Turbulence increases the risk of microcystin exposure in a eutrophic lake (Lake Taihu) during cyanobacterial bloom periods

Toxic cyanobacterial harmful algal blooms (CyanoHABs) have posed serious water use and public health threats because of the toxins they produce, such as the microcystins (MCs). The direct physical effects of turbulence on MCs, however, have not yet been addressed and is still poorly elucidated. In this study, a 6-day mesocosm experiment was carried out to evaluate the effects of wind wave turbulence on the competition of toxic Microcystis and MCs production in highly eutrophicated and turbulent Lake Taihu, China. Under turbulent conditions, MCs concentrations (both total and extracellular) significantly increased and reached a maximum level 3.4 times higher than in calm water. Specifically, short term (∼3 days) turbulence favored the growth of toxic Microcystis species, allowing for the accumulation of biomass which also triggered the increase in MCs toxicity. Moreover, intense turbulence raises the shear stress and could cause cell mechanical damage or cellular lysis resulting in cell breakage and leakage of intracellular materials including the toxins. The results indicate that short term (∼3 days) turbulence is beneficial for MCs production and release, which increase the potential exposure of aquatic organisms and humans. This study suggests that the importance of water turbulence in the competition of toxic Microcystis and MCs production, and provides new perspectives for control of toxin in CyanoHABs-infested lakes.     

Effects of the epibiotic heterotrich ciliate Mirofolliculina limnoriae and of moulting on faecal pellet production by the wood-boring isopods, Limnoria tripunctata and Limnoria quadripunctata

The heterotrich ciliate Mirofolliculina limnoriae occurs in an obligate association with wood-boring species of the isopod Limnoria. It attaches to the dorsal surface of the limnoriid pleotelson. Folliculinid-bearing populations of Limnoria tripunctata from the Ria Formosa, Portugal, and of Limnoria quadripunctata from Portsmouth, UK, were sampled. Up to four folliculinids were found on one individual of L. quadripunctata and up to twelve on L. tripunctata. There was no evidence that folliculinid load increased with host size. The nature of the epibiont/basibiont relationship was examined by observing animals with and without epibionts, kept individually with small sticks of wood in cell culture wells over periods of up to 15 days. Faecal pellet production and moulting were recorded. In both host species, feeding rate as measured by faecal pellet production was significantly lower in animals bearing folliculinids. Feeding rate also diminished with the onset of moulting, but returned to the original rate within a week after moulting. The estimated intermoult period for the population of L. tripunctata examined was about 25 days and for L. quadripunctata was about 32 days. However, the proportion of individuals moulting over the period of observation declined with increasing size in L. tripunctata, suggesting increasing length of intermoult period with age. As the host faces toward the blind end of its tunnel and ventilates the burrow with its pleopods, the folliculinids are well placed to intercept particulate food in the incoming water stream. There are no clear advantages for the host in the association, but the suppression of feeding and the potential of the folliculinids to hinder swimming during dispersal migrations indicate that the association should be viewed as ectoparasitism rather than mutualism or commensalism.     

Are the diatoms Navicula sp. and Thalassiosira fluviatilis suitable to be fed to the benthic harpacticoid copepod Tisbe biminiensis?

The objective of this study was to compare the influence of the diets of two diatoms, Navicula sp. (benthic) and Thalassiosira fluviatilis (planctonic), on the development, fecundity and survival of the harpacticoid copepod Tisbe biminiensis. In order to determine the optimal concentration of food, 35 egg-bearing females were submitted to six algal concentrations and controls (without food). After 24 h, the content of the recipients was fixed with 4% formalin and then fecal pellets produced by each female were counted and measured. The larval development was studied by surveying 50 nauplii on each diet individually until the adult stage, at intervals of 6 h. The cast exoskeletons were removed to count the number of segments and for measurement. The fecundity was obtained counting the naupliar production every 48 h of groups containing 10 females in different algal concentrations in both diets. The diet influence on fecundity was tested by submitting four groups of 10 females fed on optimal algal concentrations based on the fecal pellet experiments. In the Navicula sp. concentration of 0.4 μg Chl-a/ml, considered to be optimal for fecal pellets production, the diatoms were shown toxic, resulting in a low survival rate and inhibiting the egg production of copepods. The optimal concentration considering fecundity was estimated to be 0.1 μg Chl-a/ml for both diets. Copepods fed on Navicula sp. presented a faster development rate and higher naupliar production compared to copepods fed on T. fluviatilis. Size and survival did not vary significantly among diets. The algal concentration interfered significantly in the reproductive success of females. Both very low and very high algal concentrations reduced reproductive success. Concluding, the benthic diatom Navicula sp. was more favorable to the copepod T. biminiensis than the planktonic diatom T. fluviatilis.     

