Water quality and water-use conflicts in Lake Taabo (Ivory Coast)

The Lake Taabo (Ivory Coast, Africa) results of the construction of the Taabo dam on the Ban- dama River. The changes in the water level of the 69-km² lake depend on 1) the rainfall linked to alternating dry/wet seasons; 2) the extraction of water for human uses; 3) the discharge of water from the upstream dam and the volumes tur- bined by the Kossou dam; 4) the various an- thropic effects (discharge of untreated waste water from towns and industries, and leaching from agricultural land). The average concentra- tions of nutrients (NH4-N: 1.1 mg/L, NO3-N: 1.62 mg/L, PO4-P: 10 mg/L, SiO2: 15 mg/L) and chlo- rophyll a (from 4.8 to 16.5 μg/L, average 11.4 μg/L) indicates some degree of eutrophication. The cumulated effects that threaten the ecosys- tem (degradation of water quality and eutrophi- cation) are such that they are likely to interfere with various water uses. In a context of growing health and environmental concerns in Africa, this study demonstrates conflicts between dif- ferent uses of this water resource and the urgent need for an appropriate policy including specific monitoring of lake water quality, wastewater control, and a programme to reduce agricultural fertilizers

Fish Invasions in the World's River Systems: When Natural Processes Are Blurred by Human Activities

Because species invasions are a principal driver of the human-induced biodiversity crisis, the identification of the major determinants of global invasions is a prerequisite for adopting sound conservation policies. Three major hypotheses, which are not necessarily mutually exclusive, have been proposed to explain the establishment of non-native species: the “human activity” hypothesis, which argues that human activities facilitate the establishment of non-native species by disturbing natural landscapes and by increasing propagule pressure; the “biotic resistance” hypothesis, predicting that species-rich communities will readily impede the establishment of non-native species; and the “biotic acceptance” hypothesis, predicting that environmentally suitable habitats for native species are also suitable for non-native species. We tested these hypotheses and report here a global map of fish invasions (i.e., the number of non-native fish species established per river basin) using an original worldwide dataset of freshwater fish occurrences, environmental variables, and human activity indicators for 1,055 river basins covering more than 80% of Earth's surface. First, we identified six major invasion hotspots where non-native species represent more than a quarter of the total number of species. According to the World Conservation Union, these areas are also characterised by the highest proportion of threatened fish species. Second, we show that the human activity indicators account for most of the global variation in non-native species richness, which is highly consistent with the “human activity” hypothesis. In contrast, our results do not provide support for either the “biotic acceptance” or the “biotic resistance” hypothesis. We show that the biogeography of fish invasions matches the geography of human impact at the global scale, which means that natural processes are blurred by human activities in driving fish invasions in the world's river systems. In view of our findings, we fear massive invasions in developing countries with a growing economy as already experienced in developed countries. Anticipating such potential biodiversity threats should therefore be a priority

Паризький хранитель часу з Одеси

У астрономів є така посада — хранитель часу. Точніше, вона існувала до другої половини ХХ століття, до появи атомного годинника. Нині ця посада зветься «учений — хранитель атомного еталона часу» і більше стосується техніки. Але наша розповідь про минуле

Biological trait profiles discriminate between native and non-indigenous marine invertebrates

The increasing rate of marine invasions to Western Europe in recent decades highlights the importance of addressing the central questions of invasion biology: what allows an invader to be successful, and which species are likely to become invasive? Consensus is currently lacking regarding the key traits that determine invasiveness in marine species and the extent to which invasive and indigenous species differ in their trait compositions. This limits the ability to predict invasive potential. Here we propose a method based on trait profiles which can be used to predict non-indigenous species likely to cause the greatest impact and native species with a tendency for invasion. We compiled a database of 12 key biological and life history traits of 85 non-indigenous and 302 native marine invertebrate species from Western Europe. Using multivariate methods, we demonstrate that biological traits were able to discriminate between native and non-indigenous species with an accuracy of 78%. The main discriminant traits included body size, lifespan, fecundity, offspring protection, burrowing depth and, to a lesser extent, pelagic stage duration. Analysis revealed that the typical non-indigenous marine invertebrate is a mid-sized, long-lived, highly fecund suspension feeder which either broods its offspring or has a pelagic stage duration of 1–30 days, and is either attached-sessile or burrows to a depth of 5 cm. Biological traits were also able to predict native species classed as “potentially invasive” with an accuracy of 78%. Targeted surveillance and proactive management of invasive species requires accurate predictions of which species are likely to become invasive in the future. Our findings add to the growing evidence that non-indigenous species possess a greater affinity for certain traits. These traits are typically present in the profile of “potentially invasive” native species

Experimental bottom trawling finds resilience in large-bodied infauna but vulnerability for epifauna and juveniles in the Frisian Front

