Seasonality in Nutrients and Phytoplankton Production in Two Shallow Lakes: Waigani Lake,Papua New Guinea,and Barton Broad,Norfolk, England

Waigani Lake, near Port Moresby, Papua New Guinea and Barton Broad, Norfolk, England are both shallow lakes nutrient-enriched from sewage effluent disposal. In Waigani Lake phytoplankton biomass varied seasonally with lower levels (100-200 mg chlorophyll α m⁻³) during the wet season increasing to over 400 mg chlorophyll α m⁻³ at the end of the dry season. Secchi disc depths varied between 0. 11 and 0. 34 m. Phytoplankton productivity in Waigani Lake was very high throughout the year (range: A_max 4,370-21,000 mg O₂ m⁻³ h⁻¹) but production was lower during the wet season (range: A_max 4,370-12,700 mg O₂ m⁻³ h⁻¹). High surface productivity was recorded from August to December except on sampling days when the weather was overcast. Productivity throughout the year declined rapidly with depth. Algal biomass in Barton Broad varied from 3-10 mg chlorophyll α m⁻³ in winter but increased in spring and was very high in summer (200-500 mg chlorophyll α m⁻³). Secchi disc depth varied from 0.21 m in August 1976 to 1.76 m in December. Phytoplankton production in Barton Broad was low in winter (range: A_max 247-1,250 mg O₂ m⁻³ h⁻¹) but increased markedly in spring and summer with the highest rate (A_max 6,850 mg O₂ m⁻³ h⁻¹) being recorded in August. Surface inhibition was observed during summer except when the weather was overcast. Seasonality in nutrients and phytoplankton in Waigani Lake appear to be related to rainfall. Nutrient concentrations in Barton Broad are more closely related to phytoplankton activity which, in turn, correlates with seasonality in solar radiation.     

Phytoplankton of shallow lakes: Seasonal succession, standing crop and the chief determinants of primary productivity, 1. Cooking Lake, Alberta, Canada

Cooking Lake (113°02′W, 53°26′N), a well-mixed, shallow (mean depth (1.59 m), eutrophic lake in Alberta, Canada, is characterized by eutrophic chlorococcalean and cyanophycean phytoplankton associations, and little change in standing crop with increasing depth. Standing crop and primary productivity are low during the winter but pronounced spring and summer maxima occur. Mean yearly areal standing crop (ΔB) and primary productivity (ΔA) were 212.4 mg m^?2 chlorophyll a and 301.8 mg C h^?1 m^?2 respectively. Annual productivity was estimated at 1322 g C m^?2. The mean increase in the extinction coefficient (?) per unit increase in standing crop (B) was 0.03 In units m^?1. High non-algal light attenuation (?_q) occurred avenging 41 which prevented the ratio B/? from attaining more than 65% of the theoretical maximum except once when algal self-shading occurred. Close correlations existed between B (mg m^?3 chlorophyll a) and A _max (mg h_?1 m_?3) ΔA and ΔB, ΔA and B, A_max, and A_max/?, and ΔA and I_o′, (W m^?2). The depth of the euphotic zone (Z_eu) varied between 0.5 and 1 25 m; the average relationship between z_eu and E was Z_eu= 3.74/?, and the mean standing Crop found in the euphotic zone represented 55.2% of the theoretical maximum, The high ?_q, values made the model of Tailing (1957) inapplicable to Cooking Lake. The Q₁₀ value for the lake was 2.2. The maximum rate of photosynthesis per unit of population per h. Ø^max, (mg C sag chlorophyll a_?1 h_?1) was more closely related to temperature than irradiance and ma depressed by pH values greater than 9.1. Growth of the phytoplankton was not nutrient limited: instead irradiance and temperature were more important. Indirect evidence that free CO₂ limited photosynthetic rates, is provided by the Ø_max: pH relationship.     

