Phytoplankton Biomass Levels Research Articles

The summer distribution of coastal minke whales ( Balaenoptera acutorostrata) in the southern outer Moray Firth, NE Scotland, in relation to co-occurring mesoscale oceanographic features

Data on the distribution of northern minke whales ( Balaenoptera acutorostrata) in the coastal waters of the southern outer Moray Firth in northeast Scotland were collected from May to October, 2000 to 2004 inclusive. During this period, 127 encounters with B. acutorostrata were recorded during systematic boat-based surveys. The encounters were subsequently converted to number of animals sighted per unit of survey effort (SPUE) for comparison with mesoscale oceanographic features. Using Advanced Very High Resolution Radiometer (AVHRR) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imagery, monthly composite images of sea surface temperature (SST) and chlorophyll- a concentration (Chl-a) were obtained. In the SST imagery two oceanographic features appeared to dominate the Moray Firth region: a cold water current and a warm water plume. The results show that the SPUE of B. acutorostrata was significantly higher during warm plume events than when the cold current was dominant (Mann–Whitney U, P = 0.0167). Levels of phytoplankton biomass also appeared to be substantially greater during warm water plume events. In conclusion, it is hypothesised that those areas of highest minke SPUE are directly related to the presence of targeted prey attracted by high densities of phytoplankton. Although these whales were found to occur across the survey area, throughout the study period, their distribution is concluded to be highly dependent upon the presence of co-occurring mesoscale features. These, as well as other physiographic environmental determinants, are all thought to be important in forming this heterogeneous coastal ecosystem.

THE INFLUENCE OF LOCAL AND REGIONAL OCEANOGRAPHIC PROCESSES ON PHYTOPLANKTON DISTRIBUTION IN CONTINENTAL SHELF WATERS OFF NORTH-WESTERN IRELAND

The distribution of phytoplankton is related to local and regional oceanographic features off the north-western coast of Ireland. A thermohaline front known as the Irish Shelf Front (ISF) that separates coastal and oceanic water was observed in the study area. Phytoplankton biomass levels, as indicated by chlorophyll concentrations, were higher on the coastal side of the frontal boundary. Inshore of the front the phytoplankton species composition was dominated by diatoms such as Leptocylindrus danicus, Guinardia flaccida and Pseudo-nitzschia cf seriata. The flora of the shelf region between the ISF and the outer shelf was characterised by the presence of Halosphaera minor, Oscillatoria sp., Ptychodiscus noctiluca, Ceratium fusus and Amphidoma caudata. Further offshore along the margins of the continental shelf the floral assemblage was characterised by Gonyaulax polygramma, Ceratium furca, Oxytoxum scolopax, Podolampes palmipes, Prorocentrum compressum and Prorocentrum dentatum. The presence of Gonyaulax polygramma, an indicator species for North Atlantic Current (NAC) slope waters, indicates the presence of this current at the shelf edge. The highest Karenia mikimotoi cell concentrations were found in close proximity to bottom density fronts located inshore. The biological observations presented here further highlight the potential role of local processes such as the presence of strong, jet-like, density-driven coastal flows in transporting potentially harmful phytoplankton populations northwards along the western coast of Ireland.

THE INFLUENCE OF LOCAL AND REGIONAL OCEANOGRAPHIC PROCESSES ON PHYTOPLANKTON DISTRIBUTION IN CONTINENTAL SHELF WATERS OFF NORTH-WESTERN IRELAND

The distribution of phytoplankton is related to local and regional oceanographic features off the north-western coast of Ireland. A thermohaline front known as the Irish Shelf Front (ISF) that separates coastal and oceanic water was observed in the study area. Phytoplankton biomass levels, as indicated by chlorophyll concentrations, were higher on the coastal side of the frontal boundary. Inshore of the front the phytoplankton species composition was dominated by diatoms such as Leptocylindrus danicus , Guinardia flaccida and Pseudo -nitzschia cf seriata . The flora of the shelf region between the ISF and the outer shelf was characterised by the presence of Halosphaera minor , Oscillatoria sp., Ptychodiscus noctiluca , Ceratium fusus and Amphidoma caudata . Further offshore along the margins of the continental shelf the floral assemblage was characterised by Gonyaulax polygramma, Ceratium furca, Oxytoxum scolopax, Podolampes palmipes , Prorocentrum compressum and Prorocentrum dentatum. The presence of Gonyaulax polygramma, an indicator species for North Atlantic Current (NAC) slope waters, indicates the presence of this current at the shelf edge. The highest Karenia mikimotoi cell concentrations were found in close proximity to bottom density fronts located inshore. The biological observations presented here further highlight the potential role of local processes such as the presence of strong, jet-like, density-driven coastal flows in transporting potentially harmful phytoplankton populations northwards along the western coast of Ireland.

