Chlorophyll standing crop and phytoplankton production in the western Irish Sea during 1992 and 1993

Chlorophyll standing crop and phytoplankton production werestudied in the western Irish Sea over a 21 month period during1992 and 1993. For both years, the start of the production seasonwas first observed in Dundalk Bay and occurred progressivelylater in more northerly coastal and offshore waters. Standingcrop and production exhibited marked spatial heterogeneity with12.5- to 19-fold differences in crop observed over distancesof 20–30 km. Distinct regional differences in the lengthof the production season were apparent. The longest season,6–7 months with a production of 194 g C m^–2, occurredin Dundalk Bay. The season lasted 3–4 months in the summerstratified region with a production of 140 g C m^–2. Northerly,offshore mixed waters and coastal waters of Northern Irelandsupported a short (2–3 months) season and production of194 and 140 g C m^–2, respectively. The similarity in seasonalproduction between Dundalk Bay and coastal waters of NorthernIreland, and between the summer stratified and northern mixedregions, is attributed to the intensity of production duringthe summer. Between 59 and 79% of seasonal production in thenorthern mixed region and coastal waters of Northern Irelandtook place during June and July, compared to 29–40% inDundalk Bay and the summer stratified region. Lower summer productionin the latter two may be due to nutrient limitation and thishas implications for the sensitivity of these two regions toanthropogenic nutrient enrichment.     

A modelling investigation of the distribution of stratification and phytoplankton abundance in the Irish Sea

Thermal stratification and phytoplankton abundance are modelledon a 5 km grid covering the Irish Sea. The water column is approximatedby three layers. The top layer is uniformly mixed by wind stirringand the bottom by tidal energy, while linear gradients can occurin the middle layer. The model is forced with hourly meteorologicaldata and mean tidal energies. Primary production is representedby a model with a single nutrient and a single phytoplanktonpopulation. The results from the model show good agreement withdata collected on a Ministry of Agriculture, Fisheries and Food(MAFF) cruise in May 1992 and with historical data. When advectionis included, driven by depth-averaged currents, the surfacetemperature patterns are improved but bottom temperatures indeep water are raised and high concentrations of chlorophyllare carried offshore from coastal regions. This indicates alimitation of using depth-averaged currents and a need to accountfor differences in phytoplankton species composition in coastaland offshore waters. Calculations demonstrate the importanceof salinity variations to stratification and phytoplankton growth.Smoothing the wind mixing energy has the effect of delayingthe onset of the spring bloom in areas where wind mixing issignificant. Removing the diurnal cycle of solar heating alsodelays the spring bloom. The chlorophyll gradient in the middlelayer has a large impact on the response of the model to short-termvariability in the meteorological forcings.     

Copepod and barnacle nauplius distributions in the Irish Sea: relation to springtime hydrographic variability

The distributions and abundances of copepod and barnacle naupliiare described along a five-station transect in the Irish Seafrom Liverpool Bay, England, to Dundalk Bay, Ireland, in May1989. Correspondence analysis revealed that various hydrographicregions in the Irish Sea are characterized by distinct naupliusassemblages. Acartia, Centropages and Temora nauplii were associatedwith the Welsh coastal water east of the Liverpool Bay front.The western stratified water to the west of the seasonal, westernIrish Sea front was distinguished from the mixed water to theeast by abundances of Calanus, Pseudocalanus, Oithona, Microcalanusand harpacticoid nauplii. The Liverpool Bay and western IrishSea fronts are, apparently, boundaries between coastal and offshoreassemblages of crustacean nauplii.     

Multivariate analysis of surface water characteristics in the summer regime of the western Irish Sea

A part of the western Irish Sea is strongly stratified during the summer months, with the boundary of stratification marked by a front with horizontal temperature gradients. Continuous on-line analysis has been used to record the surface water variability of nine characteristics along a cruise path in this area.Multivariate analysis (principal component) indicates the presence of four distinct water types separated by thermal gradients. Two of these water types show land mass influence and two illustrated the effects of the mixed and stratified regimes. The stratified surface waters had a marked degree of homogeneity with respect to the measured characteristics, while the mixed surface waters exhibited greater variability. Marked micro-variations in chlorophyll a concentrations were observed in the latter water type.No consistent relationships were observed among the physical, chemical, and biological variables across the front because of the gradual change in the gross properties of the mixed surface water during its northward passage through the Irish Sea.     