Contribution of biofilm‐dwelling consumers to pelagic–benthic coupling in a large river

1. Over the course of this 17‐month study, we assessed the potential loss of plankton (bacteria, algae, heterotrophic flagellates) to consumers (ciliates and rotifers) within mature biofilms established on natural substrata exposed to the main current of the River Rhine (Germany). Once a month, in flow cells in a bypass system to the River Rhine, we measured the clearance rates of the biofilm‐associated consumers on the different groups within the natural plankton. 2. Ciliates were the most dominant consumers, among which planktivorous groups, particularly peritrichs and (in spring and summer) heterotrichs dominated. Consumer biomass varied with season, with the highest density occurring directly after the appearance of the phytoplankton spring peak. 3. Clearance rates on plankton ranged from 96 to 565 L m^?2 d^?1 for bacteria and 66–749 L m^?2 d^?1 for algae, with a preference for algae in summer and for bacteria in winter. This pattern coincided with seasonal changes in the structures of the grazer communities. The consumers (both ciliates and rotifers with total standing stocks ranging between 19 and 572 mg C m^?2) imported a substantial amount of organic matter (between 15 and 137 mg C m^?2 d^?1) into the biofilm. 4. These results highlight the potential importance of consumers in the biofilm as a trophic link between the plankton and the benthos, a function that has hitherto mostly been attributed to filter‐feeding bivalves. In contrast to bivalves, the biofilm‐dwelling consumers show a more dynamic response towards the plankton density and composition. Such dynamic components need to be considered when estimating total plankton consumption by the benthos.     

Phytoplankton primary productivity seasonality and changes in a small African lake,Lake Hora-Kilole,Ethiopia

The seasonality of primary productivity by phytoplankton in relation to physico-chemical and biological variables was studied in Lake Hora-Kilole from August 2007 to May 2008. In 1989, the Mojo River was temporarily diverted to flow into the lake, which substantially changed its physico-chemical conditions and the composition of the phytoplankton. Primary productivity was controlled primarily by soluble reactive phosphorus (SRP), ammonia (NH₃), temperature and euphotic depth (Z_eu). The light-saturated rate of photosynthesis (A_max) varied from 370 to 3 843?mg O₂ m^?3 h^?1 with the maximum value corresponding to the seasonal maximum of phytoplankton biomass. Compared to the period before the diversion of the river, A_max was reduced by more than ninety-fold in early 1990s and by less than five-fold in 2007 and 2008. Similarly, average phytoplankton chlorophyll a was reduced by more than 2.5 × in the early 1990s and to less than 50% in 2007 and 2008. This highlights the importance of the diversion river water on the physico-chemical and biological environment of the lake.     

Primary production of phytoplankton and periphyton in two humic lakes of a South American wetland

Seasonal primary productivities of periphyton and phytoplankton were compared in Grande Lake (GL) and a relict oxbow lake (ROL) in winter 2006 and summer 2007. GL was free of floating plants on the sampling dates and covered over 80 and 100% of the ROL surface in winter and summer, respectively. The ¹⁴C assimilation technique was used to obtain the P–E curves of phytoplankton and periphyton on artificial substrata. The periphytic maximum photosynthetic rate (P _max) was higher in the ROL in winter and summer, being better adapted to low irradiances than those in the GL. Phytoplankton and periphytic algae were light-limited in the ROL in summer due to complete coverage by floating macrophytes. In summer, P _max and α values for periphyton in the ROL were higher than those for phytoplankton, and were even higher than in GL. In turn, P _max and α values for phytoplankton in Grande Lake were higher than those for periphyton due to improved light conditions and the presence of algae that were adapted to movement through the water column. These results suggest that the complete coverage by floating macrophytes restricted phytoplankton productivity and allowed the development of a periphytic community that was better adapted to low-light conditions.     

