The impact of zooplankton feeding on the epilimnetic bacteria of a eutrophic lake

SUMMARY. The members of the zooplankion eat bacteria in natural systems, but the impact of this mechanism of removal of bacterial biomass on the bacterioplankton of freshwaters is unknown. Zooplankton abundance and biomass were followed for 2 years in Lake Mendota. Bacterial biomass and heterotrophic production were also assessed. Feeding of zooplankton on bacteria was measured by a cell counts method in 1979 and using radioactively labelled natural assemblages of bacteria in 1980. Total feeding was calculated and was found to account for l-60% of the bacterial biomass daily. Annually, it accounted for 1–10% of the bacterial heterotrophic production. Since bacterial biomass does not change significantly from year to year and yet bacterial production is very high compared to feeding by zooplankton, mechanisms other than feeding must exist which remove biomass from the epilimnetic bacteria in larger amounts.     

Long-term environmental impact of an oil spill in the southern part of Onega Bay,the White Sea

Complex studies were carried out in the southern part of Onega Bay (White Sea) in the summer seasons of 2003–2006 and 2011–2013. These studies revealed the dynamics of oil pollution of the water area after an accidental fuel oil spill in September 2003 and its long-term adverse effects on organisms of different trophic levels of the coastal ecosystem (benthos, fish, and sea mammal populations) in the most polluted southeastern part of the bay. The deterioration of the status of the top trophic-level white whale population (a decrease in numbers) and the accumulation of oil hydrocarbons in tissues of benthic organisms are described.     

The impact of zooplankton status on the management of Lake Kinneret (Israel)

Monthly averages of standing stock wet biomass of zooplankton in Lake Kinneret (Israel) varied between 11 and 76 g m^–2 during 1969–1981, with the exception of two months. Averaged contributions of different groups were: Cladocera 58%, Copepoda 35% and Rotifera 7%. Total standing crop wet biomass is highest during January–June, averages varied between 35 and 50 g m^–2, and decreases during summer–fall (23–36 g m^–2). The winter biomass of Cladocera fluctuated between 22 and 35 g m^–2 and dropped to a range of 9–23 g m^–2 in summer, whereas copepod biomass varied very little around an average of 18 g (ww) m^–2 with the exception of low values from April to June. The stock biomass of Rotifera is relatively high during winter floods season (December-March) whilst in summer it is very low.Young stages of fish in Lake Kinneret feed mostly on zooplankton and zoobenthic forms. The most abundant fish in the Kinneret ecosystem, Mirogrex terraesanctae terraesanctae, also feed on zooplankton at the adult stage throughout the year, and herbivorous fish consume zooplankton during the summer when lake plankton resources are limited.The summer ecosystem of Lake Kinneret is characterised as a steady state type, in which the impact of the zooplankton-chain is of great importance. Increase of predation pressure on zooplankton by fish can disequilibrate the balanced trophic relations existing between nannoplankton production and zooplankton grazing capacity. Such a situation can lead to organics accumulation as nannoplankton blooms, resulting in water quality deterioration. Management options aimed at preventing collapse of zooplankton populations are discussed.     

Evidence for in situ crude oil biodegradation after the Prestige oil spill

In November 2002, the oil tanker Prestige sank off the Spanish coast after releasing approximately 17,000 tones of heavy fuel, coating several hundred kilometers of coastline in oil sludge. In December 2002 and February 2003, samples were collected from the shore of the Galician coast to analyse the indigenous population ability to carry out crude oil degradation in situ. Carbon isotopic ratio of the dissolved inorganic carbon (DIC) in seawater samples was used as a rapid method to directly assess activity of microbes on the oil components. 12CO2/13CO2 ratio in samples from certain locations along the coast revealed degradation of a very delta13C-negative source such as the Prestige crude oil (-30.6 per thousand). Putative biodegradation processes taking place at areas with high income of fresh seawater could not be detected with this technique. Laboratory-scale biostimulation processes carried out in samples with the highest oil biodegradation activity showed that N/P deficiency in seawater is a limiting factor for crude oil degradation. The most probable number (MPN) of crude oil component degraders was estimated for several aromatic compounds (naphthalene, anthracene, phenanthrene, pyrene) and for undecane. Our results clearly show that bacteria present in the contaminated water are readily able to transform components of the crude oil into inorganic carbon.     