Phytoplankton biomass and environmental factors over a gradient of clear to turbid peri‐urban ponds

1. Small lakes and ponds with high nutrient loadings can be clear, turbid or intermediate, with low, high and intermediate phytoplankton biomass, respectively. 2. A combination of biotic and abiotic factors, such as hydraulic retention time, presence of submerged vegetation, depth, top-down phytoplankton control, and cascading effects of fish community structure, play an important role in phytoplankton biomass control when nutrients are not limiting. Different combinations of these factors lead to different levels of phytoplankton biomass. 3. Identification of the main factors controlling phytoplankton biomass in a particular pond or a small lake is essential for choosing an appropriate management strategy for the maintenance of a desired ecosystem state. 4. When a pond or a small lake ecosystem is impaired by eutrophication, a considerable degree of its ecological quality can be restored through the modification of some environmental factors when a sufficient reduction in nutrient input is not feasible. Copyright © 2006 John Wiley & Sons, Ltd.

05/01297 A generalized Fisher index approach to energy decomposition analysis

Seasonal surveys were carried out in the shallow, well-conserved temporarily open Nyara Estuary in the Eastern Cape, South Africa. Although temporarily open estuaries constitute over 70% of estuaries in South Africa, few data are available on the structure and functioning of these systems in the region. The main aim of the study was to test the hypothesis that owing to irregular nutrient input, temporarily open estuaries may exhibit poorly-developed pelagic food webs, with low phytoplankton and pelagic biomass in general. Results from the investigation indicate that phytoplankton biomass is generally low, and dominated by pico and nanophytoplankton, with almost total absence of diatoms. This may be explained in terms of the regenerated, rather than new, nutrient pool that is available to phytoplankton as a result of the semipermanently closed nature of the estuary. Chlorophyll a levels never exceeded 4·1 mg m−3. However, low levels of phytoplankton biomass were in contrast to relatively large stocks of zooplankton, which attained maximum levels of about 2 g (dry weight) m−3. Thus, there is an imbalance between the biomass of the primary producers and that of the consumers. In order to satisfy the zooplankton energy budget, either phytoplankton production rates are extremely high or a substantial proportion of their food demands must be met through utilization of alternative sources, such as detritus, protozoans and microphytobenthos. It is suggested that microphytobenthos in particular may play a major role in this regard because of the prevailing good conditions for its growth in this type of ecosystem. Microbenthic chlorophyll a concentrations in the Nyara Estuary are in the upper range of values measured in South African estuaries, with an average of ≅190 mg m−2. Further studies are needed to investigate the ability of the dominant species of zooplankton to ingest and assimilate benthic microalgae, particularly during the day when most species remain in close association with the substratum.

Mesoscale structure and its seasonal evolution in the northern California Current System

Abstract During spring and summer 2000, two mesoscale mapping cruises were carried out in the northern California Current System between 41 . 9 ∘ N and 44 . 6 ∘ N and between the shallow, inner continental shelf and up to 150 km offshore. Measurements were made using a towed undulating vehicle equipped with a conductivity-temperature-depth instrument and a chlorophyll fluorometer. A shipboard acoustic Doppler current profiler (ADCP) measured water velocities, and surface drifter trajectories and satellite sea-surface temperature imagery provide context for the mesoscale maps. Nearly identical upwelling favorable wind stresses of up to 0.2 N m - 2 existed during both the spring and summer surveys. Early in the season (late May, early June) the upwelling front and jet followed the continental shelf bottom topography. There was cold water inshore of the shelfbreak all along the coast with pockets of elevated phytoplankton biomass (chlorophyll (chl) up to 4 mg m - 3 ) near the coast. Mesoscale activity was minimal. During late-summer (August), the upwelling front and jet were much more convoluted, including significant meanders offshore associated with a major submarine bank (Heceta Bank, 44.0– 44 . 6 ∘ N ) and a large coastal promontory (Cape Blanco, 42 . 8 ∘ N ). High levels of phytoplankton biomass were found over Heceta Bank (chl ∼ 20 mg m - 3 ) and near the coast south of Cape Blanco (chl ∼ 10 mg m - 3 ). Low velocities inshore of Heceta Bank, measured by both shipboard ADCP and surface drifters, indicate the potential for retention of water over the Bank, leading to favorable conditions for phytoplankton biomass accumulation. The large offshore meander near Cape Blanco carried cold, nutrient-rich, high phytoplankton biomass (chl of 2– 5 mg m - 3 ) water over 100 km offshore. This flow–topography interaction feature was generated in mid-June and remained an important part of the regional circulation for about 2.5 months.

