The epiphytic communities of various ecological types of aquatic vegetation of five pastoral ponds

Five small water bodies located within the agricultural region of Wielkopolska (west Poland) underwent investigation. Periphyton samples were collected from various macrophyte habitats representing rush vegetation (in five water bodies), submerged aquatic plants (in three) and nymphaeids (in one): Palędzie — Ceratophyllum demersum, Potamogeton crispus, Typha latifolia; Batorowo — Phragmites australis; Piotrowo — Potamogeton natans, Ceratophyllum submersum, Typha latifolia; Tarnowo Podgórne — Typha latifolia; Dąbrówka — Zannichellia palustris, Potamogeton pectinatus, Phragmites australis. The main goal of the study was to determine the composition and abundance of the periphytic communities inhabiting various types of rush and water vegetation of five water bodies located within a mid-field landscape area. Diatoms such as Achnanthidium minutissimum, Amphora ovalis, Cocconeis placentula orNavicula cincta revealed significantly higher densities in the zone of elodeids, while green algae prevailed among nymphaeids. As a result of this study it was found that the epiphytic algae were characterised by much lower diversity in respect to a specific water body, though much greater diversity was observed in its relation to the type of substratum. Two types of habitats were distinguished — the first of simple build (helophytes and nympheids) and the second containing the complicated architecture of plant stems (elodeids).     

The Relationships Between Environmental Factors and the Submerged Potametea Associations in Lakes of North-eastern Poland

A comparative analysis of submerged Potametea communities in lakes of north-eastern Poland was conducted with respect to 16 water chemistry and 14 substrate parameters. The analysis of 187 relevés based on TWINSPAN clustering showed the existence of 8 aquatic vegetation types. Each of them is characterized by a strong dominance of one of the following macrophytes: Potamogeton lucens, P. perfoliatus, Myriophyllum spicatum, M. verticillatum, Elodea canadensis, Ceratophyllum demersum, Ranunculus circinatus and Hydrilla verticillata. The above vegetation types correspond to the plant associations distinguished using the Braun-Blanquet method (Potametum lucentis, Potametum perfoliati, Myriophylletum spicati etc.) It was demonstrated that among properties of water analysed, COD-KMnO₄, SO₄²⁻, pH, Na⁺, K⁺, Ca²⁺, total hardness, total Fe, Cl⁻ and colour appear to be most important in differentiating the habitats of the communities studied. In the case of substrates the properties which best differentiated the habitats compared were hydration, organic matter content, total N, PO₄³⁻, K⁺, dissolved SiO₂, SO₄²⁻, Cl⁻ and pH. Most of the aquatic plant communities investigated are distinct with respect to their phytocoenotic structure and ecology and could be good indicators of various types of habitats in lake ecosystems.     

Echosounding observations of coverage,height, PVI,and biomass of submerged macrophytes in the southern basin of Lake Biwa,Japan

We have developed a procedure to process echosounding data to map the distribution of submerged aquatic macrophytes in the southern basin of Lake Biwa, a water body that has a surface area of 52 km² and a mean depth of 4 m. Echosounding observations were made along 27 transect lines spaced at 500-m intervals on August 4 and September 2 and 30, 2003. Quantitative vegetation data including percent coverage, mean vegetation height, and percent vegetation infestation were directly determined using image data from the echosounder recorded digitally on videotape. Based on the image data from an echosounder, a regression model was developed for estimating biomass of submerged macrophytes. The regression model using the total echo strength as the explanatory variable could reliably estimate macrophyte biomass up to 300 g m⁻². Distribution maps of macrophyte height and biomass suggest that the recent summer decline of submerged macrophytes started earlier in shallow areas (<3 m of depth) than deep areas (>4 m) in the southern basin of Lake Biwa.     

