Primary Production In Relation Research Articles

Microplanktonic diatom assemblages dominated the primary production but not the biomass in an Antarctic fjord

The western Antarctic Peninsula (WAP) fjords, currently threatened by climate change, are known as high krill congregation areas, however, the primary productivity in relation to phytoplankton groups in these coastal areas remains uncertain. To test this, we studied the specific composition, diversity and cellular carbon content of phytoplankton communities in relation to primary production (PP) and growth rates in Andvord Bay, its connection to Gerlache Strait and a near station on the continental shelf during spring (2015) and autumn (2016). Based on the microscopic determination of the relative biomass of the different microalgal taxa we determined three main phytoplankton assemblages that differ in their composition, PP, growth, and spatial and temporal distribution: (1) an assemblage dominated by cryptophytes, with high biomass (59.2 ± 28.2 μgC L−1), intermediate PP (63.1 ± 32 mgC m−3 d−1), and low growth (0.2 ± 1.1 d−1) present in the inner part of the fjord during spring, and related to higher surface water temperatures; (2) an assemblage dominated by microplanktonic diatoms (mainly Odontella weissflogii) with intermediate biomass (40.1 ± 17.2 μgC L−1), high PP (151.2 ± 62.5 mgC m−3 d−1), and high growth (0.9 ± 1 d−1) present from the fjord mouth to the Gerlache Strait waters during spring and in shelf waters during autumn, related to high irradiance and microzooplankton biomass; and (3) an assemblage dominated by dinoflagellates, mainly small gymnodinioids (< 15 μm long), with low biomass (3.5 ± 3.5 μgC L−1), low PP (6.9 ± 5.1 mgC m−3 d−1), and intermediate growth (0.5 ± 0.6 d−1) present in the whole fjord and the Gerlache Strait during autumn and infrequently during spring, related to high meltwater fraction. During both seasons, the highest phytoplankton biomass, richness and productivity in Andvord Bay was located in a frontal area at the fjord's mouth. Overall, the results of this study support the notion that WAP fjords are highly productive, highlighting the role of microplanktonic diatom as the main organic carbon producers, even when they occur in low abundances, due to their photosynthetic potential and higher Carbon-to-Chlorophyll a ratio. Our results, together with previous phytoplankton growth rates measured in the WAP nearshore waters from King George Island to Marguerite Bay, are higher than those measured on the WAP shelf and in the Ross Sea suggesting micro- and macronutrient enrichment from glacial melt maintains high productivity throughout the growth season in fjords. Our results support the hypothesis that climate change could highly affect the coastal WAP ecosystems by changing the balance between more productive phytoplankton assemblages (diatoms) to considerably less productive phytoplankton assemblages (cryptophytes).

Dynamics of primary productivity in relation to submerged vegetation of a shallow, eutrophic lagoon: A field and mesocosm study.

Aquatic ecosystems nowadays are under constant pressure, either from recent or historical events. In most systems with increased nutrient supply, submerged macrophytes got replaced by another stable state, dominated by phytoplankton as main primary producer. Yet, reducing the nutrient supply did not yield the aimed goal of restored habitats for submerged macrophytes in systems worldwide. The question arises, why submerged macrophytes do not re-colonize, and if they are actually competitive. Therefore, primary production assays were conducted in ex-situ bentho-pelagic mesocosms and compared to the actual ecosystem, a turbid brackish lagoon of the southern Baltic Sea. Mesocosm were either manipulated to be colonized by macrophytes, or stayed phytoplankton dominated. Oxygen evolution was monitored over a period of five months in 5 min (mesocosms) to 10 min (ecosystem) intervals. Surface and depth-integrated production was calculated to analyse seasonal and areal resolved production patterns. It was found that macrophyte mesocosms were more stable, when considering only surface O2 production. However, calculating depth-integrated production resulted in net-heterotrophy in both shallow mesocosms approaches and the actual ecosystem. This heterotrophy is likely mediated by sediment respiration and POC accumulation in mesocosms, and a low share of productive to respiring water column in the actual ecosystem. Therefore, it seems unlikely that macrophytes will re-settle, as constant net-heterotrophy may allow for high-nutrient turnover at sediment-water interfaces and within the water column, favouring phytoplankton. These results will assist decision makers in developing more effective restoration measures that can mitigate the negative effects of eutrophication on ecosystem function and services.

