Showing papers in "Limnology and Oceanography in 1981"

Absorption by dissolved organic matter of the sea (yellow substance) in the UV and visible domains1

Abstract: Spectral values of absorption of light by dissolved organic matter were measured in samples originating from diverse parts of the ocean, quite different with respect to pigment and particle content. The use of llO-cm cells and then of lo-cm cells, with a highly sensitive spectrophotometer, allowed measurement throughout the UV-visible range (200-700 nm) even for the low concentrations of yellow substance encountered in the open sea. The concentration appears influenced predominantly by natural and industrial land discharges. In oceanic waters, it remains low and seems to be related to the biological activity averaged over a long period rather than to the local and temporary phytoplankton content. However, even at such low concentrations, yellow substance in the open sea may have an effect on absorption and hence on ocean color similar to that of low or moderate algal biomass. The spectral dependence law of absorption appears to vary within a restricted range, and an average law can be considered representative of rapid measurements at one selected wavelength.

An optical classification of coastal and oceanic waters based on the specific spectral absorption curves of phytoplankton pigments, dissolved organic matter, and other particulate materials1

Abstract: The variations of the spectral absorption coefficient of seawater can be attributed to three principal factors—phytoplankton, nonchlorophyllous particles, and yellow substances— whose concentrations are represented in this study in terms of chlorophyll a and pheophytin a content (C), the total scattering coefficient (b), and the absorption by filtered seawater at a given wavelength (Y). By assuming an exponential absorption by yellow substances, we developed a new iterative method for identifying the in situ apparent specific spectral absorption curves of the other two factors. The weighting coefficients for each of the three components are calculated for over 80 spectral absorption measurements from different representative marine regions. The reconstruction of spectral absorption curves from the three coefficients and the three specific absorption curves fits the original data with an overall average error of 3%. Relationships between these coefficients and C, b, and Y are examined. Results show that, though the spectral form of absorption by pigments can be considered as more or less invariant, the absorption “efficiency” per unit C depends on the nature of the water, and hence on the type of phytoplankton population considered. An optical classification based on the three optical coefficients related to three absorbing agents is proposed.

Estimating the daily contribution of carbon from zooxanthellae to coral animal respiration1

Abstract: An equation is derived which rigorously defines the photosynthesis: respiration ratio (P:R) for any alga: invertebrate symbiotic association arid permits the computation of the fractional contribution of translocated algal carbon to the daily respiratory carbon requirement of the host animal. The equation is applied to two species of symbiotic reef corals, using O2 flux data from 24-h continuous measurements in situ. Given certain assumptions, the algae in the shallow-water Hawaiian reef corals Pocillopora damicornis and Fungia scutaria can supply of the order of 63 and 69% of the daily respiratory carbon demand of their respective animal hosts.

The relative importance of protozoans, rotifers, and crustaceans in a freshwater zooplankton community1

Abstract: A complete analysis of the macro- and microzooplankton of a warm monomictic lake indicates that Protozoa dominate the community numerically. During winter mixis, ciliates are found at densities of l-8 x 103*liter-’ and constitute up to 32% of the zooplankton community biomass, With summer stratification crustaceans decline, while both the relative and absolute abundance of protozoans and rotifers increase. Densities of protozoans are highest (l-2 x 105* liter-l) in the metalimnion where scuticociliates bloom in zones of intense bacterial activity. During the period of these blooms (July-October), Protozoa account for 15-62% of the zooplankton biomass. This suggests that Protozoa make a significant contribution to rates of grazing, nutrient regeneration, and secondary productivity and should not be overlooked in

Copepod feeding currents: Food capture at low Reynolds number1

Abstract: High-speed motion pictures of dye streams around feeding calanoid copepods revealed that these important planktonic herbivores do not strain algae out of the water as previously described. Rather, a copepod flaps four pairs of feeding appendages to propel water past itself and uses its second maxillae to actively capture parcels of that water containing food particles. The feeding appendages of Eucalanus pileatus operate at Reynolds numbers of only 10−2 to 10−1. In the viscous world of a feeding copepod, water flow is laminar, bristled appendages behave as solid paddles rather then open rakes, particles can neither be scooped up nor left behind because appendages have thick layers of water adhering to them, and water and particle movement stops immediately when an animal stops beating its appendages.

