Plankton ecology in Long Pond,St. John's,Newfoundland: A polluted pond characterized by a high flushing rate

Plankton was studied seasonally and quantitatively in Long Pond, St. John's, Newfoundland. This pond receives both rural and urban runoff and is characterized by a high flushing rate. A comparison is made with Clarkes Pond, Hogans Pond and Bauline Long Pond. Long Pond phytoplankton was characterized by nannoplankton (particularly flagellated forms). The most important zooplankters were Bosmina coregoni and Daphnia catawba. Aspects of plankton ecology are discussed in relation to eutrophication and water renewal.     

The production of hemoglobin by small pond Daphnia pulex: intraspecific variation and its relation to habitat

SUMMARY.

• 1 Hemoglobin production was measured for two populations of Daphnia pulex, one from a temporary pond (GR Pond) and one from a permanent pond (Rash Pond). Surface water in Rash Pond remains high in oxygen, while by late summer very little oxygen remains in GR Pond. Hemoglobin synthesis was induced in the laboratory by artificial oxygen deficiency.
• 2 Reproductive state influenced the level of hemoglobin in Daphnia. Females with parthenogenesis eggs had higher total body hemoglobin than ephippial females. Clutches laid by pale Daphnia immediately before exposure to low oxygen conditions were aborted. Offspring produced by hemoglobin-rich females later in the treatment survived.
• 3 Hemoglobin production was higher for Rash Pond Daphnia. Visual predators exist in GR Pond, but are absent in Rash Pond. Also, Daphnia are smaller in GR Pond. Visual predation may have selected against high levels of hemoglobin in the temporary pond. Thus oxygen availability in nature is not necessarily a good predictor of hemoglobin production by Daphnia.
• 4 Feeding behavior was altered in low oxygen conditions. Browsing was dominant in low oxygen treatments while Daphnia in control treatments filtered algae normally. Browsing may increase access to sedimented iron necessary for hemoglobin synthesis.

     

Dynamics of a Boreal Lake Ecosystem during a Long-Term Manipulation of Top Predators

We assessed the long-term (16 years) effects of introducing piscivores (northern pike) into a small, boreal lake (Lake 221, Experimental Lakes Area) containing abundant populations of two planktivorous fish species. After the introduction, pearl dace were extirpated and yellow perch abundance was greatly reduced. Daphnia species shifted from D. galeata mendota to larger bodied Daphnia catawba, but the total zooplankton biomass did not increase, nor did the biomass of large grazers such as Daphnia. Phytoplankton biomass decreased after the northern pike introduction, but increased when northern pike were partially removed from the lake. Phosphorus (P) excretion by fish was ∼0.18 mg P m⁻² d⁻¹ before pike addition, declined rapidly to approximately 0.03–0.10 as planktivorous perch and dace populations were reduced by pike, and increased back to premanipulation levels after the pike were partially removed and the perch population recovered. When perch were abundant, P excretion by fish supported about 30% of the P demand by primary producers, decreasing to 6–14% when pike were abundant. Changes in phytoplankton abundance in Lake 221 appear to be driven by changes in P cycling by yellow perch, whose abundance was controlled by the addition and removal of pike. These results confirm the role of nutrient cycling in mediating trophic cascades and are consistent with previous enclosure experiments conducted in the same lake.     

Predator-Mediated Coexistence of Exotic and Native Crustaceans in a Freshwater Lake?

The predatory effects of a Dipteran insect, Chaoborus, on the competition between exotic cladoceran Daphnia lumholtzi and two natives, D. catawba and D. pulex, were studied for a period of three years in a freshwater reservoir, Lake James, North Carolina (USA). D. lumholtzi was first encountered in September 1997 and it was present only between August and October when population densities of native species were low and that of Chaoborus sp. was high. The patterns observed in the population dynamics of the exotic D. lumholtzi and two natives, Chaoborus suggest that a predator mediated coexistence phenomenon might be taking place in Lake James. The strong positive correlation between Chaoborus and D. lumholtzi and the negative correlation between Chaoborus, D. catawba and D. pulex is supportive of this hypothesis.     

