Succession Of Blooms Research Articles

Effect of a rainfall pulse on phytoplankton bloom succession in a hyper-eutrophic subtropical lagoon

In the present study, we sought to understand the succession of phytoplankton species, after a natural nutrient pulse, in a subtropical lagoon located in southern Taiwan. The lagoon was surrounded by aquaculture ponds. The present study was performed during the wet summer season, before and after an episode of heavy precipitation. Before rainfall commenced, both the phosphate concentration and the level of phytoplankton were relatively low. After heavy precipitation, physical and chemical measurements indicated that significant amounts of dissolved inorganic nutrients had drained into the lagoon. A phytoplankton bloom occurred; organism levels reached 77.6×105 cells L–1. The dominant organism was Chaetoceros curvisetus (99.3%). After the bloom ceased, the levels of inorganic nutrients, especially silicate, fell. Phytoplankton became of low abundance once more. At the end of our study period, the ecosystem was dominated once more by diatoms (75.8%); this may have been caused by a low-level nutrient pulse following rainfall that occurred one day before final sampling. Overall, our results suggest that the bloom succession of phytoplankton species was principally dependent on nutrient dynamics in the lagoon, which was associated with nutrients discharged from drainage after heavy rainfall.

Fatores determinantes das florações de cianobactérias na água do Rio Doce, Minas Gerais, Brasil

A partir de 2005 ocorreram sucessivas florações de cianobactérias tóxicas e não tóxicas na água do Rio Doce. Naquela época, foram identificadas as possíveis causas dessas florações e dentre elas se destacou principalmente o extenso período estival na região da bacia hidrográfica. O principal objetivo desse trabalho foi o de associar estatisticamente alguns parâmetros ambientais e de qualidade da água do rio em um período de cinco anos, para encontrar e explicar as possíveis correlações existentes. As cianobactérias estiveram presentes na água do Rio Doce nos 10 pontos de coleta avaliados pelo Instituto Mineiro de Gestão das Águas, no período de 2008 a 2012. Na análise de agrupamentos entre as estações de coleta, o ponto RD44 se destacou isoladamente e apresentou maiores densidades de termotolerantes durante o inverno. Por meio da análise de componentes principais, verificouse que as maiores densidades de cianobactérias estiveram associadas a reduções da temperatura da água, da turbidez, da concentração de fósforo total e condições características do período estival (inverno seco) na água de rios em Minas Gerais. Nesse mesmo período, ocorreram elevações nas concentrações de clorofila a, oxigênio dissolvido, nitratos, da relação estequiométrica N/P e do Índice de Qualidade das Águas. Após 2009 as florações se tornaram sucessivas. Isso reforça a teoria de que o represamento da água do rio exerceu uma influência nas crescentes florações de cianobactérias, pois podem ter contribuído para a redução da turbidez da água do rio, para o aumento da concentração de nitratos e da densidade de termotolerantes.

Evaluation of Passive Samplers as a Monitoring Tool for Early Warning of Dinophysis Toxins in Shellfish

From June 2006 to January 2007 passive samplers (solid phase adsorbing toxin tracking, SPATT) were tested as a monitoring tool with weekly monitoring of phytoplankton and toxin content (liquid chromatography–mass spectrometry, LC-MS) in picked cells of Dinophysis and plankton concentrates. Successive blooms of Dinophysis acuminata, D. acuta and D. caudata in 2006 caused a long mussel harvesting closure (4.5 months) in the Galician Rías (NW Spain) and a record (up to 9246 ng·g resin-week−1) accumulation of toxins in SPATT discs. Best fit of a toxin accumulation model was between toxin accumulation in SPATT and the product of cell densities by a constant value, for each species of Dinophysis, of toxin content (average) in picked cells. Detection of Dinophysis populations provided earlier warning of oncoming diarrhetic shellfish poisoning (DSP) outbreaks than the SPATT, which at times overestimated the expected toxin levels in shellfish because: (i) SPATT accumulated toxins did not include biotransformation and depuration loss terms and (ii) accumulation of toxins not available to mussels continued for weeks after Dinophysis cells were undetectable and mussels were toxin-free. SPATT may be a valuable environmental monitoring and research tool for toxin dynamics, in particular in areas with no aquaculture, but does not provide a practical gain for early warning of DSP outbreaks.

