INFLUENCE OF UV-B RADIATION ON NITROGEN UTILIZATION BY A NATURAL ASSEMBLAGE OF PHYTOPLANKTON

A 7‐day mesocosm experiment was conducted in July 1996 to investigate the effects of ambient UV‐B radiation (UVBR) exclusion and two UVBR enhancements above ambient levels on NO₃^?, NH₄⁺ and urea utilization in a natural plankton community (<240 μm) from the Lower St. Lawrence Estuary. The phytoplankton community was dominated by diatoms during the first 3 days and, afterward, by flagellates and dinoflagellates. The results of 4‐h incubations just below the water surface show that, compared with ambient UVBR conditions, UVBR exclusion generally increased NO₃^?, NH₄⁺, and urea uptakes. During the last 4 days of the experiment, the percent increase in the specific uptake rate of urea under excluded UVBR conditions varied between 17% and 130% and was a linear function of the ambient UVBR dose removed. During the first 3 days, the phytoplankton community dominated by diatoms was able to withstand UVBR enhancements without any perceptible effect on nitrogen uptake. However, during the post‐diatom bloom period, UVBR enhancements resulted in decreases in NO₃^?, NH₄⁺, and urea uptake compared with ambient UVBR conditions. The reduction of urea uptake under UVBR enhancements during the last 3 days varied between 23% and 64% and was linearly related to the enhanced UVBR dose. However, the different UVBR treatments did not affect the internal organic nitrogen composition (internal urea, free amino acids, and proteins) of the phytoplankton community experiencing vertical mixing in the mesocosms. The discrepancy between short‐term uptake measurements at the surface and long‐term effects in the mesocosms emphasizes the importance of vertical mixing on UVBR effects in natural ecosystems. This suggests that an increase in ambient UVBR would have a minimal effect on nitrogen utilization by natural phytoplankton assemblages if these are vertically mixed.     

UV RADIATION,PHOSPHORUS, AND THEIR COMBINED EFFECTS ON THE TAXONOMIC COMPOSITION OF PHYTOPLANKTON IN A BOREAL LAKE1

We examined how UV radiation and phosphorus (P) affect the taxonomic composition, abundance, and biomass of phytoplankton in an oligotrophic boreal lake. We exposed phytoplankton to three different solar radiation regimes (PAR + UV‐A radiation [UVAR]+ UV‐B radiation [UVBR], PAR + UVAR, and PAR only) and to five levels of P. The biomass of small chrysophytes was reduced by 350% after exposure to PAR + UVAR + UVBR compared with PAR only. No other taxa were found to be negatively affected by exposure to UVBR. Several taxa (e.g. Chry‐ sochromulina laurentiana Kling) were sensitive to UVAR, whereas others (e.g. Tabellaria flocculosa (Roth) Kutzing) were not affected by UV radiation exposure. Principal components analysis ordination separated phytoplankton that were negatively affected by UV radiation and/or positively affected by P treatments (e.g. small chrysophytes, Cryptomonas rostratiformis, T. flocculosa) from those that generally were unaffected by either treatment (e.g. desmids, some Cyanobacteria). Richness, Shannon‐Weaver diversity, and evenness were significantly higher in phytoplankton communities shielded from UVAR and UVBR. The relationship between diversity and richness was positive in all phytoplankton samples except in those exposed to UVBR. Thus, UVBR‐exposed phytoplankton communities were dominated by a few species even though the number of taxa remained relatively unchanged. Consequently, alterations in the UV environments of lakes resulting from climate warming (e.g. drought) and land‐use change (e.g. increased P export) will likely promote shifts in the community composition of lake phytoplankton.     

The sensitivity of Emiliania huxleyi (Prymnesiophyceae) to ultraviolet-b radiation

Emiliania huxleyi (Lohm.) Hay et Miller is an important component of the phytoplankton in open ocean waters. The sensitivity of this cosmopolitan alga to natural levels of UVB radiation has never been tested. Since DNA is believed to be a major target of natural UVB radiation (UVBR: 280–315 nm) in living cells, experiments with E. huxleyi were performed using growth rate reduction and DNA damage as indicators of UVBR stress. Specific growth rate, cell volume, pigment content, and CPD (cyclobutane pyrimidine dimer) formation (a measure for DNA damage) were followed during and after prolonged exposure of a series of cultures to a range of UVBR levels. E. huxleyi was found to be very sensitive to UVBR: at a daily weighted UVBR dose of only 400 J·m⁻² ·d⁻¹ (BED_DNA300nm), growth was halted. At this UVBR level, both cell volume and contents of the major photosynthetic and photoprotective pigments had increased. The UVBR vulnerability of E. huxleyi cannot be explained by a high potential for cyclobutane thymine dimer formation (the most abundant CPD type) due to a high T content of nuclear DNA: the CG content of this E. huxleyi strain is high (68%) compared with other species. The high UVBR sensitivity may be related to the stage of the cell cycle during UVBR exposure, in combination with low repair capacity. It is concluded that E. huxleyi may experience UVBR stress through the formation of cyclobutane pyrimidine dimers, with subsequent low repair capacity and thereby arrest of the cell cycle.     