Ciliate populations in temporary freshwater ponds: seasonal dynamics and influential factors

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (～1 ha) held water for 98 days, whereas Pond II (～0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pressure was manipulated. 2. In the natural pond water, total ciliate abundance in Pond II rose rapidly from day 1 increasing two orders of magnitude by day 7. In contrast, total abundance in Pond I began at the same level as in Pond II but increased much more slowly, reached a plateau of around 500 individuals L^?1, and increased again late in the hydroperiod. 3. Despite being only 500 m apart, the two ponds were fairly dissimilar in terms of their species richness and species composition. Pond I contained 50 species compared with 70 species for Pond II, with only 24 species shared. Additional species occurred within the enclosures raising the total species richness to 145 species; 88 from Pond I, 104 from Pond II, with 47 species (30%) in common. Pond II contained more mid‐sized ciliates (50–200 μm), whereas Pond I was dominated by smaller ciliates, especially in mid‐May and early June. In Pond I, cumulative species richness throughout the hydroperiod was highest in the predator addition enclosures (65 ± 4 species), followed by the partial‐predator exclusion enclosures (50 ± 4). Lowest species richness was found in the control enclosures (39 ± 2) and in the pondwater controls (39 ± 0). Differences between the ciliates in the natural pond water and the enclosures appeared to be related to a greater concentration of phytoplankton within the enclosures (perhaps resulting from extensive growth of duckweed, Lemna, outside), and higher densities of zooplankters in the pond. 4. The physicochemical environment influenced species richness, total abundance and the number of rare species (27 in Pond II versus 13 in Pond I). Variation in ciliate abundance in Pond I could be explained by the number of days after filling (39%) and enclosure treatment (23%). These two parameters also explained 72% of the variation in species richness in Pond I (46 and 26%, respectively). Sixty‐five per cent of the variation in abundance in Pond II could be explained by the measured parameters: number of days after filling 27%, pH 19%, and nitrate levels 12%. Fifty‐two per cent of the variation in species richness was explained by the environmental parameters, of which pH was the most influential. Species succession was a strong feature of both ponds and its relationship to environmental variables and the presence of other organisms is discussed. 5. Addition of invertebrate predators resulted in higher abundance and higher species richness for a limited time period in one of the ponds – suggesting that differences in foodweb dynamics may influence ciliate community composition.     

Is competition important to arctic zooplankton community structure?

1. Daphnia pulex and Daphnia middendorffiana are commonly found in the Toolik Lake region of arctic Alaska. These two species are very similar morphologically, although their natural distributions differ markedly: D. pulex is restricted to shallow ponds, while D. middendorffiana is widely distributed and found in a variety of ponds and lakes. We compared the reproductive capabilities of D. pulex and D. middendorffiana grown under similar resource conditions and in the absence of the invertebrate predator Heterocope septentrionalis. In situ life table and mesocosm experiments were conducted in Toolik Lake and Dam Pond, habitats that have historically contained natural populations of D. middendorffiana, but never D. pulex. 2. Daphnia pulex exhibited a significantly higher net growth rate than D. middendorffiana in both life table and mesocosm experiments although D. pulex has never been found in either Toolik Lake or Dam Pond. Daphnia middendorffiana exhibited a negative net growth rate in Dam Pond, which had lower resource levels then Toolik Lake. Therefore, the smaller D. pulex appears to have a lower food threshold concentration than the larger D. middendorffiana. 3. Our results indicate that D. pulex is a superior resource competitor in the Toolik Lake region. These results combined with distributional patterns suggest that the restricted distribution of D. pulex in these arctic lakes and ponds cannot be explained by resource competition alone. We suggest that in the presence of H. septentrionalis, predation is an important factor structuring arctic zooplankton communities in the Toolik Lake region.     

