1994. Zooplankton assemblages in the Ohio River: seasonal, tributary, and navigation dam effects. Can. 1. Fish. Aquat. Sci. 51 : 1634-1 643.Ohio River zooplankton were collected monthly or quarterly for 1 yr from littoral and pelagic (main channel) areas in three navigation pools (constricted and floodplain) with four intrapool locations (lower pool and above, below, and within major tributaries). Total densities were minimal (1.64/L) when discharge and turbidities peaked (December-April) but were relatively high otherwise (21.63/L). Seasonal rises in rotifer density preceded increases in cladocerans and cspepods; rotifers were nearly twice as abundant as cladocesans and copepods. Diversity (species richness) was not correlated with temperature, velocity, or turbidity. Density was positively linked with temperature and negatively correlated with river velocity and turbidity. Diversities in littoral and pelagic areas were not different, but densities were higher nearshore (mostly copepods and cladocerans); rotifers were usually more common in the main channel. Neither proximity to low-head navigation dams nor channel morphology had detectable effects on zooplankton. Although total diversity and density were similar in tributaries and the main channel, rstifers were more abundant in tributaries, and the Ohio contained more cladocerans and copepods. Densities in the Ohio were greater below than above tributaries for rstifers and cladocerans but lower for copepsds, primarily because of nauplii.Le zooplancton de la riviere Ohio a fait B'objet de pr6levernents mensuels ou trimestriels pendant 1 an dans des regions Bittorales et pelagiques (chenal principalj dans trois bassins de navigatisn (etranglement et plaines inondables) avec quatre emplacements 2 l'interieur du bassin (bassin inferieur et au-dessus, en dessous et A l'interieur des principaux tributaires). Les densites totales sont minimales (I ,64/L) lsrsque le debit et la turbidite sont au maximum (decembre A avril), mais relativement elevees dans les autres cas (21,63/L). Les augmentations saissnnieres de la densite des rotiferes precedent les augmentations de la densite des cladoc&res et des copepodes. L'abondance des rotif&res est pr$s de deux fsis plus elevee que celle des cladoceres et des copepodes. Aucune corr4iation n'a ete sbservee entre la diversite (richesse des especes) et la temp&ature, la vitesse ou la turbidite. On a observe une correlation positive entre la densit6 et la temperature et une correlation negative entre la densite et la vitesse du cours d'eau et sa turbidite. Aucune difference n'a 6te observee sur B e plan de la diversite entre les regions fittorales et pelagiques; cependant, les densitks sont plus elevees prPs du rivage (pour l'essentiel, copkpodes et cIadocPresj. tes rotiferes sont en gknbral plus repandus dans le chenal principal. Ni la proximite des barrages de canalisation A faible hauteur de charge, ni la morphologie du chenal ne semblent avsir d'effet detectable sur le nsoplancton. Si I'sn a observi. des valeurs similaires pou...

It has been proposed that morphological defenses against predation have demographic costs. We measured the cost of a predator-induced morphological defense, using predaceous phantom midge larvae Chaoborus americanus (Insecta, Diptera) and the prey species Daphnia pulex (Crustacea, Cladocera). The induced defense is a neck tooth (and other pleiotropic structures) developed in juvenile D. pulex in the presence of C. americanus. Laboratory life table experiments, in the absence of predation, indicated the population growth rate of typical D. pulex was 11% to 39% greater than that of D. pulex exposed to C. americanus extract, or C. americanus-conditioned water. The reduction in population growth rate was most frequently associated with an increase in the time between birth and first reproduction. Induced individuals required twenty more hours at 23°C, and twenty five more hours at 20°C, to develop to the age of first reproduction. Under limiting food conditions age-specific survivorship and the number of offspring produced per female by the induced form were reduced relative to the typical form. As a result, the difference in population growth rates among forms was greater at the low food level as indicated by a highly significant food by form interaction effect. In addition to neck teeth and lowered reproductive rates, the offspring of induced form individuals had significantly longer tail-spines (7.2-7.5%), and primiparous adults from the induction treatment were significantly shorter than controls (3-8%).

Results from a laboratory life-table study show Daphnia pulex has a unique set of rapidly induced responses to waterborne chemicals from each of two predator species.