Long-term variability of vertical chlorophyll a and nitrate profiles in the open Black Sea: eutrophication and climate change

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 294:95-107 (2005) - doi:10.3354/meps294095 Long-term variability of vertical chlorophyll a and nitrate profiles in the open Black Sea: eutrophication and climate change Oleg A. Yunev1,*, Snejana Moncheva2, Jacob Carstensen3,4 1Institute of Biology of the Southern Seas, National Academy of the Sciences of Ukraine, Nakhimov Av. 2, Sevastopol 99011, Ukraine2Institute of Oceanology, Bulgarian Academy of Sciences, Varna 9000, Bulgaria3National Environmental Research Institute, Roskilde 4000, Denmark4Joint Research Centre, Ispra 21020, Italy *Email: yunev@sevcom.net ABSTRACT: The objective of this study was to investigate long-term trends in the subsurface summer phytoplankton community and their underlying mechanisms in relation to nutrient enrichment of the open Black Sea. We analysed parameters describing the summer chlorophyll a (chl a) and annual mean nitrate depth distribution in terms of their maximum concentration and its depth, the mean nitrate gradient for the layer between the 2 maxima, and Secchi depth. Investigating the entire period from 1964 to 1996 did not reveal any direct relationship between the nitrate and phytoplankton levels. The nitrate level in the open Black Sea increased until 1984/85, corresponding with general increases in anthropogenic riverine nutrient inputs to the sea. Thus, the average maximum nitrate concentration and the nitrate gradient for all depth profiles increased between 1969 and 1984 and then remained constant. Despite the early increase in nitrate characteristics, the maximum in the chl a profile remained unaltered from 1964 to 1984. After the mid-1980s, the magnitude of the chl a profile gradually increased to 1991 and peaked with an exceptionally high concentration in 1992. In this same period there were only moderate fluctuations in the nitrate profile characteristics. The change of the summer phytoplankton biomass levels since 1984/85 coincided with an intensification of the Rim Current and the associated transport of nitrate to the euphotic zone. Prior to 1984/85 strong stratification and a deep halocline resulted in nitrate accumulation only, whereas uplifting of the halocline, combined with intensified advective currents, increased the transport of nitrate to the euphotic zone during the summer. This resulted in an associated increase in phytoplankton production and biomass in the following period. While this study shows that the open Black Sea, like the coastal regions, has been impacted by eutrophication, the response is different from the coastal region due to the different physical characteristics of the open waters. KEY WORDS: Chlorophyll profile · Nitrate profile · Secchi depth · Open Black Sea · Long-term variability · Eutrophication Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 294. Online publication date: June 09, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

LEAF LITTER COMPOSITION AND COMMUNITY STRUCTURE: TRANSLATING REGIONAL SPECIES CHANGES INTO LOCAL DYNAMICS

The temperate deciduous forest of the northeastern United States is believed to be undergoing a shift from domination by mixed oak (Quercus sp.) to red maple (Acer rubrum); a shift termed “The Red Maple Paradox.” This shift in the composition of the forest has the potential to affect ecosystems within the forest that use leaf litter as an energy source. To assess the impact of the red maple paradox on detrital food webs, we conducted a mesocosm experiment investigating the influence of red maple litter on the food web of temporary woodland ponds. Amphibian biomass and survival were significantly lower in experimental ponds that contained only maple litter. The negative effects of maple litter were most pronounced in larval wood frogs (Rana sylvatica). We hypothesize that this effect resulted from a temporary shift from a grazing-based food web in oak mesocosms to a microbial-based food web in maple mesocosms, as oak mesocosms initially had higher levels of phytoplankton biomass and lower levels of bacteri...

Global biodiversity patterns of marine phytoplankton and zooplankton.

Although the oceans cover 70% of the Earth's surface, our knowledge of biodiversity patterns in marine phytoplankton and zooplankton is very limited compared to that of the biodiversity of plants and herbivores in the terrestrial world. Here, we present biodiversity data for marine plankton assemblages from different areas of the world ocean. Similar to terrestrial vegetation, marine phytoplankton diversity is a unimodal function of phytoplankton biomass, with maximum diversity at intermediate levels of phytoplankton biomass and minimum diversity during massive blooms. Contrary to expectation, we did not find a relation between phytoplankton diversity and zooplankton diversity. Zooplankton diversity is a unimodal function of zooplankton biomass. Most strikingly, these marine biodiversity patterns show a worldwide consistency, despite obvious differences in environmental conditions of the various oceanographic regions. These findings may serve as a new benchmark in the search for global biodiversity patterns of plants and herbivores.