Spatial Dynamics of Mesocyclops edax (S. A. FORBES), Tropocyclops prasinus mexicanus KIEFER,Diaptomus pallidus HERRICK,Ceriodaphnia lacustris (BIRGE), Bosmina longirostris (O. F. MÜLLER), Daphnia parvula (FORDYCE) and Nauplii in a Northeastern Ohio Pond

A hypothesis on spatial dynamics of pelagic crustacean plankters was tested with the copepods and cladocerans of Squire Pond, Ohio. There was an agreement between the expected and the observed pattern of overall horizontal distribution in most instances for Mesocyclops edax, Tropocyclops prasinus mexicanus, Ceriodaphnia lacustris, Bosmina longirostris and nauplii, but only in a few instances for Diaptomus pallidus and Daphnia parvula. Windward accumulation was common for the first 4 species and near uniform distribution was frequent for the nauplii. Vertical-distribution trend along transect for all species rarely corresponded with the expectation. Alternation of modal depth along transect was one of the most frequently observed trends. Ways to test the hypothesis in the future are discussed.     

Ultraviolet and temperature effects on planktonic rotifers and crustaceans in northern temperate lakes

1. Anthropogenic stressors such as climate change, ozone depletion and acidification may act in concert to alter ultraviolet (UV) light and temperature regimes in freshwater ecosystems. These physical and chemical changes will inevitably affect zooplankton community dynamics, but little is known about their relative effects on different species in natural communities. During spring, species that migrate to surface waters to take advantage of warmer temperatures may be especially vulnerable as UV levels can be high. 2. The objective of this study was to investigate the in situ effects of UV and temperature on a natural assemblage of planktonic rotifers and crustaceans during the spring. We performed in situ exposure experiments in two lakes with different surface temperatures. 3. Exposure to UV had a significant effect on the abundance and/or reproduction of four rotifers: Gastropus spp., Kellicottia bostonensis, Kellicottia longispina, Keratella spp.; two cladocerans: Holopedium gibberum, Daphnia catawba, and one copepod: Leptodiaptomus minutus. Incubation under cooler temperatures had a negative effect on K. longispina and H. gibberum. Temperature and UV had a significant interactive effect on abundance and/or reproduction of L. minutus and Ploesoma truncatum. Our results indicate that changes in underwater UV and temperature can significantly influence the composition of the zooplankton community and ultimately food web dynamics.     

Positive effects of UV radiation on a calanoid copepod in a transparent lake: do competition, predation or food availability play a role?

Zooplankton tolerant to ultraviolet radiation (UVR) could beindirectly affected by UVR through interactions with UV-sensitivespecies in the same ecosystem. In Lake Giles, Pennsylvania,USA, the calanoid copepod Leptodiaptomus minutus is more UVRtolerant than the cohabiting species Daphnia catawba and Cyclopsscutifer. We asked whether L. minutus is affected by UV-inducedmortality of a food competitor (D. catawba) or a predator ofits nauplii (C. scutifer). We conducted two in situ enclosureexperiments with six treatments: L. minutus alone, L . minutus+ Daphnia and L. minutus + Cyclops in the presence and absenceof UVR. There were few differences in survival among treatmentsin Experiment 1, which had enhanced food and a cumulative UVR(320 nm) dose of 9.3 kJ m^–2. In Experiment 2, which hadambient food and a UVR (320 nm) dose of 20.0 kJ m^–2, L.minutus survival and reproduction were higher in the +UVR comparedto –UVR, regardless of competitors or predators. Chlorophylla (Chl a) in Experiment 2 was higher in the +UVR than –UVR.While interactions between zooplankton species of differingUVR tolerances are potentially important, these results insteaddemonstrate that the beneficial UVR effect on L. minutus isindependent of concurrent detrimental UVR effects on competitorsand predators. Further research on the phytoplankton communityis necessary to determine whether UVR alleviates bacterial competition,increases nutrient availability or affects phytoplankton byother mechanisms.     