Oxidation‐reduction potentials in a salt marsh: Spatial patterns and interactions with primary production1

Abstract: Spurtina alterniflora oxidizes the sediments in which it grows through both passive oxygen release and active metabolic processes. Eh is higher in the root zone of this grass than in the sediment below the root zone or in unvegetated sediments. Sediments underlying the tall form of S. aZterniJorcl are more oxidized than those under the short form, and sediment redox condition and S. aZterni$oru production are related through a positive feedback loop. Reducing conditions inhibit aboveground grass production. But also, more productive plants have a greater capacity for sediment oxidation, as shown by the increased Eh in fertilized plots. Waterlogged sediments inhibit plan growth by decreasing passive oxygen release and thereby lowering Eh.

Embryological induction and predation ecology in Daphnia pulex

Abstract: Results of laboratory experiments suggest that a water-soluble factor released into the environment by the predacious phantom midge larva Chaoborus americanus (Diptera: Chaoboridae) causes embryos of the waterflea Daphnia pulex Leydig 1860 emend. Richard 1896 (Crustacea: Cladocera) to develop into a form called Daphnia minnehaha Herrick 1884. Chaoborus larvae are unable to eat the D. minnehaha form as readily as the D. pulex form.

The effect of environmental factors on phytoplankton growth: Temperature and the interactions of temperature with nutrient limitation1

Abstract: The combined stress of nutrient limitation and suboptimal temperature on growth was studied with turbidostat and chemostat cultures of Scenedesmus sp. and Asterionella formosa. The combined effects were greater than the sum of individual effects and were not multiplicative. In N- and P-limited Scenedesmus sp. and A. formosa the cell (q) of both limiting and nonlimiting nutrients increased with decreasing temperature. At a given temperature cell quotas of limiting nutrients also increased with the growth rate (µ) and followed a saturation function. Higher values of the minimum cell quota (qo) at lower temperatures show that cells require more nutrient with decreasing temperature. The change of qo with temperature varies with the type of limiting nutrient. This change for N and P in Scenedesmus sp. suggests that their optimum ratio, the ratio at which one limitation changes over to the other, is higher at suboptimal temperatures. Cell quotas of nutrient-sufficient cultures (qm) for C, N, and P and cellular chlorophyll a concentration increased with decreasing temperature. The quota of each nonlimiting nutrient in nutrient-limited cultures had the same value as qm. The rate of protein synthesis per unit RNA decreased with temperature. The highest apparent maximum N uptake was observed at 15°C for N-limited Scenedesmus sp. growing at 0.5·d‒1. The optimal growth temperature range, however, was 20°–25°C. The highest apparent maximum P uptake in A. formosa was found at 19°–20°C, when µ = 0.4·d‒1. These temperatures were also optimal for growth.