Behavioral and Physiological Changes during Benthic-Pelagic Transition in the Harmful Alga, Heterosigma akashiwo: Potential for Rapid Bloom Formation

Many species of harmful algae transition between a motile, vegetative stage in the water column and a non-motile, resting stage in the sediments. Physiological and behavioral traits expressed during benthic-pelagic transition potentially regulate the timing, location and persistence of blooms. The roles of key physiological and behavioral traits involved in resting cell emergence and bloom formation were examined in two geographically distinct strains of the harmful alga, Heterosigma akashiwo. Physiological measures of cell viability, division and population growth, and cell fatty acid content were made using flow cytometry and gas chromatography – mass spectrometry techniques as cells transitioned between the benthic resting stage and the vegetative pelagic stage. Video-based tracking was used to quantify cell-level swimming behaviors. Data show increased temperature and light triggered rapid emergence from the resting stage and initiated cell swimming. Algal strains varied in important physiological and behavioral traits, including survivorship during life-stage transitions, population growth rates and swimming velocities. Collectively, these traits function as “population growth strategies” that can influence bloom formation. Many resting cells regained the up-swimming capacity necessary to cross an environmentally relevant halocline and the ability to aggregate in near-surface waters within hours after vegetative growth supporting conditions were restored. Using a heuristic model, we illustrate how strain-specific population growth strategies can govern the timescales over which H. akashiwo blooms form. Our findings highlight the need for identification and quantification of strain-specific physiological and behavioral traits to improve mechanistic understanding of bloom formation and successful bloom prediction.

Annual record of particle fluxes, geochemistry and diatoms in Effingham Inlet, British Columbia, Canada, and the impact of the 1999 La Niña event

Sediment traps were deployed inside the anoxic inner basin of Effingham Inlet and at the oxygenated mouth of the inlet from May 1999 to September 2000 in a pilot study to determine the annual depositional cycle and impact of the 1999 La Niña event within a western Canadian inlet facing the open Pacific Ocean. Total mass flux, geochemical parameters (carbon, nitrogen, opal, major and minor element contents, and stable isotope ratios) and diatom assemblages were determined and compared with meteorological and oceanographic data. Deposition was seasonal, with coarser grained terrestrial components and benthic diatoms settling in the autumn and winter, coincident with the rainy season. Marine sedimentary components and abundant pelagic diatoms were coincident with coastal upwelling in the spring and summer. Despite the seasonal differences in deposition, the typical temperate-zone Thalassiosira – Skeletonema – Chaetoceros bloom succession was muted. A July 1999 total mass flux peak and an increase in biogenous components coincided with a rare bottom-water oxygen renewal event in the inlet. Likewise, there were cooler-than-average sea surface temperatures (SSTs) just outside the inlet, and unusually high abundances of a previously undescribed cool-water marine diatom ( Fragilariopsis pacifica sp. nov.) within the inlet. Each of these occurrences likely reflects a response to the strong La Niña that followed the year after the strongest-ever recorded El Niño event of 1997–1998. By the autumn of 1999, SSTs had returned to average, and F. pacifica had all but disappeared from the remaining trap record, indicating that oceanographic conditions had returned to normal. Oxygenation events were not witnessed in the inlet in the years before or after 1999, suggesting that a rare oceanographic and climatic event was captured by this sediment trap time series. The data from this record can therefore be used as a benchmark for identifying anomalous environmental conditions on this coast. ► Only sediment trap study done in a western Canadian inlet facing the open Pacific ► Deposition of settling particles is clearly seasonal. ► Deposition of settling particles is also influenced by the 1999 La Niña event. ► 1999 La Niña had a strong oceanographic and biological effect on the coast. ► Sediment trap data can be used as benchmarks recording anomalous climatic events.