Pelagic food web structure and carbon budget in the northern Baltic Sea: potential importance of terrigenous carbon

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 268:13-29 (2004) - doi:10.3354/meps268013 Pelagic food web structure and carbon budget in the northern Baltic Sea: potential importance of terrigenous carbon J. Sandberg1,*, A. Andersson2,3, S. Johansson4, J. Wikner3 1Department of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden 2Marine Ecology, Dept. of Ecology and Environmental Science, Umeå University, 90185 Umeå, Sweden 3Umeå Marine Sciences Centre, Umeå University, 91020 Hörnefors, Sweden 4Swedish Environmental Protection Agency, 10648 Stockholm, Sweden *Email: johannes@system.ecology.su.se ABSTRACT: The objective of this study was to quantitatively assess the relative importance of terrigenous dissolved organic material (TDOC) as a carbon source for secondary producers (e.g. bacteria) and as a structuring factor for the pelagic food web in the Gulf of Bothnia, northern Baltic Sea. The 3 study sites, situated in Bothnian Bay (BB), the Öre Estuary (ÖE) and the Bothnian Sea (BS), had markedly different freshwater loads and water-residence times. In Bothnian Bay, bacterial biomass and production were higher than expected from the levels of phytoplankton biomass and productivity there, suggesting an uncoupling of bacterial productivity from phytoplankton production. Phytoplankton size structure and size-fractionated production were, however, relatively similar among areas. A simplified carbon budget model suggested that bacterioplankton dominated organic carbon consumption in all of the food webs studied, but was most marked in BB. The model showed that the available autochthonous primary production could not alone support the heterotrophic carbon demand in BB. The most likely explanation of this discrepancy was that the total annual input of terrigenous dissolved organic carbon was bioavailable, resulting in a budget closer to balance with the heterotrophic carbon demand. BB, receiving 38% of the carbon input from land, was consequently a net heterotrophic ecosystem. A sensitivity analysis showed that the bacterial carbon demand, and growth efficiency in particular, had the greatest influence on the resulting budget. TDOC was the dominant carbon source in ÖE, but the losses of carbon through advection to offshore areas and sedimentation was high. The evidence of net heterotrophy in ÖE was therefore weaker than in BB. In BS the input of TDOC was less important, and the carbon used for secondary production originated mainly from autochthonous primary production. Our results suggest that the supply of TDOC is of great importance for the abundance of plankton and as a structuring factor for the aquatic food webs in the Gulf of Bothnia. KEY WORDS: Food web · Heterotrophy · Bacteria · Terrigenous · Carbon · Model · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 268. Online publication date: March 09, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Pilot trophic model for subantarctic water over the Southern Plateau, New Zealand: a low biomass, high transfer efficiency system

The Southern Plateau subantarctic region, southeast of New Zealand, is an important feeding area for birds, seals and fish, and a fishing ground for commercially significant species. The Southern Plateau is a major morphometric feature, covering approximately 433,620 km 2 with average depth of 615 m. The region is noted for its relatively low levels of phytoplankton biomass and primary production that is iron-limited. In order to evaluate the implications of these attributes for the functioning of this ecosystem a steady-state, 19-compartment model was constructed using Ecopath with Ecosim software of Christensen et al. [ www.ecopath.org]. The system is driven by primary production that is primarily governed by the supply of iron and light. The total system biomass of 6.28 g C m −2 is very low compared with systems so far modelled with a total system throughput of 1136 g C m −2 year −1. In the model, the Southern Plateau retains 69% of the biomass in the pelagic system and 99% of total production. Although fish are caught demersally, most of their food is part of production in the pelagic system. Top predators represent about 0.3% of total biomass and account for about 0.24 g C m −2 year −1 of food consumed made up of birds 0.058 g C m −2 year −1, seals 0.041 g C m −2 year −1, and toothed 0.094 g C m −2 year −1 and baleen whales 0.051 g C m −2 year −1. This amounts to 105,803 tonnes carbon over the whole of the Southern Plateau and is about 17% of the total amount of food eaten by non-mesopelagic fish. Mean transfer efficiencies between trophic levels II and IV of 23% are at the high end of the range reported in the literature. In the model, adult fish production is almost completely accounted for by the fisheries take (32%), consumption by seals (7%), toothed whales (21%), other adult fish (13%), and squid (20%). Fish and squid catches are at the trophic levels of 4.8 and 5.0, respectively. The gross efficiency of the fishery is 0.018% (catch/primary production). Although not all data come from direct knowledge of this system, the model reflects its general characteristics, namely a low primary production system dominated by the microbial loop, low sedimentation to the seafloor, high transfer efficiencies, a long food web and supporting high-level predators.

