Flagellate algae (Chrysophyceae, Dinophyceae, Cryptophyceae) in 48 high mountain lakes of the Northern and Southern slope of the Eastern Alps: biodiversity, taxa distribution and their driving variables

Survey samplings on late summer phytoplankton communities were carried out on 48 high mountain lakes located on the Austrian and Italian slopes of the Eastern Alps. The lakes of North Tyrol (A) and South Tyrol (I) were sampled in 2000 as part of the EU project EMERGE (EVK1-CT-1999- 00032). The lakes of Trentino (I) were investigated in other research projects during 1996 and 1997 (Adamello mountain range) and 2000 (catchment of the River Avisio), respectively. The objectives of this paper are: (1) to study taxonomy and biodiversity of Chrysophyceae, Dinophyceae and Cryptophyceae in high altitude lakes of the Eastern Alps; (2) to identify functional flagellate groups characterising lakes with similar habitat properties, (3) to identify the environmental variables driving abundance and distribution of the three selected algal groups, thus contributing to the selection of sensitive bioindicator taxa. The lakes investigated show rather wide morphological, chemical and trophic state gradients. Flagellate algae account for a median relative abundance (R.A.) of 68%. Chrysophyceae are the most important group in terms of biodiversity and R.A. Special flagellate associations could be related to lake features, like catchment geology, mineralization level and nutrient concentrations. However, the distribution of flagellate algae did not allow a complete geographical separation of the lakes studied in the different districts. Multivariate canonical analyses indicate that the distribution of Chrysophyceae is mainly driven by NO₃-N concentration and thermal conditions, while Dinophyceae are driven by a combination of alkalinity, altitude, thermal condition and, less importantly, nutrient concentration. Physical properties of the lakes, such as thermal condition and lake depth, represent the principal driving variables for Cryptophyceae. The responses to the different environmental variables suggest that the three flagellate groups analysed might be used as indicators for environmental changes in high mountain lakes of the Eastern Alps.     

Phytoplankton communities of North African wetland lakes: the CASSARINA Project

Seasonal variations in phytoplankton species composition (frequencies) and densities (cell numbers) in nine North African coastal lakes selected in Morocco (Merja Sidi Bou Rhaba, Zerga and Bokka), Tunisia (Chitane, Ichkeul and Korba lakes) and Egypt (Edku, Burullus and Manzala lakes) were investigated during 1998. The main aim was to provide gase-line information about overall phytoplankton diversity and how phytoplanktoncharacteristics differ between these contrasting aquatic systems.Water samples were collected at approximately three monthly intervals and phytoplankton analysis revealed marked seasonal and spatial differences in the quantitative and qualitative composition of the communities at each site. The Egyptian lakes generally had larger crops (Manzala and Burullus had mean crop densities of more than 104 cells ml^–1) but in the western North African sites only Korba and Sidi Bou Rhaba had closely comparable densities. Algae belonging to Bacillariophyceae, Chlorophyceae, Chrysophyceae, Cyanophyceae, Dinophyceae and Euglenophyceae were recorded. Taxa representative of all these algal groups occurred in two lakes (Korba and Manzala) but at the other seven sites only some of the groups were present.The Chlorophyceae was the most dominant group in lakes Burullus, Manzala, Korba and Sidi Bou Rhaba whereas Bacillariophyceae were dominant in lakes Zerga, Bokka and Edku. In Ichkeul and acidic Chitane the Dinophyceae and the Cyanophyceae were the dominant groups, respectively. The maximum percentage of Euglenophyceae occurred in Edku Lake but this group was absent in Sidi Bou Rhaba and Ichkeul. Cyanophyceans were present in significant numbers in all investigated lakes except in Ichkeul. A total of fifty-three genera were recorded, 17 of Chlorophyceae, 18 of Bacillariophyceae, 11 of Cyanophyceae, 3 of Chrysophyceae, 2 of Euglenophyceae and 2 of Dinophyceae. The maximum number of species (34) occurred in Burullus Lake and the minimum (6) in Ichkeul Lake. Only one lake (acidic Chitane) possessed species indicative of oligotrophic conditions. The Nile Delta lakes were the most species diverse sites.The phytoplankton communities of the nine North African lakes were composed entirely of cosmopolitan species but with one new species (Cyclotella choctawatcheeana) was recorded for the region. The data presented provide a contemporary account of the levels of algal diversity present in these sites at the end of the 20th century. The relevance of phytoplankton communities to assessment of lake status and future monitoring studies in the region is emphasised.     

