Valve closure responses of the Asiatic clam Corbicula fluminea exposed to cadmium and zinc

The valve movement patterns of immobilized Asiatic clams (Corbicula fluminea) were monitored during exposure to constant concentrations of cadmium (0.0, 0.1, 0.2, 0.3, and 0.4 mg 1^–1) or zinc (0.0, 0.1, 0.3, 0.5, and 0.9 mg 1^–1) for 24 h following a 24-h acclimation period. Data indicate that the duration of response was concentration dependent and toxicity related. Durations of periods with valves parted declined as the concentration of heavy metal increased. Behavior was consistent for both mean time to first closure following the initial exposure and mean time per valve parting episode over a 24-h exposure period. Mean time per valve parting episode during the 24-h exposure period ranged from 600 minutes for control trials to 36 and 69 minutes for the highest concentrations of cadmium and zinc tested, respectively. There was no association between durations of periods with valves sealed and solutions of cadmium; however, lengthening durations of periods with valves sealed coincided with exposure of clams to progressively more concentrated zinc solutions. In addition, Asiatic clams demonstrated a greater rate of response (decline in the duration of periods with valves parted) to progressively more concentrated solutions of cadmium than to comparable increases in the concentrations of zinc solutions.     

The biochemical composition of the larvae of two strains of Artemia salina (L.) reared on two different algal foods

A sequential carbohydrate, protein, and lipid method of analysis has been used to determine the biochemical composition of freshly hatched and 48-h old larvae of two strains of the brine shrimp Artemia salina (L.). During a 48-h starvation period the percentage of carbohydrates and lipids of freshly hatched larvae decreases whereas the ash content increases by 40–100%. When fed with dried Scenedesmus or dried Spirulina for 2 days after hatching the protein level of the larvae increases significantly and the relative increase in ash content is lower than in the case of starvation.Amino acid analyses of the algal food and the unfed and fed larvae did not show any change except for the absence (below detection) of methionine in the starved nauplii.The fatty acid pattern of 48-h old Artemia larvae is different from that of freshly hatched nauplii both in unfed and fed larvae; in the latter case it seems to be determined to a large extent by the fatty acid composition of the food.     

A new method of monitoring ventilatory activity in mussels and its use in a study of the ventilatory patterns of Mytilus edulis L.

An apparatus for measuring pumping rates in mussels, based on the delivery of exhaled sea water into a constant flow of fresh water, is described. When food is available, pumping is continuous for several days although there are signs of satiation after ≈ 1 wk. When food is withdrawn pumping does not cease for several hours especially in animals which have been food-deprived for some time before feeding. Food-deprived mussels often fail to pump for periods of > 24 h and ventilatory bursts are carried out at flow rates well below maximum. Shell valve movements and diffusion of oxygen through the gape between open valves can supplement ciliary ventilation.     

Interaction of mineral elements in sea water and shell of oysters (Crassostrea virginica (Gmelin)) cultured in controlled and natural systems

The interaction is reported of selected chemical elements (cadmium, calcium, copper, iron, magnesium, manganese, strontium, and zinc) in cultured sea water, with soft tissues, prismatic calcite of the right valve, and foliated calcite of right and left valves of genetically similar American oysters, Crassostrea virginica (Gmelin) grown in a natural habitat and in two environmentally controlled experimental systems (flow-through and recycle). The addition of trace elements as algal nutrients in ambient sea water was reflected in higher concentrations of trace metals in shells and soft tissues of oysters grown in experimental systems. Calcium was relatively uniformly distributed in major regions of valves from the three habitats, even though its concentration fluctuated widely in sea water in experimental systems. Magnesium and strontium were most concentrated in valves of oysters grown in the recycle system (magnesium in the prismatic layer of the shell and strontium in the foliated calcite). Iron was uniformly distributed. Cadmium, copper, manganese, and zinc were most concentrated in the prismatic calcite of valves from the flow-through system. In soft tissues, calcium was more concentrated in oysters from experimental systems than in those from the natural habitat. Manganese was about equally distributed in soft tissues from the three habitats, whereas copper and iron were more concentrated in soft tissues in experimental systems than in the natural habitat, and were many times more concentrated in soft tissues than in valves from all three habitats. As concentrations of magnesium, strontium, mangenese, zinc, and cadmium increased in valves in experimental systems, pigmentation of valves decreased. The study confirmed the capacity of oysters to concentrate several elements in their valves as concentration of these elements increased in ambient sea water and disclosed the heterogeneous distribution of these elements in major regions of the valves.     