The influence of temperature variations and thermal pollution on various aspects of the biology of the prawn Palaemon pacificus (Stimpson)

The influence of different temperatures 10, 15, 20, and 25°C on the food consumption, growth, moulting rate, and respiration of Palaemon pacificus (Stimpson) from Langebaan Lagoon, west coast of South Africa, was studied under laboratory conditions. At 10°C mortality was high so that food consumption and moulting rate could not be determined as these were very low. At higher temperatures, food consumption was found to be temperature dependent, the rate at 25°C being twice that at 15°C. Growth rate was most favourable at 25°C. At 28°C growth rate was lower than at 20°C but higher than at 15°C. The intermoult period was 17 days at 15°C, and 11 and 10 days at 20, and 25°C, respectively. It seems that from an energetic point of view, 25°C is the most favourable temperature for P. pacificus. Several indices of growth efficiency at different temperatures are presented. The appearance of this prawn in South African west coast localities such as Langebaan during the summer and its disappearance during winter, can be explained by its temperature preferences. The possibility that thermal pollution from a nuclear power station may be beneficial to this prawn, is discussed.     

Turbulent mixing mediates the photosynthetic activities and biochemical composition of <Emphasis Type="Italic">Anabaena</Emphasis>: implications for bioengineering

Cyanobacteria exhibit a variety of adaptive strategies that allow them to thrive in ever-changing aquatic environments. Here, successive steady states of continuous cultures were used to investigate the effects of quantified turbulence on the biochemical compounds and physiological processes of Anabaena flos-aquae in a photobioreactor under different dilution rates. A rapid increase in cell density was clearly observed following an increase in the turbulent dissipation rate at all growth rates of A. flos-aquae. The photosynthetic response to irradiance curves showed that the turbulence-treated strains exhibited lower photosynthetic oxygen evolution and saturating irradiance as well as higher respiration in rapidly growing young cells, indicating that they might not be very adaptable to high turbulent dissipation rates. Additionally, there was an increase in the protein levels of A. flos-aquae with increasing turbulence at all growth rates, whereas carbohydrate formation and lipid accumulation demonstrated the opposite trends. At a high growth rate, the level of carbohydrates decreased whereas that of lipids increased, which was interpreted as reflecting an adaptation to the turbulent environment. These findings suggest that turbulence sensitivity is shear regimen- and growth rate-dependent in A. flos-aquae. The high respiration capacity, low saturating irradiance, and conversion of carbohydrates to lipids represent effective measures for revealing the adaptive strategies of rapidly growing young cells under hydrodynamic regimes. The results regarding optimum lipid accumulation with specific growth traits have important implications for the design of cultivation methods of cyanobacteria resource utilization with respect to regulating turbulence.     

Effect of hydrocortisone on the growth and development of larvae Tenebrio molitor

Hydrocortisone administered with the food causes inhibition of growth in larvae Tenebrio molitor. Hydrocortisone together with the reduction in the rate of growth retards the moulting cycle in larvae T. molitor. The action of hydrocortisone does not influence greatly the number of larvae moulting cycles.     