Seasonal dynamics of phytoplankton in the Gulf of Aqaba,Red Sea

Seawater samples were collected biweekly from the northern Gulf of Aqaba, Red Sea, for Phytoplankton analysis during the period May 1998 to October 1999. Microscopic counts and HPLC methods were employed. Procaryotic and eucaryotic ultraplankton dominated throughout most of the year, with larger nano- and microplankton making up only 5% of the photosynthetic biomass. Moderate seasonal variations in the 0–125 m integrated Chl a contrasted with a pronounced seasonal succession of the major taxonomic groups, reflecting the changes in the density stratification of the water column: Prochlorococcus dominated during the stratified summer period and were almost absent in winter. Chlorophyceae and Cryptophyceae were dominant during winter mixing but scarce or absent during summer. Diatoms and Synechococcus showed sharp and moderate biomass peaks in late winter and spring respectively, but remained at only low Chl a levels for the rest of the year. Chrysophyceae, Prymnesiophyceae and the scarce Dinophyceae showed no clear seasonal distribution pattern. The implications of alternating procaryotic and eucaryote dominated algal communities for the Red Sea pelagic food web are discussed. Electronic Supplementary Material Electronic supplementary material is available for this article at and accessible for authorised users.     

Phytoplankton vertical distributions and composition in Baltic Sea cyanobacterial blooms

We studied the vertical structure of the phytoplankton community in two toxic cyanobacterial blooms in the offshore Baltic Sea. In 1994, vertically separated potentially toxic, diazotrophic and mixotrophic species (belonging to Cyanophyceae, Dinophyceae and Prymnesiophyceae) dominated. In 1997, picocyanobacteria, mainly in colonies, made up 40–50% of the total phytoplankton carbon biomass in the top 20 m both day and night. Colony-forming species of picocyanobacteria seem to be occasionally important and hitherto underestimated in the Baltic Sea.We found species-specific depth distribution patterns. Nodularia spumigena and Anabaena spp. were observed mainly above 10 m depth, while Aphanizomenon sp. was mostly found deeper, especially at night. Dinophysis norvegica was only abundant near the seasonal pycnocline and showed very limited diurnal migration. Other flagellates, including small Cryptophyceae and 10 identified Chrysochromulina species, occurred down to 40 m depth. Their vertical migration may help to retrieve nutrients from below the summer pycnocline.We conclude that considerable differences in dominating functional groups may occur between years/bloom stages, and that the vertical distribution pattern of many species is recurring at similar environmental conditions, suggesting species-specific niche-separation.     

Seasonality of phytoplankton in northern tundra ponds

Thermokarst ponds are the most abundant type of water body in the arctic tundra, with millions occurring in the coastal plains of Alaska, Northwest Territories and Siberia. Because ice covers of at least 2 m in thickness are formed at these latitudes, tundra ponds freeze solid every winter As a result, the growing season is shortened to a range of 60 to 100 days, during which time the photoperiod is altered to a prolonged light phase. Tundra ponds are generally close to neutral in pH and low in ions, contain dissolved gases near saturation and are nutrient poor. In low arctic ponds there are two phytoplankton biomass and primary production peaks, whereas they may be only one in the high arctic. Nanoplanktonic flagellates of the Chrysophyceae and Cryptophyceae dominate the maxima. The mid-summer decline in phytoplankton in the low arctic can be attributed to a combination of phosphorus limitation and heavy grazing pressure. The cryptomonad Rhodomonas minuta Skuja is one of the most widespread phytoplankters in tundra ponds. Because of the altered photoperiods, many species do not form resting spores prior to ice formation but survive freezing in the vegetative state.     