Comparison of rates of feeding and biodeposition of the American oyster,Grassostrea virginica Gmelin,fed different species of phytoplankton

The feeding and biodeposition rates of small (2.4 cm) and large (5.2 cm) Crassostrea virginica were differently affected in experiments using flowing systems by moderate (292 μ C/1 sea water) and high (487 μ C/1 sea water) concentrations of the following phytoplankton: the diatoms, Thalassiosira pseudonana (Hasle & Heindal) (Cyclotella nana), Skeletonema costatum (Greville) Cleve, Nitzschia closterium (Ehrenberg) Wm. Smith, and the green alga, Dunaliella tertiolecta Butcher.The average feeding rate of the oysters on the different phytoplankton was: Dunaliella < Nitzschia < Skeletonema < Thalassiosira. In contrast, oysters fed on Thalassiosira had the lowest rate of biodeposition (1.626 × 10^?3 g ash-free dry wt/g dry flesh wt per day) but oysters cultured on Nitzschia showed the highest rate of biodeposition (2.952 × 10^?3 units).The response of the feeding rate of the two sizes of oysters to food concentration differed according to the algal food source. Oysters fed on Thalassiosira and Skeletonema exhibited a higher feeding rate at a higher food level: in contrast, oysters fed on Nitzschia showed no significant differences and those cultured on Dunaliella a depressed feeding rate at the higher food concentration. We observed no differences in feeding rate between small and large oysters fed on Skeletonema and Dunaliella, but small oysters had a higher feeding rate than large oysters when cultured on Thalassiosira and a lower feeding rate when fed on Niitzschia. The smaller size of Thalassiosira and larger size of Nitzschia might account for these differences in the feeding efficiency of small oysters.The biodeposition rates of both sizes of oysters were also affected by food concentration of the different algae. At the high food concentration with Skeletonema, Nitzschia, and Dunaliella, all oysters showed a marked increase in the rate of biodeposition, but oysters fed on Thalassiosira exhibited no great change. On all species of phytoplankton, the larger oysters produced greater biodeposition than the smaller oysters.These differences in response of feeding and biodeposition rates are important to our knowledge of food chain dynamics and may be used to optimize aquaculture systems.     

Changes in biochemical and hemocyte parameters of the Pacific oysters Crassostrea gigas fed T-Iso supplemented with lipid emulsions rich in eicosapentaenoic acid

The aim of this study was to assess the effect of dietary eicosapentaenoic acid (20:5n-3) on hemocyte parameters such as hemocyte concentration, phagocytosis, and non-stimulated reactive oxygen species (ROS) production in Pacific oysters Crassostrea gigas, as well on proximate biochemical and fatty acid compositions. One-year-old oysters (C. gigas) were fed T-Isochrysis aff. galbana (T-Iso), which is low in 20:5n-3, either alone or with supplements of a lipid emulsion rich in 20:5n-3 at 1%, 10% or 50% (dry weight of the algal ration) for up to 7 weeks. Changes in gill fatty acid composition demonstrated that the lipid emulsion was well ingested by oysters during the dietary conditioning. Biochemical analysis indicated that oysters fed supplements of 50% and, to a lesser extent, 10% lipid emulsions had a higher total lipid content compared with oysters fed other diets, suggesting a more advanced reproductive status for the oysters fed high doses of lipid emulsion. Moreover, some oysters in these two treatment groups spawned during the last three weeks of the seven-week feeding experiment. Lipid supplements had a significant influence on hemocyte concentration, phagocytic index and non-stimulated hemocyte ROS production. After 4 weeks, highest hemocyte concentrations were found in oysters fed on a supplement of 50% lipid emulsion compared with those fed on other diets but the hemocytes derived from these oysters had the lowest short-term phagocytic index. After 7 weeks of dietary conditioning, the ROS production in non-stimulated hemocytes of oysters fed 10% and 50% lipid emulsion declined. These results suggested that 20:5n-3, and perhaps its eicosanoid metabolites, affected oyster hemocyte functions; however, the reproductive status of oysters may also have interfered with the 20:5n-3 dietary effect.     