Behavioural and genetic differences in populations of Daphnia subjected to different levels of predation

1. Predictions based on a genetic control mechanism for vertical migration were tested by monitoring the vertical migration behaviour of electro-phoretically distinct clones of Daphnia longispina and Daphnia magna collected from ponds with different levels of predation. 2. The number of predator species in a pond (a measure of predation) had a significant effect on the vertical migration behaviour of the clones found within that pond, and a phenogram constructed on the basis of the percentage dissimilarity between the genotypes of the clones indicated that clones from the same site were more closely related genetically than clones from different sites. 3. There were significantly different vertical migration behaviour patterns between clones from different sites and between-site variation in behaviour was significantly greater than that found within a site. 4. Clones differed in the average depth they maintained in the waterbody regardless of the pond from which they were collected, but clones from the same site did have similar behavioural profiles suggesting a tendency to show the same behavioural patterns. 5. These findings, which support predictions based on a genetic control mechanism, are discussed in relation to phenotypically plastic mechanisms of vertical migration control widely reported in the literature.     

Effects of Ultraviolet Radiation on Diel Vertical Migration of Crustacean Zooplankton: An in situ Mesocosm Experiment

The objective of this study was to expand the spatial scale of previous experiments on the effects of ultraviolet radiation (UVR) on diel vertical migration (DVM) by freshwater zooplankton. We conducted an in situ mesocosm experiment in highly UVR transparent Lake Giles, Pennsylvania, in which we imposed two treatments: ambient UVR and UVR-shielded. Mesocosms (3440 L, 0.74 m diameter, 8 m deep) were large enough to include a spatial refuge from UVR and permit relatively large-scale DVM. Daphnia catawba adopted a significantly deeper distribution during the day in the ambient UVR treatment compared to the UVR-shielded treatment, but effects of UVR were absent at night. In contrast, DVM by Leptodiaptomus minutus was unaffected by the UVR treatment. In both treatments, Leptodiaptomus minutus were most abundant at the bottom of the mesocosms during the day and exhibited a more uniform distribution across depths at night. These results suggest that UVR, along with temperature, algal resources, and predators, may affect zooplankton DVM in aquatic ecosystems.     

Using morphological characters of subfossil daphniid postabdominal claws to improve taxonomic resolution within species complexes

Daphnia subfossils from lake sediments are useful for exploring the impacts of environmental stressors on aquatic ecosystems. Unfortunately, taxonomic resolution of Daphnia remains is coarse, as only a small portion of the animal is preserved, and so the identification of daphniid subfossils typically relies upon postabdominal claws. Daphniid claws can be assigned to one of two species complexes: D. longispina or D. pulex. Both complexes contain species with differing environmental optima, and therefore improved taxonomic resolution of subfossil daphniid claws would aid paleolimnological analyses. To identify morphological features that may be used to help differentiate between species within complexes, we used species presence/absence data from net tows to select lakes in central Ontario (Canada) containing only a single species from a particular complex, then used remains preserved in surface sediments of these lakes to isolate four Daphnia species: D. ambigua and D. mendotae from the D. longispina complex, and D. pulicaria and D. catawba from the D. pulex complex. Our analyses demonstrate that, within the D. longispina complex, postabdominal claw length (PCL) and spinule length can be used to distinguish D. mendotae from D. ambigua. In addition, within the D. pulex complex, there are differences between D. pulicaria and D. catawba in the relative lengths of the proximal and middle combs on the postabdominal claw. However, the number of stout spines on the middle comb is an unreliable character for differentiating species. Overall, our data demonstrate that greater resolution within Daphnia species complexes is possible using postabdominal claws; however, the process is arduous, and applicability will likely decrease with the number of taxa present.     