The primary production of phytoplankton in Lake Vechten

The primary production of the phytoplankton of Lake Vechten (The Netherlands) (area, 4.7 ha; mean depth, 6 m), an unpolluted and stratified sandpit was investigated from 1969 to 1980 (except in 1971, 1975 and 1976) by the in situ ¹⁴C-technique. Other data collected include: solar radiation, transparency, oxygen and thermal structure. In winter and spring diatoms, Cryptophyceae and Chlorococcales were important algal groups, while in summer Dinophyceae and Chrysophyceae were important. The chlorophyll-a concentration was compared to the cellular biovolumes (= fresh weight) of the most abundant phytoplankton species. The primary production maxima occurred in winter, spring and during the summer stratification. The vertical profiles of photosynthesis exhibit light inhibition at surface to a maximum of 4 m. The maximum of zooplankton grazing in May–June caused a sharp decrease in the phytoplankton biomass and seston concentration accompanied by the highest transparency (clear water phase).The values for cellular C-fixation range from 10 to 1307 mg C · M^–2 · day^–1 (annual mean of 280 mg C · m^–2 · day^–1). High dark fixation (up to 100%) was encountered in the metalimnion and hypolimnion from July to October together with peaks of ¹⁴C-fixation due to a crowding of phytoplankton and phototrophic anoxic bacteria. Extracellular excretion by phytoplankton, investigated in 1977 to 1979, was 15% of the annual mean of the total C-fixation. The photosynthetic efficiency, turnover rates, and activity coefficients were low, particularly in the summer months when Ceratium hirundinella was predominant. The seasonal variations were controlled mainly by solar radiation and probably phosphate, the former being more important in the non-stratification period and the latter during the stratification period.     

Winter phytoplankton community structure in three shallow temperate lakes during ice cover

The general model of seasonal phytoplankton succession in temperate lakes suggests that winter phytoplankton growth is minimal under ice-cover. However, some studies have found diverse phytoplankton communities during winter. The primary objectives of this study were to determine the species composition and the changes in the winter phytoplankton community structure under the ice. For 2 consecutive winters, phytoplankton samples were collected under ice-cover at 4 sites on 3 lakes in Arrowwood National Wildlife Refuge (ANWR), near Pingree, North Dakota. Ninety taxa were identified and enumerated. Densities of several of these taxa frequently exceeded 10⁶ cells l^–1. The winter phytoplankton communities in these lakes were dominated by flagellates, principally cryptomonads, a synurophyte (Synura uvella), small chrysophytes (Chrysococcus spp., Kephyrion spp.) and a dinoflagellate (Peridinium aciculiferum), as well as non-flagellate microchlorophytes (Monoraphidium spp., Ankistrodesmus spp., and Pseudodictyosphaerium sp.), a cyanobacterium (Gloeocapsa aeruginosa) and centric diatoms (Stephanodiscus minutulus, S. parvus and Cyclotella meneghiniana).     

The phytoplankton species composition and the seasonal periodicity in Lake Vechten from 1956 to 1979

The species composition and seasonal periodicity of the phytoplankton in Lake Vechten (The Netherlands) have been studied over a 20 year period. The results show a more or less regular pattern of algal succession during the year. Phytoplankton growth starts early in the year leading to a maximum in early spring, dominated by Bacillariophyceae and some Chlorophyceae. In summer a second maximum develops mainly consisting of a chrysophycean and a dinophycean species, accompanied by several Chlorophyceae. In September the summer species are gradually succeeded by diatoms. By the end of the summer stratification in October algal numbers decrease rapidly. The winter community consists of several species of Cryptophyceae and Chrysophyceae.When the data of 1975–1979 are compared with those from earlier records, distinct changes can be observed. These changes are discussed with reference to the trophic status of the lake. The vertical distribution of some species is described.     

Characterization of phytoplankton assemblages in a tropical coastal environment using Kohonen self‐organizing map

This study was aimed at understanding the main abiotic environmental factors controlling the distribution patterns of abundance and composition of phytoplankton (size less than 10 μm) assemblages in the coastal waters of south‐eastern Côte d'Ivoire. Data were collected during two cruises, in January (low‐water period) and October (high‐water period) of 2014. A total of 67 species were identified and assigned to Bacillariophyceae (49%), Cyanophyceae (21%), Chlorophyceae (13%), Euglenophyceae (10%), Dinophyceae (4%) and Chrysophyceae (3%). Three biotic zones (I, IIA and IIB) were distinguishable on a Kohonen self‐organizing map after an unsupervised learning process. The diatom genera Eunotia sp., Navicula sp. and Actinoptychus senarius are significantly associated with I, IIA and IIB biotic zones, respectively. A clear seasonal cum salinity trend was apparent in phytoplankton distribution patterns. Turbidity and nitrate levels were the main abiotic factors controlling phytoplankton distribution in I, the upland tidal regions of the lagoon. In regions along the lagoon–sea continuum, phosphate and turbidity exert the most control during the low‐water season (IIA), while total dissolved solids control phytoplankton distribution during the high‐water season (IIB). These are climate‐sensitive parameters whose concentrations depend on prevailing hydroclimatic processes. Therefore, seasonality can have important consequences on phytoplankton community and inadvertently the productivity of these systems.     