How does time since feeding affect the fuels pigeons use during flight?

Time between meals can vary from multiple hours to days within and among species. We investigated the effects of time since feeding on lipid, protein, and carbohydrate oxidation in flying pigeons (Columba livia) by interpreting changes in blood plasma metabolite concentrations and mass during flight. Five pigeons were flown or rested for 4 h after food deprivations of 2, 12, 24, and 48 h. After flight, blood plasma concentrations of uric acid and beta-hydroxybutyrate were elevated over control and preflight values, indicating elevated protein and lipid catabolism during flight. Lipid oxidation, as indicated by changes in beta-hydroxybutyrate concentration, increased more in unfed flying pigeons compared with recently fed flying pigeons and with resting controls. Protein oxidation, as indicated by changes in uric acid concentrations, also positively covaried with feeding time; the covariation was mostly caused by increases in 48-h food-deprived pigeons. Unfed birds lost less mass during a 4-h flight than recently fed birds. We reasoned that recently fed pigeons oxidized more glycogen in flight than pigeons not recently fed; calculated glycogen stores explained 72%-117% of mass loss differences between 2- and 48-h-fed pigeons. Thus, time since feeding was an important determinant of the fuels pigeons used in flight.     

The effect of feeding frequency on utilization of algal nutrients by the marine herbivore, the luderick, Girella tricuspidata (Quoy and Gaimard)

Utilization of whole algae, lipid, protein and total nitrogen and total carbon by the luderick, Girella tricuspidata , fed ad libitum were found to be comparable with published results obtained for other species. Periods of food deprivation were found to cause reduced efficiency of utilization for all nutrients measured, with a 4–day deprivation period having a greater effect than a 24–h deprivation period.
Only animals fed ad libitum were able to obtain a greater amount of lipid from their food than was defaecated. Utilization of protein and non–protein nitrogen is similar in fish fed ad libitum , but a greater reliance upon the non–protein nitrogen content of the food for nutrition is apparent when the fish are subjected to periods of food deprivation. Nitrogen utilization, relative to other nutrients, by fish subjected to periods of food deprivation is greatest immediately after a feeding bout. Total carbon utilization relative to other nutrients increases with increasing time of deprivation following a feeding bout.
It is suggested that these changes in nutrient utilization with time after feeding are the result of rapid utilization of the nitrogen–rich cell contents, followed later by utilization of the algal cell wall.     

Changes in proportions of acetate and carbon dioxide used as methane precursors during the anaerobic digestion of bovine waste

In an anaerobic digestor which was fed daily with bovine waste, during the early stages after feeding (4 to 7 h) acetate (via the methyl group) accounted for almost 90% of the methane produced. As time after feeding increased, acetate declined as a precursor so that in the 12- to 14-h and 21- to 23-h periods, after feeding the methyl group accounted for 80 and 73% of the methane produced, respectively. Measurements of methane production from CO2 reduction showed that in the 2- to 12-h period after feeding, CO2 accounted for 14% of the methane produced, whereas in the 12- to 24-h period it accounted for 27-5%. These results show that the percentages of methane accounted for by acetate and CO2 vary with time after feeding the digestor.     

Changes in proportions of acetate and carbon dioxide used as methane precursors during the anaerobic digestion of bovine waste.