Top‐down control of phytoplankton biomass and community structure in the monsoonal Arabian Sea

During the 1995 monsoons, phytoplankton biomass was low over large areas of the Arabian Sea in spite of often high concentrations of inorganic nutrients, characteristics typical of high‐nutrient, lowchlorophyll (HNLC) areas. The objective of this study, a part of the Arabian Sea U.S. JGOFS program, was to elucidate controls of phytoplankton biomass and community structure in these areas, using primarily pigment‐based methods. Unlike other HNLC areas, phytoplankton biomass and growth rates in the monsoonal Arabian Sea were not likely limited by the availability of trace nutrients but rather controlled by grazers. Evidence for this conclusion is high concentrations of iron, the nutrient likely limiting phytoplankton biomass in other HNLC areas; phytoplankton growth rates clearly not limited by concentrations of inorganic nutrients; blooms during grow‐out experiments in the absence of mesozooplankton; rates of microzooplankton and mesozooplankton grazing that approached rates of primary production; and the absence of blooms in situ in spite of persistently high concentrations of inorganic nutrients. A more detailed look at shifts of phytoplankton community structure with increasing levels of phytoplankton biomass, in situ and during grow‐out experiments, shows that diatoms were the only group of organisms capable of blooming in the absence of mesozooplankton, i.e., their abundance in situ was likely controlled by mesozooplankton grazing. Changes in the abundance of different picoautotroph taxa with increasing levels of phytoplankton biomass suggest that their biomass was controlled within tight bounds by microzooplankton grazing, rather than by the availability of resources. Thus, these results are consistent with the hypothesis that phytoplankton abundance and community structure in the HNLC areas of the monsoonal Arabian Sea are controlled by top‐down forces, grazing, rather than bottom‐up forces, availability of resources.

Benthic algal response to pulsed versus distributed inputs of sediments and nutrients in a Mackenzie Delta lake

The Mackenzie Delta is a lake-rich region where the distribution and abundance of phytoplankton, macrophytes, and benthic algae among lakes may be controlled by an interaction between nutrient supply and sediment in the water column, and episodic reduction in light availability associated with river flooding. To simulate the effects of episodic river inflow on benthic algae, limnocorrals (depth = 3 m) were either not manipulated (control), or received high or low weekly additions of nutrients (N and P) and sediments, delivered as a pulse (1/wk: high-pulsed, low-pulsed) or distributed incrementally through each week (⅓ of high or low load × 3 d/wk: high-distributed, low-distributed) in a balanced triplicated design (15 limnocorrals). Artificial substrates, enriched to mimic the supply of nutrients at the sediment/water interface, were suspended in the limnocorrals at 2 m depth for 6 wk beginning in mid-July 1995. Maximum average levels of phytoplankton biomass (inferred from chlorophyll) occurred in the treatment where light attenuation was highest (high-distributed), and lowest levels occurred where light attenuation was lowest (control). By contrast, maximum average accrual of benthic algal biomass on the artificial substrates occurred in the control, whereas lowest accrual occurred in the high-distributed treatment. Chlorophyll content per unit biovolume of benthic algae increased modestly in treatments experiencing low light relative to treatments with higher light, but was insufficient to explain the 3-fold difference in inferred biomass between the control and high-distributed treatment in the case of benthic algae, or the 4-fold difference in the case of phytoplankton. Under equivalent in situ light conditions, areal net photosynthesis of benthic algae was highest in the control and lowest in the high-pulsed treatment. Net photosynthetic rate per unit benthic algal chlorophyll was not significantly different among the control and treatments. Last, biomass accrual rates among treatments showed a strong inverse relation with average light attenuation among the limnocorrals over the duration of the experiment. These results indicate that light availability was primarily responsible for maximum biomass accrual in the control and was the dominant factor affecting accrual rates among treatments. Overall, this study suggests that the abundance of benthic algae among Mackenzie Delta lakes may progressively increase as flood frequency decreases and light availability becomes greater, whereas phytoplankton abundance may peak in lakes with intermediate transparencies by responding to nutrient additions despite interruption of the light environment by suspended sediments.

