Showing papers in "Journal of Plankton Research in 2004"

Effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides Margalef (Dinophyceae)

Abstract: The effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides were examined in the laboratory. From 60 different combinations of temperature (10-30°C) and salinity (10-40) under saturated irradiance, C. polykrikoides exhibited its maximum specific growth rate of 0.41 day -1 at a combination of 25°C and salinity of 34. Optimum growth rates of >0.3 day -1 were observed at temperatures ranging from 21 to 26° C and at salinities from 30 to 36. The organism did not grow at temperatures ≤10°C and only grew at salinities >30 if the temperature was >15°C. It was able to grow in temperatures ranging from 15 to 30° C and at salinities from 20 to 36. These values closely resembled those observed for this species in situ. It appears as if C. polykrikoides is a stenohaline organism that prefers high salinities, indicative of offshore waters. Temperature had the greatest influence on the growth rate, followed by salinity, and then the interaction between temperature and salinity. The optimum irradiance for growth was >90 μmol m -2 s -1 . Photoinhibition did not occur at 230 μmol m -2 s -1 , which was the maximum irradiance used in this study.

Light backscattering properties of marine phytoplankton: relationships to cell size, chemical composition and taxonomy

Abstract: Spectral backscattering coefficients were determined for 29 species of cultured marine plankton representing 12 classes using a fixed-angle backscattering meter. Using a multi-angle scattering meter, the volume scattering function was measured and a proportionality constant (X) between β(141°) and b b was determined as 0.82 (± 0.01 SE), less than the X value of 1.08 reported for natural waters. Backscattering efficiencies (at 440 nm) of cultures varied between 0.0023 and 0.081 and showed little spectral variation. Plankton backscattering coefficients at 510 nm showed the lowest variability between species when normalized to particulate organic carbon (POC) [4 x 10 -6 (± 57% SD) m 2 mg POC -1 at 510 nm], more when normalized to chlorophyll a (Chl a) [8 x 10 -4 (± 112% SD)m 2 mg Chl a -1 at 510 nm], and the greatest when normalized to cell number concentration [9 × 10 -13 (± 238% SD) m 2 mg cell -1 at 510 nm]. There were large variations in the relationships between Chl a, POC and backscattering within and between species. The dinoflagellates were the most efficient backscatterers, owing to their high POCi and D. The diatoms were mid-range in Q bb because the presence of the vacuole decreased POCi. The cyanophytes, eustigmatophytes and heterotrophic bacteria were the least efficient scatterers owing to their small cell sizes. Comparison of experimental Q bb to those predicted by Mie's scattering model that represents a phytoplankton cell as a homogeneous sphere probably overestimates the value of the real refractive index for these species. Scattering models that consider more complex cellular structure are likely to provide better closure with experimental results.

Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya—Lakes Bogoria, Nakuru and Elmenteita

Abstract: For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaias minor Geoffroy) have been observed at alkaline-saline Kenyan Rift Valley lakes. To estimate the potential influence of toxic cyanobacteria on these mass deaths, the phytoplankton communities were investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterial toxins were analyzed both in the phytoplankton from the three lakes and in isolated monocyanobacterial strains of Arthrospira fussiformis, Anabaenopsis abjjatae, Spirulina subsalsa and Phormidium terebriformis. Lake Bogoria was dominated by the cyanobacterium A. fusiformis. In L. Nakuru and L. Elmenteita the phytoplankton mainly consisted of A. fusiformis, A. abjatae and Anabaenopsis arnoldii, and in L. Nakuru an unknown Anabaena sp. was also found. Furthermore, this is the first time A. abijatae and the unknown Anabaena sp. have been found in Kenyan lakes. Phytoplankton wet weight biomass was found to be high, reaching 777 mg L -1 in L. Bogoria, 104 mg L -1 in L. Nakuru and 202 mg L -1 in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxins microgstin-LR, -RR -γR, -LF and -LA and the neurotoxin anatoxin-a were detected in phytoplankton samples from L. Bogoria and L. Nakuru. Total microcystin concentrations amounted to 155 μg microcystin-LR equivalents g -1 DW in L. Bogoria, and 4593 μg microcystin-LR equivalents g -1 DW in L. Nakuru, with anatoxin-a concentrations at 9 μg g -1 DW in L. Bogoria and 223 μg g -1 DW in L. Nakuru. In L. Elmenteita phytoplankton, no cyanobacterial toxins were found. A. fusiformis was identified as one source of the toxins. The isolated strain of A. fusiformis from L. Bogoria was found to produce both microcystin-YR (15.0 μg g -1 DW) and anatoxin-a (10.4 μg g -1 DW), whilst the A. fusiformis strain from L. Nakuru was found to produce anatoxin-a (0.14 μg g -1 DW). Since A. fusiformis mass developments are characteristic of alkaline-saline lakes, health risks to wildlife, especial the Arthrospira-consuming Lesser Flamingo, may be expected.