Radiolaria: Sinking population,standing stock,and production rate

A method is presented for estimating sinking population, rate of production, and residence time in the living zone for Radiolaria. This method employs vertical flux measurements from PARFLUX sediment traps and laboratory sinking speed measurements of the radiolarian skeletons.The estimated population sinking through the oceanic water column is approximately equal to the standing stock at several hundred meters depth reported from direct measurements by other workers. The rate of production of total Radiolaria was estimated to be approximately 80 shells m^?3 day^?1 in the western equatorial Atlantic (E) and central Pacific (P₁) stations and 230 shells m^?3 day^?1 in the Panama Basin (PB). The production of Nassellaria is greater than that of the other suborders. The average residence time for Radiolaria in the living zone (0–200 m) was estimated to be between 16 and 42 days.     

Physiological responses of phytoplankton communities in the Irish Sea to simulated upwelling

Understanding the dynamics of upwelling systems, especially the interactions between nutrients and light, has benefited from the application of models of varying complexity. Validation of such models using unialgal cultures or field observations has often proven difficult, but short-term incubations of contained natural assemblages and use of instantaneous physiological indicators offer an alternative approach. In May and June 1996, phytoplankton communities deep in the euphotic zone were sampled from nearly identical physical environments. Replicate samples (20 l volume) were incubated on deck at 50% surface irradiance with either no nutrient additions (Controls) or additions of 20 μM nitrate (Enrichments). Over 24 h, variable fluorescence (F _v:F _m), nitrate reductase activity (NR), nutrients, chlorophyll a and particulate C and N were monitored. Initial chlorophyll a (～3 μg l^?1), phosphate (～0.2 μM), nitrate (～1.5 μM) and silicate (～3 μM) were similar in both months. Changes in NR and F _v:F _m indicated clear physiological responses to changes in irradiance and added nitrate that differed between months. In May, Controls and Enrichments responded in the same way. F _v:F _m stayed constant (0.5), chlorophyll a increased slightly, and NR activity increased markedly in all samples. In contrast, in June, treatments responded quite differently. F _v:F _m was near the theoretical maximum (0.7–0.8) initially and remained constant in Enrichments, but fell sharply in Controls. Declines in controls were also seen for chlorophyll a, and NR activity. Thus, the addition of 20 μM nitrate had a significant effect even though ambient levels of nitrate (>1 μM) should not have been limiting. Small (<20 μm) flagellates predominated in the May samples, but in June large and chain-forming centric diatoms constituted a significant proportion of the phytoplankton community. We conclude that the response of a phytoplankton community to environmental changes can depend on factors that are poorly represented by bulk measurements of chlorophyll, nutrients and particulate elements.     

Regional differences in stratification and its effect on phytoplankton production and biomass in the northwestern Irish Sea

Differences in tidal mixing result in the formation of offshoremixed and stratified regions in the NW Irish Sea during springand summer. Stratification resulted from vertical gradientsin temperature, although vertical gradients in salinity wereimportant during the early stages of stratification. The northerncoastal and offshore mixed regions were characterized and distinguishedfrom the southern coastal and summer stratified regions by thepresence of more saline, cool near-surface water and incompletedepletion of dissolved inorganic nutrients. Distinct regionaldifferences in the production season of phytoplankton were observed.This lasted 6 months with a seasonal production of 155 g C m^–2in the southern coastal region. A shorter season, 4 and 2 months,and lower production of 101 and 96 g C m^–2 occurred inthe summer stratified and northern mixed regions, respectively.The southern mixed region supported the shortest season (<2months) and lowest production (66 g C m^–2). It is estimatedthat a daily light exposure of {small tilde}200 Wh m^–2is required for the onset of the production season and it isconduded that the subsurface light climate as a function ofsolar radiation and surface mixed layer depth, rather than nutrientavailability, controls its duration. The existence of a shortlate production season in the offshore regions is confirmedand this contrast with the season in the North Sea is attributedto differences in the subsurface light climate. Sustained productionin the southern coastal region may play an important role infish recruitment and offset any effect of the short late offshoreproduction season.     