Biomass and nutrient stock of submersed and floating macrophytes in shallow lakes formed by rewetting of degraded fens

Ecosystem restoration by rewetting of degraded fens led to the new formation of large-scale shallow lakes in the catchment of the River Peene in NE Germany. We analyzed the biomass and the nutrient stock of the submersed (Ceratophyllum demersum) and the floating macrophytes (Lemna minor and Spirodela polyrhiza) in order to assess their influence on temporal nutrient storage in water bodies compared to other freshwater systems. Ceratophyllum demersum displayed a significantly higher biomass production (0.86–1.19 t DM = dry matter ha⁻¹) than the Lemnaceae (0.64–0.71 t DM ha⁻¹). The nutrient stock of submersed macrophytes ranged between 28–44 kg N ha⁻¹ and 8–12 kg P ha⁻¹ and that of floating macrophytes between 14–19 kg N ha⁻¹ and 4–5 kg P ha⁻¹ which is in the range of waste water treatment plants. We found the N and P stock in the biomass of aquatic macrophytes being 20–900 times and up to eight times higher compared to the nutrient amount of the open water body in the shallow lakes of rewetted fens (average depth: 0.5 m). Thereafter, submersed and floating macrophytes accumulate substantial amounts of dissolved nutrients released from highly decomposed surface peat layers, moderating the nutrient load of the shallow lakes during the growing season from April to October. In addition, the risk of nutrient loss to adjacent surface waters becomes reduced during this period. The removal of submersed macrophytes in rewetted fens to accelerate the restoration of the low nutrient status is discussed.     

Seasonal fluctuations in macrophyte cover and water transparency of four brown-water lakes: implications for crustacean zooplankton in littoral and pelagic habitats

The dynamics of crustacean zooplankton in the littoral and pelagic zones of four forest lakes having variable water qualities (colour range 130–340 mg Pt l⁻¹, Secchi depth 70–160 cm) were studied. The biomass of zooplankton was higher in the littoral zone than in the pelagic zone only in the lake having the highest transparency. In the three other lakes, biomass was significantly higher in the pelagic zone than in the littoral zone. In the two lakes with highest transparency, the littoral biomass of cladocerans significantly followed the development of macrophyte vegetation, and cladoceran biomass reached the maximum value at the time of highest macrophyte coverage. In lakes with lowest transparency, littoral zooplankton biomass developed independently of macrophyte density and decreased when macrophyte beds were densest. The seasonal development of the littoral copepod biomass did not follow the development of macrophytes in any of the lakes. The mean size of cladocerans in the pelagic zone decreased with increasing Secchi depth of the lake, whereas in the littoral zone no such phenomenon was detected. Seasonally, when water transparency increased temporarily in two of the lakes, the mean size of cladocerans in the pelagic zone decreased steeply. For copepods, no relationship between water transparency and body size was observed. The results suggested that in humic lakes the importance of the littoral zone as a refuge decreases with decreasing transparency of the water and that low water transparency protects cladocerans from fish predation. All the observed between-lake differences could not be explained by fish predation, but were probably attributed to the presence of chaoborid larvae with variable densities. Feeding efficiency of chaoborids is not affected by visibility and thus they can obscure the relationship between water quality, fish density, and the structure of crustacean zooplankton assemblages. Handling editor: S. I. Dodson     

The influence of water level and salinity on plant assemblages of a seasonally flooded Mediterranean wetland

We studied the key environmental variables shaping plant assemblages in Mediterranean abandoned ricefields with contrasting freshwater inputs over saline sediments. Plant species cover, water levels and soil variables were studied following a stratified random sampling design. Multivariate analysis identified water regime, particularly summer and autumn irrigation, as the most important environmental variable associated with vegetation composition. Distribution of annual and emergent macrophytes was not associated to salinity as found at the study site (0.57–4.1 mS/cm). Increased soil salinity, caused by summer irrigation near the soil surface did affect shallow-marsh assemblage distribution. These key environmental characteristics allowed us to identify six main assemblages. Annual macrophytes (such as Zannichellia palustris) were defined by high (over 10 cm) annual mean water level (MWL) and early successional conditions; emergent macrophytes (such as Typha spp., Scirpus lacustris) by annual MWL of 10 to − 25 cm and continuous shallow flooding in summer and autumn (MWL of 0–10 cm). The shallow-marsh group, correlated with annual MWL − 25 to − 100 cm, separated into two subgroups by salinity: grassland (including Paspalum distichum) with summer and autumn MWL below − 25 cm and brackish (with Juncus subulatus or Agrostis stolonifera) with summer and autumn MWL just below the soil surface (0 to − 25 cm). Water levels for the grassland subgroup may equate with a salinity ‘refuge’ for P. distichum. Time was a further determinant of variation in the full data set. Abundance of a large group of agricultural annuals (such as Sonchus tenerrimus) and damp ground annuals (including ricefield weeds such as Ammania robusta) decreased with time as bare ground disappeared. Maintenance of spatial vegetation heterogeneity in abandoned ricefields is contingent on continued water regime management.     