Ammonia may play an important role in the succession of cyanobacterial blooms and the distribution of common algal species in shallow freshwater lakes

AbstractWith the human intensification of agricultural and industrial activities, large amount of reduced nitrogen enter into the biosphere, which consequently results in the development of global eutrophication and cyanobacterial blooms. However, no research had reported the effect of ammonia toxicity on the algal succession. In this study, we investigated the ammonia toxicity to 19 algal species or strains to test the hypothesis that ammonia may regulate the succession of cyanobacterial blooms and the distribution of common algal species in freshwater lakes. The bloom‐forming cyanobacterium Microcystis aeruginosa PCC 7806 suffered from ammonia toxicity at high pH value and light intensity conditions. Low NH4Cl concentration (0.06 mmol L−1) resulted in the decrease of operational PSII quantum yield by 50% compared with the control exposed to 1000 μmol photons m−2 s−1 for 1 h at pH 9.0 ± 0.2, which can be reached in freshwater lakes. Furthermore, the tolerant abilities to NH3 toxicity of 18 freshwater algal species or strains were as follows: hypertrophication species > eutrophication species > mesotrophication species > oligotrophication species. The different sensitivities of NH3 toxicity in this study could well explain the distributing rule of common algal species in the freshwater lakes of different trophic states. Meanwhile, the cyanobacterial bloom (e.g. M. aeruginosa) always happened at the low concentration of ammonia in summer, and disappeared with the decrease of ammonia. This may be attributed to the toxic effect of ammonia to M. aeruginosa in spring (the average and maximum ammonia concentration were 0.08 and 0.72 mmol L−1 in 33 Chinese lakes), and the low level of NH3‐N in summer and fall in the lakes might be used as preferred nitrogen nutrition by M. aeruginosa, rather than with toxicity. Therefore, ammonia could be a key factor to determine the distribution of common algal species and cyanobacterial bloom in the freshwater systems.

Dynamic autoinoculation and the microbial ecology of a deep water hydrocarbon irruption

The irruption of gas and oil into the Gulf of Mexico during the Deepwater Horizon event fed a deep sea bacterial bloom that consumed hydrocarbons in the affected waters, formed a regional oxygen anomaly, and altered the microbiology of the region. In this work, we develop a coupled physical-metabolic model to assess the impact of mixing processes on these deep ocean bacterial communities and their capacity for hydrocarbon and oxygen use. We find that observed biodegradation patterns are well-described by exponential growth of bacteria from seed populations present at low abundance and that current oscillation and mixing processes played a critical role in distributing hydrocarbons and associated bacterial blooms within the northeast Gulf of Mexico. Mixing processes also accelerated hydrocarbon degradation through an autoinoculation effect, where water masses, in which the hydrocarbon irruption had caused blooms, later returned to the spill site with hydrocarbon-degrading bacteria persisting at elevated abundance. Interestingly, although the initial irruption of hydrocarbons fed successive blooms of different bacterial types, subsequent irruptions promoted consistency in the structure of the bacterial community. These results highlight an impact of mixing and circulation processes on biodegradation activity of bacteria during the Deepwater Horizon event and suggest an important role for mixing processes in the microbial ecology of deep ocean environments.

The influence of light and the place of its perception on the flowering of Pharbitis nil.

The estimation of participation and density of forage species in several xerothermic communities of the Lublin Upland were carried out in 2004 and 2005. Most plants species visited by bees are grouped in plots of the <i>Brachypodio</i>-<i>Teucrietum</i> and the <i>Adonido</i>-<i>Brachypodietum pinnati</i> communities. The nectariferous and polleniferous taxons are mostly perennials predominated by hemicryptophytes (79%), others are terophytes and geophytes (21%). Successive blooming of the nectariferous and polleniferous species in both associations ensures unbroken food flow from the early spring until the late summer and early autumn. Xerothermic swards make a valuable food potential to be important for the <i>Apoidea</i> before and after blooming of the main forage cultivated crops.