Effects of UVB radiation on marine phytoplankton communities

The impact of enhanced and reduced UVB radiation (UVBR) on pelagic ecosystems was studied during two mesocosm experiments in May and June/July 1994. The ambient UVBR exposure was either reduced with mylar foil or artificially enhanced with UVB fluorescent tubes. Developments in the phytoplankton communities were followed during 11 and 8 day periods using several structural and functional parameters. In the May experiment, enhanced UVBR significantly stimulated carbon dioxide fixation, activity of alkaline phosphatase and content of fatty acids. In the June-July experiment, the effects induced by changed UVBR were smaller with some indications of decreased algal biomass with enhanced UVBR. Several of the measured parameters indicated that the two experiments represented different stages in the plankton community development. In the May experiment, the community was in a development stage, moving from nutrient-replete to nutrient-depleted conditions, while the community in June/July was depleted of nutrients from the start. The stimulating effects of UVBR in May are suggested to be the secondary effects of a photochemically induced breakdown of dissolved organic matter, resulting in an increase in available nutrients.      

Enhanced Resistance to UV-B Radiation in Anabaena sp. PCC 7120 (Cyanophyceae) by Repeated Exposure

In natural habitats, organisms especially phytoplankton are not always continuously subjected to ultraviolet-B radiation (UVBR). By simulation of the natural situation, the N₂-fixing cyanobacterium Anabaena sp. PCC 7120 was subjected to UV-B exposure and recovery cycles. A series of morphological and physiological changes were observed in Anabaena sp. PCC 7120 under repeated UVBR when compared with controls. Such as the breakage of filaments, intervals between heterocysts, heterocyst frequency, total carbohydrate, and carotenoids were increased, while the nitrogenase activity and photosynthetic activity were inhibited by repeated UVBR; however, these activities could recover when UV-B stress was removed. Unexpectedly, the over-compensatory growth was observed at the end of the second round of exposure and recovery cycle. Our results showed that discontinuous UVBR could increase the growth rate and the tolerance as well as repair capacity of Anabaena sp. PCC 7120. These results indicate that moderate UVBR may increase the growth of cyanobacteria in natural habitats.     

Inputs of seabird guano alter microbial growth,community composition and the phytoplankton–bacterial interactions in a coastal system

Seabird guano enters coastal waters providing bioavailable substrates for microbial plankton, but their role in marine ecosystem functioning remains poorly understood. Two concentrations of the water soluble fraction (WSF) of gull guano were added to different natural microbial communities collected in surface waters from the Ría de Vigo (NW Spain) in spring, summer, and winter. Samples were incubated with or without antibiotics (to block bacterial activity) to test whether gull guano stimulated phytoplankton and bacterial growth, caused changes in taxonomic composition, and altered phytoplankton–bacteria interactions. Alteromonadales, Sphingobacteriales, Verrucomicrobia and diatoms were generally stimulated by guano. Chlorophyll a (Chl a) concentration and bacterial abundance significantly increased after additions independently of the initial ambient nutrient concentrations. Our study demonstrates, for the first time, that the addition of guano altered the phytoplankton–bacteria interaction index from neutral (i.e. phytoplankton growth was not affected by bacterial activity) to positive (i.e. phytoplankton growth was stimulated by bacterial activity) in the low-nutrient environment occurring in spring. In contrast, when environmental nutrient concentrations were high, the interaction index changed from positive to neutral after guano additions, suggesting the presence of some secondary metabolite in the guano that is needed for phytoplankton growth, which would otherwise be supplied by bacteria.     