Predation, enrichment, and phytoplankton community structure1

Abstract: The significance of grazing and enrichment to the Pleasant Pond phytoplankton community was examined through a series of enclosure cxpcriments. The addition of planktivororls fish led to the removal of large herbivores and to an order-of-magnitude increase in total phytoplankton biomass. This was a result of the appearance of several new algal species as well as the increase of most initial rcsidcnt species. Aphanizomenon flos-aquae was an exception to this pattern. This filamentous blue-green attains its maximum density in the presence of large Daphnia by forming large, ungrazeable colonies; Daphnia may provide a service to Aphanixomenon by removing most potential algal competitors. The addition of phosphorus and nitrogen had no quantitative effect on total phytoplankton biomass cithcr in the presence or absence of fish; changes in species composition did occur, several algae disappearing with enrichment. WC summarize the varied rcsponscs of lakes to enrichment and suggest that the community-level effects of enrichment can only be understood in the context of a framework that considers initial nutrient status and the strrrcturc of planktivorous fish populations. Our knowledge of factors affecting zooplankton popul ation s has developed to the point where generalized models for the structure of zooplankton communities have begun to emerge (Dodson 1974; Lynch 1979). G iven a description of the predators found in a body of water, these models predict which zooplankton species will be excluded from the community. Since planktonic herbivores may have a significant impact on the composition of phytoplankton communities (Porter 1977), it logically follows that predators, through their effects on the herbivore community, may be important determinants of phytoplankton community structure (Hrbacek 1962; Losos and Hetesa 1973). The significance of nutrients in aquatic environments has also long been appreciated, and several hypotheses have been proposed to explain the dominance of certain phylogenetic lines of algae under particular nutrient regimes (Schelske and Stoermer 1971; Shapiro 1973; Schindler 1977). The chemical characteristics of a ’ Contribution 173 from the Limnological Research Center. Rcscarch supported by NSF grant EMS 74-19490 and by a grant from the U.S. EPA to J. Shapiro. z Present address: Department of Ecology, EtholWY, and Evolution, Vivarirlm Bldg., University of I Hi noi s, Champaign 6 1820. body of water may influence the structure of phytoplankton communities by direct mediation of competitive interactions or by several indirect routes determined by the connections among the members of the community (Lane and Lcvins 1977). Consequently, while the response of a phytoplankton community to enrichment is often dramatic and predictable, the mechanisms promoting the response are rarely known. We examine here the phytoplankton community structure of Pleasant Pond, Minnesota. Since the factors responsible for the distribution of zooplankton species in this pond are known (Lynch 1978, 1979), any changes in the phytoplankton community associated with herbivore activity can ultimately be related to mechanisms regulating the zooplankton community. Here we report on the structure of the Pleasant Pond phytoplankton community in relation to predator-mediated changes in zooplankton community composition, the immediate effects of herbivory as indicated by the short term removal of zooplankton, and the results of longer term enclosure experiments to determine the relative effects of enrichment and predation on the phytoplankton community. A complete description of the pond, its predators, and zooplankton community

Predator induction of crests in morphs of the Daphnia carinata King complex

Abstract: Temperature, turbulence, oxygen, and notonectid predators (Anisops calcaratus) were studied experimentally as possible factors influencing crest growth in six different forms of the Daphnia carinata complex. Predators were the most potent influence, inducing crest development in four of the morphs. Temperature had only a secondary effect which may have been indirect. When the notonectids were partitioned off from the Daphnia in the same container, crest development still resulted, suggesting that the stimulus was a water-soluble secretion from the predator. If the notonectids were starved this secretion was either not produced or was ineffective. Experiments showed that predators could induce crest development in adult daphnids that were initially uncrested and that a sustained stimulus from the predator was necessary if crested juvenile Daphnia were to produce crested adults. Under experimental conditions, daphnids with a crest were less susceptible to notonectid predation (mainly because of superior evasion powers) than were those without one. Results of a regression analysis of field data were broadly consistent with experimental results, especially in indicating that predation was a potent factor influencing crest development, and the distribution and abundance of morphs.

The effect of environmental factors on phytoplankton growth: Light and the interactions of light with nitrate limitation1

Abstract: The effects of simultaneous limitations of light and nutrient on growth were investigated with turbidostat and chemostat cultures of Scenedesmus sp and Fragilaria crotonensis The combined effects were greater than the sum of individual effects and were not multiplicative Under nitrate-limited conditions the cell quota of the limiting nutrient for a constant growth rate and the subsistancc quota (qO) increased as irradiance decreased Within a certain limit of growth rates, light and qN can compensate for each other in maintaining growth rate Under nutrient-sufficient conditions, cell quotas of C, N, and P, and cellular chlorophyll a concentration increased as light decreased below saturation The cell quotas are the maximum level (y,,[) that can be achieved at a given irradiance Cell quotas of nonlimiting nutrients in nutrient-limited cultures are the same as these (I~? values The increasing levels of g, and q with decreasing irradiance indicate that nutrient requirements increase as irradiance decreases Irradiance in an aquatic environment diminishes with depth Physical mixing of the epilimnion therefore exposes phytoplankton to a series of vertical light gradients When nutrients become limiting in this layer, phytoplankton may be sub