Plankton ecologists often kill and fix zooplankton specimens for future study. The standard protocol used by limnologists is a sucrose-formalin solution first recommended by Haney and Hall (1973). This solution is an aqueous solution of 4% formalin (final concentration) and 40 g of sucrose per liter. Commercially available formalin is a 37% by weight, or a 40% by volume, aqueous solution. Thus, a 4% formalin solution is a 1.5% formaldehyde solution.The 4% formalin solution was recommended because it reduced morphological distortion, even of soft animals like Daphnia, while taking advantage of fixation and preservation properties of formalin. Minimum distortion is particularly desirable in studies of size-selective predation or reproductive rates, in which eggs need to stay in the brood chamber of branchiopods. Whereas there are advantages of formalin fixation, there also exists significant human health concerns for formaldehyde exposure.Acute effects of exposure-The effects of greatest interest to limnologists are caused by inhalation and contact. The greatest acute exposure occurs during analysis of samples when the limnologist looks at plankton samples through a microscope, often for hours at a time. Labs are often poorly ventilated, leading to increased exposure through inhalation of formalde-hyde vapors. This inhalation is highly irritating to the upper respiratory tract and eyes.According to the United States Occupational Safety and Health Administration (OSHA 2001), concentrations of 0.5 to 2.0 ppm (in air) may irritate the eyes, nose, and throat of some individuals. Concentrations of 3 to 5 ppm also cause tearing of the eyes and are intolerable to some persons. Concentrations of 10 to 20 ppm cause difficulty in breathing, burning of the nose and throat, cough, and heavy tearing of the eyes, and 25 to 30 ppm causes severe respiratory tract injury leading to pulmonary edema and pneumonitis. A concentration of 100 ppm is immediately dangerous to life and health. Deaths from accidental exposure to high concentrations of formaldehyde have been reported. AbstractA 4% formalin-40% sucrose solution has been used by limnologists for three decades as the preferred freshwater zooplankton preservative because it kills and fixes cladocera (Branchiopoda) with relatively little distortion. Because of the increasing evidence of health hazards related to formalin, we sought an alternative, safer preservative that satisfies the need for low distortion. Our results suggest the ethanol preservative methods (70% and 95% treatments) are as good or better as using 4% sugar formalin to fix and store samples. Our results indicate the best method is to fix samples in 95% EtOH followed by storage in 70% EtOH. This technique gave us the least frequent distortion, the highest average number of eggs per female, and the fewest embryos lost from the brood chamber. None of the techniques appeared to have positive or negative effects on body length. Using hot water to fix animals before storage is not recommended. *

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Plankton ecologists often kill and fix zooplankton specimens for future study. The standard protocol used by limnologists is a sucrose-formalin solution first recommended by Haney and Hall (1973). This solution is an aqueous solution of 4% formalin (final concentration) and 40 g of sucrose per liter. Commercially available formalin is a 37% by weight, or a 40% by volume, aqueous solution. Thus, a 4% formalin solution is a 1.5% formaldehyde solution.The 4% formalin solution was recommended because it reduced morphological distortion, even of soft animals like Daphnia, while taking advantage of fixation and preservation properties of formalin. Minimum distortion is particularly desirable in studies of size-selective predation or reproductive rates, in which eggs need to stay in the brood chamber of branchiopods. Whereas there are advantages of formalin fixation, there also exists significant human health concerns for formaldehyde exposure.Acute effects of exposure-The effects of greatest interest to limnologists are caused by inhalation and contact. The greatest acute exposure occurs during analysis of samples when the limnologist looks at plankton samples through a microscope, often for hours at a time. Labs are often poorly ventilated, leading to increased exposure through inhalation of formaldehyde vapors. This inhalation is highly irritating to the upper respiratory tract and eyes.According The OSHA statement concerning short-term contact is that "formalin is a severe skin irritant and a sensitizer. Contact with formalin causes white discoloration, smarting, drying, cracking, and scaling. Prolonged and repeated contact can cause numbness and a hardening or tanning of the skin. Previously exposed persons may react to future exposure with an allergic eczematous dermatitis or hives."Acute exposure and hypersensitivity-Some individuals have an allergic-like response to formaldehyde. In our experience, a few students have developed a red rash or difficulty breathing immediately after exposure to low levels of formaldehyde. In one case, a student developed hives <1 min after a dropper bottle of formalin solution was opened in a large and wellventilated room. Another student experienced extreme tachycardia when exposed to imperceptible fumes. A colleague that AbstractA 4% formalin-40% sucrose solution has been used by limnologists for three decades as the preferred freshwater zooplankton preservative because it kills and fixes cladocera (Branchiopoda) with relatively little distortion. Because of the increasing evidence of health hazards related to formalin, we sought an alternative, safer preservative that satisfies the need for low distortion. Our results suggest the ethanol preservative methods (70% and 95% treatments) are as good or better as using 4% sugar formalin to fix and store samples. Our results indicate the best method is to fix samples in 95% EtOH followed by storage in 70% EtOH. This technique gave us the least frequent distortion, the highest average number of eggs per female, and the fewest embryos ...

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