Seasonal pattern of ammonium (methylamine) uptake by phytoplankton in an oligotrophic lake

Our primary objective was to determine if a relationship existed between seasonal change in phytoplankton and high affinity for (K _m) or uptake rates (V _maX) of ammonium which might explain seasonal phytoplankton succession in oligotrophic ecosystems. We measured ammonium uptake using [¹⁴C]-methylamine and estimatedK _m andV _max using Hanes Plots at 2-week intervals during 6 months of thermal stratification in Mountain lake, Virginia (37° 22 N, 80° 32 W). Community composition, nutrient levels, and other variables were determined in all uptake experiments. A second objective was to determine if ammonium was preferentially utilized over nitrate and to characterize further the ammonium transport system.V _max increased steadily from May until the end of July, each increase coinciding with major changes in the phytoplankton community. Cryptophyceans dominated in May, chlorophyceans in June and July, and cyanophyceans from the end of July to late October. With cyanophycean dominance,V _max declined until chlorophyceans reestablished dominance in late October. By contrast,K _m values increased from May to the end of July, but thereafter showed no correlation. Acetylene reduction experiments showed no nitrogen fixation during late summer and fall when blue-green algae were present. Preference for ammonium was implied also by negative nitrate reductase assays. Overall, the coincidence ofV _max andK _m values for [¹⁴C]-methylamine uptake and changing phytoplankton community structure suggests the possibility that successive algal communities may be changing as a result of specific species differences in ammonium affinity and uptake rates.     

Unique picoeukaryotic algal community under multiple environmental stress conditions in a shallow, alkaline pan

Winter phytoplankton communities in the shallow alkaline pans of Hungary are frequently dominated by picoeukaryotes, sometimes in particularly high abundance. In winter 2012, the ice-covered alkaline Zab-szék pan was found to be extraordinarily rich in picoeukaryotic green algae (42–82 × 10⁶ cells ml^?1) despite the simultaneous presence of multiple stressors (low temperature and light intensity with high pH and salinity). The maximum photosynthetic rate of the picoeukaryote community was 1.4 μg C μg chlorophyll a ^?1 h^?1 at 125 μmol m^?2 s^?1. The assimilation rates compared with the available light intensity measured on the field show that the community was considerably light-limited. Estimated areal primary production was 180 mg C m^?2 d^?1. On the basis of the 18S rRNA gene analysis (cloning and DGGE), the community was phylogenetically heterogeneous with several previously undescribed chlorophyte lineages, which indicates the ability of picoeukaryotic communities to maintain high genetic diversity under extreme conditions.     

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 biomass and production in northern South China Sea during summer: Influenced by Pearl River discharge and coastal upwelling

Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^?1. Integrated primary production ranged from 189.3 to 976.2 mg m^?2 d^?1 in 2007, and ranged from 652.1 to 6601 mg m^?2 d^?1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.     

Phytoplankton biomass and production in northern South China Sea during summer: Influenced by Pearl River discharge and coastal upwelling

Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^?1. Integrated primary production ranged from 189.3 to 976.2 mg m^?2 d^?1 in 2007, and ranged from 652.1 to 6601 mg m^?2 d^?1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.     

Phytoplankton structure in the White Sea after summer bloom: Spatial variability in relation to hydrophysical conditions

The species composition and phytoplankton biomass, concentrations of chlorophyll “a” (Chl) and nutrients, concurrent hydrophysical conditions were studied in the south part of the White Sea in July 10–15, 2012 during chlorophyll “a” decrease after summer peak. The water column stability varied, the concentration of dissolved silicon in upper mixed layer was closed to the range favorable for diatoms with exception of areas of intensive tide mixing and areas influenced by waters of Severnaya Dvina River. In surface layer the dinoflagellates dominated excepting of areas with intensive tide mixing where diatoms prevailed. Diatoms provided major contribution to biomass in different stations above, in and under pycnocline and in deep waters out of photic zone. Structural analysis has revealed three phytoplankton communities that corresponded to different depths: communities of photic zone, intermediate and deep layers. Extension of layers inhabited by different communities depended on water column stability and on genesis of water masses. Integrated values of phytoplankton biomass and Chl varied from 250 to 1188 mg С/m², and from 22 to 51 mg/m², correspondently.     