Primary production of microalgae in sediments measured by oxygen microprofile, H14CO3 ‐ fixation, and oxygen exchange methods1

Abstract: A platinum microelectrode was used to measure changes in dissolved oxygen profiles in surface sediment exposed to light and darkness. Estimates of production by microalgae thus derived were compared with those derived from conventional methods of measuring changes in dissolved oxygen and H14C0,- uptake. For each particular depth in the sediment, the primary production can be determined within a few seconds by the new method. Undisturbed sediment cores were used for the H14C0,- fixation assay of benthic photosynthesis. Measurements of the specific activity of HC03- within the photic zone showed a steep gradient of IP”CO,- at the sediment surface. Calculations of benthic photosynthesis taking the actual specific activity into account yielded 2-5 times higher estimates than calculations using the specific activity in the overlying water. In a highly oxidized sediment, the three methods yielded almost identical results at low light intensities (200 pEinst*m-2*s-1). The oxygen methods grossly underestimated the primary productivity at higher light intensities, due to bubble formation. The conventional oxygen method grossly underestimated the primary productivity in sulfuretm~r-type sediments as compared to the two other methods. In addition to photosynthesis, the oxygen consumption by the sediment was determined by oxygen microprofiles.

The phytoplankton and protozooplankton of the euphotic zone of Lake Tanganyika: Species composition, biomass, chlorophyll content, and spatio‐temporal distribution1

Abstract: The seasonal cycle of phytoplankton and protozooplankton 1 iomass observed at two widely separated pelagic stations in the euphotic zone of Lake Tanganyika from February through November 1975 could be divided into three phases, based oil algal abundance and species succession and coinciding with three phases of annual thermal stratification. Phytoplankton biomass was minimal (as low as 60 mg*m-“) during the phase of stable stratification and maximal, as high as 930 mg* me 3, at the end of the period of deep mixing. Diatoms, especially Nitzschin spp., were abundant only during the period of mixing, while filamentous blucgreens, principally Anahaena sp., were prominent during a p :riod of rapid surface warming which produced shallow mixed layers following the period o - deepest mixing. The biomass of Stromhidizcm cf. virile nearly equaled or exceeded the >hytoplankton biomass during much of the stably stratified period; this protozoan probably h: s a symbiotic relationship with zoochlorellae, which were always present in it. Lake Tanganyika showed a greater relative annual range bei wecn maximum and minimum phytoplankton and chlorophyll a concentrations than other tropical lakes and the temperate Great Lakes. Chlorophyll a ral.nged from 0.1 to 4.5 mg* np3 in he ellphotic zone and frorn 0.2 to 20.4 in surface waters; phytoplankton biomass ranged frctm 25 to 1,570 rng.n+ in the cuphotic zone. Annllal mean concentrations were among the Lowest known, 140 mg.rnm3 for phytoplankton biomass and 1.2 rng. mm3 for chlorophyll cc. Explanations for both the low annual means and the high annual variabilities may lie in ‘he lake’s steep morphometry, which affects nutrient regeneration, and in high loss rates kyrhich cause high algal growth rates but low algal biomass much of the year.