Can ephemeral proliferations of submerged macrophytes influence zoobenthos and water quality in coastal lagoons?

Hydrology is often the main determinant of water chemistry and structure of the aquatic communities in coastal lagoons, driven by the interaction of freshwater load from the catchment and marine intrusions. However, submerged aquatic vegetation (SAV) can have important local effects on both features, even during sporadically and short proliferations. A SAV summer proliferation was observed during 2003 in a coastal lagoon in Uruguay (Laguna de Rocha), increasing macrophyte cover and biomass in the less saline zones. SAV summer proliferations were first observed in summer 2001, with no records prior. The aim of this paper is to describe the ephemeral proliferation of SAV in this shallow brackish lagoon and to analyze its effects on the abiotic environment and on the zoobenthic community. Vegetated and unvegetated zones were sampled in the northern more limnic area (9.1 mS cm⁻¹ ± 4.8) and the southern brackish area (20.9 mS cm⁻¹ ± 5.2). Water and sediment chemistry were analyzed by standard methods and benthos and plants were collected with an Ekman grab. During SAV proliferation, suspended solids were five times lower inside macrophyte patches and water column total phosphorus and nitrogen were three and two times lower, respectively. Zoobenthos abundance and richness were higher in vegetated patches. However, no differences were found between sampling sites in the more brackish southern area and in the North after the SAV proliferation ended. This indicates that SAV can influence water chemistry and benthos structure above a biomass threshold of 100 g DW m⁻². Although hydrology is the driving force regulating communities and water chemistry in these coastal lagoons, our results showed that SAV can also be an important local factor above a certain biomass threshold.     

Successional changes in the soft-water macrophyte vegetation of (sub)atlantic, sandy, lowland regions during this century

SUMMARY.

• 1 Considerable changes in macrophyte vegetation can be noticed in 146 originally soft waters, when data on the recent aquatic vegetation are compared with historical information from the period 1900–60. Changes in nutrient status (N, P and C) and accumulation of organic material can be regarded as the operative factors.
• 2 The processes observed in soft waters are acidification, eutrophication and water hardening. Which process dominates depends on the type of soft water.
• 3 Acidification as well as eutrophication of water bodies may ultimately result in the total disappearance of all aquatic macrophytes, with the exception of the floating-leaved nymphaeids Nymphaea alba L. and Nuphar lutea (L.) Sm. Observed successional stages are described and summarized.

     

Early responses of plankton and turbidity to biomanipulation in a shallow prairie lake

We evaluated the effect of a fish removal from a shallow, turbid, eutrophic lake. By late May (following an October fish removal), the cladoceran community shifted from small-bodiedBosmina andChydorus (less than 100 l⁻¹) to largerDaphnia (over 100 l⁻¹). During the periods of peak daphnid abundance (late May–June) chlorophyll-a concentrations and edible diatoms were reduced and water transparency improved dramatically. Total phosphorus was not significantly lowered during this period. Although this clear-water phase was short-lived (May, June and early July), it corresponded to the critical period of plant growth and allowed dramatic increases in submergent macrophytes.     

Responses of four submerged macrophytes to freshwater snail density (Radix swinhoei) under clear‐water conditions: A mesocosm study

Macrophytes play a key role in stabilizing clear‐water conditions in shallow freshwater ecosystems. Their populations are maintained by a balance between plant grazing and plant growth. As a freshwater snail commonly found in shallow lakes, Radix swinhoei can affect the growth of submerged macrophytes by removing epiphyton from the surface of aquatic plants and by grazing directly on macrophyte organs. Thus, we conducted a long‐term (11‐month) experiment to explore the effects of snail density on macrophytes with distinctive structures in an outdoor clear‐water mesocosm system (with relatively low total nitrogen (TN, 0.66 ± 0.27 mg/L) and total phosphorus (TP, 36 ± 20 μg/L) and a phytoplankton chlorophyll a (Chla) range of 14.8 ± 4.9 μg/L) based on two different snail densities (low and high) and four macrophyte species treatments (Myriophyllum spicatum, Potamogeton wrightii, P. crispus, and P. oxyphyllus). In the high‐density treatment, snail biomass and abundance (36.5 ± 16.5 g/m² and 169 ± 92 ind/m², respectively) were approximately twice that observed in the low‐density treatment, resulting in lower total and aboveground biomass and ramet number in the macrophytes. In addition, plant height and plant volume inhabited (PVI) showed species‐specific responses to snail densities, that is, the height of P. oxyphyllus and PVI of M. spicatum were both higher under low‐density treatment. Thus, compared with low‐density treatment, the inhibitory effects of long‐term high snail density on macrophytes by direct feeding may be greater than the positive effects resulting from epiphyton clearance when under clear‐water conditions with low epiphyton biomass. Thus, under clear‐water conditions, the growth and community composition of submerged macrophytes could be potentially modified by the manual addition of invertebrates (i.e., snails) to lakes if the inhibitory effects from predatory fish are minor.     