The share of nectariferous and polleniferous taxons in chosen patches of thermophilous grasslands of the Lublin Upland

The estimation of participation and density of forage species in several xerothermic communities of the Lublin Upland were carried out in 2004 and 2005. Most plants species visited by bees are grouped in plots of the <i>Brachypodio</i>-<i>Teucrietum</i> and the <i>Adonido</i>-<i>Brachypodietum pinnati</i> communities. The nectariferous and polleniferous taxons are mostly perennials predominated by hemicryptophytes (79%), others are terophytes and geophytes (21%). Successive blooming of the nectariferous and polleniferous species in both associations ensures unbroken food flow from the early spring until the late summer and early autumn. Xerothermic swards make a valuable food potential to be important for the <i>Apoidea</i> before and after blooming of the main forage cultivated crops.

The anthropogenic refuge areas for bee flora in agricultural landscape

The investigations were carried out in 2002-2006 in two municipalities of Konopnica and Jastków close to the western part of Lublin, Poland. The aim of the study was to identify the condition of bee flora and determine the floristic richness depending on the biotops in agricultural landscape. Flora of the anthropogenic refuge areas consists of 214 species, among them 80% were flow taxons. Apophytes (162 species - 78%) predominated on all types of biotops under consideration. Perennials predominated in flora of boundary strips and bush communities. Mainly annual (40%) and biennial (15%) species comprise the flora of fallows. A great number of bee taxons represent meadow, segetal or ruderal communities. Most of flow plants compose loose patches, but their successive blooming ensures a source of food for <i>Apoidea</i> from early spring till the end of summer. The flora of boundary strips, bush communities and fallows significantly increases the biodiversity in agricultural landscape. The treatments including sowing, mainly on fallows with nectariferous and polleniferous species, would enrich generally weak flows in highly agricultural landscape.

Rapid successions affect microbial N‐acetyl‐glucosamine uptake patterns during a lacustrine spring phytoplankton bloom

The vernal successions of phytoplankton, heterotrophic nanoflagellates (HNF) and viruses in temperate lakes result in alternating dominance of top-down and bottom-up factors on the bacterial community. This may lead to asynchronous blooms of bacteria with different life strategies and affect the channelling of particular components of the dissolved organic matter (DOM) through microbial food webs. We followed the dynamics of several bacterial populations and of other components of the microbial food web throughout the spring phytoplankton bloom period in a pre-alpine lake, and we assessed bacterial uptake patterns of two constituents of the labile DOM pool (N-acetyl-glucosamine [NAG] and leucine). There was a clear genotypic shift within the bacterial assemblage, from fast growing Cytophaga-Flavobacteria (CF) affiliated with Fluviicola and from Betaproteobacteria (BET) of the Limnohabitans cluster to more grazing resistant AcI Actinobacteria (ACT) and to filamentous morphotypes. This was paralleled by successive blooms of viruses and HNF. We also noted the transient rise of other CF (related to Cyclobacteriaceae and Sphingobacteriaceae) that are not detected by fluorescence in situ hybridization with the general CF probe. Both, the average uptake rates of leucine and the fractions of leucine incorporating bacteria were approximately five to sixfold higher than of NAG. However, the composition of the NAG-active community was much more prone to genotypic successions, in particular of bacteria with different life strategies: While 'opportunistically' growing BET and CF dominated NAG uptake in the initial period ruled by bottom-up factors, ACT constituted the major fraction of NAG active cells during the subsequent phase of high predation pressure. This indicates that some ACT could profit from a substrate that might in parts have originated from the grazing of protists on their bacterial competitors.

