Tropicalization of seagrass macrophytodetritus accumulations and associated food webs

Seagrass, systems export significant amounts of their primary production as large detritus (i.e. macrophytodetritus). Accumulations of exported macrophytodetritus (AEM) are found in many areas in coastal environment. Dead seagrass leaves are often a dominant component of these accumulations, offering shelter and/or food to numerous organisms. AEM are particular habitats, different from donor habitats (i.e. seagrass meadow, kelp or macroalgae habitats) and with their own characteristics and dynamics. They have received less attention than donor habitats despite the fact they often connect different coastal habitats, are the place of intense remineralization processes and shelter associated detritus food web. As for seagrass meadows themselves, AEM are potentially affected by global change and by tropicalization processes. Here, we review briefly general characteristic of AEM with a focus on Mediterranean Sea and Western Australia and we provide some hypotheses concerning their tropicalization in a near future. We conclude that AEM functioning could change either through: (1) declines in biomass or loss of seagrass directly due to increased ocean temperatures or increased herbivory from tropicalized herbivores; (2) increased degradation and processing of seagrass detritus within seagrass meadows leading to reduced export; (3) replacement of large temperate seagrass species with smaller tropical seagrass species; and/or (4) loss or changes to macroalgae species in neighboring habitats that export detritus. These processes will alter the amount, composition, quality, timing and frequency of inputs of detritus into ecosystems that rely on AEM as trophic subsidies, which will alter the suitability of AEM as habitat and food for invertebrates

Tropicalization of seagrass macrophytodetritus accumulations and associated food webs

Seagrass, systems export significant amounts of their primary production as large detritus (i.e. macrophytodetritus). Accumulations of exported macrophytodetritus (AEM) are found in many areas in coastal environment. Dead seagrass leaves are often a dominant component of these accumulations, offering shelter and/or food to numerous organisms. AEM are particular habitats, different from donor habitats (i.e. seagrass meadow, kelp or macroalgae habitats) and with their own characteristics and dynamics. They have received less attention than donor habitats despite the fact they often connect different coastal habitats, are the place of intense remineralization processes and shelter associated detritus food web. As for seagrass meadows themselves, AEM are potentially affected by global change and by tropicalization processes. Here, we review briefly general characteristic of AEM with a focus on Mediterranean Sea and Western Australia and we provide some hypotheses concerning their tropicalization in a near future. We conclude that AEM functioning could change either through: (1) declines in biomass or loss of seagrass directly due to increased ocean temperatures or increased herbivory from tropicalized herbivores; (2) increased degradation and processing of seagrass detritus within seagrass meadows leading to reduced export; (3) replacement of large temperate seagrass species with smaller tropical seagrass species; and/or (4) loss or changes to macroalgae species in neighboring habitats that export detritus. These processes will alter the amount, composition, quality, timing and frequency of inputs of detritus into ecosystems that rely on AEM as trophic subsidies, which will alter the suitability of AEM as habitat and food for invertebrates

Temporal evolution of sand corridors in a <i>Posidonia oceanica</i> seascape: a 15-year study

The spatial dynamic of Posidonia oceanica meadows is a process extending over centuries. This paper shows evidence of the natural dynamics of P. oceanica “shifting intermattes” or “sand corridors” (hereafter SCs): unvegetated patches within a dense meadow. We studied features and temporal evolution (2001-2015) of 5 SCs in the Calvi Bay (Corsica) at 15 m depth and followed the characteristics the P. oceanica meadow lining the edge of patches. All SCs show a similar topography. The eroded side is a vertical edge where roots, rhizomes and sediments are visible, when on the opposite colonized side, the sand is at the same level as the continuous meadow. The vertical edge reaches a maximum height of 160 cm and is eroded by orbital bottom currents with a maximum speed of 12 cm.s-1, the erosion speed ranging from 0.6 to 15 cm.y-1. SCs progress toward the coastline with a mean speed of 10 cm.y-1, the rate of colonization by P. oceanica shoots ranging from 1.5 to 21 cm.y-1. We calculated that the studied SCs would reach the coastline within 500 to 600 years. We finally discuss the implication of such dynamic in the framework of meadows’ colonization assessment and the seascape dynamic

Grit ingestion and size-related consumption of tubers by Graylag Geese

In herbivorous birds the processing rate of food is constrained by gizzard capacity. To enhance digestive processes, many species ingest grit to grind the food. Grit ingestion, however, may further limit the capacity of file gizzard. Graylag Geese (Anser anser) wintering in SW Spain fed mainly on Alkali Bulrush (Scirpus maritimus) tubers, showing a preference for small tubers. This preference may be due to a faster disintegration of small tubers than larger ones inside the gizzard. As larger tubers are likely coarser than smaller tubers, more grit would be necessary to process larger tubers. However, the ingestion of more grit to grind large tubers would be at the expense of ingesting additional tubers because of gizzard capacity limitations. Under these circumstances, there may be an inverse relationship between tuber size and amount of grit ingested to optimize food ingestion. Indeed, we found such a relationship. Grit facilitated the disintegration of tubers. This suggests that relying on some amount of grit to facilitate the grinding of food should outweigh the loss of gizzard capacity to the amount of food ingested.Peer Reviewe