The contributions of temperature and of the input of organic matter in controlling rates of sediment methanogenesis1

Abstract: The roles of temperature and organic input in determining the rate of methane flux from anoxic sediments were examined under various laboratory and field conditions in two small Michigan lakes. As in other studies, rapid temperature increases in incubating sediment caused immediate increases in methane production rates (avg Q10 = 2.4). Under in situ conditions, where the hypolimnetic temperature is relatively cold and unchanging for long periods, methane flux was linearly related (P < 0.01) to organic input in these two and three other lakes for which data were available. In addition, the proportion of organic input released as methane (47 + 94 ) o was close to the theoretical maximum (40 -+ 8%) and was not related to temperature. When temperature is constant for long periods, as during summer stratification, CH, production adjusts maximally to organic input, When temperature changes rapidly, its effect will be predictably superimposed upon that of organic input.

An analysis of sinking rates of natural copepod and euphausiid fecal pellets1

Abstract: where L and D are the cylinder length and diameter, ps is the particle density, and SL. and p are the fluid viscosity and density. This relationship is compared with published data on the settling velocities of cylindrical fecal pellets produced by euphausiids and copepods. The agreement between data and the equation is very good. The analysis further permits the indirect evaluation of the fecal pellet density. A mean density fi, = 1.22 g*cm-” was so determined, which corresponds almost exactly to the one reliable direct measurement of fecal pellet density (1.23 g.cm-“). A second equation is available that can be used if the fecal pellets are ellipsoidal or oval rather than cylindrical.

Oceanography of the eastern Bering Sea ice-edge zone in spring1

Abstract: The ice-edge region of the southeast Bering Sea was studied in terms of the hydrographic regime, phytoplankton biomass, and primary productivity during the springs of 1975 through 1977. The results showed that a phytoplankton bloom occurs at the ice edge just as the spring ice-decay period begins, and that this accounts for a significant proportion of the annual carbon input over the shallow shelf. The bloom is intensified in time and space by the influence of the ice edge on the physical structure of the water column. Specifically, melting ice seems to increase the stability of the water column, near and under the ice, by lowering the salinity. Frontal structure in salinity and temperature are apparent at the ice edge and are attributed to the melting ice but also, at times, to wind-driven Ekman-type upwelling. These data are also related to recent short term (ca. months-year) climatic fluctuations that seem to control the seasonal position of the ice-edge zone relative to the shelf break. In “cold” years, the ice edge comes southward to the shelf break and overlies the more nutrientrich Alaska Stream/Bering Sea source water. In “warm” years, the ice-edge zone does not reach this nutrient-rich water. This may be important to the biology of the ice-edge ecosystem. The edge zones of seasonal sea ice are biologically productive, serving as focal points for the congregation of large numbers of marine birds and mammals and thus represent ecologically critical habitats in subpolar regions. The presence of a cold and solid boundary influences the biological regime in several ways, including effects on the physical and chemical regimes in the adjacent seawater. At least three structural features of the water column often associated with high oceanic primary production can occur in such an area simultaneously: water column stability, frontal structures and, under certain conditions, ice-edge upwelling. We show here that there is enhanced primary production due to water column stability and frontal structure at the edge of the seasonal sea ice in spring. Our data also suggest that ice-edge upwelling occurs. We show further that the intense

Competition and nutrient kinetics along a temperature gradient: An experimental test of a mechanistic approach to niche theory1