In an anaerobic digestor which was fed daily with bovine waste, during the early stages after feeding (4 to 7 h) acetate (via the methyl group) accounted for almost 90% of the methane produced. As time after feeding increased, acetate declined as a precursor so that in the 12- to 14-h and 21- to 23-h periods, after feeding the methyl group accounted for 80 and 73% of the methane produced, respectively. Measurements of methane production from CO2 reduction showed that in the 2- to 12-h period after feeding, CO2 accounted for 14% of the methane produced, whereas in the 12- to 24-h period it accounted for 27-5%. These results show that the percentages of methane accounted for by acetate and CO2 vary with time after feeding the digestor.     

The use of supplementary foods by Australian magpies Gymnorhina tibicen: Implications for wildlife feeding in suburban environments

Abstract The provision of foods to wild birds is an extremely common practice among householders throughout the Western world. Nonetheless, concerns over potential impacts of the practice are currently being raised, including the possibility that some species may become reliant on human‐provided food. We compared the foraging and breeding ecology of pairs of fed and unfed Australian magpies Gymnorhina tibicen living in suburban environments in Brisbane, Queensland, Australia. Detailed behavioural observations of both foraging and chick provisioning were made for males and females of both groups throughout the breeding season. Natural foods dominated the diets of both fed and unfed magpies, making up 76% and 92% of all items consumed respectively. During the morning, fed magpies obtained fewer food items during ground foraging than did unfed birds, apparently because they visited suburban feeding stations more often during the early part of the day. At other times, the amount of food items obtained during foraging was similar for both fed and unfed birds. Magpies utilizing suburban feeding stations started all breeding activities significantly earlier than unfed magpies, except during the fledgling phase. Both fed and unfed magpie parents provisioned their chicks predominantly with natural food. Magpies were not reliant or dependent on supplementary food provided by wildlife feeders at any time during the breeding season. Although many magpies did utilize suburban feeding stations extensively, they continued to forage for and provision their chicks with natural food.     

Effect of feeding regimen on diurnal variation of breathing movements in late-gestation fetal sheep

There is a diurnal variation in the mean incidence and amplitude of fetal breathing movements (FBMs) in sheep after approximately 120 days gestation. To determine whether this variation is caused by diurnal fluctuations in plasma glucose or prostaglandin (PG) concentrations, we studied two groups of pregnant sheep fed either once daily at 1100 h or every 2 h for 24 h. Maternal and fetal blood samples were taken every 2 h from 0900 to 0900 h the next day for assay of plasma glucose and PGE2 and PGF2 alpha concentrations. FBMs were recorded throughout the 24 h. The mean fetal plasma glucose concentrations of the once-daily and multifed groups were not different, but there was a significant difference between the two groups in the 24-h pattern of fetal glucose concentrations. In the once-daily fed group, plasma glucose concentrations reached a peak 8 h after maternal feeding and then declined, whereas in the multifed group, fetal plasma glucose concentrations reached a plateau and were constant from 1300 to 0900 h the next day. Fetal plasma PGE2 and PGF2 alpha concentrations did not show a significant change with time of day in either group. There was a significant diurnal variation in the incidence and amplitude of FBMs in each of the two feeding groups, and the 24-h pattern of FBMs did not differ significantly between groups. Therefore it would appear that the diurnal variation of FBMs is not a consequence of the maternal feeding regimen or diurnal changes in plasma glucose or PG concentrations.     

Daily patterns of mRNA expression of two core circadian regulatory proteins, Clock2 and Per1, and two appetite-regulating peptides, OX and NPY, in goldfish (Carassius auratus)

