Showing papers in "Limnology and Oceanography in 1979"

Chroococcoid cyanobacteria in the sea: A ubiquitous and diverse phototrophic biomass1

Abstract: In the photic zone of the open sea, procaryotic cells with an ultrastructure typical of chroococcoid cyanobacteria and similar sized populations of autofluorescent bacteria (0.5–1.0 × 1.0 µm) were observed at concentrations usually between 103–104 cells per ml. The ubiquitous ultrastructural type was an orange-autofluorescing, phycoerythrin-containing cyanobacterium amenable to culture. Two other morphological types which have not been cultured occur sporadically in larger concentrations, one apparently favoring deeper water. These phototrophs can account for about 20% of the total bacterioplankton biomass and from 6 to 15% of the total microbial plankton. These cells may play a significant role in oceanic primary productivity.

Sulfate reduction in a New England salt marsh1

Abstract: Sulfate reduction rates were measured for 2 years in the peat of a salt mars by a radiotracer technique. Rates are high throughout the peat, from the surface to more than 20 cm deep. The integrated annual rate is about 75 mol SO/sub 4//sup 2 -/.m/sup -2/.yr/sup -1/, the highest yet reported for any natural ecosystem. Sulfate reduction accounts for the consumption of 1800 g org-C.m/sup -2/.yr/sup -1/, about equal to net primary production in the marsh. Respiration using other electron acceptors (such as oxygen or nitrate) is much less important. Sulfate reduction rates in the peat of the salt marsh are probably high for at least three reasons: the belowground production of Spartina alterniflora provides a large, annual input of organic substrates over a depth of some 20 cm; sulfate is rapidly resupplied to the peat in infiltrating tidal waters, so that sulfate depletion never limits the rate of reduction; and sulfide concentrations remain below toxic levels. The stable pyrite (FeS/sub 2/) is a major end product of sulfate reduction in the marsh peat while iron monosulfide (FeS) is not. If the incorporation of /sup 35/S into pyrite were not measured, the (/sup 35/S)SO/sub 4//sup 2 -/ reduction measurements more » would greatly underestimate the true rate of sulfate reduction. Pyrite acts largely as a temporary store of reduced sulfur, with seasonal changes in its concentration. « less

A modification of the Hynes method for estimating secondary production with particular significance for multivoltine populations

Abstract: The accepted procedure for de termining production of multivoltine invertebrates by use of the Hynes method is to multiply the Hynes value by the number of generations per year. For aquatic insects, if pupal, adult, or egg stages comprise a significant portion of total generation time, this procedure will underestimate production. For crustaceans, if reproduction occurs before attaining the final size class, the procedure, using generation time, will overestimate production. It is necessary to multiply the Hynes value by 365/CPI, where CPI is the cohort production interval (in days) from hatching to the attainment of the largest aquatic size class.

Arsenic speciation in seawater and interstitial waters: The influence of biological-chemical interactions on the chemistry of a trace element1

Abstract: Four species of arsenic were found in samples of seawater and interstitial water from the northeast Pacific and the continental borderland off southern California: arsenate, arsenite, methylarsonate and dimethylarsinate. All were present in the photic zone, with a good correlation between photosynthetic activity and the concentration of the methylated arsenicals. There is less arsenite in the surface waters than in the deep waters, suggesting biological uptake and transport. A sharp increase of arsenate at the base of the photic zone indicates rapid regeneration of this species. In the deep waters arsenate is dominant, but arsenite is still present in excess of equilibrium concentrations. No arsenic biomethylation was found in the interstitial waters of oxic and anoxic sediments, but arsenite was present there. In Santa Barbara Basin arsenite accounts for 20% of the arsenic in the interstitial water, the highest proportion found. Total arsenic is lower in the interstitial than in the overlying waters, suggesting removal of arsenic into the solid phases by adsorption of coprecipitation. Biological-chemical interactions and the kinetics of redox reactions are important in influencing the speciation of arsenic.

