Effects of rotifers and ciliates on the growth and survival of Daphnia

Daphnia can suppress ciliates and rotifers through predationand interference competition, but it is not known whether thisproduces any direct benefit to Daphnia. We conducted survivorshipand cohort lifetable experiments to determine whether Daphniacan utilize ciliates and rotifers as food. Three species ofoligotrich ciliates (Halteria grandinella, Strobilidium gyransand Strobilidiumvelox) and one rotifer (Keratella cochlearis)were used. Lifetable experiments were conducted with a basallevel of algae (Cryptomonas sp.), plus either ciliates or rotifers,while survivorship experiments had only the rotifers or ciliates.Densities of 30 H.grandinella ml^–1, 50 S.gyrans ml^–1and 15 S.velox ml^–1 enhanced Daphnia pulex's populationgrowth rate 35–50% over controls with only algae. TenS.gyrans ml^–1 did not produce a significant change inDaphnia's growth rate. Densities of 100 and 300 K.cochlearis^–1 increased Daphnia population growth rates by II and10%, respectively. Both 10 and 50 S.gyrans ml^–1 enhancedDaphnia's survivorship compared to starved controls, but neither100 nor 300 K.cochlearis l^–1 enhanced its survivorship.The amount of enhancement of Daphnia growth rates by rotifersand ciliates is roughly proportional to the death rates imposedby Daphnia. The death rate imposed by Daphnia on rotifers isa function of both algal density and Daphnia size. Per unitbiomass, neither ciliates nor Keratella appear to be as nutritiousfor Daphnia as is Cryptomonas.     

Can overwintering versus diapausing strategy in <Emphasis Type="Italic">Daphnia</Emphasis> determine match–mismatch events in zooplankton–algae interactions?

Mismatches between predator and prey due to climate change have now been documented for a number of systems. Ultimately, a mismatch may have far-reaching consequences for ecosystem functioning as decoupling of trophic relationships results in trophic cascades. Here, we examine the potential for climate change induced mismatches between zooplankton and algae during spring succession, with a focus on Daphnia and its algal food. Whereas the development of an overwintering population of daphnids may parallel shifts in phytoplankton phenology due to climate warming, changes in the photoperiod–temperature interaction may cause the emerging population of daphnids to hatch too late and mismatch their phytoplankton prey. A decoupling of the trophic relationship between the keystone herbivore Daphnia and its algal prey can result in the absence of a spring clear water phase. We extended an existing minimal model of seasonal dynamics of Daphnia and algae and varied the way the Daphnia population is started in spring, i.e., from free swimming individuals or from hatching resting eggs. Our model results show that temperature affects the timing of peak abundance in Daphnia and algae, and subsequently the timing of the clear water phase. When a population is started from a small inoculum of hatching resting eggs, extreme climate warming (+6°C) results in a decoupling of trophic relationships and the clear water phase fails to occur. In the other scenarios, the trophic relationships between Daphnia and its algal food source remain intact. Analysis of 36 temperate lakes showed that shallow lakes have a higher potential for climate induced match–mismatches, as the probability of active overwintering daphnids decreases with lake depth. Future research should point out whether lake depth is a direct causal factor in determining the presence of active overwintering daphnids or merely indicative for underlying causal factors such as fish predation and macrophyte cover. Priority program of the German Research Foundation—contribution 5.     

Separation of marine seston and density determination of marine diatoms by density gradient centrifugation

An attempt has been made to separate constituents of marineseston samples: inorganic material, detritus and the algal species,by density gradient centrifugation, without affecting the physiologicalstate of the algae. A relatively inert gradient material, consistingof Percoll, salt and sucrose, was composed. Since the densitiesof detritus and algae as well as those of different algal speciesoften overlapped, only 10 of the 100 samples processed in thecourse of the year showed a reasonable separation. However,an enrichment with respect to one or more species was oftenachieved. Densities of eleven species of marine diatoms andof one dinoflagellate have been determined at different timesof the year. For eight diatom species and for the dinoflagellatethe following specific density ranges were established: Bidduiphiaaurita: 1.18–1.23 g cm^–3, Biddulphia sinensis: 1.03–1.08g cm^–3, Cerataulina bergonii: 1.03–1.06 g cm^–3,Ditylum brightwellii: 1.07–1.13 g cm^–3, Rhizosoleniadelicatula: 1.04–1.09 g cm^–3, Skeletonema costatum:1.12–1.17 g cm^–3, Streptotheca thamensis: 1.04–1.10g cm^–3 , Thalassiosira rotula: 1.05–1.10 g cm^–3,Peridinium sp.: 1.08–1.12 g cm^–3. No seasonal variationin density was demonstrated. Gradients of different compositiondid not influence density measurements.     