The phytoplankton of the internal Gulf of Olbia (North-East Sardinia) between July 1992 and July 1993

Abstract

The density variations and phytoplankton structure of the internal Gulf of Olbia (north-east Sardinia) from July 1992 to July 1993 are described.

The most important class was the Bacillariophyceae, because it accounted for the maximum values and because it dominated over about one-third of the study cycle. The picoplankton was present practically all the year round with the greatest development from September to March. Prymnesiophyceae, Dinophyceae, Cyanophyceae and Euglenophyceae were found more numerously in summer and autumn 1992 than in the rest of the year, while Bacillariophyceae, Chlorophyceae and Chrysophyceae were mostly found in spring and summer 1993.

Among the 16 species that expressed the highest mean yearly density values (greater than 1×10⁴ cell I^-1), 10 were Bacillariophyceae, 2 Dinophyceae, 3 Chrysophyceae and 1 Chlorophycea. The Bacillariophyceae have also been the dominant class in floristic terms (49 taxa on 95 total), followed by the Dinophyceae (26), the Chlorophyceae (5), the Chrysophyceae (5), the Prymnesiophyceae (4), the Prasinophyceae (2), the Euglenophyceae (2) and the Cyanophyceae (2).     

Effect of fluctuations in water level on phytoplankton development in three lakes of the Paraná river floodplain (Argentina)

The effect of fluctuations in water level on phytoplankton development (abundance, biomass, size structure, taxonomic composition, species diversity and rate of community compositional change) in three vegetated lakes of the Paraná River floodplain (27° 27′?S; 58° 55′?W) were studied. Between September 1995 and June 1996 there were two inputs of lotic water. Ordering of physical and chemical parameters (Principal Component Analysis) allowed the differentiation of two phases: I) without lotic influence (limnophase) and II) with lotic influence (potamophase). Two-hundred fifty-eight algal taxa were identified, of which Euglenophyceae showed the highest number of taxa (65% of total). Small Chlorophyceae and Cryptophyceae (C-strategists) predominated in density in both periods. During potamophase, the input of nutrients from a flood event produced an increase in algal biomass and a shift in phytoplankton composition from a Chlorophyceae (C-strategists), to a Cyanophyceae and Euglenophyceae (S-strategists), dominated comunity. Bacillariophyceae, Chrysophyceae, Dinophyceae and Xanthophyceae were best represented during limnophase. All phytoplankton attributes showed significant differences between phases (limnophase vs potamophase) but not among lakes. These results support the hypothesis that hydrology (floods) clearly exerts an overall impact on the phytoplankton community composition in lakes of the Paraná River floodplain. Hydrology effects the lake water chemistry, conditioned by the isolation time prior to a flood, the horizontal dragging and exchange of algae during floods, and the water residence time and aquatic vegetation coverage.     

Phytoplankton species abundance in Lake Kasumigaura (Japan) monitored monthly or biweekly since 1978

This data paper reports the abundance of phytoplankton species in monthly or biweekly samples collected from May 1978 through March 2010 at two stations on Lake Kasumigaura, a shallow lake that is the second-largest lake in Japan. The data set of quantitatively over several decades is unique among the available published data papers concerning lakes or plankton and continues to be freely available. The monitoring has been performed as a component of the Lake Kasumigaura Long-term Environmental Monitoring program, conducted by the National Institute for Environmental Studies since 1977. The data set details 173 phytoplankton species (or taxa), which can be identified by using an optical microscope and records their abundance. The abundance of each species is expressed in units of volume (??m³) per milliliter of lake water. This approach allows quantitative comparisons among taxa because the cell size of phytoplankton varies by several orders of magnitude among taxa. The phytoplankton data include 39 species (taxa) of Cyanophyta, 67 Chlorophyceae (Chlorophyta), 3 Prasinophyceae (Chlorophyta), 1 Raphidophyceae (Heterokontophyta), 6 Euglenophyceae (Euglenozoa), 4 Dinophyceae (Dinophyta), 38 Bacillariophyceae (Heterokontophyta), 6 Chrysophyceae (Heterokontophyta), 7 Xanthophyceae (Heterokontophyta), 1 Cryptophyceae (Cryptophyta) and 1 Prymnesiophyceae (Haptophyta). The data have been used for ecological and environmental studies and for studies on lake management.     