Predation, competition, and zooplankton community structure: An experimental study1,2

Abstract: An experimental investigation of the zooplankton community of a small Minnesota pond was conducted for 2 years to determine the mechanisms maintaining its structure and to show that it is predictably organized. A mechanistic interpretation of the structure of this community cannot be made solely on the basis of predation, but also requires evaluation of the relative competitive abilities of the herbivores. The presence of Chaoborus and fish place predictable constraints on the abundance of zooplankton species in this pond. The competitive dominant (Cerioduphniu reticulata) is of intermediate size and is removed when either predator is abundant. In the presence of intense Chaoborus predation, Cerioduphniu is replaced by a larger subordinate competitor, Daphnia pulex; when fish predation is intense, smaller species (Rosminu Zongirostris and rotifers) increase. These small species are also able to maintain large populations in vertebrate-free environments when Chaoborus is rare. When these small herbivores are abundant, two additional invertebrate predators (Cyclops vernalis and Asplunchnu priodontu) arrive, neither of which seems able to reduce its prey to extinction. Recent studies provide ample evidence that predator-prey interactions are of major significance in structuring freshwater zooplankton communities (see Hall et al. 1976). Vertebrate planktivores (fish and salamanders) feed visually and remove the largest and most conspicuous zooplankton (Brooks 1968; Werner and Hall 1974; Zaret and Kerfoot 1975; O’Brien et al. 1976); invertebrate predators (predaceous copepods and rotifers, midge larvae, and Leptodora) cannot handle the large herbivores but prey extensively on small species (Dodson 1974a; Fedorenko 197%; Kerfoot 1977); when vertebrates are present the larger, more conspicuous invertebrate predators are replaced by smaller, less conspicuous ones (Dodson 1970, 1974a). These generalizations form the bases for recent conceptual models of zooplankton community structure (Dodson 1974a; Zaret in prep.). However, despite their success at predicting the distribution of different zooplankton species, these models are phenomenological in i Contribution 172 from the Limnological Research Center, University of Minnesota. 2 Work supported by National Science Foundation grant EMS 74-19490 to J. Shapiro. nature. The information they are based on does not allow a mechanistic interpretation of zooplankton community structure. For instance, while it is well documented that large herbivores disappear when vertebrate planktivores are introduced to a community, no data exist to determine whether their extinction is entirely a result of direct removal by vertebrates. It is possible that vertebrates, through their effects on the rest of the community, may impose other deleterious conditions on the large herbivores (e.g. increased competition with riewly established smaller herbivores). Furthermore, there is no direct evidence that invertebrate predation can be sufficient to cause extinction of small herbivores. Finally, the role of herbivore competition in structuring zooplankton communities is poorly understood (Lynch 1977a), and nothing is known about competition between invertebrate predators. To eliminate these ambiguities in interpreting zooplankton community structure, I examined simultaneously the predatory and competitive interactions in the community of a small Minnesota pond. Here I report on the mechanisms determining the relative abundances of species in this pond and show that the

Ammonium adsorption in nearshore anoxic sediments1

Abstract: The distributions of dissolved, exchangeable, and fixed ammonium were measured in sediment cores from Long Island Sound, Florida Bay, and Pettaquamscutt River, Rhode Island, and in laboratory experiments to determine the importance of ammonium adsorption in anoxic sediments. Apparently, a “dynamic equilibrium” exists between dissolved, exchangeable, and fixed ammonium in sediments. The concentration of exchangeable ammonium increased linearly with increasing concentrations of dissolved ammonium; exchangeable ammonium adsorption was rapid, reversible, and predominantly associated with the organic matter rather than the clay minerals. The concentration of fixed ammonium also increased with increasing concentrations of dissolved ammonium, but this change, due to diagenesis, is small compared to the total fixed ammonium in sediments and is also smaller than the corresponding increase in exchangeable ammonium. The ammonium adsorption coefficient for Long Island Sound sediment was between one and two: of the ammonium produced by organic matter decomposition, as much or twice as much is associated with the sediment as is dissolved in the interstitial water. Therefore, ammonium adsorption by sediments is an important process in the diagenesis of nitrogen in nearshore anoxic sediments.