Phytoplankton and zooplankton seasonal dynamics in a subtropical estuary: importance of cyanobacteria

Abstract: A seasonal study of phytoplankton and zooplankton was conducted from 1999-2001 in Pensacola Bay, Florida, USA, to better understand pelagic food webs in sub-tropical estuaries. Monthly

Annual variability in ciliate community structure, potential prey and predators in the open northern Baltic Sea proper

Abstract: Biomass of ciliates, bacteria and mesozooplankton, as well as biomass estimates of phytoplankton from chlorophyll a values, were studied in the mixed layer of the northern Baltic Sea proper, between February and December 1998. Production of phytoplankton and bacteria was measured, and production of ciliates and mesozooplankton was estimated. The phytoplankton spring bloom in late March was dominated by diatoms and dinoflagellates. Ciliates had a biomass peak shortly after the spring bloom, while mesozooplankton peaked in July. Thus, the predation pressure on ciliates was low in spring, and ciliates were major predators, potentially consuming up to 15% of the primary production. In summer, there was a shift from larger to smaller ciliates coinciding with a shift from larger to smaller primary producers, an increase in bacterial production, and also an increase in mesozooplankton abundance, mainly copepods. Elevated mesozooplankton predation and selective removal of larger ciliate species and/or a shift to smaller prey size presumably caused these changes. The potential carbon consumption from ciliates and mesozooplankton was highest in summer and autumn, reaching 55 and 40% of the primary production in summer and autumn, respectively. Ciliates consumed twice as much as mesozooplankton, thus acting as important regenerators.

The next generation of Optical Plankton Counter: the Laser-OPC

Abstract: Optical Plankton Counters (OPCs) have been in operation for ∼12 years and while there have been considerable research studies by the user community, some operational issues have emerged over this time, such as its operational limitations in high densities, the lack of accompanying flow measurements and other measurement limitations. Reported here is the next generation of this device, the Laser-Optical Plankton Counter or LOPC which was designed at the Bedford Institute of Oceanography to address the future needs of optical plankton counting. Using a narrow laser beam and new sampling geometry, the LOPC is now capable of working in plankton densities of 10 6 m -3 , nearly 100 times greater than its predecessor, the OPC, and is also capable of providing shape profiles of plankton >1.5 mm. Other new features include (i) the measurement of flow speeds through the sampling tunnel by making statistical estimates of the particle time-of-transit, (ii) a lower detection limit of 100 μm, (iii) high speed towing up to 8 m s -1 , and (iv) overall smaller physical size relative to the OPC. Data are presented from an LOPC mounted on the inside of a 0.5 m plankton net (75 μm mesh size) showing linear correlation between net samples (e.g. counts of copepod eggs, nauplii) and LOPC counts. The LOPC-measured shape profiles from the same LOPC/net tows clearly show copepods and appendages and, in some cases, euphausiids. By increasing the tunnel width relative to the original OPC, the volume sampled by the LOPC can be increased by 5×. Other towing platforms that have been tested to date are the Batfish vehicle towed at 8 knots and the Moving Vessel Profiler (MVP) towed at 12-14 knots.

Spatial and temporal patterns of phytoplankton composition in subtropical coastal lagoon, the Indian River Lagoon, Florida, USA