Distribution, standing stock, growth, mortality and production of Strongylocentrotus pallidus (Echinodermata: Echinoidea) in the northern Barents Sea

The regular sea urchin, Strongylocentrotus pallidus (G.O. Sars, 1871), is a widespread epibenthic species in high-Arctic waters. However, little is known about its distribution, standing stock, population dynamics and production. In the northern Barents Sea, S. pallidus was recorded on seabed still photographs at 10 out of 11 stations in water depths of 80–360?m. Mean abundances along photographic transects of 150–300 m length ranged between <0.1 and 14.7?ind. m^?2 yielding a grand average of 3.6?ind.?m^?2. The small-scale distribution along the transects was patchy, with densities varying from nil to an overall maximum of 25.5 ind. m^?2, and exhibited a significant relation to the number of stones present. Sea urchin test diameters, measured on scaled photographs, extended from 7 to 90?mm. Median values at single stations varied from 14 to 46?mm, showing a significant inverse relationship to water depth. Biomass, estimated by combining photographic abundances, size frequencies and a size-mass function established with trawled specimens, ranged between <0.1 and 3.0?g ash-free dry mass m^?2, averaging about 1.0?g ash free dry mass m^?2. An analysis of skeletal growth bands in genital plates was carried out with 143 trawled individuals ranging in test diameter (D) from 4 to 48?mm. Assuming these bands to represent annual growth marks, the ages of the specimens analysed ranged between 3 and 42 years. A von Bertalanffy function was fitted to size-at-age data to model individual growth pattern (D_∞?=?102.3?mm, k?=?0.011 year^?1, t₀?=?0.633?year). The annual mortality rate Z of the population in the northern Barents Sea was estimated from a size-converted catch curve to be 0.08 year^?1. Applying the weight-specific growth rate method, the average P/B ratio and the mean annual production of this population were estimated as 0.07 year^?1 and 0.076?g AFDM m^?2 year^?1, respectively. In conclusion, S. pallidus is characterized by slow growth, low mortality, high longevity and low productivity. Because of its relatively high biomass, it is considered to contribute significantly to total benthic standing stock and carbon flux in the study area.     

The composition and abundance of phytoplankton in Lake Bukoni,western Uganda

Lake Bukoni is one of the crater lakes in western Uganda. Investigations into this lake is limited compared to other African lakes. Data on phytoplankton ecology in the lake are lacking. Phytoplankton consists of a community of photosynthetic, microscopic plants adapted to suspension in water. They constitute ‘hidden flora’ which make an important contribution to the primary productivity of a water mass. Some phytoplankton taxa, among them species belonging to Cyanophyta, are known to influence ecological transformations and to cause health hazards in water bodies that are used by humans. From July 2004 to December 2005, phytoplankton was collected from two sites (inshore and offshore) in Lake Bukoni. An inverted microscope, Sedgwick counting chamber and multiple tally denominator were used to quantify the phytoplankton. Phytoplankton was dominated by nonheterocystous cyanoprokaryotes especially Lyllgbya limnetica followed by the diatoms Synedra ulna and Fragillaria mutabilis. The inshore site had more phytoplankton species. Differences in phytoplankton diversity and density were mainly attributed to mixing and presence of macrophytes. The occurrence of large numbers of cyanoprokaryotes poses a potential health hazard to the local people who utilize the water from Lake Bukoni. The dominance of cyanoprokaryotes might result in ecological transformations like loss of biodiversity.     