Nitrate and phytoplankton production in southern California coastal waters1

Abstract: The transport of nitrate into the euphotic zone appears to be a major factor regulating the standing stock and production of phytoplankton in southern California coastal waters. The evidence is as follows. (1) The rate of photosynthetic carbon assimilation is proportional to the rate of nitrate assimilation and to the ratio of nitrate;total N assimilated. (2) The phytoplankton standing stock (g C.m/sup -3/) and its production rate are related to the depth of the vertical nitrate concentration gradient. (3) The chemical composition of the particulate organic matter, as the POC:PON ratio, is related to the carbon:nitrogen assimilation ratio of the phytoplankton. (4) Regenerated production, measured as ammonium assimilation, is proportional to the nitrate assimilation rate, implying parallel and concurrent increases in the production of heterotrophic microplankton and phytoplankton attending new imputs of nitrate into the euphotic zone. (5) The vertical diffusion of nitrate, when calculated from the vertical nitrate concentration gradients and nitrate assimilation rates, appears to give reasonable estimates of the vertical eddy diffusivity coefficient for nitrate.

Bacterial populations and adaptations in the mucus layers on living corals1

Abstract: The external mucus layers of the stony coral Porites astreoides and the soft corals Palythoa sp. and Heteroxenia fuscesens are inhabited by communities of marine heterotrophic bacteria. Population levels of bacteria in coral mucus may be regulated by the self-cleaning behavior of the host. Bacterial populations in coral mucus respond to stresses applied to the host coral by growing to higher population levels in the mucus, indicating that these are populations of viable organisms closely attuned to host metabolism. Members of these microbial populations utilize the mucus compounds and may play a role in processing coral mucus for reef detritus feeders. One such species, Vibrio alginolyticus, grows rapidly on Heteroxenia mucus, is attracted to dissolved mucus, and possesses a mechanism to maintain itself on the coral surface.

Microbial Transformations of Sulfur-Compounds in a Stratified Lake (Solar Lake, Sinai)

Abstract: Microbiological and chemical aspects of the sulfur cycle were studied in the chemocline of a tropical salt lake. Oxygen and sulfide coexisted in a O-lo-cm layer which migrated up and down during a diurnal cycle. Sulfide was rapidly oxidized by oxygen, with a half-life of 5-10 min, to produce mainly sulfate and thiosulfate. Thiosulfate and elemental sulfur had concentration maxima in the chemocline while polysulfide was abundant throughout the sulfide zone. Radiotracer experiments showed that the elemental sulfur was produced by anoxygenic photosynthesis in cyanobacteria. The elemental sulfur was further oxidized or again reduced, depending on the presence or absence of oxygen. Cyanobacteria in the che- mocline shifted between anoxygenic photosynthesis in the morning and oxygenic photosyn- thesis in the afternoon. A high dark CO, fixation was found in the chemocline which could be stimulated by sulfide, elemental sulfur, and thiosulfate. The oxidation rate of sulfide in the chemocline was dependent on the presence of bacteria.

Release of weak and strong copper-complexing agents by algae1

Abstract: By means of potentiometric titrations, the copper-complexing properties of organic compounds released by 21 algal species are characterized. Most eucaryotic species released measurable amounts (10/sup -6/ M) of copper-complexing agents that could be modeled as weak organic acids with log)*K/sub CuL./ = 0.5. Of seven blue-green algal species studied, four produced about 5 x 10/sup -7/ M concentrations of strong copper-complexing agents with conditional stability constants in the range 10/sup 8/ to 10/sup 12/; two produced complexing agents similar to those produced by the eucaryotes. In time-course experiments with three chlorophytes and two cyanophytes, the release of measurable concentrations of copper-complexing agents occurred principally during stationary phase.

Nutrient dependence of primary productivity in lakes1

Abstract: An analysis of growing season measurements of daily primary productivity, chlorophyll, water chemistry, and transparency from 58 north temperate lakes shows a strong correlation between volumetric rates of photosynthesis, chlorophyll, and nutrients. Mean daily rates of photosynthesis per unit volume euphotic zone, v, are correlated with mean chlorophyll concentration (r2 = 0.80). The mean daily rate of photosynthesis at optimal depth, Āopt, is highly correlated with mean total P(r2 = 0.95), and with mean total N(r2 = 0.91). In contrast, integral rates of photosynthesis are linked less tightly to nutrient concentration because of their simultaneous dependence on transparency. The Dillon-Rigler phosphorus loading model is extended to predict volumetric rates of photosynthesis (v and Āopt) in lakes where the N:P balance indicates control by phosphorus (N:P ⩾ 13).