The aim of this study was to examine the daily hypothalamic mRNA expression profiles for two core circadian regulatory proteins, CLOCK2 and PER1, and for two neuropeptides that regulate wakefulness and food intake, OX and NPY, in goldfish. The profiles were determined for fish at different nutritional states (i.e. fed or unfed on sampling day) and held at different photoperiods (i.e. 16L:8D photoperiod vs. constant light LL). Our results show that under a 16L:8D photoperiod, both fed and unfed goldfish exhibit clear antiphasic daily rhythms of hypothalamic Clock2 and Per1 mRNA expression levels, whereas under LL, daily Clock2 rhythms are seen in both fed and unfed fish while significant rhythms of Per1 mRNA expression only persist in unfed fish. In fish held under 16L:8D, but not under LL, there was significantly higher Per1 expression in fed fish at feeding time than in unfed fish. Daily variations in hypothalamic OX mRNA expression levels with peaks observed prior to both feeding time and the onset of darkness, were displayed under a 16L:8D photoperiod, whereas exposure to LL resulted in lower expression levels with no significant daily variations. Fish held under LL, but not under 16L:8D, showed significant daily variations in NPY mRNA expression with a peak prior to feeding time. Taken together, our results suggest that the mRNA expression of both appetite-regulating and circadian proteins display daily variations and that these patterns can be affected by external cues such as feeding and photoperiod.     

Time-dependent transition probabilities and the assessment of seasonal effects on within-day variations in chewing behaviour of housed sheep

State transitions in the chewing behaviour of six half-breed (?le de FrancexTexel) yearling female sheep (Ovis aries L.) were studied by using jaw movements recorded continuously over 5 days at the end of a number of experimental periods from 21 September 1992 to 4 April 1993. The sheep were housed in individual pens. Each of them received the same diet, that is, 250 g/day of concentrate mix (15.5% crude protein (CP), 36.5% neutral detergent fibre (NDF)) fed at 0900 h and natural grass hay (6.7% CP, 69.1% NDF) fed ad libitum at 0915 and 1600 h. Mineral salt blocks and water were continuously available. The main objective was to assess seasonal effects on within-day variations in the chewing behaviour of sheep, at small to large time scales within a day. We therefore focused on two experimental periods characterised by contrasting conditions of daylength and temperature (i.e., 'Period 1': 610 min daylight, mean temperature of 10.9 degrees C, and 'Period 4': 550 min daylight, mean temperature of 7.2 degrees C). In particular, differences between periods in the nycterohemeral pattern of chewing behaviour and the quality of forecasts of chewing states were tested. We submitted our data to a new method of analysis that we developed: the method of time-dependent transition probabilities, and compared the results to those obtained using other methods that were available in the literature.Overall, the sheep spent more time eating in Period 1 than in Period 4. Specifically, a secondary peak in eating activity, which was observed in the early afternoon in Period 1, was absent in Period 4. The nycterohemeral pattern of eating activity showed significant differences between periods, at the main rhythmic component of 24 h and at short components around 2 h. Such differences were not observed for ruminating and idling activities. The quality of forecasts of chewing states decreased from Periods 1 to 4, in terms of accuracy (based on R(2)) and lead of reliable forecasts (i.e., &z.sfnc;forecast-observation&z.sfnc;<0.1). The most (least) accurate forecasts were obtained for the ruminating (eating) state in both periods. We have attributed the differences that we found between periods to daylength instead of temperature because the sheep were mostly within the thermoneutral zone in our study. By comparison, using mean hourly times of eating activity, significant differences between periods were detected for the 24-h rhythmic component and the 4-h component, instead of the 2-h component, probably because of aliasing (i.e., when the sampling time interval used is longer than suited; the minute was found to be a suitable interval length in the calculation of time-dependent transition probabilities). Using the age-dependent model of Rook and Penning, minor differences between periods were detected. On that basis, the method of time-dependent transition probabilities may be brought forward as a complement of value to existing methods of behavioural data analysis.     

Does the diurnal pattern of enteric methane emissions from dairy cows change over time?