Strong and regionally distinct links between ice‐retreat timing and phytoplankton production in the Arctic Ocean

AbstractRecent rapid sea‐ice changes in the Arctic Ocean have been widely considered to alter phytoplankton bloom timing and primary production, but the magnitude and regionality of this effect remain unclear. Here, we examined the spatial patterns in bloom timing, bloom magnitude, and primary productivity in relation to ice‐retreat timing, using a combination of satellite observations and numerical modeling. We found distinct regional differences in how the phytoplankton bloom relates to ice‐retreat timing. In the Arctic shelf regions, earlier and stronger blooms follow earlier annual ice retreats and enhanced light availability. By contrast, in some parts of the central Arctic, especially in the Canada Basin, there have been weakened blooms and reduced primary production in recent years. This reduction is largely due to a chain reaction triggered by earlier ice‐melt and enhanced haline stratification, which further suppress vertical nutrient exchange and reduce surface nutrients in an already nutrient‐limited system. Recognizing and quantifying strong and regionally distinct links between sea‐ice retreat and primary production will improve spatiotemporal projections of biogeochemical cycles and trophic flows in Arctic marine ecosystems.

Forest structure, diversity, and primary production in relation to disturbance severity.

Differential disturbance severity effects on forest vegetation structure, species diversity, and net primary production (NPP) have been long theorized and observed. Here, we examined these factors concurrently to explore the potential for a mechanistic pathway linking disturbance severity, changes in light environment, leaf functional response, and wood NPP in a temperate hardwood forest.Using a suite of measurements spanning an experimental gradient of tree mortality, we evaluated the direction and magnitude of change in vegetation structural and diversity indexes in relation to wood NPP. Informed by prior observations, we hypothesized that forest structural and species diversity changes and wood NPP would exhibit either a linear, unimodal, or threshold response in relation to disturbance severity. We expected increasing disturbance severity would progressively shift subcanopy light availability and leaf traits, thereby coupling structural and species diversity changes with primary production.Linear or unimodal changes in three of four vegetation structural indexes were observed across the gradient in disturbance severity. However, disturbance‐related changes in vegetation structure were not consistently correlated with shifts in light environment, leaf traits, and wood NPP. Species diversity indexes did not change in response to rising disturbance severity.We conclude that, in our study system, the sensitivity of wood NPP to rising disturbance severity is generally tied to changing vegetation structure but not species diversity. Changes in vegetation structure are inconsistently coupled with light environment and leaf traits, resulting in mixed support for our hypothesized cascade linking disturbance severity to wood NPP.

Vertical distribution of phytoplankton and primary production in relation to nutricline depth in the open ocean

Vertical distribution of phytoplankton and primary production in relation to nutricline depth in the open ocean

A Comparative Study on Pelagic Primary Productivity in the Coastal Areas of Eritrean Red Sea

Primary Productivity is the process by which inorganic forms of carbon are synthesized by living organisms into simple organic compounds. Most carbon on Earth is in inorganic oxidized forms such as carbon dioxide (CO2), bicarbonate (HCO3-), and carbonate (CO3). Inorganic carbon must be chemically reduced to form the organic molecules which are the building blocks of life and the mechanism by which energy is stored in living organisms. Eritrea’s coastal and marine ecosystems are characterized by rich and diverse coral reefs, isolated mangrove forests, sea-grass beds, bays, beaches and pristine unpolluted waters that are at the critical juncture between development and conservation. These ecosystems represent a physical resource base for the potentially rich and unexploited marine fisheries. This study is basically aimed at the measurement of primary productivity in relation to fisheries. The study results will also high light the plankton assemblage of a coastal environment and this study will also examine the productivity of the coastal environment.