Composition of mucus released by coral reef coelenterates1

Abstract: Mucus from selected Red Sea coelentcrates was analyzed for protein, polysaccharide, lipid, monosaccharides, and amino acids. While the proportions of the macromolecular fractions of the different mucins varied widely, the individual makeup of the component proteins and polysaccharides was more uniform. The appearance and transformation of liquid mucus into mucus floc or web material was revealed by scanning electron microscopy (SEM). Observations on the mucus web-forming coral Porites astreoides from Barbados suggested that sediment capture is at least partly responsible for the apparent denaturation of secreted mucus and the transformation of liquid mucus into particulate detritus.

Effects of elevated nitrogen and phosphorus on coral reef growth1

Abstract: Long term phosphate (2 ..mu..M) and nitrogen (20 ..mu..M urea + ammonium) enrichment of a patch reef at One Tree Island, Great Barrier Reef, caused > 50% suppresson of reef calcification. This is attributed primarily to the phosphate. It is suggested that this effect is involved, together with algal competition and the more usually accepted depression of temperature, in reducing the growth rate of reefs adjacent to upwellings. It is possible that the effect was more general during the first half of the Holocene transgression.

A relation between lake morphometry and primary productivity and its use in interpreting whole-lake eutrophication experiments

Abstract: Rates of primary production during the ice-free season expressed per unit volume of epilimnion were linearly related to the ratio of epilimnion sediment area to epilimnion volume in unfertilized lakes in the Experimental Lakes Area (ELA), northwestern Ontario This ratio is mathematically equivalent to the probability of retention of sedimenting particles in the epilimnion of a lake divided by the mean depth of the epilimnion and is a measure of the nutrient recycling rate of a lake Evidence indicates that epilimnetic nutrient recycling in ELA lakes is dominated by processes occurring at the sediment-water interface and not within the sediment The relationship between the ratio of sediment area to epilimnion volume and primary production is used as the basis for interpreting whole-lake eutrophication experiments In comparison to control lakes, the ratio of production to chlorophyll in the experimental lakes was high when chlorophytes dominated and low when cyanophytes dominated Lakes that were fertilized with both nitrogen and phosphorus had much higher chlorophyll concentrations and productivities than control lakes Lakes that receive either of these nutrients alone showed weaker responses Both elements appear to be in short supply relative to the metabolic requirements of phytoplankton Phosphorus control is still the keymore » to controlling eutrophication« less

Quantitative description of steady state, nutrient‐saturated algal growth, including adaptation

Abstract: Steady state, nutrient-saturated phytoplankton growth can be quantitatively described by four equations: an empirical equation relating growth rate ~1, to absorbed irradiance [; a different equation relating b and 4 derived from the empirical equation relating instantaneous rate of gross photosynthesis to irradiance; an empirical equation relating the respiratory rate constant R, to growth rate; and an equation stating the approximate constancy of the ratio &JO of the light saturation parameter & of the photosynthetic light curve and the C:Chl a quotient 8. The equations involve eight constant parameters which were evaluated for Chlorella pyrenoidosa from data in the literature. The four equations do not incorporate an cmpirical description of the adaptive parameter functions &&) or @(CL,). However, the equations can be solved simultaneously to obtain these functions. The derived functions agree with the experimental ones for C. pyrenoidosa. Since the equations not only describe respiration and the light curves of growth and photosynthesis, but also predict &, and 8, they constitute an improved model of nutrient-saturated algal growth: given any irradiance, the equations predict 11.8, R,, &,, and 8 and the specific light curve of photosynthesis. The model provides a necessary foundation for subsequent description of nutrient-limited growth in culture and in nature.

Marine snow: Microscale nutrient patches1

Abstract: Measurements of ammonia, nitrite, nitrate, and phosphate indicate significant differences in nutrient concentrations associated with marine snow from those of the surrounding water, In eight sets of nutrient measurements, ammonia was more concentrated in aggregates in seven sets, nitrite in three sets, and nitrate in one set, Phosphate was more concentrated in one set, but less concentrated in three sets. Aggregates represent nutrient micropatches ranging in size from

Organic carbon export from upland and forested wetland watersheds1

Abstract: Export of organic carbon per unit runoff from five small, eastern North Carolina watersheds with considerable swamp drainage was severalfold higher than the export rates from upland watersheds reported in the literature This reflects the higher concentrations of organic carbon, especially dissolved forms, in swamp waters and is probably attributable to increased contact time between water and organic debris as well as to concentration effects of high evapotranspiration in swamps