The impact of zooplankton size structure on phosphorus cycling in field enclosures

Plastic bag field enclosures (1570 1) were used to investigate the relationship between zooplankton size distributions and the turnover rate of pelagic phosphorus. Water within the enclosures was filtered to simulate either low (200 µm mesh net) or high (80 µm) planktivory. The bags were then spiked with radiolabelled phosphorus and sampled 7 times during the following 24 h period. Zooplankton communities dominated by smaller size classes cycled more phosphorus than those composed of larger species. These experiments reveal that higher trophic level interactions, such as size selective predation, may have a significant impact upon nutrient regeneration rates and, hence, primary production.     

Field evaluations of marine oil spill bioremediation.

Bioremediation is defined as the act of adding or improving the availability of materials (e.g., nutrients, microorganisms, or oxygen) to contaminated environments to cause an acceleration of natural biodegradative processes. The results of field experiments and trials following actual spill incidents have been reviewed to evaluate the feasibility of this approach as a treatment for oil contamination in the marine environment. The ubiquity of oil-degrading microorganisms in the marine environment is well established, and research has demonstrated the capability of the indigenous microflora to degrade many components of petroleum shortly after exposure. Studies have identified numerous factors which affect the natural biodegradation rates of oil, such as the origin and concentration of oil, the availability of oil-degrading microorganisms, nutrient concentrations, oxygen levels, climatic conditions, and sediment characteristics. Bioremediation strategies based on the application of fertilizers have been shown to stimulate the biodegradation rates of oil in aerobic intertidal sediments such as sand and cobble. The ratio of oil loading to nitrogen concentration within the interstitial water has been identified to be the principal controlling factor influencing the success of this bioremediation strategy. However, the need for the seeding of natural environments with hydrocarbon-degrading bacteria has not been clearly demonstrated under natural environmental conditions. It is suggested that bioremediation should now take its place among the many techniques available for the treatment of oil spills, although there is still a clear need to set operational limits for its use. On the basis of the available evidence, we have proposed preliminary operational guidelines for bioremediation on shoreline environments.     

Deepwater Horizon oil spill impacts on sea turtles could span the Atlantic

We investigated the extent that the 2010 Deepwater Horizon oil spill potentially affected oceanic-stage sea turtles from populations across the Atlantic. Within an ocean-circulation model, particles were backtracked from the Gulf of Mexico spill site to determine the probability of young turtles arriving in this area from major nesting beaches. The abundance of turtles in the vicinity of the oil spill was derived by forward-tracking particles from focal beaches and integrating population size, oceanic-stage duration and stage-specific survival rates. Simulations indicated that 321 401 (66 199–397 864) green (Chelonia mydas), loggerhead (Caretta caretta) and Kemp''s ridley (Lepidochelys kempii) turtles were likely within the spill site. These predictions compared favourably with estimates from in-water observations recently made available to the public (though our initial predictions for Kemp''s ridley were substantially lower than in-water estimates, better agreement was obtained with modifications to mimic behaviour of young Kemp''s ridley turtles in the northern Gulf). Simulations predicted 75.2% (71.9–76.3%) of turtles came from Mexico, 14.8% (11–18%) from Costa Rica, 5.9% (4.8–7.9%) from countries in northern South America, 3.4% (2.4–3.5%) from the United States and 1.6% (0.6–2.0%) from West African countries. Thus, the spill''s impacts may extend far beyond the current focus on the northern Gulf of Mexico.     

The grounding of the Bahia Paraiso: Microbial ecology of the 1989 Antarctic oil spill

On 28 January 1989 the Bahia Paraiso ran aground and sank near Palmer Station, Antarctica. At least 6.8 × 10⁵ liters of diesel fuel arctic (DFA) were released into semi-enclosed Arthur Harbor and deposited in the nearby intertidal regions. Approximately 6 weeks later, a group of scientists was deployed to evaluate the impact of the oil spill on the surrounding coastal marine ecosystem.Microbial hydrocarbon oxidation potential (¹⁴CO₂ evolved from ¹⁴C-labeled hexadecane) was detected throughout both the oil-impacted and control regions. Hexadecane was mineralized at extremely low rates (0.13–1.21 pmol g^–1 sediment dry weight day^–1); microbiological turnover time exceeded 2 years. The acute effects of DFA (measured over exposure periods of 3–7 days) on the metabolic activities of sedimentary microorganisms appear to be negligible even at seawater saturation concentrations of DFA. Long-term exposure (120 days) to varying concentrations of DFA resulted in significant decreases (>90%) in total ATP, but had either no effect or a slight stimulatory effect on metabolic activity and production. In contrast to planktonic microbial communities, increasing incubation temperatures of between 0 and 30°C had a positive effect on rates of metabolism and production of sedimentary assemblages. These results may influence the overall weathering rates of hydrocarbons deposited in the intertidal and supratidal regions of Arthur Harbor and other polar regions.     