Peculiarities of summer phytoplankton spatial distribution in Onega Bay of the White Sea under local hydrophysical conditions

The species composition and phytoplankton biomass, concentrations of chlorophyll “a” (Chl) and nutrients in the surface water layer, and accompanying hydrophysical conditions were studied in Onega Bay of the White Sea in June 2015. The temperature and salinity of surface water layer and the water column stability varied greatly in the bay. The nutrients' concentrations exceeded the limiting threshold necessary for the phytoplankton development. The phytoplankton abundance was relatively low, averaged as 13.46 ± 9.00 mg C/m³ (total phytoplankton biomass), 0.78 ± 0.43 mg/m³ (concentration of chlorophyll “a”), and 0.18 ± 0.27 mg C/m³ (picophytoplankton biomass). The highest phytoplankton biomass has been registered along the frontal zones. Three phytoplankton communities that differed significantly in their structure have been found.     

Seasonal abundance and distribution of drift algae and seagrasses in the mid-Indian river lagoon,Florida

The distribution of seagrasses in a 15-ha area in the mid-Indian River lagoon on Florida's central east coast was mapped. Halodule wrightii Aschers. dominated in shallow (< 0.4 m) and Syringodium filiforme Kutz. in deeper water (> 0.5 m). Thalassia testudinum Banks ex König occurred as scattered patches. Areal coverage of monospecific stands of the three major seagrasses was: Syringodium 35%, Halodule 14%, Thalassia 6% and bare sand 21%. Mixed species stands, mostly Syringodium with Hallodule, covered 25% of the total study area. Above-ground seagrass biomass was maximum in summer (June–July) and minimum in late winter (February–March). Summer maxima ranged from 60 g dry wt. m^?2 for Syringodium to ～ 300 g dry wt. m^?2 for Thalassia, with Halodule intermediate at 160 g dry wt. m^?2.Because distribution of unattached benthic macroalgae (“drift algae”), primarily Gracilaria spp., was highly aggregated, aggregations were first mapped, followed by stratified quadrat sampling in order to estimate total drift algal abundance. In April 1982, high-density patches covering a few hectares averaged 409 g dry wt. m^?2. At maximum abundance, averaged over the entire 15-ha mapped area, drift algal biomass was 164 g dry wt. m^?2; mean above-ground seagrass biomass was only 49 g dry wt. m^?2. Other large expanses of the lagoon had similar accumulations of drift algae; densities of some accumulations exceeded 15 000 g dry wt. m^?2. Year-to-year variability of seagrass and drift algal abundance was high and may be related to variations in light levels.Drift algae harbor high densities of animals and at times may be quantitatively more important locally than seagrasses in terms of habitat, nutrient dynamics and primary production.     

Heterotrophic bacterial activity and primary production in a hypertrophic African lake

The relationship between heterotrophic bacteria and phytoplankton in the epilimnion (0–10 m) of hypertrophic Hartbeespoort Dam, South Africa, was examined by statistically analyzing three years of parallel measurements of heterotrophic bacterial activity (glucose uptake) and phytoplankton particulate and dissolved organic carbon production. Algal biomass ranged between 4.0 and 921.1 mg Chl a m^-3 at the surface. Primary production varied between 69.5 and 3010.0 mg C m^-2h^-1 while algal production of dissolved organic carbon (EDOC) ranged from 2.5 to 219.2 mg C m^-2h^-1. Bacterial numbers reached a summer peak of 44.23 × 10⁶ cells ml^-1 in the first year and showed no depth variation. The maximum rate of glucose uptake, V_max, reached a peak of 5.52 g C l^-1h^-1. V_max, maximum glucose concentration (K_t + S_n) and glucose turnover time (T_t) were usually highest at the surface and decreased with depth concomitant with algal production. At the surface, V_max was correlated to EDOC (r = 0.59, n = 67, p < 0.001) and primary production (r = 0.71, n = 70, p < 0.001). At 5 and 10 m, V_max was correlated to integral euphotic zone (~ 4 m) algal production and bacterial numbers. Glucose turnover time was inversely related to integral algal production (r = -0.72, n = 70, p < 0.001) and less strongly to bacterial numbers. The data indicated that although bacterial numbers and biomass were low relative to algal biomass in this hypertrophic lake, the heterotrophic bacteria attained high rates of metabolic activity as a result of enhanced algal production of available organic carbon.     