The role of sediments and bryophytes in phosphorus dynamics in a headwater stream ecosystem1

Abstract: Streambed sediments and the bryophyte community are sites of retention and processing of dissolved phosphorus (DP) in Bear Brook, an undisturbed headwater stream in the Hubbard Brook Experimental Forest. Sorption of DP by sediments in an equilibrium phosphorus concentration for silty and sandy sediments was equal to the mean ambient DP concentration (2 micrograms P/liter). The buffering capacity of the sediments was at a maximum in the pH range characteristic of Bear Brook. Silty sediments had a higher phosphorus buffering capacity than sandy sediments, and leaf-leachate phosphorus was sorbed less than orthophosphate. Phosphorus sorption increased as sediment particle size decreased and as aluminum and organic matter content increased. The microbial community appears to be a relatively minor component of phosphorus buffering capacity in these sediments.

Denitrification in a salt marsh ecosystem1

Abstract: The rate of denitrification measured throughout the year in various habitats of a New England salt marsh was correlated to temperature and was highest in the wettest habitats. Over 60% of the denitrification took place in the muddy creek bottoms. Annual denitrification exceeds nitrogen fixation. An amount of nitrate similar to the quantity consumed by denitrifiers is supplied by the flow of groundwater into the marsh and by nitrifiers within the marsh itself.

Estimating cladoceran birth rates: The importance of egg mortality and the egg age distribution1