Abstract: A resource-based model of competition correctly predicted the ecluilibriulil orltc,omtJ ,tn(l approximated the population and nutrient dynamics of many nutri~l~t-lilnitt,~~ compr~tition experiments with two algal species at temperatures from 8” to 24°C. Silicate growth kinetics of temperature-acclimated Asterionella formosu and Sync~dra ulncl predicted that AstrJrionella should competitively displace Synedra below 20°C and Synudru should displace Astcrionella above 2O”C, as was observed. Although the growth kinetics showed no significant tlifference in silicate requirements at 2o”C, S ynedru displaced Asterionulla for all starting conditions at 20°C. These experiments support a major prediction of an equilibrium thtlor> of competition for a single resource: independent of initial population densities, thtb \pcxc.icJ\ with the lowest resource requirement should displace all competitors. Thus rc’sourcc’ recluirctnents, as defined by a mechanistic model, may be appropriate for defining niche boundaritss. In single species experiments, fit to the Monod model with a nutrient threshold, the II~trient-saturated grcwth rate of Synedra increased from 0. Ifi.&’ at 8”<1 to 0.7ri at 13°C and above; its half-saturation constant for growth was ca. .5.0 /.~%l SiO, , independent of temprraturch from 8” to 24°C. The nutrient-saturated growth rate of Astwionella inc*rcaascxd frown 0.3Fj.d ’ at 4°C to 0.8 at 13”C, and decreased to 0.66 at 24°C; its half-saturation constant for grou+h hurl a temperature-independent value of 2.1 PM SiO, from 4” to 13”C, but increast~cl to 10 ~11 SiO, at 24°C. Half-saturation constants for silicate-limited growth ma) 1)~ t~lnp~‘ratur~~-indt~pendent for temperatures within or below the optimal temperature rnngr~, but illcrch,lso \harpl) fi)r temperatures above it.

Photosynthetic response of lake plankton to nutrient enrichment: A test for nutrient limitation

Abstract: Measurements of carbon uptake by lake plankton at different levels of added phosphorus reveal some phytoplankton strategies that contribute to their survival in low-nutrient waters. Nutrient-deficient populations seem to temporarily reduce, rather than enhance, photosynthesis when phosphorus becomes available. This contradicts the basic hypothesis of the 14C bioassay used to determine “limiting” nutrients in natural waters. The reduction of carbon uptake rate continues until either the nutrient addition is taken up or no further storage is possible; at this time carbon upake may be enhanced. Concurrent measurements of phosphorus uptake showed no light response unless the plankton were exposed to significant phosphorus concentrations in the dark for several hours. Phytoplankton seem to be adapted for and dependent upon intermittent events exposing them to nutrient-enriched water. The ability of phosphate-depleted plankton to take up phosphate in excess of their growth requirements was used to develop an index for phosphate deficiency. To normalize for different biomass levels, the optimum photosynthetic rate was divided by the maximum uptake velocity giving a range for the C:P maximum uptake from 1.2 to 206 for plankton samples of varying phosphate deficiency.

Postdepositional mobility of phosphorus in lake sediments1

Abstract: Fifteen sediment cores from Lake Mcmphremagog showed pronounced peaks of total phosphorus concentration within the “‘“Pb-defined mixed layer, suggesting that P was migrating upward and accumulating near the mud surface. The mobility of P in the sediments was confirmed by the rapid development (5 weeks) of a marked total P maximum in the upper centimeter of a previously homogenized sediment. Associated with the P migration was a steep gradient of soluble reactive P (SRP) concentration, preslrmably the result of a redox gradient in the sediments. Similar gradients of total P and SRP were observed in nondisturbed sediments, strongly suggesting that such an upward migration mechanism also operates under natural conditions. The remobilized P seems to be isotopically exchangeable (mobile) under anaerobic conditions. These observations indicate that profiles of sediment total P may not always be useful in determining historical P loading or P sedimentation rates in lakes.

Summer internal phosphorus supplies in Shagawa Lake, Minnesota

Abstract: Phosphorus budget calculations for Shagawa Lake show that significant increases in lake P during July and August 1971-1975 originated from within the lake basin. Mass increases of 2,000-2,900 kg (3550 pgeliter-‘) were measured, corresponding to internal supply rates of 240-680 kg* wk-’ over a 3-9-week interval. After anaerobi : conditions developed in late June, release from the profundal zone sediments contributed :ignificant amounts of P to lake water. Sediment chemical properties were determined to estimate: the size of the P reservoir in the profundal zone (at water depths > 6.5 m). The P content of the surficial profundal zone sediments was 0.2-0.5% (dry wt) and a significant fraction \fas potentially mobile (NaOH extractable). We calculate that the upper 10 cm of these sediments contain 50,000 kg of potentially mobile P, of which a small fraction is released each summer. Although external sources of phosphorus have been reduced by about 80%, the feedback ofP from the sediments is supporting the productivity of Shagawa Lake and may continue to do so for many years.