The effects of northern italian rivers and Eastern Mediterranean ingressions on the phytoplankton of the Adriatic Sea

An analysis of the distribution of the phytoplankton standing crop during a period of high stability characterized the relative influence of northern Italian rivers and Mediterranean waters on the Adriatic Sea. The region influenced by northern Italian rivers was marked by low community diversities, relatively high chlorophyll a standing crops and cell densities, high microplankton to nannoplankton community volume ratios, and the dominance of Nitzschia seriata. To the contrary, the region influenced by Mediterranean waters exhibited high community diversities with prominent oceanic and warm water elements, low chlorophyll a standing crops and microplankton cell densities, low microplankton to nannoplankton ratios, and a relatively conspicuous coccolithophore flora.Nannoplankton populations remained relatively constant throughout the Adriatic. However eutrophication resulted in a marked increase in the microplankton component of the community, with the diatom Nitzschia seriata serving as a prime indicator of the process, even in regions several hundred kilometers downstream from nutrient sources.Even under relatively low rates of river discharge, the influence of northern Italian rivers could be traced along the entire western sode of the sea to the Otranto Strait, with low north to south and high west to east gradients resulting from the effect of a cyclonic surface circulation pattern on inflowing Mediterranean waters in the south and river discharge in the north.     

Diel patterns of UVBR-induced DNA damage in picoplankton size fractions from the Gulf of Aqaba,Red Sea

This study focuses on the impact of natural levels of UVBR (ultraviolet-B radiation: 280 to 315 nm) on bacterio- and phytoplankton (<10 mm) from the Gulf of Aqaba, Red Sea. Incident biologically effective doses (BEDs) and attenuation of biologically effective radiation in the water column were measured using a DNA biodosimeter. UVBR-induced DNA damage was measured as cyclobutane pyrimidine dimers (CPDs), using an antibody directed to CPDs followed by chemiluminescent detection. Depth profiles of DNA damage were determined in two plankton size fractions (0.2 to 0.8 mm and 0.8 to 10 mm) collected down to 50 m depth. Furthermore, accumulation and removal of CPDs were monitored in surface plankton samples during several daily cycles. Small plankton (plankton <10 mm) composition was determined by flow cytometry. The plankton community in the Gulf of Aqaba was dominated by nonphototrophic bacteria and the free-living prochlorophyte Prochlorococcus spp. (<0.8 mm). In general, no DNA damage could be detected in dosimeter DNA below 15 m. In contrast, DNA damage (up to 124 CPD Mnucl-1) could be detected in all bacterio- and phytoplankton samples. DNA damage accumulated throughout the day, indicating that plankton in the Gulf of Aqaba undergo UVBR stress via CPD induction. Although the numbers of CPDs decreased during darkness, both size fractions showed some residual DNA damage at the end of the night. This suggests that dark repair processes did not remove all CPDs, or that part of the plankton community was incapable of repair at all. CPD levels in the two size fractions showed no significant differences in situ. During full solar radiation exposures (samples incubated in bags), more CPDs were detected in the smaller (0.2 to 0.8 mm) size fraction as compared to the larger (0.8 to 10 mm) size fraction. In these experiments, initial plankton composition was significantly different from the field samples. This implies that a shift in the population structure or irradiance conditions can lead to a significant change in UVBR sensitivity. In conclusion, the results show that the picoplankton-dominated phyto- and bacterioplankton communities in the clear surface waters from the Gulf of Aqaba undergo UVBR stress. Repair pathways are not sufficient to eliminate damage during or after UVBR exposure hours, suggesting photomortality as a potential loss parameter of the plankton community.     

Emergent multiple predator effects in an experimental microbial community

Studies on multiple predator effects have typically focused on metazoans. Here we examined the effects of multiple consumers on bacteria. Specifically, we investigated the separate and combined effects of two common bacterivorous ciliates, Colpidium striatum and Paramecium caudatum, on a simple bacterial assemblage. Non-additive multiple predator effects emerged for all bacterial species significantly affected by grazing, where bacterial responses in the two-consumer treatment cannot be predicted by summing the separate effects of the two consumers. Some species showed risk reduction (observed responses less than expected), whereas others showed risk enhancement (observed responses larger than expected). We attributed risk alteration to the interference between the two consumers. Contradictory to theoretical predictions, total bacterial abundance in the two-consumer treatment did not differ from single-consumer treatments and consumer-free controls, due largely to risk reduction and compensatory responses within the bacterial assemblage. Decomposition of particulate organic matter was greater in the two-consumer treatment than the Paramecium single-consumer treatment, but did not differ among other treatments. These results suggest that the presence of multiple consumers may have unexpected impacts on the structure and functioning of bacterial communities.     