Variation in Primary Production in Relation to Physico-Chemical Parameters of Kadwai Reservoir, Ratnagiri, Maharashtra, India.

The present study has been carried out to study the status of primary productivity in relation to physiochemical parameters of the Kadwai reservoir of Ratnagiri district, Maharashtra. The primary productivity was determined by estimating gross and net primary productivity. The experiment was conducted during the monsoon and post monsoon seasons from 1st June to 30th Nov 2015 to know the effect of organic run off on primary production of Kadwai reservoir. The physiochemical parameters such as temperature, pH, dissolved oxygen, total hardness, total alkalinity and transparency ranged from 27oC-30.5oC, 7.5-8.6, 3.2-7.0 mg/l, 46-75 mg/l, 56-95 mg/l, and 118-130 cm, respectively. The gross primary productivity (GPP) during monsoon was 0.07-0.11 gC/m3/hr in June, July and August 2015, respectively, which was very low, whereas GPP were increased during post monsoon season. The values were recorded as 0.12-0.48 gC/m3/hr in the months of September, October, and November 2015, respectively. The results indicated that during monsoon season, organic load is coming along with water in to the reservoir, but phytoplankton growth is minimum due to the heavy rain and flushing rate were high from the downstream of the reservoir. During post monsoon, primary productivity was increased. The results indicate that Kadwai reservoir is more productive during post monsoon season suitable for stocking fish seed.

Phytoplankton Primary Production in Relation to Limno-chemical Feature in the Context of Fish Yield Potential of Running Water

Phytoplankton Primary Production in Relation to Limno-chemical Feature in the Context of Fish Yield Potential of Running Water

A calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the Sinemurian/Pliensbachian (early Jurassic, ~ 191 Ma) in Portugal

The Sinemurian/Pliensbachian boundary (~191Ma) is acknowledged as one of the most important steps in the radiation of planktonic organisms, especially primary producers such as dinoflagellates and coccolithophores. To date, there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary. The aim of this study is to characterize the palaeoenvironmental changes occurring across the Sinemurian/Pliensbachian boundary at the São Pedro de Moel section (Lusitanian Basin, Portugal) using micropalaeontology and organic geochemistry approaches. Combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea-level rise occurring above the boundary. The Lusitanian Basin was particularly restricted during the late Sinemurian with a relatively low sea level, a configuration that led to the recurrent development of black shales. After a sharp sea-level fall, the basin became progressively deeper and more open during the earliest Pliensbachian, subsequently to a major transgression. This sea-level increase seems to have been a global feature and could have been related to the opening of the Hispanic Corridor that connected the Tethys and palaeo-Pacific oceans. The palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of Tethyan waters by placolith-type coccoliths.

Interactive effects of temperature and light during deep convection: a case study on growth and condition of the diatom Thalassiosira weissflogii

AbstractAim of this study was to expose phytoplankton to growth conditions simulating deep winter convection in the North Atlantic and thereby to assess changes in physiology enabling their survival. Growth rate, biochemical composition, and photosynthetic activity of the diatom Thalassiosira weissflogii were determined under two different light scenarios over a temperature range of 5–15°C to simulate conditions experienced by cells during winter deep convection. These metrics were examined under a low light scenario (20 µmol m−2 s−1, 12/12 h light/dark), and compared with a scenario of short light pulses of a higher light intensity (120 µmol m−2 s−1, 2/22 h light/dark). Both experimental light conditions offered the same daily light dose. No growth was observed at temperatures below 8°C. Above 8°C, growth rates were significantly higher under low light conditions compared with those of short pulsed light exposures, indicating a higher efficiency of light utilization. This could be related to (i) a higher content of Chl a per cell in the low light trial and/or (ii) a more efficient transfer of light energy into growth as indicated by constantly low carbohydrate levels. In contrast, pulsed intense light led to an accumulation of carbohydrates, which were catabolized during the longer dark period for maintaining metabolism. Light curves measured via Chl a fluorescence indicated low light assimilation for the algae exposed to short pulsed light. We postulate that our trial with short light pluses did not provide sufficient light to reach full light saturation. In general, photosynthesis was more strongly affected by temperature under pulsed light than under low light conditions. Our results indicate that model estimates of primary production in relation to deep convection, which are based on average low light conditions, not considering vertical transportation of algae will lead to an overestimation of in situ primary production.

Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea-ice at the shelf break of the eastern Bering Sea: Implications for off-shelf carbon export

[1] Particulate organic carbon (POC) export fluxes and net primary production (NPP) rates are used to assess seasonal patterns in the export ratio (e-ratio = POC export/NPP) in relation to proximity of the sea-ice edge near the shelf break of the eastern Bering Sea during 2008–2010. POC fluxes were relatively low in April (4.6 ± 1.6, trap, and 5.7 ± 4.3 mmol C m−2 d−1, 234Th-derived) and increased in May–early June (19.9 ± 13.3 and 17.0 ± 8.8 mmol C m−2 d−1). POC export reached a maximum in mid-June–mid-July (30.0 ± 12.6 and 48.1 ± 17.4 in 2009; 33.1 ± 27.6 and 57.0 ± 68.4 mmol C m−2 d−1 in 2010) and decreased by late July (13.1 ± 4.7 and 14.1 ± 8.0 mmol C m−2 d−1). NPP rates were relatively high and export fluxes low near the ice-edge in spring leading to e-ratios 1, which is attributed to a temporal decoupling, or offset, of spring NPP and export during summer. While these observations reveal a seasonal progression in POC export and the e-ratio, there is no direct relationship to sea-ice proximity. Furthermore, based on a water column-sediment 234Th budget, the off-shelf export of POC during spring-summer is estimated to be 24 ± 35 mmol C m−2 d−1, which represents an off-shelf e-ratio of 0.07 and 0.21 for contemporaneous seasonally averaged daily NPP and 0.17 and 0.52 for historical monthly averaged daily NPP. An implication is that off-shelf POC transport may represent a seasonal net sink for CO2 in this and other polar shelf regions.

Primary Production in River Birupa, India

Seasonal changes of primary production in relation to water temperature, secchi transparency and rainfall were measured from January 2009 to December 2010 by using light-and-dark bottle technique at three different sampling sites along the course of river Birupa between 20°36′57″ north latitude and 86°24′29″ east longitude of Odisha, India. The Gross Primary Production (GPP) and Net Primary Production (NPP) were least during monsoon (August) and attained peak during summer (April) at all stations except GPP during March at station 3. Community Respiration (CR) was minimum from February to April and maximum from October to January among the stations. GPP and NPP were significantly correlated,both temporally and spatially,with water temperature, secchi transparency and rainfall. Annual GPP was maximum at station 2 and minimum at station 3. Annual GPP for both the years was found to be 1.364 gC m−2 day−1 or 497.86 gC m−2 year−1 in river Birupa. This value was compared to some other temperate and tropical rivers.