Abstract: A 2 year study of the phytoplankton community was carried out in the Indian River Lagoon, USA. In terms of biovolume, the phytoplankton community was generally dominated by dinoflagellates, diatoms or cyanobacteria. Mean phytoplankton standing crops were highest in the most flow-restricted regions of the lagoon, which had the lowest mean salinity values and comparatively high total nitrogen:total phosphorus ratios. In this region, blooms of dinoflagellates were common in the first year of the study, which was characterized by an El Nino event that yielded exceptionally high rainfall levels and freshwater outflow. Picoplanktonic cyanobacteria blooms became more prominent in the second year of the study, which was characterized by below average rainfall conditions. In unrestricted flow regions of the lagoon, located near inlets to the Atlantic Ocean, diatoms were most often the dominant taxa. Regions of intermediate water turnover rates and high external loading of phosphorus had a prevalence of diatom blooms. However, the average phytoplankton standing crops in the latter regions did not reach the levels experienced in the flow-restricted parts of the lagoon. In terms of individual phytoplankton taxa, the most common bloom-forming diatoms in the Indian River Lagoon system included: Skeletonema costatum, Dactyliosolen fragilissimus, Skeletonema menzelii, Cerataulina pelagica, Odontella regia, Chaetoceros lorenzianus, Rhizosolenia setigera and Thalassionema nitzschioides. The major bloom-forming dinoflagellate species included: Pheopolykrikos hartmannii, Akashiwo sanguinea, Prorocentrum micans, the potentially toxic species Pyrodinium bahamense var. bahamense and Prorocentrum minimum. Several picoplanktonic cyanobacteria were also prominent members of the phytoplankton community, including Synechococcus elongates. The spatial and temporal patterns observed in some of these dominant species were attributable to patterns in key environmental variables, including salinity, temperature and nutrient concentrations.

Relationship between vegetative cells and cyst production during Alexandrium minutum bloom in Arenys de Mar harbour (NW Mediterranean)

Abstract: A recurrent Alexandrium minutum bloom in the Arenys de Mar harbour (Catalan coast, North Western Mediterranean) was monitored in order to establish the relationship between vegetative cells and cyst production. The bloom lasted from January 21 to February 24, 2002 and reached cell concentrations of up to 47 � 10 6 cell L � 1 . Two aspects related to the resting cysts deposition were studied: (i) production of resting cysts during the bloom period (by means of sediment traps) and (ii) distribution of resting cysts in the sediment after the bloom (May 2002). Cyst formation in Arenys clearly started in a period with high vegetative cell densities in the water column. Once production was initiated encystment fluxes remained constant for two weeks, and covering the periods of maintenance and decline of the bloom. High cyst fluxes (up to 6000 cysts cm � 2 day � 1 ) were quantified as a result of the high vegetative cell concentration. Moreover, encystment occurring in less than 1% of the total population indicates that mostof the cellsare not involved in resting cysts formation. A comparison of the resting cyst flux values obtained from the sediment traps and the resting cyst concentrations in surface sediment (628‐3270 cysts cm � 3 ) three months later, revealed that the number of cysts in the sediment decreased during that time. The studies of excystment showed a high germination percentage (91%) and germling viability (100%). These data, together with the resting cyst distribution in the sediment, are important in assessing the role of resting cysts in the bloom dynamics of A. minutum in confined waters.

Phytoplankton community assemblage in the English Channel: a comparison using chlorophyll a derived from HPLC-CHEMTAX and carbon derived from microscopy cell counts

Abstract: The phytoplankton community assemblage in surface water of the English Channel (Station L4) was measured and compared from March 1999 to October 2002 using two different methods. Pigment-CHEMTAX was used to derive class apportioned chlorophyll a (Chl a) and cell counts obtained using microscopy were used to derive phytoplankton carbon (phyto-C) estimations. Phyto-C (10-340 μg C L -1 ) showed a strong linear relationship with total Chl a (0.5-4.8 μg Chl a L -1 ) when the Chl a:phyto-C ratio was >0.04 (r2 = 0.80; average Chl a:phyto-C = 0.044) but the relationship was weaker when the Chl a:phyto-C ratio was <0.04 (r2 = 0.42; average Chl a:phyto-C = 0.013). Correlation between class biomass estimates for phyto-C and Chl a was strong for diatoms during winter (r2 = 0.80) but poor for other classes during both summer and winter. The Chl a:phyto-C ratio declined as irradiance increased with strongest correlation on clear sky days in 2001 when diatoms dominated (r 2 = 0.80). The Chl a:phyto-C versus irradiance relationship agrees with that produced from an empirically based dynamic model of phytoplankton acclimation to light. Results are discussed in relation to differences in the techniques used, the species present, cellular pigment concentrations and surface mixed layer irradiance.