Relative importance of inefficient feeding and consumer excretion to organic carbon flux from Daphnia

1. Sloppy and inefficient feeding by zooplankton is generally thought to make a major contribution to the regeneration of the dissolved organic carbon (DOC) pool in aquatic environments. In this study, we tested experimentally the regeneration of DOC by a freshwater zooplankter feeding on two species of phytoplankton at different food concentrations and C : P ratios. We separated the DOC production because of inefficient feeding (pre‐ingestive regeneration) and zooplankton excretion and faeces release (postdigestive regeneration). 2. Within a brief incubation period (10 min), DOC production in the presence of Daphnia was not significantly different from that in the control treatment without grazers. During a longer incubation period (4 h), the amounts of radiocarbon retained in the algal cells per se were constant or were not different from those in the control treatments. These experimental results strongly suggest that inefficient feeding did not contribute significantly to DOC production in the grazer–prey system. 3. During the 4‐h incubation, calculations of the DOC per ingestion rate (i.e. DOC produced by Daphnia alone) showed that food concentration and algal species did not affect the relative DOC production, but there was considerable difference at different algal C : P ratios and grazer densities. We found that direct excretion of DOC by Daphnia occurred rapidly following food digestion and accounted for >65% of the total DOC production. Maximum DOC leakage from Daphnia faeces contributed less to DOC production than the grazer excretion, except under P‐limited conditions. 4. This study highlights the dominant role of postingestive process, especially the direct excretion by zooplankton, in DOC production in a grazer–prey system.     

A laboratory assay for measuring feeding and mortality of the marine wood borer Limnoria under forced feeding conditions: A basis for a standard test method

Quick simple testing methods are needed to evaluate alternative wood materials for marine construction because traditional borer resistant materials are becoming scarce or are no longer permitted due to concerns over environmental emissions of preservatives. Laboratory tests can provide species-specific information on rates of wood biodeterioration by wood borers under optimum conditions, in contrast to field trials where more than one borer species may be present and conditions are variable.The methodology described herein relies on the assumption that faecal pellet production rate in limnoriids must match feeding rate quite closely. Thus, the number of faecal pellets produced by individual specimens of Limnoria quadripunctata, while feeding on a non-durable and non-toxic wood species – Pinus sylvestris sapwood – in different test conditions, was monitored over a period of 15 days. Mortality and moulting were also registered. Several variables likely to affect survival and feeding rates were investigated in order to optimise the test conditions. Temperature and salinity regime affected both survival and feeding rates while moulting cycle affected feeding rates.The optimisation of this test methodology aims to provide the basis for a standard laboratory test with the wood-boring crustacean Limnoria.     

Growth in length of Mytilus edulis L. fed on different algal diets

Mytilus edulis L. was fed on different algal diets and the increase in shell length was measured every 12–24 h. The mussels respond within 12 h to major changes in the diet. When pre-starved mussels were fed every 24 h with monocultures of Tetraselmis suecica (Kylin) Butch, there was a pronounced lag period followed by a linear increase in shell growth rate. When both pre-starved and pre-fed mussels were fed on equal rations of T. suecica with concentrations ranging from 2.5 to 10.0 × 10⁷ cells · 1^?1, the growth rate levelled off at about the same rate. Within the same range of concentrations there was a linear correlation between final growth rates and algal cell concentration. Feeding with monocultures of Isochrysis galbana (Parke) or Thalassiosira pseudonana Hasle et Heimdal (Hustedt) gave approximately the same shell growth as with Tetraselmis suecica alone, while combinations of these three algal species produced significant synergistic effects. When filtrate only from T. suecica cultures was supplied to the mussels there was a rapid initial stimulation of the shell growth. Centrifugated cells of T. suecica which were resuspended in filtered sea water, homogenized and sonicated to rupture the cells, gave 13% less growth than with untreated cells (P < 0.05). The use of the accurate laser diffraction method for length growth measurements may greatly reduce the time and effort involved in growth experiments.     