Primary productivity of the River Ely,South Wales,U.K.

The present study was carried out on the non-tidal reaches of the River Ely, South Wales, from October 1979 to October 1980. The seasonal variations of the chlorophyll-a content of the phytoplankton was unimodal with one maximum in May and a minimum in December. The chlorophyll-a content varied from 0.277 to 41.259 mg m^?3. The primary productivity showed a bimodal seasonal distribution with two maxima in May and September and lower values throughout the remainder of the year, particularly in winter. The value for the primary productivity varied from 0.269 to 24.302 mg C m^?3 h^?1. A positive correlation was obtained between chlorophyll-a content and primary productivity. The seasonal distribution of the dominant algal species and the saprobity of the River Ely were also studied. The diatom species almost showed a similar seasonal periodicity. Their concentrations were low during the winter months and high during most of the spring and summer months. Many of the dominant diatom species found in the phytoplankton populations were either considered by the other authors as saprobic (Nitzchia palea) or as inhabitants of eutrophic waters (Gomphonema parvulum, Navicula cryptocephala and Synedra ulna). Chlamydomonas spp. were the most abundant green algae followed by Chlorella vulgaris. The effect of sewage effluent disposal and cattle excreta at three of the sampling sites might partly explain the presence of high Chlamydomonas spp. populations at those sites. Physical factors (low flow rates, high transparency and water temperature) and organic pollution at some sampling sites seemed to play an important role in increasing the number of algal species during spring and summer. The non-tidal reaches of the River Ely were found to be β-mesosaprobic above and below Station 5 and α-mesosaprobic at the latter station and therefore, the river can be considered as polluted at Station 5 and mildly polluted at the others.     

Phytoplankton dynamics in the Congo River

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The phytoplankton community of the River Meuse,Belgium: seasonal dynamics (year 1992) and the possible incidence of zooplankton grazing

Qualitative and quantitative aspects of the phytoplankton of the River Meuse were studied during 1992, at a point 537 km from the source. The phytoplankton was dominated by diatoms and green algae. The Stephanodiscus hantzschii-group was especially prominent. Other important taxa were Cyclotella meneghiniana, small Cyclotella and Thalassiosira, Aulacoseira ambigua and Nitzschia acicularis. Cell abundances varied from less than 1000 units ml^–1 to about 25 000 – 30 000 units ml^–1 during the blooms. The Stephanodiscus hantzchii-group constituted almost entirely the first spring bloom. During the summer period, small Thalassiosiraceae developed markedly and large Thalassiosira weissflogii appeared. During this period, green algae dominated diatoms as expressed in cell abundances. The main Chlorococcales were Scenedesmus quadricauda, Scenedesmus div. sp., Dictyosphaerium ehrenbergianum and Pediastrum duplex. Dinophyceae contributed a significant biomass during the summer period. Total biomass varied between 100 and 3 650 µg Cl^–1. As previously observed (Descy, 1987), the factors regulating the phytoplankton growth were clearly physical variables: discharge, temperature and irradiance. However, in the summer period, low abundances might indicate a regulation by biotic factors. The impact of grazing by zooplankton is discussed, on the basis of observations of zooplankton development in the River Meuse and on the basis of simulation by a mathematical model. A comparison is carried out with recent data of phytoplankton in large European rivers.     