Sperm number assessed by flow cytometry in species of Daphnia (Crustacea,Cladocera)

Daphnia magna and Daphnia pulex are two important model species in ecotoxicology. In daphniids, studies of the effects of contaminants have mostly focused on female life history traits, yet it would also be important to examine male reproductive traits, particularly in relation to endocrine disruptors. In this study, we developed a protocol that uses flow cytometry to measure sperm number in individual males of different species of Daphnia. We tested our protocol on 114 males from several clones of three common species of Daphnia. Sperm count varied widely among individuals and reached high numbers (up to 1.45 × 10⁵). Positive relationships between male length and sperm number were observed in D. pulex and Daphnia pulicaria, but not in D. magna. Important inter‐clonal differences in sperm production were observed in all species, with some clones producing very little sperm. Duplicated sperm samples showed on average only 6% difference in sperm counts. Sperm counts were stable at least over a 2‐hr period and up to 5 hr for most samples. This sperm isolation protocol and flow cytometric enumeration approach will be of major interest to ecotoxicologists.     

Polymorphism and Food Limitation in Three Daphnia carinata Populations

The annual cycles of Daphnia carinata in three fish-free ponds in southern New Zealand (Quarry, Taieri and Raupo Ponds) are described. Although breeding was continuous, the populations were frequently dominated by distinct cohorts and there was a sexual phase in spring. Growth rates, particularly in Quarry Pond, were often slow, and clutch sizes generally small. Egg and neonate sizes changed seasonally, but changes were not closely related to clutch sizes and body lengths. In Taieri Pond and Raupo Pond some D. carinata grew to 6.14 mm and carried clutches of up to 154 eggs. The potentially high fecundity associated with large size makes D. carinata a good coloniser, but our studies showed that it also survives well in poor food conditions by growing slowly and producing only 1–2 eggs per clutch. D. carinata showed marked seasonal polymorphism in tailspine length and development of head crests. In winter, crests were absent and tailspines were short and varied little with body length. Crests were first apparent, and tailspines began to elongate, in early spring, before the first appearance of a notonectid, Anisops wakefieldi. By midsummer, tailspines had increased markedly with body length but the slope of the relationship declined in autumn. Laboratory trials showed that both tailspine length and crest development increased in the presence of Anisops. These increases may be due to water-soluble factor(s) produced by Anisops.     

Resource partitioning in two coexisting cladocerans,Daphnia magna and Scapheloberis kingi (Anomopoda: Daphniidae), in north-eastern Algeria

Life-history traits of two coexisting cladocerans, Daphnia magna Straus and Scapheloberis kingi Sars, inhabiting a temporary pond in north-eastern Algeria were monitored in 2013 under laboratory conditions. Their life histories were compared for differences in traits such as age and size at first reproduction, size of neonates, brood size, number of broods per female, total life span and intrinsic rate of increase (r_m). Data were recorded during their entire life cycle. Daphnia magna, the larger species, could possibly be more successful in colonising temporary habitats than S. kingi because it allocates more energy to reproduction. Scapheloberis kingi, the smaller species, starts reproduction early, resulting in a smaller brood size and a shorter life span with fewer broods. Consequently, S. kingi produces a smaller number of neonates during its lifetime and has a lower r_m. In contrast, D. magna delays reproduction but produces a larger brood size and, because it is longer-lived, produces more broods and so produces a greater number of neonates and has a higher r_m over its lifetime.     

The effect of suspended sediments on Lake Texoma Daphnia: field distributions and in situ incubations

1. We measured the abundance and eggs per female of four Daphnia species in turbid and relatively clear regions of Lake Texoma (Oklahoma‐Texas, U.S.A.) on 12 dates over the course of 5 years. 2. Two species, Daphnia lumholtzi and Daphnia parvula, occurred and reproduced in turbid locations, but two other species, Daphnia mendotae and Daphnia pulicaria, occurred almost exclusively in relatively clear conditions. 3. To test the hypothesis that interference with foraging excludes clear‐water Daphnia species from turbid locations, we incubated adult D. mendotae at both a clear and a turbid site. In three successive experiments D. mendotae individuals incubated at the turbid site carried as many or more eggs than individuals incubated at the clear site.     