Organic matter production during late summer–winter period in a temperate sea

The quantity and quality of fresh organic matter (OM) formed by primary production in relation to phytoplankton community structure was calculated for the late summer–winter 2009/2010 in the northern Adriatic Sea (Mediterranean). Phytoplankton species, as a direct measure of fresh OM, chlorophyll a, the OM pool (DOC and POC) and lipids, including classes, were analyzed. Data for temperature, salinity and nutrients enabled deeper insight into the conditions that promoted fresh OM production and associated processes at two stations of different trophic status. Phytoplankton growth was controlled by bottom regenerated nutrients and to lesser extent by riverine nutrients. The phytoplankton community was mainly dominated by nanoplankton. Species of moderate carbon content Chaetoceros compressus, Asterionellopsis glacialis, Leptocylindrus danicus and Bacteriastrum jadranum dominated the microplankton fraction. Availability of orthophosphates was the key factor influencing fresh OM production. POC varied from 37–522μgl−1. Freshphyto POC, i.e. carbon fixed in phytoplankton cells, contributed 7–79% to the POC pool. The DOC (890–1560μgl−1) level decreased during the investigated period. Calculation of fresh DOC, i.e. carbon fixed during primary production and released as dissolved OM, revealed it as a minor part (0–2%) of the DOC pool. Lipid concentrations varied from 9.9–55.0μgl−1 and 20.0–40.2μgl−1 in the particulate and dissolved fractions, respectively. Nutrient limitation caused increased synthesis of lipids, among which energy reserve lipids triacylglycerols, which are further immobilized for the construction of glycolipids with increasing depletion of orthophosphates.

Sea ice impacts on spring bloom dynamics and net primary production in the Eastern Bering Sea

In the Eastern Bering Sea, changes in sea ice have been implicated in recent major upper‐trophic level shifts. However, the underlying relationships between sea ice and primary producers have not been well tested. Here, we combine data from multiple satellite platforms, reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions. In the northern Bering Sea, sea ice consistently retreated in late spring, leading to ice‐edge phytoplankton blooms in cold (0–1 °C) waters. However, in the southeastern Bering Sea, sea ice retreat was far more irregular. Although this did not significantly alter bloom timing, late retreat led to blooms at the ice‐edge while early retreat led to blooms in open waters that were warmer (≤5.4 °C) and &gt;70% more productive. Early sea ice retreat also led to higher productivity in summer, likely due to weaker thermal stratification. Overall, annual net primary production during warm years of early sea ice retreat was enhanced by 40–50% compared to years with late sea ice retreat in the southeastern Bering Sea. These findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern Bering Sea ecosystem. Consistently warm blooms in the future may also channel more energy flow toward the pelagic, rather than benthic, environment. To date, however, neither sea ice extent nor the timing of its retreat have undergone long‐term changes in the Eastern Bering Sea.

Marine Primary Production in Relation to Climate Variability and Change

Marine photosynthetic plankton are responsible for approximately 50 petagrams (10(15)) of carbon per year of net primary production, an amount equivalent to that on land. This primary production supports essentially all life in the oceans and profoundly affects global biogeochemical cycles and climate. This review discusses the general distribution of primary production in the sea, the processes that regulate this distribution, and how marine primary production is sensitive to climate variability and change. Statistical modes of ocean variability and their characteristic interannual to multi-decadal timescales over the last century are described. Recent in situ and satellite time-series of primary production can be clearly linked to interannual ocean variability. Global marine primary production appears to have increased over the past several decades in association with multi-decadal variations. A paleoclimate record extends discussion to the centennial scale, providing contrasting insights into how marine primary production might vary in the future.

Genomic Footprints of a Cryptic Plastid Endosymbiosis in Diatoms

Diatoms and other chromalveolates are among the dominant phytoplankters in the world's oceans. Endosymbiosis was essential to the success of chromalveolates, and it appears that the ancestral plastid in this group had a red algal origin via an ancient secondary endosymbiosis. However, recent analyses have turned up a handful of nuclear genes in chromalveolates that are of green algal derivation. Using a genome-wide approach to estimate the "green" contribution to diatoms, we identified >1700 green gene transfers, constituting 16% of the diatom nuclear coding potential. These genes were probably introduced into diatoms and other chromalveolates from a cryptic endosymbiont related to prasinophyte-like green algae. Chromalveolates appear to have recruited genes from the two major existing algal groups to forge a highly successful, species-rich protist lineage.