Noctiluca scintillans MACARTNEY in the Northern Adriatic Sea: long-term dynamics, relationships with temperature and eutrophication, and role in the food web

Abstract: The first 'bloom' of Noctiluca scintillans in the Northern Adriatic Sea was recorded in 1977. The organism caused several red tides in the whole basin during the late 1970s, a period characterized by increasing nutrient loads. During the 1980s and early 1990s, there was no 'red tide', but the species was an almost constant summer presence, associated with high temperatures. Noctiluca scintillans was almost completely absent from 1994 until May 1997, concurrent with a general plankton decrease. From summer 1997, N. scintillans was recorded again in the whole basin, although there was no other signal of increasing eutrophication. In contrast to all previous observations, during winter 2002-2003, N. scintillans was continuously sampled in the Gulf of Tieste. We estimated experimentally growth and grazing rates of the dinoflagellate at 9-10°C in culture and consuming the natural assemblage. Noctiluca scintillans was able to reproduce actively at low temperatures, showing similar growth rates in both experiments (k = 0.2 day -1 ). The values found were close to those reported in the literature for higher temperatures. The natural diet was mainly composed of phytoplankton (ingestion = 0.008 μg C Noctiluca -1 day -1 ), micro-zooplankton (ingestion = 0.008 μg C Noctiluca -1 day -1 ) and bacteria (ingestion = 0.005 μg C Noctiluca -1 day -1 ) with an average carbon content of 0.138 + 0.020 leg C Noctiluca cell -1 .

Species-specific differences in phytoplankton responses to N and P enrichments and the N:P ratio in the Archipelago Sea, northern Baltic Sea

Abstract: A nutrient enrichment experiment was conducted in order to study the role of nitrogen (N), phosphorus (P) and the N:P ratio on the early summer phytoplankton community in the Archipelago Sea, northern Baltic Sea. The phytoplankton community was, in terms of chlorophyll a and total biomass, primarily N-limited, but the individual species varied in their responses to the nutrient supply. The recorded overall N limitation was due to fast growth responses of a few N- limited species such as the diatom Chaetoceros wighamii (Brightwell) and the mixotrophic chrysophyte Uroglena sp. Another dominating diatom, Skeletonema costatum (Greville) Cleve was most clearly P-limited. The N:P ratio had the strongest effect on Uroglena sp., which grew exponentially in the enrichments with a high N:P ratio. This can be explained by the ability of the species to feed on P-rich bacteria, which gives it a competitive advantage in P-limited conditions. The species-specific differences in the responses to the nutrient enrichments can generally be explained by differences in the species physiology and they were consistent with the theory of resource competition.

The China Coastal Current as a driving force for transporting Calanus sinicus (Copepoda: Calanoida) from its population centers to waters off Taiwan and Hong Kong during the winter northeast monsoon period

Abstract: Calanus sinicus is a copepod with wide geographical distribution in the continental shelf waters of China. Its occurrence in oceans around Taiwan and Hong Song is limited by temperature to winter and spring. We present evidence to show that C. sinicus is carried into the coastal waters of Taiwan and Hong Kong from population centers in the Yellow Sea and the East China Sea by the China Coastal Current during the northeast monsoon period in winter.

Comparison of pelagic food webs in lakes along a trophic gradient and with seasonal aspects: influence of resource and predation

Abstract: Composition and seasonal dynamics of phytoplankton, bacteria, and zooplankton (including heterotrophic flagellates, ciliates, rotifers and crustaceans) were studied in 55 lakes in Northern Germany with different trophic status, ranging from mesotrophic to hypertrophic. Mean abundance and biomass of all groups increased significantly with trophic level of the lake, but bacteria and metazooplankton showed only a weak correlation and a slight increase with chlorophyll concentration. Composition of phytoplankton showed a dominance of cyanobacteria in hypertrophic lakes, whereas the importance of chrysophytes and dinophytes decreased with an increase in trophic status. Protozoans (heterotrophic flagellates and ciliates) made up 24% (mesotrophic lakes) to 42% (hypertrophic lakes) of total zooplankton biomass on average, and were dominated by ciliates (62‐80% of protozoan biomass). Seasonally, protozoans can build up to 60% of zooplankton biomass in spring, when heterotrophic flagellates can contribute � 50% to protozoan biomass. Correlation analyses revealed significant relationships between the planktonic groups and indicated that pelagic food webs are influenced by both bottom-up as well as top-down mechanisms. Comparing lakes along a trophic gradient, resource parameters seem to be of major importance, whereas seasonal changes within a lake were perhaps regulated by the presence of predators.

Sloppy feeding in marine copepods: prey-size-dependent production of dissolved organic carbon

Abstract: An equation predicting dissolved organic carbon (DOC) production by sloppy feeding was developed from literature data on apparent gross growth efficiency and copepod-to-prey size ratio based on the assumption that real gross growth efficiency is independent of relative prey size. The equation suggests that, for copepod-to-prey size ratios <55, DOC production by sloppy feeding can be quantitatively important. It can be calculated as: Q = 0.714 - 0.013 x (ESD copepod /ESD prey ), where Q is the fraction of carbon removed from suspension that is lost as DOC and ESD is equivalent spherical diameter. Predictions by the equation were corroborated by actual measurements of copepod DOC production from the literature.