Benthic macroinvertebrates associated with four species of macrophytes

Benthic macroinvertebrates associated with four species of macrophytes (Nymphoides peltata, Ceratophyllum demersum, Polygonum amphibium and Carex sp.) were investigated during two growing seasons (2001 and 2002) in the slow-flowing Čonakut Channel in the Kopački rit Nature Park in Croatia. A total of 31 macroinvertebrate taxa were found. C. demersum, a submerged plant with dissected leaves, supported the highest macroinvertebrate abundance, almost seven times more than N. peltata, a floating plant with undissected leaves, which harboured the lowest abundance during the research period. Chironomidae larvae (50–83%) and Oligochaeta (14–46%) were the most abundant groups recorded on all macrophyte species. Water-level fluctuation, because of its influence on the appearance and growth of aquatic vegetation, and the trophic state of water within the macrophyte stands seemed to be the main factors which affected the taxonomic composition and abundance of macroinvertebrates.     

Statistical medium optimization for enhanced azadirachtin production in hairy root culture of Azadirachta indica

Azadirachtin, a well-known biopesticide, is a secondary metabolite extracted from the seeds of Azadirachta indica. In the present study, azadirachtin was produced in hairy roots of A. indica, generated by Agrobacterium rhizogenes-mediated transformation of leaf explants. Liquid cultures of A. indica hairy roots were developed with a liquid-to-flask volume ratio of 0.15. The kinetics of growth and azadirachtin production were established in a basal plant growth medium containing MS medium major and minor salts, Gamborg’s medium vitamins, and 30 g l⁻¹ sucrose. The highest azadirachtin accumulation in the hairy roots (up to 3.3 mg g⁻¹) and azadirachtin production (∼44 mg l⁻¹) was obtained on Day 25 of the growth cycle, with a biomass production of 13.3 g l⁻¹ dry weight. To enhance the production of azadirachtin, a Plackett–Burman experimental design protocol was used to identify key medium nutrients and concentrations to support high root biomass production and azadirachtin accumulation in hairy roots. The optimal nutrients and concentrations were as follows: 40 g l⁻¹ sucrose, 0.19 g l⁻¹ potassium dihydrogen phosphate, 3.1 g l⁻¹ potassium nitrate, and 0.41 g l⁻¹ magnesium sulfate. Concentrations were determined by a central composite design protocol and verified in shake-flask cultivation. The optimized medium composition yielded a root biomass production of 14.2 g l⁻¹ and azadirachtin accumulation of 5.2 mg g⁻¹, which was equivalent to an overall azadirachtin production of 73.84 mg l⁻¹, 68% more than that obtained under non-optimized conditions.     

Drift-ice and under-ice water communities in the Gulf of Bothnia (Baltic Sea)