Der metabolismus von 3H-α-ecdyson bei larven von Tenebrio molitor

The metabolism of ³H-α-ecdysone has been investigated in larvae of Tenebrio molitor within a moulting cycle. The metabolization occurs by hydroxylation, dehydration, and conjugation. A total of 8 metabolites including α- and β-ecdysone were found. Peak I was cleaved enzymatically up to 56%. The hydrolized part consists of esters of sulfuric- and glucuronic acid with compounds II and III, also with α-ecdysone and 3-dehydroecdysterone to a lesser degree.The hydroxylation of α-ecdysone to β-ecdysone is a very rapid one. Velocity and intensity depends on the physiological stage of the larvae. On days with a large endogenous hormone titer they are maximal and on days with a low endogenous titer they are lower. The rate of conversion of α- to β-ecdysone shows a correlation with the endogenous titer and vice versa.At a low endogenous titer the rate of excretion is very strong, in larvae aged to 2 to 5 days and also 7 to 8 days, 8 h after injection 50 to 80% of injected activity was recovered in the faeces. At the beginning of the moulting cycle 3% and at the 6th day 30% (hormone titer maximum) of activity is excreted. The unexpected high rate of excretion at the first day is compensated by increasing metabolism and storage.The faeces mainly consist of conjugates and α- and β-ecdysone. A correlation between the appearance of these compounds and the physiological stage of the larvae could be found. On those days with low endogenous titer the quota of ecdysone (α and β) is higher.     

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.     

Dietary influence on the biology and metabolism of Isotoma viridis (Collembola)

(1) Two groups of individually cultured Isotoma viridis were studied. They were given a diet of Tetramin fishfood and Pleurococcus algae respectively, in order to monitor individual changes in oxygen uptake during culture. (2) Growth rate, moulting frequency and the maximal live weight reached were higher when fed on Tetramin. (3) Egg production in the culture fed Pleurococcus was twice that fed on Tetramin, due to the more fertile intermoult periods without oviposition in animals fed Tetramin. The egg quality seemed to be lowered in the algae-fed animals rather less than in those fed with fishfood. (4) In both cultures, an increase of 35–40% of the metabolic rate at the start of the experiment was observed. This increase was maintained with a Tetramin diet, whilst it disappeared in cultures fed Pleurococcus. The F₁ generation of both groups showed an increased metabolic rate, that from Tetramin-fed being significantly higher than that from Pleurococcus-fed animals. (5) It is suggested that the initial increase in metabolism is a result of excess food, and the increased level of oxygen uptake in animals on a Tetramin diet the result of inadequacy of the composition of the fishfood for egg production, thus channelling the energy uptake mainly into growth and metabolism. (6) Neither Tetramin nor Pleurococcus are considered to provide an adequate diet for I. viridis, as reproductive success differed considerably from field conditions.     

A simple theory of algal deposition

SUMMARY. A model describing the deposition of algae in a turbulent environment is outlined, it being assumed that all algae falling on the bed are trapped there forever. Its main features are that, above a certain threshold of turbulence the rate of deposition is independent of the turbulent intensity, and the rate of algal loss by sedimentation, in such conditions, is described by a first order kinetic equation. The hydraulic conditions under which algae settle at their intrinsic, still-water rate and those for which the model is applicable, are examined. Some ecological implications of the model are discussed.     

Some effects of turbulence on the activity of the sea urchin Centrostephanus coronatus Verrill

Effects of turbulence on activity of the sea urchin Centrostephanus coronatus Verrill were studied using a new method referred to as the trip-thread method which recorded incidences of emergence from burrows during activity periods. During calm conditions, the number of C. coronatus emerging at 5 m depth was not significantly different from the number emerging at 15 m depth, representing 97% and 92% activity in the populations, respectively; however, during turbulent conditions, the number of individuals emerging at 5 m was significantly less than the number emerging at 15 m, representing 48% and 92% activity, respectively. These results suggest an inverse relationship between turbulence and activity. Although behavioral adaptations, such as reduced activity, allow urchins to occupy turbulent areas, extreme conditions may exclude them entirely. Differences in activity may affect grazing by sea urchins which can significantly affect the species composition and abundance of benthic communities.     

The seasonal succession and vertical distribution of the phytoplankton in Abbot's Pond,North Somerset,U.K.