Zooplankton in the Schelde estuary, Belgium and the Netherlands: spatial and temporal patterns

Abstract: The zooplankton fauna of the Zeeschelde estuary (Belgium) was investigated over 10 months by means of monthly sampling. Canonical Correspondence Analysis (CCA) was used to relate the species distribution to environmental factors. The variation in the species data was significantly (P < 0.05) related to a set of 10 environmental variables (chlorinity, NH4 + , temperature, PO4-P � , DW, Chl a and Chl b, NO2-N, NO3-N and pH). The main spatial and seasonal gradients were associated with chlorinity and temperature respectively. The brackish water zone was dominated by the calanoid Eurytemora affinis in spring, succeeded by Acartia tonsa and mysid species during summer. In the freshwater transect, cyclopoids dominated, together with several cladoceran species. Thermophilic cyclopoid species (Thermocyclops oithonoides, Th. crassus and Mesocyclops leuckarti) occurred during periods of maximal temperature. The cyclopoids Acanthocyclops robustus, Paracyclops poppei and Cyclops vicinus, the cladocerans Daphnia longispina, Chydorus sphaericus and Bosmina longirostris together with the numerically dominant rotifers, oligochaetes, nematodes and juvenile copepods seemed little affected by environmental gradients.

Dinophysis blooms in Greek coastal waters (Thermaikos Gulf, NW Aegean Sea)

Abstract: The first documented Dinophysis bloom from Greek coastal waters associated with a diarrhetic shellfish toxins outbreak was recorded in January 2000 during the HAB monitoring program in Thermaikos Gulf. A species with morphological features similar to D. acuminata Claparede and Lachmann dominated this bloom. Maximum D. cf. acuminata abundance (85.4 x 10 3 cells L -1 ) appeared in February 2000. In 2001, high numbers of D. cf. acuminata (5 x 10 3 cells L -1 ) were recorded in April under conditions of weak thermal stratification, while in 2002 maximum numbers (37 x 10 3 cells L -1 ) of the same species were found in February under low temperature levels (11.5-12.5°C). All Dinophysis blooms persisted for no more than 4 months. In addition to cells resembling typical D. cf. acuminata, cells of similar shape but smaller in size were observed at different stages of the blooms. Other observations include couplets of large and small-sized cells, and also a larger robust form with a dense granular cytoplasm. The D. cf. acuminata population always presented a stratified vertical distribution with vertical peaks positioned in or just above the pycnocline. Among the plysico-chemical parameters, water temperature appears to be the most important factor influencing the distribution of Dinophysis abundance.

A global assessment of mesozooplankton respiration in the ocean

Abstract: Published data on the biomass and specific respiration rates of mesozooplankton in the oceans across all latitudes were combined to assess their community respiration on a global basis. Mesozooplankton biomass was higher in boreal/anti-boreal and polar waters, intermediate in equatorial waters and lowest in the subtropical gyres. Specific respiration rates were the highest in equatorial waters and decreased rapidly poleward. Global community respiration of mesozooplankton in the upper 200 m of the oceans integrated over all latitudes was 10.4 � 3.7 (SE) Gt C year � 1 (n = 838). Below the epipelagic zone, mesozooplankton respiration living in the mesopelagic (200‐1000 m) and bathypelagic (below 1000 m) zones was estimated as 2.2 � 0.4 (n = 57) and 0.40 � 0.2 (n = 12) Gt C year � 1 , respectively. Thus, global depth-integrated mesozooplankton respiration was 13.0 � 4.2 Gt C year � 1 (17‐32% of global primary production), which is 3‐8-fold higher than the values assigned to mesozooplankton respiration in recent estimates of total respiration in the ocean. Thus, it appears that mesozooplankton represent a major, but neglected component of the carbon cycle in the ocean.

Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Abstract: Selectivity-size spectra, clearance and ingestion rates and assimilation efficiencies of Acartia clausi (Copepoda), Penilia avirostris (Cladocera) and Doliolum denticulatum (Doliolida) from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluated in grazing experiments over a wide range of food concentrations (0.02-8.8 mm 3 L -1 plankton assemblages from Blanes Bay, grown in mesocosms at different nutrient levels). Acartia clausi reached the highest grazing coefficients for large algae >70 μm (longest linear extension), P. avirostris for intermediate food sizes between 15 and 70 μm, and D. denticulatum for small sizes from 2.5 to 15 μm. Penilia avirostris and D. denticulatum acted as passive filler-feeders. Acartia clausi gave some evidence for a supplementary raptorial feeding mode. Effective food concentration (EFC) decreased linearly with increasing nutrient enrichment for D. denticulatum and followed domed curves for A. clausi and for P. avirostris with maximum values at intermediate and high enrichment levels, respectively. Clearance rates of crustacean species showed curvilinear responses with narrow modal ranges to increasing food concentration. Clearance rates of D. denticulatum increased abruptly and levelled into a plateau at low food concentrations. Mean clearance rates were 13.9, 25.5 and 64.1 mL ind. -1 day -1 , respectively. No clearance could be detected for A. clausi at food concentrations <0.1 mm 3 L -1 and for P. avirostris at food concentrations <0.02 mm 3 L -1 . Ingestion rates indicate a rectilinear functional response for A. clausi and for P. avirostris and showed a sigmoidal curve for D. denticulatum. Mean ingestion rates were 1.3, 2.8 and 7.7 μg C μg C ind . -1 day -1 , respectively. Conversion of ingested carbon to tissue was 30-80% for the investigated crustaceans and 20-50% for doliolids. Food niche calculations suggest that food niche separation may explain the coexistence of the three species in summer in Blanes Bay.

Some ideas about the role of lipids in the life cycle of Calanus finmarchicus

Abstract: A conceptual model of the possible role of lipids in the life cycle of Calanus finmarchicus is proposed. Lipid storage could play a key role at various levels: (i) by triggering diapause through variations in cholesterol and fatty acid derived hormone levels; (ii) by determining the overwintering depth in relation to the convective mixed layer; and (iii) by playing an important role in the population adaptation to the hydrological conditions of the basin. A number of ways to test the validity of the proposed hypotheses are proposed.

Effect of a Waveband Shift on Chlorophyll Retrieval from MERIS Imagery of Inland and Coastal Waters

Abstract: A chlorophyll-retrieval algorithm for use with imagery from the Medium Resolution Imaging Spectrometer (MERIS) aboard ENVISAT relying on wavebands centred at 665, 705 and 775 nm was described in a previous paper (Gons et al. 2002, J. Plankton Res., 24, 947-951). The present study reexamined the performance for the current nominal setting to 708.75 nm of the previously envisaged 705 nm band. Validation of the algorithm with reviled coefficients gave the same standard error of estimate for the inland and coastal waters as in the original work. The algorithm has been transcribed for direct application with the MERIS level-2 standard product 'water-leaving reflectance'. By this correction, chlorophyll estimation will generally improve, especially for high concentrations.

A methodology to determine primary production and phytoplankton photosynthetic parameters from Fast Repetition Rate Fluorometry

Abstract: Estimating the primary productivity of phytoplankton as they are mixed through the surface layer is often hampered by methodological or conceptual constraints. Fast Repetition Rate Fluorometry (FRRF) allows some of these constraints to be overcome by providing measurements of the instantaneous, depth-dependent rates of primary productivity of phytoplankton in situ. Data acquired by FRR fluorescence is used in this paper to determine the parameters of the photosynthesis‐irradiance curve and the instantaneous photosynthetic rates for phytoplankton from the mixed layer during a cruise in the Celtic Sea in May 2000. FRR fluorescence-based estimates of the initial slope of the photosynthesis‐light curve (� B ) ranged from 7.5 in well-mixed conditions to 12.7 g C (mol photons) � 1 m 2 (g Chl a) � 1 under stratified conditions. FRR fluorescence-based estimates of the light saturation parameter, Ek, were strongly correlated with the logarithm of the surface PAR. FRR fluorescence-based estimates of the Chl a-specific, light saturated photosynthesis rate (Pm B ) ranged from 1.4 to 2.8 g C (g Chl a) � 1 h � 1 . The FRRF determined values of Pm B were consistent with those measured using radiocarbon techniques, however, there were systematic differences

Decadal change in zooplankton seasonal succession in the Bahía Blanca estuary, Argentina, following introduction of two zooplankton species

Abstract: Seasonal zooplankton succession (mainly of the mesozooplankton) in the inner zone of Bahia Blanca estuary during the period 1990-1991 was compared to that from the period 1979-1980 in order to detect changes having taken place in 10 years. Taxonomic composition, zooplankton abundance, species occurrence and temperature-salinity conditions were studied within the two annual cycles. This estuarine ecosystem has been deeply affected by a population increase and by the rapid growth of industrial activity and maritime traffic over the last two decades. Several changes in the zooplankton assemblage composition and structure were detected, probably due to temperature- salinity gradient patterns, which showed discernible differences. Dominance, during winter-spring, of two new invading species, namely, the cirriped Balanus glandula and the copepod Eurytemora americana, causing a decrease in the autochthonous key copepod Acartia tonsa, was one of the principal features of the period 1990-1991. Seasonal changes in diversity and species richness, as well as differences in the multivariate general pattern of the zooplankton community structure with a consequent decrease in the community stability during the second period, were also observed.