SPECIES COMPOSITION,BIOMASS, AND NUTRIENT CONTENT OF PERIPHYTON IN THE FLORIDA EVERGLADES1

Periphyton biomass, nutrient dynamics in the biomass, and species composition were studied in two Florida Everglades sloughs from August 1991 to August 1992. Periphyton biomass on macrophytes was strongly season-dependent. Maximum biomasses, 1180, 161, and 59 g dry mass.m^?2 on Eleocharis vivipara, E. cellulosa, and Nymphaea odorata, respectively, occurred in summer and early autumn; winter and spring periphyton biomass was very low (practically not measurable). Periphyton was dominated by blue-green algae (cyanobacteria) during the summer and autumn; diatoms dominated during the winter and spring. Green algae occurred mostly during the summer and autumn, but their growth was sparse and did not contribute significantly to periphyton biomass. Nitrogen-to-phosphorus ratios in the periphyton were very high (59–121:1), suggesting phosphorus limitation of periphyton growth. The periphyton contained large concentrations of calcium (up to 22.3% on dry mass basis) especially in late summer and autumn.     

Population dynamics and production of Daphnia hyalina and Bosmina longirostris in a shallow, eutrophic reservoir

SUMMARY. 1. The population densities, dynamics and production of Daphnia hyalina and Bosmina longirostris were studied over a 2-year period in a shallow eutrophic reservoir in eastern England. The diet of the two species was assessed and their ecology was compared in relation to environmental factors. 2. Daphnia hyalina was characterized by small overall body size, probably due to heavy size-selective predation by fish. The first generation produced from the overwintering population appeared in April and Depopulation peaked in late spring and early summer. Adult survival was poor. Peak egg production varied between years, while mean brood size fell in summer probably due to food limitation during the cyanobacterial bloom. At this time selection for individual algal species was high and many guts were empty. Reproductive ratios were inversely related to population density. Bosmina longirostris exhibited a similar annual cycle. 3. Patterns of production were very different in the 2 years in D. hyalina. In 1981 production was high from August to early October, but in 1982 the peak was in spring. Annual production was 32.4 g C m^?2 in 1981 and 13.3 g C m^?2 in 1982. In 1981 B. longirostris production peaked in spring and late summer; in 1982 there was a high production in summer only. Annual production was 3.2 g C m^?2 in 1981 and 2.2 g Cm^?2 in 1982. 4. The number of adult D. hyalina was highly correlated with water temperature and total phytoplankton biomass, but these were negatively correlated with the number of eggs, mean brood size and instantaneous birth rate. In contrast, clutch size of B. longirostris was positively correlated with water temperature while birth rate was positively correlated with both temperature and phytoplankton biomass. The biomass of both species was positively related to total phytoplankton biomass, but neither relationship explained much of the variation in zooplankton biomass. 5. The significance of the observations on plankton in terms of managing the water quality in eutrophic reservoirs is discussed.     

Mesozooplankton beneath the summer sea ice in McMurdo Sound,Antarctica: abundance,species composition,and DMSP content

The summer Phaeocystis antarctica bloom increases under-ice phytoplankton biomass in McMurdo Sound, Antarctica. The magnitude of mesozooplankton grazing on this bloom is unknown, and determines whether this production is available to the pelagic food web. We measured mesozooplankton abundance and body content of dimethylsulfoniopropionate (DMSP) during the McMurdo Sound austral summer (2006 and 2006–2007). Abundance varied from 20 to 4,500 ind. m⁻³ (biomass 0.02–274.0 mg C m⁻³), with peaks in mid-December and late-January/February. Abundance was higher but total zooplankton biomass lower in our study compared to previous reports. Copepods and the pteropod Limacina helicina dominated the zooplankton in both abundance and biomass. DMSP was detected in all zooplankton groups, with highest concentrations in copepod nauplii and L. helicina (95 and 54 nmol mg⁻¹ body C, respectively). Experiments suggested that L. helicina obtains DMSP by directly grazing on P. antarctica, which often accumulates to high biomass under the summer sea ice in McMurdo Sound.