Assessment of the Particulate Food Supply Available for Mussel (Mytilus spp.) Farming in a Semi-enclosed, Northern Inlet

Temporal variability in the quantity, organic content, and phytoplankton composition of the particulate food supply available to a cultured mussel population was assessed for a 3-year period in a small inlet of Notre Dame Bay, Newfoundland, Canada. The study site had a restricted flushing rate estimated at 1–2·75 timeswk−1for a complete water exchange. The quantity of both total (TPM) and organic (POM) seston varied temporally from 0·7–23·7mgl−1and 0·05–1·97mgl−1respectively during the 3-year sampling period. TPM typically remained relatively high (>10mgl−1) through the winter and spring period. Most of the seasonal variation in total seston was due to seasonal variability in the PIM component. Both PIM and POM concentrations were seasonally lowest during summer. The organic fraction of the seston (POM/TPM ratio) was seasonally low in winter and increased steadily through spring and summer to reach its maximum in the autumn. The living phytoplankton component of the seston was typically dominated, both numerically and in biomass, by a variety of diatom and autotrophic nanoflagellate species in the 2– 20-μm diameter size range. Discrete diatom population blooms occurred in the autumn of all three years and largely consisted of a single species, Skeletonema costatum. Phytoplankton:detritus ratios were significantly lower during winter. Total phytoplankton biomass levels were seasonally low during winter and summer and were associated with seasonal variation in diatom biomass. We conducted modelling simulations of relationships among seston organic food levels, their temporal variability, tidal flushing rates, cultured mussel biomass and production indices, and estimates of mussel maintenance ration requirements to predict the adequacy of northern inlets to sustain commercial-scale mussel farm development. We conclude from these simulations that small, semi-enclosed, northern inlets likely frequently experience periods when naturally occurring organic seston levels are insufficient to meet basic mussel stock maintenance ration requirements when such inlets are stocked to commercial-scale densities. We infer that periods of food-limited mussel growth and/or production are likely to occur at these high mussel population levels, particularly during summer. Qualitatively poor (low POM:TPM ratio; low phytoplankton:detritus ratio) food supply during winter may also be a further limiting factor. The implications of our conclusions in relation to aquaculture industry development and environmental management are discussed.

Relationships between Zoo- and Phytoplankton in a Warm-temperate, Semi-permanently Closed Estuary, South Africa

Seasonal surveys were carried out in the shallow, well-conserved temporarily open Nyara Estuary in the Eastern Cape, South Africa. Although temporarily open estuaries constitute over 70% of estuaries in South Africa, few data are available on the structure and functioning of these systems in the region. The main aim of the study was to test the hypothesis that owing to irregular nutrient input, temporarily open estuaries may exhibit poorly-developed pelagic food webs, with low phytoplankton and pelagic biomass in general. Results from the investigation indicate that phytoplankton biomass is generally low, and dominated by pico and nanophytoplankton, with almost total absence of diatoms. This may be explained in terms of the regenerated, rather than new, nutrient pool that is available to phytoplankton as a result of the semipermanently closed nature of the estuary. Chlorophyll a levels never exceeded 4·1mgm−3. However, low levels of phytoplankton biomass were in contrast to relatively large stocks of zooplankton, which attained maximum levels of about 2g (dry weight) m−3. Thus, there is an imbalance between the biomass of the primary producers and that of the consumers. In order to satisfy the zooplankton energy budget, either phytoplankton production rates are extremely high or a substantial proportion of their food demands must be met through utilization of alternative sources, such as detritus, protozoans and microphytobenthos. It is suggested that microphytobenthos in particular may play a major role in this regard because of the prevailing good conditions for its growth in this type of ecosystem. Microbenthic chlorophyll a concentrations in the Nyara Estuary are in the upper range of values measured in South African estuaries, with an average of ≅190mgm−2. Further studies are needed to investigate the ability of the dominant species of zooplankton to ingest and assimilate benthic microalgae, particularly during the day when most species remain in close association with the substratum.

Microcystis bloom formation in the lower Nakdong River, South Korea: importance of hydrodynamics and nutrient loading

A cyanobacterial bloom in the lower part of the Nakdong River was investigated during the dry summer of 1994. High levels of phytoplankton biomass, mainly Microcystis aeruginosa, in the surface waters (chl. α 193 ± 436 µg L-1, mean ± s.d.; >105 cells mL-1 , n = 15) were maintained for three months from mid July to mid October. After the last major rainfall in mid June, water temperature increased sharply within three weeks (18 June, 24°C; 9 July, 33°C). The highest cell density (5 × 106 cells mL-1) and highest concentration of chl. α (>500 µg L-1) in the surface water were recorded in the early phase of the bloom (21–26 July) as the drought persisted. Concentrations of dissolved inorganic nitrogen (DIN) and total phosphorus (TP) during the bloom were high (DIN 2.5 ± 0.9 mg L-1 ; TP 155 ± 98 mg L-1 ; n = 23). pH was low (~7) until the initial stage but was high (pH >9) as the bloom formed. Elevated water temperature (>30°C) along with low discharge and high irradiance were major factors contributing to the Microcystis spp. bloom in this river–reservoir system.