Diet of the larval ctenophore Mnemiopsis leidyi A. Agassiz (Ctenophora, Lobata)

Abstract: Larvae and post-larvae of the lobate ctenophore Mnemiopsis leidyi consumed significant quantities of microphytoplankton and microzooplankton prey in controlled experiments where they were fed in situ assemblages of microplankton prey. Prey taxa ingested included phototrophic and heterotrophic dinoflagellates, choreotrich ciliates, cyclotrich ciliates and euglenoid flagellates. Per capita clearance and ingestion rates varied with consumer size, prey taxon and prey abundance. Average per capita clearance rates for the 11 size classes of larvae and post-larvae examined ranged from 9 to 230 mL individual � 1 h � 1 . Average per capita clearance rates for tentaculate-stage, transition-stage and lobate-stage individuals were 40, 31 and 95 mL individual � 1 h � 1 , respectively. Total ingestion rate varied similarly with consumer size, prey taxon and prey abundance, ranging from 1 to 6259% body carbon day � 1 . All size classes of M. leidyi larvae and post-larvae derived more nutrition from dinoflagellates than from ciliates. Both positive and negative selection of specific prey taxa were observed, and varied with larval size and prey taxonomic composition. The results contradict the prevailing view that all life history stages of M. leidyi are primarily carnivorous. The measured clearance rates are sufficiently high that the larvae, when abundant, have the potential to exert a significant predation impact on their prey populations in the water column. Understanding the processes that influence survival during early developmental stages may provide one key to understanding the initiation and maintenance of the adult M. leidyi blooms that are commonly observed in coastal waters.

Simultaneous changes in cell quotas of microcystin, chlorophyll a, protein and carbohydrate during different growth phases of a batch culture experiment with Microcystis aeruginosa

Abstract: The cell quotas of microcystin (Q mcyst), protein (Q prot), chlorophyll a (Q chloro) and carbohydrate (Q carbo), as well as the net production rates of these parameters, were determined during the exponential and stationary phases in nine batch cultures of Microcystis aeruginosa (CYA 228) at light regimes from 33 to 53 mol photons m � 2 s � 1 . The following results were obtained. (i) A parallel pattern was found in the changes of Q mcyst ,Q prot ,Q chloro and Q carbo during the entire growth cycle and significant correlations were recorded between Q mcyst and Q prot ,Q chloro and Q carbo. (ii) The net microcystin production rate (mcyst) was positively correlated with the specific cell division rate (c), the chlorophyll production rate (chloro) and the protein production rate. (iii) A significant inverse linear relationship was found between c and Q mcyst, i.e. cultures with a positive c had a Q mcyst between 110 and 400 fg microcystin cell � 1 , while declining cultures had Q mcyst values >400 fg microcystin cell � 1 .M aximum variation in Qmcyst within cultures was 3.5-fold. Collectively, the results show that cells produced microcystin at rates approximating those needed to replace losses to daughter cells during division and that microcystin was produced in a similar way to protein and chlorophyll, indicating a constitutive microcystin production.

Development of specific rRNA probes to distinguish between geographic clades of the Alexandrium tamarense species complex

Abstract: The globally occurring Alexandrium tamarense/fundyense/catenella species complex consists of toxic and non-toxic strains that are morphologically difficult to distinguish. We developed four specific ribosomal RNA probes that can identify the entire species complex, the strains of the toxic .orth American clade and the strains of the two non-toxic clades from Western Europe and the Mediterranean Sea by DNA dot blot and fluorescence in situ hybridization. These probes are a first step for the development of an early warning system for the presence of A. tamarense.