Abstract: An equation independently derived by Edmondson and Paloheimo for estimating instantaneous birth rates without a knowledge of mortality rates has been extensively employed by zooplankton ecologists. This expression is exactly true only under the unlikely conditions that the age distribution is stable and that egg mortality is equal to that averaged across the entire population. Here I compare estimates of instantaneous birth rates ( h )using the Edmondson-Paloheimo equation to those determined with a general model which accounts for age structure instability and egg mortality in two Daphnic~ pulr~x populations. Despite the fact that the assumptions of the Edmondson-Paloheimo model are rarely met, it mimics the seasonal pattern of b quite well, with few exceptions. An analysis of variance suggests that the model will provide an adequate approximation of the true population birth rate when a variance in b of 0.003 can be tolerated. A much more critical factor in the analysis of instantaneous rates in plankton populations is the development of accurate sampling techniques. Key n,ord.s: birth rutes; Clrrdoc~eru; Daphnia pulex; dr,nzogrcrphy; egg rc~tio; rotifcrs; ;ooplanXton. A great deal can often be inferred about the factors h,,, = INN, + C,) In(N,) regulating population densities from measures of two n population parameters, the instantaneous birth and mortality rates, h and m. The estimation of h has been --In(l + E ) (2) D thought to be particularly simple for planktonic cladocerans and rotifers whose adulta bear live young (Edmondson 1968). The attractiveness of both of these which are easily enumerated in preserved samples and expressions lies in their independence from m which whose egg development rates are simple functions of is often the final product of interest. Given an additemperature. Edmondson (1960) first introduced the tional estimate of the actual rate of population growth, egg ratio technique as a means of estimating instanr , the population mortality rate can then be detertaneous birth rates with preserved samples of plankmined by difference using the relation tonic rotifers. In theory the method can be extended m = h r . (3) to any population characterized by continuous growth. Under the special conditions of zero population Since few populations are either free from egg morgrowth, zero egg mortality and a stable age distributality o r stable in size or age distribution, Eqs. 1 and tion, the age distribution of eggs will be even, and the 2 would seem to be inappropriate. However, the use finite birth rate of the population is of Eq. 2 has been further encouraged by a derivation p = EID by Paloheimo (1974) which, despite its incorporation of egg mortality, turns out to be independent of morwhere E = C,IN, is the average number of eggs per tality and identical to Eq. 2. This convenient absence individual in the population (the egg ratio), C, and N, of egg mortality from Eq. 2 occurs only when the morbeing the total number of eggs and individuals in the tality rate of eggs is exactly equal to that averaged population at time t , and D is the duration of egg across the entire population ( m ) . Furthermore, the indevelopment (days). Under these constraints, p is redependence of Eq. 2 from r is still a consequence of lated to the instantaneous birth rate by assuming a stable population age distribution. Threlkeld (1979) has suggested that the accuracy of birth rate estimates could be improved by examining the age distribution of eggs. Although this approach would seem to be an advance over the Edmondson-Palohei(1) mo model, it is not yet clear whether the additional An alternate expression for h which makes no aswork is warranted. sumptions about the age distribution of eggs, but A large part of the problem is that, with few excepwhich still assumes zero population growth and zero tions (DeMott 1980. Keen and Nassar 1981), previous egg mortality, is investigations involving the egg ratio method have not attempted to estimate the variance of the rates in Eq. Manuscript received 25 September 1980; revised 5 ~~~~h 3. In the absence of such information it is not only 1981; accepted 27 April 1981. impossible to compare the adequacy of different tech1 Febr~~u l -y 1982 ZOOPLANKTON BIRTH RATES 13 niques, but a comparison of instantaneous rates between dates o r sites is risky at best. An analysis of variance for b and r becomes particularly critical when /?I is estimated by difference. Many studies show dramatic fluctuations in in over very short time intervals (Clark and Carter 1974, Kwik and Carter 1975, Goldman et al. 1979). and without variance estimates these cannot be identified a s real o r artifactual. Negative estimates of in, which often arise from Eq. 3, are usually attributed to the hatching of uncensused resting eggs, although they are just as likely to be a consequence of poor estimates of r resulting from inadequate sampling or biased determinations of h resulting from faulty assumptions of the EdmondsonPaloheimo model. Despite these problems, zooplankton ecologists continue to rely heavily on Eq. 2 (see Bottrell et al. 1976, Goldman et al. 1979. Kerfoot and Peterson 1979, Lynch 1979 for several recent applications), and it seems likely that many will continue to d o so in the interest of time. Thus. it is of interest to know the extent to which deviations from the assumptions inherent in the Edmondson-Paloheimo equation are reflected in Door estimates of birth rates in field studies. Such an analysis has not been possible in the past because the magnitude by which the assumptions have been violated has been difficult to quantify. Computer simulations are of only limited value in examining this problem (Seitz 1979) because the choice of input parameters is necessarily subjective. The application of a sequential sampling technique for estimating sizespecific mortality rates in cladoceran populations (M. Lynch, pc~r~oncll oh,cert~atiotl) now allows the collection of the necessary information. This paper provides an empirical test of the efficacy of the Edmondson-Paloheimo model by comparing estimates of b by Eq. 2 with those obtained for two Daphnicl p~rlex populations for which instabilities in age structure and differential egg mortality are accounted for. Since a generalized model for estimating instantaneous birth rates from egg ratio data has not been previously published I will start by deriving such an expression. Throughout this paper I will assume a homogeneous population, i.e., one in which all individuals are exposed to the same physical and biological factors. I also assume that egg development times and size-specific rates of growth, egg laying, and mortality are constant over the interval ( t L), t). (Since the structure of the population may change over [t D, t] , this does not imply constancy of these rates as population parameters.) For populations for which L) is on the order of a few days, as it is in most of the planktonic organisms to which the egg ratio model has been applied, such approximations do not seem unreasonable. However, where these assumptions are significantly violated, no simple expression for estimating b by an egg ratio method can be derived, and alternate empirical approaches must be sought. The ideal egg ratio model makes no assumptions about the internal structure of the population, but considers the individual contribution of each class of individuals to the total population birth rate. Although the classification scheme is arbitrary, I will derive the model in the context of a population of an arbitrary number of size classes ( i t , ) since most organisms may be more easily classifed by size than by age. The total number of eggs derived from size class x which hatch during time ( t , t + dt) is equal to the total number of eggs laid during time ( t L), t L) + dt ) by individuals of that size class which survive to hatching (most planktonic organisms, especially cladocerans, do not change size classes while carrying a clutch), b,. N,., ,tit = tit, I,.N,, , , e r = l J e i \" ~ (4) where h,. = the instantaneous birth rate of size class x (day-'), N,,,, = the number of individuals in size class s at time t (number per square metre), r,. = (In &,,, In N,,,-7)/~ is the growth rate of size class x (day-') I , = the instantaneous rate of egg laying by size class x (day-'), and tn, = the instantaneous mortality rate of size class x (day-'). The size-specific rate of egg laying, I,. , can be re-expressed in terms of the mean size-specific clutch size E,{ . as follows. The total number of eggs carried by size class x at time r is