Cyclomorphosis in Daphnia lumholtzi induced by temperature

• 1 Cyclomorphosis is a well known phenomenon in Daphnia that involves a regular, seasonal, or induced change in body allometry. Long helmets and tail spines were induced in laboratory cultures of Daphnia lumholtzi with temperature of 31 °C as the proximal cue (temperature of locally occurring peak abundance in Kentucky Lake). The effect was greater in embryos than juveniles or adults exposed to the temperature cue.
• 2 The temperature cue appears to have a threshold value (animals cultured at 25 or 28 °C did not develop elongated helmets or spines). The helmet and spine length receded both with D. lumholtzi kept at a constant 31 °C temperature and when water temperature was decreased.
• 3 The induced helmet in this experiment (0.66 mm, 1.0 mm animal) was significantly longer than values reported in the literature for induction by planktivorous fish kairomones (0.25 mm, 1.2 mm animal). The strong response to a proximal cue of temperature may require the second weaker chemical cue for maintenance. It is suggested that a synergistic explanation with two cues may be more appropriate for cyclomorphosis induction and maintenance in Daphnia lumholtzi that could be tested with further studies.

     

Characterizing a zooplankton neighbourhood: small-scale patterns of association and abundance

• 1 This study compares small-scale (i.e. neighbourhood) associations among distributions of phytoplankton, zooplankton, and zooplankton grazing rates using a combination of correlations and analyses of spatial patchiness.
• 2 All zooplankton and phytoplankton populations had patchy distributions. On average, individuals experienced members of their same taxon at a density that was 42% greater than the mean sample density.
• 3 The various zooplankton taxa experienced different average neighbourhoods, even within the same stratum of the lake. For example, Daphnia galeata mendotae (Birge) experienced phytoplankton concentrations that were nearly 50% greater than those experienced by Daphnia pulicaria (Forbes) at the same depth.
• 4 The distributions of the various phytoplankton taxa were positively correlated with each other, but the distributions of zooplankton were negatively correlated, or more often, unrelated to each other.
• 5 Phytoplankton abundance was negatively correlated with zooplankton grazing rates.
• 6 We hypothesize that while phytoplankton distributions are driven by common external factors, the factors that determine horizontal distributions of zooplankton are species specific. In addition, zooplankton grazing appears at least partially responsible for the generation of patchiness in the distribution of phytoplankton.

     

Ecological fish production in Long Pond,a lakeshore lagoon on Long Point,Lake Erie

Synopsis Long Pond, a recently formed 2.4 ha lagoon on Long Point, Lake Erie (Canada), was treated with piscicide and found to contain 47,768 fishes of 22 species. Nine dominant species (Notropis heterolepis, Pimephales notatus, Notemigonus crysoleucas, Lepomis gibbosus, L. macrochirus, Perca flavescens, Cyprinus carpio, Micropeterus salmoides and Carassius auratus) comprised 91% and 97% of total numbers and standing crop respectively. Age, growth and production were determined giving a total fish production estimate (corrected for all species) of 87.5 kg ha^–1 y^–1 for this lagoon. Dominant species were deemed either invaders (Cyprinus carpio, Carassius auratus), which had entered the lagoon to spawn and been trapped, or residents. The invaders comprised 82% of the 277.8 kg ha^–1 total standing crop. Their successful spawning and subsequent escape of the young from the lagoon would have resulted in some 615 kg y^–1 of fish production outside the lagoon. Resident stocks were dominated by young fishes, a characteristic of exploitation or early colonization. This may have been due to the recent formation and subsequent expansion of the lagoon or high annual mortality due to extreme physical conditions but was most likely the result of excessive predation by Micropterus salmoides. Relationship between biomass and production show that the chance inclusion of the invaders produces an immediate shift from a characteristically early to a characteristically late phase of ecological development.     

The genusDaphnia in Cameroon,West Africa

Three species of the genusDaphnia are recorded from Cameroon.Daphnia obtusa was found in a single lake out of 37 sampled.Daphnia laevis was found in the same lake asD. obtusa and in two other lakes, whileD. rosea was found in three other lakes. All the lakes were at altitudes over 1 000 m. The records can be interpreted either as altitudinal survivals of continually dispersing species, or as relicts in an area whereDaphnia is usually very rare or absent.