The interaction between zinc deficiency and copper toxicity as it affects the silicic acid uptake mechanisms in Thalassiosira pseudonana1

Abstract: Zinc-deficient cultures of Thalassiosira pseudonana exhibited reduced silicic acid uptake rates. Copper toxicity decreased the silicic acid uptake rate at any zinc concentration. This resulted in the uptake rate being a function of the ratio in the medium of the cupric ion activity to the zinc activity rather than of either metal activity separately. These results are consistent with a proposed mechanism for the interaction between silicic acid and cupric ion activity involving a zinc-dependent active site. In work to be published elsewhere (Rueter and Morel in prep.) we found a competitive relationship between cupric ion activity and silicic acid concentration as they affect growth, silicic acid uptake, and copper uptake in the marine diatom Thalassiosira pseudonana (3H) (Hust.) Hasle and Heimdal. The result of this competitive interaction was that relatively high cupric ion activities resulted in higher rates of copper uptake and lower rates of silicic acid uptake. Conversely, high silicic acid concentrations could reverse the effect of copper toxicity, causing lower copper uptake rates and near maximal silicic acid uptake rates. We have considered a mechanism for this interaction in which an active site for silicic acid uptake is inhibited by the cupric ion activity and protected by high substrate (silicic acid) concentrations. This form of inhibition is similar to nonreversible competitive binding to the active site that has been studied in other enzyme systems (Zeffren and Hall 1973). We also thought that the binding of copper at this active site was one possible pathway for copper to enter the cell. In order to explain this proposed mechanism, we considered that zinc could be involved in silicic acid uptake. Zinc was

Chromatic adaptation of photosynthesis in benthic marine algae: An examination of its ecological significance using a theoretical model

Abstract: All available action spectra of photosynthesis for benthic marine algae have been multiplied by the spectral distribution of the light at different depths in all Jerlov water types to predict the photosynthesis per unit quantum irradiance of each species in each habitat. Comparison of the predictions indicates that red algae are best adapted chromatically to photosynthesize at all depths (including 0 m) in all except the clearest oceanic waters. The results show little correlation with the patterns of vertical distribution of green, brown, and red algae in benthic marine habitats, and suggest, therefore, that light quality is not a major factor in the control of that distribution. A review of physiological evidence supports the hypothesis that the changes in pigment composition that are observed with increasing depth in marine algae are largely adaptations to low irradiance, and not to the spectral composition of underwater light.

Role of Gulf Stream frontal eddies in forming phytoplankton patches on the outer southeastern shelf1

Abstract: Continuous surface mapping of temperature, salinity, and chlorophyll along a 300-km segment of the Gulf Stream cyclonic front defined the spatial scales of a large diatom patch that persisted throughout a 10-day study. The patch was localized in the upwelled cold core of a Gulf Stream frontal eddy centered over the 200-m isobath off Jacksonville, Florida, in April 1979. The 2 ..mu..g.liter/sup -1/ surface chlorophyll isopleth enclosed in area >1,000 km/sup 2/ with an alongshore dimension of 130 km. Surface chlorophyll exceeded 5 ..mu..g.liter/sup -1/ within the upwelled cold core of the eddy, 10-100x higher than concentrations in Gulf Stream or resident shelf surface water. Diatoms dominated the patch with the maximum observed abundance >10/sup 6/ cells.liter/sup -1/. Several days after the initial shipboard mapping, the size, location, and strong chlorophyll gradients of the patch were confirmed with a surface chlorophyll image generated from an ocean color scanner (OCS) flown aboard a NASA U-2 aircraft. We show that the upwelling associated with eddies forming along the Gulf Stream cyclonic front results in localized zones of high near-surface production and plant biomass that lie adjacent to oligotrophic surface waters of the Gulf Stream.