Comparative feeding ecology of Tropocyclops prasinus mexicanus (Copepoda, Cyclopoida)

The herbivorous and carnivorous feeding biology of Tropocyclopsprasinus mexicanus, an especially small cyclopoid copepod, wasstudied under in situ food conditions in three different lakesand under experimentally augmented food supplies. The mass-specificfood uptake is compared to that of two larger species—Cyclopskolensis and Cyclops vicinus. Under in situ food conditions,T.p.mexicanus depended to a larger extent on algae than invertebrateprey and showed lower mass-specific ingestion rates than thetwo larger species. Daily mass-specific uptake rates for algaeranged between 10 and 24% of its body mass versus 0.7–7%for invertebrate prey. The larger species C.vicinus and C.kolensisingested a total dry mass equivalent to 106% or up to 143% oftheir body mass with algae contributing 66 and 81%. However,under enriched food availability, T.p.mexicanus is able to ingesta biomass equivalent to its body mass, with an algae (54%) andprey (40%) portion similar to that of the larger species. Bodysize appears to be an important factor for the relative importanceof algal versus invertebrate prey for cyclopoid copepods.     

The influence of food resources on the development, survival and reproduction of the two cyclopoid copepods: Cyclops vicinus and Mesocyclops leuckarti

Laboratory experiments were conducted to determine whether thetwo cyclopoid copepods. Cyclops vicious and Mesocyclops leuckaru.exploit the same food resources. The food requirements of juvenilesof the two cyclopoid copepods were investigated. Moreover, theimportance of algae for the predaceous adults was studied. Naupliiof both M leuckaru and C.vicinus successfully developed intocopepodites when fed the motile algae Chlamydomonas reinhardtii.Chlamydomonas sphaeroides and Cryptomonas sp. Threshold foodconcentrations for naupliar development varied between offeredalgae and between the two cyclopoid species. The food thresholdfor successful naupliar development, when reared on C.reinhardui,was lower for M.leuckarti (0.3 mg C 1^–1) than for C.vicinus(0.5 mg C l^–1) whereas a similar food threshold was foundusing Cryptornonas sp (0.3 mg C ^–1) and C.sphaeroides(<0.2 mg C 1^–1), Naupliar development time was inverselyrelated to food concentration. Food required for copepoditedevelopment differed for the two cyclopoid species. Cyclopsvicinus was able to develop to the adult stage on a pure dietof any one of the three algal species. whereas M.leuckarti requireda prey supply of the rotifer Brachionus rubens. Food composition.i.e. algal species, algal concentration and rotifer abundance,influenced copepodite survivorship of both cyclopoids and wasalways higher in the presence of B.rubens. Under similar foodconditions, mortality was higher for M.leuckarti than for Cvicinus. Mesocyclops leuckaru females were very dependent onanimal food. The predation rate of M.leuckaru was not lowerin the presence of algae. Egg production of M.leuckarti waslow on a pure algal diet and significantly higher when B rubenswas present. The results were used to discuss the life cyclestrategy and the possibility of exploitative competition ofthe two cyclopoid copepods.     

Environmentally controlled Daphnia spring increase with implications for sockeye salmon fry in Lake Washington, USA

In Lake Washington, juvenile sockeye salmon (Oncorhynchus nerka)strongly prefer Daphnia over other prey, switching uniformlyto Daphnia when the threshold abundance of 0.4 Daphnia L^–1is achieved. Using long-term Lake Washington data (1978–2001)and fry trap data (1992–2001) from a major tributary,we examined the following: (i) factors that predict Daphniapulicaria and Daphnia thorata increase to this threshold "switching"abundance, (ii) trends in Daphnia dynamics that may affect sockeyeforaging and (iii) temporal correspondence of Daphnia increaseand fry arrival. The winter abundance of D. pulicaria, in combinationwith basic parameters of spring conditions, was an importantpredictor of the date of D. pulicaria spring increase, indicatinggreater reliance on pelagic population dynamics (versus diapausehatch) than D. thorata exhibited. In addition, D. pulicariawas a more consistent prey than D. thorata, the latter exhibitinglarger population fluctuations. Thus, recently increasing D.thorata prominence could decrease diet consistency for sockeyefry. Additionally, the timing of sockeye arrival to Lake Washingtonand Daphnia’s increase to the switching threshold hasbecome less concordant, so that fry in recent years have hadto rely upon less profitable prey for longer periods. Long-termtrends and species-specific differences in Daphnia phenologymay affect fry through altering diet composition, with additionalimplications for other zooplankton withstanding greater predationpressure in Daphnia’s absence. Recent decades of warmingin Lake Washington are consistent with the warming of lakesworldwide, and complex phenological responses such as thosereported here may be common as the climate continues to change.     