Abbot's Pond provided constrasting environments through the year which supported differing algal populations. Permanent thermal stratification and the depletion of oxygen in the hypolimnion together with accumulation of nutrients within the latter provided two distinct regions that supported different algal populations. In the photic epilimnion, Chlamydomonas, Pandorina, Scenedesmus and Stephanodiscus formed dominant populations whereas in the lower regions, to where very little light penetrated, Cryptomonas rufescens and Trachelomonas volvocina formed dominant populations. The irregular occurrence of the “other main phytoplankters” indicated that their ecological niches were smaller than those of the Diatoms and Chlorophyceae which occur each year. Chrysococcus was able to develop large populations in conditions of low turbulence and to maintain itself again in low turbulent conditions at the limit of light penetration when turbulence did increase in the upper regions of the water column. The occurrence of the small Rhodomonas appeared to be associated with high nutrient levels in the water and not with temperature of water. Similarly Trachelomonas volvocina populations were associated with high nutrient levels but in conditions of very low oxygen levels, as were C. rufescens populations. Trachelomonas volvocina var. minuta occurred for the first time in 1969 and appeared to die as the water column became more stable and nutrient levels in the epilimnion fell. Therefore, growth of algal populations of Abbot's Pond was dependent upon the physical, chemical and biological factors found within the water column. The populations were characteristic of a eutrophic body of water, (Hutchinson 1967), (Moss & Karim 1969) and were usually large at most times of the year except November/December. The high biological production in the epilimnion (Hickman, in press) producing elaborated organic compounds was responsible for producing very large oxygen deficits in the hypolimnion. Thus, this high biological activity played an important role in determining the conditions found in the water and on what organisms would grow there.     

Acid Protease Production by Fungi Used in Soybean Food Fermentation

Growth conditions for maximum protease production by Rhizopus oligosporus, Mucor dispersus, and Actinomucor elegans, used in Oriental food fermentations, were investigated. Enzyme yields by all three fungi were higher in solid substrate fermentations than in submerged culture. The level of moisture in solid substrate must be at about 50 to 60%. Very little growth of these fungi was noted when the moisture of substrate was below 35%, whereas many fungi including most storage fungi generally grow well on solid substrate with that level of moisture. Among the three substrates tested—wheat bran, wheat, and soybeans—wheat bran was the most satisfactory one for enzyme production. The optimal conditions for maximum enzyme production of the three fungi grown on wheat bran were: R. oligosporus, 50% moisture at 25 C for 3 to 4 days; M. dispersus, 50 to 63% moisture at 25 C for 3 to 4 days; A. elegans, 50 to 63% moisture at 20 C for 3 days. Because these fungi are fast growing and require high moisture for growth and for enzyme synthesis, the danger of contamination by toxin-producing fungi would be minimal.     

Quantified small-scale turbulence inhibits the growth of a green alga

1. Laboratory experiments were conducted to elucidate the effect of small-scale turbulent fluid motion on the growth of laboratory cultures of the freshwater algae Scenedesmus quadricauda . Turbulent flow was generated using an oscillating-grid apparatus. The experiments were performed under the range of fluid flow conditions similar to those occurring in nature. The only growth limiting factor was the effect of small-scale fluid motion; all other environmental factors, such as light, temperature and nutrients, were kept constant.
2. Growth of Scenedesmus quadricauda , measured in terms of chlorophyll a concentration, was inhibited when the level of turbulence in the water column was increased. Algal growth was maximum in a quiescent fluid. The inhibitory effect of fluid motion was observed independently of flow regime (laminar, transitional, turbulent) in the water column.
3. Cell destruction and aggregation of dead and living cells of algae were observed in a turbulent flow. High shear rates, estimated from the dissipation of turbulent kinetic energy, caused the cell destruction, algal collision and agglomeration of algae. Data on Scenedesmus responses to small-scale fluid motion will enhance and broaden our ability to develop predictive multispecies models for freshwater phytoplankton communities.     