In this study, we analysed the benthic effects of two in situ fisheries disturbance experiments using a combination of side-scan sonar, high definition underwater video, sediment profile imagery, and box core sampling techniques after conventional beam trawling and box core sampling after electric pulse trawling in a southern North Sea habitat. Acoustic and optical methods visualised the morphological changes induced by experimental beam trawling, showing the flattening and homogenisation of surface sediments. Video transects found a 94% decrease in epibenthos in beam trawled sediments compared to an untrawled control site and a 74% decrease in untrawled sediments of the same transect. Box core samples taken 5.5 h, 29 h and 75 h after trawling detected a downward trend in infaunal densities and species richness that continued after the initial impact with small-bodied and juvenile taxa being especially prone to depletion. Data from shallow sediment samples showed trawl resilience in large mud shrimps and evidence of their upward movement towards the sediment surface after disturbance. Both trawl gears induced significant changes to infaunal communities, with no differential effect between the two gears. Our results suggest that in the Frisian Front, trawling may favour the survival of deep burrowers while removing surficial macrofauna

Reef communities associated with ‘dead’ cold-water coral framework drive resource retention and recycling in the deep sea

Cold-water coral (CWC) reefs create hotspots of metabolic activity in the deep sea, in spite of the limited supply of fresh organic matter from the ocean surface (i.e. phytodetritus). We propose that ‘dead’ coral framework, which harbours diverse faunal and microbial communities, boosts the metabolic activity of the reefs, through enhanced resource retention and recycling. Analysis of a video transect across a 700-540 m-deep CWC mound (Rockall Bank, North-East Atlantic) revealed a high benthic cover of dead framework (64%). Box-cored fragments of dead framework were incubated on-board and showed oxygen consumption rates of 0.078–0.182 μmol O2 (mmol organic carbon, i.e. OC)-1 h-1, indicating a substantial contribution to the total metabolic activity of the CWC reef. During the incubations, it was shown that the framework degradation stage influences nitrogen (re)cycling, corresponding to differences in community composition. New (less-degraded) framework released ammonium (0.005 ± 0.001 μmol NH4+ (mmol OC) 1 h 1), probably due to the activity of ammonotelic macrofauna. In contrast, old (more-degraded) framework released nitrate (0.015 ± 0.008 μmol NO3- (mmol OC)- 1 h- 1), indicating that nitrifying microorganisms recycled fauna-excreted ammonium to nitrate. Furthermore, the framework community removed natural dissolved organic matter (DOM) from the incubation water (0.005–0.122 μmol C (mmol OC)- 1 h- 1). Additional feeding experiments showed that all functional groups and macrofauna taxa of the framework community incorporated 13C-enriched (‘labelled’) DOM, indicating widespread DOM uptake and recycling. Finally, the framework effectively retained 13C-enriched phytodetritus, (a) by physical retention on the biofilm-covered surface and (b) by biological filtration through suspension-feeding fauna. We therefore suggest that the dead framework acts as a ‘filtration-recycling factory’ that enhances the metabolic activity of CWC reefs. The exposed framework, however, is particularly vulnerable to ocean acidification, jeopardizing this important aspect of CWC reef functioning

Macrobenthos recovering from eutrophication at the scale of the northwestern continental shelf of the Black Sea

The northwestern continental shelf of the Black Sea has been affected by severe eutrophication and bottom hypoxia since the seventies due to an increase of anthropogenic activities. As a direct consequence, macrozoobenthos has suffered well-established decline in terms of biomass and diversity with modification in the benthic communities assemblage. In this study, we compiled macrozoobenthos data for 138 stations over the shelf from 1995 to 2017 within the framework of the EROS-2000 (1995), SESAME (2008), HYPOX (2010-2011) and EMBLAS (2016-2017) projects. Environmental data are also computed from a coupled physical biogeochemical model. A comparison is made between the 1995 and 2008-2017 period to evidence a potential recovery of the benthic communities in terms of species assemblage and extension in the hypoxic area. The 2008-2017 period is characterized by a significantly higher taxonomic richness compared to the 1995 period. Taxonomic richness is positively correlated with the dissolved oxygen concentration and the extent of the bottom hypoxic area at the scale of the shelf. There is a reduction in bottom hypoxia from 1995 to 2008-2017 due to the decrease of nutrient loads from the rivers and its subsequent eutrophication. A sharp decrease in the total share of the class Polychaeta is observed between both periods and an increase in the total share of epibenthic species (i.e. molluscs, crustaceans) is noticed for the 2008-2017 period. On the path to recovery, decrease of the class Polychaeta can be explained by a reduction in anthropogenic stress on the Black Sea ecosystem leading to a reduction of opportunistic deposit-feeder (oligochaetes and some species of polychaetes) simultaneously with the increase of sensitive epibenthic species. However, development of invasive species and persistence of opportunistic species tend to mitigate the recovery tendency