Resistance to blue-green algal toxins by Bosmina longirostris

Bosmina longirostris was resistant to strains of Microcysrtsaeruginosa and Anabaena flosaquae previously reported to havelethal toxic effects on cladocerans. These blue-green algaewere of poor nutritional value to B.longirostris; survivorshipwas increased when fed these algae but reproduction was negligible.Results of feeding selectivity experiments showed that B.longirostrisdid not avoid consuming these blue-green algae, indicating thatthe mechanism for resistance must be post-ingestion. These resultssuggest that, unlike the other cladocerans tested, B.longirostriscould potentially coexist with toxic blue-green algal blooms.     

Effects of nitrogen stressed algae on different Acartia species

We studied the reproductive response of two copepod species,Acartia tonsa and Acartia clausii, fed algae with differentC:N ratios (4.5 and 9.1 molar ratios respectively) in orderto investigate the influence of nutritional imbalances on calanoidcopepods egg production. Adult females were incubated with thecryptophyte Rhodomonas sp. at saturating concentrations. Thealgae were cultured under nitrogen depleted and sufficient conditions.Ingestion rates of the animals fed with different algae andtheir response in terms of egg production and hatching successof the eggs were quantified. Both species produced more eggwhen fed with nitrogen-limited algae. Ingestion rates and egghatching differed between species, but were not significantlyaffected by the quality of the food. The only difference betweenthe two species in their reaction to food quality was that A.tonsa increased the number of resting eggs, whereas no restingegg production was observed in A. clausii when fed with nitrogenlimited algae. These results support the recent suggestion thata moderately high prey C:N ratio (10–15) supports a higheregg production than a C:N ratio substantially <10.     

Influence of two Daphnia species on summer phytoplankton assemblages from eutrophic lakes

We conducted grazing experiments to test whether larger-bodiedDaphnia pulicaria have a different effect from smaller-bodiedDaphnia galeata mendotae on the composition of summer algalassemblages in eutrophic lakes. Three separate cubitainer experimentswere run for 5 days in a replicated factorial design utilizingtwo algal community types and the two Daphnia species. Inorganicphosphorus and nitrogen were added to prevent nutrient limitationof the algae. Both edible and inedible size fractions of chlorophylla increased in cubitainers without Daphnia spp. Grazer additionusually resulted in a reduction in edible chlorophyll; reductionswere greater in D.pulicaria cubitainers. Grazing by Daphniaspp. on presumed inedible chlorophyll was variable. Algal sizewas not always a good predictor of grazeability. The resultsof this study indicate that D.pulicaria, because of its greaterfiltration potential and ability to ingest larger particles,provides a stronger control on inedible-sized algae when comparedto equal numerical densities of D.g.mendotae. However, Aphanizomenonincreased as a response to heavy grazing pressure by D.pulicariaon other algal species. This suggests that biomanipulation effortsthat promote large-bodied Daphnia may not produce desirableresults if nutrient inputs remain high.     

Omnivory in cyclopoid copepods: comparisons of algae and invertebrates as food for three, differenfly sized species

We examined the importance of algal versus invertebrate preyfor three cyclopoid copepods by comparing reproductive successfor females fed on three diets: exclusively algal food, exclusivelyinvertebrate prey and a combination of algal plus invertebrateprey. The three cyclopoid species represent a distinct gradientin body size: Tropocyclops prasinus mexicanus (small body size),Diacyclops thomasi (medium body size) and Mesocyclops edax (largebody size). Our results provide strong evidence for the potentialimportance of algae in the diet of adult cyclopoid copepods.However, the role of herbivory is dependent on species bodysize. We found that algae are the key dietary factor for reproductivesuccess of the small T.p.mexicanus. In contrast, the availabilityof invertebrate prey had a greater influence on reproductionby the two larger species. Overall, cyclopoid copepods shouldbe generally considered as having the potential to derive theirenergy from either animal or algal sources. This has importantconsequences for interpretations of the forces influencing zooplanktoncommunity diversity as well as for general food web theory.     