Photosynthetic production and exoenzymatic degradation of organic matter in the euphotic zone of a eutrophic lake

Photosynthetic production of organic matter, and its exoenzymaticdecomposition were studied in the euphotic zone of a naturallyeutrophic lake during early spring phytoplankton bloom, andafter its breakdown. Phytoplankton were the major biomass producerswhen algae were actively growing, and the algal fraction (>3.0µm) contributed on average 75–80% to the total biomassof microplankton. When the phytoplankton bloom began to declinebacterial biomass increased rapidly and, at the end of the bloom,bacteria contributed 48.7–69.98% to the total biomassof microplankton. The high bacterial abundance during phytoplanktonbloom breakdown followed the highest rates of glucose uptake,and the highest rates of alkaline phosphatase, leucine-amino-peptidase,ß-galactosidase and ß-glucosidase activities.The majority of enzyme activity was associated with the bacterialsize fraction of seston. The activities of free (dissolved inwater) exoenzymes were negligible. The synthesis of bacterialexoenzymes was under control of an induction/derepression mechanism,and depended on the amount of easily assimilable substrates,and/or the presence of polymeric organic compounds in the water,which served as substrates for exoenzymatic hydrolysis. Thetight metabolic coupling between bacterial exoenzymatic hydrolysisand uptake of low molecular weight substrates, and its ecologicalsignificance is discussed.     

An Examination of Cell Volume in Dominant Phytoplankton Species of the Central and Southern Adriatic Sea

The phytoplankton biomass expressed as total cell volume is often of doubtful value due to cell size and volume variations in the organisms present. Cell volume calculations for 95 phytoplankton species and volume-frequency diagrams for 25 dominant species were analyzed for the Adriatic Sea. Recommendations for more precise work dealing with phytoplankton cell volume and biomass are given. Temporal variations in the average microplankton cell volume are presented and discussed.     

Depth profiles of plankton,particulate organic matter and microbial activity in the eastern Canadian Arctic during summer

Summary Deep profiles of particulate organic matter, microplankton (phytoplankton and bacteria), zooplankton and their metabolic activities were investigated during two summer voyages to the eastern Canadian Arctic. Magnitudes and depth distributions were similar in many respects to observations from temperate and tropical waters. Strong gradients in most properties were observed in the upper 50–100 m and subsurface maxima were generally associated with the upper mixed-layer (>50 m). In addition to the general vertical decreases in plankton biomass and metabolic activity there was evidence for both rapid transport (sinking) of organic matter and for enhanced (above background) levels of microbial metabolic activity in deep waters (>500 m). Zooplankton depth distributions differed from the pattern generally observed at lower latitudes; in the Arctic, zooplankton abundance decreased to a lesser degree with depth than particulate organics and microplankton. The overwintering behavior of high-latitude zooplankton appeared to be the best explanation for their relatively high abundance at depth. Despite this, however, zooplankton apparently contributed little to the total column community metabolism.     

High-resolution spatio-temporal distribution of a coastal phytoplankton bloom using laser in situ scattering and transmissometry (LISST)

Development of optical observation technologies provides new insights into harmful algal bloom (HAB) detection and assessment of HAB species dynamics. Based on preliminary laboratory tests, a laser in situ scattering and transmissometry instrument (LISST-100X) was used to monitor a high-biomass phytoplankton proliferation in the field. Short-term spatial and temporal changes in particle size distribution were measured during a recurrent Alexandrium taylori outbreak. Since the bloom was not monospecific, a size-fraction method to discriminate particular species from LISST-100X measurements was proposed. The results were validated to simultaneous microscopic counts of phytoplankton, and the significantly positive correlation obtained between the two methodologies confirmed the instrument's ability to discriminate phytoplankton at the group and species level. The LISST-100X obtains high-resolution in situ data, and is therefore a better alternative than the traditional microscope for assessing temporal and spatial evolution of HABs. Field observations showed high variability over a short time scale associated with diel vertical migration of A. taylori and the whole phytoplankton population (nanoplankton and microplankton). A numerical circulation model was used to investigate the influence of beach hydrodynamics in the observed horizontal variability. Simulations of the model suggested an important role of daily coastal circulation in determining the distribution of A. taylori in coastal environments.     