Response of Sargasso Sea phytoplankton biomass, growth rates and primary production to seasonally varying physical forcing

The response of phytoplankton biomass, growth rates and primaryproduction to seasonally varying physical forcing was studiedat a station southeast of Bermuda over an 18 month period. Phytoplanktongrowth rates and primary production were measured using thepigment-labeling method, and phytoplankton biomass was calculatedfrom these measurements. Phytoplankton carbon biomass variedsystematically over the year. Highest values were observed duringthe winter and spring. Seasonal variations of chlorophyll (Chi)a in the surface layer could primarily be attributed to variationsin phytoplankton biomass and secondarily to photoacclimation.During the summer period, average values of carbon (C)/Chl ratios(g C g^–1 Chi) ranged from 160 at the surface to 33 atthe 1.6% light level, changes attributed to photoacclimationof the phytoplankton, consistent with the observation that phytoplanktonbiomass did not vary as a function of depth. Phytoplankton growthrates in the surface layer did not vary systematically overthe year, ranging from 0.15 to 0.45 day^–1, in spite ofseasonally varying concentrations of nitrate. Growth rates variedas a function of depth from average values of 0.3 day^–1in the surface layer to <0.1 day¹ at the 1.6% light level.Thus, the primary response of the phytoplankton community tonutrient enrichment during the winter period was an increasein phytoplankton biomass rather than an increase in growth rates.A simple nutrient-phyto-plankton-zooplankton model was usedto explore this phenomenon. The model demonstrated that theobserved response of the phytoplankton to nutrient enrichmentis only possible when phytoplankton growth is not severely limitedby nutrients.     

2006年冬季南海北部浮游植物生物量和初级生产力及其环境调控

通过2006年2月在南海北部现场调查所获得的数据分析研究了海域的浮游植物现存量和生产力,结果表明冬季浮游植物的分布特征与东北季风引起的环流场的变化关系密切。调查海域水柱平均Chla浓度的变化范围为0.03～1.21mg&#183;m-3（平均（0.33&#177;0.33）mg&#183;m^-3）,高值区出现在广东沿岸及海南岛东部附近海域;初级生产力的分布范围为41.3～1040.0mgC&#183;m^-2d^-1。由于东北季风引起近岸水体混合剧烈,不利于浮游植物生长,因此虽然沿岸带Chla浓度（（0.53&#177;0.50）mg&#183;m^-3）较高,但初级生产力却是最低的,只有41.3mgC&#183;m^-2d^-1,同时冬季反气旋涡强度下降和底层富营养水的涌升,营养盐充足,因此开阔海的Chla浓度（（0.31&#177;0.30）mg&#183;m^-3）和初级生产力（（631.3&#177;578.0）mgC&#183;m^-&#183;2d^-1）均高。浮游植物粒度级份测定表明,Pico级份对冬季南海北部浮游植物现存量和生产力的贡献很大,特别是在开阔海区,分别占47%和66%。     

The diversity,abundance and fate of ice algae and phytoplankton in the Bering Sea

Despite being an essential part of the marine food web during periods of ice cover, sea ice algae have not been studied in any detail in the Bering Sea. In this study, we investigated the diversity, abundance and ultimate fate of ice algae in the Bering Sea using sea ice, water and sub-ice sediment trap samples collected during two spring periods in 2008 and 2009: ice growth (March–mid-April) and ice melt (mid-April–May). The total ice algal species inventory included 68 species, dominated by typical Arctic ice algal diatom taxa. Only three species were determined from the water samples; we interpret the strong overlap in species as seeding of algal cells from the sea ice. Algal abundances in the ice exceeded 10⁷ cells l^?1 in the bottom 2-cm layer and were on average three orders of magnitude higher than in the water column. The vertical flux of algal cells beneath the ice during the period of ice melt (>10⁸ cells m^?2 day^?1) exceeded export during the ice growth period by one order of magnitude; the vertical flux during both periods can only be sustained by the release of algae from the ice. Differences in the relative species proportions of algae among sample types indicated that the fate of the released ice algae was species specific, with some taxa contributing to seeding in the water column, while other taxa were preferentially exported.     