Stoichiometric impacts of increased carbon dioxide on a planktonic herbivore

The partial pressure of carbon dioxide (pCO₂) in lake ecosystems varies over four orders of magnitude and is affected by local and global environmental perturbations associated with both natural and anthropogenic processes. Little is known, however, about how changes in pCO₂ extend into the function and structure of food webs in freshwater ecosystems. To fill this gap, we performed laboratory experiments using the ecologically important planktonic herbivore Daphnia and its algal prey under a natural range of pCO₂ with low light and phosphorus supplies. The experiment showed that increased pCO₂ stimulated algal growth but reduced algal P : C ratio. When feeding on algae grown under high pCO₂, herbivore growth decreased regardless of algal abundance. Thus, high CO₂‐raised algae were poor food for Daphnia. Short‐term experimental supplementation of PO₄ raised the P content of the high CO₂‐raised algae and improved Daphnia growth, indicating that low Daphnia growth rates under high pCO₂ conditions were due to lowered P content in the algal food. These results suggest that, in freshwater ecosystems with low nutrient supplies, natural processes as well as anthropogenic perturbations resulting in increased pCO₂ enhance algal production but reduce energy and mass transfer efficiency to herbivores by decreasing algal nutritional quality.     

Daphnia as keystone predators: effects on phytoplankton diversity and grazing resistance

Theory predicts that a predator can promote coexistence amongcompeting prey, and so enhance prey diversity (the keystonepredation effect), by fostering dominance of slow-growing, consumption-resistantprey. In contrast, if the predator promotes dominance by fast-growingvulnerable prey, theory predicts that the predator is unlikelyto promote prey diversity. Theory is silent about keystone predationeffects when the predator does not cause a net change in thevulnerability of the prey assemblage. I present experimentalevidence that Daphnia can act as a keystone predator withoutcausing a net change in the grazing resistance of the phytoplanktonassemblage. No change in resistance was observed, despite strongDaphnia effects on the species composition of the phytoplankton.     

Linking herbivore-induced defences to population dynamics

1. Theoretical studies have shown that inducible defences have the potential to affect population stability and persistence in bi‐ and tritrophic food chains. Experimental studies on such effects of prey defence strategies on the dynamics of predator–prey systems are still rare. We performed replicated population dynamics experiments using the herbivorous rotifer Brachionus calyciflorus and four strains of closely related algae that show different defence responses to this herbivore. 2. We observed herbivore populations to fluctuate at a higher frequency when feeding on small undefended algae. During these fluctuations minimum rotifer densities remained sufficiently high to ensure population persistence in all the replicates. The initial growth of rotifer populations in this treatment coincided with a sharp drop in algal density. Such a suppression of algae by herbivores was not observed in the other treatments, where algae were larger due to induced or permanent defences. In these treatments we observed rotifer population densities to first rise and then decline. The herbivore went extinct in all replicates with large permanently defended algae. The frequency of herbivore extinctions was intermediate when algae had inducible defences. 3. A variety of alternative mechanisms could explain differential herbivore persistence in the different defence treatments. Our analysis showed the density and fraction of highly edible algal particles to better explain herbivore persistence and extinctions than total algal density, the fraction of highly inedible food particles or the accumulation of herbivore waste products or autotoxins. 4. We argue that the rotifers require a minimum fraction and density of edible food particles for maintenance and reproduction. We conjecture that induced defences in algae may thus favour larger zooplankton species such as Daphnia spp. that are less sensitive to shifts in their food size spectrum, relative to smaller zooplankton species, such as rotifers and in this way contributes to the structuring of planktonic communities.     