Biodeposit production by the mussel Mytilus edulis L. on rocky shores

Seasonal changes in the amount of biodeposit (faeces and pseudofaeces) produced by the mussel Mytilus edulis L., which is one of the representative suspension-feeders in the rocky intertidal and shallow subtidal regions of Mutsu Bay, were studied in the laboratory. The effects of water temperature, light, food concentration, flow rate, body size, age, and spawning on biodeposit production were investigated. More biodeposit was produced in summer than in other seasons. Throughout the year, the amount of biodeposit was positively correlated with body size. Relatively more biodeposit was produced by smaller than by larger individuals. A M. edulis population living in one square meter was estimated to produce 9.20 kg of faeces and 2.71 kg of pseudofaeces per year (dry wt). More biodeposit was produced at water temperatures of 17.6–20.2° C than at 4.5–7.6° C and 25.2–26.0° C. The optimum temperature for biodeposit production was found to be ≈ 20.0 °C. When kept in the dark, M. edulis produced more biodeposit than in the light. When food concentration is increased, more psuedofaeces are produced; the amount of faeces, however, remains constant. With increasing flow rate, the amount o f biodeposit per h increased but the biodeposition rate decreased. Larger amounts of faeces and smaller amounts of pseudofaeces were produced by younger mussels than by older ones of a similar size. Spawning also affected biodeposit production.     

Exclosure study on the exploitation of macrophytes by summering and moulting waterbirds at Lower Lake Constance

Owing to synchronous moult, most waterbird species are constrained by flightlessness and limited mobility for several weeks. As new feather production is energy demanding, these birds need to choose a safe moulting site with appropriate food supply. Up to 20,000 waterbirds carry out moult at Lake Constance, gathering at sites where they find food close to safe hiding places from predators and human-caused disturbance. In this study, we focused on the food supply at one prominent moulting site, Mettnau Südbucht, at Lower Lake Constance. We aimed to determine the food items and quantity as well as their utilization by summering and moulting waterbirds. We conducted experiments with exclosure cages which protected macrophytes from bird grazing and compared these sites with unprotected grazed sites. In these experiments, we found that the summering and moulting waterbird community, dominated by Eurasian Coots (Fulica atra Linnaeus), caused a significant decline of the macrophyte biomass at 1.5-m depth (MWL), where they were responsible for a loss of over 40% of the total charophyte biomass. No grazing effect was found at a greater depth (2-m MWL). The available food consisted mostly of Chara spp. with a biomass density of about 350 g m^?2. Animal food items were negligible: Macroinvertebrates, mainly Asellus aquaticus Linnaeus, that were associated with the macrophytes, made up only 2% of total biomass, and were very unevenly distributed.     

Importance of copepod faecal pellets to the fate of the DSP toxins produced by Dinophysis spp.

An ingestion experiment was carried out in Rı́a de Pontevedra (Spain) with the copepod Temora longicornis in order to determine ingestion rates of the DSP toxin-producers, Dinophysis spp. (Dinophyceae), and the excretion rate of Dinophysis spp. cells within the faecal pellets. Ingestion rate was a function of dinoflagellate abundance and did not vary with either the amount, or the composition of the co-occurring phytoplankton species in the food suspension. Faecal pellet production increased at higher food concentrations. Intact Dinophysis spp. cells representing 34.4% of the total Dinophysis cells ingested by the copepods were found within the pellets. T. longicornis was the only dominant copepod species in the area that fed on Dinophysis spp., thus the pellets produced by T. longicornis were the main source of copepod “toxic” pellets in the media during blooms of Dinophysis spp. These “toxic” pellets might contribute to the maintenance of the toxic algal blooms, if the cells inside the pellets remain viable, can spread the potential toxicity of the toxic dinoflagellates throughout the pelagic food web due to coprophagy, and/or be an important toxic vector into the benthic food web. However, during a Dinophysis spp. bloom, the percentage of cells excreted daily within the pellets was lower than 1% of the total dinoflagellate population and, moreover, copepod faecal pellets represent a small fraction of the sinking material in this area. Although it was not possible to measure the amount of toxins in the pellets, we concluded that copepod faecal pellets do not have an important role in the transport of DSP toxins through the food web in this area.