Effects of N:P:Si ratios and zooplankton grazing on phytoplankton communities in the northern Adriatic Sea. I. Nutrients, phytoplankton biomass, and polysaccharide production

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 18:37-54 (1999) - doi:10.3354/ame018037 Effects of N:P:Si ratios and zooplankton grazing on phytoplankton communities in the northern Adriatic Sea. I. Nutrients, phytoplankton biomass, and polysaccharide production Edna Granéli1,*, Per Carlsson1, Jefferson T. Turner2, Patricia A. Tester3, Christian Béchemin4, Rodger Dawson5, Enzo Funari6 1University of Kalmar, Department of Marine Sciences, POB 905, S-391 29 Kalmar, Sweden 2Biology Department, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, USA 3National Marine Fisheries Service, NOAA, Southeast Fisheries Science Center, Beaufort Laboratory, Beaufort, North Carolina 28516, USA 4CREMA-L'Houmeau (CNRS-IFREMER), BP5, F-17137 L'Houmeau, France 5Chesapeake Biological Laboratory, University of Maryland, Solomons, Maryland 20688, USA 6Laboratorio di Igiene Ambientale, Istituto di Sanita, Viale R. Elena 299, I-00161 Rome, Italy *E-mail: edna.graneli@ng.hik.se ABSTRACT: The northern Adriatic Sea has been historically subjected to phosphorus and nitrogen loading. Recent signs of increasing eutrophication include oxygen deficiency in the bottom waters and large-scale formation of gelatinous macroaggregates. The reason for the formation of these macroaggregates is unclear, but excess production of phytoplankton polysaccharides is suspected. In order to study the effect of different nutrient (nitrogen:phosphorus:silicon) ratios on phytoplankton production, biomass, polysaccharides, and species succession, 4 land-based enclosure experiments were performed with northern Adriatic seawater. During 2 of these experiments the importance of zooplankton grazing as a phytoplankton loss factor was also investigated. Primary productivity in the northern Adriatic Sea is thought to be phosphorus limited, and our experiments confirmed that even low daily phosphorus additions increased phytoplankton biomass. However, this only occurred when nitrogen additions were high. Alternatively, when nitrogen was added in low concentrations, with simultaneous high phosphorus additions, phytoplankton biomass declined. Nitrogen deficiency induced the highest production of polysaccharides per unit of cell carbon, while nutrient-sufficient and phosphorus-deficient treatments caused a higher production of polysaccharides in total. In order to decrease the frequency of algal blooms and high polysaccharide production in the northern Adriatic, it appears necessary to reduce the amounts of incoming nutrients. Since phosphorus has a high turnover rate in low P:high N waters of the northern Adriatic, and since our experiments show that a shortage of nitrogen can produce reduced levels of phytoplankton biomass and total polysaccharides, a reduction of the nitrogen discharge would probably be the best countermeasure for eutrophication in the northern Adriatic Sea. KEY WORDS: Adriatic Sea · Nitrogen · Silicon · Limitation · Phytoplankton · Phosphorus · Polysaccharide · Chemical composition Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 18, No. 1. Publication date: July 16, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Dimethylsulfide (DMS) production by size-fractionated particles in the Labrador Sea

We measured the production of dimethylsulfide (DMS) by size-fractionated particles during a cruise in the Labrador Sea in May-June 1997. The experiments were conducted at 2 stations characterised by low levels of nitrate and high levels of phytoplankton biomass and particulate dirnethylsulfo~~~opropionate (DMSP,). Samples were size fractionated to assess the size distribution of DMSPp and the potential DMS production associated with the different size fractions. The potential for DMS production was estimated by incubating the filters in pre-filtered and boiled seawater amended with 500 nM of dissolved DMSP (DMSPd). At both stations, the highest DMSPp concentrations were measured in the 2 to 11 and >20 1-lm size fractions. Elevated potential net DMS production rates were also associated with these 2 size fractions, whch were responsible for 40 to 53% and 23 to 31 % of the cumulative production, respectively. Only 4 /, of the potential net DMS production was measured in the 0.7 to 2 I.lm fraction, which presumably contained many of the freeliving bacteria. The potential net DMS production rates of the different size fractions were linearly related (Spearman correlation coefficient = 0.86) to the concentratlons of DMSPp in the fractions. These results suggest that DMSP-cleaving activity was spatially associated with DMSP-producing algae or DMSP-rich detritus (e.g. faecal pellets, marine snow).