Seasonal variation in composition and production of planktonic communities in the lower River Rhine

1. The composition and activity of phytoplankton, zooplankton and bacterioplankton in the lower River Rhine were measured in 1990 as part of an international biological inventory of the river. A seasonal study was carried out on two stations: one in the river mouth (km 1019) and one at the German/Dutch border (km 863). 2. High densities of phytoplankton (with up to 140 μg chlorophyll a 1-^?1) and occasional depletion of dissolved silicate were observed at the upstream station. Phosphate concentrations were also lowered during blooms. 3. Phytoplankton blooms, dominated by a few species of centric diatoms, declined one order of magnitude during downstream transport. During non-bloom conditions (low) algal densities were maintained during transport, or increased slightly, indicating the suitability of the river reach for algal growth. 4. Bacterial cell number and production (measured by the ³H-thymidine method) showed a broad summer maximum with activity peaks (0.5 nK < M thymidine h^?1) coincident with declining phytoplankton blooms. Winter values of bacterial production (0.02–0.05 n < Mh^?1) were substantial, probably as a result of allochthonous input of organic matter. 5. Rotifers and crustaceans made up the greater part of the zooplankton biovolume, but at the upstream station the contribution of Dreissena larvae and rhizopods was also substantial. High zooplankton biovolumes, of over 500 × 10⁶μm³1-^?1, were observed only during the phytoplankton spring bloom. 6. Quantitative relationships between the high phytoplankton production (2.1–3.4 gCm^?2 day^?1), the high bacterial substrate uptake (0.5–1gCm^?2 day^?1), and grazing were analysed for the growing season 1990. Algal grazing by metazoan herbivores was substantial only during spring, while the role of phagotrophic microplankton and cell lysis were indicated as major factors responsible for the downstream decline of phytoplankton blooms in the lower Rhine.     

Possible consequences of containing microplankton for physiological rate measurements

Ten experiments were done in oligotrophic North Pacific waters to examine the effects of small-volume, short-period containment (6–24 h) on plankton and their implications for productivity measurements. Effects of pre-filtering samples were also considered. Chlorophyll α and adenosine triphosphate were measured, but the major emphasis was on changes in the taxonomic composition and abundance of the microplankton.Chlorophyll α measurements indicate the variability of replicate samples increased significantly during incubation; the coefficient of variation of duplicate productivity measurements ranged between 3 % and 40 %. A large fraction of this may be due to increasing heterogeneity of the phytoplankton during incubation.Pre-filtering samples through 202, 102, 35 and 15μm mesh filters removed a small but consistent fraction of phytoplankton (as estimated by chlorophyll α) but a highly variable amount of total biomass (as estimated by ATP). The effect of pre-filtration on primary production was very inconsistent between experiments, varying both in magnitude and direction.The composition of the contained microplankton changed markedly during incubation. Nearly all components decreased in abundance regardless of pre-filtration treatment and some ciliate groups completely disappeared.     

Spatial distributions of dimethyl sulfur compounds,DMSP-lyase activity,and phytoplankton community in the East China Sea during fall

The spatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), DMSP-lyase activity (DLA) and their controlling factors including nutrients, phytoplankton community and bacterial abundance were investigated in the East China Sea (ECS) during fall from October 19 to November 2, 2015. Diatoms and dinoflagellates dominated the phytoplankton community, while other taxonomic groups were rare and mainly found in the oligotrophic open sea. Affected by the high nutrients concentrations, Chl a, DMS, DMSP and DLA showed high values in eutrophic inshore waters, and decreased from the costal zones to the open sea. Statistical analysis suggested that diatoms and dinoflagellates were the main controlling factors of DMS, DMSP, and DLA in ECS. For size-fractionated samples, a reduced contribution of the microplankton from inshore stations to offshore stations affected by the trophic conditions was noted. Meanwhile, this decrease in microplankton led to an increase in the ratio of DLA contributed by picoplankton and free-living bacteria from the estuary area to the offshore region. The DMS sea-to-air flux was calculated using the equation of Nightingale et al. (Glob Biogeochem Cy 14(1):373–387, 2000), and approximately 2.88 × 10^?2 Tg of sulfur was transferred from the sea into the atmosphere in the form of DMS in ECS during fall.     

Climate change and the timing, magnitude, and composition of the phytoplankton spring bloom

In this article, we show by mesocosm experiments that winter and spring warming will lead to substantial changes in the spring bloom of phytoplankton. The timing of the spring bloom shows only little response to warming as such, while light appears to play a more important role in its initiation. The daily light dose needed for the start of the phytoplankton spring bloom in our experiments agrees well with a recently published critical light intensity found in a field survey of the North Atlantic (around 1.3 mol photons m^?2 day^?1). Experimental temperature elevation had a strong effect on phytoplankton peak biomass (decreasing with temperature), mean cell size (decreasing with temperature) and on the share of microplankton diatoms (decreasing with temperature). All these changes will lead to poorer feeding conditions for copepod zooplankton and, thus, to a less efficient energy transfer from primary to fish production under a warmer climate.     