The adaptive significance of color polymorphism in two species of Diaptomus (Copepoda)1

Abstract: In the Lower Grand Coulee, Washington, Diaptomus nevadensis in Soap Lake contains larger amounts of the carotenoid astaxanthin than in Lake Lenore. During winter, Diaptomus sicilis contains larger amounts of pigment in both lakes, but in summer individuals from Lake Lenore are much reduced in pigment while those from Soap Lake are unchanged. The amount of astaxanthin might be a reflection of the amount of pigment in the copepods’ diet or might reflect the relative importance of selective forces acting for and against pigmentation, Seasonal variations in copepod carotenoid content did not correspond with variations in total lipid content. Algal abundance was measured by chlorophyll a and plant carotenoids correlated with copepod carotenoids only in the case of D. neuadensis in Soap Lake. The percent of D. nevadensis guts containing algae was correlated with their pigment content in both lakes. Visually oriented predators, such as damselfly nymphs from both lakes and salamander larvae from Lake Lenore, selected red copepods, but few predators from Lake Lenore contained D. nevadensis. Since members of this species were rare, the probability of finding a predator that had consumed one was low. When fed identical diets, copepods from Lake Lenore were a fifth to a thirtieth as efficient at assimilating carotenoid as those from Soap Lake. This supports the hypothesis that the pigment differences are the result of natural selection. Selective predation is implicated as the explanation for the small amounts of pigment in Lake Lenore copepods.

Zooplankton grazing and phytoplankton species richness: Field tests of the predation hypothesis1

Abstract: The hypothesis that herbivory plays a major role in the maintenance of high algal diversity was tested over a e-year period in polyethylene enclosures at Heney Lake, Quebec. Reduction of grazing pressure resulted in a significant decrease in the number of inedible species, whereas the diversity of edible algae remained unaffected. Lowering the herbivore levels may cause an intensification of exploitative competition among phytoplankton, which favors edible species and a few inedible algae like Synedra at the expense of many inedible species that are eliminated.

Functionally distinct classes of complex phosphorus compounds in lake water1

Abstract: Abstmct Complex phosphorus compounds were classified functionally according to the manner by which orthophosphate was released. Filtrable phosphorus compounds in two cutrophic lakes (East and West Twin lakes) and a humic bog (Crazy Eddie Bog) in northeastern Ohio wcrc fractionated by anion-exchange and gel-filtration chromatography. Fractions were analyzed for soluble reactive phosphorus and total dissolved phosphorus; absorbance at 400 nm was used as a measure of filtrable “yellow acids.” The cutrophic lakes contained numerous low molecular weight compounds which were resistant to low-dose ultraviolet irradiation but readily released orthophosphate upon treatment with alkaline phosphatase. Filtrable phosphorus compounds of the humic bog were predominantly high molecular weight, cochromatographed with the yellow acids in each fractionation procedure, and resisted enzyme hydrolysis, but released orthophosphate upon irradiation with low doses of ultraviolet light.

An evaluation of errors in the 14C method of primary production measurement

Abstract: Membrane filtration is an integral part of the /sup 14/C method of measuring primary productivity in natural waters. Polycarbonate, cellulose ester, and glass-fiber filters retan about 0.0003, 0.09, and 0.24 mg water per mm/sup 2/ surface area. The (/sup 14/C)bicarbonate in this retained water must be eliminated before the filter is assayed for radioactivity. Airdrying, desiccator-drying in the presence or absence of a CO/sub 2/ absorbant, and oven-drying are only partially effective decontamination procedures; washing with pH 2 filtered lake water removes most of the contaminating activity. A plot (dpm.filter/sup -1/ vs. volume filtered) is used to diagnose the efficiency of decontamination. A simple and safe decontamination procedure is shown to eliminate effectively all residual (/sup 14/C)bicarbonate activity. Membrane filters are placed in scintillation vials, 0.1 to 1.0 ml of 0.5 N HCl is added, and, after a 2 to 3-h interval, the scintillation fluor is added.