Settlement of vegetative fragments of Ulva prolifera confirmed as an important seed source for succession of a large‐scale green tide bloom

Ulva prolifera green tides in the Yellow Sea of China in the past 3 yr are among the largest macroalgal blooms ever recorded. Satellite images, as well as wind and current patterns, provide a clear picture of the formation of these green tides; however, their place of origin remains unclear. Terrestrial investigation along the coastline of the Jiangsu Province and two shipboard surveys in the Yellow Sea in 2009 showed that filamentous Ulvaceae algae were prevalent in various environments in Jiangsu Province including floating rafts for Porphyra cultivation, land‐based bivalve culturing ponds, estuaries, embankments, intertidal stones, wharfs, and hard muddy coasts. Vegetative fragments in sediment samples were found in both shipboard surveys during the bloom and postbloom periods, and all of the samples were U. prolifera. Phylogenetic analysis of 5S spacer sequences showed that the green tide in the Yellow Sea was not of terrestrial origin. However, settled vegetative fragments of U. prolifera were an important seed source for the successive and more serious green tide blooms.

Succession and fate of the spring diatom bloom in Disko Bay, western Greenland

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 419:11-29 (2010) - DOI: https://doi.org/10.3354/meps08813 Succession and fate of the spring diatom bloom in Disko Bay, western Greenland Michael Dünweber1,4, Rasmus Swalethorp1,4, Sanne Kjellerup1,4, Torkel Gissel Nielsen1,4,*, Kristine Engel Arendt2, Morten Hjorth1, Kajsa Tönnesson3, Eva Friis Møller1 1National Environmental Research Institute, Department of Marine Ecology, University of Aarhus, Frederiksborgvej 399, 4000 Roskilde, Denmark 2Greenland Climate Research Centre, Greenland Institute of Natural Resources, Kivioq 3, Po Box 570, 3900 Nuuk, Greenland 3Department of Marine Ecology—Göteborg, University of Gothenburg, Box 461, 405 30 Göteborg, Sweden 4Section for Oceanecology and Climate, National Institute of Aquatic Resources, Technical University of Denmark, Kavalergården 6, 2920 Charlottenlund, Denmark *Corresponding author. Email: tgin@aqua.dtu.dk ABSTRACT: Phytoplankton and copepod succession was investigated in Disko Bay, western Greenland from February to July 2008. The spring phytoplankton bloom developed immediately after the breakup of sea ice and reached a peak concentration of 24 mg chl a m–3 2 wk later. The bloom was analyzed during 3 phases: the developing, the decaying, and the post-bloom phases. Grazing impact by the copepod community was assessed by 4 methods; gut fluorescence, in situ faecal pellet production, and egg and faecal pellet production from bottle incubations. Calanus spp. dominated the mesozooplankton community. They were present from the initiation of the bloom but only had a small grazing impact on the phytoplankton. Consequently, there was a close coupling between the spring phytoplankton bloom and sedimentation of particulate organic carbon (POC). Out of 1836 ± 180 mg C m–2 d–1 leaving the upper 50 m, 60% was phytoplankton based carbon (PPC). The composition and quality of the sedimenting material changed throughout the bloom succession from PPC dominance in the initial phase with a POC/PON ratio close to 6.6 to a dominance of amorphous detritus with a higher POC/PON ratio (>10) in the post-bloom phase. The succession and fate of the phytoplankton spring bloom was controlled by nitrogen limitation and subsequent sedimentation, while grazing-mediated flux by the Calanus-dominated copepod community played a minor role in the termination of the spring bloom of Disko Bay. KEY WORDS: Spring bloom · Calanus spp. · Grazing · Faecal pellets · Sedimentation · Arctic · Greenland Full text in pdf format PreviousNextCite this article as: Dünweber M, Swalethorp R, Kjellerup S, Nielsen TG and others (2010) Succession and fate of the spring diatom bloom in Disko Bay, western Greenland. Mar Ecol Prog Ser 419:11-29. https://doi.org/10.3354/meps08813 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 419. Online publication date: November 30, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Unveiling a phytoplankton hotspot at a narrow boundary between coastal and offshore waters