Dynamics and metabolic activity of the benthic cyanobacterium Microcystis aeruginosa in the Grangent reservoir (France)

Abstract: The dynamics of benthic colonies of Microcystis aeruginosa (cyanobacteria) play an important part in the formation of the summer bloom underlying many harmful effects. Because this benthic phase remains somewhat unknown, we developed an approach usingflow cytometry to follow the esterase activity of this species in the Grangent reservoir. The esterase activity of benthic cyanobacteria extractedfrom two layers of sediment (0-2 cm and 2-4 cm deep) was measured weekly, as an indicator of viability, by flow cytometry with carboxyfluorescein diacetate. In parallel, the concentration of benthic cyanobacteria was estimated under epifluorescence microscopy and the water temperature and dissolved oxygen concentration were measured in the hypolimnion. Esterase activity increased gradually as spring temperatures increased. This metabolic reactivation allowed one part of the benthic cyanobacteria to regain the water column, entailing a simultaneous decrease of their number in the upper sediment (0-2 cm). Then, after a maximum in summer, esterase activity decreased while the number of colonies increased. This corresponded with the domination of the senescent planktonic form following the decline of the bloom.

Calanus the cannibal

Abstract: Recent modelling efforts have suggested that cannibalism on eggs and young nauplii is an important factor controlling the population dynamics of Calanus. We measured cannibalistic feeding rates on eggs and nauplii of Calanus helgolandicus in the laboratory. Clearance rates on nauplii were � 102 mL ind. � 1 day � 1 , while generally higher on eggs (320 mL ind. � 1 day � 1 ). Female starvation did not affect ingestion rates of eggs. We discuss our results in light of published model predictions, cannibalistic feeding rates of other copepods, and field distributions of Calanus developmental stages.

Occurrence of mycosporine-like amino acids (MAAs) in the bloom-forming cyanobacterium Microcystis aeruginosa

Abstract: Here we report the finding of two mycosporine-like amino acids (shinorine and Porphyra-334) in both a culture of the cyanobacterium Microcystis aeruginosa isolated from Lake Taihu (China) and a natural phytoplankton sample collected from this lake which included Microcystis spp. Our results are the first to clearly document the occurrence of these UV-sunscreen compounds in a freshwater bloom-forming cyanobacterium.

A study of phytoplankton spatial distributions, flow structure and characteristics of mixing in a river reach with groynes

Abstract: Prolonged retention of water in riverine recirculation zones and the consequences for phytoplankton growth are the subjects of ongoing debate and a challenge for intensive research. In the present study, conducted in a reach of the River Elbe with groynes, detailed field surveys of phytoplankton abundance and composition were accompanied by a comprehensive investigation of flow structure during low and high water stages. Settling ofthe suspended particulate matter, and the embedded phytoplankton, controls the phytoplankton dynamics. Processes of phytoplankton growth were shown to be insignificant because of insufficient residence times. The spatial patterns of the total suspended particulate matter (seston) concentration,the organic content, the chlorophylla concentration,the mean velocity and turbulencefields exhibited a marked agreement, thus revealing the mutual relationship between phytoplankton abundance and local flow characteristics. The geometry of the groyne fields, expressed by the aspect ratio between length of groyne and the length of the side of the groyne field, was shown to determine these patterns. The study outlines the importance of numerical description of mixing processes in river flow and detailed field studies of turbulence for advanced research of phytoplankton dynamics in riverine ecosystems.

Phytoplankton community growth-rate response to nutrient pulses in a shallow turbid estuary, Galveston Bay, Texas

Abstract: Phytoplankton growth is a physiological process often limited by temperature, nutrients or light, while biomass accumulation is a function of growth rates, grazing and deposition. Although primary productivity measurements are usually used to assess responses to limiting factors, the rates are proportional to biomass and inversely related to grazing pressure during experimental incubations. Alternatively, carbon-specific growth-rate determinations provide insights into physiological responses without the confounding acts of biomass and grazing. The objective of this study was to quantify the growth-rate responses of phytoplankton to enhanced nutrient availability (nitrate and phosphate) over a range of in situ irradiances. Growth rates were determined based on chlorophyll a-specific 14 C-uptake rates by phytoplankton. Phytoplankton demonstrated high (24 h) growth rates when exposed to increased concentrations of limiting nutrients, independent of the surface irradiances (12-41%). Growth-rate responses were also compared zenith the biomass (chlorophyll a) responses and community composition. Observed and estimated phytoplankton biomass changes during the incubations differed, emphasizing the structural role of graders on the phytoplankton community. The phytoplankton community in Galveston Bay has the potential to instantaneously respond to nutrient pulses, facilitating diatom biomass accumulations in spring and summer and small, flagellated species and cyanobacteria during periods of low nutrient inputs. Thus, Galveston Bay phytoplankton biomass and community composition reflect a dynamic balance between the frequency of nutrient pulsing and grazing intensity.