Diet manipulation and genetic selection are two important mitigation strategies for reducing enteric methane (CH₄) emissions from ruminant livestock. The aim of this study was to assess whether the diurnal pattern of CH₄ emissions from individual dairy cows changes over time when cows are fed on diets varying in forage composition. Emissions of CH₄ from 36 cows were measured during milking in an automatic (robotic) milking station in three consecutive feeding periods, for a total of 84 days. In Periods 1 and 2, the 36 cows were fed a high-forage partial mixed ration (PMR) containing 75% forage, with either a high grass silage or high maize silage content. In Period 3, cows were fed a commercial PMR containing 69% forage. Cows were offered PMR ad libitum plus concentrates during milking and CH₄ emitted by individual cows was sampled during 8662 milkings. A linear mixed model was used to assess differences among cows, feeding periods and time of day. Considerable variation was observed among cows in daily mean and diurnal patterns of CH₄ emissions. On average, cows produced less CH₄ when fed on the commercial PMR in feeding Period 3 than when the same cows were fed on high-forage diets in feeding Periods 1 and 2. The average diurnal pattern for CH₄ emissions did not significantly change between feeding periods and as lactation progressed. Emissions of CH₄ were positively associated with dry matter (DM) intake and forage DM intake. It is concluded that if the management of feed allocation remains constant then the diurnal pattern of CH₄ emissions from dairy cows will not necessarily alter over time. A change in diet composition may bring about an increase or decrease in absolute emissions over a 24-h period without significantly changing the diurnal pattern unless management of feed allocation changes. These findings are important for CH₄ monitoring techniques that involve taking measurements over short periods within a day rather than complete 24-h observations.     

Sutural loosening and skeletal flexibility during growth: determination of drop-like shapes in sea urchins

The shape of sea urchins may be determined mechanically by patterns of force analogous to those that determine the shape of a water droplet. This mechanical analogy implies skeletal flexibility at the time of growth. Although comprised of many rigid calcite plates, sutural collagenous ligaments could confer such flexibility if the sutures between plates loosened and acted as joints at the time of growth. We present experimental evidence of such flexibility associated with weight gain and growth. Over 13-, 4-, and 2-week periods, fed urchins (Strongylocentrotus droebachiensis) gained weight and developed looser sutures than unfed urchins that maintained or lost weight. Further, skeletons of fed urchins force-relaxed more than did those of unfed urchins and urchins with loose sutures force-relaxed more than those with tight sutures. Urchins (Strongylocentrotus franciscanus) fed for two and a half weeks, gained weight, also had looser skeletons and deposited calcite at sutural margins, whereas unfed ones did not. In field populations of S. droebachiensis the percentage having loose sutures varied with urchin diameter and reflected their size-specific growth rate. The association between feeding, weight gain, calcite deposition, force relaxation and sutural looseness supports the hypothesis that urchins deform flexibly while growing, thus determining their drop-like shapes.     

Protocols for thawing and cryoprotectant dilution of heart valves

PURPOSE: To reduce the time taken for thawing and removal of cryoprotectant from heart valves. METHODS: Three sets of experiments were carried out using porcine heart valves. The valves in all three experiments were first exposed to 10% (v/v) dimethyl sulphoxide (DMSO) by a 2-step protocol. Outcome was determined after the various experimental treatments by monitoring the outgrowth of cells from valve leaflet explants. Experiment 1-Dilution protocol. Valves exposed to 10% DMSO were subjected to 4-, 2- or 1-step dilution to remove the DMSO. Experiment 2-Warming rate. The rate of warming was increased by reducing the volume of cryoprotectant medium in which the valves were frozen. Valves were exposed to 10% DMSO, frozen in different volumes (100, 50, 25 or 0 ml) of cryoprotectant medium, and warmed in a 37 degrees C water bath. The DMSO was removed by 4-step dilution. Experiment 3-Standard vs. Modified protocol. Valves were either frozen in 100 ml 10% DMSO, thawed, and subjected to 4-step dilution (Standard) or frozen in 50 ml 10% DMSO, thawed, and the DMSO removed by single-step dilution (Modified). RESULTS: Neither the rate of warming nor the rate of dilution of DMSO had any influence on the subsequent outgrowth of valve leaflet fibroblasts. There were no differences in the outgrowth of cells from valve leaflets cryopreserved by the Standard or Modified protocols. CONCLUSION: The time taken for thawing and dilution of heart valves could be reduced from >20 min to <10 min without detriment to the viability of the leaflet fibroblasts. This should have a positive impact on valve replacement surgery as the thawing and dilution of valves are typically carried out while the patients are on cardiopulmonary bypass.     