Algal Assemblages Across a Wetland, from a Shallow Lake to Relictual Oxbow Lakes (Lower Paraná River, South America)

This study deals with the variation in the algal assemblages across the transversal dimension of a wetland of the Lower Paraná River from October 1998 to September 1999. The relationship between the algal composition and the physico-chemical variables is analyzed by means of Canonical Correspondence Analysis. The abundant floating macrophytes generated a severe reduction in light penetration in the relictual oxbow lakes (ROLs), almost anoxic conditions and high values of P, N and K. Such characteristics accounted for their very particular algal flora dominated by Cyanobacteria and several diatoms, species probably mixotrophic regarding their capacity to grow in darkness and tolerate very low oxygen contents. In the shallow lake, the phytoplankton comprised many small autotrophic green algae, accompanied by many flagellates of the classes Cryptophyceae, Euglenophyceae and Dinophyceae. Our results indicate that the macrophyte cover was probably the stirring factor in the selection of algal species along the transitional zone comprising a floodplain shallow lake and several ROLs.     

Phytoplankton periodicity of the Waitaki Lakes,New Zealand

The Waitaki River system in the South Island of New Zealand includes three large glacially-formed headwater lakes, Tekapo, Pukaki and Ohau, which drain into the manmade Lake Benmore. Phytoplankton periodicity was followed from December 1975 to January 1980 as part of a study investigating possible changes in these lakes as a consequence of hydroelectric development. The phytoplankton was highly dominated by diatoms, e.g., Diatoma elongatum, Cyclotella stelligera, Asterionella formosa, and Synedra acus, but in lakes Ohau and Benmore populations of green algae occasionally developed. In all four lakes seasonal phytoplankton periodicity was observed with maximum biomass in spring and summer. In Lake Tekapo, the first lake in the chain, maximum biomass did not exceed 300 mg m^–3, but in the very turbid Lake Pukaki the maximum summer biomass ranged between 300 and 800 mg m^–3. In Lake Ohau, the least turbid lake, maximum biomass was around 1 000 mg m^–3. In the newly created Lake Benmore periodicity was less evident and summer maxima reached over 1 500 mg m^–3. The phytoplankton periodicity in these lakes is greatly influenced by seasonal patterns of turbidity from inflowing glacial silt.     

Phytoplankton distribution patterns in the northwestern Sargasso Sea revealed by small subunit rRNA genes from plastids

Phytoplankton species vary in their physiological properties, and are expected to respond differently to seasonal changes in water column conditions. To assess these varying distribution patterns, we used 412 samples collected monthly over 12 years (1991–2004) at the Bermuda Atlantic Time-Series Study site, located in the northwestern Sargasso Sea. We measured plastid 16S ribosomal RNA gene abundances with a terminal restriction fragment length polymorphism approach and identified distribution patterns for members of the Prymnesiophyceae, Pelagophyceae, Chrysophyceae, Cryptophyceae, Bacillariophyceae and Prasinophyceae. The analysis revealed dynamic bloom patterns by these phytoplankton taxa that begin early in the year, when the mixed layer is deep. Previously, unreported open-ocean prasinophyte blooms dominated the plastid gene signal during convective mixing events. Quantitative PCR confirmed the blooms and transitions of Bathycoccus, Micromonas and Ostreococcus populations. In contrast, taxa belonging to the pelagophytes and chrysophytes, as well as cryptophytes, reached annual peaks during mixed layer shoaling, while Bacillariophyceae (diatoms) were observed only episodically in the 12-year record. Prymnesiophytes dominated the integrated plastid gene signal. They were abundant throughout the water column before mixing events, but persisted in the deep chlorophyll maximum during stratified conditions. Various models have been used to describe mechanisms that drive vernal phytoplankton blooms in temperate seas. The range of taxon-specific bloom patterns observed here indicates that different ‘spring bloom'' models can aptly describe the behavior of different phytoplankton taxa at a single geographical location. These findings provide insight into the subdivision of niche space by phytoplankton and may lead to improved predictions of phytoplankton responses to changes in ocean conditions.     