Green for Diatoms

Diatoms account for 20% of global carbon fixation and, together with other chromalveolates (e.g., dinoflagellates and coccolithophorids), represent many thousands of eukaryote taxa in the world's oceans and on the tree of life. Moustafa et al. (p. [1724][1]; see the Perspective by [ Dagan and Martin ][2] ) have discovered that the genomes of diatoms are highly chimeric, with about 10% of their nuclear genes being of foreign algal origin. Of this set of 1272 algal genes, 253 were, as expected, from a distant red algal secondary endosymbiont, but more than 1000 of the genes were derived from green algae and predated the red algal relationship. These protist taxa are important not only for genetic and genomic investigations but also for their potential in biofuel and nanotechnology applications and in global primary productivity in relation to climate change. [1]: /lookup/volpage/324/1724 [2]: /lookup/doi/10.1126/science.1175765

Relations of phytoplankton in situ primary production, chlorophyll concentration and underwater irradiance in turbid lakes

In order to study the relationships among primary productivity, chlorophyll content and light conditions (underwater quantum irradiance, diffuse attenuation coefficient) in turbid lakes, we performed a series of measurements in three Estonian lakes (Peipsi, Vortsjarv and Harku) during 2003–2005. We focused on (1) comparison of in situ vertical profiles of planar and scalar quantum irradiances in the water, (2) extremely high values of chlorophyll content and primary production in some turbid lakes and (3) analysis of the formation of the vertical profiles of primary production (shape and the depth of its maximum value) as a function of incident irradiance. The following parameters were measured: (a) primary production at different depths, (b) incident planar quantum irradiance in the region of 400–700 nm, (c) underwater downwelling planar and scalar quantum irradiances at different depths in the same waveband, (d) relative transparency of water (Secchi depth), (e) concentrations of chlorophyll a and (f) spectra of beam attenuation coefficient for unfiltered and filtered water in the wavelength range of 350–700 nm (from water samples). During 36 measurement days (14 in Peipsi, 14 in Vortsjarv and 8 in Harku), and we collected reliable dataset for 53 measurement series. Our data showed the relative difference between underwater planar and scalar quantum irradiance in a range of about 25–65% implying big differences in primary production models if instead of the preferable scalar quantum irradiance planar irradiance data are used. The results showed a large variation of vertical profiles of primary production in relation to illumination conditions. The depth of maximum primary production depended on water turbidity and incident irradiance, and was located at the water surface in case of low illumination. The relationship between vertically integrated primary production and chlorophyll concentration could be described by a power function with an exponent of 0.64 (R 2 = 0.81).