The algal, protozoan and metazoan communities within different drift-ice types (newly formed, pancake and rafted ice) and in under-ice water were studied in the Gulf of Bothnia in March 2006. In ice, diatoms together with unidentified flagellates dominated the algal biomass (226 ± 154 μg ww l⁻¹) and rotifers the metazoan and protozoan biomass (32 ± 25 μg ww l⁻¹). The under-ice water communities were dominated by flagellates and ciliates, which resulted in lower biomasses (97 ± 25 and 21 ± 14 μg ww l⁻¹, respectively). The under-ice water and newly formed ice separated from all other samples to their own cluster in hierarchical cluster analysis. The most important discriminating factors, according to discriminant analysis, were chlorophyll-a, phosphate and silicate. The under-ice water/newly formed ice cluster was characterized by high nutrient and low chlorophyll-a values, while the opposite held true for the ice cluster. Increasing trends in chlorophyll-a concentration and biomass were observed with increasing ice thickness. Within the thick ice columns (>40 cm), the highest chlorophyll-a concentrations (6.6–22.2 μg l⁻¹) were in the bottom layers indicating photoacclimation of the sympagic community. The ice algal biomass showed additional peaks in the centric diatom-dominated surface layers coinciding with the highest photosynthetic efficiencies [0.019–0.032 μg C (μg Chl-a ⁻¹ h⁻¹) (μE m⁻² s⁻¹)⁻¹] and maximum photosynthetic capacities [0.43-1.29 μg C (μg Chl-a ⁻¹ h⁻¹)]. Rafting and snow-ice formation, determined from thin sections and stable oxygen isotopic composition, strongly influenced the physical, chemical and biological properties of the ice. Snow-ice formation provided the surface layers with nutrients and possibly habitable space, which seemed to have favored centric diatoms in our study.     

Repeated Batch Cultivation of Ralstonia eutropha for Poly (β-hydroxybutyrate) Production

Batch cultivation of Ralstonia eutropha NRRL B14690 attained 21 g biomass l⁻¹ and 9.4 g poly(β-hydroxybutyrate) l⁻¹ (0.45 g PHB g⁻¹ dry wt⁻¹) in 60 h. Repeated batch operation (empty-and-fill protocol) to remove 20% (v/v) of the culture broth and to supplement an equal volume of fresh media resulted in 49 g biomass l⁻¹ and 25 g PHB l⁻¹ (0.51 g PHB g⁻¹ dry wt⁻¹) with an overall productivity of 0.42 g PHB l⁻¹ h⁻¹ in 67 h. In the two cycles of repeated batch fermentation there was a 3-fold increase in productivity as compared to batch.     

Growth and nutrient absorption of two submerged aquatic macrophytes in mesocosms, for reinsertion in a eutrophicated shallow lake

Aquatic macrophytes play a central role in preserving the ecological equilibrium of shallow lakes and in the restoration of eutrophic lakes that have switched to phytoplankton-dominated turbid water. Massaciuccoli Lake, a shallow lake located along the Tuscan coast in Italy, has shown a constant and progressive simplification of the submerged plant community, for anthropogenic reasons, leading, in recent years, to turbid water. The growth and nutrient absorption capability of two macrophyte species, Myriophyllum verticillatum L. and Elodea canadensis Michaux, in the lake was investigated, with the prospect of a future lake restoration programme centred on their replacement. Mesocosm experiments were conducted to monitor the plant growth and nutrient (NO₂⁻, NO₃⁻, NH₄⁺, Ntot, PO₄³⁻, Ptot) content in the plant dry matter and water at the beginning and at the end of the trial. Bacterial activity was analysed in the water in order to verify the possible nutrient absorption contribution by organisms other than plants. Both M. verticillatum and E. canadensis showed satisfactory growth and nutrient reduction in the water body. Moreover, their different growth patterns suggested that optimal replacement can be performed with their introduction in two steps, starting with M. verticillatum, which shows the best capacity to colonise the aquatic environment, due to its tendency towards lengthening.     

Decomposition of dominant submerged macrophytes: implications for nutrient release in Myall Lake, NSW, Australia

Breakdown and nutrient dynamics of submerged macrophytes were studied in Myall Lake, Australia. Mass loss of Myriophyllum sulsagineum was the lowest (64.90%) among the studied macrophytes during the 322 days followed by charophytes (60.79%), whereas Najas marina and Vallisneria gigantea lost 91.15 and 86.02% of their respective initial mass during that time. The overall exponential breakdown rates of Najas marina and Vallisneria gigantea were similar, with k-values of 0.24 and 0.23 day⁻¹, respectively. These rates were significantly higher than the break down rates of charophytes (0.007 day⁻¹) and M. sulsagineum (0.008 day⁻¹). During growth phase, water column depicted lower nutrient concentrations while during decay period, significant increase in water column nutrients resulted. Release of nutrients from decomposing macrophytes and incorporation of these nutrients into sedimentary phase as well as uptake of nutrients by the growing macrophytes, can present a considerable cycling pathway of nutrients in Myall lake system. The results of this study suggest that different submerged macrophytes may differ appreciably in quality and may exhibit different decomposition rates, patterns and nutrient dynamics in aquatic ecosystems in general, and Myall lakes in particular.     

Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient

Replicated, factorial mesocosm experiments were conducted across Europe to study the effects of nutrient enrichment and fish density on macrophytes and on periphyton chlorophyll a (chl-a) with regard to latitude. Periphyton chl-a densities and plant decline were significantly related to nutrient loading in all countries. Fish effects were significant in a few sites only, mostly because of their contribution to the nutrient pool. A saturation-response type curve in periphyton chl-a with nutrients was found, and northern lakes achieved higher densities than southern lakes. Nutrient concentration and phytoplankton chl-a necessary for a 50% plant reduction followed a latitudinal gradient. Total phosphorus values for 50% plant disappearance were similar from Sweden (0.27 mg L⁻¹) to northern Spain (0.35 mg L⁻¹), but with a sharp increase in southern Spain (0.9 mg L⁻¹). Planktonic chl-a values for 50% plant reduction increased monotonically from Sweden (30 μg L⁻¹) to València (150 μg L⁻¹). Longer plant growing-season, higher light intensities and temperature, and strong water-level fluctuations characteristic of southern latitudes can lead to greater persistence of macrophyte biomass at higher turbidities and nutrient concentration than in northern lakes. Results support the evidence that latitudinal differences in the functioning of shallow lakes should be considered in lake management and conservation policies.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Modeling interactions of submersed plant biomass and environmental factors in a stream using structural equation modeling

This study investigated the interactions of submersed plants with environmental factors using structural equation modeling (SEM) and evaluated the effect strength of respective factors in an aquatic ecosystem using a data set collected at a fourth order stream in Japan. A model that simultaneously examines the relative importance of factors of the system has developed. The investigated factors included plant biomass (Biomass) of submersed macrophytes (Potamogeton malaianus and Potamogeton oxyphyllus) and other environmental factors, i.e. water velocity and water depth (Hydraulic), pore water nitrogen (TNL), pore water phosphorus (TPL), sediment organic matter (Organic) and sediment particle size (Texture). The estimated model showed that the Biomass was negatively correlated with Hydraulic but positively correlated with Organic whilst TNL and TPL affected the Biomass with almost equal strength. The effects caused by Hydraulic to Texture were greater than the ones caused by Biomass. At the narrow ranges of water velocity (0–7 cm s⁻¹) and shallow depth (0–35 cm), the effect of wash-away of Organic by Hydraulic were smaller than the retention effect of Organic by Biomass. These results provide more insights into interactions of the submersed macrophytes with environmental factors. Handling editor: K. Martens     

Phytoplankton biomass in the sub-Antarctic area of the Straits of Magellan (53°S), Chile during spring-summer 1997/1998

In order to provide a better understanding of the dynamics of phytoplankton in the coastal regions of high latitudes, a study was carried out to estimate the dynamics of carbon biomass of autotrophic and heterotrophic algal groups over the austral spring-summer 1997/1998 period. At a fixed station located in the central basin (Paso Ancho) of the Straits of Magellan (53°S), surface water samples were collected at least once a week from September 1997 (early spring) to March 1998 (late summer). Quantitative analysis of biomass of phytoplankton was estimated from geometric volumes, using non-linear equations, and converted to biomass. The pattern of chlorophyll a showed a strong temporal variability, with maximum values (mean 2.8 mg m⁻³) at the austral spring phytoplankton increase or bloom (October/November) and minimum values during early spring (September: <0.5 mg m⁻³) and summer (January/March: 0.5–1.0 mg m⁻³). During the spring bloom, diatoms made up to 90% of the total phytoplankton carbon (0.01–189 μg l⁻¹), followed by a maximum of thecate dinoflagellates (0.08–34 μg l⁻¹), and sporadic high biomass of phytoflagellates during summer. Heterotrophic algal groups such as Gymnodinium and Gyrodinium spp. dominated (70%, in the 5- to 25-μm size range) shortly before the main diatom bloom, and small peaks were observed within spring and early summer periods (0–0.4 μg l⁻¹). Phytoflagellates dominated earlier (spring) with higher carbon biomass (8 μg l⁻¹) and post-bloom periods (summer) when carbon biomass ranged between 1 and 4 μg l⁻¹. Accepted: 6 September 2000