Enclosure Study Research Articles

Effects of golden perch (Macquaria ambigua (Richardson)) larvae, fry and fingerlings on zooplankton communities in larval-rearing ponds: An enclosure study

In the absence of fish, the plankton community in enclosures in a larval-rearing pond showed a marked successional pattern from rotifers and Moina to copepod and then Daphnia-calanoid dominance. The impact of growing larvae and fry, with densities of 40-118 m-2 at harvest, on zooplankton was conspicuous only after Day 22 when Daphnia became rare and calanoid numbers were suppressed. Predation by fry caused reductions in the size of Moina, cyclopoids and calanoids found. An increase in Daphnia size, 'gigantism', occurred because of limitations in the mouth gape of the fry. Low densities of fingerlings (0.65 g wet weight and stocked at 1 and 2 m-2) had little effect on zooplankton succession, whereas high density (15 fingerlings m-2) caused a shift to a zooplankton community dominated by small cladocerans, rotifers and cyclopoids. High fingerling density also caused a reduction in the size of the microcrustaceans found. The size and density of fish determined their impact on zooplankton composition and succession, demonstrating that similar starting times and consistency in fish density are necessary in obtaining 'sensible' statistical inferences in field fish-zooplankton experiments.

Separate and Combined Effects of Larval Walleye and Fertilization on Plankton Community Structure in Enclosures

ABSTRACT Community impacts of larval walleye (Stizostedion vitreum vitreum) and nutrient addition were examined in an experimental enclosure study. Larval walleye significantly suppressed Daphnia, Diaptomus and Cyclops, but enhanced rotifers. Suppression of zooplankton by larval fish alone did not increase phytoplankton blooms unless fertilizers were added. Nutrient levels (NH3-N, NO3N, and PO4-P) were enhanced in enclosures with fertilizer additions, but were not enhanced in enclosures with both fish and fertilizer additions. Fertilizer applications significantly increased phytoplankton biovolume, pH and dissolved oxygen, but did not increase zooplankton biomass. The highest algal abundance was found in enclosures with both fish and fertilizer additions. This could be due to the release of zooplankton grazing pressure by fish together with nutrient enrichment. Our results suggest that larval fish are important in regulating the zooplankton community, but their effects on phytoplankton depend on nutrient ...

Field Evaluation of the Littoral Ecosystem Risk Assessment Model's Predictions of the Effects of Chlorpyrifos

The Littoral Ecosystem Risk Assessment Model (LERAM) is described and evaluated using field data from a littoral enclosure study of the effects of the insecticide chlopyrifos. LERAM is a bioenergetic ecosystem effects model that links single species toxicity data to a bioenergetic model of the trophic structure of an ecosystem in order to simulate community and ecosystem level effects of chemical stressors. It uses Monte Carlo iterations of these simulations in order to calculate probabilistic ecological risk assessments of chemical stressors. The means and standard deviations of the model parameters were calibrated using data from the control enclosures in the field. LERAM produced reasonable representations of the ecosystems in the littoral enclosures

Clutch-size variability in Daphnia: Body-size related effects of egg predation by cyclopoid copepods

Cyclopoid copepods had unexpected effects on four species of Daphnia in an enclosure study. Small copepodites entered the brood pouch of large Daphnia and preyed on eggs. The resulting low clutch sizes could erroneously be ascribed to food limitation, but a clear difference between copepodite and food-limited populations could be seen when clutch sizes were plotted vs. body lengths. Food limitation resulted in consistently lower egg numbers for all individuals; egg predation resulted in large variability of clutch sizes because individuals were randomly affected by the copepods. Only small copepodites could enter brood pouches, and only large daphniids were affected. Daphniids below a body size of 2.25 mm were immune to egg predation regardless of species or size at first reproduction. This unusual mechanism of size-selective invertebrate predation (affecting large cladocerans) may explain unexpected results found in field studies.

Body-size related survival of cladocerans in a trophic gradient: an enclosure study

Body-size related survival of cladocerans in a trophic gradient: an enclosure study

Statistical Comparison of Seasonal Trends for Autocorrelated Data: A Test of Consumer and Resource Mediated Trophic Interactions

A 2 × 2 factorial enclosure study of food web biomanipulation was conducted in 1986 and again in 1987 to assess the relative importance of fish and nutrients on zooplankton biomass and size, chlorophyll-a concentration, and water clarity. Seasonally autocorrelated data were analyzed using Kendall's median trend slopes and compared with a randomization test. These results were then compared to the within-subjects effects from repeated measures analysis of variance (ANOVAR). Both methods produce complimentary conclusions when contrasting the different results between years

Giant marine viruses?

Giant marine viruses?

Microhabitat Utilization, Feeding Periodicity, Home Range and Population Size of the Banded Sculpin, Cottus carolinae

Underwater observations were used to examine the microhabitat utilization, feeding periodicity, home range and population size of Cottus carolinae, the banded sculpin, in the Little River of eastern Tennessee. Most sculpins resided under rocks during the day, but on tops of rocks at night. Analyses of the gut contents indicated that C. carolinae fed primarily at night. Underwater counts of individually marked sculpins suggested these fish have a small average home range, with a maximum of 47 m2. Based on a mark-recapture enclosure study and the Jolly-Seber mark-recapture method, mean density estimates for C. carolinae were 0.4 and 0.9 fish/m2, respectively. U NDERWATER observations in coral reefs and lentic environments have shown that the ecology and behavior of fishes are intimately

Microbial response to crude oil and Corexit 9527: SEAFLUXES enclosure study

The response of marine bacteria to Corexit 9527, with and without Prudhoe Bay crude oil labeled withn-(1-(14)C)hexadecane, in a temperate pelagic environment was monitored over 22 days using controlled ecosystem enclosures. The results indicated that Corexit and Corexit-dispersed crude oil stimulated bacterial production by serving as substrates and/or by inducing the release of organic compounds from the indigenous phytoplankton population. Highest bacterial standing stock was observed in the enclosure treated with a mixture of Corexit and crude oil, in which a large fraction of the predominant bacterivores were eliminated. Biodegradation appeared to be more significant than abiotic processes in contributing to the loss of low volatility n-alkanes in Corexit-dispersed oil. Twenty-two days following its addition, 50% of the radiotracer was recovered: 3% in the suspended particulate fraction, 10% in sedimentary material, 36% as CO2, and less than 1% in the dissolved organic pool.

Seasonal and daily activity patterns in a Canadian population of the prairie rattlesnake, Crotalus viridus viridis

The seasonal and daily activity patterns of a Saskatchewan population of Crotalus viridus viridis is presented. Snakes emerged from hibernation in late April and migrated into the surrounding river valley and upland regions in early May. Adult migration preceded that of immature age-classes. Several gravid females occupied a rookery near the hibernaculum during the summer months and remained there until parturition. Females did not occupy this site in successive years and may have a biennial or greater reproductive cycle. Snakes returned to the hibernaculum in early September and remained active until early October. The behaviour of snakes in a field enclosure in response to time of day and body temperature (Tb) was recorded during the spring, summer, and fall. Significant differences in the Tb values of sunning, movement, and shading behaviours were noted. Gravid females were significantly more active in all seasons. However, no significant difference in mean Tb was found between males and females in the field, enclosure study, or laboratory thermal gradient. The observed greater level of activity may reflect the high energy demands of gravid females.