Some characteristics of the carbon compounds released by Daphnia

The Daphnia species studied released 18–100% of the algalcarbon ingested as dissolved and particulate carbon compounds,presumably mainly as feces. The particulate fraction constitutedon average 79 5% of the total released compounds, leaving21% as dissolved compounds. The particles released were verysmall and transparent, not visible by light microscopy Moreover,they contained significant amounts of chlorophyll derivatives.The dissolved compounds consisted mainly of small molecules(mol. wt >10³ daltons), and were shown to be utilized byplanktonic bacteria. Our results show that particulate organiccarbon and chlorophyll a should not be used as measures foralgal carbon in grazing experiments with Daphnia. Both theseparameters were influenced by the animals' fecal particles,yielding lowered clearance rates compared with those obtainedby using cell numbers as a measure for algal carbon.     

Temporal pattern of feeding response of Chaoborus larvae to starvation

The effect of starvation on the feeding rate of larval Chaoborus(Diptera. Chaoboridae) was investigated using Daphnia roseaas prey. The starvation period varied from 12 h to 22 days.The starved Chaoborus were individually incubated with 10 Daphniaunder controlled light and temperature conditions. Observationswere made on prey mortality every 2 h for the first 12 h andonce after 24 h. Feeding rates gradually increased to a maximumbetween 7–11 days of starvation. After this period, feedingrates declined to previous low levels. Generally, feeding rateswere significantly higher during the first 2–4 h of feeding.Thereafter, feeding rates were lower and exhibited no consistentpattems with length of feeding time.     

Remote detection of algae by copepods: responses to algal size, odors and motility

Selective feeding on large algae by copepods involves remotedetection of individual particles and subsequent active captureresponses In this study we use radiotracer experiments to quantifythe clearance rates of five coexisting freshwater copepods andto investigate the relative merits of the chemoreception andmechanoreception hypotheses of remote detection Tropocyclopsand three diaptomid copepods exhibited relatively high clearancerates when feeding on low concentrations of large algae, suggestingthat most previous studies with freshwater copepods have underestimatedmaximal clearance rates and the degree of size selectivity.All five species of copepods exihibited strong selection foran intermediate-sized flagellate (25 µm Cartena) or alarge-sized nonmotile alga (80 µ.m Pediastrum) over asmall-sized flagellate (6 µ.m Chlamydomonas). The weight-specificclearance rate for Tropocylops prasmus feeding on motile Cartena(271 ml mg^–1 h^–1) was about twice that of threediaptomid copepods and more than an order-of-magnitude higherthan the estimate for Epischura lacustris feeding on its preferredalga, Pediastrum Assuming that distance chemoreception (‘smell’)is important in remote detection, we predicted that the additionof high concentrations of ‘algal odors’ would obscureany chemical gradients emanating from individual algal cellsand would thereby hinder the remote detection and active captureof large algae Contrary to this hypothesis, the addition ofamino acids, sucrose, and algal extracts had no effect on theclearance rates and selectivity of Diaptomus birgei. These results,together with recent cinematographic studies (Vanderploeg etal.,1990), suggest that mechanoreception is the primary mechanismfor the remote detection of large particles by diaptomid copepods.A raptorial cyclopoid, Tropocyclops prasinus, exhibited strongpreferences for motile algae, whereas a suspension-feeding calanoid,D birgei, did not select between motile and nonmotile cells.Motility appears to be an important factor in algal detectionfor small cyclopoid copepods but not for suspension-feedingdiaptomids     

Keystone predator effects and grazer control of planktonic primary production

If prey species exhibit trade-offs in their ability to utilize resources versus their ability to avoid predation, predators can facilitate prey turnover along gradients of productivity, shifting dominance from edible to inedible prey (the keystone predator effect). I tested this model under controlled, laboratory conditions, using a model aquatic system composed of zooplankton as the top consumer, a diverse community of algae as prey, and nutrients as basal resources. Nutrient manipulations (low and high) were crossed with presence–absence of zooplankton. Results supported theoretical predictions. Algal biomass increased in response to enrichment regardless of predator presence/absence. However, predators and nutrients had an interactive effect on algal biomass and size structure. At the low nutrient level, algal-prey were dominated by edible forms and attained similar biomass regardless of zooplankton presence/absence. At the high level of enrichment, presence of zooplankton favored higher levels of algal biomass and shifted dominance to large, inedible taxa. At the termination of the experiment, I performed a series of lab-based assays on the resultant algal community in order to quantify trade-offs among algal size classes in maximal population growth rates (as a measure of competitive ability for nutrients) and susceptibility to zooplankton grazing. Assays provided support for a size-based keystone trade-off. Small size classes of algae displayed higher maximal growth rates but were more susceptible to grazing effects. Large size classes were protected from grazing but showed low rates of population growth in response to enrichment.     