Macromolecular production of phytoplankton in the northern Bering Sea, 2007

Photosynthetic carbon allocations into different macromolecular classes provide important clues regarding physiological conditions of phytoplankton and the nutritional status of potential grazers. The productivity experiments for photosynthetic carbon allocations were conducted at three light depths (100, 30, and 1 %) for nine different stations in the northern Bering Sea as an important gateway into the western Arctic Ocean, using the ¹³C isotope tracer technique to determine the major controlling factors and physiological conditions of phytoplankton. The photosynthetic carbon allocations into different macromolecular classes [Low molecular weight metabolites (LMWM), lipids, proteins, and polysaccharides] of primary producers were determined based on the productivity experiments. LMWM and polysaccharides had similar vertical patterns whereas lipids and proteins had reverse vertical patterns at all the stations, which is consistent with other results under different light depths. The overall average allocations were 37.9 (SD = ± 18.8 %), 26.6 (SD = ± 17.4 %), 26.5 (SD = ± 20.7 %), and 9.1 % (SD = ± 7.8 %), for LMWM, lipids, proteins, and polysaccharides, respectively. Based on a general pattern of macromolecular production in the northern Bering Sea, phytoplankton was in a physiologically transitional phase from an unlimited status to a nitrogen-deficient condition during our cruise period, 2007. However, more in situ field measurements for macromolecular production under a variety of environmental conditions will improve the understanding of the physiological responses of phytoplankton to the ongoing environmental changes in the Arctic Ocean.     

Pyrosoma atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux

Pyrosomas are the large group of pelagic tunicates whose trophicrole in pelagic communities has not yet been sufficiently studied.We ran across a local area of high concentration of the mostwidespread and commonest species of pyrosomas, Pyrosoma atlanticum,450 miles off the Congo river mouth. The following was estimated:gut pigment content, defecation rate, organic carbon and pigmentcontent of fecal pellets, and sinking rate. Based on these dataand the measured number of pyrosomas colonies the grazing impacton phytoplankton and the fecal pellet flux were calculated.During the night swarms of 50–65 mm P.atlanticum removed53% of phytoplankton standing stock in the 0–10 m layer;sparsely distributed pyrosomas consumed only 4%. The grazingimpact in the 0–50 m layer was only 12.5 and <1% respectively.The fecal pellet flux resulting from nocturnal feeding of P.atlanticumwhile swarming made up 1.4–1.6 x 10⁶ pellets m^–210 h^–1 or 305–1035 mg C m^–2 10 h^–1 and1.4 x 10⁵ pellets m^–2 10 h^–1 or 87.4 mg C m^–210 h^–1 while non-swarming. Incubation experiments showedthe rapid degradation of fecal pellets at 23°C: the lossof pigment and carbon content was {small tilde}60–70%after 45 h. We believe that given the sinking rate of 70 m day^–1the main part of fecal material does not leave the upper watercolumn and is retained in the trophic web of the epipelagiclayer.     

A decline in primary production in the North Sea over 25 years,associated with reductions in zooplankton abundance and fish stock recruitment

Phytoplankton primary production is at the base of the marine food web; changes in primary production have direct or indirect effects on higher trophic levels, from zooplankton organisms to marine mammals and seabirds. Here, we present a new time‐series on gross primary production in the North Sea, from 1988 to 2013, estimated using in situ measurements of chlorophyll and underwater light. This shows that recent decades have seen a significant decline in primary production in the North Sea. Moreover, primary production differs in magnitude between six hydrodynamic regions within the North Sea. Sea surface warming and reduced riverine nutrient inputs are found to be likely contributors to the declining levels of primary production. In turn, significant correlations are found between observed changes in primary production and the dynamics of higher trophic levels including (small) copepods and a standardized index of fish recruitment, averaged over seven stocks of high commercial significance in the North Sea. Given positive (bottom‐up) associations between primary production, zooplankton abundance and fish stock recruitment, this study provides strong evidence that if the decline in primary production continues, knock‐on effects upon the productivity of fisheries are to be expected unless these fisheries are managed effectively and cautiously.     