Security Analysis of Signature Schemes with Key Blinding

Digital signatures are fundamental components of public key cryptography. They allow a signer to generate verifiable and unforgeable proofs---signatures---over arbitrary messages with a private key, and allow recipients to verify the proofs against the corresponding and expected public key. These properties are used in practice for a variety of use cases, ranging from identity or data authenticity to non-repudiation. Unsurprisingly, signature schemes are widely used in security protocols deployed on the Internet today. In recent years, some protocols have extended the basic syntax of signature schemes to support key blinding, a.k.a., key randomization. Roughly speaking, key blinding is the process by which a private signing key or public verification key is blinded (randomized) to hide information about the key pair. This is generally done for privacy reasons and has found applications in Tor and Privacy Pass. Recently, Denis, Eaton, Lepoint, and Wood proposed a technical specification for signature schemes with key blinding in an IETF draft. In this work, we analyze the constructions in this emerging specification. We demonstrate that the constructions provided satisfy the desired security properties for signature schemes with key blinding. We experimentally evaluate the constructions and find that they introduce a very reasonable 2-3x performance overhead compared to the base signature scheme. Our results complement the ongoing standardization efforts for this primitive

AxIOM: Amphipod crustaceans from insular <i>Posidonia oceanica</i> seagrass meadows

Background The Neptune grass, Posidonia oceanica (L.) Delile, 1813, is the most widespread seagrass of the Mediterranean Sea. This foundation species forms large meadows that, through habitat and trophic services, act as biodiversity hotspots. In Neptune grass meadows, amphipod crustaceans are one of the dominant groups of vagile invertebrates, forming an abundant and diverse taxocenosis. They are key ecological components of the complex, pivotal, yet critically endangered Neptune grass ecosystems. Nevertheless, comprehensive qualitative and quantitative data about amphipod fauna found in Mediterranean Neptune grass meadows remain scarce, especially in insular locations. New information Here, we provide in-depth metadata about AxIOM, a sample-based dataset published on the GBIF portal. AxIOM is based on an extensive and spatially hierarchized sampling design with multiple years, seasons, day periods, and methods. Samples were taken along the coasts of Calvi Bay (Corsica, France) and of the Tavolara-Punta Coda Cavallo Marine Protected Area (Sardinia, Italy). In total, AxIOM contains 187 samples documenting occurrence (1775 records) and abundance (10720 specimens) of amphipod crustaceans belonging to 72 species spanning 29 families. The dataset is available at http://ipt.biodiversity.be/resource?r=axiom

Long-term feeding ecology and habitat use in harbour porpoises Phocoena phocoena from Scandinavian waters inferred from trace elements and stable isotopes

BACKGROUND: We investigated the feeding ecology and habitat use of 32 harbour porpoises by-caught in 4 localities along the Scandinavian coast from the North Sea to the Barents Sea using time-integrative markers: stable isotopes (δ(13)C, δ(15)N) and trace elements (Zn, Cu, Fe, Se, total Hg and Cd), in relation to habitat characteristics (bathymetry) and geographic position (latitude). RESULTS: Among the trace elements analysed, only Cd, with an oceanic specific food origin, was found to be useful as an ecological tracer. All other trace elements studied were not useful, most likely because of physiological regulation and/or few specific sources in the food web. The δ(13)C, δ(15)N signatures and Cd levels were highly correlated with each other, as well as with local bathymetry and geographic position (latitude). Variation in the isotopic ratios indicated a shift in harbour porpoise's feeding habits from pelagic prey species in deep northern waters to more coastal and/or demersal prey in the relatively shallow North Sea and Skagerrak waters. This result is consistent with stomach content analyses found in the literature. This shift was associated with a northward Cd-enrichment which provides further support to the Cd 'anomaly' previously reported in polar waters and suggests that porpoises in deep northern waters include Cd-contaminated prey in their diet, such as oceanic cephalopods. CONCLUSION: As stable isotopes and Cd provide information in the medium and the long term respectively, the spatial variation found, shows that harbour porpoises experience different ecological regimes during the year along the Scandinavian coasts, adapting their feeding habits to local oceanographic conditions, without performing extensive migration

Distribution, incidence and farmers knowledge of banana Xanthomonas wilt in Burundi

Banana Xanthomonas wilt (BXW) is a devastating bacterial disease caused by Xanthomonas campestris pv. musacearum. The disease was simultaneously reported in Cankuzo and Bubanza provinces, Burundi, in November 2010. However, the extent to which the disease has spread to other banana growing regions in the country is unknown. Therefore, to ascertain the distribution and incidence of the disease and farmers’ knowledge on measures to control the disease, a survey was conducted in all 16 banana growing provinces of Burundi in August 2011. A total of 208 farms were sampled, selecting six farms per surveyed commune, three affected and three non-affected. The survey was conducted using a structured questionnaire. The disease was present in 10 out of 16 provinces constituting all agricultural lands in Burundi. The highest incidence was recorded in Ruyigi province (34%), where the Kayinja system is dominant and the lowest in Muyinga (3%), where the East African Highland bananas (EAHB) dominate. Awareness of BXW symptoms, modes of spread and control measures was generally low, ranging from 8 to 30% of households surveyed. The limited knowledge of the disease among farmers was thought to be largely responsible for driving the epidemic in Burundi

Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients