Factors driving the seasonal dynamics of Pseudo-nitzschia species and domoic acid at mussel farming in the SW Mediterranean Sea

ABSTRACT

The seasonal variations in Pseudo-nitzschia species and domoic acid (DA) concentration were investigated, at three shellfish farms in SW coastal Mediterranean. In parallel, the toxicity of mussels was tested. Two distinct groups of species were enumerated according to morphology and size (Pseudo-nizschia delicatissima and P. seriata groups). DA was detected over a nine-week period from July to October 2012 in the Lagoon, with a maximum concentration recorded in July (12.71?ng?DA?L^?1). DA was positively correlated with the presence of P. seriata-group and P. delicatissima-group and was mostly occurred during P limitation period in seawater. No DA was found in mussels that were collected during the period of DA absence in seawater. Our results suggest that temperature, salinity, inorganic and organic nutrients were significant for the seasonal dynamics of P. seriata and P. delicatissima groups, but that the P limitation was the most driving factor for DA production in these areas. The relative influence of environmental factors should be further studied to better understand the recent surfacing of massive blooms of toxigenic Pseudo-nitzschia in SW Mediterranean coast.     

Variations in time budget of the polychaete Nereis virens as a function of density and acclimation after introduction to a new burrow

Behavioural patterns of Nereis virens (Sars) were monitored in the laboratory to determine variations in the time budget (i.e., percentage of time spent in various activities) as a function of density and acclimation period (number of days following the introduction of worms into experimental enclosures). Experiments were carried out from 17 June to 13 August 1989, using worms collected from intertidal sand flats of l'Anse à l'Orignal in the lower Saint Lawrence estuary, Canada. Inactivity, locomotion and irrigation were, in that order, the most frequent behaviours for solitary individuals. Correlations between the time spent in the various activities and time of day indicated a general increase in activity during the night (21.00 to 06.00 hrs). Locomotory activity increased at night, inactivity during the daytime. A general sequence of behaviour of N. virens was revealed. Inactivity, locomotion and irrigation were still the most frequent activities for individuals observed in high-density conditions, but their respective importance differed significantly (locomotion, irrigation and inactivity, in that order). There was also less variability in the time spent for each behaviour in the high-density aquarium. Comparisons between behaviour and time of day suggested fewer correlations among the different components of the time budgets under conditions of high density. Finally, the time budget varied but little over time (number of days alloved for acclimation) in the low-density aquarium as opposed to the high-density aquarium. Our study revealed that population density and acclimation are important in determining behavioural patterns of N. virens.     

Effects of 9–10 dihydroanthracene and its biodegradation products on the marine diatom Phaeodactylum tricornutum

Growth, photosynthetic capacity and chlorophyll a content of the marine diatom Phaeodactylum tricornutum Bohlin were observed after exposure to the aromatic hydrocarbon 9–10 dihydroanthracene and its biodegradation products. Growth was inhibited after exposure to the aromatic hydrocarbon, whereas no inhibition occurred in the presence of the biodegradation products alone. The degradation products were found to enhance the chlorophyll a cellular content. Synergistic effects between dihydroanthracene and its biodegradation products increased the toxicity of this aromatic hydrocarbon.     

Degradation of crude oil by a mixed population of bacteria isolated from sea-surface foams

A mixed bacteria population (EM₄) was isolated from foams formed on the surface of a zone chromically polluted by hydrocarbons (Gulf of Fos, French Mediterranean coast, October 1981). The population was able to degrade crude oil very effectively in the presence of sea water supplemented with nitrogen, phosphorus and iron. The percentage of hydrocarbon degradation was 81% at 30°C, pH 8, and partial oxygen pressure of 100%. After 12 d incubation, 92 and 83% of satured and aromatic compounds (mono-, di- and triaromatics) were degraded, respectively, as well as 63% of polar products and 48.5% of asphaltenes. Maximum degradation was attained at a sodium chloride concentration of between 400 and 800 mM with Population EM₄, which is constituted of 8 strains, four of which are weak halophiles. Bacterial growth on hydrocarbons induces the production in the culture medium of surface-active agents which are able to emulsify the substrate. There is high specificity between the nature of the growth substrate and such emulsifying activity, particularly as far as petroleum is concerned: only the culture medium from Population EM₄ is able to emulsify petroleum. These surface-active agents contain sugars and lipids (fatty acids, mono- and diglycerides). The foams, which always contain a high concentration of both hydrocarbons (100 to 180 mgl^-1) and bacteria that are able to grow on these types of substrates, have a strong emulsifying activity. Our results would seem to demonstrate the importance of biosurfactants in the elimination of hydrocarbons from polluted biotopes.     

Photocatalytic removal of nitrogen oxides via titanium dioxide

We studied the removal of nitrogen oxides pollutants via TiO₂ Degussa P25 powder by photocatalysis. Parameters such as mass of catalyst, geometric irradiated surface, catalyst morphology, and thermal treatment were tested to explain the photocatalytic concentration decrease of nitrogen oxides. According to our working conditions, the conversion rates increased until an optimal value of the TiO₂ weight, 35% of NO concentration and around 20% of NOx, was decomposed by the photocatalysis. The NOx removal increased proportionally with the irradiated geometric surface. The structural transformation of anatase to rutile performed by thermal treatment involved the decrease of the photocatalytic activity.     