Selection for a red tide organism: Physiological responses to the physical environment1,2

Abstract: The dinoflagellate Prorocentrum mariae-Zehouriae has specific physiological characteristics that allow it to participate in a subsurface transport from the southern Chesapeake Bay to the northern bay, where it upwells and forms red tides. A particular growth rate dependence both on temperature and salinity restricts its year-round distribution to”the high-salinity southern bay. At summer temperatures, increased tolerance to low salinities allows rapid growth in the low-salinity waters of the northern bay. Positive phototaxis is proposed to act in conjunction with downwelling convergence at a frontal region to form the initial subsurface concentration maximum or lens. Repression of positive phototaxis at a salinity interface appears to prevent the subsurface concentrations from crossing the sharp halocline, retaining the lens population in northward-flowing bottom waters. Prorocentrum increases its pigment concentration and retains its photosynthetic capacity at the extremely low light intensities encountered during the 200-km northward transport. In nutrient-poor surface waters in surnmer, Prorocentrum migrates at night to the higher nutrient pycnocline region. The winterspring phasing of the strcamflows in both northern and soiithern bays may be used to predict the degree of Prorocentrum blooming in the northern bay in summer. Tyler and Seliger (1978) described a subsurface transport of a red tide organism, Prorocentrum mariae-lebouriae, from the southern to the northern Chesapeake Bay, a distance of about 240 km. The evidence for this transport consisted of a temporal series of synoptic measurements of salinity stratification and destratification in the southern and northern bay respectively upon which were superimposed the sequential concentration isopleths of Prorocentrum. The entire sequence thus appeared as a series of snapshots indicating the progression of Prorocentrum in bottom waters from its winter quarters in the southern bay to its summer bloom area in the northern. We here describe and present evidence for specific physical hydrographic mecha

Role of nutrient limitation and competition in controlling the populations of Asterionella formosa and Microcystis aeruginosa in semicontinuous culture1

Abstract: Ahstruct The nutrient uptake and growth kinetics of the freshwater diatom Asterionellu formosu and the blue-green alga Microcystis aeruginosa under P or Si limitation were determined in batch cultures at 20°C. Asterionellu had a higher maximum growth rate and a lower halfsaturation constant for growth than Microcystis under P limitation. The maximum uptake velocity for P was higher for Asterionellu than for Microcystis while the half-saturation constants for P uptake were similar for the two species. The Monad model of growth predicted a switch from Si limitation to P limitation for Asterionella at Si:P of about 93 (215). I n experiments with the two species grown together at various Si:P ratios, Asterionellu dominated steady state semicontinuous cultures when both species were P-limited, Si:P > 100. Microcystis became dominant when Asterionellu was Silimited, Si:P < 100. The competition experiments showed the importance of the conccntration of nutrients, as well as the ratio of the nutrients and rate of supply, in controlling the cell densities of the algal species.

The impact of appendicularian grazing on natural food concentrations in situ1

Abstract: The filtering rates of Oikopleura dioica and Stegasoma magnum (Tunicata: Appendicularia) were measured in situ by a SCUBA diver in the Gulf of California. Simultaneous measurement of the age class structure of each appendicularian population, natural food densities, and the rate of increase of food particles allowed calculation of the grazing impact of each population on natural food assemblages in the field. Filtering rates increased exponentially with animal size and reached maxima of 12.5 ml* animal-‘. h * for 0. dioica and 627 for S. magnum. The filtering rate of S. magnum was an order of magnitude higher than that of copepods of similar ash-fret dry weight. At densities ranging from 205 to 4,587 animals * mP3, 0. dioica populations filtered from 1.3 to 37.7% of each cubic meter in 24 h. At maximum population densities clearance exceeded the replacement rate of the particulate food. Stegasoma magnum ranged from 11 to 63 animals em -3 and filtered from 5.4 to 13.4% of each cubic meter in 24 h. Direct field evidence indicates that appendicularian grazers exert significant grazing pressure on natural food assemblages in situ.