grew (2^12 g), signi¢cant increases in the activities of lipase and chymotrypsin were observed. The total protease activity decreased from 6 g onwards. Trypsin activity showed a peak at 6 g and amylase activity increased two-fold after 2 g. Additionally, the stomach contents were analysed microscopically for shrimp between 2 and 10 g. Plant matter contributed above 30% of the total stomach content in 6-, 8- and 10-g shrimp. Detritus represented 58% and 62% of the total stomach content in 2- and 4-g shrimp, respectively, decreasing to 33^43% at greater shrimp weights. Arti¢cial feed showed a maximum contribution of 20% in 6-g shrimp. The present results show changes in the enzyme activity after the shrimp reach 6 g in body weight, evidenced by a decrease in total protease and an increase in lipase and amylase activities. The amylase/protease ratio was 2.6 in 2-g shrimp and increased steadily to 9.6 in 12-g shrimp. These ¢ndings suggest an adaptation of the enzymatic activity to diets with lower protein content as body weight increases, and may be related to the variation of the diierent items found in the stomach.

The aim of this study is to establish a baseline for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) lifetime prediction in a marine environment, by means of mechanical and physico-chemical characterization of specimens immersed in continuously renewed and filtered natural seawater in the laboratory at different temperatures (4, 25 and 40°C). Samples were also aged at sea in Lorient harbour in order to compare laboratory and natural degradation mechanisms and kinetics. Due to its morphology, hydrolysis of PHBV in natural seawater is quite slow, and samples were observed to undergo preferentially an enzymatic surface degradation. Increasing the aging temperature in the laboratory promotes the water uptake and causes hydrolysis. As two degradation mechanisms occur in parallel, the choice of test conditions is critical, and the lifetime of PHBV in a marine environment is difficult to predict accurately.

Sediment-hosted marine sulfur cycling has played a significant role in regulating Earth's surface chemistry over our planet's history. Microbially-mediated reactions involving sulfur are often accompanied by sulfur isotope fractionation that, in turn, is captured by sulfate and sulfide minerals, providing the opportunity to track changes in the microbial utilization of sulfur and thus the marine sulfur cycle. Studying sulfur diagenesis within the Bornholm Basin, Baltic Sea, we explore the interplay between carbon, sulfur and iron, focusing on the fate of sulfur and the dynamics of the sulfur and oxygen isotopic response as a function of the varying thickness of the organic carbon-rich Holocene Mud Layer (HML) across the basin. Using a one-dimensional reaction-transport model, porewater sulfate and sulfide profiles were used to calculate net sulfate reduction rates (SRR) and net sulfide production rates, respectively. These calculations suggest a positive relationship between the thickness of the HML and net rates of sulfate reduction and sulfide production. Given that ascending sulfide is enriched in 34S relative to that produced in-situ, a heightened sulfide flux promotes spatially variable precipitation of 34S-enriched pyrite (δ34S ≈ −10‰) close to the sediment–water interface. Modeling results indicate that this isotopically “heavy” sulfide is formed as a consequence of mixing between ascending sulfide (up to +6.3‰) and that produced in-situ (ca. −40‰). Further, we show that the sulfur and oxygen isotopic composition of porewater sulfate is controlled by the net SRR: when the net SRR is high (i.e., in sulfide-replete settings) the downcore increase in δ18OSO4 is dampened relative to increase in δ34SSO4, whereas when net SRR is low (i.e., in iron-rich parts of the basin) downcore δ18OSO4 values increase while δ34SSO4 values remain invariant. We conclude that sedimentation rates and open system diffusion strongly influence the distribution of sulfur species and their sulfur isotopic composition, as well as the oxygen isotopic composition of sulfate, through the interaction between iron, sulfur and methane. This work highlights the importance of considering diffusion to better understand open system diagenesis and the δ34S signatures of sulfate and sulfide in both modern settings and ancient rocks.

International audience; A unique late Glacial–Preboreal record of changes in sea-level and sediment fluxes originating from the Alps is recorded in the Rhône subaqueous delta in the Western Mediterranean Sea. The compilation of detailed bathymetric charts, together with high-resolution seismic profiles and long cores, reveals the detailed architecture of several sediment lobes, related to periods of decreased sea-level rise and/or increased sediment flux. They are situated along the retreat path of the Rhône distributaries, from the shelf edge and canyon heads up to the modern coastline. They form transgressive backstepping parasequences across the shelf, the late Holocene (highstand) deltas being confined to the inner shelf. The most prominent feature is an elongated paleo-shoreface/deltaic system, with an uppermost sandy fraction remolded into subaqueous dunes. A long piston core into the bottomsets of this prograding unit allows precise dating of this ancient deltaic system. In seismic data, it displays aggradation, starting at not, vert, similar 15 cal kyr BP, followed by progradation initiated during the first phase of the Younger Dryas, a period of reduced sea-level rise or stillstand. The delta kept pace with resumed sea-level rise during the Preboreal (which is estimated at about 1 cm/yr), as a result of increased sediment supply from the Alps (melting of glaciers and more humid climate “flushing” the sediment down to the sea). Abandonment of the delta occurred around 10,500 cal yr BP, that is to say about 1000 yr after the end of the Younger Dryas, probably because of decreased sediment flux.

International audience; Subduction mega-thrust earthquakes in the SW Ryukyu trench pose a seismic and tsunami hazard. One of the objectives of this study is to estimate the downdip width of the seismogenic zone using numerical modeling to determine the temperature distribution along the plate interface. However, this approach depends strongly on the thermal parameters of the subducting slab. While the Philippine Sea plate (PSP) subducting beneath the central and eastern Ryukyu arc is of Eocene age (35-50 Ma), its age west of the Gagua Ridge is uncertain, with proposed ages ranging from Lower Cretaceous (140 Ma) to Upper Eocene (35 Ma). Since the sparse available heat flow data are insufficient to resolve this debate, both end-member hypotheses are tested as input parameters. We examined two transects at 122.5°E and 123.5°E on either side of the N-S trending, 4-km high, Gagua Ridge. The shallow forearc geometry is obtained from wide-angle seismic data. The deep slab geometry was obtained from hypocenter distribution and tomography. For an Eocene slab age, we obtain a 100 km and 110 km wide seismogenic zone (between the 150 °C and 350 °C isotherms) west and east of Gagua Ridge, respectively. This is in good agreement with the observed distribution of hypocenters. Using a Cretaceous slab west of Gagua Ridge predicts a deep seismogenic zone (25 km-60 km depth), inconsistent with observed thrust earthquakes. Tomographic images at 122.5°E and 123.5°E show a similar slab thickness of 70-80 km suggesting that the oceanic lithosphere has a young (Eocene) thermal age. The westernmost PSP (Huatung Basin) may have been thermally rejuvenated by mantle convection near the slab corner. The tectonic history since 6 Ma (transition from subduction to collision beneath Taiwan) may have also perturbed the thermal structure.