Chemical characterization of contact semiochemicals for host-recognition and host-acceptance by the specialist parasitoid <Emphasis Type="Italic">Cotesia plutellae</Emphasis> (Kurdjumov)

Summary. Cotesia plutellae is a specialist parasitoid of Plutella xylostella. This specificity is potentially under the control of several factors before and after oviposition. Thereby, the stimuli that lead female parasitoids to host locations and to oviposition, might be at the basis of the specificity. We explore here the response of C. plutellae females exposed to host cuticular lipids. A total cuticular lipid extract of host caterpillars was fractionated into a hydrocarbon fraction and a non-hydrocarbon fraction. Neither fraction alone had any effect on oviposition behaviour in C. plutellae but the hydrocarbon fraction alone did seem to have a positive effect on the rate of antennal contact by the females. To induce oviposition behaviour, both fractions were necessary and reflect cooperation between at least one compound in each fraction. Identification of cuticular lipids shows that hydrocarbons were dominant (77%). Non-hydrocarbon compounds were mainly represented by 15-nonacosanone (18% of the total lipid extract). This ketone is rare in insect cuticle lipids and is thought to originate from the cabbage epicuticle where it is dominant with n-C₂₉ and 14- and 15-nonacosanol also found among the cuticular lipids of the host caterpillar.     

Scale-invariant movements of fishermen: the same foraging strategy as natural predators.

We analyzed the movement of fishing vessels during fishing trips in order to understand how fishermen behave in space while searching for fish. For that purpose we used hourly geo-referenced positions of vessels, provided by a satellite vessel monitoring system, for the entire industrial fleet (809 vessels) of the world's largest single species fishery (Peruvian anchovy, Engraulis ringens) from December 1999 to March 2003. Observed trajectories of fishing vessels are well modeled by Lévy random walks, suggesting that fishermen use a stochastic search strategy which conforms to the same search statistics as non-human predators. We show that human skills (technology, communication, or others) do not result in the fishermen's spatial behavior being fundamentally different from that of animal predators. With respect to probability of prey encounter, our results suggest that fishermen, on average, evolved an optimal movement pattern (mu = 2.00) among the family of Lévy random walks. This Lagrangian approach opens several perspectives in terms of operational management of the pelagic fish stock.     

Defining patch mosaic functional types to predict invasion patterns in a forest landscape.

Alien plant invasions contribute significantly to global changes by often affecting biodiversity and ecosystem processes. Operational methods for identifying landscape attributes that promote or constrain plant invasions are urgently needed to predict their future spread and manage them efficiently. We combined landscape and functional ecology concepts to define patch mosaic functional types (PMFTs) as groups of cells showing the same response to a plant invasion in a heterogeneous forest landscape. The invasion of a European temperate forest by the American black cherry (Prunus serotina) has been chosen as a case study. A set of variables was collected, mapped using a Geographic Information System, and analyzed with multivariate analyses to correlate landscape traits with Prunus serotina abundance in each cell of a grid overlaid on the forest. A risk index was derived and mapped for three invasion levels: seedling colonization, tree establishment, and ecosystem invasion. Five PMFTs were identified and characterized by a set of traits related to soil properties, land use, disturbance, and invasion history. Scots pine plantations on podzols were the most invasible, while cells dominated by hydromorphic or calcareous soils were the most resistant. Most colonized patch mosaics provided suitable conditions for future establishment and invasion. Being strongly spatially connected, suitable patches provide corridors for Prunus serotina to colonize new parts of the forest. Conversely, the most resistant PMFTs were spatially agglomerated in the south of the forest and could act as a barrier. Colonization, establishment, and invasion risk maps were finally obtained by combining partial risks associated with each landscape trait at the cell scale. Within a heterogeneous landscape, we defined and organized PMFTs into a hierarchy, according to their associated risk for colonization, establishment, or invasion by a given invasive species. Each hierarchical level should be associated with a management strategy aiming at reducing one or more partial risk. Monitoring safe areas, extending cutting rotations, harvesting recently colonized stands tree by tree, promoting a multilayered understory vegetation, cutting down reproducing alien trees, favoring shade-tolerant, fast-growing, native tree species, removing alien trees at the leading edge, and proposing soil enrichment or irrigation in heavily invaded areas are recommended.     

Effects of noise on growth and reproduction of Crangon crangon in rearing tanks

Brown shrimp, Crangon crangon (L.), were reared in Angoulins, France from April to June 1981. Rearing in a soundproof box reproduced acoustical conditions similar to those prevailing in the shrimps' original environment. Growth and reproduction were compared to those of shrimp from the same source but reared in acoustical conditions prevailing in a thermoregulated aquarium; other experimental conditions were identical. In the aquarium, the noise-level attained 30 dB in the 25 to 400 Hz frequency range; this permanently high sound-level resulted in a significant reduction in growth and reproduction rates of the shrimp. To a lesser degree, noise also appears to increase aggression (cannibalism) and mortality rate and to decrease food uptake. These symptoms are extremely similar to those induced by adaptation to stress.     

Influence du niveau sonore de bruit ambiant sur le métabolisme de Crangon crangon (Decapoda: Natantia) en élevage

The influence of ambient noise on the metabolism of the sand-shrimp Crangon crangon L. was estimated from NH₄ excretion and O₂ consumption rates. Two ambient noise levels were compared: the first (+32 dB bar⁺¹) was that present under usual rearing conditions, the second (+5 to 0 dB bar⁺¹) was the level in a soundproof rearing tank. Over a 24 h period, NH₄ excretion and O₂ consumption rates were higher by 1.4 times and 1.2 to 1.4 times, respectively, under the noisy conditions than in the sound-proof tank. The influence of ambient noise level on the shrimp's metabolic level appears to be long-lasting(>1 month). When the acoustic pressure of the environment was increased abruptly, the excretion rate was strongly enhanced but oxygen consumption was reduced; these stress-effects usually disappeared within 3 h. The influence of ambient noise on the metabolic level of this shrimp should be taken into consideration during physiological studies as well as rearing experiments in the laboratory.