Effects of feeding frequency and sugar concentrations on lifetime reproductive success of Meteorus pulchricornis (Hymenoptera: Braconidae)

Many species of parasitoids can increase their reproduction through feeding on supplemental sugar sources. We evaluated the longevity both with and without hosts and progeny production of a uniparental strain of Meteorus pulchricornis by varying concentration of the sugar solution and feeding frequency. A 1:1:1 sucrose–glucose–fructose-mixture was tested in a range of concentrations (0–70% (w/v)). The parasitoid lifespan did not increase with the concentration of sugar solutions, but parasitoids feeding on a 30% sugar solution attained greater longevity than parasitoids feeding on other sugar concentrations in the absence of hosts. The same effect of sugar concentration was also observed on progeny production, where when the parasitoid was fed 30% (w/v) sugar solution, its lifetime progeny production doubled in comparison to that fed water, and increased by 50% compared to those fed the other sugar solutions. In the last experiment, we studied the effect of feeding intervals on the longevity and progeny production of M. pulchricornis. Parasitoids fed with a 30% (w/v) 1:1:1 sucrose–glucose–fructose-mixture continuously lived six times longer than unfed parasitoids, three times longer than parasitoids fed only once and two times longer than parasitoids fed once every two days in the absence of hosts. Parasitoids with continuous access to the sugar solution produced considerably more progeny than those with fewer feeding frequencies. This increasing progeny production was accomplished more through an increase in daily offspring production rather than through extending reproductive lifespan.     

Behaviour of Scrobicularia plana (Da Costa) in water of various salinities

Valve movements, heart and pumping rates have been recorded from Scrobicularia plana (Da Costa) when transferred stepwise from natural sea water to sea water of S = 30% (termed 100%) and then to 80, 60, 40, and 20% sea water, and after direct transfer from 100 to 20% Scrobicularia exhibits short periods of pumping alternating with short ventilatory pauses down to 40% sea water. These are termed activity cycles and contrast with periods of complete quiescence each ≈ 4–12 h long. The heart rate of animals in these salinities is fairly constant during activity cycles. When transferred to 20% sea water, either directly or gradually, short pumping phases alternate with long ventilatory pauses during the initial 72 h. At the same time the heart rate shows wide variation during activity cycles.On transference from 100 to 60% sea water, the valves opened and valve activity pattern returned to normal within 30 min and within 6 h of transfer from 60 into 40% SW. Transfer to 20%, whether stepwise or directly, resulted in valves remaining closed initially for ≈ 10 or 34 h, respectively before opening gradually to expose the mantle margin. The valve adductions were then of reduced frequency and extent.     

Effects of a macroalgal mat (Ulva lactuca) on estuarine sand flat copepods: an experimental study

The effects of a macroalgal mat (Ulva lactuca) on intertidal sand flat copepods were studied in Jamaica Bay, NY. In 1999, Ulva was removed from paired quadrats in the algal mat. Density and species richness were estimated from sediment cores over seven biweekly periods and compared with Ulva-removal quadrats and with an unvegetated reference site. In a separate analysis at the same site, species composition and density of all copepods within the algal mat were determined from replicated quadrat samples over seven dates. Emergence traps were deployed in all treatments in 1999 to quantify copepod movements from sediments into the water column during flooding tide. Dissolved oxygen (DO) was continuously monitored over several 96-h periods in and above the algal mat. In 2000, three biomass levels of Ulva (0, 100, 200 g DW per m²) were added to paired quadrats in the unvegetated zone. Density and species richness were estimated over eight time periods. Ulva removal resulted in significant increases in density and species richness, but levels remained lower than at the unvegetated site. Likewise, addition of Ulva biomass produced significant declines in copepod density. However, the differences between low- and high-Ulva-addition treatments were insignificant. Increases in phytal copepods after Ulva addition did not compensate for losses of epibenthic and infaunal species. The overall effect of the Ulva mat was a net loss of copepod density, including the loss of nearly all infaunal species. Anoxia in sediments and within the algal mat are correlated with declines in infaunal species and with escape by some infaunal species from the sediment into the water column.