Effects of fire on sward structure and grazing in western Serengeti, Tanzania

Fire is one of the major ecological factors that determines structure and function of grassland and savanna ecosystems through its effects on soil nutrient pools, floristic composition and primary production, and foraging behaviour and distribution of populations of wildlife species. Therefore, some wildlife protected area authorities in African savannas have a fire management scheme to cater for a variety of purposes such as, to prevent bush encroachment into grassland, to increase production of quality forage, to control wild fires from outside the protected areas and their spread, and to keep animals in tourist areas for visitors’ enjoyment. The responses to fire of ecosystem processes can be quantified but the outcomes are generally complex depending on the nature of the fire regime, primarily the frequency and timing of the fire events. For example, while ash after fire may have a fertilising effect that will facilitate seedling establishment and increase the growth and production, there is evidence that in East Africa, fire may lead to the dominance of a few species over several other species. Fire may also lead to loss of nutrients, for example nitrogen, through volatilisation. Such variaty in responses to fire makes the use of fire as a tool in the management of wildlife and protected areas usually controversial. Therefore, the main challenge of management is to strike a fire management regime as close as possible to a natural fire regime in this ecosystem.In the Serengeti ecosystem, fire has been regarded to have a critical role on herbivores and their forage resources. Thus, burning has been a management tool in protected areas and a common practice of range management by pastoralists. Herdsmen use fire to improve the pasture quality for cattle. Removal of old or dead grass material by fire enhances sprouting of plants, which improves, at least for a short-term, the quality of the sward. In the Serengeti National Park, early dry-season burns had been executed by the Serengeti Ecological Monitoring Program Department from end of May to mid August without clear understanding about grassland responses to the prescribed burns.The perceived importance of fire to the management and conservation of Serengeti ecosystem has driven this thesis to focus on the effects of fire on large herbivores and their forage resources in the Serengeti National Park. To accomplish that, the thesis examines the relationships between burning and 1) above ground net primary productivity in relation to sward structure and precipitation (Paper I), 2) forage quality, i.e. the concentration of macronutrients (N, P, K, Na, Mg and Ca), in vitro organic matter digestibility and levels of acid detergent fibre per phytomass component (Paper II), and 3) the temporal and spatial patterns of herbivores’ consumption (Paper III), and 4) the patch selection by ungulate species, individually and/or grouped in diet groups (Paper IV).The result of the early dry season burns is a significantly higher daily above ground net primary production (ANPP) on burnt plots at early post-fire stages, coinciding with the dry season (July-September) and during the short rainy period (October-December). Though not significantly different, it was also high on burnt plots at the end of the main rain period (March – May), but higher on non-burnt plots in December-February, and in early dry season, June- July of the subsequent year.Results from this area with high diversity of large herbivore species show that grazing herbivores switch between burnt and non-burnt patches by trading off between forage quantity and quality along growing season. The quality on burnt areas appears to be governed by enhanced concentrations of macronutrients, increased digestibility and reduced concentration of acid detergent fibres. The above quality variables are linked to increased ratio between live and total phytomass. Quality of forage explains the preference by grazing animals for burnt areas during some periods, and in non-burnt areas due to high phytomass in other periods.Selection for non-burnt or burnt patches or against patches burnt more than once in a period of three years by some species of ungulates and/or diet groups are also indicative that quality and/or quantity of forage in the respective patch underlay patch choice. The cause of temporal variation in selectivity of the patches needs further investigation. However, it is unequivocal that maintenance of mosaic of burnt and non-burnt areas with adequate provision of forage amount and quality all year round is of paramount importance.

Primary production across the Scotia Sea in relation to the physico-chemical environment

During the austral summer of 2003, a large scale survey of the Scotia Sea was undertaken by the British Antarctic Survey as part of the Southern Ocean Global Ocean Ecosystems Dynamics programme. This cruise provided a unique opportunity to examine the distribution of phytoplankton biomass and primary production in relation to the physico-chemical environment of the Scotia Sea. Phytoplankton were sampled from a range of oceanographic regimes including the open ocean, in the wake of oceanic islands, across major fronts such as the Southern Antarctic Circumpolar Current Front, submarine topographical features such as the South Scotia Ridge and the marginal ice zone. Generally the Scotia Sea was characterised by low biomass (< 30 mg chlorophyll- a m − 2 ), low production rates (< 0.31 g C m − 2 d − 1 ) and an abundance of macronutrients (e.g., surface nitrate > 28 mmol m − 3 ) despite favourable environmental conditions for growth caused by shallow mixed layers and deep euphotic depths. Three areas of elevated biomass (77–295 mg chlorophyll- a m − 2 ) and production (0.73–2.04 g C m − 2 d − 1 ) as well as substantial macronutrient depletion (e.g., surface nitrate ∼12 mmol m − 3 ) were observed during the cruise: to the northwest of the island of South Georgia, to the southwest of South Georgia and further south over the South Scotia Ridge in a region of rapid ice retreat. These productive regions were also characterised by shallow mixed layer depths, although near to South Georgia euphotic depths were reduced due to the high biomass of phytoplankton in the water column. The biomass was composed of over 80% diatoms. We speculate that the contrasting production regimes observed during the cruise were the result of differences in iron availability. Throughout much of the survey area, the eastward flowing Antarctic Circumpolar Current is unlikely to have encountered any shallow bathymetric features that may introduce sedimentary iron into the euphotic zone. However, shallow topographic features, may cause upwelling of iron into the euphotic zone. This, together with shallow mixed layers and a favourable light environment, may then account for the dense blooms observed near topographic features during our cruise.