Ecology under lake ice

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under‐ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter‐summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake‐specific, species‐specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.     

Phytoplankton of a mountain lake (L’adové pleso,the Tatra Mountains,Slovakia): Seasonal development and first indications of a response to decreased acid deposition

A one-year study of the phytoplankton of remote mountain lake L’adové pleso (2057 m. a.s.l.), situated in the High Tatra Mountains, was carried out in 2000–2001. Seasonal development of the species structure and depth distribution of biomass, as well as chlorophyll-a concentrations, and chemical characteristics of the lake water were examined. The phytoplankton was made up of a low number of nanoplanktonic unicellular species, mainly flagellates from Cryptophyceae and Chrysophyceae. Plagioselmis lacustris, Cryptomonas cf. erosa and Ochromonas spp. were the most important with regards to both abundance and biomass. The phytoplankton showed a marked seasonal development. During most of the ice-covered period, abundances of phytoplankton remained very low. In regard to the vertical distribution, both species composition and total biomass were clearly stratified during most sampling dates. The amount of chlorophyll-a per unit biovolume varied considerably, and significantly higher values were found on sampling dates with complete or partial ice cover. Our data on pH and phytoplankton were compared with a previous study in 1990–1991 in order to evaluate possible changes associated with the decrease of acid deposition. The extent of episodic acidification of the lake water has diminished both in time and space, and lake water pH has slightly increased. We observed a shift in species composition, and an important increase of total phytoplankton abundance. This could be considered as a first sign of biological response to changing chemical conditions.     

Phytoplankton Periodicity in a Eutrophic Coastal Water of the Baltic Sea

The phytoplankton periodicity in the Darss-Zingst bodden chain, an estuary-like coastal water of the southern Baltic Sea, was investigated from 1984 to 1990. The following functional groups were established: 1.) nitrogen-fixing Cyanobacteria plus Oscillatoria limnetica, 2.) coccoid Chlorophyceae, Gomphosphaeria pusilla, Lyngbya contorta and Stephanodiscus hantzschii, 3.) coccoid Cyanobacteria except Gomphosphaeria, 4.) diatoms except Stephanodiscus, 5.) Cryptophyceae and some other flagellates. A general seasonal pattern was observable: in cold winters group 5 dominates; in spring a diatom bloom (= group 4) occurred, which was followed by the development of group 2; steep temperature increases caused a summer bloom of nitrogen-fixing cyanobacteria (= group 1), which was followed by groups 2 and 3 in autumn; in bland winters group 2 lasts until spring. Grazing was shown to be of minor importance for the phytoplankton periodicity.     

Variation in temporal [14C]plankton photosynthesis among warm monomictic lakes of coastal British Columbia

Seasonal patterns of [¹⁴C]phytoplankton photosynthesis (PP)were examined in six warm monomictic lakes of coastal BritishColumbia. Four of our study lakes followed typical lake patternswith maximum PP occurring in the spring and minimal rates occurringduring the winter. However, the spring maximum occurred severalweeks earlier than lakes in other climatic regions. In addition,maximum rates of daily photosynthesis were observed to occurduring the winter months in Maxwell Lake, rather than duringthe standard growing season. All study lakes except MaxwellLake had large Daphnia in the plankton community. Maxwell wasdominated by small crustacean zooplankton implying the importanceof trophic structure in mediating seasonal patterns of productivity.The four oligotrophic lakes in our study also exhibited P-deficiencyduring winter, as indicated by P-debt bioassays and rapid ³²PO₄^3–turnover rates. Our data suggest that these coastal oligotrophiclakes were co-limited by nutrients and light during winter.The importance of winter (November–March) photosyntheticproduction to the total annual carbon budget in the six lakesstudied here is greater than that typically reported for othertemperate zone lakes. If plankton community respiration decreasesmore than photosynthetic production with wintertime temperatures,then >50% of annual net pelagic carbon fixation could occurin winter in some coastal lakes.     

Food and growth relations of the marine microzooplankter,Synchaeta cecilia (Rotifera)

The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species; a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1⁻¹, the population growth constant increased from 0.17 to 0.60 d⁻¹ at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 10⁴ cells ml⁻¹, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1⁻¹ (0.3 to 1.9 individuals 1⁻¹), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod⁻¹ day⁻¹.