Copepod feeding behaviour and egg production during a dinoflagellate bloom in the North Sea

Feeding strategies of copepods were studied during a dinoflagellate-dominated bloom in the North Sea in August 2001. The aim of this study was to evaluate the importance of mesozooplankton grazing as a biological loss factor of harmful algal blooms under natural conditions. Therefore, ingestion, egestion and egg production experiments were performed with the most abundant copepod species Calanus helgolandicus, Temora longicornis and Acartia sp. feeding on the natural phytoplankton community. Dinophysis norvegica and Ceratium furca were the most abundant dinoflagellate species at the time of the experiments. Grazing experiments as well as examination of fecal pellet content revealed C. helgolandicus fed efficiently on D. norvegica. Ingestion rates up to 47 cells female⁻¹ h⁻¹ were measured and a large proportion of the C. helgolandicus fecal pellets contained intact D. norvegica cells. Dinophysis cells were rarely seen in fecal pellets produced by T. longicornis, and never observed in pellets produced by Acartia sp. The ingestion rate of C. furca, which was the dominating Ceratium species, mimicked that of D. norvegica. C. helgolandicus grazed significantly on C. furca (16 cells female⁻¹ h⁻¹), while the ingestion rate of T. longicornis was low and Acartia sp. was not able to graze on C. furca. Egg production experiments revealed that 92% of the C. helgolandicus females produced eggs. The specific egg production rate and the proportion of females producing eggs among T. longicornis were low. This field experiment clearly shows that some copepod species feed efficiently on D. norvegica and C. furca under natural conditions, which may affect the bloom development of these dinoflagellates.     

Biomass, carbonate standing stock and production of the mediterranean coralCladocora caespitosa (L.)

Summary The Mediterranean coralCladocora caespitosa often occurs in large beds, i.e. populations of hemispherical clonies with stock densities varying between 1.9 and 4 coloneis ·m⁻². Laboratory measurements of volume, skeleton weight, surface and number of corallites per colony, coupled with mean annual growth rates evaluated through sclerochronology, allowed for the estimation of biomass, skeleton bulk density, calcimass (carbonate standing stock) and secondary production (both organic and inorganic) of twoC. caespitosa beds at 4 and 9 m depth. The mean colony biomass varied between 0.73 and 0.99 kg dw ·m⁻², corresponding to a calcimass between 2 and 5 kg CaCO₃·m⁻². Organic secondary production was 215.5–305.4 g dw of polyps ·m⁻²·y⁻¹, while the potential (mineral) production was 1.1–1.7 kg CaCO₃·m⁻²·y⁻¹, for the year 1996–1997. These values show thatC. caespitosa is one of the major carbonate producers within the Mediterranean and one of the major epibenthic species originating stable carbonate frameworks both in recent and past times.     

Carbonate standing stock and carbonate production of the bryozoanPentapora fascialis in the North-Western Mediterranean

Summary Pentapora fascialis, one of the largest living bryozoan, is often a predominant part of the benthos on hard subtidal bottoms in the Mediterranean Sea. Conversion factors calculated from laboratory measurements of colony size, biomass and skeleton weight, combined with density of colonies and mean annual growth rate allowed the estimation of carbonate standing stock, biomass and carbonate production ofPentapora fascialis in five sites in the Ligurian Sea. Carbonate standing stock ranged from 281 to 2490 g·m⁻², colony biomass varied from 8.82 to 78.01 g·m⁻², with a ratio biomass to carbonate standing stock of about 3%. Carbonate production of the bryozoan ranged in the five sites from 358 to 1214 g·m⁻²·y⁻¹. If compared with the few data available on carbonate production of bryozoans and other sublittoral benthic bioconstructors in the temperate regions,Pentapora fascialis has to be considered one of the major contributors to the carbonatebudget.     

Large seasonal variation in phytoplankton production in the Amundsen Sea

Polar Biology - To better estimate annual primary production in the Amundsen Sea, which is one of the highest productivity regions in the Southern Ocean, the seasonal variations in carbon and...