Differential grazing on protozoan microplankton by developmental stages of the calanoid copepod Eurytemora affinis Poppe

Nauplii and adults of the copepod Eurytemora affinis Poppe collectedfrom the Multiscale Experimental Ecosystem Research Center (MEERC)mesocosms and from the Choptank River (a subestuary of ChesapeakeBay) reduced ciliate and dinoflagellate microplankton densitiessignificantly during grazing experiments. Protozoan microplanktongenerally were consumed in proportion to their availability,although both adult copepod and naupliar clearance rates werehigher for larger prey ({small tilde}40µm). Ingestionof ciliate microplankton was confirmed by examining copepodgut fluorescence after brief (1 h) incubations with ciliateslabeled with a fluorescent vital stain (5-chloromethylfluoresceindiacetate). In addition, both adults and nauplii of E.affiniscleared protozoan microplankton at considerably higher ratesthan chlorophyll a. Naupliar clearance rates were generallyan order of magnitude lower than adult rates, but given naupliarabundances in copepod assemblages, they should contribute substantiallyto total grazing on protozoan microplankton. Grazing by thetotal copepod assemblage in mesocosms and in the field may beunderestimated if juvenile stages are ignored.     

SHORT-TERM EFFECTS OF UVB RADIATION ON CHLOROPHYLL FLUORESCENCE, BIOMASS, PIGMENTS, AND CARBOHYDRATE FRACTIONS IN A BENTHIC DIATOM MAT

The effects on UVB radiation on a subtidal, cohesive-sediment biofilm dominated by the diatom Gyrosigma balticum (Ehrenberg) Rabenhorst were investigated. Chlorophyll fluorescence parameters ( F _v/ F _m, φ_PSII), pigment concentrations, cell densities, and carbohydrate fractions were measured in four treatments (no UVBR, ambient UVBR, +7%, and +15% enhancement with UVBR). Enhanced UVBR was provided by a computer-controlled system directly linked to natural diel UVBR levels. Increases in φ_PSII values in the UVBR-enhanced treatments and a decrease in the steady-state fluorescence yield ( F _s) from the surface of the biofilms during the middle and latter part of daily exposure periods suggested that G. balticum responded to enhanced UVBR by migrating down into the sediment. Diatoms in the +15% UVBR treatment also had significantly higher concentrations of β-carotene after 5 days of treatment. Although G. balticum responded to enhanced UVBR by migration and increased β-carotene concentrations, significant reduction in maximum quantum yield of PSII ( F _v/ F _m) and in minimal fluorescence ( F _o) and decreases in cell densities occurred after 5 days. Concentrations of different carbohydrate fractions (colloidal carbohydrate, glucan, exopolymers [EPS]) associated with diatom biomass and motility also decreased in the UVBR-enhanced treatments. Short-term responses (migration) to avoid UVBR appear insufficient to prevent longer-term decreases in photosynthetic potential and biofilm carbohydrate concentration and biomass.     

Corticosteroid and thyroid responses of larval and juvenile turbot exposed to the water-soluble fraction of crude oil

Turbot larvae (24–590 degree C days; 2–32 days post-hatch) and juveniles (1345 degree C days; 98 days post-hatch), were exposed for 6 h to 25, 33 and 50% water-soluble fraction (WSF) of crude oil in either static or flow-through test systems. Larvae showed generalized primary endocrine responses, identified by elevated whole body cortisol content from as early as 2 days post-hatch. In older larvae and juveniles, the response was related to the WSF concentration. This dose-response relationship was not apparent in younger and yolk-sac larvae. Whole body thyroxine content of turbot larvae exposed to the WSF of crude oil was increased, but triiodothyronine content remained stable. Aromatic hydrocarbon concentrations [benzene, toluene, ethylbenzene and xylene (BTEX) and naphthalenes] remained constant during flow-through tests, but 65% of the initial level of BTEX hydrocarbons and 40% of the naphthalenes were lost during static exposures. Larval mortalities increased with exposure to an increasing concentration of crude oil WSF. Larval activity was significantly reduced even at the lowest WSF concentration.