In terrestrial ecosystems, transitional areas between different plant communities (ecotones) are formed by steep environmental gradients and are commonly characterized by high species diversity and primary productivity, which in turn influences the foodweb structure of these regions. Whether comparable zones of elevated diversity and productivity characterize ecotones in the oceans remains poorly understood. Here we describe a previously hidden hotspot of phytoplankton diversity and productivity in a narrow but seasonally persistent transition zone at the intersection of iron-poor, nitrate-rich offshore waters and iron-rich, nitrate-poor coastal waters of the Northeast Pacific Ocean. Novel continuous measurements of phytoplankton cell abundance and composition identified a complex succession of blooms of five distinct size classes of phytoplankton populations within a 100-km-wide transition zone. The blooms appear to be fueled by natural iron enrichment of offshore communities as they are transported toward the coast. The observed succession of phytoplankton populations is likely driven by spatial gradients in iron availability or time since iron enrichment. Regardless of the underlying mechanism, the resulting communities have a strong impact on the regional biogeochemistry as evidenced by the low partial pressure of CO(2) and the nearly complete depletion of nutrients. Enhanced phytoplankton productivity and diversity associated with steep environmental gradients are expected wherever water masses with complementary nutrient compositions mix to create a region more favorable for phytoplankton growth. The ability to detect and track these important but poorly characterized marine ecotones is critical for understanding their impact on productivity and ecosystem structure in the oceans.

Nutrient dynamics and phytoplankton development along an estuary–coastal zone continuum: A model study

This study presents a first attempt to quantify the biogeochemical transformations and fluxes of carbon and nutrients along the entire mixing zone of the shallow, tidally-dominated estuary–coastal zone continuum of the Scheldt (Belgium/The Netherlands). A fully transient, two-dimensional, nested-grid hydrodynamic model of the continuum is coupled to the biogeochemical MIRO model for the coastal zone and the CONTRASTE model for the estuary. Transient model simulations are performed with a high spatial (80–750 m) and temporal (30 min) resolution over a period of one year (January–December 1995). The high temporal resolution allows including the short-term variability triggered by the tides, the freshwater discharge and the wind stress. System scale simulations provide time series of nutrient transformations and fluxes along the entire estuary–coastal zone continuum, as well as highly resolved nutrient inventories for the estuarine and the coastal zone sub-domains. Simulation results reveal that the balance between highly variable estuarine nutrient inputs and physical constrains set by the unsteady residual transport field exert an important control on the magnitude and succession of phytoplankton blooms and the ecosystem structure in the coastal zone. In addition, they suggest that the poorly surveyed estuarine–coastal zone interface plays a central role in the continuum. In this dynamic area, marked spatial concentration gradients develop and episodically lead to a reversal of material fluxes from the coast into the estuary. During distinct episodes of the productive period, euryhaline coastal diatoms intrude far upstream into the saline estuary. This intrusion reduces the estuarine nutrient concentrations and export fluxes, thereby reinforcing the nutrient limitation in the coastal area. As a consequence, the estuarine filter does not operate independently from the processes in the coastal zone. The dynamic interplay between the two ecosystems and the intense process rates operating at their transition, therefore, strongly supports our continuum approach.

Temporal dynamics of Prochlorococcus ecotypes in the Atlantic and Pacific oceans

To better understand the temporal and spatial dynamics of Prochlorococcus populations, and how these populations co-vary with the physical environment, we followed monthly changes in the abundance of five ecotypes-two high-light adapted and three low-light adapted-over a 5-year period in coordination with the Bermuda Atlantic Time Series (BATS) and Hawaii Ocean Time-series (HOT) programs. Ecotype abundance displayed weak seasonal fluctuations at HOT and strong seasonal fluctuations at BATS. Furthermore, stable 'layered' depth distributions, where different Prochlorococcus ecotypes reached maximum abundance at different depths, were maintained consistently for 5 years at HOT. Layered distributions were also observed at BATS, although winter deep mixing events disrupted these patterns each year and produced large variations in ecotype abundance. Interestingly, the layered ecotype distributions were regularly reestablished each year after deep mixing subsided at BATS. In addition, Prochlorococcus ecotypes each responded differently to the strong seasonal changes in light, temperature and mixing at BATS, resulting in a reproducible annual succession of ecotype blooms. Patterns of ecotype abundance, in combination with physiological assays of cultured isolates, confirmed that the low-light adapted eNATL could be distinguished from other low-light adapted ecotypes based on its ability to withstand temporary exposure to high-intensity light, a characteristic stress of the surface mixed layer. Finally, total Prochlorococcus and Synechococcus dynamics were compared with similar time series data collected a decade earlier at each location. The two data sets were remarkably similar-testimony to the resilience of these complex dynamic systems on decadal time scales.