Potential impact of size-selective planktivory on phosphorus release by zooplankton

A laboratory model of phosphorus release by Daphnia rosea was implemented for published zooplankton data from lakes characterized by different abundances of size-selective planktivores. Size-selective feeding reduces average prey size and increases P release per unit biomass. At the system level, decreased prey standing crop associated with higher planktivore abundance could balance the size dependent increase in P release rate. However, estimates of both net reduction and net increase in rate of P release from zooplankton resulted from model application. Size-selective feeding might be important not only in energetic or evolutionary relationships between predator and prey but also in determination of the relative importance of different pathways of phosphorus flow through pelagic systems.     

The predation impact of juvenile herring Clupea harengusand sprat Sprattus sprattus on estuarine zooplankton

The consumption of estuarine copepods by juvenile herring and sprat during estuarine residency was estimated using fish biomass data and daily rations calculated from two models of feeding in fish: a bioenergetic model and a gastric evacuation model. The bioenergetic model predicted daily rations that were, on average, three times higher than those estimated by a model based on field records of stomach contents. The biomass of herring and sprat in the estuary was negatively correlated with the daily ration suggesting that the clupeid fish populations were resource-limited. Copepod production decreased towards the winter and peaked in spring and summer. The relative importance of predation changed seasonally in function of the migration pattern of herring and sprat. In the spring and the summer, in situ production ofcopepod biomass was higher than the in situ consumption by fish. During the fall and the winter, consumption exceeded production. This suggests that top–down control exerted by marine pelagic fish may be an important force structuring estuarine copepod populations.     

The impact of density-independent mortality on species coexistence: an experimental test with zooplankton

Mortality (e.g. predation, disturbance) is often thought to lower the intensity of interspecific competition and thereby promote the coexistence of competing species. However, surprisingly few tests of this idea exist, especially for metazoans feeding on a self-renewing resource. Here we examined the effect of density-independent mortality on the coexistence of four species of pond zooplankton (microcrustacean grazers) in a series of laboratory microcosms. Across the experimental mortality gradient, consumer biomass decreased and resource abundance increased with an increase in mortality. Thus, the treatments resulted in an increase in resource availability per consumer (one measure of reduced competitive intensity). There was no significant effect of mortality treatment on species relative abundances or species evenness, and the zooplankter Diaphanosoma dominated community biomass at all mortality levels. Mortality rate did have a marginally significant effect on species richness (p<0.07), but richness did not increase monotonically with mortality level. Instead, richness tended to be highest in the low- and no-mortality treatments.     

Mesocosm experiment on the impact of invertebrate predation on zooplankton of a tropical lake

Invertebrate predation on zooplankton was investigated in mesocosms in the shallow tropical Lake Monte Alegre, São Paulo State, Brazil, in the summer of 1999. Two treatments were applied: one with natural densities of prey and the predators Chaoborus brasiliensis and the water mite Krendowskia sp. (Pr+), and another without predators (Pr-). Three enclosures (volume: 6.6 m³ of water per enclosure) per treatment were installed in the sediment of the deepest area of the lake (5.0 m). At the beginning, Chaoborus larvae were present in Pr- enclosures, because of technical difficulties in preventing their entrance, but they virtually disappeared in the course of the experiment. Water mites were almost absent in Pr- enclosures. Chaoborus predation negatively influenced the Daphnia gessneri population, but not the populations of the copepods Tropocyclops prasinus and Thermocyclops decipiens and the rotifers Keratella spp. Death rates of Daphnia were generally significantly higher in the Pr+ treatment; Daphnia densities increased after the disappearance of Chaoborus in Pr-. Copepod losses to predation in the experiment may be compensated by higher fecundity, shorter egg development time, and lower pressure on egg-bearing females, resulting in a lower susceptibility to Chaoborus predation. The predation impact of water mite on microcrustaceans and rotifers in the experiment was negligible.     

Shewanella putrefaciens in a fuel-in-water emulsion from the Prestige oil spill

Microorganisms that colonize the fuel-in-water emulsion from the Prestige spill have been compared with those from Exxon-Valdez. Both emulsions contained non-fermentative gram-negative rods but unlike Exxon-Valdez's, the Prestige's spill contained anaerobic bacteria and no fungi. Our main finding has been the identification of Shewanella putrefaciens , a bacterium promising for bioremediation.     