Response of phytoplankton community structure and taxon-specific growth rates to seasonally varying physical forcing in the Sargasso Sea off Bermuda

The response of phytoplankton community structure and dynamics to varying physical forcing was studied at a station southeast of Bermuda over a period of 18 months. The dominant groups of algae, as delineated by taxonspecific carotenoids, were prymnesiophytes, pelagophytes, and cyanobacteria. Other groups such as diatoms, dinoflagellates, prasinophytes, chlorophytes, and cryptophytes were never abundant. Although phytoplankton biomass varied over the year with maxima in the winter, likely in response to elevated nutrient concentrations, the composition of the eucaryotic phytoplankton community and the relative biomass of cyanobacteria in the surface layer did not change. The distribution of phytoplankton biomass and primary production over five size classes was virtually constant over the year as well: picoplankton (<3 Frn) contributed 79% to total Chl a and primary production. Taxon-specific phytoplankton growth rates were measured using the pigment-labeling method. Growth rates of prymnesiophytes and pelagophytes did not vary systematically over the year; rates in the surface layer ranged from 0.2 to 0.6 d-l, declining to values <O.l d-l at the 1.6% light level. Growth rates of cyanobacteria in the surface layer were highest during the winter (0.6 d-l) and lowest during the summer (0.3-0.4 d-l). These results are surprising since it was expected that the increased physical forcing during the winter period would affect growth rates of all phytoplankton, not only cyanobacteria, and shift the composition of the phytoplankton community from picoplankton toward larger phytoplankton, possibly diatoms. These results suggest that the structure of the phytoplankton community, particularly the eucaryotic component, is extremely resilient to change. Similar conclusions have been drawn from studies of the distribution and abundance of phytoplankton and zooplankton in the North Pacific Central Gyres. The properties that convey these characteristics to the communities are likely the physiological attributes of the organisms and the parameters governing their interactions with grazers. Open-ocean phytoplankton communities respond dramatically to seasonally varying physical forcing in most temperate and polar environments. Phytoplankton biomass and productivity can change by orders of magnitude over the seasons, and the composition of the community often changes from a large-celled, diatom-dominated community during the spring to a small-celled, flagellate-dominated community during the summer (Raymont 1983). In contrast, dramatic seasonal changes are thought to be absent in the central subtropical gyres (Blackburn 1981). An exception is the Sargasso Sea, whose northern part is subject to severe physical forcing during the winter when the upper water column is mixed to a depth of up to 400 m and the euphotic zone is enriched with nutrients (Riley 1957; Hulburt 1990). As a consequence, diatom-dominated spring blooms, characterized by high levels of phytoplankton biomass and productivity, are regularly observed (Riley 1957). The southern Sargasso Sea, in contrast, does not experience wintertime mixing and nutrient enrichments and is highly oligotrophic throughout the year (Ryther and Menzel 1960, 1961), similar

Functional complementarity in plankton communities along a gradient of acid stress

This study considered changes in the plankton communities of 50 Adirondack Mountain lakes, along an acidity gradient from pH 7.3 to 4.2. The objective was to test the hypothesis that changes in the biomass of certain species are compensated by opposite changes in the biomass of other species having similar ecosystem functions. This hypothesis was proposed by Frost et al. (1995); Linking Species and Ecosystems. Chapman and Hall, NY, pp. 224–239.) and referred to as `complementarity'. Results from the multi-lake survey, as well as data from two experimental studies, provide support for the hypothesis. With increasing acidity, there were declines in the number of plankton species, and pronounced changes in taxonomic composition. There were also reductions in food web complexity, measured as number of trophic links per species. The most acidic lakes displayed extreme dominance of a few taxa per trophic level, and characteristic acid-tolerant species such as Diaptomus leptopus (a calanoid copepod), Keratella taurocephala (a rotifer), and Chlamydomonas sp. (a chlorophyte alga). In contrast, the total biomass of producers and herbivores was unrelated to lakewater acidity. Acid lakes contained levels of phytoplankton biomass (chlorophyll a) consistent with measured levels of nutrients, and zooplankton biomass was consistent with its resource base (the phytoplankton). Experimental results indicated that complementary changes can occur rapidly at lower trophic levels when replacement species are already present in the community.