Food supply to the seafloor in the Pacific Ocean after the Cretaceous/Paleogene boundary event

Deep-sea benthic foraminifera show important but transient assemblage changes at the Cretaceous/Paleogene (K/Pg) boundary, when many biota suffered severe extinction. We quantitatively analyzed benthic foraminiferal assemblages from lower bathyal–upper abyssal (1500–2000 m) northwest Pacific ODP Site 1210 (Shatsky Rise) and compared the results with published data on assemblages at lower bathyal (~ 1500 m) Pacific DSDP Site 465 (Hess Rise) to gain insight in paleoecological and paleoenvironmental changes at that time. At both sites, diversity and heterogeneity rapidly decreased across the K/Pg boundary, then recovered. Species assemblages at both sites show a similar pattern of turnover from the uppermost Maastrichtian into the lowermost Danian: 1) The relative abundance of buliminids (indicative of a generally high food supply) increases towards the uppermost Cretaceous, and peaks rapidly just above the K/Pg boundary, coeval with a peak in benthic foraminiferal accumulation rate (BFAR), a proxy for food supply. 2) A peak in relative abundance of Stensioeina beccariiformis, a cosmopolitan form generally more common at the middle than at the lower bathyal sites, occurs just above the buliminid peak. 3) The relative abundance of Nuttallides truempyi, a more oligotrophic form, decreases at the boundary, then increases above the peak in Stensioeina beccariiformis. The food supply to the deep sea in the Pacific Ocean thus apparently increased rather than decreased in the earliest Danian. The low benthic diversity during a time of high food supply indicates a stressed environment. This stress might have been caused by reorganization of the planktic ecosystem: primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly (<10 kyr) filled by other, possibly opportunistic, primary producers, leading to delivery of another type of food, and/or irregular food delivery through a succession of opportunistic blooms. The deep-sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep-sea floor became severely food-depleted following the K/Pg extinction due to the mass extinction of primary producers (“Strangelove Ocean Model”) or to the collapse of the biotic pump (“Living Ocean Model”).

Relationships between nitrogen and phosphorus forms and ratios and the development of dinoflagellate blooms in the East China Sea

During late spring and early summer of 2005, large-scale (> 15 000 km(2)), mixed dinoflagellate blooms developed along the the coast of the East China Sea. Karenia mikimotoi was the dominant harmful algal bloom species in the first stage of the bloom (late May) and was succeeded by Prorocentrum donghaiense approximately 2 wk later. Samples were collected from different stations along both north-south and west-east transects, from the Changjiang River estuary to the south Zhejiang coast, during 3 cruises of the Chinese Ecology and Oceanography of Harmful Algal Blooms Program, before and during the bloom progression. Nitrogen isotope tracer techniques were used to measure rates of NO3-, NH4+, urea, and glycine uptake during the blooms. High inorganic nitrogen (N), but low phosphorus (P) loading from the Changjiang River led to high dissolved inorganic N:dissolved inorganic P ratios in the sampling area and indicate the development of P limitation. The rates of N-15-uptake experiments enriched with PO43- were enhanced compared to unamended samples, suggesting P limitation of the N-uptake rates. The bloom progression was related to the change in availability of both organic and inorganic N and P. Reduced N forms, especially NH4+, were preferentially taken up during the blooms, but different bloom species had different rates of uptake of organic N substrates. K mikimotoi had higher rates of urea uptake, while P. donghaiense had higher rates of glycine uptake. Changes in the availability of reduced N and the ratios of N:P in inorganic and organic forms were suggested to be important in the bloom succession. Nutrient ratios and specific uptake rates of urea were similar when compared to analogous blooms on the West Florida Shelf.