Foraging behavior by <Emphasis Type="Italic">Daphnia</Emphasis> in stoichiometric gradients of food quality

Mismatches in the elemental composition of herbivores and their resources can impact herbivore growth and reproduction. In aquatic systems, the ratio of elements, such as C, P, and N, is used to characterize the food quality of algal prey. For example, large increases in the C:P ratio of edible algae can decrease rates of growth and reproduction in Daphnia. Current theory emphasizes that Daphnia utilize only assimilation and respiration processes to maintain an optimal elemental composition, yet studies of terrestrial herbivores implicate behavioral processes in coping with local variation in food quality. We tested the ability of juvenile and adult Daphnia to locate regions of high-quality food within a spatial gradient of algal prey differing in C:P ratio, while holding food density constant over space. Both juveniles and adults demonstrated similar behavior by quickly locating (i.e., <10 min) the region of high food quality. Foraging paths were centred on regions of high food quality and these differed significantly from paths of individuals exposed to a homogeneous environment of both food density and food quality. Ingestion rate experiments on algal prey of differing stoichiometric ratio show that individuals can adjust their intake rate over fast behavioral time-scales, and we use these data to examine how individuals choose foraging locations when presented with a spatial gradient that trades off food quality and food quantity. Daphnia reared under low food quality conditions chose to forage in regions of high food quality even though they could attain the same C ingestion rate elsewhere along a spatial gradient. We argue that these aspects of foraging behavior by Daphnia have important implications for how these herbivores manage their elemental composition and our understanding of the dynamics of these herbivore–plant systems in lakes and ponds where spatial variation in food quality is present. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The role of feeding behavior in sustaining copepod populations in the tropical ocean

A fundamental question regarding marine copepods is how themany species coexist and persist in the oligotrophic environment(i.e. Hutchinson’s paradox). This question is addressedwith a stochastic, object-oriented Lagrangian model that explicitlysimulates the distinct foraging behaviors of three prominenttropical species: Clausocalanus furcatus, Paracalanus aculeatusand Oithona plumifera. The model also individually tracks allprey cells. Each particle’s motion combines sinking, turbulentdiffusion and active swimming when applicable. The model successfullysimulates observed size-partitioned carbon uptake rates. Basedon the model results, the wide-ranging translational ambit employedby C. furcatus is best suited for the acquisition of passiveprey while the relatively stationary behavior of O. plumiferapromotes the capture of larger, quickly sinking cells. The modelresults further suggest that the slow velocities and feedingcurrent employed by P. aculeatus are best suited for acquiringthe smallest cells though it also has a slight advantage overC. furcatus in acquiring the largest prey. A resource threshold,at a prey concentration of 530 cells mL^–1, is consistentlyexhibited by all three modeled species. Overall, these resultsimply that the size-partition preferences due to their differentforaging behavior contribute to the coexistence of these threespecies. This paper is one of six on the subject of the role of zooplanktonpredator–prey interactions in structuring plankton communities.     

Use of time-series analysis to demonstrate advection rates of different variables in a small lake

Time-series analysis of daily data from 3 stations (maximumseparation – 1 km) in a small lake (Guelph Lake, Ontario)has demonstrated the existence of (0 strong horizontal advectionwithin the basin at a time scale of 2–3 d and (ii) longerterm periodicities (10–20 d) associated with the passageof atmospheric weather systems. Different rates and directionsof horizontal advection were observed for different variables.Fluctuations in integral SRP concentrations at station 1 (outflowend) consistently occurred 3 d later than at station 3 (inflowend). The algal biomass (chlorophyll a) at station 1 laggedthat at station 3 by half a day. The time lag between station1 and station 3 for Aphanizomenon flos-aquae was 7 d, whereasfor Ceratitun hirundinella station 1 led station 3 by 3 d indicatingmotion by the species in opposite directions. The distributionof the algal biomass in space and time was a composite of theindividual species patterns. Longer term (10–20 d) periodicitieswere also observed. Examination of the periodicities in theaverage daily wind speed and water column stability showed thatsuch lags or leads were likely due to periods of vertical mixing.The significance of these results is then discussed in relationto sampling schemes for the analysis of phytoplankton dynamicsin small basins.