Interspecific hybridization increased in congeneric flatfishes after the Prestige oil spill

Marine species with relatively low migratory capacity are threatened by habitat alterations derived from human activities. In November 2002 the tanker Prestige sank off the Spanish northwest coast releasing 70,000 tons of fuel and damaging biota in the area. Despite efforts to clean the damaged areas, fuel remnants have affected marine species over the last nine years. This study is focused on two flatfish, Lepidorhombus boscii (four-spotted megrim) and L. whiffiagonis (megrim), whose spawning areas are located at the edge of the continental platform. We have analyzed megrim samples from North Spanish and French waters obtained before and after the oil spill. Genotypes at the nuclear marker 5S rDNA indicate a significant increase in interspecific hybridization after the Prestige accident, likely due to forced spawning overlap. The mitochondrial D-Loop region was employed for determining the direction of hybrid crosses, which were most frequently L. boscii female x L. whiffiagonis male. Reduced ability of L. boscii females to select conspecific mates would explain such asymmetric hybridization. To our knowledge this is the first time that increased hybridization between fish species can be associated to an oil spill. These results illustrate the potential long-term effect of petrol wastes on wild fish species.     

Long-term reproductive impairment in a seabird after the Prestige oil spill

Large oil spills are dramatic perturbations on marine ecosystems, and seabirds are one of the worst affected organisms in such events. It has been argued that oil spills may have important long-term consequences on marine organisms, but supporting evidence remains scarce. The European shag (Phalacrocorax aristotelis) was strongly impacted at population level by the Prestige oil spill, the biggest spillage in the eastern North Atlantic. In this paper, we report on the long-term consequences on reproduction of this coastal seabird, using temporal and spatial replicated data (before–after–control–impact design). Our study revealed long-term reproductive impairment during at least the first 10 years since the Prestige oil spill. Annual reproductive success did not differ before the impact, but after the impact it was reduced by 45% in oiled colonies compared with unoiled ones. This is a rare documentation of long-term effects after a major oil spill, highlighting the need for long-term monitoring in order to assess the real impact of this type of disturbance on marine organisms.     

Evaluation of differential cytotoxic effects of the oil spill dispersant Corexit 9500

Aims

The British Petroleum (BP) oil spill has raised several ecological and health concerns. As the first response, BP used a chemical dispersant, Corexit-9500, to disperse the crude oil in the Gulf of Mexico to limit shoreline contamination problems. Nevertheless, portions of this oil/Corexit mixture reached the shoreline and still remain in various Gulf shore environments. The use of Corexit itself has become a significant concern since its impacts on human health and environment is unclear.

Main methods

In this study, in vitro cytotoxic effects of Corexit were evaluated using different mammalian cells.

Key findings

Under serum free conditions, the LC50 value for Corexit in BL16/BL6 cell was 16 ppm, in 1321N1 cell was 33 ppm, in H19-7 cell was 70 ppm, in HEK293 was 93 ppm, and in HK-2 cell was 95 ppm. With regard to the mechanisms of cytotoxicity, we hypothesize that Corexit can possibly induce cytotoxicity in mammalian cells by altering the intracellular oxidative balance and inhibiting mitochondrial functions. Corexit induced increased reactive oxygen species and lipid peroxide levels; also, it depleted glutathione content and altered catalase activity in H19-7 cells. In addition, there was mitochondrial complex-I inhibition and increase in the pro-apoptotic factors including caspase-3 and BAX expression.

Significance

The experimental results show changes in intracellular oxidative radicals leading to mitochondrial dysfunctions and apoptosis in Corexit treatments, possibly contributing to cell death. Our findings raise concerns about using large volumes of Corexit, a potential environmental toxin, in sensitive ocean environments.     

石油泄漏对暴风海燕群体的短期影响

2002年11月原油泄漏前后,我们对伊比利亚半岛比斯开湾内的Aketx岛上的暴风海燕(Hydrobatespelagicus)进行了监测。1993 -2005年期间,利用雾网法调查了暴风海燕的数量,并通过直接观察法来统计雏鸟出飞率。在石油泄漏前,暴风海燕的种群数量亦存在年际波动,天气变化和食物丰盛度可能是引起这一现象的根本原因。在2003年,繁殖个体的身体条件较前些年差,繁殖对的数量和雏鸟成活率也有所下降。2004年繁殖对的数量明显少于2003年,繁殖个体的身体状况稍强于2003年,且所有卵都孵化成功。2005年的种群数量已经回升到石油泄漏前的水平,几乎所有配对的暴风海燕都能成功繁殖,亲鸟的身体条件也恢复到了石油泄漏前的水平。值得注意的是,这一群体中幼年个体的数量仍在减少,表明石油污染对种群数量的影响仍然存在,确定污染物在体内积累对这些海鸟所造成的影响将是下一步研究的重点。