Strong bottom–up effects on phytoplankton community caused by a rainfall during spring and summer in Sagami Bay, Japan

To assess the consequences of bottom-up effects on phytoplankton community composition during the rainy season, phytoplankton levels and environmental factors were monitored daily from 12 April to 22 July 2003 in Sagami Bay, Japan. The relevant environmental factors were analyzed using cross-correlation analyses. Based on time-series analysis, low surface salinity conditions lasting 0 or 2 days after heavy rainfalls resulted in significant nutrient loading, such as dissolved inorganic nitrogen (DIN), into the coastal area. Also, Chlorophyll- a (Chl- a) concentration frequently increased 2 and 6 days after rainfall. Based on the high total Chl- a concentration, the time was divided into three periods, from 1 to 11 May (Period A), 26 May to 9 June (Period B) and 30 June to 22 July (Period C). The phytoplankton assemblages during Period A were dominated by two dinoflagellates, Ceratium furca and Ceratium fusus. Prior to these species blooming, the heterotrophic dinoflagellate Noctiluca scintillans was dominant. During Period B, the phytoplankton communities were dominated primarily by the diatoms Rhizosolenia delicatula, Hemiaulus sinensis and Navicula spp. Finally, Cerataulina dentata, Rhizosolenia spp., Lauderia borealis and Neodelphineis pelagica were dominant during Period C. After increases in phytoplankton abundance, available nitrogen (N) and phosphorous (P) were consumed and exhausted, which were considered a potential cause of the shift in the dominant organisms from large diatoms to pico- and nano-plankton in the low Chl- a environment. In particular, silicate (Si) was not a major limiting factor for phytoplankton production, since the Si:DIN and Si:P ratios clearly demonstrated that there were no any potential stoichiometric Si limitations, and almost all silicate concentrations were > 2.0 µM during this study. Our results reveal that nutrient sources supplied by river discharge are a main cue for strong bottom–up effects on algal bloom succession during the early summer season in Sagami Bay.

Biostratigraphic and isotopic record of the Cenomanian–Turonian deposits in the Ohaba-Ponor section (SW Haţeg, Romania)

The middle Cenomanian–lower Turonian deposits of Ohaba-Ponor section (Southern Carpathians) were studied from biostratigraphic and isotopic points of view. Both the qualitative and semiquantitative nannofloral analyses, as well as the stable isotope (δ 13C and δ 18O) data support significant palaeoenvironmental changes in the investigated interval. Two δ 13C positive excursions were recognized: (1) an excursion up to 1.8‰ (PDB) within the middle/late Cenomanian boundary; (2) an excursion up to 2.2‰ (PDB) in the Cenomanian/Turonian boundary interval. The oldest δ 13C positive excursion recorded (placed within the Acanthoceras jukes-brownei/Eucalycoceras pentagonum Ammonite Zone boundary interval, and in the NC11 Calcareous Nannofossil Zone respectively) could be assigned to the middle Cenomanian Event II (MCEII). During the above-mentioned event, significant increase in abundance of Watznaueria barnesae, followed by successive blooms of Biscutum constans and Eprolithus floralis, were observed. The youngest δ 13C positive excursion was identified in the Cenomanian/Turonian boundary interval (in the NC12 and lower part of the NC13 Calcareous Nannofossil Zones). Even the amplitude of this δ 13C positive excursion is lower in the Ohaba-Ponor section, as generally reported, this may represent the regional record of the OAE2. The successive peaks of the nannofossils Biscutum constans, Zeugrhabdotus erectus and Eprolithus floralis indicate episodes of cooler surface water and high fertility, which preceded and lasted the Cenomanian/Turonian boundary event. Additionally, fluctuations of δ 18O values between −2 and −6‰ suggest also cooler conditions within the Cenomanian/Turonian boundary interval.